H.N.Gupta-Fundamentals-of-Internal-Combustion-Engine (1).pdf
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About This Presentation
Internal Engines
Slide Content
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D punonuNTALS OF INTERNAL COMBUSTION ENGINES
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Contents
Preface ait
1. Introduction to Internal Combustion Engines 1-24
11 An Overview 1
12 Historical Development 2
13 Modem Developments 3
LA Engine Classifications — 4
15 Classification of Reciprocating Engines by Application 6
18 Classifiations of Engines by Cylinder Arrangement — 6
17 Engine Components — 9
118 Basic Terminology — 14
19 Fourstroke Sparkigoition Engine 15
1:10. Valvectiming of Fourstroke St Engine — 17
1401 Inlet Valve 18
1.10.2 Exhaust Valve 18
1:11. Fouratroke Compression Ignition (CI) Engines — 19
1.12. Comparison of SI and CI Engines — 20
113 Two-suoke Engines 27
1:14. Comparison of Fovrstroke and Two-sroke Engines — 23
Review Questions — 28
2. Air-Standard Cycles and Their Analysis 25-61
21 Introduction 25
22 dard Cycle 25
23 Ono Cycle or Constant Volume Cycle 26
24 Diesel Cycle 30
25 Dual Combustion Cyele 34
2.6 Comparison of Otto, Diesel and Dual Combustion Cycles 37
27 Atkinson Cycle #1
Review Questions 59
Problems — 60
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D punonuNTALS OF INTERNAL COMBUSTION ENGINES
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> Pr ring Privat Line, Nam Dob A pts esamad No part ons back may
a tam by nina or any or rene, witout persion weg,
Die purser
Yisensreet 20920549
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Contents
Preface ait
1. Introduction to Internal Combustion Engines 1-24
11 An Overview 1
12 Historical Development 2
13 Modem Developments 3
LA Engine Classifications — 4
15 Classification of Reciprocating Engines by Application 6
18 Classifiations of Engines by Cylinder Arrangement — 6
17 Engine Components — 9
118 Basic Terminology — 14
19 Fourstroke Sparkigoition Engine 15
1:10. Valvectiming of Fourstroke St Engine — 17
1401 Inlet Valve 18
1.10.2 Exhaust Valve 18
1:11. Fouratroke Compression Ignition (CI) Engines — 19
1.12. Comparison of SI and CI Engines — 20
113 Two-suoke Engines 27
1:14. Comparison of Fovrstroke and Two-sroke Engines — 23
Review Questions — 28
2. Air-Standard Cycles and Their Analysis 25-61
21 Introduction 25
22 dard Cycle 25
23 Ono Cycle or Constant Volume Cycle 26
24 Diesel Cycle 30
25 Dual Combustion Cyele 34
2.6 Comparison of Otto, Diesel and Dual Combustion Cycles 37
27 Atkinson Cycle #1
Review Questions 59
Problems — 60
iv Coments €
_ Conens Y €
3. Reactive Systems ot 5.3 Effect of Engine Variables on Flame Speed 148 (
34 troduction 62 531 FoslAirRado 149
32 Proper of Air 62 332. bebes 1 €
33 Combustion with Air 63 533 Engine Speed 149 €
34 Equivalence Ratio 65 534 EngineSize 100
35 Enbalpy of Formation 74 535 Residual Gas 150 €
36 Fit Law Analysis for Steady-state Reacting Systems 75 54 Bees of Sparkadvance on the Actual Cycle of SI Engines 150 (
37 Enhalpy of Combustion, nereal Energy of Combustion 55. Power and Efficiency ofthe Acwal Cycle 133
and Heating Values 80 5.51 Effect of Compression Ratio 157 €
38 Adibatc Combustion Temperaure 86 352 Effect of Fuer Ratio 154 €
39 Dissocition 93 56 Ficionat Losses 154
370 Chemical Equliteam 95 52 The Al CSS Common En. 26 €
Review Questions — 102 58 Actual and Fuelair Cycles of CI Engines 136 N
Problems 108 Review Questions 137
4.. Fuel-Air Cycles and Their Analysis 106-142 6. Combustion in Sparklgnition Engines 158-197 ‘
A ntoduetion 106 6 Introduction 158
42 FuckairCyele 106 62 Normal Combustion 158 €
43 Factors Affecting the Fuel Cycle 107 621 Stages of Combustion in SI Engine 139 €
431 Composition of Cylinder Gases — 107 622 Flame Speed Patem 167
432 Vanation of Specific Heats 108 623 Faction of Bumed Mass 162 €
433 Elfe of Dissociation — 110 624 Pressure and Temperature Variation as a (
434 Eifet of Number of Molecules 112 Function of Crank Angle 163
44 Effect of Engine Variables on the Performance of Fuel-air Cycle ms 625 Effect of Spark Timing on Indicator Diagram — 163 €
45. Equiibaum Cham 126 626 Effect of Fusl/ir Ratio on Indicator Diagram 161 (
451 Unbumed Mixture Chans — 126 63 Factors Affecting Ignition Lag 165
452 Bumed Miture Churs 134 634 Natur of Fuel and AidFuel Ratio — 165 €
453 Relation between Unburned and Bumed Mixtores 136 632 Intel Temperature and Pressure 165
Review Questions 141 633 — Compresion Rato 166 €
Problems 162 634 Spark Timing 166 (
635 Turbulence and Engine Speed — 166
5. The Actual Cycle 143-157 636 Electrode Gap of Spark Plug /66 €
5.1 invodueion 143 64 Factors Affecting Combustion in Spetkigition Engines 167 €
522. Differenee between the Acta! Cycle and the Fucbair Cycle 143 641 Composition of the Mixture 767. E
521 Leakage 24 642 Load 167
522 impec Mixing of Fuel and Air 144 643 Compression Ratio 267 €
523 Progressive Burning 145 644 Speed 168
524 — Burning Time Los 145 64.5 Turbulence and Shape of Combustion Chamber 168 €
525 Heat Loses to the Cylinder Walls 146 648 Spark Plug Posiion 169 €
526 Eihası Blowdown Lose 146 65 Cie Variation 169
527 Fluid Friction 148 $6 Reo of rescue Rise 170 €
28 Gas Exchange or Pumping Loss 148 Anormal Combustion—Autignition and Detonation — 171
S23) See eae oc ne 8 Deuimental Effects of Detonation 172 c
69 Theories of Detonation 173 €
€
€
_ Conens Y €
3. Reactive Systems ot 5.3 Effect of Engine Variables on Flame Speed 148 (
34 troduction 62 531 FoslAirRado 149
32 Proper of Air 62 332. bebes 1 €
33 Combustion with Air 63 533 Engine Speed 149 €
34 Equivalence Ratio 65 534 EngineSize 100
35 Enbalpy of Formation 74 535 Residual Gas 150 €
36 Fit Law Analysis for Steady-state Reacting Systems 75 54 Bees of Sparkadvance on the Actual Cycle of SI Engines 150 (
37 Enhalpy of Combustion, nereal Energy of Combustion 55. Power and Efficiency ofthe Acwal Cycle 133
and Heating Values 80 5.51 Effect of Compression Ratio 157 €
38 Adibatc Combustion Temperaure 86 352 Effect of Fuer Ratio 154 €
39 Dissocition 93 56 Ficionat Losses 154
370 Chemical Equliteam 95 52 The Al CSS Common En. 26 €
Review Questions — 102 58 Actual and Fuelair Cycles of CI Engines 136 N
Problems 108 Review Questions 137
4.. Fuel-Air Cycles and Their Analysis 106-142 6. Combustion in Sparklgnition Engines 158-197 ‘
A ntoduetion 106 6 Introduction 158
42 FuckairCyele 106 62 Normal Combustion 158 €
43 Factors Affecting the Fuel Cycle 107 621 Stages of Combustion in SI Engine 139 €
431 Composition of Cylinder Gases — 107 622 Flame Speed Patem 167
432 Vanation of Specific Heats 108 623 Faction of Bumed Mass 162 €
433 Elfe of Dissociation — 110 624 Pressure and Temperature Variation as a (
434 Eifet of Number of Molecules 112 Function of Crank Angle 163
44 Effect of Engine Variables on the Performance of Fuel-air Cycle ms 625 Effect of Spark Timing on Indicator Diagram — 163 €
45. Equiibaum Cham 126 626 Effect of Fusl/ir Ratio on Indicator Diagram 161 (
451 Unbumed Mixture Chans — 126 63 Factors Affecting Ignition Lag 165
452 Bumed Miture Churs 134 634 Natur of Fuel and AidFuel Ratio — 165 €
453 Relation between Unburned and Bumed Mixtores 136 632 Intel Temperature and Pressure 165
Review Questions 141 633 — Compresion Rato 166 €
Problems 162 634 Spark Timing 166 (
635 Turbulence and Engine Speed — 166
5. The Actual Cycle 143-157 636 Electrode Gap of Spark Plug /66 €
5.1 invodueion 143 64 Factors Affecting Combustion in Spetkigition Engines 167 €
522. Differenee between the Acta! Cycle and the Fucbair Cycle 143 641 Composition of the Mixture 767. E
521 Leakage 24 642 Load 167
522 impec Mixing of Fuel and Air 144 643 Compression Ratio 267 €
523 Progressive Burning 145 644 Speed 168
524 — Burning Time Los 145 64.5 Turbulence and Shape of Combustion Chamber 168 €
525 Heat Loses to the Cylinder Walls 146 648 Spark Plug Posiion 169 €
526 Eihası Blowdown Lose 146 65 Cie Variation 169
527 Fluid Friction 148 $6 Reo of rescue Rise 170 €
28 Gas Exchange or Pumping Loss 148 Anormal Combustion—Autignition and Detonation — 171
S23) See eae oc ne 8 Deuimental Effects of Detonation 172 c
69 Theories of Detonation 173 €
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D 610. Be of Entine Variables om Knock 774
6101 Temperature, Pressure and Density Factors — 178
) 6102 Time Factors 176
) 6.103 Composition Factors 17
6104 Effect of Design 179
) GAL Detection of Knocking 180
612 Uncontoled Combustion 187
) 6.121 Preignition — /81
) 6.122 Rumon Surface Ignition — 182
6.123 Runaway Surface Ignition — 182
> 6124 Wild Ping 182
) 6125 Rumble 182
y 623 Corn Chan fr Sport gins
1... Basic Requirements of a Good Combustion Chamber — 184
) S14 Comunion Chamber Design Panopis 183
5 Combustion Chamber Optimization Procedure 186
) 615.1 Geomeris Considerations 186.
) 6.152 Considerations for Cyelic Variations — 186
6153 Consideration for Proper Turbulence 187
) 616. Tps of Combustion Chamber 187
1 Thead Type Combustion Ch
) h pe Combustion Chamber 187
162 L-head Type or Side Valve Combustion Chamber
) 6163 Ricardo Turbulent Head Side Valve Combi sl
163 Redo Tu mbustion Chamber 188
; 6164 Ovetendalve ot Lheed Type Combustion Chamber 190
; 6165. Fad Bos Combustion Chanter” 13)
lemisphericel Combustion Chamber 191
) 6167 Paton Cavity Combustion Chumber 192
‘ombustion Chamber with a Pre-chamt
) for Lean Burn Enke 0
4 6.169 Future Trends 194
617 Octane Requirement 194
y Review Questions — 195
) Combustion in Compression-Ignition Engines 198-227
D 71 Introduction 198
72 Air Motion in CI Engines 199
) 73 Spray Structure 200
) 74 Stages of Combustion — 203
y 25 Heat Rele Rate 205
T6 AifFuet Ratio in CI Engines 206
) 77 Influence of Various Factors on Delay Period
y 73 Combusion Knock in CI Engines a 7
7.8 Comparison of Knock in SI and CI Engines — 214
) 7:10. Methods of Controlling Knock in CI Engines 215
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7.11. Combustion Chamber for CI Engines — 216
FALL Combustion Chamber Characterisics 276
7112 Classification of CI Engine Combustion Chambers 216
7.12. Direct Injection (DI) Engines or Open Combustion Chamber Engines 277.
7.12. Semiguiescent or Low Swirl Open Chamber — 277
7122 Medium Swirl Open Chamber 218
7.123 High Swirl Open Chamber CM’ type) 218
7.13 Indirectánjection (IDD) Engines or Divided Combustion
Chamber Engines 2/9
713.4 Swirl or Turbulent Chamber 219
7332 Precombastion Chamber — 221
7133 Aie Cells 227
7.134 Energy Cells 222
7.14 Comparison of Characteristics of Combustion Chambers of CI Engine 223
7.15 Staring Methods and Aids — 223
Review Questions — 226
Fuels for Internal Combustion Engines 228-257
8.1 Introduction — 228
$2 Classification of Fuels 228
83 Solid Fuels — 229
8.3.1 Brief Description of Solid Fuels — 229
832 Use of Solid Poels in IC Engines 230
84 Liquid Fuels 230
34.1 Petroleum Fuels (Petra = rock + oleum = oil) 230
842 — Refining Process of Petroleum — 233
8453 Peuoleumbased Liquid Fuels 235
$44 — Non-perroleum Based Liquid Fuels — 236
85 Guscous Fuels 237
$51 Natural Gas 237
852 — Liquified Pewoleum Gas (LPG) — 238
853 Producer Gas 238
854 Coal Gas 238
855 Hydrogen 238
8.6 Fuels for SI Engines 239
861 Volatility of Liquid Fuels — 240
862 Eilfect of Volatility on the Performance of SI Engines 243
363 Sulphur Content — 243
864 Gum Deposits 245
865 — Curburettor Detergent Additives — 243
36.6 — Amiknock Quality 246
87 Fuels for CI Engines — 246
8.7.1 Ignition Qualiy 246
822 Volatility 247
Comenss_vil
)
>
D 610. Be of Entine Variables om Knock 774
6101 Temperature, Pressure and Density Factors — 178
) 6102 Time Factors 176
) 6.103 Composition Factors 17
6104 Effect of Design 179
) GAL Detection of Knocking 180
612 Uncontoled Combustion 187
) 6.121 Preignition — /81
) 6.122 Rumon Surface Ignition — 182
6.123 Runaway Surface Ignition — 182
> 6124 Wild Ping 182
) 6125 Rumble 182
y 623 Corn Chan fr Sport gins
1... Basic Requirements of a Good Combustion Chamber — 184
) S14 Comunion Chamber Design Panopis 183
5 Combustion Chamber Optimization Procedure 186
) 615.1 Geomeris Considerations 186.
) 6.152 Considerations for Cyelic Variations — 186
6153 Consideration for Proper Turbulence 187
) 616. Tps of Combustion Chamber 187
1 Thead Type Combustion Ch
) h pe Combustion Chamber 187
162 L-head Type or Side Valve Combustion Chamber
) 6163 Ricardo Turbulent Head Side Valve Combi sl
163 Redo Tu mbustion Chamber 188
; 6164 Ovetendalve ot Lheed Type Combustion Chamber 190
; 6165. Fad Bos Combustion Chanter” 13)
lemisphericel Combustion Chamber 191
) 6167 Paton Cavity Combustion Chumber 192
‘ombustion Chamber with a Pre-chamt
) for Lean Burn Enke 0
4 6.169 Future Trends 194
617 Octane Requirement 194
y Review Questions — 195
) Combustion in Compression-Ignition Engines 198-227
D 71 Introduction 198
72 Air Motion in CI Engines 199
) 73 Spray Structure 200
) 74 Stages of Combustion — 203
y 25 Heat Rele Rate 205
T6 AifFuet Ratio in CI Engines 206
) 77 Influence of Various Factors on Delay Period
y 73 Combusion Knock in CI Engines a 7
7.8 Comparison of Knock in SI and CI Engines — 214
) 7:10. Methods of Controlling Knock in CI Engines 215
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>
0
8.
7.11. Combustion Chamber for CI Engines — 216
FALL Combustion Chamber Characterisics 276
7112 Classification of CI Engine Combustion Chambers 216
7.12. Direct Injection (DI) Engines or Open Combustion Chamber Engines 277.
7.12. Semiguiescent or Low Swirl Open Chamber — 277
7122 Medium Swirl Open Chamber 218
7.123 High Swirl Open Chamber CM’ type) 218
7.13 Indirectánjection (IDD) Engines or Divided Combustion
Chamber Engines 2/9
713.4 Swirl or Turbulent Chamber 219
7332 Precombastion Chamber — 221
7133 Aie Cells 227
7.134 Energy Cells 222
7.14 Comparison of Characteristics of Combustion Chambers of CI Engine 223
7.15 Staring Methods and Aids — 223
Review Questions — 226
Fuels for Internal Combustion Engines 228-257
8.1 Introduction — 228
$2 Classification of Fuels 228
83 Solid Fuels — 229
8.3.1 Brief Description of Solid Fuels — 229
832 Use of Solid Poels in IC Engines 230
84 Liquid Fuels 230
34.1 Petroleum Fuels (Petra = rock + oleum = oil) 230
842 — Refining Process of Petroleum — 233
8453 Peuoleumbased Liquid Fuels 235
$44 — Non-perroleum Based Liquid Fuels — 236
85 Guscous Fuels 237
$51 Natural Gas 237
852 — Liquified Pewoleum Gas (LPG) — 238
853 Producer Gas 238
854 Coal Gas 238
855 Hydrogen 238
8.6 Fuels for SI Engines 239
861 Volatility of Liquid Fuels — 240
862 Eilfect of Volatility on the Performance of SI Engines 243
363 Sulphur Content — 243
864 Gum Deposits 245
865 — Curburettor Detergent Additives — 243
36.6 — Amiknock Quality 246
87 Fuels for CI Engines — 246
8.7.1 Ignition Qualiy 246
822 Volatility 247
€
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973 Visosiy 247 9142 Vapo Lock in Fuel Systems 292 (
B24 Specie Gavi 29 9143 Bakftng or Poping inte Caburetor 299
875 Comoson and Wear 249 948 Carburetor Drawbacks 293 €
876 Handling Ease 250 9.16 Fuclinjetion Systems in SI Engines 293 (
B19 Satay 250 917 Types of Fusion Systeme ln SI Engines 296
B28 Cleanliness 250 9:74" ConingousIjertion System. 26 €
88 Kock Rang ous 257 9.172 Timed ton System 295 i
881 Knock Rating o SI Ens Fuels 251 938 Eicionk Finnen Systeme (EFL) 297
832 Kock Rang of Cl Engine Pues 254 948.4 Single pin Thole Body Ines 297 €
Review Qustont 238 9182 Mali po Por Ijecion 297 4
2.9 Advantages ofthe SI Engine Fue nection System 501
9. Carburetors and Fuel Injection in SI Engines 258-305 9.20 Disadvantages of the SI Engine Fuel-injection System — 301 €
91 ncodusion 258 Review Quetion 302 i
92 Limits of Flammability 258 Problems 304 (
93 Steady-wming Mixture Requirements 259
951. Mine Rog fr Music Power 259 10. CI Engines: Fuel-Injection System mL
932 Mixture Requremens for Minimum Spee 101 Induction 306
Fuel Consumption 260 102 Requirements of nection Systems 206 €
933 Mixtur Requirements fr Vas Oupus 260 103 Injection Syueme 307 i
534 Mixure Requienens for King, Cols and High Power 261 1031 Aion Sytem 307
9.4 Transient requirements 263 10.3.2 Airless- or Solid-injection System 308 €
941" Siting und Warmup Reqiremens 263 1033 Indl Pop Sytem ote Divided cut Device 30 (
942 Acceleration Regunmen 207 1034 Un injector System or the Undivided Fueb fens Device 308
9:5 Mure Regiments loa Muhreylinder Engine — 263 1035 The Ditnbutor Soom 31! «
96 Carburetor Requirements 264 1036 Commonnil Sym” 312 i
37 A Simple Cano 264 104 Pactinecion mgs 313
9.8 Calculation of the Air/Fuel Ratio for a Simple Carburetor 266 104.1 Jerk Type Bosch Fuel-injection Pump 313 €
99 ‘Ail Ratio Neglesting the Compress of Air 268 1042 Unit nee 318 >
510. Comment on Aus Rao Suppe by a Simple Cutter 269 1042 Dista: Type Puchijestion Pump 319
3.1 Deters of te Hementry Cutter 270 10S Foclinecor 320 €
9.12. Essenal Pars ofa Modem Cartuetor — 270 1054" Putin Holder 320 i
921 Choke 270 1052 clin Nowe 320
9122 Main Meunng Sysem 271 106 Type of None 32) €
915 ling Sem 274 1061 Pie None 322
9124 Accelerating System — 276 1062 Single-hole (Orifice) Nozzle 323 €
9125 Bemonier Sum and Power System 26 1063 Mali hole Nocale 324 (
9126 Anipecolaor Vale 27 1064 Pie More 324
9.13 Types of Carburetors 277 107. Electronically Controlled Unit Fuel-injection System — 325 €
9134 Dow, Updraupht and Horizon drug 108 CL Engine Govemors 326 (
Caburetor 277 109 Spray Charros. 327
9132 Connie and Rote Cubuetars 278 01 Spay Fume 327 €
9.133 Maltvemas Carburetor 29 1092 Momias 327 i
9.14 Problems associated wih Carburetors 292 1093 Demmin 327
Dual Le Fomation 292 1094 Dian 229 €
€
€
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973 Visosiy 247 9142 Vapo Lock in Fuel Systems 292 (
B24 Specie Gavi 29 9143 Bakftng or Poping inte Caburetor 299
875 Comoson and Wear 249 948 Carburetor Drawbacks 293 €
876 Handling Ease 250 9.16 Fuclinjetion Systems in SI Engines 293 (
B19 Satay 250 917 Types of Fusion Systeme ln SI Engines 296
B28 Cleanliness 250 9:74" ConingousIjertion System. 26 €
88 Kock Rang ous 257 9.172 Timed ton System 295 i
881 Knock Rating o SI Ens Fuels 251 938 Eicionk Finnen Systeme (EFL) 297
832 Kock Rang of Cl Engine Pues 254 948.4 Single pin Thole Body Ines 297 €
Review Qustont 238 9182 Mali po Por Ijecion 297 4
2.9 Advantages ofthe SI Engine Fue nection System 501
9. Carburetors and Fuel Injection in SI Engines 258-305 9.20 Disadvantages of the SI Engine Fuel-injection System — 301 €
91 ncodusion 258 Review Quetion 302 i
92 Limits of Flammability 258 Problems 304 (
93 Steady-wming Mixture Requirements 259
951. Mine Rog fr Music Power 259 10. CI Engines: Fuel-Injection System mL
932 Mixture Requremens for Minimum Spee 101 Induction 306
Fuel Consumption 260 102 Requirements of nection Systems 206 €
933 Mixtur Requirements fr Vas Oupus 260 103 Injection Syueme 307 i
534 Mixure Requienens for King, Cols and High Power 261 1031 Aion Sytem 307
9.4 Transient requirements 263 10.3.2 Airless- or Solid-injection System 308 €
941" Siting und Warmup Reqiremens 263 1033 Indl Pop Sytem ote Divided cut Device 30 (
942 Acceleration Regunmen 207 1034 Un injector System or the Undivided Fueb fens Device 308
9:5 Mure Regiments loa Muhreylinder Engine — 263 1035 The Ditnbutor Soom 31! «
96 Carburetor Requirements 264 1036 Commonnil Sym” 312 i
37 A Simple Cano 264 104 Pactinecion mgs 313
9.8 Calculation of the Air/Fuel Ratio for a Simple Carburetor 266 104.1 Jerk Type Bosch Fuel-injection Pump 313 €
99 ‘Ail Ratio Neglesting the Compress of Air 268 1042 Unit nee 318 >
510. Comment on Aus Rao Suppe by a Simple Cutter 269 1042 Dista: Type Puchijestion Pump 319
3.1 Deters of te Hementry Cutter 270 10S Foclinecor 320 €
9.12. Essenal Pars ofa Modem Cartuetor — 270 1054" Putin Holder 320 i
921 Choke 270 1052 clin Nowe 320
9122 Main Meunng Sysem 271 106 Type of None 32) €
915 ling Sem 274 1061 Pie None 322
9124 Accelerating System — 276 1062 Single-hole (Orifice) Nozzle 323 €
9125 Bemonier Sum and Power System 26 1063 Mali hole Nocale 324 (
9126 Anipecolaor Vale 27 1064 Pie More 324
9.13 Types of Carburetors 277 107. Electronically Controlled Unit Fuel-injection System — 325 €
9134 Dow, Updraupht and Horizon drug 108 CL Engine Govemors 326 (
Caburetor 277 109 Spray Charros. 327
9132 Connie and Rote Cubuetars 278 01 Spay Fume 327 €
9.133 Maltvemas Carburetor 29 1092 Momias 327 i
9.14 Problems associated wih Carburetors 292 1093 Demmin 327
Dual Le Fomation 292 1094 Dian 229 €
€
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x _Conents
_ Coment x
10.10 Rate of Fue Injection in CI Engines 32 ~
I foun Funerales 330 ° D PRE ae
) 10.11.1 Fuel Compressibility 320 u
10.112 Pressure Waves ri
) in Fuel Lines 330
cate ee 126 Requirements of Good Spark Plug 385
y roms 1262 Factors affecting the Establishment of Spark 385
, 1263 SparkcPlug Hest Range — 385
Tora 12.7 Magneto-ignition System 386
345-375 ompatison of Bat
e, 128. Gato of Baten Mapa in Spe 307
) 112 Chassiteaon of Twostoke Engies 345 a San ee
y PS Seg Argen E BOY, Tail Iris (OD Sym 3
pacte Sscharge Temtion (CDI) System
yy E on Son 6 PE EN SES
) Da Semen M, 1212 Spack-advance Mechanisms 392
) he Heals fr Semen Paces 354 12122 Vewumadance Mec 393
Ba Meds o Sen .2 Vacuum advance Mechanism
> 1162 Carrie Ming Me 255 nn
) 1163 Shorecireviing 356 13. Engine Friction and Lubrication
117. Relationship of Scavenging Ratio and Scovenging Efiieney 356 : es ae
) 118. Measurement of Scavenging EMfcieney 357 Poe
à Messe of Scene 132 Components of Engine Friction 336
1182 Govsampling Method — 358 Be rue:
D 119 ose Pra 359 opens
ne 3 223 Auxiliay Component Losses 397
Dr a 133 Tol Pétion Work 397
|, mena à 134 Sone Mae Components of Engine Pion 398
1113 Advantages and Disadvantaes of Two-troke Engines Cine ae
D AIS En of uen Stn CT Engines 08 F6 Dar Bien ort
| ca 136.1 Hydrodynamic or Flïd-flm Friction 399
> pcos 1362 Panialfilm Fiction 299
1363 Rolling Frction 400
a 1364 Dry Friction 400
M2. Ignition Syster 376-395 137. Mechanical Friction in Major Engine Cor
Y (21 Unrodueton 376 o
1371 Pistoo Assembly Friction 400
122 Ignition System Requirements 376 137.2 Bearing Friction 407
) 123 Baterysigeiion Syrem 378 1373 Vane Train Friction 40
) aa Bate 378 nn
A 1232 pon Sieh 379 139 Effet of Engine Variables on Friction 403
3 Ballet Resistor 379 13.10 Side Thrust un the Piston 405
\ 34 Ign Cot” 79 13.11 Labrcaton — 407 .
.S Contact Breaker Points 3 r
, 1235 Goat rene Fos 20 13.12 Puncions of a Lubricant 407
136 Conder 8 13.13 Labricaio Principles 408
; tor 38 13.134. Hydrodyeanic Lubrication Ful Film or Thick Film) 408
>
)
_ Coment x
10.10 Rate of Fue Injection in CI Engines 32 ~
I foun Funerales 330 ° D PRE ae
) 10.11.1 Fuel Compressibility 320 u
10.112 Pressure Waves ri
) in Fuel Lines 330
cate ee 126 Requirements of Good Spark Plug 385
y roms 1262 Factors affecting the Establishment of Spark 385
, 1263 SparkcPlug Hest Range — 385
Tora 12.7 Magneto-ignition System 386
345-375 ompatison of Bat
e, 128. Gato of Baten Mapa in Spe 307
) 112 Chassiteaon of Twostoke Engies 345 a San ee
y PS Seg Argen E BOY, Tail Iris (OD Sym 3
pacte Sscharge Temtion (CDI) System
yy E on Son 6 PE EN SES
) Da Semen M, 1212 Spack-advance Mechanisms 392
) he Heals fr Semen Paces 354 12122 Vewumadance Mec 393
Ba Meds o Sen .2 Vacuum advance Mechanism
> 1162 Carrie Ming Me 255 nn
) 1163 Shorecireviing 356 13. Engine Friction and Lubrication
117. Relationship of Scavenging Ratio and Scovenging Efiieney 356 : es ae
) 118. Measurement of Scavenging EMfcieney 357 Poe
à Messe of Scene 132 Components of Engine Friction 336
1182 Govsampling Method — 358 Be rue:
D 119 ose Pra 359 opens
ne 3 223 Auxiliay Component Losses 397
Dr a 133 Tol Pétion Work 397
|, mena à 134 Sone Mae Components of Engine Pion 398
1113 Advantages and Disadvantaes of Two-troke Engines Cine ae
D AIS En of uen Stn CT Engines 08 F6 Dar Bien ort
| ca 136.1 Hydrodynamic or Flïd-flm Friction 399
> pcos 1362 Panialfilm Fiction 299
1363 Rolling Frction 400
a 1364 Dry Friction 400
M2. Ignition Syster 376-395 137. Mechanical Friction in Major Engine Cor
Y (21 Unrodueton 376 o
1371 Pistoo Assembly Friction 400
122 Ignition System Requirements 376 137.2 Bearing Friction 407
) 123 Baterysigeiion Syrem 378 1373 Vane Train Friction 40
) aa Bate 378 nn
A 1232 pon Sieh 379 139 Effet of Engine Variables on Friction 403
3 Ballet Resistor 379 13.10 Side Thrust un the Piston 405
\ 34 Ign Cot” 79 13.11 Labrcaton — 407 .
.S Contact Breaker Points 3 r
, 1235 Goat rene Fos 20 13.12 Puncions of a Lubricant 407
136 Conder 8 13.13 Labricaio Principles 408
; tor 38 13.134. Hydrodyeanic Lubrication Ful Film or Thick Film) 408
>
)
xii Contents
13.132. Boundary Lubrication (Thin Film) 409
13.133 Mixed-film Lubrication (Partial Film) — 409
13.14 Bearings Lubrication — 410
13.14.1 Rotating Journal Bearings 410
13.142. Oscillating Joumal Bearings #13
13.143 Reciprocating Bearings 413
13144 Gear Teeth 414
13.15 Properties of Lubricants 414
13.154 Viscosity 44
13.152. Viscosity Index (VD 424
13453 Pour Point 415
13154 Fash and Fire Poims 415
13155 Subilay 415
13156 Oilness 415
13.157 Corrosiveness — 415
13158 Detergeney — 416
13159 Foaming 416
13.16 Additives for Lubricants 416
13.17 SAE Viscosity Number — 418
13.18 Lubricating Systems 419
13182 Petrol Lubrication System — 419
13182 Wecsump Lubrication System — 419
13183 Dry-sump Lubrication System 427
13.19 Engine Performance and Lubrication — 423
Review Questions 426
14. Heat Transfer in Engines and Cooling Systems
14.1 Introduction — 428
Necessity of Engine Cooling 428
Disadvantages of Overcooling 429.
Engine Temperature Distribution 429
Engine Warm-up 430
Gas Temperature Variation 437
Heat Transfer Considerations 432
147.1 Conduction — 432
14.7.2 Convection — 432
1473 Radiation 434
14,8 Heat Transfer in Intake System 435
14.9 Heat Transfer in Combustion Chambers 435
14.10 Heat Transfer in Exhaust System — 437
14.11 Piston Cooling — 437
14.12 ValveCooling 438
14.13 Effect of Operating Variables on Heat Transfer 439
14.131. Mixture Strength — 439
428-455
15.
Contans_xili
14.132 Compression Ratio 4#0
14.133 Spark Timing — 44)
14134 Engine Size — 44)
14.135. Engine Speed 442
14136 Load 423
1413.7 Inlet Temperature 445
14.138. Coolant Temperature 443
14.139 Engine Materials — 493
14.13.10 Knock 444
14.13.11 Swirl and Squish 444
14.14 Cooling Systems 444
14.15 Alrcooled System 444
1415.1 Cooling Fins — 445
14.16 Liguid-cooted Systems — 446
14.164 Direct or Non-retum System 946
14.162 Thermosypton or Natural Circulation System — 446
14.163 Forced or Pump Circulation System — 447
14.164 Pressure Cooling System — 449
14.165. Evaporative Cooling System — 450
14.17 Comparison of Air- and Liquid-cooling Systems — 451
14.17.1. Advantages of the Ait-cooling System 452
14.172 Disadvantages of the Aircooling System — 451
14.173. Advantages of the Liguid-cooling System 452
14.174. Disadvantages of the Liquid-cooling System — 452
14.18 Modern Cooling Concepts — 452
14.19 Adiabatic Engines — 453
Review Questions — 454
Air Capacity and Supercharging
15.1 Introduction 456
152 Elleet of Air Capacity on Indicated Power 456
153. Ideal Air Capacity 457
154. Volumetic Efficiency — 458
15.5 Effect of Variables on Volumetric Ef
1551 Fuel 459
155.2 Heat Transfer in the Intake System 460
1553 Valve Overlap 160
1554 Viscous Drag and Restrictions 460
1555 Timing of Intake Valve Closing 467
1556 Intake Tuning — 461
ST Exhaust Residual 467
155.8 Exhaust Gas Recirulaion (EGR) 462
456-489
13.132. Boundary Lubrication (Thin Film) 409
13.133 Mixed-film Lubrication (Partial Film) — 409
13.14 Bearings Lubrication — 410
13.14.1 Rotating Journal Bearings 410
13.142. Oscillating Joumal Bearings #13
13.143 Reciprocating Bearings 413
13144 Gear Teeth 414
13.15 Properties of Lubricants 414
13.154 Viscosity 44
13.152. Viscosity Index (VD 424
13453 Pour Point 415
13154 Fash and Fire Poims 415
13155 Subilay 415
13156 Oilness 415
13.157 Corrosiveness — 415
13158 Detergeney — 416
13159 Foaming 416
13.16 Additives for Lubricants 416
13.17 SAE Viscosity Number — 418
13.18 Lubricating Systems 419
13182 Petrol Lubrication System — 419
13182 Wecsump Lubrication System — 419
13183 Dry-sump Lubrication System 427
13.19 Engine Performance and Lubrication — 423
Review Questions 426
14. Heat Transfer in Engines and Cooling Systems
14.1 Introduction — 428
Necessity of Engine Cooling 428
Disadvantages of Overcooling 429.
Engine Temperature Distribution 429
Engine Warm-up 430
Gas Temperature Variation 437
Heat Transfer Considerations 432
147.1 Conduction — 432
14.7.2 Convection — 432
1473 Radiation 434
14,8 Heat Transfer in Intake System 435
14.9 Heat Transfer in Combustion Chambers 435
14.10 Heat Transfer in Exhaust System — 437
14.11 Piston Cooling — 437
14.12 ValveCooling 438
14.13 Effect of Operating Variables on Heat Transfer 439
14.131. Mixture Strength — 439
428-455
15.
Contans_xili
14.132 Compression Ratio 4#0
14.133 Spark Timing — 44)
14134 Engine Size — 44)
14.135. Engine Speed 442
14136 Load 423
1413.7 Inlet Temperature 445
14.138. Coolant Temperature 443
14.139 Engine Materials — 493
14.13.10 Knock 444
14.13.11 Swirl and Squish 444
14.14 Cooling Systems 444
14.15 Alrcooled System 444
1415.1 Cooling Fins — 445
14.16 Liguid-cooted Systems — 446
14.164 Direct or Non-retum System 946
14.162 Thermosypton or Natural Circulation System — 446
14.163 Forced or Pump Circulation System — 447
14.164 Pressure Cooling System — 449
14.165. Evaporative Cooling System — 450
14.17 Comparison of Air- and Liquid-cooling Systems — 451
14.17.1. Advantages of the Ait-cooling System 452
14.172 Disadvantages of the Aircooling System — 451
14.173. Advantages of the Liguid-cooling System 452
14.174. Disadvantages of the Liquid-cooling System — 452
14.18 Modern Cooling Concepts — 452
14.19 Adiabatic Engines — 453
Review Questions — 454
Air Capacity and Supercharging
15.1 Introduction 456
152 Elleet of Air Capacity on Indicated Power 456
153. Ideal Air Capacity 457
154. Volumetic Efficiency — 458
15.5 Effect of Variables on Volumetric Ef
1551 Fuel 459
155.2 Heat Transfer in the Intake System 460
1553 Valve Overlap 160
1554 Viscous Drag and Restrictions 460
1555 Timing of Intake Valve Closing 467
1556 Intake Tuning — 461
ST Exhaust Residual 467
155.8 Exhaust Gas Recirulaion (EGR) 462
456-489
>
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15.6 Supercharging 462
156.1 Uses of Supercharged Engines 462
15.6.2 Factors which Increase the Power Output by Supercharging 462
15.7. Methods of Supercharging 463
15.2.1 Mechanical Supercharging 463
15.2 Tutbocharging 463
15.7.3 Pressure Wave Supercharging 464
15.8 Thermodynamic Cycle with Supercharging 465
159 Supercharging of Spark-ignition Engine 468
1510 Supercherging of Compression-ignition Engine 469
ISL Advantages of Supercharging Over High Compression — 469
15.12 Effects of Supercharging — 471
15121 Power Output 477
15122 Fuel Consumption 471
15.123 Mechanical Efficiency — 471
15124. Volumen Efficiency — 471
15.13 Supercharging, Limits — 471
15.13.1. Supercharging Limits of SI Engines 472
15132. Superchasging Limits of CI Engines 472
15.14 Engine Modifications for Supercharging — 472
15.15 Types of Supercharger — 473
15151 Roots Blower — 473
15152 Vane Blower 474
155.3 Cenuifugal Compressor — 474
Review Questions 487
Problems 488
Engine Testing and Performance
16.1 Introduction — 490
162 Measurement of Brake Power — 490
1621 Prony Brake — 490
162.2 Rope Brake — 491
162.3 Hydraulic Dynamometer 492
162.4 Eddy Current Dynamometer 493
162.5 Swinging Field DC Dynemometer — 494
163 Indicated Power — 494
163.1 Mechanical Indicator 495
1632 Electronio Indicator 497
1633 — Willan's Line Method 500
1634 The Morse Test — 501
163.5 Motoring Test 502
164 Fuel Consumption — 502
164.1 Gravimetric Fuel-flow Measurement — 503
490-539
165
166
167
168
169
16.10
va
m2
u
ns
no
1710
CAT
1642 Volumetcic Type Flowmeters 503
1643 Rotameter 505
Measurement of Air Flow Rate 505
165.1 Airbox and Orifice Method — 505
165.2 Viscous Flowmeter 507
Speed Measurement 507
Spark-timing Measurement 508
Combustion Photography and Plame Speed Detection 508
Performance Characteristics 509.
169.1 Variable Speed Characteristics 309
1692 Constant Speed Characteristics S17
1693 Performance Maps — 514
Heat Balance Sheet — 516
Review Questions — 536
Problems — 537
Exhaust Emissions
Introduction 540
Measurement of Exhaust Emissions — 542
17.2.1 Non-dispenive Infra-red (NDIR) Analyzer — 54
172.2 Flame-ionization Detector (FID) 543
172.3 Chemiluminescence Analyzers (CLA) — 544
1724 Oxygen Analyzer 545
Measurement of Pariculates 46
Measurement of Exhaust Smoke 546
174.1 Harteidge Smoke-meter 546
1742 Bosch Smoke-meter — 547
Gas Chromatography — 547
Pollutant Formation — 548
17.6.1 Hydrocarbons (HC) 548
1762 Carbon Monoxide (C0) 549
17.63 Oxides of Nitrogen (NO) 550
1764 Paniculates 550
540-562
Effect of Operating Variables on SI Engine Exhaust Emissions 351
Design and Operating Variables that Decrease HC Concentration
from the Exhaust of SI Engine 553
Design and Operating Variables that Reduce NO, Concentration
from the Exhaust of SI Engine 554
Effect of Operating Variables on CI Engine Exhaust Emission 554
Control of Exhaust Emissions 355
17111 Catalytic Converters — 555
17.412 Thermal Reactor 560
17113 Partieulate Traps 561
Review Questions — 561
y xiv_Comens
Contents _ xv
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15.6 Supercharging 462
156.1 Uses of Supercharged Engines 462
15.6.2 Factors which Increase the Power Output by Supercharging 462
15.7. Methods of Supercharging 463
15.2.1 Mechanical Supercharging 463
15.2 Tutbocharging 463
15.7.3 Pressure Wave Supercharging 464
15.8 Thermodynamic Cycle with Supercharging 465
159 Supercharging of Spark-ignition Engine 468
1510 Supercherging of Compression-ignition Engine 469
ISL Advantages of Supercharging Over High Compression — 469
15.12 Effects of Supercharging — 471
15121 Power Output 477
15122 Fuel Consumption 471
15.123 Mechanical Efficiency — 471
15124. Volumen Efficiency — 471
15.13 Supercharging, Limits — 471
15.13.1. Supercharging Limits of SI Engines 472
15132. Superchasging Limits of CI Engines 472
15.14 Engine Modifications for Supercharging — 472
15.15 Types of Supercharger — 473
15151 Roots Blower — 473
15152 Vane Blower 474
155.3 Cenuifugal Compressor — 474
Review Questions 487
Problems 488
Engine Testing and Performance
16.1 Introduction — 490
162 Measurement of Brake Power — 490
1621 Prony Brake — 490
162.2 Rope Brake — 491
162.3 Hydraulic Dynamometer 492
162.4 Eddy Current Dynamometer 493
162.5 Swinging Field DC Dynemometer — 494
163 Indicated Power — 494
163.1 Mechanical Indicator 495
1632 Electronio Indicator 497
1633 — Willan's Line Method 500
1634 The Morse Test — 501
163.5 Motoring Test 502
164 Fuel Consumption — 502
164.1 Gravimetric Fuel-flow Measurement — 503
490-539
165
166
167
168
169
16.10
va
m2
u
ns
no
1710
CAT
1642 Volumetcic Type Flowmeters 503
1643 Rotameter 505
Measurement of Air Flow Rate 505
165.1 Airbox and Orifice Method — 505
165.2 Viscous Flowmeter 507
Speed Measurement 507
Spark-timing Measurement 508
Combustion Photography and Plame Speed Detection 508
Performance Characteristics 509.
169.1 Variable Speed Characteristics 309
1692 Constant Speed Characteristics S17
1693 Performance Maps — 514
Heat Balance Sheet — 516
Review Questions — 536
Problems — 537
Exhaust Emissions
Introduction 540
Measurement of Exhaust Emissions — 542
17.2.1 Non-dispenive Infra-red (NDIR) Analyzer — 54
172.2 Flame-ionization Detector (FID) 543
172.3 Chemiluminescence Analyzers (CLA) — 544
1724 Oxygen Analyzer 545
Measurement of Pariculates 46
Measurement of Exhaust Smoke 546
174.1 Harteidge Smoke-meter 546
1742 Bosch Smoke-meter — 547
Gas Chromatography — 547
Pollutant Formation — 548
17.6.1 Hydrocarbons (HC) 548
1762 Carbon Monoxide (C0) 549
17.63 Oxides of Nitrogen (NO) 550
1764 Paniculates 550
540-562
Effect of Operating Variables on SI Engine Exhaust Emissions 351
Design and Operating Variables that Decrease HC Concentration
from the Exhaust of SI Engine 553
Design and Operating Variables that Reduce NO, Concentration
from the Exhaust of SI Engine 554
Effect of Operating Variables on CI Engine Exhaust Emission 554
Control of Exhaust Emissions 355
17111 Catalytic Converters — 555
17.412 Thermal Reactor 560
17113 Partieulate Traps 561
Review Questions — 561
xvi Comer
18. Alternative Potential Engines
184
182
183
184
185
186
187
Stratificd-charge Engine — 563
Wankel Engine — 565
Fcee-piston Engine 367.
Stirling Engine 569
Variable Compression Ratio (VCR) Engine 573
Dua-fuel Engines 575
Multi-fuet Engines 577.
18.7.1 Suitability of Other Engines as Mul-fuel Units
Review Questions — 578
Bibliography
Answers to Problems
Index
578
563-579
581-586
587-590
591-597
Preface
‘This book is intended to cover the vast and fast growing field of internal combustion engines
in accordance with the curriculum for a bechelor’s degree in mechanical engineering and
aeronautical engineering. The contents of Ihe book will be equally helpful to the postgraduate
students as well, and to those preparing for various competitive examinations such as Civil
Services, Engineering Services, GATE, etc. Students pursuing AMIE (Section B) in mechanical
engineering will also derive full benefi from this book as the coneemed syabus is exhaustively
and fully covered, The book can also be used as a reference by research scholars and practising
engineers specially engaged in the field of design ard development of engines.
‘The book is written in a simple and fucid language with good diagrammatie ilustrativos
‘Tae various topics are explained right from the fundamentals so as to build an understanding
‘of concepts and emphasize the relationship between conceptual understanding and problem
solving approaches. However, the students are expected to have basic knowledge of
‘thermodynamics, Avid mechanics and heat transfer as prerequisites in order to extract maximum
‘benefit from the text
‘The book has been divided into eighteen chapters to cover the important topics on ¿neral
combustion engines. It comprehensively discusses the fundamentals of both spark ignition (ST)
and compression-ignition (CI) engines operating on fourstroke and two-stroke cycles. It also
includes the basic design and operation of internal combustion engines, analysis of cycles,
combustion charts, combustion in SI and CI engines, fuels, fuel injection techniques, ignition
systems, friction and lubrication, heat transfer and cooling systems, supercharging, testing and
performance, exhaust emissions, modern developments, and alternate potential engines, tc
‘The SI units have been consistently used throughout the text. With a view to developing
the students" problem-solving skills, many typical worked-out examples have been included.
‘The chaptercend review questions and problems offer students practice opportunities that will
stimolate their interest in the subject.
Ina nutshell, my goal has been to help the students acquire a soli theoretical background
of intemal combustion engines. Solved numerical examples are used extensively Ihroughont the
text to help them understand how theory is applied to analyze practical applications.
In writing this book, the author has made use of information of general interes collected
by him while teaching courses and pursuing research in the field of intemal combustion
engines. A list of references that has been particularly helpful to the author is incloded in the
bibliography section at the end of the book.
18. Alternative Potential Engines
184
182
183
184
185
186
187
Stratificd-charge Engine — 563
Wankel Engine — 565
Fcee-piston Engine 367.
Stirling Engine 569
Variable Compression Ratio (VCR) Engine 573
Dua-fuel Engines 575
Multi-fuet Engines 577.
18.7.1 Suitability of Other Engines as Mul-fuel Units
Review Questions — 578
Bibliography
Answers to Problems
Index
578
563-579
581-586
587-590
591-597
Preface
‘This book is intended to cover the vast and fast growing field of internal combustion engines
in accordance with the curriculum for a bechelor’s degree in mechanical engineering and
aeronautical engineering. The contents of Ihe book will be equally helpful to the postgraduate
students as well, and to those preparing for various competitive examinations such as Civil
Services, Engineering Services, GATE, etc. Students pursuing AMIE (Section B) in mechanical
engineering will also derive full benefi from this book as the coneemed syabus is exhaustively
and fully covered, The book can also be used as a reference by research scholars and practising
engineers specially engaged in the field of design ard development of engines.
‘The book is written in a simple and fucid language with good diagrammatie ilustrativos
‘Tae various topics are explained right from the fundamentals so as to build an understanding
‘of concepts and emphasize the relationship between conceptual understanding and problem
solving approaches. However, the students are expected to have basic knowledge of
‘thermodynamics, Avid mechanics and heat transfer as prerequisites in order to extract maximum
‘benefit from the text
‘The book has been divided into eighteen chapters to cover the important topics on ¿neral
combustion engines. It comprehensively discusses the fundamentals of both spark ignition (ST)
and compression-ignition (CI) engines operating on fourstroke and two-stroke cycles. It also
includes the basic design and operation of internal combustion engines, analysis of cycles,
combustion charts, combustion in SI and CI engines, fuels, fuel injection techniques, ignition
systems, friction and lubrication, heat transfer and cooling systems, supercharging, testing and
performance, exhaust emissions, modern developments, and alternate potential engines, tc
‘The SI units have been consistently used throughout the text. With a view to developing
the students" problem-solving skills, many typical worked-out examples have been included.
‘The chaptercend review questions and problems offer students practice opportunities that will
stimolate their interest in the subject.
Ina nutshell, my goal has been to help the students acquire a soli theoretical background
of intemal combustion engines. Solved numerical examples are used extensively Ihroughont the
text to help them understand how theory is applied to analyze practical applications.
In writing this book, the author has made use of information of general interes collected
by him while teaching courses and pursuing research in the field of intemal combustion
engines. A list of references that has been particularly helpful to the author is incloded in the
bibliography section at the end of the book.
xy Price
1 am grateful to several individuals who eld me in ih development of the text. Ham
artcatarly indeed to Late Prof. RS. Benson, my PhD. supevisr atthe University of
Martes Int of Sas and Teton (UMS, UK. who as alos ben à
source of inspiraon o me in the siting of tis book. Several ar people deserve special
Meta Enge se ef Teel Ban nd hry Yana Te a
of our many discussione and hie valuable suggestions and constructve eich ar incorporate
in the text. a
AS the text evolved from my ct
lecture notes over a period of years, my students offered
helpfol suggestions and asked questions tht really needed tooght-provokingclaifeatins
Feet ds vi ny en 1 1 sof ove aa be
It is my hope that this text will form a useful part of an educational programme in ho
relevant engineering disciplines. qe “
HN. GUPTA
aes
Introduction to Internal
Combustion Engines
14. AN OVERVIEW
Amengin is à vice which wanafoms the chemical ebergy of a fu imo thermal energy and uses
ay to produce mechanical work. Engines normally conver thermal energy into mechan
ea And. therefore, they ae called eat engines. When fuel bums in the presence of amo-
Shenae, a remendous amount of heat energy released. The products of combustion tin
SE eh temperature, A bea engin conver he released heat energy nt useful work with he
lp of a working Mud
Heat engines are broadly classified into:
(a) External Combustion Engines (EC Engines)
(6) Internal Combustion Engines (IC Engines)
In extemal combustion engines, the combustion ofthe fuel in presence of air takes place
“outside te engine cylinder. The heat energy released from the fuel i utiliza o rise the high
esse sea in oiler from wate, team isa woking ui, which eters into the eying of
Prim engine to perform mechanical work. Here, the products of combustion of fuel do not
Enter into the engine cylinder and hence they donot form the working fluid
‘The steam tubing in a steam power plant is another example of an external combustion
engine, The steam engine may be called an interment external combustion engine and the stam
Fame a continuous extemal combustion engine. A closed cycle gas turbine plant is also an
sample ofan external combustion engine. Here, normally the aris a working substance which
Completes a thermodynamic eye I receives beat fom products of combustion of fel ina heat
ter and ejects heat from another beat exchanger o the surroundings, Here also the prod-
cer ot combustion do rat enter into the turbine. Sting engine is also an external combustion
engine.
Tn imernal combustion engines. either the combustion ofthe fuel takes place inside he engine
cinder or the products of combustion enter int he cylinder sa working fluid. In recprocating
hgines having eylinder and piston, te combustion of he uel takes place inside the eyinder and
Suh engines may be called inermiten intemal combustion engines. In an open cycle gas turbine
plant, the products of combustion of fuel enter oto the gas turbine and work is obtained in the
oom of reaton ofthe tatine shaft. Such a turbine is an example of a continuous intemal com-
bustion engine.
1 am grateful to several individuals who eld me in ih development of the text. Ham
artcatarly indeed to Late Prof. RS. Benson, my PhD. supevisr atthe University of
Martes Int of Sas and Teton (UMS, UK. who as alos ben à
source of inspiraon o me in the siting of tis book. Several ar people deserve special
Meta Enge se ef Teel Ban nd hry Yana Te a
of our many discussione and hie valuable suggestions and constructve eich ar incorporate
in the text. a
AS the text evolved from my ct
lecture notes over a period of years, my students offered
helpfol suggestions and asked questions tht really needed tooght-provokingclaifeatins
Feet ds vi ny en 1 1 sof ove aa be
It is my hope that this text will form a useful part of an educational programme in ho
relevant engineering disciplines. qe “
HN. GUPTA
aes
Introduction to Internal
Combustion Engines
14. AN OVERVIEW
Amengin is à vice which wanafoms the chemical ebergy of a fu imo thermal energy and uses
ay to produce mechanical work. Engines normally conver thermal energy into mechan
ea And. therefore, they ae called eat engines. When fuel bums in the presence of amo-
Shenae, a remendous amount of heat energy released. The products of combustion tin
SE eh temperature, A bea engin conver he released heat energy nt useful work with he
lp of a working Mud
Heat engines are broadly classified into:
(a) External Combustion Engines (EC Engines)
(6) Internal Combustion Engines (IC Engines)
In extemal combustion engines, the combustion ofthe fuel in presence of air takes place
“outside te engine cylinder. The heat energy released from the fuel i utiliza o rise the high
esse sea in oiler from wate, team isa woking ui, which eters into the eying of
Prim engine to perform mechanical work. Here, the products of combustion of fuel do not
Enter into the engine cylinder and hence they donot form the working fluid
‘The steam tubing in a steam power plant is another example of an external combustion
engine, The steam engine may be called an interment external combustion engine and the stam
Fame a continuous extemal combustion engine. A closed cycle gas turbine plant is also an
sample ofan external combustion engine. Here, normally the aris a working substance which
Completes a thermodynamic eye I receives beat fom products of combustion of fel ina heat
ter and ejects heat from another beat exchanger o the surroundings, Here also the prod-
cer ot combustion do rat enter into the turbine. Sting engine is also an external combustion
engine.
Tn imernal combustion engines. either the combustion ofthe fuel takes place inside he engine
cinder or the products of combustion enter int he cylinder sa working fluid. In recprocating
hgines having eylinder and piston, te combustion of he uel takes place inside the eyinder and
Suh engines may be called inermiten intemal combustion engines. In an open cycle gas turbine
plant, the products of combustion of fuel enter oto the gas turbine and work is obtained in the
oom of reaton ofthe tatine shaft. Such a turbine is an example of a continuous intemal com-
bustion engine.
2 Ffuntarenal of Intern Combustion Engines
ail
Ingeduction 0 ternal Combustion Enge 3
‘The intermittent intemal combustion engines are most popular because of thie use as the
primemaver in motor vehicles, and usually these engines are reciprocling engines. The recipro-
eating engine mechanism consists ofa piston which moves ina cylinder and forms a movable gas.
right seal. By means of a connecting od and a crankshaft arrangement, the reciprocating motion
‘of the piston is converted to rotary motion a the erankshaf
‘The steam turbine plants the most popular continuous extemal combustion engine used for
large elecrie power generation. The essential components are boiler, steam turbine, condenser,
and feed pump.
‘The main advantages of an internal combustion engine over an external combustion engine
(2) Greater mechanical simplicity
(0), Higher power output per unit weight because ofthe absence of auxiliary unis lke boiler,
‘condenser, and feed pump
(6) Lower inital cost
(@) Higher brake thermal efiiency as only a small fr
dissipated to the cooling system,
of heut energy of the fuel is
‘The advantages of intemal combustion engine accrue from the fact that they work at an
average temperature whichis much below the maximum temperature of the working lid in the
cycle.
‘The disadventages ofthe internal combustion engine over he external combustion engine are
(2) The IC engines cannot use solid fuels which are cheaper. Only liquid or gascous fuels of
given specifications can be efficiently used. These fucs are relatively more expensive.
(0) The IC engines are not self starting whereas the EC engines have a hih-stating torque
(©) The intermittent IC engines have reciprocating parts and hence they are susceptible o the
problems of vibration
‘Wankel engine isa rotary intcmitent interna! combustion engine. Jet engines and rockets are
also internal combustion engines. They fall under the category of rotary continuous intemal com
bustion engine. This book deals with the intermiuene intemal combustion engines, mainly of
reciprocating type and thus excludes the gas turbine. Reciprocating IC engines are used in auto
mobiles, motoseyeles and scooters, power bouts, ships locomotives, and small aircraft. Due to
scarcity of electric power, the use of IC engines as a portable power output unit has gained
tuemendous momentum. These engines are alo used in farm tractors, Iawamowers and in many
other devices
1.2 HISTORICAL DEVELOPMENT
‘The fie IC engine for commercial use was developed by a Frenchman, 1J.E. Lenoir (1822-
1900) inthe year 1860. Coal gas and air mixture were drawn into the engine cylinder ducing Ihe
firschal of be piston stoke. A this point the charge was ignited by a spark. This caused rise in
pressure and the burned gases, the so-called products of combustion, delivered power to the
piston forthe second-half of the stroke. On the retum stroke, the gases were discharged fromthe
cylinder. The return stroke was possible by using a large flywheel which stored energy during he
power stroke and dissipated energy during the return stroke, exactly i the same manner as inthe
Case of a steam engine. By the year 1865 about 5000 engines were buil in sizes up to 6 hp
providing efficiency, however, not exceeding 5 percent, but it was beter han te efficiency of a
mal steam engine of those times
"Nicolaus A. Oto (1832-1891) and Eugen Langen (1833-1895) developed a free piston engine
in 1867 in Germany. Air-usl mixture was taken in cylinder and ignited by a gas flame during the
carly pat ofthe outward stroke to accelerate a free piston, and a vacuum was thus generated in
the cylinder. The piston was brought inward by atmospheris pressure acting onthe piston rom
the other side. During the inward stroke the burned gas was exhausted through a lid valve, The
piston od was connected by ratchet and a rack and pinion device tothe flywheel mounted en the
Output haf The inertia ofthe flywhee! moved the piston outwards and induced afresh charge
‘through a side valve to repeat the cycle, The thermal efficiency of this engine was found o be 11
Pr Th 1862, Alphonse Besu de Rochas (1815-1993) a Frenchman, described the principles of
four-stroke cycle and the conditions under which maximum efficiency could be obiained in IC
engines. It gave an idea of igniting fucl at higher pressures, nearly atthe end of compression
instead of During the fuel at atmospheric pressure. Increased cylinder volume with minimum
‘arface-to-volume ratio, maximum possible speed and higher expansion ratio were also suggested
{oc higher thermal efficiency,
Beau de Roches could no, however, build any engine himself based on his principles, In 1876,
‘Nicolaus August Oto built an engine based on these principles. This engine worked on the Four.
stroke principle—intake, compression, expansion or power and exhaust stokes. Ignition was
nearly a he end of compression, Otto engine results in reduced weight and volume and gave
higher thermal efficiency. This was the breakthrough that effectively founded the IC engine indus-
try. By 1890, almost 50,000 of these engines had been sold in Europe and the USA.
By the 1880s, Dugald Clek and James Robson ofthe UK and Karl Benz of Germany devel-
‘oped the two-suoke intemal combustion engine In this engine, compression of he charge takes
place during the inward or upward stroke and expansion or power is obtained during the outward
or downward stoke. Exhaust and intake processes occur during the nd of the power stroke and
a: te beginning of the compression stoke. In 1885, James Atkinson of England developed an
engine with an expansion stoke larger than dhe compression stoke. The larger expansion stroke
was used to increase the efficiency ofthe engine, Efficiency could also have been increased by
increasing the compression ratio, but in orde to avoid knocking problems the compresion rai at
that time with the quality of fuel availabe had to be kept below four.
In 1892, Rudolf Diesel (1858-1913) developed a diferen type of engine in which a high
compression ratio was used to ignite the fuel. Fuel was injected nearly atthe end of compression
which was then ignited by hot compressed ar, The efficiency of the engine was increased due to
higher compression and expansion ratios. The knocking problem was also overcome. The present
diesel engine is designed on the same working principle. Both four-stroke and two-stroke diesel
engines have been developed,
13. MODERN DEVELOPMENTS
In 1957, Wankels rotary IC engine was tested successfully after being under research and
_\
ail
Ingeduction 0 ternal Combustion Enge 3
‘The intermittent intemal combustion engines are most popular because of thie use as the
primemaver in motor vehicles, and usually these engines are reciprocling engines. The recipro-
eating engine mechanism consists ofa piston which moves ina cylinder and forms a movable gas.
right seal. By means of a connecting od and a crankshaft arrangement, the reciprocating motion
‘of the piston is converted to rotary motion a the erankshaf
‘The steam turbine plants the most popular continuous extemal combustion engine used for
large elecrie power generation. The essential components are boiler, steam turbine, condenser,
and feed pump.
‘The main advantages of an internal combustion engine over an external combustion engine
(2) Greater mechanical simplicity
(0), Higher power output per unit weight because ofthe absence of auxiliary unis lke boiler,
‘condenser, and feed pump
(6) Lower inital cost
(@) Higher brake thermal efiiency as only a small fr
dissipated to the cooling system,
of heut energy of the fuel is
‘The advantages of intemal combustion engine accrue from the fact that they work at an
average temperature whichis much below the maximum temperature of the working lid in the
cycle.
‘The disadventages ofthe internal combustion engine over he external combustion engine are
(2) The IC engines cannot use solid fuels which are cheaper. Only liquid or gascous fuels of
given specifications can be efficiently used. These fucs are relatively more expensive.
(0) The IC engines are not self starting whereas the EC engines have a hih-stating torque
(©) The intermittent IC engines have reciprocating parts and hence they are susceptible o the
problems of vibration
‘Wankel engine isa rotary intcmitent interna! combustion engine. Jet engines and rockets are
also internal combustion engines. They fall under the category of rotary continuous intemal com
bustion engine. This book deals with the intermiuene intemal combustion engines, mainly of
reciprocating type and thus excludes the gas turbine. Reciprocating IC engines are used in auto
mobiles, motoseyeles and scooters, power bouts, ships locomotives, and small aircraft. Due to
scarcity of electric power, the use of IC engines as a portable power output unit has gained
tuemendous momentum. These engines are alo used in farm tractors, Iawamowers and in many
other devices
1.2 HISTORICAL DEVELOPMENT
‘The fie IC engine for commercial use was developed by a Frenchman, 1J.E. Lenoir (1822-
1900) inthe year 1860. Coal gas and air mixture were drawn into the engine cylinder ducing Ihe
firschal of be piston stoke. A this point the charge was ignited by a spark. This caused rise in
pressure and the burned gases, the so-called products of combustion, delivered power to the
piston forthe second-half of the stroke. On the retum stroke, the gases were discharged fromthe
cylinder. The return stroke was possible by using a large flywheel which stored energy during he
power stroke and dissipated energy during the return stroke, exactly i the same manner as inthe
Case of a steam engine. By the year 1865 about 5000 engines were buil in sizes up to 6 hp
providing efficiency, however, not exceeding 5 percent, but it was beter han te efficiency of a
mal steam engine of those times
"Nicolaus A. Oto (1832-1891) and Eugen Langen (1833-1895) developed a free piston engine
in 1867 in Germany. Air-usl mixture was taken in cylinder and ignited by a gas flame during the
carly pat ofthe outward stroke to accelerate a free piston, and a vacuum was thus generated in
the cylinder. The piston was brought inward by atmospheris pressure acting onthe piston rom
the other side. During the inward stroke the burned gas was exhausted through a lid valve, The
piston od was connected by ratchet and a rack and pinion device tothe flywheel mounted en the
Output haf The inertia ofthe flywhee! moved the piston outwards and induced afresh charge
‘through a side valve to repeat the cycle, The thermal efficiency of this engine was found o be 11
Pr Th 1862, Alphonse Besu de Rochas (1815-1993) a Frenchman, described the principles of
four-stroke cycle and the conditions under which maximum efficiency could be obiained in IC
engines. It gave an idea of igniting fucl at higher pressures, nearly atthe end of compression
instead of During the fuel at atmospheric pressure. Increased cylinder volume with minimum
‘arface-to-volume ratio, maximum possible speed and higher expansion ratio were also suggested
{oc higher thermal efficiency,
Beau de Roches could no, however, build any engine himself based on his principles, In 1876,
‘Nicolaus August Oto built an engine based on these principles. This engine worked on the Four.
stroke principle—intake, compression, expansion or power and exhaust stokes. Ignition was
nearly a he end of compression, Otto engine results in reduced weight and volume and gave
higher thermal efficiency. This was the breakthrough that effectively founded the IC engine indus-
try. By 1890, almost 50,000 of these engines had been sold in Europe and the USA.
By the 1880s, Dugald Clek and James Robson ofthe UK and Karl Benz of Germany devel-
‘oped the two-suoke intemal combustion engine In this engine, compression of he charge takes
place during the inward or upward stroke and expansion or power is obtained during the outward
or downward stoke. Exhaust and intake processes occur during the nd of the power stroke and
a: te beginning of the compression stoke. In 1885, James Atkinson of England developed an
engine with an expansion stoke larger than dhe compression stoke. The larger expansion stroke
was used to increase the efficiency ofthe engine, Efficiency could also have been increased by
increasing the compression ratio, but in orde to avoid knocking problems the compresion rai at
that time with the quality of fuel availabe had to be kept below four.
In 1892, Rudolf Diesel (1858-1913) developed a diferen type of engine in which a high
compression ratio was used to ignite the fuel. Fuel was injected nearly atthe end of compression
which was then ignited by hot compressed ar, The efficiency of the engine was increased due to
higher compression and expansion ratios. The knocking problem was also overcome. The present
diesel engine is designed on the same working principle. Both four-stroke and two-stroke diesel
engines have been developed,
13. MODERN DEVELOPMENTS
In 1957, Wankels rotary IC engine was tested successfully after being under research and
_\
4. Fundamt of Internal Gomburden Engines
lnroducton to Intern Comburvon Engines _5
evelopment for many years. l was based on the design of Felix Wankel of Germany. Ie used an
equilateraly shaped wiangolr piston that moved in achamber. Other modem developraent reihe
revival of siting engine, fee piston engine, stetfied charge engine, variable compression ratio
engine, variable valve timing engine ete
Fuels and air pollution problems have also had a major impact on engine development. Gaso-
ine ad lighter fractions of rude ol were used in IC engines. During the First World War, serious
rude oil shonage was experienced due 10 high demand. William Burton and his associates of
Standard Oil of Indiana developed a thermal cracking process where heavier oils were heated
under pressure and decomposed into more volatile compounds. These thermally cracked
gasolines satisfied the demand ofthat ime,
During the recent years here hasbeen a growing demand for petroleum fuels and as time goes,
this demand will grow fuer causing greater scarcity of conventional fuels. Apart from this
Problem, gasoline powered engines discharge significant amount of pollutants like carbon monox-
ide, unburned hydrocarbons oxides of nitrogen and lead compounds if the petrol isnot unleaded,
Diesel engines ae a significant source of small soot or smoke particles as well as hydrocarbons
and oxides of nitrogen. Much work is being done on the use of alternative fuels. The mor prom.
nent among these are natural gas, liquified petroleum gas, metanol, ethanol and hydrogen
Recently. he biodiesel fue has been teste in the engine. Its a fc! made from renewable fat and
oils, such as vegetable oil, trough a simple refining process. One of the principal commodities
used as a source for biodiesel soyabeans. From an environmental point of view these pases are far
less polluing than the conventional fuels. New materials now becoming available offer the possi
bilities of reduced engine weigh, ess cost, reduced heat losses, and increased efficiency.
1.4 ENGINE CLASSIFICATIONS
‘There are different types of intenal combustion engines that can be classified onthe following
basis
‘Thermodynamic cycle -
+ Constant volume heat supplied or Oto cycle
+ Constant pressure heat supplied or Diesel cycle
+ Party constant volume and party constant pressure heat supplied or dual cycle
+ Joule or Brayton cycle
Working cycle
+ Four-stroke eycle--narally aspirated, supercharged, and turbocharged
+ Two-stroke cycle—crankease scavenged, supercharged, and turbocharged,
Fuel
+ Light oil engines using erosene or petrol
+ Heavy oil engines using diese! or mineral ols
+ Gas engines using gaseous fuels, The gas used may be natural gas, igified petroleum gas
(LPG), hydrogen, eto.
* Bi-fuel engines. In these engines the gas is used as the base fel and the liquid fut is used
for string the engine
Method of fuel supply
+ uel supply through carburetor. Inthe pet! engine the fuels mixed with rin the carbure
toc and the charge enters imo the cylinder during the suction stroke
+ Muli-poin port injection (MPD, used in modern spaccignition engines
+ Single point role body injection—this method is lso apple to sparkigniton engines.
+ Fuel injection at high pressure into the engine eylindes—it is used in diesel engines or
compression ipnition engines
Method of ignition
‘Spark ignition (SI) used in conventional petrol engines, known as SI engines.
* Compression ignition (CD used in conventional diesel engines, known es CL engines
+ Pilot injection of fuel oil in gas engines
Method of cooling
+ Witer-cooled engine—cylinder walls are cooled by circulating water in the jacket
surrounding the cylinder.
+ Aircooled engines —aumospheri ar blows over the hot surfaces (motor cycles, scooters,
ete).
Speed
+ Low speed engine
+ Medium speed engine
+ High speed engine
Field ot application
stationary engines for power generation
+ Marine engines for propulsion of ships
+ Automotive engines for land transport
+ Aero-engines for areraft
+ Locomotive engines for Railways
Lubrication system
+ Wet sump lubrication
+ Dry sump lubvication
+ Pressure lubrication
Mathod of control under variable load
+ Quanity contol engines he aru rio remain almost ont. Te quantity ofthe
(arg increases a the lod linces An example te engine ta uses carburo.
+ Quality control engines ae the lon Inereats, the quant of fli increased, ts
ng the quality of su a, An exp is the engine using injector.
+ Combine cool pss In hese engine bh the qn and quay ote care
are changed depending on the variation in load.
lnroducton to Intern Comburvon Engines _5
evelopment for many years. l was based on the design of Felix Wankel of Germany. Ie used an
equilateraly shaped wiangolr piston that moved in achamber. Other modem developraent reihe
revival of siting engine, fee piston engine, stetfied charge engine, variable compression ratio
engine, variable valve timing engine ete
Fuels and air pollution problems have also had a major impact on engine development. Gaso-
ine ad lighter fractions of rude ol were used in IC engines. During the First World War, serious
rude oil shonage was experienced due 10 high demand. William Burton and his associates of
Standard Oil of Indiana developed a thermal cracking process where heavier oils were heated
under pressure and decomposed into more volatile compounds. These thermally cracked
gasolines satisfied the demand ofthat ime,
During the recent years here hasbeen a growing demand for petroleum fuels and as time goes,
this demand will grow fuer causing greater scarcity of conventional fuels. Apart from this
Problem, gasoline powered engines discharge significant amount of pollutants like carbon monox-
ide, unburned hydrocarbons oxides of nitrogen and lead compounds if the petrol isnot unleaded,
Diesel engines ae a significant source of small soot or smoke particles as well as hydrocarbons
and oxides of nitrogen. Much work is being done on the use of alternative fuels. The mor prom.
nent among these are natural gas, liquified petroleum gas, metanol, ethanol and hydrogen
Recently. he biodiesel fue has been teste in the engine. Its a fc! made from renewable fat and
oils, such as vegetable oil, trough a simple refining process. One of the principal commodities
used as a source for biodiesel soyabeans. From an environmental point of view these pases are far
less polluing than the conventional fuels. New materials now becoming available offer the possi
bilities of reduced engine weigh, ess cost, reduced heat losses, and increased efficiency.
1.4 ENGINE CLASSIFICATIONS
‘There are different types of intenal combustion engines that can be classified onthe following
basis
‘Thermodynamic cycle -
+ Constant volume heat supplied or Oto cycle
+ Constant pressure heat supplied or Diesel cycle
+ Party constant volume and party constant pressure heat supplied or dual cycle
+ Joule or Brayton cycle
Working cycle
+ Four-stroke eycle--narally aspirated, supercharged, and turbocharged
+ Two-stroke cycle—crankease scavenged, supercharged, and turbocharged,
Fuel
+ Light oil engines using erosene or petrol
+ Heavy oil engines using diese! or mineral ols
+ Gas engines using gaseous fuels, The gas used may be natural gas, igified petroleum gas
(LPG), hydrogen, eto.
* Bi-fuel engines. In these engines the gas is used as the base fel and the liquid fut is used
for string the engine
Method of fuel supply
+ uel supply through carburetor. Inthe pet! engine the fuels mixed with rin the carbure
toc and the charge enters imo the cylinder during the suction stroke
+ Muli-poin port injection (MPD, used in modern spaccignition engines
+ Single point role body injection—this method is lso apple to sparkigniton engines.
+ Fuel injection at high pressure into the engine eylindes—it is used in diesel engines or
compression ipnition engines
Method of ignition
‘Spark ignition (SI) used in conventional petrol engines, known as SI engines.
* Compression ignition (CD used in conventional diesel engines, known es CL engines
+ Pilot injection of fuel oil in gas engines
Method of cooling
+ Witer-cooled engine—cylinder walls are cooled by circulating water in the jacket
surrounding the cylinder.
+ Aircooled engines —aumospheri ar blows over the hot surfaces (motor cycles, scooters,
ete).
Speed
+ Low speed engine
+ Medium speed engine
+ High speed engine
Field ot application
stationary engines for power generation
+ Marine engines for propulsion of ships
+ Automotive engines for land transport
+ Aero-engines for areraft
+ Locomotive engines for Railways
Lubrication system
+ Wet sump lubrication
+ Dry sump lubvication
+ Pressure lubrication
Mathod of control under variable load
+ Quanity contol engines he aru rio remain almost ont. Te quantity ofthe
(arg increases a the lod linces An example te engine ta uses carburo.
+ Quality control engines ae the lon Inereats, the quant of fli increased, ts
ng the quality of su a, An exp is the engine using injector.
+ Combine cool pss In hese engine bh the qn and quay ote care
are changed depending on the variation in load.
$ Fundamontals of Internal Comkusion Engines
Basic engine design
+ Reciprocating engines—subdivided by arrangement of cylinder, for example, in-line
engines, engines, opposed cylinder engine, opposed piston engine radial engine.
+ Rotary engines Wankel engines
Number of cylinders
+ Single-cylinderengines
+ Multicylinder engines,
Valve or port design
+ Valves—overhead valves (Head), underhead valves (L-head), rotary valves
+ Ports—-cross-scavenged, logp-scavenghé, through or uniflow-scavenged.
‘Combustion chamber design
+ Open chamber, for example, battrub, wedge, bowl-in-postion. hemispherical
+ Divided chamber—small and large auxiliary chambers, for example, swid chambers,
prechambers.
15 CLASSIFICATION OF RECIPROCATING ENGINES BY
APPLICATION
‘Table 1.1 shows the classification of reciprocating engines by application. For different applica-
tions, the approximate range of engine power, predominant types suchas compression
ignition, number of working strokes, and methods of cooling ar listed.
1.6 CLASSIFICATIONS OF ENGINES BY CYLINDER
ARRANGEMENT
Mali <ylinderreciprocating engines are commonly classified by cylinder arrangement. Some of
the bate types Of these engines are shown in Figure 1.1
nine engines
All eyinders are arranged linearly in one cylinder bank and transmit power toa single crankshaft.
Four-cyliner, in-line engines are common for passenger cars, Maruti car has three cylinders
in-line. Sixeylinder,in-Line engines are also common. More than six cylinders tend tobe very long.
and usually have problems involved wih crankshaft torsional vibration. Up to 12 ylinders in-line
‘engines are used for large ships
Vengines
‘The 'V’ type is essenilly two “n-line’ engines set at an angle, and utlizes a common crankshaf
Vrengines of eight cylinders or more have excellent balance and also relatively fic from vibra-
tional problems. V-8 and V-12 amangements are commonly used to produce more power from a
compact engine. They run smoothly without much vibration.
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Opposed cylinder engines
‘oe appre cline engines cond feo r mar yde on opposite ais of common (
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Basic engine design
+ Reciprocating engines—subdivided by arrangement of cylinder, for example, in-line
engines, engines, opposed cylinder engine, opposed piston engine radial engine.
+ Rotary engines Wankel engines
Number of cylinders
+ Single-cylinderengines
+ Multicylinder engines,
Valve or port design
+ Valves—overhead valves (Head), underhead valves (L-head), rotary valves
+ Ports—-cross-scavenged, logp-scavenghé, through or uniflow-scavenged.
‘Combustion chamber design
+ Open chamber, for example, battrub, wedge, bowl-in-postion. hemispherical
+ Divided chamber—small and large auxiliary chambers, for example, swid chambers,
prechambers.
15 CLASSIFICATION OF RECIPROCATING ENGINES BY
APPLICATION
‘Table 1.1 shows the classification of reciprocating engines by application. For different applica-
tions, the approximate range of engine power, predominant types suchas compression
ignition, number of working strokes, and methods of cooling ar listed.
1.6 CLASSIFICATIONS OF ENGINES BY CYLINDER
ARRANGEMENT
Mali <ylinderreciprocating engines are commonly classified by cylinder arrangement. Some of
the bate types Of these engines are shown in Figure 1.1
nine engines
All eyinders are arranged linearly in one cylinder bank and transmit power toa single crankshaft.
Four-cyliner, in-line engines are common for passenger cars, Maruti car has three cylinders
in-line. Sixeylinder,in-Line engines are also common. More than six cylinders tend tobe very long.
and usually have problems involved wih crankshaft torsional vibration. Up to 12 ylinders in-line
‘engines are used for large ships
Vengines
‘The 'V’ type is essenilly two “n-line’ engines set at an angle, and utlizes a common crankshaf
Vrengines of eight cylinders or more have excellent balance and also relatively fic from vibra-
tional problems. V-8 and V-12 amangements are commonly used to produce more power from a
compact engine. They run smoothly without much vibration.
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Tasca msc eet ain :
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Light commercial 375-150 SLCI 4 w €
Er
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Ergo IN
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— oe 3 RE à
Inboard mororbosts 4-750 sa 4 w {
ue 2 Eu à <
= a a À
Ships auiares 75-750 a 4 wf
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Opposed cylinder engines
‘oe appre cline engines cond feo r mar yde on opposite ais of common (
A (
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in light aircraft. ¢
{
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Fundamental of nera! Combustion Engines
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Invoduecon to Inter Comburson Engines 9
opposed piston engines
‘When a single cylinder houses two pistons, each of which drives a separate crankshaft, is called
an opposed piston engine, The advantages of this engine type include the absence of eylinder
fads lesding 10 reduction in heat loss and piston controlled ports for through seavenging. The
disodvantages include the requirement of two crankshafts geared together, and a shape that may
be award in many installations. These engines are used in large diese installations
Radial engines
“The radial type of engine consists of cylinders placed radially, and equally space, around a
common erankshaf. These engines are used mostly for airraft. Basically, the radial arrangement
‘gives the lowest weight per unit displacement because the material used in crankshaft and
-rankease is minimum for a given number of cylinders,
Xaype engine
‘The Xxype engine is a more complicated version ofthe V-type, essentially fou inline arange-
mente utlizing a single erankshaft. The X-types do not presently find wide use, except in some
sel installations.
Haypoengino
“The Haype engine essentially comprises two opposed cylinders, milizng two separate but inter“
connected erankshafts, The H-iypes do not presently find wide use.
1.7. ENGINE COMPONENTS
Figure 12 shows the cutaway view of Chrysler 2.2 litre, foureylinder, four-stroke, spark-igaition
engine. The arrangement of different engine pars is shown clearly.
The engine cylinders are contained in a cylinder block. The cylinder block and the upper-half
of the erankcase are generally cast together. The boom half of the crankcase consists of a
combined transmission casing and an oil sump. The block is normally made of gray cast iron
because of is good wear resistance and low cost implementation. T also has a water jacket
surrounding the engine cylinder For cooling purposes. The cylinder liner is used to increase the Life
‘of the cylinder. When the cylinder surfaces wear ou, the ines can be renewed easily. The wear
resistance of the liner materia is more than that of the cylinder block material. Metals suitable for
liners are nickel alloy steels, heat ested chromium, and other alloy cast irons
‘The piston reciprocaes inside the engine cylinder and transmits the gas force tothe connect
ng rod and thea 0 the crank, which in tum rotas the crankshaft from where the power output
is obtained, The pistons are made from anodized aluminium alloy, Three compression rings and a
sloted oil contol ring are generally provided over the piston, The piston rings prevent the escapo.
of the expanding gases from the combustion chamber to the crankcase, An oil conto! ring
scrapes the excess oil from the cylinder wall. The comecting rod and the crark arm of the
crankshaft translate the linear motion of the piston into rotational motion ofthe crankshaft. The
smal-end ofthe connecting rod reciprocates and the large-end follows the rotational motion. A
‘connecting rod is normally a drop forging of steel with a brass small-end bush and a detachable
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Invoduecon to Inter Comburson Engines 9
opposed piston engines
‘When a single cylinder houses two pistons, each of which drives a separate crankshaft, is called
an opposed piston engine, The advantages of this engine type include the absence of eylinder
fads lesding 10 reduction in heat loss and piston controlled ports for through seavenging. The
disodvantages include the requirement of two crankshafts geared together, and a shape that may
be award in many installations. These engines are used in large diese installations
Radial engines
“The radial type of engine consists of cylinders placed radially, and equally space, around a
common erankshaf. These engines are used mostly for airraft. Basically, the radial arrangement
‘gives the lowest weight per unit displacement because the material used in crankshaft and
-rankease is minimum for a given number of cylinders,
Xaype engine
‘The Xxype engine is a more complicated version ofthe V-type, essentially fou inline arange-
mente utlizing a single erankshaft. The X-types do not presently find wide use, except in some
sel installations.
Haypoengino
“The Haype engine essentially comprises two opposed cylinders, milizng two separate but inter“
connected erankshafts, The H-iypes do not presently find wide use.
1.7. ENGINE COMPONENTS
Figure 12 shows the cutaway view of Chrysler 2.2 litre, foureylinder, four-stroke, spark-igaition
engine. The arrangement of different engine pars is shown clearly.
The engine cylinders are contained in a cylinder block. The cylinder block and the upper-half
of the erankcase are generally cast together. The boom half of the crankcase consists of a
combined transmission casing and an oil sump. The block is normally made of gray cast iron
because of is good wear resistance and low cost implementation. T also has a water jacket
surrounding the engine cylinder For cooling purposes. The cylinder liner is used to increase the Life
‘of the cylinder. When the cylinder surfaces wear ou, the ines can be renewed easily. The wear
resistance of the liner materia is more than that of the cylinder block material. Metals suitable for
liners are nickel alloy steels, heat ested chromium, and other alloy cast irons
‘The piston reciprocaes inside the engine cylinder and transmits the gas force tothe connect
ng rod and thea 0 the crank, which in tum rotas the crankshaft from where the power output
is obtained, The pistons are made from anodized aluminium alloy, Three compression rings and a
sloted oil contol ring are generally provided over the piston, The piston rings prevent the escapo.
of the expanding gases from the combustion chamber to the crankcase, An oil conto! ring
scrapes the excess oil from the cylinder wall. The comecting rod and the crark arm of the
crankshaft translate the linear motion of the piston into rotational motion ofthe crankshaft. The
smal-end ofthe connecting rod reciprocates and the large-end follows the rotational motion. A
‘connecting rod is normally a drop forging of steel with a brass small-end bush and a detachable
10 Fundamental of Ineral Combvrion Engines
Imtoducin to Internal Combustion Engines II
an
adjuster
combat Lo ve
Sprocket
st ae
Piston
Timing bat Connecting
Timing an À
Canstatt
ranks Olpickup r CA
pr
Source: Heywood 3: ema Combustion Engine Fundamentals, MéOr-Hil New York, 1988
Figure 12 Carine 2 2e ou einer spain rg
hie mel rec sel bering. Figure 1 shows de o
wath deaf pion piso gs, comet
rod and bearings. The crane ad nah sec gd nd machined toa soot ist
The cash 1 suppned inn Sang ud a steal and dynamical as Ths
cra caes yee 0 ven cul de uns or que
bison
2 Piston Fing—seraper
5, Pion rngs—taper
3 Pisco ing perl
Sealed bash
5 Gudgeon pin
Gel
8. Gudpeon pin bic ote
9 Connecting rus
10, Gide wall et jet
11, Connecting rod sp
12 Leck washer
Er
14, Connecting ro earings
15, Coneting rod ad cap making
Sources Haynes, LH: Owner Rorkshop Monaal IM. Haynes & Co, England, 191
guna. Ps ping andenmscngmd.
{An exploded view ofthe cylinder hes is shown in Figure 1.4. The cylinder head seats of the
cylinders and is made of east iron or aluminium. The cylinder head contains spark plugs for an SI
Engine ora fuetinjetor fora CI engine. In overhead valve engines, the cylinder head also contains
parts of the valve mechanism. Normally there are wo valves per eylinder—an inlet valve for
fdiring the charge int the cylinder and an exhaust valve for exhausting the burt gas out from
the cylinder. Te inlet valve is of larger diameter than that ofthe exhaust valve, Valves are made
from forged alloy steel. The exhaust valve operates at about 700°C, as the hot burned gas passes
through The cooling of the exhaust valve is therefore required. can be done by filing parti
‘a hollow stem of the valve with sodium. Bvaporation and condensation of sodium provide heat
Flow from ths bot valve head to the cooler stem. The overbead valves are operated by means of
rocker arms mounted on the rocker shaft running along the top of the cylinder head. The rocker
“rms are activated by pushzode and tappets which in num rise and fall in accordance with the cams
‘onthe camshaft. The valves are held close by small powerful springs. A camshaft made of cast
fon or forged steel with one cam per valve is used to open and close the valve, In four-stroke
‘engines, to rotations ofthe crankshaft provide one rotation of the camshaft. The two shafts are
‘connected together by gears, bel, or chain. The exploded view of crankshaft and camshaft i
shown in Figure 15
"The erankesse is sealed atthe bottom with a pressed steel or cast aluminium oil pan which
acts as an ol reservoir for the Iubreatng system. The oil pump is driven from the gear ofthe
Gamshaft, The centrifugal water pump and radiator cooling fan are driven together along with the
“dynamo from the crankshaft pulley wheel by a bell.
Imtoducin to Internal Combustion Engines II
an
adjuster
combat Lo ve
Sprocket
st ae
Piston
Timing bat Connecting
Timing an À
Canstatt
ranks Olpickup r CA
pr
Source: Heywood 3: ema Combustion Engine Fundamentals, MéOr-Hil New York, 1988
Figure 12 Carine 2 2e ou einer spain rg
hie mel rec sel bering. Figure 1 shows de o
wath deaf pion piso gs, comet
rod and bearings. The crane ad nah sec gd nd machined toa soot ist
The cash 1 suppned inn Sang ud a steal and dynamical as Ths
cra caes yee 0 ven cul de uns or que
bison
2 Piston Fing—seraper
5, Pion rngs—taper
3 Pisco ing perl
Sealed bash
5 Gudgeon pin
Gel
8. Gudpeon pin bic ote
9 Connecting rus
10, Gide wall et jet
11, Connecting rod sp
12 Leck washer
Er
14, Connecting ro earings
15, Coneting rod ad cap making
Sources Haynes, LH: Owner Rorkshop Monaal IM. Haynes & Co, England, 191
guna. Ps ping andenmscngmd.
{An exploded view ofthe cylinder hes is shown in Figure 1.4. The cylinder head seats of the
cylinders and is made of east iron or aluminium. The cylinder head contains spark plugs for an SI
Engine ora fuetinjetor fora CI engine. In overhead valve engines, the cylinder head also contains
parts of the valve mechanism. Normally there are wo valves per eylinder—an inlet valve for
fdiring the charge int the cylinder and an exhaust valve for exhausting the burt gas out from
the cylinder. Te inlet valve is of larger diameter than that ofthe exhaust valve, Valves are made
from forged alloy steel. The exhaust valve operates at about 700°C, as the hot burned gas passes
through The cooling of the exhaust valve is therefore required. can be done by filing parti
‘a hollow stem of the valve with sodium. Bvaporation and condensation of sodium provide heat
Flow from ths bot valve head to the cooler stem. The overbead valves are operated by means of
rocker arms mounted on the rocker shaft running along the top of the cylinder head. The rocker
“rms are activated by pushzode and tappets which in num rise and fall in accordance with the cams
‘onthe camshaft. The valves are held close by small powerful springs. A camshaft made of cast
fon or forged steel with one cam per valve is used to open and close the valve, In four-stroke
‘engines, to rotations ofthe crankshaft provide one rotation of the camshaft. The two shafts are
‘connected together by gears, bel, or chain. The exploded view of crankshaft and camshaft i
shown in Figure 15
"The erankesse is sealed atthe bottom with a pressed steel or cast aluminium oil pan which
acts as an ol reservoir for the Iubreatng system. The oil pump is driven from the gear ofthe
Gamshaft, The centrifugal water pump and radiator cooling fan are driven together along with the
“dynamo from the crankshaft pulley wheel by a bell.
14 Fundamentals of serra! Comburion £ngnes
In moli-eylinder SI engines, a distributor is mounted towards the rear of the cylinder block
and it advances and rears the ignition timing by mechanical and vacuum means, The distritos
is driven at half the crankshaft speed by a short shaft and skew gear ftom a skew gear on the
‘crankshaft, In CI engines, a high pressure fuel pump and injectors are used, One injector per
‘ylinder is mounted in the cylinder head, The pump is driven by the camshaft.
1.8. BASIC TERMINOLOGY
‘The basic terminology used for volumes and measurement in the cylinder egion is presented and
shown in Figure 1.6.
me
ide |
Pisten
Cranks
1. Bore (d): Its the inside diameter of the engine cylinder I Is called the bore as itis made
rough a boring. process.
2. Stroke (L}: During the travel of he piston, there i an upper as well as a lower limiting
Position at which the direcion of motion ofthe piston is reversed. The linear distance through
‘hich the piston travels between the extreme upper and wer positions ofthe piston is called the
stoke Is equal to two times the eran radius, L= 2a, where a is he erank radius
3. Top Dead Centre (TDC): When the piston sat the topmost position of the cylinder during ts
travel, that position is called the Top Dead Centre At this positon the piston velocity is zero and
the piston reverses its direction of motion to wavel dosmnwards, I is the dead centre when the
piston is farthest from the crankshaft,
4. Bottom Dead Centre (BDC): When te pistons atthe bottom-most position of he cylinder
¿ring its travel, tha positon is celled the Bottom Dead Cente. Atthis position the piston velocity
is zero and the piston reverses ts direction of motion o travel upwards. tis the dead centre when
the piston is nearest tothe crankshaft.
5. Clearance volume (V): When the piston is atthe TDC positon, the volume contained in the
ylinder above the to of te piston is called the clearance volume. The piston cannot occupy any
part ofthis volume and always keeps this volume clear
e =
loraducion to ternal Comburcon Engines _ 15
6. Piston displacement or swept volume (V2 isthe volume swept through bythe piston in
moving between the TDC and the BDC, ie. Y = =a,
7. Cylinder volume (Y): The eylinder volume includes both the clearance volume and the
swept volume, Le. = K + Y,
8. Compression ratio (ris te ratio ofthe volume when the piston i at BDC tothe volume
‘when the pista is at TDC. Hence it isthe ratio of rota cylinder volume to clearance volume
tb
vo
9. Mean piston speed: As the piston moves inside the engine cylinder is speed changes con-
tinuously ts zero at TDC and BDC and maximum at the mid-postion of TDC and BDC. The
crank angle Bis zero at TDC, it is 90° when the piston speed i maximum and 180° at BDC. Thus
ina half rotation ofthe crank the piston moves a distance equal othe eagih of the stoke, . In
full rotation, the distance tavelld by piston will be 22. IF isthe engine speed in evolutions per
2LN
tvinate (rpm) and Ls in meurs, he mean piston speed will be ZEN rs.
1.9 FOUR-STROKE SPARK-IGNITION ENGINE
Ina four-swoke eyes engine, the cycle of operation is completed in foursrokes of he piston or
two revolutions ofthe erankshaf. Thus 720°CA (crank angle) is required to complete a cycle.
Figure 17 shows the movement of he piston andthe position of the valves during each stoke.
‘The individual stokes are:
+ Induction or suction stoke
+ Compression stoke
+ Expansion or power stoke
+ Exhaust soke,
Figure 1.8 shows the p-V diagram indicating the pressure variation during a four-stroke cycle
with respect tothe volume of the cylinder
open
Induction or suction stroke (0-1)
‘The inet valve opens at point O just before the TDC. As the piston moves from TDC 10 BDC, 4
‘mixture of air and fuel (charge) is introduced into the cylinder through the ile valve. Dueto the
movement ofthe piston he pressure in he cylinder is reduced to a valve below the atmospheric
pressure and the charge flows through the induction system because of this pressure difference
call, the inet valve should close at poin 1, but in fact it does not happen so until the piston Pas
moved par of the way along the reum stoke (point 17.
‘Compression stroke (1-2)
‘With both the valves closed, the charge which is taken into the cylinder during the suction stroke
is compressed by the return stroke ofthe piston. At the TDC postion the charge occupies the
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In moli-eylinder SI engines, a distributor is mounted towards the rear of the cylinder block
and it advances and rears the ignition timing by mechanical and vacuum means, The distritos
is driven at half the crankshaft speed by a short shaft and skew gear ftom a skew gear on the
‘crankshaft, In CI engines, a high pressure fuel pump and injectors are used, One injector per
‘ylinder is mounted in the cylinder head, The pump is driven by the camshaft.
1.8. BASIC TERMINOLOGY
‘The basic terminology used for volumes and measurement in the cylinder egion is presented and
shown in Figure 1.6.
me
ide |
Pisten
Cranks
1. Bore (d): Its the inside diameter of the engine cylinder I Is called the bore as itis made
rough a boring. process.
2. Stroke (L}: During the travel of he piston, there i an upper as well as a lower limiting
Position at which the direcion of motion ofthe piston is reversed. The linear distance through
‘hich the piston travels between the extreme upper and wer positions ofthe piston is called the
stoke Is equal to two times the eran radius, L= 2a, where a is he erank radius
3. Top Dead Centre (TDC): When the piston sat the topmost position of the cylinder during ts
travel, that position is called the Top Dead Centre At this positon the piston velocity is zero and
the piston reverses its direction of motion to wavel dosmnwards, I is the dead centre when the
piston is farthest from the crankshaft,
4. Bottom Dead Centre (BDC): When te pistons atthe bottom-most position of he cylinder
¿ring its travel, tha positon is celled the Bottom Dead Cente. Atthis position the piston velocity
is zero and the piston reverses ts direction of motion o travel upwards. tis the dead centre when
the piston is nearest tothe crankshaft.
5. Clearance volume (V): When the piston is atthe TDC positon, the volume contained in the
ylinder above the to of te piston is called the clearance volume. The piston cannot occupy any
part ofthis volume and always keeps this volume clear
e =
loraducion to ternal Comburcon Engines _ 15
6. Piston displacement or swept volume (V2 isthe volume swept through bythe piston in
moving between the TDC and the BDC, ie. Y = =a,
7. Cylinder volume (Y): The eylinder volume includes both the clearance volume and the
swept volume, Le. = K + Y,
8. Compression ratio (ris te ratio ofthe volume when the piston i at BDC tothe volume
‘when the pista is at TDC. Hence it isthe ratio of rota cylinder volume to clearance volume
tb
vo
9. Mean piston speed: As the piston moves inside the engine cylinder is speed changes con-
tinuously ts zero at TDC and BDC and maximum at the mid-postion of TDC and BDC. The
crank angle Bis zero at TDC, it is 90° when the piston speed i maximum and 180° at BDC. Thus
ina half rotation ofthe crank the piston moves a distance equal othe eagih of the stoke, . In
full rotation, the distance tavelld by piston will be 22. IF isthe engine speed in evolutions per
2LN
tvinate (rpm) and Ls in meurs, he mean piston speed will be ZEN rs.
1.9 FOUR-STROKE SPARK-IGNITION ENGINE
Ina four-swoke eyes engine, the cycle of operation is completed in foursrokes of he piston or
two revolutions ofthe erankshaf. Thus 720°CA (crank angle) is required to complete a cycle.
Figure 17 shows the movement of he piston andthe position of the valves during each stoke.
‘The individual stokes are:
+ Induction or suction stoke
+ Compression stoke
+ Expansion or power stoke
+ Exhaust soke,
Figure 1.8 shows the p-V diagram indicating the pressure variation during a four-stroke cycle
with respect tothe volume of the cylinder
open
Induction or suction stroke (0-1)
‘The inet valve opens at point O just before the TDC. As the piston moves from TDC 10 BDC, 4
‘mixture of air and fuel (charge) is introduced into the cylinder through the ile valve. Dueto the
movement ofthe piston he pressure in he cylinder is reduced to a valve below the atmospheric
pressure and the charge flows through the induction system because of this pressure difference
call, the inet valve should close at poin 1, but in fact it does not happen so until the piston Pas
moved par of the way along the reum stoke (point 17.
‘Compression stroke (1-2)
‘With both the valves closed, the charge which is taken into the cylinder during the suction stroke
is compressed by the return stroke ofthe piston. At the TDC postion the charge occupies the
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16 Funsamentl of term! Cambon Engines
Evo" ive! we eye
(2) Compresion stroke
Ne BVO
(Op Sapansin or power soe
VO -inetvaveopen, VC net valve cased,
VO ext vane opens, EVO ex valve closed,
Fgwe17. Fetes gr
(9 Beha stoke
volume space above the piston, which i calle the clearance volume, Just before the end of the
compression stoke, the spark is timed to occur ata point S. There is timo delay between Sand
the actual commencement of combustion. The combustion process occurs mainly at almost con-
stant volume, and thers is large increase in pressure and temperature of the charge during this
process (2-3)
D
Intoducion to neral Comdunten Eng V7
Piguet p-Véagan dater sicko Slengos
Expansion or power stroke (3-4)
‘The hot high pressre burn gases force the piston towards the BDC. Both the inlet and cxhaost
valves remain closed. It appears that his expansion proceeds to completion at point 4 but in order
Lo asis in exhausting the gaseous product the exhaust valve opens al some point £, which is
before the BDC. Power is obtained during this stioke, Both pressure and temperature decrease
during expansion,
Exhaust etroke (4-0)
As the piston further moves from BDC to TDC it sweeps out he burt gases through the exhaust
valve. The inet valve remains closed. The pressure during this stroke je slightly higher than the
atmosphere pressure. The exhaust valve closes nearly atthe end ofthe exhaust stroke (point 07.
‘The clearance volume cannot be exhausted and at the commencement of the next cycle this
volume is full of exhaust gas from the previous cycle at about the atmospheric pressure. The
exhaost gases remaining in the clearance space ac called the residual gases, Tee mixture which is
further compressed consists of both the fresh charge and the residual gases,
Bach cylinder of a four-stroke engine completes all the operations in two engine revolutions
‘Thus for one complete cycle, there is only one power stroke while the crankshaft makes two
evolutions,
1.10. VALVE-TIMING OF FOUR-STROKE SI ENGINE
For the successful running ofthe engine, the precise timing ofthe opening and closing of inlet and
exhaust valves and the exact point at which ignition takes place are very important. Theoretically,
valves should open and close and the spark should ocou tthe dead centre positions ofthe piston
strokes. Actually, ese events ae displaced somewbat from the dead centre positions. The main
factors that affect the timing of valves are the high velocity of the charge atthe entry to the
ylinder and the high velocity ofthe exhaust gases atthe ext from the cylinder
Evo" ive! we eye
(2) Compresion stroke
Ne BVO
(Op Sapansin or power soe
VO -inetvaveopen, VC net valve cased,
VO ext vane opens, EVO ex valve closed,
Fgwe17. Fetes gr
(9 Beha stoke
volume space above the piston, which i calle the clearance volume, Just before the end of the
compression stoke, the spark is timed to occur ata point S. There is timo delay between Sand
the actual commencement of combustion. The combustion process occurs mainly at almost con-
stant volume, and thers is large increase in pressure and temperature of the charge during this
process (2-3)
D
Intoducion to neral Comdunten Eng V7
Piguet p-Véagan dater sicko Slengos
Expansion or power stroke (3-4)
‘The hot high pressre burn gases force the piston towards the BDC. Both the inlet and cxhaost
valves remain closed. It appears that his expansion proceeds to completion at point 4 but in order
Lo asis in exhausting the gaseous product the exhaust valve opens al some point £, which is
before the BDC. Power is obtained during this stioke, Both pressure and temperature decrease
during expansion,
Exhaust etroke (4-0)
As the piston further moves from BDC to TDC it sweeps out he burt gases through the exhaust
valve. The inet valve remains closed. The pressure during this stroke je slightly higher than the
atmosphere pressure. The exhaust valve closes nearly atthe end ofthe exhaust stroke (point 07.
‘The clearance volume cannot be exhausted and at the commencement of the next cycle this
volume is full of exhaust gas from the previous cycle at about the atmospheric pressure. The
exhaost gases remaining in the clearance space ac called the residual gases, Tee mixture which is
further compressed consists of both the fresh charge and the residual gases,
Bach cylinder of a four-stroke engine completes all the operations in two engine revolutions
‘Thus for one complete cycle, there is only one power stroke while the crankshaft makes two
evolutions,
1.10. VALVE-TIMING OF FOUR-STROKE SI ENGINE
For the successful running ofthe engine, the precise timing ofthe opening and closing of inlet and
exhaust valves and the exact point at which ignition takes place are very important. Theoretically,
valves should open and close and the spark should ocou tthe dead centre positions ofthe piston
strokes. Actually, ese events ae displaced somewbat from the dead centre positions. The main
factors that affect the timing of valves are the high velocity of the charge atthe entry to the
ylinder and the high velocity ofthe exhaust gases atthe ext from the cylinder
18 _Fuceamenals of intemal Combustion Engines
Inradaston to Hera! Combustion Engines 19
‘The opening ofthe valves occurs earlier than the dead centre position and the closing contin
ues even later crank angles. The ignition is alo timed 0 occur eater
1.10.1 Inlet Valve
Due to the inertia effect and the ti required in eaining fll opening, the inlet valve is made 10
‘open somewhat ele than the TDC, so that by he tine the piston reaches the TDC, the valve is.
fully open.
Majority of IC engines un at high speeds. As he piston moves down during the suction
stcoke, the charge enters the eylinder through he inlt valve with considerable momentum due to
pressure difference. Ifthe alt valve is closed exacly at BDC, the cylinder would not be ful of
charge asthe tendency is fr te rapidly moving piston to run away from the incoming charge.
Consequently, during the suction stoke the piston will rach the BDC before the charge could get
enough time to enter the cylinder through the resucted inlet valve passages, Moreover, there is
‘considerable resistance tothe low of charge through the ait-cleaner, carburettor, int manifold,
and ports, This means that ifthe inlet valve is closed at BDC the cylinder foreach cycle would
receive charge less than its capacity and the pressure inside the cylinder woutd remain somewhat
less than the atmosphere.
‘Consequently, in actual operation, te int valve is kept open ll the cylinder pressure equals
the atmospheric pressure. As the piston reverses and commences the compression stroke, it
appears that some of the charge may be sent back tothe induction pipe. So, it Tooks to be impos-
sible to leave the inet valve open ater BDC. However, there wil bea period around bth he dead
centre positions when the crank could swing through a wide angle while the piston remains
relatively stationary. Therefore, this extra period during which the piston does not move very far
up on the stroke, makes it possible vo keep the inet valve open after BDC. The momentum ef the
incoming charge help tt continue o il and rus itself nto the eylinder, thereby improving the
volumetric efficiency ofthe engine.
1.102 ExhaustValve
In order to exhaust as much of the products of combustion as possible, the exhaust valve opens
somewhat before the BDC position. Thus, some ofthe exhaust gas leaves by vie of its excess
pressure above aimospherie and hence the exhaust gas is already flowing freely from the cylinder
by the time the piston commences the exhaust stoke. During the exhaust stoke tr piston has to
30 less work in oder to push the exhaust gas ot
By closing the exhaust valve late, the kinetic energy ofthe exhaust gas can be utilized to asist
in maximum exhausting of the cylinder before the exhaust valve closes and thus reducing the
‘mount of residual gases.
Figure 1.9 shows the valve timing diagram for a four-stroke cycle engine, The diagram must
actually coasist of two circles, one superimposed over the other, since the four-stroke cycle is
complete in two revolution ofthe crankshaft Bu o present a clear concept, itis usual o draw
the diagram ss a spiral
Tt should be noted tha the values ofthe angular postions showa inthe diagram are average
‘ones, and considerable differences occur between different engines. Spark is provided before the
‘end ofthe compresion stroke by the ignition system
revois
poe
Crankshaft in ces diction
gene13. Vakiingdagarmelakunsnen Siege
[Note that here may be a period when both the valves are open at the same time, This happens
sear he TDC. The set valve has opened 10° before Ihe TDC andthe exhaust valve has nt yet
rite may close 15° after the TDC. This period is called the valve overiap period. This period
‘Shoutd not be excessive. otherwise the but ases wil be sucked into the cylinder, ort may allow
the fresh charge to escape through the exhaust valve,
4,11 FOUR-STROKE COMPRESSION IGNITION (CI) ENGINES
“The four-stroke CI engine is similar to the four-stroke SI engine except that a high compression
Tati e used in the CI engines, During the suetion stroke, the inlet valve opens and only the air
‘enters ino the eylinde a the piton moves from TDC 10 BDC.
‘Wh the il and exhaus valves closed, th piston compresses the ar. Bot the ir pressure
“and ianpotarure se. When the piston almost reaches the TDC, fuel is injected in finely divided
Form into the hot swiling air inthe combustion space. Ignition occurs after a short delay, the gas
pressure rises rapidly and a pressure wave is set Up.
‘Work is done by the gas pressure onthe piston as he piston sweeps the maximum cylinder
volume. Duting ths expansion or power stroke, the temperature and pressure ofthe burnt gs fal,
"As the piston approaches the BDC, the exhaust valve opens and he products of combustion
are ejected rom the cylinder during the exhaust stoke. Near the TDC, he inlet valve opens again
and the cycle is pente.
The typical valve tings for a four-stroke CI engine ae a follows:
Inet valve opens about 30° before TDC (TDC)
Inlet valve closes about 50 after BDC (ABDC)
"Exhaust valve opens about 45° before BDC (bBDC)
Exhaust valve closes about 30° after TDC (4TDC)
Injection of fuel is about 15° before TDC.
Inradaston to Hera! Combustion Engines 19
‘The opening ofthe valves occurs earlier than the dead centre position and the closing contin
ues even later crank angles. The ignition is alo timed 0 occur eater
1.10.1 Inlet Valve
Due to the inertia effect and the ti required in eaining fll opening, the inlet valve is made 10
‘open somewhat ele than the TDC, so that by he tine the piston reaches the TDC, the valve is.
fully open.
Majority of IC engines un at high speeds. As he piston moves down during the suction
stcoke, the charge enters the eylinder through he inlt valve with considerable momentum due to
pressure difference. Ifthe alt valve is closed exacly at BDC, the cylinder would not be ful of
charge asthe tendency is fr te rapidly moving piston to run away from the incoming charge.
Consequently, during the suction stoke the piston will rach the BDC before the charge could get
enough time to enter the cylinder through the resucted inlet valve passages, Moreover, there is
‘considerable resistance tothe low of charge through the ait-cleaner, carburettor, int manifold,
and ports, This means that ifthe inlet valve is closed at BDC the cylinder foreach cycle would
receive charge less than its capacity and the pressure inside the cylinder woutd remain somewhat
less than the atmosphere.
‘Consequently, in actual operation, te int valve is kept open ll the cylinder pressure equals
the atmospheric pressure. As the piston reverses and commences the compression stroke, it
appears that some of the charge may be sent back tothe induction pipe. So, it Tooks to be impos-
sible to leave the inet valve open ater BDC. However, there wil bea period around bth he dead
centre positions when the crank could swing through a wide angle while the piston remains
relatively stationary. Therefore, this extra period during which the piston does not move very far
up on the stroke, makes it possible vo keep the inet valve open after BDC. The momentum ef the
incoming charge help tt continue o il and rus itself nto the eylinder, thereby improving the
volumetric efficiency ofthe engine.
1.102 ExhaustValve
In order to exhaust as much of the products of combustion as possible, the exhaust valve opens
somewhat before the BDC position. Thus, some ofthe exhaust gas leaves by vie of its excess
pressure above aimospherie and hence the exhaust gas is already flowing freely from the cylinder
by the time the piston commences the exhaust stoke. During the exhaust stoke tr piston has to
30 less work in oder to push the exhaust gas ot
By closing the exhaust valve late, the kinetic energy ofthe exhaust gas can be utilized to asist
in maximum exhausting of the cylinder before the exhaust valve closes and thus reducing the
‘mount of residual gases.
Figure 1.9 shows the valve timing diagram for a four-stroke cycle engine, The diagram must
actually coasist of two circles, one superimposed over the other, since the four-stroke cycle is
complete in two revolution ofthe crankshaft Bu o present a clear concept, itis usual o draw
the diagram ss a spiral
Tt should be noted tha the values ofthe angular postions showa inthe diagram are average
‘ones, and considerable differences occur between different engines. Spark is provided before the
‘end ofthe compresion stroke by the ignition system
revois
poe
Crankshaft in ces diction
gene13. Vakiingdagarmelakunsnen Siege
[Note that here may be a period when both the valves are open at the same time, This happens
sear he TDC. The set valve has opened 10° before Ihe TDC andthe exhaust valve has nt yet
rite may close 15° after the TDC. This period is called the valve overiap period. This period
‘Shoutd not be excessive. otherwise the but ases wil be sucked into the cylinder, ort may allow
the fresh charge to escape through the exhaust valve,
4,11 FOUR-STROKE COMPRESSION IGNITION (CI) ENGINES
“The four-stroke CI engine is similar to the four-stroke SI engine except that a high compression
Tati e used in the CI engines, During the suetion stroke, the inlet valve opens and only the air
‘enters ino the eylinde a the piton moves from TDC 10 BDC.
‘Wh the il and exhaus valves closed, th piston compresses the ar. Bot the ir pressure
“and ianpotarure se. When the piston almost reaches the TDC, fuel is injected in finely divided
Form into the hot swiling air inthe combustion space. Ignition occurs after a short delay, the gas
pressure rises rapidly and a pressure wave is set Up.
‘Work is done by the gas pressure onthe piston as he piston sweeps the maximum cylinder
volume. Duting ths expansion or power stroke, the temperature and pressure ofthe burnt gs fal,
"As the piston approaches the BDC, the exhaust valve opens and he products of combustion
are ejected rom the cylinder during the exhaust stoke. Near the TDC, he inlet valve opens again
and the cycle is pente.
The typical valve tings for a four-stroke CI engine ae a follows:
Inet valve opens about 30° before TDC (TDC)
Inlet valve closes about 50 after BDC (ABDC)
"Exhaust valve opens about 45° before BDC (bBDC)
Exhaust valve closes about 30° after TDC (4TDC)
Injection of fuel is about 15° before TDC.
20_ Fundament of tera Combustion Engines
Introduction to Inem! Combustion Engnas 21
‘The reasons for opening and closing the valves before or after dead centre for Clengines are
‘actly the sume as those for ST engines, Four srokes of bot the SI and Cl engines ace the same.
1.12 COMPARISON OF SI AND CI ENGINES
‘The basic differences between the SI and CI engines are given in Table 12
Table 1.2 Comparison of Sland Gl engines
Sergi
+ Tt works on One Ja
+ A fuel having higher sl
igion temperature
de Si se pel Gai)
+ Air and fel mixture in
sous form i induce
through the caco inte rider ding
the suction stoke
+ Tie te alo heater cna the
eat othe chars Te ga ae ns
Sin sno aed cag Sern Sa
Contre ve el ua oe
‘panty gnome ss
2 Saeed ar Fe a
in Sytem wh pu ge ae
Becaute ofthis itis called à parer (SD
cis
+ A ones i of 616 1055 amp
‘Tue upper limit is fixed by the rer
set of fit Ten sos a
pore copos a
Pat lá fío inc ven a pa
loathe aufero nt much vane, der
ini prat sl
gin he MUY che of o
used in modem engines. “er
2 Die cont ofthe peo is higher han tat of he
Noise and vibration ao ess Because of less
engine weight
‘Tae ain polluants ar carbon monoxide (CO).
oxides of nütogen (NO) and hydreerbons (HC).
Cl engine
Te works on Dizse or Dual combustion yee,
A fuel having lower sell gain temperate
is desile such as diesel ol
Only ati introduced into ie cylinder during
(he suction stroke and therefore th carburetor
is ot require, Peli nected at high pressure
"rough foc injectors dre into the combus |
tion chamber,
“The amount of ir indcte fixed but the
amount of Re injected i ved by regulating
the quantity of fol ia the pump. The sirfoel 1
Falo l vare at varying toad. So, ie a quality
‘governed engine
Corbustion of fe takes place on it own with
‘So any external gion sistem. Fel bum in
the presence of highly Compressed air inside
teenie ee
A compresion ati of 14102 employed. The
upper mic of compression eto limited by the
play Increasing weight of he engine. Engine
ends 10 knock at Joer compression ratios.
Par loa efiieney is good. AS the load
(decreases, the fuel supply 1 the engine can
‘ho be reduced and lean ter o the engine
ds then supe.
“The cou of diesel oil less than that of petro
Moreover, as fue so on volume bass and
‘ine il has higher specific gravity, move
‘weight is obaied in oe Hire
Noise end vibeatons ae more because of
heavier engine components due 1 higher
compression at.
“par fora CO, NO, and HC, s0ot or smoke
parles ae alto emite 1 the stmosphece,
A
1.13 TWO-STROKE ENGINES
“The two stokes of the cycle are completed once during each revolution of the crankshaf
Figure 110 represents a two-stoke SI engine with erankcase compression, As the piston moves.
‘apwatds inthe cylinder and covers both the transfer port (T) and exhaust port (E), there is
compression ofthe charge ino the cylinder. At the same time in the crankcase the charge expands
and the pressure is reduced below the atmospheric pressure, So, fish charge enters into the
crankease though the spring-loaded automatic valve (9). Ignition occurs before the TDC. The
as pressure rises rapidly and pushes the piston downwards to produce power
A Spa los
4
ob Onde
EL tutos
re)
Taster
pot)
Gres
Induction
po
NS Crane
Can
CS
Fue 110 Trot Starr,
“As the piston descends through about 80 percent of the working stroke, the exaust port (E)
is uncovered by the piston and exhaust begins. The transfer port (T) is uncovered a lite later in
the stroke due tits position in relation tothe exhaust port (E). The charge in the erankense, which
as been compressed by the descending piston, enters the cylinder through the transfer port (D).
Introduction to Inem! Combustion Engnas 21
‘The reasons for opening and closing the valves before or after dead centre for Clengines are
‘actly the sume as those for ST engines, Four srokes of bot the SI and Cl engines ace the same.
1.12 COMPARISON OF SI AND CI ENGINES
‘The basic differences between the SI and CI engines are given in Table 12
Table 1.2 Comparison of Sland Gl engines
Sergi
+ Tt works on One Ja
+ A fuel having higher sl
igion temperature
de Si se pel Gai)
+ Air and fel mixture in
sous form i induce
through the caco inte rider ding
the suction stoke
+ Tie te alo heater cna the
eat othe chars Te ga ae ns
Sin sno aed cag Sern Sa
Contre ve el ua oe
‘panty gnome ss
2 Saeed ar Fe a
in Sytem wh pu ge ae
Becaute ofthis itis called à parer (SD
cis
+ A ones i of 616 1055 amp
‘Tue upper limit is fixed by the rer
set of fit Ten sos a
pore copos a
Pat lá fío inc ven a pa
loathe aufero nt much vane, der
ini prat sl
gin he MUY che of o
used in modem engines. “er
2 Die cont ofthe peo is higher han tat of he
Noise and vibration ao ess Because of less
engine weight
‘Tae ain polluants ar carbon monoxide (CO).
oxides of nütogen (NO) and hydreerbons (HC).
Cl engine
Te works on Dizse or Dual combustion yee,
A fuel having lower sell gain temperate
is desile such as diesel ol
Only ati introduced into ie cylinder during
(he suction stroke and therefore th carburetor
is ot require, Peli nected at high pressure
"rough foc injectors dre into the combus |
tion chamber,
“The amount of ir indcte fixed but the
amount of Re injected i ved by regulating
the quantity of fol ia the pump. The sirfoel 1
Falo l vare at varying toad. So, ie a quality
‘governed engine
Corbustion of fe takes place on it own with
‘So any external gion sistem. Fel bum in
the presence of highly Compressed air inside
teenie ee
A compresion ati of 14102 employed. The
upper mic of compression eto limited by the
play Increasing weight of he engine. Engine
ends 10 knock at Joer compression ratios.
Par loa efiieney is good. AS the load
(decreases, the fuel supply 1 the engine can
‘ho be reduced and lean ter o the engine
ds then supe.
“The cou of diesel oil less than that of petro
Moreover, as fue so on volume bass and
‘ine il has higher specific gravity, move
‘weight is obaied in oe Hire
Noise end vibeatons ae more because of
heavier engine components due 1 higher
compression at.
“par fora CO, NO, and HC, s0ot or smoke
parles ae alto emite 1 the stmosphece,
A
1.13 TWO-STROKE ENGINES
“The two stokes of the cycle are completed once during each revolution of the crankshaf
Figure 110 represents a two-stoke SI engine with erankcase compression, As the piston moves.
‘apwatds inthe cylinder and covers both the transfer port (T) and exhaust port (E), there is
compression ofthe charge ino the cylinder. At the same time in the crankcase the charge expands
and the pressure is reduced below the atmospheric pressure, So, fish charge enters into the
crankease though the spring-loaded automatic valve (9). Ignition occurs before the TDC. The
as pressure rises rapidly and pushes the piston downwards to produce power
A Spa los
4
ob Onde
EL tutos
re)
Taster
pot)
Gres
Induction
po
NS Crane
Can
CS
Fue 110 Trot Starr,
“As the piston descends through about 80 percent of the working stroke, the exaust port (E)
is uncovered by the piston and exhaust begins. The transfer port (T) is uncovered a lite later in
the stroke due tits position in relation tothe exhaust port (E). The charge in the erankense, which
as been compressed by the descending piston, enters the cylinder through the transfer port (D).
Z2_ fondamientals of neral Comision Engines =
Inraducion co nara! Combustion Engines 23
The piston is shaped to deflect the fresh charge upwards in te cylinder and prevent is escape
‘hough the exhaust port. As the piston rise, he transfer port is closed slightly before the exhaust
port and after the exhaust por is closed, compression ofthe charge inthe eylinder begins. The
cle is then repeated
‘The pressure diagram and the timing diagram for a two-stroke SI engine are shown in
Figures 1.116) and 11165) respectively
Ho ro
Inlet sage ("approx
me ‘ro Ext angle (1207708)
Tenner angle (100 px)
ave
1PO--Inducion portopene — EPO—Exhast por opens TPO—Transfe port opens
IPCInduclonpenchees ERC-Änhaustporichuen TPC Taste par elses
ques), Trgdagamet rosie egos
“The description ofthe two-stroke cycle as given in this section also applies 10 the Cl engines
vith the exception that only ir is compressed and the spark plug is replaced by the fuel injector.
[A higher compression rato is also used in the case of Cl engines
1.4 COMPARISON OF FOUR-STROKE AND TWO-STROKE
ENGINES
‘A comparison of four
is presented in Table 13.
troke and two-stroke engines indicating ther relative merits and demerits
Table 1.3 Comparison offour-iroho and to stroke engines
Fourcirake engine
Tios engine
One power soke is tine in every suo
revoltion o the crankstaft as the eye
is completed in foursokes of the piston
for into revolutions of the cranks
One power stoke in to revolutions ofthe
craneal makes de turing movement of
the safl non uniform and hen a heavier
Aye! is needed 10 rotate the af
for.
Power produced fr the same size ofthe
‘engine is les and forthe ame power curp,
the engine Is lager in size, because only one
power sole is obtained in two revolutions
Te contains valves nd valve mechani
Because of heavy weight and complicated
valve mechaniem, the iil os is high.
= Due to positive savenging and greater
Be of odio, er! efficiency
and volume efficiency ae higher
Used where high efficiency is important
as in automobiles, power generation and
aeroplanes.
Normal water cook the wear ad ta is.
therfore Is, I eonsumes less amount of
lubsicant. The Mbicant is placed inthe
ranas, not mixed wih the fe
‘One power stoke is obaiod in each revolution
ofthe craft asthe cycle is completed in two
‘stokes or in one revolution ofthe cre
‘The timing movement ofthe shat is more ro
and hence a lighter yes needed orte
the aha enfers,
Power produced forthe same size ofthe engine is
‘more and for the same power sup, ih engine is
taller inst, because ene power seoke is
obtained in every evolution.
has ports Some engines ae filed with ext
valve or red valve
Wis gi in weight and has mo valve mechani
Tu iia cost therefore low.
Te hs lower thermal efficieney and volumetric
ii). Som ofthe fresh charge escapes unburt
“during scavenging in perl engines
Used where low cost Low weight and compacness
se important sin scooters, mopeds, Immonet,
(motor ees, e. TWwo-soke diesel engines aro
ted in very lage sizes fr ship proplion becas
flow weight and compacts.
Normal air-cooled, tbo wear and tear is therefore
mor. eguizs move aman of icant. Vall
tobi ie ited with il,
1 may be noted thatthe two-stroke cycle has twice as many power strokes per crank revo:
tution as the fourstcoke cycle. However in two-stroke cycle engines the power output per unit
Inraducion co nara! Combustion Engines 23
The piston is shaped to deflect the fresh charge upwards in te cylinder and prevent is escape
‘hough the exhaust port. As the piston rise, he transfer port is closed slightly before the exhaust
port and after the exhaust por is closed, compression ofthe charge inthe eylinder begins. The
cle is then repeated
‘The pressure diagram and the timing diagram for a two-stroke SI engine are shown in
Figures 1.116) and 11165) respectively
Ho ro
Inlet sage ("approx
me ‘ro Ext angle (1207708)
Tenner angle (100 px)
ave
1PO--Inducion portopene — EPO—Exhast por opens TPO—Transfe port opens
IPCInduclonpenchees ERC-Änhaustporichuen TPC Taste par elses
ques), Trgdagamet rosie egos
“The description ofthe two-stroke cycle as given in this section also applies 10 the Cl engines
vith the exception that only ir is compressed and the spark plug is replaced by the fuel injector.
[A higher compression rato is also used in the case of Cl engines
1.4 COMPARISON OF FOUR-STROKE AND TWO-STROKE
ENGINES
‘A comparison of four
is presented in Table 13.
troke and two-stroke engines indicating ther relative merits and demerits
Table 1.3 Comparison offour-iroho and to stroke engines
Fourcirake engine
Tios engine
One power soke is tine in every suo
revoltion o the crankstaft as the eye
is completed in foursokes of the piston
for into revolutions of the cranks
One power stoke in to revolutions ofthe
craneal makes de turing movement of
the safl non uniform and hen a heavier
Aye! is needed 10 rotate the af
for.
Power produced fr the same size ofthe
‘engine is les and forthe ame power curp,
the engine Is lager in size, because only one
power sole is obtained in two revolutions
Te contains valves nd valve mechani
Because of heavy weight and complicated
valve mechaniem, the iil os is high.
= Due to positive savenging and greater
Be of odio, er! efficiency
and volume efficiency ae higher
Used where high efficiency is important
as in automobiles, power generation and
aeroplanes.
Normal water cook the wear ad ta is.
therfore Is, I eonsumes less amount of
lubsicant. The Mbicant is placed inthe
ranas, not mixed wih the fe
‘One power stoke is obaiod in each revolution
ofthe craft asthe cycle is completed in two
‘stokes or in one revolution ofthe cre
‘The timing movement ofthe shat is more ro
and hence a lighter yes needed orte
the aha enfers,
Power produced forthe same size ofthe engine is
‘more and for the same power sup, ih engine is
taller inst, because ene power seoke is
obtained in every evolution.
has ports Some engines ae filed with ext
valve or red valve
Wis gi in weight and has mo valve mechani
Tu iia cost therefore low.
Te hs lower thermal efficieney and volumetric
ii). Som ofthe fresh charge escapes unburt
“during scavenging in perl engines
Used where low cost Low weight and compacness
se important sin scooters, mopeds, Immonet,
(motor ees, e. TWwo-soke diesel engines aro
ted in very lage sizes fr ship proplion becas
flow weight and compacts.
Normal air-cooled, tbo wear and tear is therefore
mor. eguizs move aman of icant. Vall
tobi ie ited with il,
1 may be noted thatthe two-stroke cycle has twice as many power strokes per crank revo:
tution as the fourstcoke cycle. However in two-stroke cycle engines the power output per unit
24 Fundamentals of Inemal Combustion Engines
displaced volume is ess than twice the power output of an equivalen four-stroke cycle engine at
the same engine sped. This is because of (a) the reduction inthe effective expansion stroke and
(6) some fresh charge escaping unburat during the scavenging process.
1
2
3.
a
REVIEW QUESTIONS
Define a heat engine, How are heat engines classified?
‘What do you understand by an external combustion engine? Give some examples ofthis
typeof the engine.
‘What do you understand by an internal combustion engine? Give some examples ofthis
type of engine,
Distinguish between internal combustion and extemal combustion engines. What are the
relative merits and demerits of internal combustion engines over the external combustion
engines?
. Distinguish between itermittet and continuous IC engines. Give some examples ofthese
types of engines.
Give an account of historial development of IC engines.
Give an account of the modem development of IC engines,
How ace the reciprocating IC engines classified? Briefly describo the each ype
How are the reciprocating LC engines classified according to their applications? Mer
the predominant type of engines used in each case.
How ae the reciprocating IC engines elassiied according to cylinder arangement? Briefly
describe the each type withthe help of suitable diagrams,
Desecbe the functions of important engine components in a four-stroke IC engine. Also
mention the materials used for these engine components
2. Define swept volume, clearance volume, compression ratio and mean piston speed.
. Describe with the help of diagrams, the working principle of the four-sroke SI engine.
. Describe the valve timing of a four-stroke SI engine. Draw the p-V diagram and valve
ing diagram Foran
engine.
Describe the wozking principle ofthe fourstoke CI engine. Mention the typical values of
s for afour<troke CI engine
. Distinguish between spak-ignition and compresson-igniion engines.
. Describe a two-stroke SI engine withthe help of a diagram. What modifications are rc-
quid forthe two-stoke CI engine?
. Distinguish between four-stroke and two-stroke IC engines. Menton their relative merits
and demerits,
. Draw the p-V diagram end the typical valve Gming diagram fora two-stroke IC engin.
. What are the major pollutants from the exhaust of SI and CI engines?
i
Air-Standard Cycles
and Their Analysis
2.1 INTRODUCTION
In internal combustion engines, the conversion of heat energy into mechanical work is a complt-
fated process. As the working fui passes trough the engine and combustion of fuel akes place,
complicated chemical, thermal, and physical changes occur. ction and het transfer between
the gases and cylinder walls in actual engines, make te analysis more complicated. To examine all,
these changes quamitaively and to account fr all the variables, creates a very complex problem,
‘The usual method of approach is through the use of certain theoretical approximations. The two
commonly employed approximations ofan actua engine in order oftheir increasing accuracy aro
(@) the airsiandard cycle nd (5) the fuckair cycle. They give an insight ito some af the impor
‘ant parameters that influence engine pecformance.
Th alestandard cycle the working fluids assumed 1 be air. The values of the specific heat
of air are assumed o be constant at all temperatures. This ideal cycle represents the upper limit of
the performance, which an engine may theoretically alain. One step closer to the conditions
existing in the actual engine isto consider the fuel air cycle, This cycle considers the effect of
variation of specific eat with temperature andthe dissociation of some ofthe lighter molecules
that occur at high temperatures. The analysis ofthe fuel-ac cycle is presented in Chapter 4.
2.2 AIR-STANDARD CYCLE
‘The analysis of the ain standard cycle is based upon the following assumptions:
1. The working fluid in the engine is always an ideal gas, namely pure sir with constant
specific heats
2. A fixed mass of airs taken asthe working id throughout de entre cycle. The cycle is
‘considered closed withthe same air remaining in the cylinder to repeat the cycle. The
intake and exhaust processes are not considered,
‘The combustion process is eplaced by a heat transfer process from an extemal source,
4. The cycle is completed by heat rejection o he surrounding until the ai temperature and
pressure correspond lo initial conditions. This is in contrast to the exhaust and intake
processes in an actual engin.
5. All the processes that constitute the cyel ae reversible
displaced volume is ess than twice the power output of an equivalen four-stroke cycle engine at
the same engine sped. This is because of (a) the reduction inthe effective expansion stroke and
(6) some fresh charge escaping unburat during the scavenging process.
1
2
3.
a
REVIEW QUESTIONS
Define a heat engine, How are heat engines classified?
‘What do you understand by an external combustion engine? Give some examples ofthis
typeof the engine.
‘What do you understand by an internal combustion engine? Give some examples ofthis
type of engine,
Distinguish between internal combustion and extemal combustion engines. What are the
relative merits and demerits of internal combustion engines over the external combustion
engines?
. Distinguish between itermittet and continuous IC engines. Give some examples ofthese
types of engines.
Give an account of historial development of IC engines.
Give an account of the modem development of IC engines,
How ace the reciprocating IC engines classified? Briefly describo the each ype
How are the reciprocating LC engines classified according to their applications? Mer
the predominant type of engines used in each case.
How ae the reciprocating IC engines elassiied according to cylinder arangement? Briefly
describe the each type withthe help of suitable diagrams,
Desecbe the functions of important engine components in a four-stroke IC engine. Also
mention the materials used for these engine components
2. Define swept volume, clearance volume, compression ratio and mean piston speed.
. Describe with the help of diagrams, the working principle of the four-sroke SI engine.
. Describe the valve timing of a four-stroke SI engine. Draw the p-V diagram and valve
ing diagram Foran
engine.
Describe the wozking principle ofthe fourstoke CI engine. Mention the typical values of
s for afour<troke CI engine
. Distinguish between spak-ignition and compresson-igniion engines.
. Describe a two-stroke SI engine withthe help of a diagram. What modifications are rc-
quid forthe two-stoke CI engine?
. Distinguish between four-stroke and two-stroke IC engines. Menton their relative merits
and demerits,
. Draw the p-V diagram end the typical valve Gming diagram fora two-stroke IC engin.
. What are the major pollutants from the exhaust of SI and CI engines?
i
Air-Standard Cycles
and Their Analysis
2.1 INTRODUCTION
In internal combustion engines, the conversion of heat energy into mechanical work is a complt-
fated process. As the working fui passes trough the engine and combustion of fuel akes place,
complicated chemical, thermal, and physical changes occur. ction and het transfer between
the gases and cylinder walls in actual engines, make te analysis more complicated. To examine all,
these changes quamitaively and to account fr all the variables, creates a very complex problem,
‘The usual method of approach is through the use of certain theoretical approximations. The two
commonly employed approximations ofan actua engine in order oftheir increasing accuracy aro
(@) the airsiandard cycle nd (5) the fuckair cycle. They give an insight ito some af the impor
‘ant parameters that influence engine pecformance.
Th alestandard cycle the working fluids assumed 1 be air. The values of the specific heat
of air are assumed o be constant at all temperatures. This ideal cycle represents the upper limit of
the performance, which an engine may theoretically alain. One step closer to the conditions
existing in the actual engine isto consider the fuel air cycle, This cycle considers the effect of
variation of specific eat with temperature andthe dissociation of some ofthe lighter molecules
that occur at high temperatures. The analysis ofthe fuel-ac cycle is presented in Chapter 4.
2.2 AIR-STANDARD CYCLE
‘The analysis of the ain standard cycle is based upon the following assumptions:
1. The working fluid in the engine is always an ideal gas, namely pure sir with constant
specific heats
2. A fixed mass of airs taken asthe working id throughout de entre cycle. The cycle is
‘considered closed withthe same air remaining in the cylinder to repeat the cycle. The
intake and exhaust processes are not considered,
‘The combustion process is eplaced by a heat transfer process from an extemal source,
4. The cycle is completed by heat rejection o he surrounding until the ai temperature and
pressure correspond lo initial conditions. This is in contrast to the exhaust and intake
processes in an actual engin.
5. All the processes that constitute the cyel ae reversible
26_ Fundamentals of Internal Cambon Engines
6, The compression and expansion processes are reversible ediabatc
7. The working medium does not undergo any chemical change throughout the cycle.
8. The operation ofthe engine is fitonless.
Because of the above simplified assumptions, the peak temperature, the pressure, the work
‘ouput, and the thermal efficiency calculated by the analysis of an ai-sandard cycle are higher
than those found in an actual engine. However, he analysis shows the relative effects of the
principal variables, suchas compresion rai, inet pressure, inlet temperature, ec. onthe engine
performance.
In the present chapter, the following aistandard cycles are described and their work output,
‘thermal efficiency, and mean effective pressure are evaluated:
(a) Oto cycle
(&) Diesel cycle
(€) Dual combustion cycle
(@) Atkinson cycle.
The frst thee cycles are particularly relevant othe reciprocating internal combustion engine
and the fourth one i relevant toa combination of engine and turbine. Some shortcomings ofthese
ideal eycles are obvious, but these cycles give a valuable insight into real effects and possibilities,
2.3 OTTO CYCLE OR CONSTANT VOLUME CYCLE
‘A German scientist, A. Nicolaus Oto in 1876 proposed an ideal ar-standard cycle with constant
volume heat addition, which formed the bass forth practical spark-ignitioa engines (petrol and
as engines). The eycle is shown on p-V and T=s diagrams in Figure 2.1) and Figure 2.10)
respectively.
a r ‘Y= constant
Can
3
y sexe
$ 02077
:
, :
ARE
rra Porn
Fig Cor
At point, the piston sat he bottom dead centre (BDC) position and air is rapped inside the
engine eylindet. As the piston moves upwards with valves closed, aris compressed isentropically,
represented by process 1-2. At point 2, the piston reaches the top dead centre (TDC) position
Air Sandad yes and Tet Any 27
Heat is supplied to the air fom an outer source during the constant volume process 2-3, In an
actual engine tis equivalent to burning of fut instantaneously by aneeciic spark. At point 3, air
fs atts highest pressure and temperature. is now able o pu the piston from TDC to BDC and
hence produces the work output. Tis process of expansion isan isentropic process represented
by process 3-4, At the end ofthis expansion proces, he heat is rejected at constant volume
represented by process 4-1. The cycle is thus completed
‘Lets summarize:
Process 1-2 is reversible adiabatic or isentropic compression. There is no heat transfer.
Process 2-3 is reversible constant volume heating.
Process 3-4 is reversible adiabatic o isentropic expansion. There is no heat transfer
Process 4-1 is reversible constant volume heat rejection.
V, = swept volume
Y. =clearance volume
Vi = total cylinder volume = Y, + Ve
al cylinder volume
Compression ratio, IS
‘clearance volume
EA
oat en
Thermal efficiency of any cycle,
work done _ heat supplied hear ejected
"ea supiid Beat supplied
a1 etes _ en
heat supplied © ! 7 Q,
where
(01 = het supplied during the ele
G = heat ete.
In the Otto cycle, here is no heat transfer during the processes 1-2 and 3-4 as they are
reversible adiabatic processes. Heat i supplied only during the constant volume process 2-3 and
beat is rejected only during the constant volam process 4-1
x 9 = mets 7)
wd 9 = mes -T)
ly mem
a mAH)
1-5
ay
For isentopie process 1-2,
a Er
nn
Tann es
6, The compression and expansion processes are reversible ediabatc
7. The working medium does not undergo any chemical change throughout the cycle.
8. The operation ofthe engine is fitonless.
Because of the above simplified assumptions, the peak temperature, the pressure, the work
‘ouput, and the thermal efficiency calculated by the analysis of an ai-sandard cycle are higher
than those found in an actual engine. However, he analysis shows the relative effects of the
principal variables, suchas compresion rai, inet pressure, inlet temperature, ec. onthe engine
performance.
In the present chapter, the following aistandard cycles are described and their work output,
‘thermal efficiency, and mean effective pressure are evaluated:
(a) Oto cycle
(&) Diesel cycle
(€) Dual combustion cycle
(@) Atkinson cycle.
The frst thee cycles are particularly relevant othe reciprocating internal combustion engine
and the fourth one i relevant toa combination of engine and turbine. Some shortcomings ofthese
ideal eycles are obvious, but these cycles give a valuable insight into real effects and possibilities,
2.3 OTTO CYCLE OR CONSTANT VOLUME CYCLE
‘A German scientist, A. Nicolaus Oto in 1876 proposed an ideal ar-standard cycle with constant
volume heat addition, which formed the bass forth practical spark-ignitioa engines (petrol and
as engines). The eycle is shown on p-V and T=s diagrams in Figure 2.1) and Figure 2.10)
respectively.
a r ‘Y= constant
Can
3
y sexe
$ 02077
:
, :
ARE
rra Porn
Fig Cor
At point, the piston sat he bottom dead centre (BDC) position and air is rapped inside the
engine eylindet. As the piston moves upwards with valves closed, aris compressed isentropically,
represented by process 1-2. At point 2, the piston reaches the top dead centre (TDC) position
Air Sandad yes and Tet Any 27
Heat is supplied to the air fom an outer source during the constant volume process 2-3, In an
actual engine tis equivalent to burning of fut instantaneously by aneeciic spark. At point 3, air
fs atts highest pressure and temperature. is now able o pu the piston from TDC to BDC and
hence produces the work output. Tis process of expansion isan isentropic process represented
by process 3-4, At the end ofthis expansion proces, he heat is rejected at constant volume
represented by process 4-1. The cycle is thus completed
‘Lets summarize:
Process 1-2 is reversible adiabatic or isentropic compression. There is no heat transfer.
Process 2-3 is reversible constant volume heating.
Process 3-4 is reversible adiabatic o isentropic expansion. There is no heat transfer
Process 4-1 is reversible constant volume heat rejection.
V, = swept volume
Y. =clearance volume
Vi = total cylinder volume = Y, + Ve
al cylinder volume
Compression ratio, IS
‘clearance volume
EA
oat en
Thermal efficiency of any cycle,
work done _ heat supplied hear ejected
"ea supiid Beat supplied
a1 etes _ en
heat supplied © ! 7 Q,
where
(01 = het supplied during the ele
G = heat ete.
In the Otto cycle, here is no heat transfer during the processes 1-2 and 3-4 as they are
reversible adiabatic processes. Heat i supplied only during the constant volume process 2-3 and
beat is rejected only during the constant volam process 4-1
x 9 = mets 7)
wd 9 = mes -T)
ly mem
a mAH)
1-5
ay
For isentopie process 1-2,
a Er
nn
Tann es
28 Fandamansls of Inerral Combustion Engines
AirSandard Cycles ard Ther Arabs 29
Also for isentropic process 3-4,
EGY “Eo
Tye Tet! es
Substituting the values of Tp and 7, from Ts. (24) and (2.5) in Eg. (23), the thermal
efficiency or the ale tandard efficiency of Oto eyele is
es
I is clear from En, (6) thatthe thermal efficiency of the Otto eycle depends only on the
‘compression ratio, rand it increases with an increase inthe compression ratio, where yor air is
taken as constant and equal to 14. For the combustion products ofthe fuel-air mixture, y is
approximately taken as 13,
‘The effect of compression ratio on the ai-standard efficiency for two values of adiabatic
‘exponent, Y= 14 and 7= 1.3, i shown in Figure 22,
E” rua
E PR
é
Eno
y 6 8 10 12
Compresion aio, y
Fgure22 Tomas compren ere vabes ea pat:
‘The variation of compression ratio is taken from 4 o 12, These are the possible values in
sparkignition engines. Figure 22 shows that the thermal efficiency of the cycle increases with
the increase in compression rato. At a higher value of adiabaic exponent 7 the efficiency also
increases. Fora given value of compression ratio and siabatic exponent, the thermal efficiency is
a constant and does rot depend upon the arvount of heat supplied. Heat supplied is proportional to
the engine load and hence the thermal efficiency ofthe Oto cycle does not depend upon the engine
load,
rom the first law of thermodynamics, fr a closed system the work done during a cycle,
7 2 heat supplied heat rejected
Wa Qi - Qi met -T)= malle Ti)
med 7) (Ti TO) en
For constant volume process 2-3,
es
where a a it is the pressure ratio with heat added in a process at constant volume.
Subt te vals of in Ea (2) fom E, 24,
Beaty"! es
From Ba, 23),
Sesiutig in de above equa he valu of rom Eg (29),
O a es
Substituting the values of 7, T and 7 from Eqs. (24), (2.9) and (210) respectively in Eg. (2.7)
We me (OT Tye“) = (a; = TO)
mer a 1) -(a~ IT;
mea 1100-10 en
work done Y ein
Mean efecive pres, Pm = Sept volume Y
Septum, a =) em
meto Nor" np, „made
PT) (DE ous
Using Bq. (2.6),
pie nn
9-De-D
10)
AirSandard Cycles ard Ther Arabs 29
Also for isentropic process 3-4,
EGY “Eo
Tye Tet! es
Substituting the values of Tp and 7, from Ts. (24) and (2.5) in Eg. (23), the thermal
efficiency or the ale tandard efficiency of Oto eyele is
es
I is clear from En, (6) thatthe thermal efficiency of the Otto eycle depends only on the
‘compression ratio, rand it increases with an increase inthe compression ratio, where yor air is
taken as constant and equal to 14. For the combustion products ofthe fuel-air mixture, y is
approximately taken as 13,
‘The effect of compression ratio on the ai-standard efficiency for two values of adiabatic
‘exponent, Y= 14 and 7= 1.3, i shown in Figure 22,
E” rua
E PR
é
Eno
y 6 8 10 12
Compresion aio, y
Fgure22 Tomas compren ere vabes ea pat:
‘The variation of compression ratio is taken from 4 o 12, These are the possible values in
sparkignition engines. Figure 22 shows that the thermal efficiency of the cycle increases with
the increase in compression rato. At a higher value of adiabaic exponent 7 the efficiency also
increases. Fora given value of compression ratio and siabatic exponent, the thermal efficiency is
a constant and does rot depend upon the arvount of heat supplied. Heat supplied is proportional to
the engine load and hence the thermal efficiency ofthe Oto cycle does not depend upon the engine
load,
rom the first law of thermodynamics, fr a closed system the work done during a cycle,
7 2 heat supplied heat rejected
Wa Qi - Qi met -T)= malle Ti)
med 7) (Ti TO) en
For constant volume process 2-3,
es
where a a it is the pressure ratio with heat added in a process at constant volume.
Subt te vals of in Ea (2) fom E, 24,
Beaty"! es
From Ba, 23),
Sesiutig in de above equa he valu of rom Eg (29),
O a es
Substituting the values of 7, T and 7 from Eqs. (24), (2.9) and (210) respectively in Eg. (2.7)
We me (OT Tye“) = (a; = TO)
mer a 1) -(a~ IT;
mea 1100-10 en
work done Y ein
Mean efecive pres, Pm = Sept volume Y
Septum, a =) em
meto Nor" np, „made
PT) (DE ous
Using Bq. (2.6),
pie nn
9-De-D
10)
30, Fundamental of neral Corbier Engines
Air Standard Cels and Their Ari 31
‘Equation (2.11) shows thet the work output of the cycle increases with the incresss in
pressure ratio a, and compression ratio . The increase in pressure ratio isthe result of en increase
in the amount of heat received, Equation (2.15) shows thatthe mean effective pressor Pa.
increases in proportion to initial pressure, p;. An increase in the compression ratio 1, also
increases the mean effective pressure Pu,
Figure 23 shows the vacation of mean effective pressure versus pressure rato for various
values of the compression ratio. The intial pressure py is taken as 1 bar and the value of the
adiabatic exponent ÿ is taken as 1.3. It is observed that he mean effective pressure increases with
an increase in pressure ratio and also with an increase in compression rato
Mean effective pete, (dr)
o nn
i El 3 à
‘Presse rao, a
Fgun23Meanetecie passers. presse alo Sewn aus conpenon ie
‘The analysis of the expressions used to determine the thermal efficiency and the mean
effective pressure of the cycle shows thatthe use of higher compression ratios is the most
clfetive way of improving the performance ofthe engine. However the maximum value of the
compression ratio in an actual engine is restricted, so that normal combustion ofthe fuel in SI
‘engines is ensured without creating problems of detonation and slf-igition,
24 DIESEL CYCLE
Rudolf Diesel in 1892 introduced this cycle. Isa theoretical cycle for slow speed compression»
ignition Diesel engine. In this cycle, heat is added at constant pressure and rejected at constant
volume. The compression and expansion processes are isentropic. The p-V and T-s diagrams are
shown in Figure 24(a) and Figure 2.4(b) respectively.
= >
pcs
3
y sos
2
x
7
ee ‘i
. Er
orga CE
Panza. Dos
Leu soma
Process 1-2 is isentropic compression. There is no heat transfer.
Process 2-3 is reversible constant pressure process. Heat is supplied during this process.
Process 3-4 i isetropie expansion. There is no heat transfer: Z
Process 4-1 is reversible constant volume process. Hea is rejected during this process.
Heat supplied, Qi = mes To 2)
Heatejected, Da = mest em
‘Trea efficiency, a
E em
“Two ratios are used to analyse the Diesel cycle:
Itistheraocof the total cylinder volume tothe clearance volume,
1. Compression aso,
019
2. Curoff ratio, At point 3, ihe heat supplied Re. the fuel supply in an actual engine) is
SA Ta oe vahme a pit of eat he cence Yume o de
Volume from where the heat supplied begins is called the cu-o rai, Le.
dis ab
am
Y
xao, od
Air Standard Cels and Their Ari 31
‘Equation (2.11) shows thet the work output of the cycle increases with the incresss in
pressure ratio a, and compression ratio . The increase in pressure ratio isthe result of en increase
in the amount of heat received, Equation (2.15) shows thatthe mean effective pressor Pa.
increases in proportion to initial pressure, p;. An increase in the compression ratio 1, also
increases the mean effective pressure Pu,
Figure 23 shows the vacation of mean effective pressure versus pressure rato for various
values of the compression ratio. The intial pressure py is taken as 1 bar and the value of the
adiabatic exponent ÿ is taken as 1.3. It is observed that he mean effective pressure increases with
an increase in pressure ratio and also with an increase in compression rato
Mean effective pete, (dr)
o nn
i El 3 à
‘Presse rao, a
Fgun23Meanetecie passers. presse alo Sewn aus conpenon ie
‘The analysis of the expressions used to determine the thermal efficiency and the mean
effective pressure of the cycle shows thatthe use of higher compression ratios is the most
clfetive way of improving the performance ofthe engine. However the maximum value of the
compression ratio in an actual engine is restricted, so that normal combustion ofthe fuel in SI
‘engines is ensured without creating problems of detonation and slf-igition,
24 DIESEL CYCLE
Rudolf Diesel in 1892 introduced this cycle. Isa theoretical cycle for slow speed compression»
ignition Diesel engine. In this cycle, heat is added at constant pressure and rejected at constant
volume. The compression and expansion processes are isentropic. The p-V and T-s diagrams are
shown in Figure 24(a) and Figure 2.4(b) respectively.
= >
pcs
3
y sos
2
x
7
ee ‘i
. Er
orga CE
Panza. Dos
Leu soma
Process 1-2 is isentropic compression. There is no heat transfer.
Process 2-3 is reversible constant pressure process. Heat is supplied during this process.
Process 3-4 i isetropie expansion. There is no heat transfer: Z
Process 4-1 is reversible constant volume process. Hea is rejected during this process.
Heat supplied, Qi = mes To 2)
Heatejected, Da = mest em
‘Trea efficiency, a
E em
“Two ratios are used to analyse the Diesel cycle:
Itistheraocof the total cylinder volume tothe clearance volume,
1. Compression aso,
019
2. Curoff ratio, At point 3, ihe heat supplied Re. the fuel supply in an actual engine) is
SA Ta oe vahme a pit of eat he cence Yume o de
Volume from where the heat supplied begins is called the cu-o rai, Le.
dis ab
am
Y
xao, od
32 Fondemenuls llora! Comburion Engines
For isentropic process 1-2,
Wer
nn
Tyo Tak Brenn (2.22)
oes
ul
me a
Substituting the values of 7, Ts and Ta from Eqs. (221), (222) and (2.23) respectively in
a. (2.18), the thermal efficiency or air-standard efficiency ola Diesel cycle can be expressed as
as
Alea] #5
Equation (2:24) shows Unt the thermal efficiency of a Diesel cycle depends on the compression
rato r, the adiabatic exponent 7, andthe curo ratio A. By comparing Eqs. (2.24) and (2.6), itis
‘observed that the efficiency ofa Diese cele differs from the efficiency of an Otto cycle by the
term (BY 1 7(B~ 1), which i always greater than unity. Therefore, the ai-standard efficiency
‘ofthe Diesel cycle is less than that ofthe Out cycle for the same compression ratio, For the given
value of the cut-off ratio the efficiency ofthe Diesel cycle increases with increase in compres.
sion ratio . In actual practice, the normal range of compression ratio for diesel engines is from 16
1o 20, whereas for sparkignition engines, iti 6 to 10. Because of the higher compresion ratio
‘wedi diesel engines, the efficiency ofa diesel engine is more than that of a petol engine.
Figure 25 shows thatthe thermal cficieney of a Diesel cyle increases withthe increase in
‘compression ratio r, and adiabatic exponent y However an increase in te cut-off rato f teduces
is efficiency. An increase in he value of the cut-off ratio means tht the heat addition at constant
pressure is increased, which corresponds to an increase in load onthe engine. Therefore, as the
Air andará Cydes and Their Ana 33
Thermal eficieney. 0)
Cote, $
Fiwe25 Tama Mato drones foraine.
load increases, the thermal efficiency drops. The maximum value of thermal efficiency will be
‘beained at no Toad, i. at idle running condition ofthe engine. A this condition, the entre work
that the engine performs goes to overcome frition in mating parts and to drive the auxiliary
mechanisms, However, his conclusion wil be further examined in ih light of actual engines with,
parameters other than dhose mentioned at this stage to avoid misleading results.
"Work done during a cele,
We Q-Q
= me = Ta) = male To 225)
Substiuting the values of Ta, Ty and Ta from Eqs. (2.21), (222) and (223), respectively, in
Eq (29,
Wa me (BTP 2 Ty AY) me (TO Ti)
= meal em
Senn voue, mener!)
em
ii w
Mean effective pressure, py JE
moje
For isentropic process 1-2,
Wer
nn
Tyo Tak Brenn (2.22)
oes
ul
me a
Substituting the values of 7, Ts and Ta from Eqs. (221), (222) and (2.23) respectively in
a. (2.18), the thermal efficiency or air-standard efficiency ola Diesel cycle can be expressed as
as
Alea] #5
Equation (2:24) shows Unt the thermal efficiency of a Diesel cycle depends on the compression
rato r, the adiabatic exponent 7, andthe curo ratio A. By comparing Eqs. (2.24) and (2.6), itis
‘observed that the efficiency ofa Diese cele differs from the efficiency of an Otto cycle by the
term (BY 1 7(B~ 1), which i always greater than unity. Therefore, the ai-standard efficiency
‘ofthe Diesel cycle is less than that ofthe Out cycle for the same compression ratio, For the given
value of the cut-off ratio the efficiency ofthe Diesel cycle increases with increase in compres.
sion ratio . In actual practice, the normal range of compression ratio for diesel engines is from 16
1o 20, whereas for sparkignition engines, iti 6 to 10. Because of the higher compresion ratio
‘wedi diesel engines, the efficiency ofa diesel engine is more than that of a petol engine.
Figure 25 shows thatthe thermal cficieney of a Diesel cyle increases withthe increase in
‘compression ratio r, and adiabatic exponent y However an increase in te cut-off rato f teduces
is efficiency. An increase in he value of the cut-off ratio means tht the heat addition at constant
pressure is increased, which corresponds to an increase in load onthe engine. Therefore, as the
Air andará Cydes and Their Ana 33
Thermal eficieney. 0)
Cote, $
Fiwe25 Tama Mato drones foraine.
load increases, the thermal efficiency drops. The maximum value of thermal efficiency will be
‘beained at no Toad, i. at idle running condition ofthe engine. A this condition, the entre work
that the engine performs goes to overcome frition in mating parts and to drive the auxiliary
mechanisms, However, his conclusion wil be further examined in ih light of actual engines with,
parameters other than dhose mentioned at this stage to avoid misleading results.
"Work done during a cele,
We Q-Q
= me = Ta) = male To 225)
Substiuting the values of Ta, Ty and Ta from Eqs. (2.21), (222) and (223), respectively, in
Eq (29,
Wa me (BTP 2 Ty AY) me (TO Ti)
= meal em
Senn voue, mener!)
em
ii w
Mean effective pressure, py JE
moje
34_Fondamenatt of nern! Combustion Engines
MED BM 028)
2,
Ta
era:
= 22)
Equation (2.29) shows that the mean effective pressure of a Diesel cycle increases with the
increas in initial pressure, adiabatic exponent compression ratio r and thermal efficiency 7.
‘The cutoff ratio increases when a large amount of hea 6 received, which increases the mean
fective pressure and reduces the thera efficiency.
25 DUAL COMBUSTION CYCLE
Its a theoretical cycle for modern high speed diesel engines. The heat supplied is patty at con-
stant volume and party at constant pressure, This cycle is alo called the mixed cycle or limited
‚Pressure cycle. The compression and expansion processes are isentrople and heal is rejected at
constant volume. The p-V and 7-s diagrams are shown in Figures 2.6 (3) and 2.6 (b) respectively,
a
prin
Der
Tina
Dalton.
Here:
Process 1-2 is isentropic compression. There is no het transfer. Work is done onthe system,
Process 2-3 is reversible constant volume process. Part of the heat is supplied during this
process.
Process 3-4 is reversible constant pressure process. The remaining par ofthe heat is sup-
plied during this process.
A Sandaré Cydes and Thor Amis 35
Process 4-5 is isentropie expansion. There is no heat transfer. Work is done by the system.
Process 5-1 is reversible constant volume process, Heat is rejected during tis process
Heat supplied during the process 2-3 = me, (Ts Ta)
Heat supplied during the process 3-4 = me (Ta = 75)
“Total heat supplied, Dime (TT + re, 2.30)
Heat rejected during process 5-1, Qs = mc, (fs = 7) a
Taten a
me
mo
es
(1) Compression ratio, 0)
(0) Pressure rato, 03
Y
6) Caoft ratio, one @39
‘These ratios are always greater tan 1
For isenropie process 1-2,
030
es
1)
MED BM 028)
2,
Ta
era:
= 22)
Equation (2.29) shows that the mean effective pressure of a Diesel cycle increases with the
increas in initial pressure, adiabatic exponent compression ratio r and thermal efficiency 7.
‘The cutoff ratio increases when a large amount of hea 6 received, which increases the mean
fective pressure and reduces the thera efficiency.
25 DUAL COMBUSTION CYCLE
Its a theoretical cycle for modern high speed diesel engines. The heat supplied is patty at con-
stant volume and party at constant pressure, This cycle is alo called the mixed cycle or limited
‚Pressure cycle. The compression and expansion processes are isentrople and heal is rejected at
constant volume. The p-V and 7-s diagrams are shown in Figures 2.6 (3) and 2.6 (b) respectively,
a
prin
Der
Tina
Dalton.
Here:
Process 1-2 is isentropic compression. There is no het transfer. Work is done onthe system,
Process 2-3 is reversible constant volume process. Part of the heat is supplied during this
process.
Process 3-4 is reversible constant pressure process. The remaining par ofthe heat is sup-
plied during this process.
A Sandaré Cydes and Thor Amis 35
Process 4-5 is isentropie expansion. There is no heat transfer. Work is done by the system.
Process 5-1 is reversible constant volume process, Heat is rejected during tis process
Heat supplied during the process 2-3 = me, (Ts Ta)
Heat supplied during the process 3-4 = me (Ta = 75)
“Total heat supplied, Dime (TT + re, 2.30)
Heat rejected during process 5-1, Qs = mc, (fs = 7) a
Taten a
me
mo
es
(1) Compression ratio, 0)
(0) Pressure rato, 03
Y
6) Caoft ratio, one @39
‘These ratios are always greater tan 1
For isenropie process 1-2,
030
es
1)
36_ Fundumene of loser! Conbuston Engines
ASandard Cycles and Their Anais 37
For isentropic process 4-5,
Ea RCE
OS
as, 239)
Seti eva Pa Tad fm i (236), 3,239 a (29 ro
tively in Eg. (2.32), u
(BT, =)
Ta] e
Equation (40) shows se fees in ho compresion ai, nd tn higher values of he
adiabai exponen cause an increas in e comal ne}. With a Corsa amour of het
add, he values of nd depen on wht par ofthe hea de at corsa vo and wha
par at conan pressure. An increas inte vel of and Ue comespondng reduction ID
resul ina higher hema en. = leds to Ono cyte and llendo Diesel elo
‘Work done dings eel,
W=Q-Q
= me, (Ts ~ Ti) + mep Te ~ Ti) = me, (Ts = Ti)
= me llar =") + (Part! = art") - (aßr- 1)
RT :
(a 1) TB 1) = (a Vy] am
7
nf
Swept valine, === (11) = ME
a (u) am
Mosa ee presse, p = À
Pa = py Ga D + 707" B= 1) = raf" =D) (243)
ATEN
alone mp-n-
wea 7
a
DD
Pan fr]
rta 1) + ET - 1)
= Grey Me + GD) 22]
26 COMPARISON OF OTTO, DIESEL AND DUAL
COMBUSTION CYCLES.
“The significant parameters in eycle analysis are compression ratio, peak pressure, peak tempera-
ture, Rest ation, het rejection, and the net work. In order to compare the performance ofthese
cycles, some of the parameters are kept ed.
For the same compression ratio and heat addition
For the comparison of Otto, Diesel and Dual combustion cycles, these cycles are drawn on a
single p-V and T-s diagram, as shown in Figures 2.7() and 2.70) respectively In drawing these
disgrams, the compresion ratio and the heat input are kept the same forthe thee cycles. Here,
1-2-3-4-1 represents the Oto cycle.
122-394" represents the Dual combustion cycle.
1-2-31-4"=A represents the Diesel cycle,
isthe compression ratio fr al ho hres eyes.
n
5 see
»
Fue 2? p-VardF-sdoganehein te sare comprend conf os
‘The Ps diagram is drawn in such a way, 50 that the area $236 = area 52236 = area 52316".
‘These areas represent heat input which isthe same for the thee cycle. Area 5146, area S14'6'
and arca 51476" represent heat rejection in Oto cycle, Dual combustion cycle and Diesel cycle
respectively, As the area 5146 < area SIA'Ó < area 51476" and
ner. dates,
Theat supplied
‘therefore, 7 ofthe Otto cycle > 7 ofthe Dual combustion cycle > 7 of te Diesel cycle.
ASandard Cycles and Their Anais 37
For isentropic process 4-5,
Ea RCE
OS
as, 239)
Seti eva Pa Tad fm i (236), 3,239 a (29 ro
tively in Eg. (2.32), u
(BT, =)
Ta] e
Equation (40) shows se fees in ho compresion ai, nd tn higher values of he
adiabai exponen cause an increas in e comal ne}. With a Corsa amour of het
add, he values of nd depen on wht par ofthe hea de at corsa vo and wha
par at conan pressure. An increas inte vel of and Ue comespondng reduction ID
resul ina higher hema en. = leds to Ono cyte and llendo Diesel elo
‘Work done dings eel,
W=Q-Q
= me, (Ts ~ Ti) + mep Te ~ Ti) = me, (Ts = Ti)
= me llar =") + (Part! = art") - (aßr- 1)
RT :
(a 1) TB 1) = (a Vy] am
7
nf
Swept valine, === (11) = ME
a (u) am
Mosa ee presse, p = À
Pa = py Ga D + 707" B= 1) = raf" =D) (243)
ATEN
alone mp-n-
wea 7
a
DD
Pan fr]
rta 1) + ET - 1)
= Grey Me + GD) 22]
26 COMPARISON OF OTTO, DIESEL AND DUAL
COMBUSTION CYCLES.
“The significant parameters in eycle analysis are compression ratio, peak pressure, peak tempera-
ture, Rest ation, het rejection, and the net work. In order to compare the performance ofthese
cycles, some of the parameters are kept ed.
For the same compression ratio and heat addition
For the comparison of Otto, Diesel and Dual combustion cycles, these cycles are drawn on a
single p-V and T-s diagram, as shown in Figures 2.7() and 2.70) respectively In drawing these
disgrams, the compresion ratio and the heat input are kept the same forthe thee cycles. Here,
1-2-3-4-1 represents the Oto cycle.
122-394" represents the Dual combustion cycle.
1-2-31-4"=A represents the Diesel cycle,
isthe compression ratio fr al ho hres eyes.
n
5 see
»
Fue 2? p-VardF-sdoganehein te sare comprend conf os
‘The Ps diagram is drawn in such a way, 50 that the area $236 = area 52236 = area 52316".
‘These areas represent heat input which isthe same for the thee cycle. Area 5146, area S14'6'
and arca 51476" represent heat rejection in Oto cycle, Dual combustion cycle and Diesel cycle
respectively, As the area 5146 < area SIA'Ó < area 51476" and
ner. dates,
Theat supplied
‘therefore, 7 ofthe Otto cycle > 7 ofthe Dual combustion cycle > 7 of te Diesel cycle.
38_ Fundamento of neral Combustion Engines
AlrSadará Cycles nd Their Anns 39
For the same compression ratio and heat rejection
Figure 2.8 shows the p-V and Tos diagrams forthe three cycles having the same compresion
vaio and heat rejection.
r
wo
1-2-3741 represents the Diesel cycle
Y, don
Fr is he compression ratio for ll he thre cycles.
Heat rejection is shown by the process 4-1 forall the tee cycles, It is the area under the
curve 4-1 on
(On the T-s diagram, heat supplied in Otto cycle is represented by the area 2365; in the Dual
combustion cycle it is Ue area 22965 and in the Diesel eye, it isthe area 23°65. Its seen that
ren 2365 > area 229/65 > area 23765
Bron ot > Liar ce > Pince
mi
For the same value of heat rejection Qs,
Moore > Mer PT Dime
‘The above relation is applicable for the same compression ratio and heat rejection,
For the same peak pressure, peak temperature and heat rejection
Figure 2.9 eepresents the p-V and Tes diagrams for he three cycles having the same peak pres-
sure, peak temperature, and heat rejection,
Pen
Wa me E g
Fguezo paré -sdoyamahsiogto san pa pss peak pecado taras.
Here
1-2-3-4-1 represents the Quo cycle.
1-2-3-3-4-1 represents the Dual combustion cycle.
|-2°-3-4-1 represents the Diesel cycle.
In all the (ee cycles, the maximum pressure yg if he same. The peak temperature isthe
temperature at point 3, he. ais also the same forthe three cycles. Heat rejection is during tbe
process 4=1-—this i also the same for he tree cycles
“The compression ratio will now be different fos the the cycles, suchas
Y”
r= HL for ono cycle
Fr One ea
Dat comio e
Phase ? Fate > Fou de
Heat supplied as follows:
Opinas = 216427265 onthe Tos diagrama
AlrSadará Cycles nd Their Anns 39
For the same compression ratio and heat rejection
Figure 2.8 shows the p-V and Tos diagrams forthe three cycles having the same compresion
vaio and heat rejection.
r
wo
1-2-3741 represents the Diesel cycle
Y, don
Fr is he compression ratio for ll he thre cycles.
Heat rejection is shown by the process 4-1 forall the tee cycles, It is the area under the
curve 4-1 on
(On the T-s diagram, heat supplied in Otto cycle is represented by the area 2365; in the Dual
combustion cycle it is Ue area 22965 and in the Diesel eye, it isthe area 23°65. Its seen that
ren 2365 > area 229/65 > area 23765
Bron ot > Liar ce > Pince
mi
For the same value of heat rejection Qs,
Moore > Mer PT Dime
‘The above relation is applicable for the same compression ratio and heat rejection,
For the same peak pressure, peak temperature and heat rejection
Figure 2.9 eepresents the p-V and Tes diagrams for he three cycles having the same peak pres-
sure, peak temperature, and heat rejection,
Pen
Wa me E g
Fguezo paré -sdoyamahsiogto san pa pss peak pecado taras.
Here
1-2-3-4-1 represents the Quo cycle.
1-2-3-3-4-1 represents the Dual combustion cycle.
|-2°-3-4-1 represents the Diesel cycle.
In all the (ee cycles, the maximum pressure yg if he same. The peak temperature isthe
temperature at point 3, he. ais also the same forthe three cycles. Heat rejection is during tbe
process 4=1-—this i also the same for he tree cycles
“The compression ratio will now be different fos the the cycles, suchas
Y”
r= HL for ono cycle
Fr One ea
Dat comio e
Phase ? Fate > Fou de
Heat supplied as follows:
Opinas = 216427265 onthe Tos diagrama
ee we eins UY WA
40 _Feadamerate of neral Combustion Engines
AirSanird Coles and Their Aal 41
Osos = area 73368 on the Ts diagram,
Dion qe = area 2365 on the T-s diagram,
Now, area 27365 > area 23,365 > area 2365
inate > Prom qu? Clove
For agiven vale of 23
ose je > My? Mono
“This comparison is moe realistic. In an actual compression igniion engine, ie. diesel engine,
a higher compression ro is used in comparison with Le compression ratio used in he spark
ignition i. petrol engine. Keeping the same peak temperature and peak pressure, both he engines
can withstand the same thermal and mechanical sess,
For the same maximum pressure and heat input
Figure 2.10 represents the p-V and T-s diagrams forthe three cycles having the same maximum
Pressure and heat input.
Pour} ERA r
à
n
> «
5 wee
Fgure210_ p-Verd stor tang te sane aupa lotes os.
Here:
153-344 represents the Ono cycle
1-2-3-31-47-1 represents he Dual combustion cycle
12-947 represent the Diesel ele
‘The maximum pressure Pa the same foral the thre cls. Aste heat input i alo the
same forthe thee cycles, therefore, onthe Ps digg,
ATICO q) 23782736 sy)
a8 2365(Qhons ie)
Heat ejected forthe Ono cycle isthe area 1465, heat rejected forthe Dual combustion cycle the
area 14/65, andthe heat ejected forthe Diesel cycle i the area 146",
area 1465 > rea 1665 > ares 14705
Proves e? Pou ye? Lope
For the same value of Qu.
is? Mere” Tone eya
For the same maximum pressure and work output
Bee,
work dove
Work done + heat rejected
From the Tos diagram of Figure 210, i is clear that if the work done forthe three cycles isthe
same then
area 12341 (work done in Oto cycle) = area 123 Y4'L(work done in Dual combustion eyets)
= area 12°3"4" (work done in Diesel cycle)
These areas will be equal, only when the heat rejected
Digne? Pro ? Pinto
w
vo
For he same work output W,
Musa? Mou xa? Move ce
2.7 ATKINSON CYCLE
Atkinson eycle is shown on p-V and T-s diagrams in Figure 2.11. This isan ideal cycle for
Ono engine exhausting toa gas turbine. If re cylinder contents coulé be expanded o the inal
pressure py, more work will be obtained and the efficiency will be increased. The incompleto
‘expansion in Otto cycle (process 3-4) is further allowed to proceed o the lowest cycle pressure.
‘A large increase in volume is required o reduce
Process 2-3 is reversible constant volume process. Heat is supplied during this process.
Process 3-4 is reversible adiabatic expansion, There is no heat transfer
Process 4-1 is reversible constant pressure process. Heat is rejected during this process.
40 _Feadamerate of neral Combustion Engines
AirSanird Coles and Their Aal 41
Osos = area 73368 on the Ts diagram,
Dion qe = area 2365 on the T-s diagram,
Now, area 27365 > area 23,365 > area 2365
inate > Prom qu? Clove
For agiven vale of 23
ose je > My? Mono
“This comparison is moe realistic. In an actual compression igniion engine, ie. diesel engine,
a higher compression ro is used in comparison with Le compression ratio used in he spark
ignition i. petrol engine. Keeping the same peak temperature and peak pressure, both he engines
can withstand the same thermal and mechanical sess,
For the same maximum pressure and heat input
Figure 2.10 represents the p-V and T-s diagrams forthe three cycles having the same maximum
Pressure and heat input.
Pour} ERA r
à
n
> «
5 wee
Fgure210_ p-Verd stor tang te sane aupa lotes os.
Here:
153-344 represents the Ono cycle
1-2-3-31-47-1 represents he Dual combustion cycle
12-947 represent the Diesel ele
‘The maximum pressure Pa the same foral the thre cls. Aste heat input i alo the
same forthe thee cycles, therefore, onthe Ps digg,
ATICO q) 23782736 sy)
a8 2365(Qhons ie)
Heat ejected forthe Ono cycle isthe area 1465, heat rejected forthe Dual combustion cycle the
area 14/65, andthe heat ejected forthe Diesel cycle i the area 146",
area 1465 > rea 1665 > ares 14705
Proves e? Pou ye? Lope
For the same value of Qu.
is? Mere” Tone eya
For the same maximum pressure and work output
Bee,
work dove
Work done + heat rejected
From the Tos diagram of Figure 210, i is clear that if the work done forthe three cycles isthe
same then
area 12341 (work done in Oto cycle) = area 123 Y4'L(work done in Dual combustion eyets)
= area 12°3"4" (work done in Diesel cycle)
These areas will be equal, only when the heat rejected
Digne? Pro ? Pinto
w
vo
For he same work output W,
Musa? Mou xa? Move ce
2.7 ATKINSON CYCLE
Atkinson eycle is shown on p-V and T-s diagrams in Figure 2.11. This isan ideal cycle for
Ono engine exhausting toa gas turbine. If re cylinder contents coulé be expanded o the inal
pressure py, more work will be obtained and the efficiency will be increased. The incompleto
‘expansion in Otto cycle (process 3-4) is further allowed to proceed o the lowest cycle pressure.
‘A large increase in volume is required o reduce
Process 2-3 is reversible constant volume process. Heat is supplied during this process.
Process 3-4 is reversible adiabatic expansion, There is no heat transfer
Process 4-1 is reversible constant pressure process. Heat is rejected during this process.
42 Fundumentas of Inaral Combuton Engines
ArSundard Gyles and Their Anas 43
8 rn
Fawezn Aiaen
Compression ratio,
Expansion ato,
Pressure ratio,
Air standard thermal efiioney,
„1.
un
Heat supplied, Q) = me, (TT)
Heat rejected, Q = ne Ta Ti)
ay hd
ah
For isentropic process 1-2,
as)
249
am
am
a
(250)
es”
For constant volume process 2-3,
ph
hot
Dalineansannte (Jen
es)
For isenropje process 3-4,
es)
Substituting the values of Ty, Ts and Ta from Eqs. (2.51), 2.52) and (2.53) respectively in
Eg. (250),
14% as)
Work done, W=0/-02
= miley (Ta ~ 7) ~ ep (Te 70
ess
‘Swept volume, 256)
u a —
ArSundard Gyles and Their Anas 43
8 rn
Fawezn Aiaen
Compression ratio,
Expansion ato,
Pressure ratio,
Air standard thermal efiioney,
„1.
un
Heat supplied, Q) = me, (TT)
Heat rejected, Q = ne Ta Ti)
ay hd
ah
For isentropic process 1-2,
as)
249
am
am
a
(250)
es”
For constant volume process 2-3,
ph
hot
Dalineansannte (Jen
es)
For isenropje process 3-4,
es)
Substituting the values of Ty, Ts and Ta from Eqs. (2.51), 2.52) and (2.53) respectively in
Eg. (250),
14% as)
Work done, W=0/-02
= miley (Ta ~ 7) ~ ep (Te 70
ess
‘Swept volume, 256)
u a —
44. Furdımenalt of nea Comburion Engnes
AirSandard Cycles and Tir Ansys 45
a
Y
Mean effective pressure, py
NAT]
TO O
esn
e
GE
= ane =)
VDD
ass
A gas engine working on the Otto eyele has cylinder bore of 200 mm and
Stroke length of 250 mm, The clearance volume i 1570 em, The pressure and temperature at the
beginning of compression are 1 bar and 27°C respectively, The maximum temperature of the
‘ele is 1400°C. Determine the presture and temperature at the salient points the airtandacd
«efficiency, the work done and the meta effective
pressure. (For ai, take c,=0.71813/(kg K)andR= p
0.287 Kg K). Also calculate the ideal power
developed by the engine, ifthe number of working
cycles per minute is 500.
Solution: Refer 10 Figure 2.12.
Given date:
Cylinder bore, a= dem
Stroke, L=25em
Clearance volume, = 1570 em?
Pis bar
m+2M=
Maximum temperature, Ty = 1400 4 27
v-TeL
(207 25 = 7854 om?
M = Y + We = 7854 + 1570 = 9424 em?
We 1570 cm?
Laer}
% "1570
Sepi volume,
4
Compression ato, 7
For isentropic process 1-2
Ta = Ty! = 300 = 6143 K
= [2150] ans.
satis
wy. 2,
m (E > memrsix
For constant volume process 2-3,
CRETE
An
nos
ñ 1673
od 2 2 [Bede var] ans.
Pompa © 12.286 x 2075 = [Faber] A
Air-standad efficiency of Ouo cycle,
O
None
[ara ver] Ane
05
ES
Heatsuppied, Qi = 64757) for nit mass
0.718(1673 — 6143) = 76015 srg
Heat rjected, a = e Ty =T;) for unit mass
= 0.738(817 - 300) =3712
Work done per unit mass,
Qi- Qs = 760.15 371.2
mal.
ES
Work done = 389 x 0.0108:
‘This is the work done for one Oto cycle.
work done
Mean elective pressure. Ae So o
1x10° 9424 x10
sig
song
= 0.01085 kg
Ans.
AirSandard Cycles and Tir Ansys 45
a
Y
Mean effective pressure, py
NAT]
TO O
esn
e
GE
= ane =)
VDD
ass
A gas engine working on the Otto eyele has cylinder bore of 200 mm and
Stroke length of 250 mm, The clearance volume i 1570 em, The pressure and temperature at the
beginning of compression are 1 bar and 27°C respectively, The maximum temperature of the
‘ele is 1400°C. Determine the presture and temperature at the salient points the airtandacd
«efficiency, the work done and the meta effective
pressure. (For ai, take c,=0.71813/(kg K)andR= p
0.287 Kg K). Also calculate the ideal power
developed by the engine, ifthe number of working
cycles per minute is 500.
Solution: Refer 10 Figure 2.12.
Given date:
Cylinder bore, a= dem
Stroke, L=25em
Clearance volume, = 1570 em?
Pis bar
m+2M=
Maximum temperature, Ty = 1400 4 27
v-TeL
(207 25 = 7854 om?
M = Y + We = 7854 + 1570 = 9424 em?
We 1570 cm?
Laer}
% "1570
Sepi volume,
4
Compression ato, 7
For isentropic process 1-2
Ta = Ty! = 300 = 6143 K
= [2150] ans.
satis
wy. 2,
m (E > memrsix
For constant volume process 2-3,
CRETE
An
nos
ñ 1673
od 2 2 [Bede var] ans.
Pompa © 12.286 x 2075 = [Faber] A
Air-standad efficiency of Ouo cycle,
O
None
[ara ver] Ane
05
ES
Heatsuppied, Qi = 64757) for nit mass
0.718(1673 — 6143) = 76015 srg
Heat rjected, a = e Ty =T;) for unit mass
= 0.738(817 - 300) =3712
Work done per unit mass,
Qi- Qs = 760.15 371.2
mal.
ES
Work done = 389 x 0.0108:
‘This is the work done for one Oto cycle.
work done
Mean elective pressure. Ae So o
1x10° 9424 x10
sig
song
= 0.01085 kg
Ans.
46_ Fundamental of Iaral Combien Engines
[NeStandud Cycles and Thai Aras 47
= 426x10?°
AN, à 8x 10 Nm = [EIER] Ame
7854x 10% id E
ower developed wok on per yen, of els er cond
24260
426 x 52» [SETA] a.
A perl engine is supplied wi fe having caorii value 42,000 kg, The
pressure in the eyinder at 3% and 75% of the compresion stoke are 1.2 bar and 4.8 bar
respectively, Assume thal Ue compression follows the aw pV = constant. Find the compression
Talo of the engine. Ifthe relative efficiency ofthe engine compared with the a standard
ecency is 60% calelate We spec fue consumption in kg
Solution: In Figure 2.13, the process 1-2 represents compression, following the law pv =
sont ora given pt engine. The paint a andthe poim respectively represent he 8% and
175% of the compression stoke. The ofr processes re completed on hcoaical basis.
From Figure 2.13: os
v,-005v,
= ue V.-005%,
Y + 095%,
We 035%,
Ye v,-0784
Y 40254
CAES
«2905
car, Fous,
Faure213 Eanç22.
or —— «2.905
‘Compression ratio,
sis
sis
1+095(r—1)
= 170280
ns ogi nina 1
or 0957 + 005 = 2.905(0257 + 0.75)
= [55] ans.
‘Theoretical cycle for the pero engine isthe Otto cele.
+ Alrstandar efficiency
ir sandare efficiency
«Indicated thermal efficiency, o, = 0.6 x 05936 = 0356
Now,
ver th nated power iin Y, CV (sore val) ofthe felis
Specific fuel consumption (indicated) smi.
1 1
Ten, * 10x08
.688 x 10% x 3600 ke/kWh
0241 kan -
Indicted pei ul consumption iste = (EAN Ans.
Show tht he compression iio foc he maximum wok in an Ono eye s
Send
Ag and ft isin Kg
688 x 10° kgs
um na
a
ñ
where amd Tete lower and pp isa ab
tie empacar especie.
‘Als, prove tthe Inrmediatetempestares for
this condone
ets TE
Solution: Refer 10 Figure 2.14
Heateuplied, Q,=me fs)
Heated, Qs =me(te—1) aurait ane
Work done = Qi - O2
ines TOT Pr
[NeStandud Cycles and Thai Aras 47
= 426x10?°
AN, à 8x 10 Nm = [EIER] Ame
7854x 10% id E
ower developed wok on per yen, of els er cond
24260
426 x 52» [SETA] a.
A perl engine is supplied wi fe having caorii value 42,000 kg, The
pressure in the eyinder at 3% and 75% of the compresion stoke are 1.2 bar and 4.8 bar
respectively, Assume thal Ue compression follows the aw pV = constant. Find the compression
Talo of the engine. Ifthe relative efficiency ofthe engine compared with the a standard
ecency is 60% calelate We spec fue consumption in kg
Solution: In Figure 2.13, the process 1-2 represents compression, following the law pv =
sont ora given pt engine. The paint a andthe poim respectively represent he 8% and
175% of the compression stoke. The ofr processes re completed on hcoaical basis.
From Figure 2.13: os
v,-005v,
= ue V.-005%,
Y + 095%,
We 035%,
Ye v,-0784
Y 40254
CAES
«2905
car, Fous,
Faure213 Eanç22.
or —— «2.905
‘Compression ratio,
sis
sis
1+095(r—1)
= 170280
ns ogi nina 1
or 0957 + 005 = 2.905(0257 + 0.75)
= [55] ans.
‘Theoretical cycle for the pero engine isthe Otto cele.
+ Alrstandar efficiency
ir sandare efficiency
«Indicated thermal efficiency, o, = 0.6 x 05936 = 0356
Now,
ver th nated power iin Y, CV (sore val) ofthe felis
Specific fuel consumption (indicated) smi.
1 1
Ten, * 10x08
.688 x 10% x 3600 ke/kWh
0241 kan -
Indicted pei ul consumption iste = (EAN Ans.
Show tht he compression iio foc he maximum wok in an Ono eye s
Send
Ag and ft isin Kg
688 x 10° kgs
um na
a
ñ
where amd Tete lower and pp isa ab
tie empacar especie.
‘Als, prove tthe Inrmediatetempestares for
this condone
ets TE
Solution: Refer 10 Figure 2.14
Heateuplied, Q,=me fs)
Heated, Qs =me(te—1) aurait ane
Work done = Qi - O2
ines TOT Pr
48 Fundumanss of Internal Conbasion Engines Air Standard Cycles and Their Anais 49
al Solution: Given: 4 = 02m Le 03 py 1 ba, Ti = 274273 © 300K,
? TH Y = = 00, r= 16
From the adiabatic process 1-2, art Figure 215
Tet ai)
and rom he aabt process 3-4
het
Ts Tyr Gi)
Work done, We me, (Ty - Toren)
Ti and 7; ace fixed, therefore, for maximum work,
1
moy dr
e Hoyts Tar? Er
Bar Faue215 Eurpe24
i (6) Pressure, volume and temperature at salient points:
<TH WT pete 0 i
r
re (3) Pr ‘Swept volume, Y = FAL = 302703) = 0.00982 n°
From Eq. (D, 1 ‘Compression ratio, +1
Font,
ie
nen oe
Ys = 1,0 Y = 00002 000026 = [JOE] am
nan si standard Diesel eye, the compression ratio is 16, the cylinder bore is fi oa
200 mm and the stroke is 300 mm, Compression begins at | bar and 27°C. The cut-off takes place mo Ped. DEDO X0010048 901167 kg
at 8 per cent of he tro. 3 EE
one - a
(a) The pesar, the volume and engere al an pin ES CTN
© Te ct rs ”
(c) The work done per cycle aes: A
(d) The air-standard efficiency q Ty = (16) x 300: Ans.
E Tw au ae es .
0) wat, pot,
al Solution: Given: 4 = 02m Le 03 py 1 ba, Ti = 274273 © 300K,
? TH Y = = 00, r= 16
From the adiabatic process 1-2, art Figure 215
Tet ai)
and rom he aabt process 3-4
het
Ts Tyr Gi)
Work done, We me, (Ty - Toren)
Ti and 7; ace fixed, therefore, for maximum work,
1
moy dr
e Hoyts Tar? Er
Bar Faue215 Eurpe24
i (6) Pressure, volume and temperature at salient points:
<TH WT pete 0 i
r
re (3) Pr ‘Swept volume, Y = FAL = 302703) = 0.00982 n°
From Eq. (D, 1 ‘Compression ratio, +1
Font,
ie
nen oe
Ys = 1,0 Y = 00002 000026 = [JOE] am
nan si standard Diesel eye, the compression ratio is 16, the cylinder bore is fi oa
200 mm and the stroke is 300 mm, Compression begins at | bar and 27°C. The cut-off takes place mo Ped. DEDO X0010048 901167 kg
at 8 per cent of he tro. 3 EE
one - a
(a) The pesar, the volume and engere al an pin ES CTN
© Te ct rs ”
(c) The work done per cycle aes: A
(d) The air-standard efficiency q Ty = (16) x 300: Ans.
E Tw au ae es .
0) wat, pot,
[50 _Fundamanat of heal Conburten Engines
AirSandard Cycles nd Their And SI
Give M = vy 2008,
or 2
%
Now,
ler
Va = Vi [ODIOS] Ans.
(6) Weatsupplied, 01 = nes To
= 001167 x 1.005200! - 9094) = 12.813
Heat rejected, Op = mesa TD
= 0.01167 x 0:718(904.8 - 300) = 5.068 KI
Work done per cycle, W= Q; ~ Q2= 128-5068 = [F734] Ans.
& _ Ainstandardoficieney = Y = 2232
(©) Mean effective pressure, Pa
121 x 10° Nin?
Be] Ans.
‘The mean effective pressure ofa Diesel ycle is 7 bar the compression rai is
12 andthe inal pressure is 1 ba. Determine the cu-of ratio and he sitstandard efficiency.
Solution: The mean effective pressure is given by
A tye
Pee RER BD
Given: Do = 7 bar,
12, pelbar
Te Da
or 308 = 4548-454 ~ 129! + 12
or 45.49 - 1294 ~ 642=0
Solving by wial-and-error method, the cut-off ratio
B= [ZZ] Ans.
Airstandard efficiency,
SENDA ln on engine working on the Diese cle the air-fuel ratios 30:1. The temper
ture of air atthe beginning ofthe compresion is 27°C, the compression ratio is 16:1. What isthe
ideal efficiency ofthe engine based on the szstandard cycle? The caloii value ofthe fuel used
is 42,000 KR,
Solution: Refer to Figure 2.16. » A
à mass of air _ Mar
pen ass Ott. Mae = 39
e ina off me
T=27+213=300K
jé 4
CV = 42,000 ns i
From the process 1-2,
Ta= Ty?! = 300 16" = y
094K gue 216 Gane 26,
For constant pressure process 2-3,
Heat supplied mu KT; To) = Ma CV
CRC
Tone 393
e. 1393 + 909.4 2302 K
2m
Curof rio, “home
-l
AirSandard Cycles nd Their And SI
Give M = vy 2008,
or 2
%
Now,
ler
Va = Vi [ODIOS] Ans.
(6) Weatsupplied, 01 = nes To
= 001167 x 1.005200! - 9094) = 12.813
Heat rejected, Op = mesa TD
= 0.01167 x 0:718(904.8 - 300) = 5.068 KI
Work done per cycle, W= Q; ~ Q2= 128-5068 = [F734] Ans.
& _ Ainstandardoficieney = Y = 2232
(©) Mean effective pressure, Pa
121 x 10° Nin?
Be] Ans.
‘The mean effective pressure ofa Diesel ycle is 7 bar the compression rai is
12 andthe inal pressure is 1 ba. Determine the cu-of ratio and he sitstandard efficiency.
Solution: The mean effective pressure is given by
A tye
Pee RER BD
Given: Do = 7 bar,
12, pelbar
Te Da
or 308 = 4548-454 ~ 129! + 12
or 45.49 - 1294 ~ 642=0
Solving by wial-and-error method, the cut-off ratio
B= [ZZ] Ans.
Airstandard efficiency,
SENDA ln on engine working on the Diese cle the air-fuel ratios 30:1. The temper
ture of air atthe beginning ofthe compresion is 27°C, the compression ratio is 16:1. What isthe
ideal efficiency ofthe engine based on the szstandard cycle? The caloii value ofthe fuel used
is 42,000 KR,
Solution: Refer to Figure 2.16. » A
à mass of air _ Mar
pen ass Ott. Mae = 39
e ina off me
T=27+213=300K
jé 4
CV = 42,000 ns i
From the process 1-2,
Ta= Ty?! = 300 16" = y
094K gue 216 Gane 26,
For constant pressure process 2-3,
Heat supplied mu KT; To) = Ma CV
CRC
Tone 393
e. 1393 + 909.4 2302 K
2m
Curof rio, “home
-l
— "7
>
Ale Sandard Cele and Their Ani 53
aL. BE.
DETTE)
1
16? 140.
= 0586
HE] Ans.
In an engine working on Diesel cycle, the inet pressure is I bat The pressure
a the end of isentopic compression is 32425 bar. The ratio of expansion is 6. Caleulat the ai
Standard elficiency andthe mean effective pressure ofthe cycle.
Solution: Refer to Figure 2.16.
Consider the process 1-2,
Compression rai,
Expansion ato,
Cutoff rato,
Alestandard efficiency, a
ee ale
in ab
= 0.5667 = [S657] Au
Mean effective pressure,
= ue
DIS
Aa 05667 140-0)
E)
= [SEAS] Ans.
asic standard Dl yee has acompresin ri of 15 ante comprsion
A The maxim peur mid 10 bar Te ban rasero ir at
at volumes eis ta constr peste Catal) he pressor a temperate at
5
pren
be cardinal points ofthe eye, (9) he cycle efficiency, and (e) the
eycke.
Solution: Refer to Figure 2.7.
effective pressure ofthe
Given: Compression raio,r = 15
pis bar
Ti 2274278 = 300 K
= pa = 60 bar
Qa=2X Oss
(6) Considering the process 1-2,
CN Par rs
Tan Ty?! = 300 x (159% = [HEC] ans.
Also, DAV = pv
a =o( it) = py"
Consideing the process 2-3,
x (15)! = [TS bar] Ans.
ES
a5
new
a
386 x = [TOR] Ans.
5 =2%Qs4 (Given)
GT -T) = 2g Ty
or O:718(1200 ~ 886) = 2 x LOS, - 1200)
nan
Pr
Te
Considering the process 3-4,
Curoft rato,
>
Ale Sandard Cele and Their Ani 53
aL. BE.
DETTE)
1
16? 140.
= 0586
HE] Ans.
In an engine working on Diesel cycle, the inet pressure is I bat The pressure
a the end of isentopic compression is 32425 bar. The ratio of expansion is 6. Caleulat the ai
Standard elficiency andthe mean effective pressure ofthe cycle.
Solution: Refer to Figure 2.16.
Consider the process 1-2,
Compression rai,
Expansion ato,
Cutoff rato,
Alestandard efficiency, a
ee ale
in ab
= 0.5667 = [S657] Au
Mean effective pressure,
= ue
DIS
Aa 05667 140-0)
E)
= [SEAS] Ans.
asic standard Dl yee has acompresin ri of 15 ante comprsion
A The maxim peur mid 10 bar Te ban rasero ir at
at volumes eis ta constr peste Catal) he pressor a temperate at
5
pren
be cardinal points ofthe eye, (9) he cycle efficiency, and (e) the
eycke.
Solution: Refer to Figure 2.7.
effective pressure ofthe
Given: Compression raio,r = 15
pis bar
Ti 2274278 = 300 K
= pa = 60 bar
Qa=2X Oss
(6) Considering the process 1-2,
CN Par rs
Tan Ty?! = 300 x (159% = [HEC] ans.
Also, DAV = pv
a =o( it) = py"
Consideing the process 2-3,
x (15)! = [TS bar] Ans.
ES
a5
new
a
386 x = [TOR] Ans.
5 =2%Qs4 (Given)
GT -T) = 2g Ty
or O:718(1200 ~ 886) = 2 x LOS, - 1200)
nan
Pr
Te
Considering the process 3-4,
Curoft rato,
54 Fundamentals of Ina! Comburden Engines
AirSandard Cycles and Their Anais 55
$0 (TS) Ans.
Considering the process 4-5,
BUY
TW)
Tea
Considering te process 5-1 (Vs
2.»
BT
5
xk
eo
(0) Heat supplied per unit mas,
ATI + GT)
94 = 0.718.200 - 886) + 1.005(1312 - 1200)
338 AS
Heat rejected per unit mass,
Q=0 ATT)
Qs = 0.718(460 — 300) = 115 kag
Work done, W=01-0;
338-115 = 223 ke
Airstandard efficiency,
HB. ogg
338
(e) Swept volume,
For unit mass,
Mean effective pressure,
77x 10 Nit
[SEMIN] A Dual combustion cycle operates with a compression ratio of 12 and with a
cutoff ratio Of 1.615. The maximum pressure is $2.17 bar, The pressure and temperature before
compression ae 1 bar and 62°C respectively. Assuming indices of compression and expansion of
1.35, ealeulae (a) the temperatures at cardinal points, () the cycle efficiency. and (0) the mean
effective pressure ofthe cycle.
Solution: Refer to Figure 2.8.
Given: Compression ratio,r = 12
Cutoff rato, fx tos
Maximum pressure, Ps 2 py = 52.17 bar
by = bar
T= 242732335 K
Indices of compression and expansion.
ne 35
Fgue239 Example.
DER an
Sn nan te
Ta= TP 335 x (129995
Pave = PAV
‘
MA
sol) em
Considering the process 2-3,
x (125 = [SE
a 7x 22 2 709 x 27
ARRET
Considering the process 3-4,
A
Considero te roces 45,
A A
Tw) A,
21x (189)
1
(0) Processes 1-2 and 4-5 are polytropic, therefore, here will be het transfer during these
processes as wel
"Heat transfer during the process 1-2,
Ans.
AirSandard Cycles and Their Anais 55
$0 (TS) Ans.
Considering the process 4-5,
BUY
TW)
Tea
Considering te process 5-1 (Vs
2.»
BT
5
xk
eo
(0) Heat supplied per unit mas,
ATI + GT)
94 = 0.718.200 - 886) + 1.005(1312 - 1200)
338 AS
Heat rejected per unit mass,
Q=0 ATT)
Qs = 0.718(460 — 300) = 115 kag
Work done, W=01-0;
338-115 = 223 ke
Airstandard efficiency,
HB. ogg
338
(e) Swept volume,
For unit mass,
Mean effective pressure,
77x 10 Nit
[SEMIN] A Dual combustion cycle operates with a compression ratio of 12 and with a
cutoff ratio Of 1.615. The maximum pressure is $2.17 bar, The pressure and temperature before
compression ae 1 bar and 62°C respectively. Assuming indices of compression and expansion of
1.35, ealeulae (a) the temperatures at cardinal points, () the cycle efficiency. and (0) the mean
effective pressure ofthe cycle.
Solution: Refer to Figure 2.8.
Given: Compression ratio,r = 12
Cutoff rato, fx tos
Maximum pressure, Ps 2 py = 52.17 bar
by = bar
T= 242732335 K
Indices of compression and expansion.
ne 35
Fgue239 Example.
DER an
Sn nan te
Ta= TP 335 x (129995
Pave = PAV
‘
MA
sol) em
Considering the process 2-3,
x (125 = [SE
a 7x 22 2 709 x 27
ARRET
Considering the process 3-4,
A
Considero te roces 45,
A A
Tw) A,
21x (189)
1
(0) Processes 1-2 and 4-5 are polytropic, therefore, here will be het transfer during these
processes as wel
"Heat transfer during the process 1-2,
Ans.
56. Fondamenals of Inemal Combustion Engos
‚AirSandard Gels and Ther Anais 57
For unit mass,
Heat transfer during the process 2-3,
Qs = CAT, ~ TD = 0.718(1456 — 799)
= 4117 ONE,
eat transfer during the process 3-4,
Que = 6
= 899.5 King
Heat transfer during the process 45,
Ju
KE \
= 1216108
‘eat taster during the process 5-1,
Drs = cdf 79 = 0.718635 - 1165)
ET
135
“The positive sign of heat ranfer represents the heat supplied and the negative sign represents the
eat ejected
Heusupplied, 01 = Ora + Qu + Des
= 471.7 + 8995 + 1216
14928 Ag
Orar Osa
4736 + 596
643.56 Ki
Work done W=Q-0
. = 1492.8 - 64356 = $492 King
w
and heatrejected, Dr
Bieieney,
(2351-1165)
E 22 = 0569 = [3658]
=) = 100502351 - 1456)
)
Ans.
(6) Swept volume,
287335,
For unit mass, De
rica)
= 0.8813 mig
ean cio pene, pus À
849210
08813
A perfect gas undergoes an Atkinson cycle. The gas is compressed adiabati-
‘ally from I bar, 27°C to 4 bar. The maximum pressure of he cycle is 16 bar Calculate (a) the
‘work done per kg of gas, () the eiciency ofthe cycle, and (c) the mean effective pressure ofthe
sy.
Take ¢ = 0.761 ke K) and ¢, = 0.573 KG K)
Solution: Refer to Figure 2.19.
Given
= 9.635 10° Nin
pr = constant
ee, = 07610573 = 1.328
For adiabatic compression process 1-2,
4
Fue 219 Asian eye: Bape 210
For constant volume process 2-3,
Ben
a5
1, = 2 x t= 18 x 4225 = 1690 K
Pr 4
‚AirSandard Gels and Ther Anais 57
For unit mass,
Heat transfer during the process 2-3,
Qs = CAT, ~ TD = 0.718(1456 — 799)
= 4117 ONE,
eat transfer during the process 3-4,
Que = 6
= 899.5 King
Heat transfer during the process 45,
Ju
KE \
= 1216108
‘eat taster during the process 5-1,
Drs = cdf 79 = 0.718635 - 1165)
ET
135
“The positive sign of heat ranfer represents the heat supplied and the negative sign represents the
eat ejected
Heusupplied, 01 = Ora + Qu + Des
= 471.7 + 8995 + 1216
14928 Ag
Orar Osa
4736 + 596
643.56 Ki
Work done W=Q-0
. = 1492.8 - 64356 = $492 King
w
and heatrejected, Dr
Bieieney,
(2351-1165)
E 22 = 0569 = [3658]
=) = 100502351 - 1456)
)
Ans.
(6) Swept volume,
287335,
For unit mass, De
rica)
= 0.8813 mig
ean cio pene, pus À
849210
08813
A perfect gas undergoes an Atkinson cycle. The gas is compressed adiabati-
‘ally from I bar, 27°C to 4 bar. The maximum pressure of he cycle is 16 bar Calculate (a) the
‘work done per kg of gas, () the eiciency ofthe cycle, and (c) the mean effective pressure ofthe
sy.
Take ¢ = 0.761 ke K) and ¢, = 0.573 KG K)
Solution: Refer to Figure 2.19.
Given
= 9.635 10° Nin
pr = constant
ee, = 07610573 = 1.328
For adiabatic compression process 1-2,
4
Fue 219 Asian eye: Bape 210
For constant volume process 2-3,
Ben
a5
1, = 2 x t= 18 x 4225 = 1690 K
Pr 4
5B _Fundamanats of neral Comburtion Engres
AlrStadard Cycles and Ther Araya 59
For adiabatic expansion process 3-4,
“wy
(2) acosa
(6) Work done per kg W.
Heat supplied perkg, Qi # 64% 75)
0.571690 - 4225)
7263 Woks
A)
= 0.761(852 - 300)
= 4201088
W= 7263-4201
Heat ejected per kg, Os
(0) Efficiency ofthe eye
Y
a
(6) Mean effective pressure,
2062
76
Swept volume,
For adiabatic proces 1
DWE = PVE
“
ur
de m uo
Impression ratio, 7 =
Compre (2) a
= 0.761 - 0573 = 0.188 0/0 K)
%
Raq
‘Swept volume for unit mass,
0188.10? 300 2
Y
bag 284
0.3654 mk
306210? wa
ET 83810 Nin?
= [Ex] An.
REVIEW QUESTIONS
1. Mention te two commonly employed approximations of an actual engine. How ar they
different?
2. Wat are he assumptions made in analyzing the airsrandard cycle?
3. Why is the analysis of ar-standard cycle important, though the results obtained are mech
higher than the actual results?
4. Describe te Otto cycle withthe help of p-V and T-s diagrams. Where does this cycle find
its application?
5. Define the terms compression ratio and pressure ratio. Derive the expressions to evaluate
e ficiency, work done and mean efectivo pressure of an Otto eycle using the terms of
pressure ratio and compression ratio,
6. Show and explain the variation of thermal efficiency of an Ono cycle with compression
ratio a different adiabatic exponents. Does the thermal efficiency ofthe Oto cycle depend
upon the engine load?
7. Show and explain the variation of mean effective pressure of an Oo cycle with pressure
ratio at different compression ratios.
8, Describe a Diesel cycle with the help of p-V and Ts diagrams. Where does this cycle find
its application?
9. Define the term cutoff ratio. Derive expressions to evaluate thermal efficiency, work done
and mean effective pressure using compression ratio and cutoff ri.
10. Show and explain the variation of thermal efficiency of a Diesel cycle with cut-off ratio at
different compression ratios and adiabatic exponents.
11, Describe a Dual combustion cycle withthe help of p-V and T-s diagrams, Where docs this
cycle find its aplication?
12. Derive expressions to evaluate thermal efficiency, work done and mean effective pressure
using compresion ro, pressure ratio and cut-off rato.
13. Compare the thermal efficiencies of Otto, Diesel and Dual combustion cycles under the
following conditions
(a) For the same compression rato and heat addition
(0) Forte same compression ratio and heat rejection
(€) For the same peak pressure, peak temperature and heat rejection
(8) For the same maximum pressure and beat input
(6) For the same maximum pressure and woık output
Describe the Atkinson cycle with the help of p-V and Tos diagrams, Where does this eyele
Find it application?
Define compression ratio and expansion ratio, Derive expressions o evaluate thermal efi
ciency, work done and mean effective pressure of an Atkinson cycle using the terms
compression ratio and expansion ratio.
AlrStadard Cycles and Ther Araya 59
For adiabatic expansion process 3-4,
“wy
(2) acosa
(6) Work done per kg W.
Heat supplied perkg, Qi # 64% 75)
0.571690 - 4225)
7263 Woks
A)
= 0.761(852 - 300)
= 4201088
W= 7263-4201
Heat ejected per kg, Os
(0) Efficiency ofthe eye
Y
a
(6) Mean effective pressure,
2062
76
Swept volume,
For adiabatic proces 1
DWE = PVE
“
ur
de m uo
Impression ratio, 7 =
Compre (2) a
= 0.761 - 0573 = 0.188 0/0 K)
%
Raq
‘Swept volume for unit mass,
0188.10? 300 2
Y
bag 284
0.3654 mk
306210? wa
ET 83810 Nin?
= [Ex] An.
REVIEW QUESTIONS
1. Mention te two commonly employed approximations of an actual engine. How ar they
different?
2. Wat are he assumptions made in analyzing the airsrandard cycle?
3. Why is the analysis of ar-standard cycle important, though the results obtained are mech
higher than the actual results?
4. Describe te Otto cycle withthe help of p-V and T-s diagrams. Where does this cycle find
its application?
5. Define the terms compression ratio and pressure ratio. Derive the expressions to evaluate
e ficiency, work done and mean efectivo pressure of an Otto eycle using the terms of
pressure ratio and compression ratio,
6. Show and explain the variation of thermal efficiency of an Ono cycle with compression
ratio a different adiabatic exponents. Does the thermal efficiency ofthe Oto cycle depend
upon the engine load?
7. Show and explain the variation of mean effective pressure of an Oo cycle with pressure
ratio at different compression ratios.
8, Describe a Diesel cycle with the help of p-V and Ts diagrams. Where does this cycle find
its application?
9. Define the term cutoff ratio. Derive expressions to evaluate thermal efficiency, work done
and mean effective pressure using compression ratio and cutoff ri.
10. Show and explain the variation of thermal efficiency of a Diesel cycle with cut-off ratio at
different compression ratios and adiabatic exponents.
11, Describe a Dual combustion cycle withthe help of p-V and T-s diagrams, Where docs this
cycle find its aplication?
12. Derive expressions to evaluate thermal efficiency, work done and mean effective pressure
using compresion ro, pressure ratio and cut-off rato.
13. Compare the thermal efficiencies of Otto, Diesel and Dual combustion cycles under the
following conditions
(a) For the same compression rato and heat addition
(0) Forte same compression ratio and heat rejection
(€) For the same peak pressure, peak temperature and heat rejection
(8) For the same maximum pressure and beat input
(6) For the same maximum pressure and woık output
Describe the Atkinson cycle with the help of p-V and Tos diagrams, Where does this eyele
Find it application?
Define compression ratio and expansion ratio, Derive expressions o evaluate thermal efi
ciency, work done and mean effective pressure of an Atkinson cycle using the terms
compression ratio and expansion ratio.
60 Fundament lars! Combuion Enger
AirSandard Cycles and Their Anis 61
PROBLEMS
2.1 An engine working on Otto cycle has a pressure and temperature atthe beginning of
‘compression as 1 bar and 20°C respectively. After compression, the temperature becomes
580°C. The maximum temperature ofthe cycle is limied to 1800*C. Calculate the com
pression ratio, the temperature and pressure at all cardinal points, the aiestandard
‘fcieny, the work done per kg and the mean effective pressure.
22 An engine working on Oto cycle has cylinder bore of 210 mum and stroke length of
240 mm. The clearence volume is 1550 ce The pressure and temperature a the Beginning
‘of compression are | bar and 17°C respectively. The maximum pressure of the cycle is
50 bar. Determine the pressure and temperature atthe salient points, the ae-standard
efficiency, the work done, and the mean effective pressure. What will be the idea! power
‘developed bythe engine, if the working cycle per minute i 6007
2.3 A Diesel cycle operates ata pressure of 1 bar atthe beginning of compression and the
‘compressed to 1/18t ofthe inital volume. Heat is supplied until the volume twice
that of the clearance volume, Calculate th air-standard efficiency and the mean effective
pressure of the cycle,
2.4 A four-cylinder engine operating on a Diesel cycle as cylinder bore of 200 mm and stroke
length of 250 mm. The engine speed is 3000 rpm. The pressure and temperatur ofthe ait
atthe beginning of compression are 1 bar and 27°C respectively. The clearance volume is
Sth ofthe swept volume. The maximum temperature anained by the cycle is 1800°C.
Determine the pressure and temperature atthe salient points the compression ratio, the
aicstandard efficiency, the work done per kg of ar, the mean effective pressure, and the
power developed by the engine.
2.5 For an engine working on a Diese cycle, the pressures inthe cylinder at 20 per cent and
25 per cent ofthe compression stroke are 1.5 bar and 4 bar respectively. Assuming that the
compression follows the law pV! = constant, find the compression ratio. The cutoff
takes place at % ofthe stoke. What will be the cutoff rato? Ifthe relative efficiency of
the engine compared with the air-standard efficiency is 60%, evaluate the fuel consump
tion in kg/kWh, ifthe calorific value ofthe fuel is 40,000 kg
26 An oil engine operting on a Dual eycle has cylinder hore of 250 mm and stoke length
‘of 300 mm. The compression and expansion ratios are 10 and 6 respectively. The initial
Pressure and temperatoreof the rare I bar and 27°C respectively, Determine the pressure
and temperature at all salient points, the aie standard efficiency of the cycle, the mean
effective pressure, and the power ofthe engine, if the working cycles per second are 12.
‘Assume thatthe heat added al constant pressure is twice the heat added at constant
volume.
221 An ol engine operating on a Dual cycle has a compression ratio of 15 and compression
begios u 1 bar, 30°C. The maximum pressure reached is 65 bar The heat transferred 1 air
a constant pressure is equal o that at constant volume. The expansion and compression
follow the law pV? = constant, Determine the pressure and temperature al cardinal
points, the cycle efficiency, and the mean effective pressure of he cycle.
2.8 Determine the percentage increase inefficiency of an Atkinson eye in comparison with
29
210
the Otto cycle for a compression ratio of 8.5. The pressure and temperature of ar at the
beginning of compression are 1 bar and 27°C respectively. The peak pressure is 45 bar for
both cycles.
‘An aic-standard Dual combustion cycle has a maximum cycle pressure of 65 bar. The
minimum pressure and temperature ae I bar and 22°C respectively. The compression ratio
17 and the mean effective pressure ofthe cycle is 11 ar. Determine the maximum cycle
temperature when the thermal efficiency ofthe cycle is 65%
‘Air undergoes an Atkinson cycle, The ai is compressed adiabatically from 1 bar, 17°C 10
5 bar. The maximum pressure ofthe cycle i 20 ba. Calculate the work done per kg of as,
the efficiency of he cycle, and the mean effective pressure,
AirSandard Cycles and Their Anis 61
PROBLEMS
2.1 An engine working on Otto cycle has a pressure and temperature atthe beginning of
‘compression as 1 bar and 20°C respectively. After compression, the temperature becomes
580°C. The maximum temperature ofthe cycle is limied to 1800*C. Calculate the com
pression ratio, the temperature and pressure at all cardinal points, the aiestandard
‘fcieny, the work done per kg and the mean effective pressure.
22 An engine working on Oto cycle has cylinder bore of 210 mum and stroke length of
240 mm. The clearence volume is 1550 ce The pressure and temperature a the Beginning
‘of compression are | bar and 17°C respectively. The maximum pressure of the cycle is
50 bar. Determine the pressure and temperature atthe salient points, the ae-standard
efficiency, the work done, and the mean effective pressure. What will be the idea! power
‘developed bythe engine, if the working cycle per minute i 6007
2.3 A Diesel cycle operates ata pressure of 1 bar atthe beginning of compression and the
‘compressed to 1/18t ofthe inital volume. Heat is supplied until the volume twice
that of the clearance volume, Calculate th air-standard efficiency and the mean effective
pressure of the cycle,
2.4 A four-cylinder engine operating on a Diesel cycle as cylinder bore of 200 mm and stroke
length of 250 mm. The engine speed is 3000 rpm. The pressure and temperatur ofthe ait
atthe beginning of compression are 1 bar and 27°C respectively. The clearance volume is
Sth ofthe swept volume. The maximum temperature anained by the cycle is 1800°C.
Determine the pressure and temperature atthe salient points the compression ratio, the
aicstandard efficiency, the work done per kg of ar, the mean effective pressure, and the
power developed by the engine.
2.5 For an engine working on a Diese cycle, the pressures inthe cylinder at 20 per cent and
25 per cent ofthe compression stroke are 1.5 bar and 4 bar respectively. Assuming that the
compression follows the law pV! = constant, find the compression ratio. The cutoff
takes place at % ofthe stoke. What will be the cutoff rato? Ifthe relative efficiency of
the engine compared with the air-standard efficiency is 60%, evaluate the fuel consump
tion in kg/kWh, ifthe calorific value ofthe fuel is 40,000 kg
26 An oil engine operting on a Dual eycle has cylinder hore of 250 mm and stoke length
‘of 300 mm. The compression and expansion ratios are 10 and 6 respectively. The initial
Pressure and temperatoreof the rare I bar and 27°C respectively, Determine the pressure
and temperature at all salient points, the aie standard efficiency of the cycle, the mean
effective pressure, and the power ofthe engine, if the working cycles per second are 12.
‘Assume thatthe heat added al constant pressure is twice the heat added at constant
volume.
221 An ol engine operating on a Dual cycle has a compression ratio of 15 and compression
begios u 1 bar, 30°C. The maximum pressure reached is 65 bar The heat transferred 1 air
a constant pressure is equal o that at constant volume. The expansion and compression
follow the law pV? = constant, Determine the pressure and temperature al cardinal
points, the cycle efficiency, and the mean effective pressure of he cycle.
2.8 Determine the percentage increase inefficiency of an Atkinson eye in comparison with
29
210
the Otto cycle for a compression ratio of 8.5. The pressure and temperature of ar at the
beginning of compression are 1 bar and 27°C respectively. The peak pressure is 45 bar for
both cycles.
‘An aic-standard Dual combustion cycle has a maximum cycle pressure of 65 bar. The
minimum pressure and temperature ae I bar and 22°C respectively. The compression ratio
17 and the mean effective pressure ofthe cycle is 11 ar. Determine the maximum cycle
temperature when the thermal efficiency ofthe cycle is 65%
‘Air undergoes an Atkinson cycle, The ai is compressed adiabatically from 1 bar, 17°C 10
5 bar. The maximum pressure ofthe cycle i 20 ba. Calculate the work done per kg of as,
the efficiency of he cycle, and the mean effective pressure,
Reactive Systems
3.1 INTRODUCTION
‘Combustion ofthe fuelairnixtare inside Ihe engine cylinder is ane ofthe processes that controls
engine power, efficiency, and emissions. Its therefore essential to understand the combustion
phenomenon. There are two types of chemical reactions. One i exothermic, in which hea energy
is liberated andthe otter is endothermic, in which heat energy is absorbed. The combustion of
fuel in internal combustion engines is a fast exothermic reaction in the gaseous phase where
‘oxygen obtained from ai is usually one of the reactants,
In the present chapter the thermodynamic analysis of the combustion process of fuel is
cared out The change of chemical energy into thermal energy is important for producing power
in IC engines. The law of thermodynamics and the conservation of mass are used for the
analysis.
In IC engines, the liquid and gascous fuel are used. The liquid hydrocarbons such as gaso-
line, kerosene and diesel fuc are the common fuels. Any fuel, such se gasoline is actually mixture
of many hydrocarbons. Alcohols are sometimes used as fuel in IC engines. Gaseous hydıocar-
bon fucls are alo a mixture of various constituent hydrocarbons.
3.2 PROPERTIES OF AIR
In IC engines, the combustion of fuel takes place inthe presence o sr and not pure oxygen. Air
contains many constiuents, particularly oxygen, nitrogen, argon and other vapours and inert
ses. Its volumetric composition is approximately 21% Os, 78% N and 1% argon. Since nether
hitrogen nor argon enters into the chemical reaction is suficiently accurate to assume thatthe
volumetric air proportions are 21% oxygen and 79% nitrogen and tht for 100 moles ofa there
are 21 moles of oxygen and 79 moles of nitrogen. That is,
molesof Ny _ 79
Boleat ty. 29
‘moles of ~ 21 "76
‚Therefore, foreach mole of oxygen in ai, tere are 3.76 moles of nitrogen, the molecular
‘weight of dry airis taken es 28.967 or 29, To acount for argon, which is clubbed with nitrogen,
the equivalent moleculas weight of nitrogen is taken as 28.16. However forthe analysis, nitrogen
7
Rene Spars 63
in aie may be considered as pure and the molecular weight of nitrogen can be taken 2828. Items
‘of mass, air contains approximately 23% oxygen and 77% nitrogen
33 COMBUSTION WITH AIR
‘The general formula forthe fuel used in IC engines can be taken as C,„H,0,, where m. a, and p
represent the number of moles of carbon, hydrogen and oxygen atoms in a mole of fuel
"The basie stoichiometric (chemically corre) equation for Fuel-ai reaction is
BIO, + Ka + 316 My = MO + À HO + 3767 Ma on
were Yo the chemically correct soles of Os per mole of fuel. The Nz does not take part in the
reaction. There ae 3.76 moles of N, per mole of O, and since Y,. moles of Oz are theoretclly
necessary for the oxidation ofthe fuel, 3.76Y,, moles of N; ae present,
By balancing the number of moles of O; on both sides of Ba. (3.1).
Brom
62
Yazmı
The stoichiometric equation now becomes
Gao o(mo3-£)o.0006(m+3-8)x arco, + 210 +200(m+
‘The stoichiometric equation for pure hydrocarbons (CH), where the oxygen atom isnot
present (p = 0) can be waiten as
Cot (m+)0,4376 (m+ JE + mon + $140 +36 (m2)
03
The combustion equation for octane (CH) can be writen with = 8 and n = 18 as
Coll + 12.503 + 376(12.5IN; — 8603 + 910 + 3.76(12.5)N
or Call + 1250, + 47N > 8CO, + 9,0 4470, es
Inthe aove chemical equations, only a chemically corest amount of oxygen is included, The
stoichiometric or the chemically corect amount of air require to oxiize the reactants is called
the theoretical air. When combustion is achieved with theoretical air, no oxygen is obtained in the
products In practice, his is not possible. More oxygen than is theoretically necessary is required
10 achieve complete combustion of reactants. The excess aris needed because the fuels of finite
size, and each droplet must be surrounded by more than the necessary number of oxygen
molecules to assure oxidation ofall he fuel molecules. The excess air is usualy expressed as a
percentage of the theoretical ai Thus, if 20% more air dan is theoretically required i ured, this
is expressed as 120% theoretical air or 20% excess ar. There i 12 times as much si acwally
3.1 INTRODUCTION
‘Combustion ofthe fuelairnixtare inside Ihe engine cylinder is ane ofthe processes that controls
engine power, efficiency, and emissions. Its therefore essential to understand the combustion
phenomenon. There are two types of chemical reactions. One i exothermic, in which hea energy
is liberated andthe otter is endothermic, in which heat energy is absorbed. The combustion of
fuel in internal combustion engines is a fast exothermic reaction in the gaseous phase where
‘oxygen obtained from ai is usually one of the reactants,
In the present chapter the thermodynamic analysis of the combustion process of fuel is
cared out The change of chemical energy into thermal energy is important for producing power
in IC engines. The law of thermodynamics and the conservation of mass are used for the
analysis.
In IC engines, the liquid and gascous fuel are used. The liquid hydrocarbons such as gaso-
line, kerosene and diesel fuc are the common fuels. Any fuel, such se gasoline is actually mixture
of many hydrocarbons. Alcohols are sometimes used as fuel in IC engines. Gaseous hydıocar-
bon fucls are alo a mixture of various constituent hydrocarbons.
3.2 PROPERTIES OF AIR
In IC engines, the combustion of fuel takes place inthe presence o sr and not pure oxygen. Air
contains many constiuents, particularly oxygen, nitrogen, argon and other vapours and inert
ses. Its volumetric composition is approximately 21% Os, 78% N and 1% argon. Since nether
hitrogen nor argon enters into the chemical reaction is suficiently accurate to assume thatthe
volumetric air proportions are 21% oxygen and 79% nitrogen and tht for 100 moles ofa there
are 21 moles of oxygen and 79 moles of nitrogen. That is,
molesof Ny _ 79
Boleat ty. 29
‘moles of ~ 21 "76
‚Therefore, foreach mole of oxygen in ai, tere are 3.76 moles of nitrogen, the molecular
‘weight of dry airis taken es 28.967 or 29, To acount for argon, which is clubbed with nitrogen,
the equivalent moleculas weight of nitrogen is taken as 28.16. However forthe analysis, nitrogen
7
Rene Spars 63
in aie may be considered as pure and the molecular weight of nitrogen can be taken 2828. Items
‘of mass, air contains approximately 23% oxygen and 77% nitrogen
33 COMBUSTION WITH AIR
‘The general formula forthe fuel used in IC engines can be taken as C,„H,0,, where m. a, and p
represent the number of moles of carbon, hydrogen and oxygen atoms in a mole of fuel
"The basie stoichiometric (chemically corre) equation for Fuel-ai reaction is
BIO, + Ka + 316 My = MO + À HO + 3767 Ma on
were Yo the chemically correct soles of Os per mole of fuel. The Nz does not take part in the
reaction. There ae 3.76 moles of N, per mole of O, and since Y,. moles of Oz are theoretclly
necessary for the oxidation ofthe fuel, 3.76Y,, moles of N; ae present,
By balancing the number of moles of O; on both sides of Ba. (3.1).
Brom
62
Yazmı
The stoichiometric equation now becomes
Gao o(mo3-£)o.0006(m+3-8)x arco, + 210 +200(m+
‘The stoichiometric equation for pure hydrocarbons (CH), where the oxygen atom isnot
present (p = 0) can be waiten as
Cot (m+)0,4376 (m+ JE + mon + $140 +36 (m2)
03
The combustion equation for octane (CH) can be writen with = 8 and n = 18 as
Coll + 12.503 + 376(12.5IN; — 8603 + 910 + 3.76(12.5)N
or Call + 1250, + 47N > 8CO, + 9,0 4470, es
Inthe aove chemical equations, only a chemically corest amount of oxygen is included, The
stoichiometric or the chemically corect amount of air require to oxiize the reactants is called
the theoretical air. When combustion is achieved with theoretical air, no oxygen is obtained in the
products In practice, his is not possible. More oxygen than is theoretically necessary is required
10 achieve complete combustion of reactants. The excess aris needed because the fuels of finite
size, and each droplet must be surrounded by more than the necessary number of oxygen
molecules to assure oxidation ofall he fuel molecules. The excess air is usualy expressed as a
percentage of the theoretical ai Thus, if 20% more air dan is theoretically required i ured, this
is expressed as 120% theoretical air or 20% excess ar. There i 12 times as much si acwally
64 _fendanents of Irma! Combustion Engines
Reacive Stems 65,
used chen i theoretically required, The combustion of octane with 20% excess air con be
Cilia + 12012590; + 1247; > 8CO, + 91,0 + S6AN +20,
or Citi + 150, + S6AN, => CO} + 9H,0+564N +250, 00)
in general, Y moles FO; are supplied for complete combustion of 1 mole of fuel CHO,
and Y2 Ka (exces ar), ihe combustion equation can be weiten as
CHLO + YO; + 37678
> CO, + HO HITLER
1f the amount of ais nsufficient to provide complete combustion, then ll he carbon wi not be
oxidized to carbon dioxide but some carbon monoxide will also be formed. When incomplete
combustion occurs, information about the products is necessary in order to balance the combus-
tion equation. The products of combustion can be obtained by experimental methods. However,
with certain assumptions the combustion equation can be writen. These assumptions ae: () all
hydrogen appears as HO and (i) all cabon is oxidized to CO. I any oxygen remains, part ofthe
‘CO is oxidized to COs
Let Yin denote the moles ofthe minimum allowable O; content inthe reactants per mole of
fuel, so that all Hy is converted 10 H,O and all Cis converted to CO. There is no formation of CO»
with Yan mole of O, The combustion equation becomes. “
CO, + Fa: + 316 na CO + HO 4376 es
By bang the moles O on bh ies Eg 8),
Baty = Met
qt
ee es
Yuin = BH BAB ere as,
For insfcet amount os such ht Yu, € Y. combustion equi under the shove
sumptions can be mien
Gall, + YO) + 3.767%, = XCO +(m=1X)CO, + ZH:O +36IN2 310)
By bacs the moles o 0; on bot sides of (5.10),
Ber-Kumenst
Pero
x=2{m+3-8-r)=a00.-n am
‘The moles of CO formed in the combustion product is therefore equal (© AY. - Y) and the.
moles of CO; formed in the combustion product is m — 2(Yee~ YY which is equal 0 2(— Yan).
“Therefore, be combustion equation becomes
CO, + 7034 37000 > A 1900 + 207 = FCO) + 1,04 37000, (3.12)
or a reactant mixture containing 1 mole of C-H,0,, Y moles of O; and 3.76Y moles of Ny,
the number of moles of products of combustion for dhe (wo cases are shown in Table 3.1
Table3.1 Moles of products of combustion
ame ofthe product ambar of moles of the product constant
constituent CEA Case: Ven Val
(Fromea 02) Font”
co N&=0 ND= 2e)
co, N@=m NQ)=20~ Ys)
Ho Nod Noyes
M NO=3767 NO=3767
D ERA NS=0
In Table 3.1, he ubseriping system is adopted such thatthe correspondence between mole
numbers and gases is
CO, 3-0, 4=N; and 5=03
34 EQUIVALENCE RATIO
“The soichiometic equation definestheoetically the correct mixture of fuel and air for complete
combustion. To allow for a mixture different from the correct mixture, the equivalence ratio $
fs inivoduced, This is defined asthe ratio of the actual fucar ratio (WA), tothe stoichiometric
oe rau (RIA), Tt may also be defined as stoichiometric arte ratio (A/F), to actual arfuel
ratio (AMF), Ths,
(PIA, „A,
TA), "wm,
the equivalence rato Pis greater than uit, he mixture is sad tobe rch nd fis less han
‘wit the mixture is said to be weak. The spark-igntion engines may aormaly un with both sich
nd weak mixtures but the corpresson-igntion engines normally run with weak mixtures only.
Tre inverso of equivalence rato gis called the relative al aio A. Therefore,
$ CE)
aL AP),
aad ne 614)
or lean mistures,0< 1, A> 1
For stoichiometric mixtures, @= A= 1
For ich mistues, > 1, À < 1
“The fueVair rai or the arf ratio 3 normally expressed in the ratios of corresponding masses
Reacive Stems 65,
used chen i theoretically required, The combustion of octane with 20% excess air con be
Cilia + 12012590; + 1247; > 8CO, + 91,0 + S6AN +20,
or Citi + 150, + S6AN, => CO} + 9H,0+564N +250, 00)
in general, Y moles FO; are supplied for complete combustion of 1 mole of fuel CHO,
and Y2 Ka (exces ar), ihe combustion equation can be weiten as
CHLO + YO; + 37678
> CO, + HO HITLER
1f the amount of ais nsufficient to provide complete combustion, then ll he carbon wi not be
oxidized to carbon dioxide but some carbon monoxide will also be formed. When incomplete
combustion occurs, information about the products is necessary in order to balance the combus-
tion equation. The products of combustion can be obtained by experimental methods. However,
with certain assumptions the combustion equation can be writen. These assumptions ae: () all
hydrogen appears as HO and (i) all cabon is oxidized to CO. I any oxygen remains, part ofthe
‘CO is oxidized to COs
Let Yin denote the moles ofthe minimum allowable O; content inthe reactants per mole of
fuel, so that all Hy is converted 10 H,O and all Cis converted to CO. There is no formation of CO»
with Yan mole of O, The combustion equation becomes. “
CO, + Fa: + 316 na CO + HO 4376 es
By bang the moles O on bh ies Eg 8),
Baty = Met
qt
ee es
Yuin = BH BAB ere as,
For insfcet amount os such ht Yu, € Y. combustion equi under the shove
sumptions can be mien
Gall, + YO) + 3.767%, = XCO +(m=1X)CO, + ZH:O +36IN2 310)
By bacs the moles o 0; on bot sides of (5.10),
Ber-Kumenst
Pero
x=2{m+3-8-r)=a00.-n am
‘The moles of CO formed in the combustion product is therefore equal (© AY. - Y) and the.
moles of CO; formed in the combustion product is m — 2(Yee~ YY which is equal 0 2(— Yan).
“Therefore, be combustion equation becomes
CO, + 7034 37000 > A 1900 + 207 = FCO) + 1,04 37000, (3.12)
or a reactant mixture containing 1 mole of C-H,0,, Y moles of O; and 3.76Y moles of Ny,
the number of moles of products of combustion for dhe (wo cases are shown in Table 3.1
Table3.1 Moles of products of combustion
ame ofthe product ambar of moles of the product constant
constituent CEA Case: Ven Val
(Fromea 02) Font”
co N&=0 ND= 2e)
co, N@=m NQ)=20~ Ys)
Ho Nod Noyes
M NO=3767 NO=3767
D ERA NS=0
In Table 3.1, he ubseriping system is adopted such thatthe correspondence between mole
numbers and gases is
CO, 3-0, 4=N; and 5=03
34 EQUIVALENCE RATIO
“The soichiometic equation definestheoetically the correct mixture of fuel and air for complete
combustion. To allow for a mixture different from the correct mixture, the equivalence ratio $
fs inivoduced, This is defined asthe ratio of the actual fucar ratio (WA), tothe stoichiometric
oe rau (RIA), Tt may also be defined as stoichiometric arte ratio (A/F), to actual arfuel
ratio (AMF), Ths,
(PIA, „A,
TA), "wm,
the equivalence rato Pis greater than uit, he mixture is sad tobe rch nd fis less han
‘wit the mixture is said to be weak. The spark-igntion engines may aormaly un with both sich
nd weak mixtures but the corpresson-igntion engines normally run with weak mixtures only.
Tre inverso of equivalence rato gis called the relative al aio A. Therefore,
$ CE)
aL AP),
aad ne 614)
or lean mistures,0< 1, A> 1
For stoichiometric mixtures, @= A= 1
For ich mistues, > 1, À < 1
“The fueVair rai or the arf ratio 3 normally expressed in the ratios of corresponding masses
66 _Fundamensas of nera! Combutin Engines
Resetve Stems 67
For octane (CH) the stoichiometric ai/ful ratio can be obtained from Eq. (3.5) as
{nas of O) + mass of) per mole fuel
mass of fel per mole fuel
(Nii io» EE
2 (25x32+47x29 _ 40041316 _ 1716
CT = Ta 7 1595
If 20% excess al is used in actul practice, then from Eq. 0.6)
15%32 456428
(Ai ratio) = =
« io) T4 1806
jivalence ratio = BOS
Egpivalence ato, Ps 08
‘As the equivalence rato is less than 1, it indjetes alan mixture Le. excess iris used for the
combustion of fuel.
Methanol is bared with 20% excess a
supplied per knoe of fuel, Demi he molecular weight ofthe reactants and prod. Ab
determine the dew pont ofthe products.
Solution: The svichiometric combustion equation is
CHOR + 1.50, 41.50.7085 => CO, + 20 + SIN
18 x 324564 x28
2
‘Stoichiometric airfel ratio
=6435
‘The combustion equation with 20% excess ar is
CHJOH + 1.2% 1.50, + 12% 5.61; = CO; + 28,0 4 6.768N +030,
or CHOR + 180, + 6.768N; -> CO, + 2140 + 6.768N + 030,
‘Actual ius ratio = 18232 4
1 mole of fuel (CHOR) reacts with 1.8 + 6.768
LO ay aT] Am.
‘The total number of moles inthe reactants when excess aris supplied
1 mole of CHOH + 1.8 moles of 0% + 6.768 moles of Ny
568 moles
Mole fraction ofthe species are:
568 kmole of air.
Volume of air, ¥
Molecular wight of reactants = x M,
1045 x 32 + 0.1881 x 32 + 0.7074 x 2 Ans.
Total number of moles in products
1 mole CO) +2 moles HO + 6768 moles N + 0.3 moles Op
= 10.068 moles
Mole fraction ofthe products are:
1
Où To 08s
Hoe 2
71006
676
10068
03
Toost
Molecular weight of products = 2, M,
10993 x 44 + 0.1987 18 + 06722 x 28 + 0.0298 x 32
CFE] ame
Para pesar of water vapour = 0987901 ar
198 bar
‘Tee dw pins trato temperate comeponing to pai pres of 0.987 bar
= [BFE] (one rom sen ule) Ans
EEES A fuel mixture of 40% CH, and 60% Cp by volume is used in an engine
having a bore of 120 mm and stroke length of 145 mm. The compression ratio is 8.5. The
percentage composition of dry products of combustion by volume is CO, = 12%, CO = 1.5%,
(O3 =2.5% and the restis Ny Calculate the ac/fue ratio and the mass ofthe residual gases left in
the cylinder atthe end ofthe exhaust stroke if the pressure and temperature are 1.1 bar and 720 K.
Perentage of Ny inthe dy products of combustion
= 100 - (12+ 1.5 +25) = 100-16 = 84%
‘The combustion equation can be weten as
DAXC¡Hs + O.6XC Hig + YO; + 2.76N) > 1200, + 1.5CO +2,50; + SAN: + 2H,O
Solution:
Resetve Stems 67
For octane (CH) the stoichiometric ai/ful ratio can be obtained from Eq. (3.5) as
{nas of O) + mass of) per mole fuel
mass of fel per mole fuel
(Nii io» EE
2 (25x32+47x29 _ 40041316 _ 1716
CT = Ta 7 1595
If 20% excess al is used in actul practice, then from Eq. 0.6)
15%32 456428
(Ai ratio) = =
« io) T4 1806
jivalence ratio = BOS
Egpivalence ato, Ps 08
‘As the equivalence rato is less than 1, it indjetes alan mixture Le. excess iris used for the
combustion of fuel.
Methanol is bared with 20% excess a
supplied per knoe of fuel, Demi he molecular weight ofthe reactants and prod. Ab
determine the dew pont ofthe products.
Solution: The svichiometric combustion equation is
CHOR + 1.50, 41.50.7085 => CO, + 20 + SIN
18 x 324564 x28
2
‘Stoichiometric airfel ratio
=6435
‘The combustion equation with 20% excess ar is
CHJOH + 1.2% 1.50, + 12% 5.61; = CO; + 28,0 4 6.768N +030,
or CHOR + 180, + 6.768N; -> CO, + 2140 + 6.768N + 030,
‘Actual ius ratio = 18232 4
1 mole of fuel (CHOR) reacts with 1.8 + 6.768
LO ay aT] Am.
‘The total number of moles inthe reactants when excess aris supplied
1 mole of CHOH + 1.8 moles of 0% + 6.768 moles of Ny
568 moles
Mole fraction ofthe species are:
568 kmole of air.
Volume of air, ¥
Molecular wight of reactants = x M,
1045 x 32 + 0.1881 x 32 + 0.7074 x 2 Ans.
Total number of moles in products
1 mole CO) +2 moles HO + 6768 moles N + 0.3 moles Op
= 10.068 moles
Mole fraction ofthe products are:
1
Où To 08s
Hoe 2
71006
676
10068
03
Toost
Molecular weight of products = 2, M,
10993 x 44 + 0.1987 18 + 06722 x 28 + 0.0298 x 32
CFE] ame
Para pesar of water vapour = 0987901 ar
198 bar
‘Tee dw pins trato temperate comeponing to pai pres of 0.987 bar
= [BFE] (one rom sen ule) Ans
EEES A fuel mixture of 40% CH, and 60% Cp by volume is used in an engine
having a bore of 120 mm and stroke length of 145 mm. The compression ratio is 8.5. The
percentage composition of dry products of combustion by volume is CO, = 12%, CO = 1.5%,
(O3 =2.5% and the restis Ny Calculate the ac/fue ratio and the mass ofthe residual gases left in
the cylinder atthe end ofthe exhaust stroke if the pressure and temperature are 1.1 bar and 720 K.
Perentage of Ny inthe dy products of combustion
= 100 - (12+ 1.5 +25) = 100-16 = 84%
‘The combustion equation can be weten as
DAXC¡Hs + O.6XC Hig + YO; + 2.76N) > 1200, + 1.5CO +2,50; + SAN: + 2H,O
Solution:
68. Fundamental nera! Combustion Enger
Reactive Stems 69
(Nas not reacting
3.76 = 84
or Yoru
22.34 moles of Os is supplied.
By balancing C on both sides ofthe reaction,
28X + 48x #135
x= 176
By Opbalance
r=n+075+25+
2
2
or masas. E
2 2=1418
‘The combustion equation now becomes
DATO) Hyg + 0.6(1-716)C4Hyy + 223400, + 3.76)
> 1200, + 1.500 + 2.50; +84N + 14.180.
“The combustion equation per mule of fuel can be written as
OAC Hyg + O.6C¿Hys + 12.5800; + 3.76N,)
=> GTSICO; + 0.8446C0 + 1.4080) + 47.303 +7.98H,0
“The above equation must be checked for H balance as wel.
No.of moles of Hy on LHS, = 44108 6
2
No. of moles of Hz on RAS.
98
Difference of Hy moles = 846 ~ 7.98 = 0.62
"This difference must be added to R.H.S. to balance the above combustion equation,
Let us asume that this H is also present in the form of HO in products; corresponding o.
this 031 moles of; is assumed to be present in reactants From the other sources. The balanced
‘equation now becomes
OAC + OGC + 12.58(03 + 3.76N,) + 0310;
> 6:1S7CO, + 0.8446C0 + 1.4080, + 473N; + 8.6440
1258024296029 ETS) Am.
04x 100+06x114 ~
Swept volume of pin + E d= HO12} (165) =1.64% 10m?
Aisfvet ratio =
68x10?
E = 02187 x 10° m
Clearance volume,
Molecular weight of the product = Ex, M4
LL 6.157% 44-4 08446 x 28 + 1408 X32 4 473%28 + 86218
- ‘6157 = 08446 + LAOS +473 + 86
22843
Ree.
sate Ran 10
Mass of the exhaust gases inthe clearance space,
BM, _ Utx10* 0.218710
Ar DATO
Gas constan
ATs RE] Ans.
‘The analysis of a fue is found to be carbon 86%, hydrogen 5%, oxygen 2%,
sulphur 0.5% by weight andthe remainder is nitrogen. Determine the weight of stoichiometric air
per kg of fuel for complete combustion. If the actual supply of airs 25% in excess of
this, estimate the percentage of dry products of combustion by weight and by volume.
Solution: The combustion reactions can be written as
C+0,>C0,
2H) +0) 9240
5 +0; —+ 50;
1 Kg of fuel contains 0.86 kg C, 0.05 kg Ha, 002 kg On and 0.005 kg 5.
Nein 1 kg fuel = 1 - (086 + 0.05 + 0.02 + 0005) = 1 - 0.935
= 0.065 kg
LE eed 32 4 O and podes kg Oster, 06 Cos 22 x086= 2203
1a and pokes # x086=315E CO;
{ag eus 32 yan pres 36 De 005 gh els 32 005 20436 0
an mo 3 005 045 Kg
52g qe 3g Oy pres 6 SOS Bl, OSA ri 0101 Os
and produces 0.01 kg SO;
Total oxygen required for the complete combustion of fuel
= 2.293 +04 + 0.005 = 2.698 kg Oz
“The amount of oxygen required per kg of fuel for complete combustion (theoretically)
678 kg
Reactive Stems 69
(Nas not reacting
3.76 = 84
or Yoru
22.34 moles of Os is supplied.
By balancing C on both sides ofthe reaction,
28X + 48x #135
x= 176
By Opbalance
r=n+075+25+
2
2
or masas. E
2 2=1418
‘The combustion equation now becomes
DATO) Hyg + 0.6(1-716)C4Hyy + 223400, + 3.76)
> 1200, + 1.500 + 2.50; +84N + 14.180.
“The combustion equation per mule of fuel can be written as
OAC Hyg + O.6C¿Hys + 12.5800; + 3.76N,)
=> GTSICO; + 0.8446C0 + 1.4080) + 47.303 +7.98H,0
“The above equation must be checked for H balance as wel.
No.of moles of Hy on LHS, = 44108 6
2
No. of moles of Hz on RAS.
98
Difference of Hy moles = 846 ~ 7.98 = 0.62
"This difference must be added to R.H.S. to balance the above combustion equation,
Let us asume that this H is also present in the form of HO in products; corresponding o.
this 031 moles of; is assumed to be present in reactants From the other sources. The balanced
‘equation now becomes
OAC + OGC + 12.58(03 + 3.76N,) + 0310;
> 6:1S7CO, + 0.8446C0 + 1.4080, + 473N; + 8.6440
1258024296029 ETS) Am.
04x 100+06x114 ~
Swept volume of pin + E d= HO12} (165) =1.64% 10m?
Aisfvet ratio =
68x10?
E = 02187 x 10° m
Clearance volume,
Molecular weight of the product = Ex, M4
LL 6.157% 44-4 08446 x 28 + 1408 X32 4 473%28 + 86218
- ‘6157 = 08446 + LAOS +473 + 86
22843
Ree.
sate Ran 10
Mass of the exhaust gases inthe clearance space,
BM, _ Utx10* 0.218710
Ar DATO
Gas constan
ATs RE] Ans.
‘The analysis of a fue is found to be carbon 86%, hydrogen 5%, oxygen 2%,
sulphur 0.5% by weight andthe remainder is nitrogen. Determine the weight of stoichiometric air
per kg of fuel for complete combustion. If the actual supply of airs 25% in excess of
this, estimate the percentage of dry products of combustion by weight and by volume.
Solution: The combustion reactions can be written as
C+0,>C0,
2H) +0) 9240
5 +0; —+ 50;
1 Kg of fuel contains 0.86 kg C, 0.05 kg Ha, 002 kg On and 0.005 kg 5.
Nein 1 kg fuel = 1 - (086 + 0.05 + 0.02 + 0005) = 1 - 0.935
= 0.065 kg
LE eed 32 4 O and podes kg Oster, 06 Cos 22 x086= 2203
1a and pokes # x086=315E CO;
{ag eus 32 yan pres 36 De 005 gh els 32 005 20436 0
an mo 3 005 045 Kg
52g qe 3g Oy pres 6 SOS Bl, OSA ri 0101 Os
and produces 0.01 kg SO;
Total oxygen required for the complete combustion of fuel
= 2.293 +04 + 0.005 = 2.698 kg Oz
“The amount of oxygen required per kg of fuel for complete combustion (theoretically)
678 kg
TO Fundamentals of Internal Combien Engines
Rein Sytem TI
Amount of theoretical ai require per kg of fuel
2678x100
1.64 ke
2
Soiehiometeaivfcirao = Ans.
Since 25% encess ai is supplied, the actual quantity of ai supplied per kg of fuel
= LGA x 1.25 = 1455 ke
‘The combustion products will be
CO, =3.153 kg
> HO = 0450 kg.
SO, = 00010 kg
(gin excess air = 0.23 x 0.25 x 11.64 = 0.6693 kg,
Nainair = 0.77 1.25 x 11.64 = 11.2035 kg
pin fuel = 0.065 kg
Total Np in exhaust = 11.2035 + 0.065
1.2685 kg,
Omiting the wet gases, water vapour and SO, which ace condensed, Ihe products of combustion
Of dey gases will contain only CO; Na, and Oz.
CO, = 3.1530 kg
Na = 11.2685 kg
0 = 0.6693 kg
‘Toa weight = 15.0908 kg
Percentage composition by weight:
DEL]
AGE
Ans.
KA
Volumetric analysis of dry products:
09716 10911
ra [1448]
040245 „409
ae 130%] | Ans.
0.0209 , 100 IE]
Dans, *100-[428]
A tydrocatbon fel asthe following composition of dry products of combus-
by volume:
CO,=12%, CO=05%, 0=4%, and the rest Np
Determine th iefüel ratio the per cen theoretical air and the percentage composition of fuel on
a mass basis,
Solution: The combustion equation of an unknown hydrocarbon fuel can be wetten as
Cab, +20, + yNy=> 1200, + 0.5CO + 40; + 83.50 + BHO
Cane: "me 12405-0123
Nybalance: y=83S y=3.76x + 376 “222!
ose: 2221 212408 4492
gone
Bitar Ped 1192
mens
‘The combustion equation becomes.
CizsHas y + 22.210; + 83.50, > 12CO, + 0.5CO + 40) + 83.5N + 11.9240
sive rio = 222062483909 „ 204872 =
orar) Tras Le) A
Proportionate moles of: ‘The stoichiometric combustion equation is
cos» EI = 007166 | Cira + 1.460; + IBACIONG -> 1230, + 1192110 + PAIN,
112685 Vettel ratio (stoichiometric) = (1346)(32) + (69.428)
0.40265 3 Ait/fuel ratio (stoichi ) 17384
8
0 29 om pe
Rs | Per cet coria = 1784 x 100 [HOE] Ane
|
1
|
nn — A > —
Rein Sytem TI
Amount of theoretical ai require per kg of fuel
2678x100
1.64 ke
2
Soiehiometeaivfcirao = Ans.
Since 25% encess ai is supplied, the actual quantity of ai supplied per kg of fuel
= LGA x 1.25 = 1455 ke
‘The combustion products will be
CO, =3.153 kg
> HO = 0450 kg.
SO, = 00010 kg
(gin excess air = 0.23 x 0.25 x 11.64 = 0.6693 kg,
Nainair = 0.77 1.25 x 11.64 = 11.2035 kg
pin fuel = 0.065 kg
Total Np in exhaust = 11.2035 + 0.065
1.2685 kg,
Omiting the wet gases, water vapour and SO, which ace condensed, Ihe products of combustion
Of dey gases will contain only CO; Na, and Oz.
CO, = 3.1530 kg
Na = 11.2685 kg
0 = 0.6693 kg
‘Toa weight = 15.0908 kg
Percentage composition by weight:
DEL]
AGE
Ans.
KA
Volumetric analysis of dry products:
09716 10911
ra [1448]
040245 „409
ae 130%] | Ans.
0.0209 , 100 IE]
Dans, *100-[428]
A tydrocatbon fel asthe following composition of dry products of combus-
by volume:
CO,=12%, CO=05%, 0=4%, and the rest Np
Determine th iefüel ratio the per cen theoretical air and the percentage composition of fuel on
a mass basis,
Solution: The combustion equation of an unknown hydrocarbon fuel can be wetten as
Cab, +20, + yNy=> 1200, + 0.5CO + 40; + 83.50 + BHO
Cane: "me 12405-0123
Nybalance: y=83S y=3.76x + 376 “222!
ose: 2221 212408 4492
gone
Bitar Ped 1192
mens
‘The combustion equation becomes.
CizsHas y + 22.210; + 83.50, > 12CO, + 0.5CO + 40) + 83.5N + 11.9240
sive rio = 222062483909 „ 204872 =
orar) Tras Le) A
Proportionate moles of: ‘The stoichiometric combustion equation is
cos» EI = 007166 | Cira + 1.460; + IBACIONG -> 1230, + 1192110 + PAIN,
112685 Vettel ratio (stoichiometric) = (1346)(32) + (69.428)
0.40265 3 Ait/fuel ratio (stoichi ) 17384
8
0 29 om pe
Rs | Per cet coria = 1784 x 100 [HOE] Ane
|
1
|
nn — A > —
72 finterence 0 neral Combunien Engines
encino Syteme_73
uel composition:
c
=0363 =[86.3%]
o1s7=[T37%_)
A sparkcigniion engine feel has a composition of 86% carbon and 14% hyéro-
en by weight, The engines supplied with fuel having equivalence rato of 1.25. Assuming that
all he hydrogen is burt and thar the carbon burns o carbon monoxide and carbon dioxide so that
there is no fee carbon lft, calculate the percentage analysis of dry exhaust gases by volume.
Solution: The fuel can be represented by a general formula C,H,- The molecular weight ofthe
fuel = m+n
H
EXAMPLE
12m
Faction of C= 22 086
or 12m = 1032n + 0860
o. 1.6m = 086n
2 096
ni
d
I
>
>
>
>
>
)
)
>
)
4
}
>
>
> ‘ge rent crois of xh q eur, ee, the pro formal
asin ais SR ae
) For complete combustion,
>
}
>
)
)
>
>
>
>
3
)
>
)
Clin + 1480; #5595N4 CO + 2210. 5958,
Euler, 92125
¿E
ors
i means 80% ais supplied in comparison to steichiomatrie ai.
‘The chemical equation becomes
Relative seve ratio, A=
=08
Hip + (1.4880, + 5395N (0.9) > x00 + (1 - CO; + 0.976540 + 4.476N;
By oxygen balance,
000 Fra E
x= 05957
CH, 9s + 1190803 + 4.476N => 0.5957CO + 0.4043C0, + 09768410 + 44768,
‘Total number of moles of ry exhaust gas
15957 + 04043 + 4476 = 5.476
Volumetic analysis of dey products of combustion:
0.5957,
co= S595 100 = [108%
0.4043 190 - ns.
co, = 4498 x 100=[738B] } Ans.
4.476
Ne = $8 100 = [51748
Alternative Solution: Proporionate formula forthe fuel
m= 086, n= 1.68
CyB + FO #3767, Ni > m CO + À HO +3:761,No
Yes the chemically contest moles of O for complete combustion of fel
de ems 086» 168 086+042= 128
Colis
By Opbalance:
CH + Von + 376 > CO + BHO + 3.76% ada
Ya she minimum number of moles of O, 10 convert all hydrogen to HO and all carbon o CO.
286, 188 anna
Bquivaiencernio, 9= 1.25
Relaiveairfuelratio, A: 08
15
lt means 80% airis supplied in comparison to stoichiometric ar.
Therefore, moles of oygen acmlly suppied Y = 08%.
Estas gas analysis of y produ:
Number of moles of CO = 2(¥ee - ¥) = 2(128 - 1.024)
se
Number of moles of Ny
‘Total number of moles of dry products
encino Syteme_73
uel composition:
c
=0363 =[86.3%]
o1s7=[T37%_)
A sparkcigniion engine feel has a composition of 86% carbon and 14% hyéro-
en by weight, The engines supplied with fuel having equivalence rato of 1.25. Assuming that
all he hydrogen is burt and thar the carbon burns o carbon monoxide and carbon dioxide so that
there is no fee carbon lft, calculate the percentage analysis of dry exhaust gases by volume.
Solution: The fuel can be represented by a general formula C,H,- The molecular weight ofthe
fuel = m+n
H
EXAMPLE
12m
Faction of C= 22 086
or 12m = 1032n + 0860
o. 1.6m = 086n
2 096
ni
d
I
>
>
>
>
>
)
)
>
)
4
}
>
>
> ‘ge rent crois of xh q eur, ee, the pro formal
asin ais SR ae
) For complete combustion,
>
}
>
)
)
>
>
>
>
3
)
>
)
Clin + 1480; #5595N4 CO + 2210. 5958,
Euler, 92125
¿E
ors
i means 80% ais supplied in comparison to steichiomatrie ai.
‘The chemical equation becomes
Relative seve ratio, A=
=08
Hip + (1.4880, + 5395N (0.9) > x00 + (1 - CO; + 0.976540 + 4.476N;
By oxygen balance,
000 Fra E
x= 05957
CH, 9s + 1190803 + 4.476N => 0.5957CO + 0.4043C0, + 09768410 + 44768,
‘Total number of moles of ry exhaust gas
15957 + 04043 + 4476 = 5.476
Volumetic analysis of dey products of combustion:
0.5957,
co= S595 100 = [108%
0.4043 190 - ns.
co, = 4498 x 100=[738B] } Ans.
4.476
Ne = $8 100 = [51748
Alternative Solution: Proporionate formula forthe fuel
m= 086, n= 1.68
CyB + FO #3767, Ni > m CO + À HO +3:761,No
Yes the chemically contest moles of O for complete combustion of fel
de ems 086» 168 086+042= 128
Colis
By Opbalance:
CH + Von + 376 > CO + BHO + 3.76% ada
Ya she minimum number of moles of O, 10 convert all hydrogen to HO and all carbon o CO.
286, 188 anna
Bquivaiencernio, 9= 1.25
Relaiveairfuelratio, A: 08
15
lt means 80% airis supplied in comparison to stoichiometric ar.
Therefore, moles of oygen acmlly suppied Y = 08%.
Estas gas analysis of y produ:
Number of moles of CO = 2(¥ee - ¥) = 2(128 - 1.024)
se
Number of moles of Ny
‘Total number of moles of dry products
74_Fondamentas of Inarma! Comburdon Engines
Reactive Spee
Percentage analysis by volume,
0512
BER:
0348, 100. ne
00, = S348 x 100 Ans.
a
Na = 388 100 = [81748
25 ENTHALPY OF FORMATION
In dealing with the thermodynamic properies of a fixed chemical composition, tables were
developed desrbing the properties of he sabsarecs. I each af ese ables he émane
roperies ae given relative 1 some arbitrary datum. ln th seam lables, for champ he
Estay of stated Haid water a 0°C i assume tobe er, This procedure qui deus
‘when o change in compostons i invelved, because we are concemed with he change in
the properties of a given substance, However, this Prosdur 1 nor adequate when desing
wi a chemical reaction, because of composition changes dig the proven, To avoue tg
icy, the ethalp of al element some? tobe er tan ira fees state
Entelpy of formation Bis the enthalpy of reaction for the formation ofa suban fom is
lees in ber most stable forms tan arbitrary reference sat of 29°C and 1 am, By able
forms of elemens, we mean fons such a Hy, O, for hydrogen and oxygen instead of Ht snd O.
‘The sable form of carbon i apie instead of diamond. The enthalpy of formation of any
element in is most sable form a an subia reference ste of 25% an tam ke a zur,
‘The station of aba ssigning the Vale of zr tothe enthalpy of elements a 25°C and
Y atm, ests on the fet ha in the absence of clear reactions the mass of ech element ft
conserve in a chemical reaction. No cons aise with this choice of ference state a
proves 1 be very conveni in stodying the chemical reactions fom à demande ot of
The enthalpy of formation i denoted by, where the superscil refers 1 the standard
pressure. The bar over h represents the mola ently ie the ebay pr unt mle
Conside a steady-state combustion proces in which | mole of CO) la forme from its
ments of 1 wole of C and 1 mole of Oya th ference sie of 25°C and 1 am Heat
transfered, so the CO, Fly exit at the reference sate. The encom equation ea be weten ae
C+0,-+ C0, (15)
Let Abe the total enthalpy ofall the resctants and Hp be the total enthalpy of al eh products. ©
is the heat transfer required to carry out the reaction. The first law of thermodynamics for this
process, having no work transfer and no kinetic energy change is
Or Ha = Hp 016
For the reaction Eg. (3.15) the enthalpy of all the eeactants is zero, since they are al elements,
hence He
- 393.52 Mol em
Heat transfer Q has been carefully measured and found to be 193.52 MI/Kmol. Actually the
enthalpy of formation is usually found by the application of statistical thermodynamics, using the
‘observe spectroscopic data. The negative sign indicates that hear sliberated in the Formation of
{CO from its elements. Therefore, the enhalpy of formation of CO, atthe standard state of 25°C
and 1 at is 393.52 MI/kmoL. That is,
Feo, == 393.52 Mikmol 619
The negative sign forthe enthalpy of formation is due 1 the reaction being exathemie. The
enthalpy of reactants is zero at 25°C and Y se, Therefore, the enthalpy of CO, at 25°C and tm,
must be negative
‘Table 32 lists the enthalpy of formation or several diferent substances at 25°C and 1 atm.
pressure, in front of the formula, g and ! within parntheses represent the gaseous and liquid state
respectively
Table32_ Enthalpy of formation at 25°C and 1 atm.
Subriance Formula Wf QUO) Substance Formula AOA
Carbon monoxide CON) -1052 Cetane Cu
Carbon dioside CO) 29352 Acetiene Cattle) aa
Water MOD 58 Eitene Ca) ‚on
Vater HO@ “MA? Propyiene ca) +0
Methane chute) HAS) Benzene Cas) 45298
Ethane CH) 8868 Methanol HONG) =201.17
Propane D-10085 Methanol CHOND 23838
Botane Cl 12622 Ethanol CLOUS) 20845
Ihootane Cu) 241 Ethanol GO -293
Isooctane CH -2928 Armonia Sn pr
Octane Cu) 20858 Hydraine Nas) +9541
Online Cu 2010 Hlyérogen peroxide HO) IN
Dodecane Culte) 29097
36 FIRST LAW ANALYSIS FOR STEADY-STATE
REACTING SYSTEMS
The steady-state combustion process will transfer heat and may produce work. An energy bal
ance would give
Qe Ma = We Ho
« 0+ añ = ws Dini,
‘The enthalpies of formation may be used inthis analysis since they are al relative tothe same
reference base.
019
Reactive Spee
Percentage analysis by volume,
0512
BER:
0348, 100. ne
00, = S348 x 100 Ans.
a
Na = 388 100 = [81748
25 ENTHALPY OF FORMATION
In dealing with the thermodynamic properies of a fixed chemical composition, tables were
developed desrbing the properties of he sabsarecs. I each af ese ables he émane
roperies ae given relative 1 some arbitrary datum. ln th seam lables, for champ he
Estay of stated Haid water a 0°C i assume tobe er, This procedure qui deus
‘when o change in compostons i invelved, because we are concemed with he change in
the properties of a given substance, However, this Prosdur 1 nor adequate when desing
wi a chemical reaction, because of composition changes dig the proven, To avoue tg
icy, the ethalp of al element some? tobe er tan ira fees state
Entelpy of formation Bis the enthalpy of reaction for the formation ofa suban fom is
lees in ber most stable forms tan arbitrary reference sat of 29°C and 1 am, By able
forms of elemens, we mean fons such a Hy, O, for hydrogen and oxygen instead of Ht snd O.
‘The sable form of carbon i apie instead of diamond. The enthalpy of formation of any
element in is most sable form a an subia reference ste of 25% an tam ke a zur,
‘The station of aba ssigning the Vale of zr tothe enthalpy of elements a 25°C and
Y atm, ests on the fet ha in the absence of clear reactions the mass of ech element ft
conserve in a chemical reaction. No cons aise with this choice of ference state a
proves 1 be very conveni in stodying the chemical reactions fom à demande ot of
The enthalpy of formation i denoted by, where the superscil refers 1 the standard
pressure. The bar over h represents the mola ently ie the ebay pr unt mle
Conside a steady-state combustion proces in which | mole of CO) la forme from its
ments of 1 wole of C and 1 mole of Oya th ference sie of 25°C and 1 am Heat
transfered, so the CO, Fly exit at the reference sate. The encom equation ea be weten ae
C+0,-+ C0, (15)
Let Abe the total enthalpy ofall the resctants and Hp be the total enthalpy of al eh products. ©
is the heat transfer required to carry out the reaction. The first law of thermodynamics for this
process, having no work transfer and no kinetic energy change is
Or Ha = Hp 016
For the reaction Eg. (3.15) the enthalpy of all the eeactants is zero, since they are al elements,
hence He
- 393.52 Mol em
Heat transfer Q has been carefully measured and found to be 193.52 MI/Kmol. Actually the
enthalpy of formation is usually found by the application of statistical thermodynamics, using the
‘observe spectroscopic data. The negative sign indicates that hear sliberated in the Formation of
{CO from its elements. Therefore, the enhalpy of formation of CO, atthe standard state of 25°C
and 1 at is 393.52 MI/kmoL. That is,
Feo, == 393.52 Mikmol 619
The negative sign forthe enthalpy of formation is due 1 the reaction being exathemie. The
enthalpy of reactants is zero at 25°C and Y se, Therefore, the enthalpy of CO, at 25°C and tm,
must be negative
‘Table 32 lists the enthalpy of formation or several diferent substances at 25°C and 1 atm.
pressure, in front of the formula, g and ! within parntheses represent the gaseous and liquid state
respectively
Table32_ Enthalpy of formation at 25°C and 1 atm.
Subriance Formula Wf QUO) Substance Formula AOA
Carbon monoxide CON) -1052 Cetane Cu
Carbon dioside CO) 29352 Acetiene Cattle) aa
Water MOD 58 Eitene Ca) ‚on
Vater HO@ “MA? Propyiene ca) +0
Methane chute) HAS) Benzene Cas) 45298
Ethane CH) 8868 Methanol HONG) =201.17
Propane D-10085 Methanol CHOND 23838
Botane Cl 12622 Ethanol CLOUS) 20845
Ihootane Cu) 241 Ethanol GO -293
Isooctane CH -2928 Armonia Sn pr
Octane Cu) 20858 Hydraine Nas) +9541
Online Cu 2010 Hlyérogen peroxide HO) IN
Dodecane Culte) 29097
36 FIRST LAW ANALYSIS FOR STEADY-STATE
REACTING SYSTEMS
The steady-state combustion process will transfer heat and may produce work. An energy bal
ance would give
Qe Ma = We Ho
« 0+ añ = ws Dini,
‘The enthalpies of formation may be used inthis analysis since they are al relative tothe same
reference base.
019
16 Fundumanı of Inara! Combustion Engines
Reactive Spreng 77
Table 2.3 Change inenthalpy (R°— ii) between the reference stale and the actual stale or
different substances (Miri)
Temp. T0 © EN EN] N 5;
o 38 Fa 990 305 EI
100 Sm 6156 5615 sm Sm
20 “2355 ais 3280 288 2066
E 0000 000 0000 0000 oo
xo ast ost 1068 oss ost
w 2075 RTS 3452 zum 309
so 5909 as 6520 son 88
ao 8341 12916 10498 u 327
mo 12021 ms 1104 1195 12m
wo oz mr 15036. 1550
0 18397 on ass lent 19246
1000 2686 sas 25078 21260 2m
1100 250 Er 30367 24757 26217
‘200 2m aa 76 2108 Er
1500 sus 50158 Ben 31501 ss
1400 35258 55907 Ba 34936 16966
150 E] eins 805 ‘3840s so
100 am os sus ‘1903 u
‚mo 45900 Ta E73 45230 097
1800 4952 mar a am Er
1900, Er 3529 Ge ss sa
2000 so 91450 765 Em 2
2100 ass 97300 mas sous 673
zu 6019 103575 sé an am
230 sis 106 ws am Ts
2400 30 15.788 Er mass nm
290 75003 mins 98964 Aa as
200 ma 08s 01370 nos am
zu 2408 14286 sis 81659 sa
2300 3615 vase 13294 sus ua
2900 39326 as. ras sou saint
3000 93.582 152862 125361 9278 0098
5200 100998 165351 131553 100161 106.127
3400 108409 meo 108354 100.008. mes
3600 115976 150205 160207 sos m
3300 13495 nm mama 12570 Er
400 131038 21565 183280, 130016. 18915
220 EU zum 194905 176 19724
40 146107 ET) 206585, 115103 1508
460 15374 ame ass 12699 164006
430 161322 266500 zo 160272 msn
3000 168929 219255, 241997 167858, 150987
In most ofthe cases, the reactants andthe products are no at the reference condón of 25°C
and I atm, In these cases the property change between the reference sue andthe actual state
{post be accounted fo. Table 33 shows the change in enthalpy between the reference state and
the otal sat, de. A The temperature 298 K isthe temperature ofthe reference sae
‘The soperscrpt denotes that he pressure is 1 am. If these ablated values ae nt availble,
then he deal gas aw, A = 5,7, can be used
‘The first sw fora steady-state, steady-flow reaction may now be writen as
+ Ep + i li WY nlp HE), 620)
“The pressure effect is very small and need not be included.
Gaseous propane (Cyl) undergoes a steady-state, steady-flow reaction with
smospheric air. Determine the heat transfer per mole of fuel when the reactats and products are
both at 25°C and À alm, pressure,
Solution: The combustion equation can be weten as
CH + 50, + 50.708, => 3CO, + 41,00) + 18.8
At 25°C, HO will bein the liquid state
‘The First law, with no work being done inthe control volume is
EE Enr
Since the enthalpy of al the elements at25*C and I ar is zero, he summation terms contain
‘only the enthalpies of formation forthe compounds. Using Table 32,
Dak = ea, «103.85 Mikmol
and LA co, +4 yom = 39952) + 42853)
22287 Mol
2- Ya -Yh
7 F
2219.85 Miño! fuel
CASSER] Ans.
‘The gaseous fuel Cy, and the ar enter the diesel engine at 29°C. The prod-
cts of combustion leave at 600 K, and 200% theoretical airs used, The heat loss from the engine
is 93 MI/Kmol fuel. Determine the work for a fuel rte of 1 kmolh.
2323.7 + 10385
Reactive Spreng 77
Table 2.3 Change inenthalpy (R°— ii) between the reference stale and the actual stale or
different substances (Miri)
Temp. T0 © EN EN] N 5;
o 38 Fa 990 305 EI
100 Sm 6156 5615 sm Sm
20 “2355 ais 3280 288 2066
E 0000 000 0000 0000 oo
xo ast ost 1068 oss ost
w 2075 RTS 3452 zum 309
so 5909 as 6520 son 88
ao 8341 12916 10498 u 327
mo 12021 ms 1104 1195 12m
wo oz mr 15036. 1550
0 18397 on ass lent 19246
1000 2686 sas 25078 21260 2m
1100 250 Er 30367 24757 26217
‘200 2m aa 76 2108 Er
1500 sus 50158 Ben 31501 ss
1400 35258 55907 Ba 34936 16966
150 E] eins 805 ‘3840s so
100 am os sus ‘1903 u
‚mo 45900 Ta E73 45230 097
1800 4952 mar a am Er
1900, Er 3529 Ge ss sa
2000 so 91450 765 Em 2
2100 ass 97300 mas sous 673
zu 6019 103575 sé an am
230 sis 106 ws am Ts
2400 30 15.788 Er mass nm
290 75003 mins 98964 Aa as
200 ma 08s 01370 nos am
zu 2408 14286 sis 81659 sa
2300 3615 vase 13294 sus ua
2900 39326 as. ras sou saint
3000 93.582 152862 125361 9278 0098
5200 100998 165351 131553 100161 106.127
3400 108409 meo 108354 100.008. mes
3600 115976 150205 160207 sos m
3300 13495 nm mama 12570 Er
400 131038 21565 183280, 130016. 18915
220 EU zum 194905 176 19724
40 146107 ET) 206585, 115103 1508
460 15374 ame ass 12699 164006
430 161322 266500 zo 160272 msn
3000 168929 219255, 241997 167858, 150987
In most ofthe cases, the reactants andthe products are no at the reference condón of 25°C
and I atm, In these cases the property change between the reference sue andthe actual state
{post be accounted fo. Table 33 shows the change in enthalpy between the reference state and
the otal sat, de. A The temperature 298 K isthe temperature ofthe reference sae
‘The soperscrpt denotes that he pressure is 1 am. If these ablated values ae nt availble,
then he deal gas aw, A = 5,7, can be used
‘The first sw fora steady-state, steady-flow reaction may now be writen as
+ Ep + i li WY nlp HE), 620)
“The pressure effect is very small and need not be included.
Gaseous propane (Cyl) undergoes a steady-state, steady-flow reaction with
smospheric air. Determine the heat transfer per mole of fuel when the reactats and products are
both at 25°C and À alm, pressure,
Solution: The combustion equation can be weten as
CH + 50, + 50.708, => 3CO, + 41,00) + 18.8
At 25°C, HO will bein the liquid state
‘The First law, with no work being done inthe control volume is
EE Enr
Since the enthalpy of al the elements at25*C and I ar is zero, he summation terms contain
‘only the enthalpies of formation forthe compounds. Using Table 32,
Dak = ea, «103.85 Mikmol
and LA co, +4 yom = 39952) + 42853)
22287 Mol
2- Ya -Yh
7 F
2219.85 Miño! fuel
CASSER] Ans.
‘The gaseous fuel Cy, and the ar enter the diesel engine at 29°C. The prod-
cts of combustion leave at 600 K, and 200% theoretical airs used, The heat loss from the engine
is 93 MI/Kmol fuel. Determine the work for a fuel rte of 1 kmolh.
2323.7 + 10385
TB fandamenats of etre! Combustion Enga
Reactive Spams 79
Solution: The combustion equation can be written as
Chaos) + 2018.90; + 2(18.5)3.76)Ny — 12C0, + 13H,0 + 18.50, + 139.12,
FO at 600 K and at standard pressure will be in gaseous state
‘The first law for open system can be writen as
Fgh = We E + Fen,
O =-93 Memo fuel (given)
‘The negative sign indicates heat Joss from the system.
Using Tables 32 and 33,
Emir
ad AA,
29097 Mike
RR Flo, + 13TH? +0 Ba o
ISA) Falo, HZ,
(239352 + 12916) + 13¢-261.82 + 10.498)
+ 18:50 + 9.247) + 139120 + 8891)
== 4567-3007 + 17141237
=-6166 Memol = Hp
O+ Hy = We Hy
or 9329097 = W- 6166
W = 5782 Mol fuel
W =, W= 15782) « 5782 M
where iy kom
META
3600
w
TOS GR] Ans.
produces 600 kW of power and uses isooctane Coya as a fuel at
25°C; 150% theoretical air is used and te ar enters a 400 K. The products of combustion lave
at 700 K. The heat loss from the engine is 150 KW. Determine the fuel consumption for complete
‘combustion,
Solution: The combustion equation canbe writen as
Cathy + 1.512905 + LIN TON = ECO, + HO + 6250; + 705%,
Using Tables 32 and 33,
Hae Emi
= 259.28 + 96.79 à 209.46 = 697 Mirko! ue
Figg = 1259.28) + (1.5)(12.5).029) + 70.502.971)
En +A, = 038882 + 17761) + 9624182 + 14.180
+ 625(12.502) + 70.501.937)
3005: + (-2048.5) + 78.1 + 841.6
4134.7 Mol vel
4134.7 ~ 697 = - 4141.67 Mme fuel
‘The fis law for open system can be writen as
Mp = Hy
de iytty = Weite
or D = tp ~My)
G-W _ 150-600
or ñ ER mo
CET TETE PTT)
150x 3600
- = 0.6519 kmol/n
MALE
Molecular weight of fuel = (1298) + 18 = 114
fig My= 0.6519 x 114 = [HSE] Ans.
my
DESIRE A mixture of propane and oxygen, in the proper rato, fr che complete com-
bustion and at 25°C and 1 atm. reais In a constant volume bomb calorimeter. Heat i tranfered
uni the products of combustion are at 400 K, Determine the heat transfer per mole of propane
Solution: The combustion equation can be written as
CH + 50; > 300, + 41,0
‘The First law for closed system, V = constant, can be weiten as
Zn
Now, Ug= Yon = Dntht+ FR Rr
[103.85 + 0 - 8.314 x 10” x 298] + SO + 0 ~ 8.314 x 107 x 298]
= 10623 - 12.39 = 118.2 Memo fal
and Up= nn, = Eh) EN,
=3(-393.52 + 4,008 - 8.314 x 10? x 400) + 4(-241.82 + 3.452 - 8.314 x 10 x 400)
= 11784 ~ 9667 = 21451 Momo fel
Ug ~21451 à 11872 =~ 20264 Mimo fue
|
|
Reactive Spams 79
Solution: The combustion equation can be written as
Chaos) + 2018.90; + 2(18.5)3.76)Ny — 12C0, + 13H,0 + 18.50, + 139.12,
FO at 600 K and at standard pressure will be in gaseous state
‘The first law for open system can be writen as
Fgh = We E + Fen,
O =-93 Memo fuel (given)
‘The negative sign indicates heat Joss from the system.
Using Tables 32 and 33,
Emir
ad AA,
29097 Mike
RR Flo, + 13TH? +0 Ba o
ISA) Falo, HZ,
(239352 + 12916) + 13¢-261.82 + 10.498)
+ 18:50 + 9.247) + 139120 + 8891)
== 4567-3007 + 17141237
=-6166 Memol = Hp
O+ Hy = We Hy
or 9329097 = W- 6166
W = 5782 Mol fuel
W =, W= 15782) « 5782 M
where iy kom
META
3600
w
TOS GR] Ans.
produces 600 kW of power and uses isooctane Coya as a fuel at
25°C; 150% theoretical air is used and te ar enters a 400 K. The products of combustion lave
at 700 K. The heat loss from the engine is 150 KW. Determine the fuel consumption for complete
‘combustion,
Solution: The combustion equation canbe writen as
Cathy + 1.512905 + LIN TON = ECO, + HO + 6250; + 705%,
Using Tables 32 and 33,
Hae Emi
= 259.28 + 96.79 à 209.46 = 697 Mirko! ue
Figg = 1259.28) + (1.5)(12.5).029) + 70.502.971)
En +A, = 038882 + 17761) + 9624182 + 14.180
+ 625(12.502) + 70.501.937)
3005: + (-2048.5) + 78.1 + 841.6
4134.7 Mol vel
4134.7 ~ 697 = - 4141.67 Mme fuel
‘The fis law for open system can be writen as
Mp = Hy
de iytty = Weite
or D = tp ~My)
G-W _ 150-600
or ñ ER mo
CET TETE PTT)
150x 3600
- = 0.6519 kmol/n
MALE
Molecular weight of fuel = (1298) + 18 = 114
fig My= 0.6519 x 114 = [HSE] Ans.
my
DESIRE A mixture of propane and oxygen, in the proper rato, fr che complete com-
bustion and at 25°C and 1 atm. reais In a constant volume bomb calorimeter. Heat i tranfered
uni the products of combustion are at 400 K, Determine the heat transfer per mole of propane
Solution: The combustion equation can be written as
CH + 50; > 300, + 41,0
‘The First law for closed system, V = constant, can be weiten as
Zn
Now, Ug= Yon = Dntht+ FR Rr
[103.85 + 0 - 8.314 x 10” x 298] + SO + 0 ~ 8.314 x 107 x 298]
= 10623 - 12.39 = 118.2 Memo fal
and Up= nn, = Eh) EN,
=3(-393.52 + 4,008 - 8.314 x 10? x 400) + 4(-241.82 + 3.452 - 8.314 x 10 x 400)
= 11784 ~ 9667 = 21451 Momo fel
Ug ~21451 à 11872 =~ 20264 Mimo fue
|
|
30, Fuedarenals of nera! Combustion Engines
Reactive Stems BI
“The negative sign indices that heat is iberted andthe reaction is exothermic
Heatiberated = 2026.4 MIMkzno propane
= [AO propane] Ans.
3.7. ENTHALPY OF COMBUSTION, INTERNAL ENERGY OF
COMBUSTION AND HEATING VALUES
“The enthalpy of combustion AH is the difference between the enthalpy of products and the en-
thalpy of the reactants when complete combustion of unit quantity of fuel occurs at à given
temperature and pressure,
aH
au = Yoni od
in Hy
= Diy + Rh 62)
“The standard values of enthalpy of combustion AR? of vaious fuels ata temperature of 25°C
and pressure of } at. are given in Table 3.4
‘Table 34 Enthalpy ot vaporization fj, and enthalpy of combustion AA? at 25°C and 1 alm.
Fuel DE] TEN
ion) Ola
Hydrogen, Rx) - ET 106
carbon, CG) - 209582 3955
‘Carbon monoxide, CO) - Saas Es
‘Methane, CHa) - 890303 “ao
Acetylene, CHE) - =1255680 1255680
Eine, Cid) - 1411200 aaa
Fre, Cle) son “1560690 Br
Propane, Ce) ed 1020 72033290
Butane, CH) 21066 caen 2657690
rPetane, Calla) zum 3550 290060
rene, Cu) a2 4195050 Casse
Hear, Cul) xs “asso 4801820
-Octare, CH) sa =3311900 soo
Osta, Cy as seo, 01500
Benzene, Cle? ao 3301680, nee
Meihanol, CHOW) am Er
Methaeol, CHOW) 3950 nom
Eitapol, CHO) 2360 1009584.
Etanol, HOM) as “1367004
Hydnzin, NHC ao
auution (3.21) ce also be writen as
a= (Sat Zu) Sth, Ent
or an = ako Sn
mi End
view ak = Dai Lele 02
Hd:
am)
Equation (323) suggests that standard enthalpy of combustion can be obtained with the help of
ceathalpes of formation.
Take an example of methane, CH, The combustion equation for methane can be written as
CH, 420; + CO, 4 2,00
Mo, Bio, +0 ges" Pet Hig
(2398.52) + 262853) - (19-7487)
= 890.25 Mikmol
“This value of AR? for methane, when HO in the product is liquid, almost matches with the
corresponding value given in Table 34.
The intemal energy of combustion, AU, is the difference between the internal energy of
products andthe intemal energy ofthe reactants, when complete combustion of unit quantity of
fuel occurs ata given temperature and volume. That i,
AU = Ur Un = (= pr IH = PV
BU = Sn Br — 97), - Yom 7 += Ra) pol, 629
all he products and reactants are gases,
80 Dr th +? Fe) Dn +e 629
Equations (32) and 0.29) give the elation between AH and AU ie.
suau-Rr(En- En)
or AH = AU + AnRT 6.26)
where n= Y - En 6m
Fr +
Reactive Stems BI
“The negative sign indices that heat is iberted andthe reaction is exothermic
Heatiberated = 2026.4 MIMkzno propane
= [AO propane] Ans.
3.7. ENTHALPY OF COMBUSTION, INTERNAL ENERGY OF
COMBUSTION AND HEATING VALUES
“The enthalpy of combustion AH is the difference between the enthalpy of products and the en-
thalpy of the reactants when complete combustion of unit quantity of fuel occurs at à given
temperature and pressure,
aH
au = Yoni od
in Hy
= Diy + Rh 62)
“The standard values of enthalpy of combustion AR? of vaious fuels ata temperature of 25°C
and pressure of } at. are given in Table 3.4
‘Table 34 Enthalpy ot vaporization fj, and enthalpy of combustion AA? at 25°C and 1 alm.
Fuel DE] TEN
ion) Ola
Hydrogen, Rx) - ET 106
carbon, CG) - 209582 3955
‘Carbon monoxide, CO) - Saas Es
‘Methane, CHa) - 890303 “ao
Acetylene, CHE) - =1255680 1255680
Eine, Cid) - 1411200 aaa
Fre, Cle) son “1560690 Br
Propane, Ce) ed 1020 72033290
Butane, CH) 21066 caen 2657690
rPetane, Calla) zum 3550 290060
rene, Cu) a2 4195050 Casse
Hear, Cul) xs “asso 4801820
-Octare, CH) sa =3311900 soo
Osta, Cy as seo, 01500
Benzene, Cle? ao 3301680, nee
Meihanol, CHOW) am Er
Methaeol, CHOW) 3950 nom
Eitapol, CHO) 2360 1009584.
Etanol, HOM) as “1367004
Hydnzin, NHC ao
auution (3.21) ce also be writen as
a= (Sat Zu) Sth, Ent
or an = ako Sn
mi End
view ak = Dai Lele 02
Hd:
am)
Equation (323) suggests that standard enthalpy of combustion can be obtained with the help of
ceathalpes of formation.
Take an example of methane, CH, The combustion equation for methane can be written as
CH, 420; + CO, 4 2,00
Mo, Bio, +0 ges" Pet Hig
(2398.52) + 262853) - (19-7487)
= 890.25 Mikmol
“This value of AR? for methane, when HO in the product is liquid, almost matches with the
corresponding value given in Table 34.
The intemal energy of combustion, AU, is the difference between the internal energy of
products andthe intemal energy ofthe reactants, when complete combustion of unit quantity of
fuel occurs ata given temperature and volume. That i,
AU = Ur Un = (= pr IH = PV
BU = Sn Br — 97), - Yom 7 += Ra) pol, 629
all he products and reactants are gases,
80 Dr th +? Fe) Dn +e 629
Equations (32) and 0.29) give the elation between AH and AU ie.
suau-Rr(En- En)
or AH = AU + AnRT 6.26)
where n= Y - En 6m
Fr +
(82 _fundananals of Ineral Combustion Engines
[should be noted that for fuels both AH and AU are nogsive, These reactions ae exothermie
as heats liberated by combustion of fuels, and by convention the heat released is taken as negative
and the heat added as positive. AA may also be called heat of reaction at constant pressure in 2
closed system or heat of reaction in a flow process and AU as heat of reaction at constant volume
in a closed system. AH and AU are the properties ofthe fuel hey rofer specifically o chemically
correct oxygen mixtures reacting at 25°C and are measured quantities,
‘The heating value or calorific value of a fue is equal tothe enthalpy of combustion but is of
‘opposite sign. The heating valve is a positive number. There are two types of heating values,
depending on the phase of water formed in the products of combustion, The higher heating value
(HIV) is measured when al the water vapour is condensed athe reference temperature of 25°C.
If the water is in the vapour phase, the lower heating value (LHV) is measured. The relation
between the two heating values i given by
where mois the mass of water in kg formed in the combustion product per kof fel. The value
Of ha 25°C is obtained as 2442 Kg rom steam ables, The heating values ae in fg of fuel,
ET Determine the enthalpy of combustion (enthalpy of reseton) Foe
0+40,->C0; a11500K
Solution: Figure 3.1 shows the AH at 1500 K on the H-T diagram,
”
Tr TOK
Figs. Ext Tempore dar Ep 310.
AH Hp Ha
Hee Luk = E p+ ORR,
? +
Rene Sons 83
= nc + (it — Ho ico,
= hoo Uh? + (ii Fa lco + 20 thf +
(11052 + 38.848) + 0.50 + 40610)
- 31367 Mifkmol
— 331.806 + 51.367 = [ADEME] Ans.
Deter ie amount of et raster pr Kg of fos reg he compl
combustion of pope isan open sy. how system wih 308 een et, Popa one a
(OO ad ar na 2300 K ante pods eave x OR. The average molar pc et ot
propane conan pesar may Be ken a 897 IE)
‚Solution: Figure 32 shows the flow process in an open, steady-flow system.
St 400.
Cont | C0 #0: Ms, Op
volume [500K
2
Figure 2 Ope, ste om pen: range 21
Ha
The reaction equations
Cala + 1.3950, + (1N0-IÓN, — 300; + 44,01) + 24:44N) +1.50,
o. Call + 650; + 24:N; > 3CO + 41,068) + 24.44N; + 1.50
‘The value of pressure is not give, therefore, we assume ideal gas behaviour Since the products
leave at 900 K, the water will be considered in the gaseous state.
Energy balance gives, Q = Hp — Hp, where
He = Ln +0? Fy,
00, 0} + (ip A3a)lco, + 83,0 097 + to Fo.
ÓN
339952 + 28041) + 4(-241.82 + 21924)
+ 24440 + 18221) + 1500 + 19246)
=-1501.83 Mino!
y= En +0
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[should be noted that for fuels both AH and AU are nogsive, These reactions ae exothermie
as heats liberated by combustion of fuels, and by convention the heat released is taken as negative
and the heat added as positive. AA may also be called heat of reaction at constant pressure in 2
closed system or heat of reaction in a flow process and AU as heat of reaction at constant volume
in a closed system. AH and AU are the properties ofthe fuel hey rofer specifically o chemically
correct oxygen mixtures reacting at 25°C and are measured quantities,
‘The heating value or calorific value of a fue is equal tothe enthalpy of combustion but is of
‘opposite sign. The heating valve is a positive number. There are two types of heating values,
depending on the phase of water formed in the products of combustion, The higher heating value
(HIV) is measured when al the water vapour is condensed athe reference temperature of 25°C.
If the water is in the vapour phase, the lower heating value (LHV) is measured. The relation
between the two heating values i given by
where mois the mass of water in kg formed in the combustion product per kof fel. The value
Of ha 25°C is obtained as 2442 Kg rom steam ables, The heating values ae in fg of fuel,
ET Determine the enthalpy of combustion (enthalpy of reseton) Foe
0+40,->C0; a11500K
Solution: Figure 3.1 shows the AH at 1500 K on the H-T diagram,
”
Tr TOK
Figs. Ext Tempore dar Ep 310.
AH Hp Ha
Hee Luk = E p+ ORR,
? +
Rene Sons 83
= nc + (it — Ho ico,
= hoo Uh? + (ii Fa lco + 20 thf +
(11052 + 38.848) + 0.50 + 40610)
- 31367 Mifkmol
— 331.806 + 51.367 = [ADEME] Ans.
Deter ie amount of et raster pr Kg of fos reg he compl
combustion of pope isan open sy. how system wih 308 een et, Popa one a
(OO ad ar na 2300 K ante pods eave x OR. The average molar pc et ot
propane conan pesar may Be ken a 897 IE)
‚Solution: Figure 32 shows the flow process in an open, steady-flow system.
St 400.
Cont | C0 #0: Ms, Op
volume [500K
2
Figure 2 Ope, ste om pen: range 21
Ha
The reaction equations
Cala + 1.3950, + (1N0-IÓN, — 300; + 44,01) + 24:44N) +1.50,
o. Call + 650; + 24:N; > 3CO + 41,068) + 24.44N; + 1.50
‘The value of pressure is not give, therefore, we assume ideal gas behaviour Since the products
leave at 900 K, the water will be considered in the gaseous state.
Energy balance gives, Q = Hp — Hp, where
He = Ln +0? Fy,
00, 0} + (ip A3a)lco, + 83,0 097 + to Fo.
ÓN
339952 + 28041) + 4(-241.82 + 21924)
+ 24440 + 18221) + 1500 + 19246)
=-1501.83 Mino!
y= En +0
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84 _Fundomanals of nera! Combustion Engines
Reacts Spems 8
reli + ido Raat ro + Ce = Ro,
+ my Lif A,
= 1-103 85 + 00837400 298) + 6510 + 0054) + 24.440 + 0054)
9564 Mot
O=Hp- Hy
150133 + 98.64 == 140519 Mio!
110019
a
222 Mike
“The negative sign shows that heat is berated
Heat liberated = [SEMI] Aus.
"Nate: This heat liberated isnot he heat of reaction or enthalpy of reaction, asthe products are not
‘brought back othe inital temperature. Moreover, he reactants ar alo at diferent temperatures.
[ERWUVAGENFA Methane burns in the presence of 150% of theoretical air. Calculate the
standard enthalpy of combustion and the standard internal energy of combustion, when the water
in the products of combustion appears () asa liquid and (b) asa gas.
Solution: The chemical equation is
(CH + (15)(2)0, + STONE —> CO; + 2H0 + O, + 1.280
or (CH, + 30, + 112883 > CO, + 28,0 + 0; + 11280,
D Water appears as a quid
Hy Im 1? +
At standard condition,
Hs Di = Vip, sh, (For On and Na Ff =0)
393524 20-2858) =
and Has Sink = Vif, =-7487 Monel
965.12 Minko!
AW = ARS = Hp = Hy =~ 965.12 +7487
MAA] Ans.
‘This valve is approximately the same as given in Table 3.4.
Now, AU=AH-AnRT
‘
No. of moles of product = 2 ( for CO; and 1 for Oj, no. of moles of N; cancells
but rom te two sides and the no. of moles of 0
being nud eglecd)
No, of moles of eactant =4 (for CH nd 3 for 03)
Ann2-4=-2
AU = = 89025 = (208.314 10208)
= ASUMA] Ans
(9 Water appear sagas
Hp = 1439352 4 2.2412)
877.16 Min
AH = OR = He Hu 8716 4 7487
(99 Winei] Ans
‘This value of AR is approximately he same as given in Table 34.
Now, AU = AH- Aner
No, of moles of product = 4
No. of moles of reactant
(U for COs, 2 for H3O and 1 for 03)
KIIHRBENEI ‘Te lower calorific value of a liquid fuel at constant pressure is 44,000 Kg.
‘The analysis of feel by mass is 84% carbon and 16% hydrogen. Determine the higher caloriic
value at constant pressure and the lower and higher calorific values at constant volume. At 25°C,
dy for HO is 2442 kil.
Solution: ‘The combustion equations ar:
+0900;
1
and H,+}0; 9140
(0.84 kg of C produces 0:34 x E] = 3.08 k of CO, per kg of fuel,
u 016 of prods 0.16% E = Lat kg of 140 perk fe
HR), = 44,000 + 3516
= [Sica ie] Ans.
Reacts Spems 8
reli + ido Raat ro + Ce = Ro,
+ my Lif A,
= 1-103 85 + 00837400 298) + 6510 + 0054) + 24.440 + 0054)
9564 Mot
O=Hp- Hy
150133 + 98.64 == 140519 Mio!
110019
a
222 Mike
“The negative sign shows that heat is berated
Heat liberated = [SEMI] Aus.
"Nate: This heat liberated isnot he heat of reaction or enthalpy of reaction, asthe products are not
‘brought back othe inital temperature. Moreover, he reactants ar alo at diferent temperatures.
[ERWUVAGENFA Methane burns in the presence of 150% of theoretical air. Calculate the
standard enthalpy of combustion and the standard internal energy of combustion, when the water
in the products of combustion appears () asa liquid and (b) asa gas.
Solution: The chemical equation is
(CH + (15)(2)0, + STONE —> CO; + 2H0 + O, + 1.280
or (CH, + 30, + 112883 > CO, + 28,0 + 0; + 11280,
D Water appears as a quid
Hy Im 1? +
At standard condition,
Hs Di = Vip, sh, (For On and Na Ff =0)
393524 20-2858) =
and Has Sink = Vif, =-7487 Monel
965.12 Minko!
AW = ARS = Hp = Hy =~ 965.12 +7487
MAA] Ans.
‘This valve is approximately the same as given in Table 3.4.
Now, AU=AH-AnRT
‘
No. of moles of product = 2 ( for CO; and 1 for Oj, no. of moles of N; cancells
but rom te two sides and the no. of moles of 0
being nud eglecd)
No, of moles of eactant =4 (for CH nd 3 for 03)
Ann2-4=-2
AU = = 89025 = (208.314 10208)
= ASUMA] Ans
(9 Water appear sagas
Hp = 1439352 4 2.2412)
877.16 Min
AH = OR = He Hu 8716 4 7487
(99 Winei] Ans
‘This value of AR is approximately he same as given in Table 34.
Now, AU = AH- Aner
No, of moles of product = 4
No. of moles of reactant
(U for COs, 2 for H3O and 1 for 03)
KIIHRBENEI ‘Te lower calorific value of a liquid fuel at constant pressure is 44,000 Kg.
‘The analysis of feel by mass is 84% carbon and 16% hydrogen. Determine the higher caloriic
value at constant pressure and the lower and higher calorific values at constant volume. At 25°C,
dy for HO is 2442 kil.
Solution: ‘The combustion equations ar:
+0900;
1
and H,+}0; 9140
(0.84 kg of C produces 0:34 x E] = 3.08 k of CO, per kg of fuel,
u 016 of prods 0.16% E = Lat kg of 140 perk fe
HR), = 44,000 + 3516
= [Sica ie] Ans.
86 Fundament of Internal Combustion Engines
‘The combustion equation becomes,
2 16
Oster sorte std? eier hero 2081900, rate D
where HO is taken as liquid a 25°C.
or O84 kg C + 0.16 kg H, + 3.52 kg Op > 3.08 ke CO, à 144 kg HOC)
Note that mass is conserved. On both sides of reaction, the total mas is 4.52 kg. The volume
oceupiedby liquid is neligblein comparison o gases, therefore che moles of liquid H O and liquid
fuels are neglected,
No. of moles of product,
= 0.07 kote fuel
and no of motes of eacient, ne = 352 20.11 mo fuel
An =np~ m =007-0.1 =-008 kmol
AnRT =- 0.04 x 8.314 x 298 =- 99 kg fuel
aH = au + anktT
Ifthe calor vaue is denaed by CV,
~My,
or (CV), = (CV), An
GV), = (HEV), + Anker
1516-9 = [MATTER] Ans
and (UV), = LUV),+ An FT
= $4,000 - 9 = [BSTEAE A] Ans.
3.8 ADIABATIC COMBUSTION TEMPERATURE
The caen of the temperature ofthe products oF a comburtion recon s very Important
the design of intemal combustion engines, I no work, no heat transfer, no change in potenti
energy and kinetic energy occur, then all the thermal energy goes to als the temperature ofthe
products of combustion. When the combustion is complet, the maximum amount of chemical
{energy is converted into heat energy and the temperature of the products reaches its maximum.
‘We cam use this temperature a the upper limit forthe actual combustion temperature and then this
temperature i called the maximum adiabatic combustion or Name temperature.
TE the combustion is incomplete or exces air is used, the temperature of the products of
‘combustion will be les than the maximum adiabaie combustion temperature. Incomplete com
‘bustion resrct the conversion of al he chemical energy into thermal energy and excess ir will
Have cooling effect, hence the temperate willbe lower than Ihe maximum temperature in both
Route Syrems_ 87
the cases. Dissociation of the combustion products at high temperature also reduces the fame
temperature.
‘The adiabatic ame temperature can be calculated as flows:
Consider a stedy-flow adiabatic combustion reaction in which there is no work transfer,
[Neglecting the changes in potential energy and kinetic energy and applying the fsa of thermo.
dynamics,
Q= Hp =Ha
As ie process is adiabatic, © = 0,
5 Hp~Hg=0
or Hs
Lett + GR, = Dates GE, G28)
Figure 3.3 shows the process on A-T diagram for steady-low adiabatic combustion.
gue Sad fon fotaccorbson
In a closed system for constant pressure process, the adiabatic flame temperature can be
obtained from Hp = Hg and for a constant volume process it can be obtained from Up = U,
A trialand-eror method can be used to obtain adiabatic Mame temperature. Initially, some
Product temperature is guessed and then the validity of Eq, (3.28) is checked. If this equation is
ot satisfied, a new value of temperature is guessed. When Eq, (3.28) is sisi, the guessed
temperature isthe adiabatic Name temperature.
‘A computer program using the Newion-Raphson iteration technique can also be used 10
brain the adiabatie flame temperature.
[EIERIIZABEREN Gaseous propane is bumed with 100 per cet excess air Determine the
‘ale flame temperature for steady-flow process.
Solution: The combustion equation with 100% excess ai is
CH + 2090, + ASNB-TON, => 300; + 4HO 4 50, + 37.6
|
‘The combustion equation becomes,
2 16
Oster sorte std? eier hero 2081900, rate D
where HO is taken as liquid a 25°C.
or O84 kg C + 0.16 kg H, + 3.52 kg Op > 3.08 ke CO, à 144 kg HOC)
Note that mass is conserved. On both sides of reaction, the total mas is 4.52 kg. The volume
oceupiedby liquid is neligblein comparison o gases, therefore che moles of liquid H O and liquid
fuels are neglected,
No. of moles of product,
= 0.07 kote fuel
and no of motes of eacient, ne = 352 20.11 mo fuel
An =np~ m =007-0.1 =-008 kmol
AnRT =- 0.04 x 8.314 x 298 =- 99 kg fuel
aH = au + anktT
Ifthe calor vaue is denaed by CV,
~My,
or (CV), = (CV), An
GV), = (HEV), + Anker
1516-9 = [MATTER] Ans
and (UV), = LUV),+ An FT
= $4,000 - 9 = [BSTEAE A] Ans.
3.8 ADIABATIC COMBUSTION TEMPERATURE
The caen of the temperature ofthe products oF a comburtion recon s very Important
the design of intemal combustion engines, I no work, no heat transfer, no change in potenti
energy and kinetic energy occur, then all the thermal energy goes to als the temperature ofthe
products of combustion. When the combustion is complet, the maximum amount of chemical
{energy is converted into heat energy and the temperature of the products reaches its maximum.
‘We cam use this temperature a the upper limit forthe actual combustion temperature and then this
temperature i called the maximum adiabatic combustion or Name temperature.
TE the combustion is incomplete or exces air is used, the temperature of the products of
‘combustion will be les than the maximum adiabaie combustion temperature. Incomplete com
‘bustion resrct the conversion of al he chemical energy into thermal energy and excess ir will
Have cooling effect, hence the temperate willbe lower than Ihe maximum temperature in both
Route Syrems_ 87
the cases. Dissociation of the combustion products at high temperature also reduces the fame
temperature.
‘The adiabatic ame temperature can be calculated as flows:
Consider a stedy-flow adiabatic combustion reaction in which there is no work transfer,
[Neglecting the changes in potential energy and kinetic energy and applying the fsa of thermo.
dynamics,
Q= Hp =Ha
As ie process is adiabatic, © = 0,
5 Hp~Hg=0
or Hs
Lett + GR, = Dates GE, G28)
Figure 3.3 shows the process on A-T diagram for steady-low adiabatic combustion.
gue Sad fon fotaccorbson
In a closed system for constant pressure process, the adiabatic flame temperature can be
obtained from Hp = Hg and for a constant volume process it can be obtained from Up = U,
A trialand-eror method can be used to obtain adiabatic Mame temperature. Initially, some
Product temperature is guessed and then the validity of Eq, (3.28) is checked. If this equation is
ot satisfied, a new value of temperature is guessed. When Eq, (3.28) is sisi, the guessed
temperature isthe adiabatic Name temperature.
‘A computer program using the Newion-Raphson iteration technique can also be used 10
brain the adiabatie flame temperature.
[EIERIIZABEREN Gaseous propane is bumed with 100 per cet excess air Determine the
‘ale flame temperature for steady-flow process.
Solution: The combustion equation with 100% excess ai is
CH + 2090, + ASNB-TON, => 300; + 4HO 4 50, + 37.6
|
BB. Fundumenals of Inma Comburden Engines
Coy + 100: + 37.6N > 3CO + HO + 50, + 37.00;
‘The product temperature is normally very high, so water may be considered in a gaseous state
‘The temperature ofthe reactants is not given; we will therefore assume thatthe ceactants ae at
25°C (7 = 298 K).
Pan Lips ie
D
Mp Din pa EE
2
él
tg Hy, 1103.85) = 10385 Memo fut
= neo; [hg + Oi? Fico, + ro +? oo
+ no, lig +6 No, + m2 157 +05 Fo,
= 3(-399,52 + (hp.
217.344 Sr
For adiabatic combustion,
p= Hy =~ 10385 Mel fae
37 =Kilco, +46 -
= 2187.84 103.85 = 2044 Mol fue,
Rado, +3767 Fi),
Most of the combustion products are Np, the frst guess forthe temperature can be obtained by
assuming that he products of combustion contain nitrogen ony.
2086
= 54.36 Mifano!
‘Coresponding to this value the temperarue from Table 3.3 is approximately equal to 1900 K.
Since CO; and HO in the products bave higher specific heats than N, they will absorb more heat
energy than Ny. Hence, the temperature wil be much lower than 1900 K.
For fist wil, assume T= 1500 K; at his temperature,
Hp = -2147.94 + 361.714) + 4(48.095) + 5(40.610) + 37.608.209)
= -123.24 MI/kmol fuel
‘This value of He is lower than -103.85 MI/Kinol fuel
Try Te 1600K; at this temperate,
Hy = 2147.84 + 3(67.580) + 4(52844) + 5(44.279) + 37.6(41.903)
63:22 Mismo! fuel
‘This value of pis higher han 103,85 Memo of Fuel. Therefore, the adiebaie flame tempera-
ture les between 1500 K and 1600 K. This can be estimated by linear interpolation as follows
T-150.
1600-1500 * ~6222-=(-12324)
1939100
500 + LEE
= 1500 + 104
15102K] Ans.
RENATA Calculate the adiabatic Name temperature, when achemicaly correct mixture
fof methane and ai intially at 600 K and atm. burns at (4) constant pressure process and (b)
constant volume process.
Specfie heat at constan pressure can be obtained from the relation:
mar TA sar sert
Ze marbricr
For means, 424503, D=-8965x 10% c=3736x 104,
36.49% 107 and
Solution: The combustion equation becomes
CH +20; + 20708; - CO, + 2H,0 + 7.52%
Ho= Day + ht, =
1222 x 10%.
where AR” = FPF
Hp = 1629382 + AR) + 228182 + Aig) + 75200 + Of)
= AR, + 20h80 + 7528 - 87116 Mol fuel
ai, = [OP ear R [arar sent var? er) ar
814[a(600~298) + x10" (6-298) + S108 0298)
area Sarre a]
eos (ES) 10.6258?) 238 6-209)
2549 rasen à 22-20
2 6-09 ea]
314 (1360 - 1215.6 + 2361.6 - 11103 + 184.3)
= 131,36 KIfemol = 13.136 Mol
Coy + 100: + 37.6N > 3CO + HO + 50, + 37.00;
‘The product temperature is normally very high, so water may be considered in a gaseous state
‘The temperature ofthe reactants is not given; we will therefore assume thatthe ceactants ae at
25°C (7 = 298 K).
Pan Lips ie
D
Mp Din pa EE
2
él
tg Hy, 1103.85) = 10385 Memo fut
= neo; [hg + Oi? Fico, + ro +? oo
+ no, lig +6 No, + m2 157 +05 Fo,
= 3(-399,52 + (hp.
217.344 Sr
For adiabatic combustion,
p= Hy =~ 10385 Mel fae
37 =Kilco, +46 -
= 2187.84 103.85 = 2044 Mol fue,
Rado, +3767 Fi),
Most of the combustion products are Np, the frst guess forthe temperature can be obtained by
assuming that he products of combustion contain nitrogen ony.
2086
= 54.36 Mifano!
‘Coresponding to this value the temperarue from Table 3.3 is approximately equal to 1900 K.
Since CO; and HO in the products bave higher specific heats than N, they will absorb more heat
energy than Ny. Hence, the temperature wil be much lower than 1900 K.
For fist wil, assume T= 1500 K; at his temperature,
Hp = -2147.94 + 361.714) + 4(48.095) + 5(40.610) + 37.608.209)
= -123.24 MI/kmol fuel
‘This value of He is lower than -103.85 MI/Kinol fuel
Try Te 1600K; at this temperate,
Hy = 2147.84 + 3(67.580) + 4(52844) + 5(44.279) + 37.6(41.903)
63:22 Mismo! fuel
‘This value of pis higher han 103,85 Memo of Fuel. Therefore, the adiebaie flame tempera-
ture les between 1500 K and 1600 K. This can be estimated by linear interpolation as follows
T-150.
1600-1500 * ~6222-=(-12324)
1939100
500 + LEE
= 1500 + 104
15102K] Ans.
RENATA Calculate the adiabatic Name temperature, when achemicaly correct mixture
fof methane and ai intially at 600 K and atm. burns at (4) constant pressure process and (b)
constant volume process.
Specfie heat at constan pressure can be obtained from the relation:
mar TA sar sert
Ze marbricr
For means, 424503, D=-8965x 10% c=3736x 104,
36.49% 107 and
Solution: The combustion equation becomes
CH +20; + 20708; - CO, + 2H,0 + 7.52%
Ho= Day + ht, =
1222 x 10%.
where AR” = FPF
Hp = 1629382 + AR) + 228182 + Aig) + 75200 + Of)
= AR, + 20h80 + 7528 - 87116 Mol fuel
ai, = [OP ear R [arar sent var? er) ar
814[a(600~298) + x10" (6-298) + S108 0298)
area Sarre a]
eos (ES) 10.6258?) 238 6-209)
2549 rasen à 22-20
2 6-09 ea]
314 (1360 - 1215.6 + 2361.6 - 11103 + 184.3)
= 131,36 KIfemol = 13.136 Mol
90 Fundamentals of bueral Combustion Engines
Reaeive Stems 91
ita = Et sah,
7
= MAT + 13.136) + 29.247) + 752(8691) = 23.62 Moo! fel
(8) For constan pres proces, Hp = Hy = 2362 Memo asl
‘cg, + 24h 0+ 7529, = 877.16 + 232 = 900.78 Milo! fel
“To gues the quired temperature, assume
752k, = 90078
akg, = 2078 = 119.8 M0/kmo!
Vas
Corresponding to his T = 3700 K (from Table 3.3)
AAdiabatie combustion temperature is much below this value.
Ty, T=280K
Hp = Alga, + Zahl +752 Aft, 87116
40.444 + 2115294) + 75285345) - 87.16 = 135.67 Mine fuel
He, Hy nach higher than Ll, 6 y with a smaller value of temperature.
Try, T=2500K
He = 121.926 + 208.964) + 752014312) — 877.16 = 1.52 Mo Mel
ere, Hy less than H, sy with itl higher temperature
Ty. T=2600K
‘My = 128085 + 210437) + 75207379) -877.16= 4602 Maro fuel
ere, Hy is more than i. So, the required temperate es between 2500 K and 2600 K. By linear
interpolsion,
2362-152
2
ETE
2500
() For constant volume procest:
Internal energy of reactant, Un
2 Up
2599.7 K = [550K] Ane
la - RT
362 1032 x 8314 x 107 x 600
2886 Mino fel
p= an,
= Hp 10.52 x 8.314 x 10° Tp = Hp - 0.08746 To.
Up = Aig, +248, + 752 At, -STTI6- 0.08746 Tp
Internal energy of products, Up
‘The reactants burned at constant pressure transfer work to the surroundings, whereas the
reactants bumed at constant volume do not transfer work to the surroundings. Therefore, che
adiabatic Name temperature at constant volume is higher than that obtained at constan pressure
process
For constant volume process, Up = U = ~28.86 Memo fuel
Ty. 7 =3000K
Up = 146.645 + 2(120.813) + 7.52(89.036) - 877.16 - 0.08746 x 3000
= 81.72 Mikel fuel
“This value of Ups less than Up. Therefore, try with an increased value of 7:
Ty. 7 =3200K
Up = 165.331 42(137.553) + 7.52(100.161) ~ 877.16 - 0.08746 x 3200
3662 Mirko fuel
‘This value of Up i more than Up. Therefore, the required temperature les betweeo 3000 K and
3200K.
By linear interpolation,
T-300 _ 2886 +8172
7200-3006 * 360248172
2 3000 + 2083286 _ 3900 +89: [ÜBTE] Ans.
= 2000 + PES — 3000 +895 = [30893K] A
Calculate the adiabatic flame temperature when methane bums nthe presence
of air at constant pressure process at 600 K and 1 atm, having (a) 50% excess air and (0) 20%
less ir leading to incomplete combustion. Calculate the lost of thermal energy due to incomplete
combustion. Take the mean value of, for methane as 32234 kml K.
Soltion: (4) The combustion equation with 50% exces ai fr 1 mol of ful i
(Cg 304 + 3x 3.763 => CO; + 2840 + 11.28N5 + Où
y= Snip HF
= 1[- 74.87 + 52.234(600 - 298) x 10)
#30 + 9247) + 11.2800 + 8891)
= 63936 MI
He = Zn} +7 Fa)
En +aro,
where AÑ = ithe
Hy 1639252 + ARfp,) + 2(-241.82+ aÑo)
+112500+ Af) + 10+ ag)
Reaeive Stems 91
ita = Et sah,
7
= MAT + 13.136) + 29.247) + 752(8691) = 23.62 Moo! fel
(8) For constan pres proces, Hp = Hy = 2362 Memo asl
‘cg, + 24h 0+ 7529, = 877.16 + 232 = 900.78 Milo! fel
“To gues the quired temperature, assume
752k, = 90078
akg, = 2078 = 119.8 M0/kmo!
Vas
Corresponding to his T = 3700 K (from Table 3.3)
AAdiabatie combustion temperature is much below this value.
Ty, T=280K
Hp = Alga, + Zahl +752 Aft, 87116
40.444 + 2115294) + 75285345) - 87.16 = 135.67 Mine fuel
He, Hy nach higher than Ll, 6 y with a smaller value of temperature.
Try, T=2500K
He = 121.926 + 208.964) + 752014312) — 877.16 = 1.52 Mo Mel
ere, Hy less than H, sy with itl higher temperature
Ty. T=2600K
‘My = 128085 + 210437) + 75207379) -877.16= 4602 Maro fuel
ere, Hy is more than i. So, the required temperate es between 2500 K and 2600 K. By linear
interpolsion,
2362-152
2
ETE
2500
() For constant volume procest:
Internal energy of reactant, Un
2 Up
2599.7 K = [550K] Ane
la - RT
362 1032 x 8314 x 107 x 600
2886 Mino fel
p= an,
= Hp 10.52 x 8.314 x 10° Tp = Hp - 0.08746 To.
Up = Aig, +248, + 752 At, -STTI6- 0.08746 Tp
Internal energy of products, Up
‘The reactants burned at constant pressure transfer work to the surroundings, whereas the
reactants bumed at constant volume do not transfer work to the surroundings. Therefore, che
adiabatic Name temperature at constant volume is higher than that obtained at constan pressure
process
For constant volume process, Up = U = ~28.86 Memo fuel
Ty. 7 =3000K
Up = 146.645 + 2(120.813) + 7.52(89.036) - 877.16 - 0.08746 x 3000
= 81.72 Mikel fuel
“This value of Ups less than Up. Therefore, try with an increased value of 7:
Ty. 7 =3200K
Up = 165.331 42(137.553) + 7.52(100.161) ~ 877.16 - 0.08746 x 3200
3662 Mirko fuel
‘This value of Up i more than Up. Therefore, the required temperature les betweeo 3000 K and
3200K.
By linear interpolation,
T-300 _ 2886 +8172
7200-3006 * 360248172
2 3000 + 2083286 _ 3900 +89: [ÜBTE] Ans.
= 2000 + PES — 3000 +895 = [30893K] A
Calculate the adiabatic flame temperature when methane bums nthe presence
of air at constant pressure process at 600 K and 1 atm, having (a) 50% excess air and (0) 20%
less ir leading to incomplete combustion. Calculate the lost of thermal energy due to incomplete
combustion. Take the mean value of, for methane as 32234 kml K.
Soltion: (4) The combustion equation with 50% exces ai fr 1 mol of ful i
(Cg 304 + 3x 3.763 => CO; + 2840 + 11.28N5 + Où
y= Snip HF
= 1[- 74.87 + 52.234(600 - 298) x 10)
#30 + 9247) + 11.2800 + 8891)
= 63936 MI
He = Zn} +7 Fa)
En +aro,
where AÑ = ithe
Hy 1639252 + ARfp,) + 2(-241.82+ aÑo)
+112500+ Af) + 10+ ag)
92 Fantamenale ol inter! Combustion Engines
_ race Syms 93
ot Ag + 112848 + A
For constant pressure adiabatic combustion, Hp = Hp
= 77.16 MI
+ 28h60 + 1128408 à ARS = 877.16 + 68.936 = 946.096 MI
"To guess the required temperature, assume
946.096
946096
1128
y LO is, we have 7 2800 K.
= 8387 Miko!
"The ediabtic combustion temperature is much below this value due tothe presence of other
‘constituents in the product.
my 2000 K
1.45 + 2072689) + 11.28(56.141) + 59.199 - 877,16
2.137 MI < Ha
Increase the temperature. Try, 7 = 2100 K
E 7.5 + 2(77831) + 11.28(59:748) + 62.986 - 877.16
1295 MI > Ha
“The required temperature therefore lies between 2000 K and 2100 K.
By linear interpolation,
+ 1609x100 — 2090 +276 = [HIRE] Ans.
(0) For incomplete combustion with 20% fess air, Le. with 80% of chemically correct ar.
For 1 kiol.of fuel the combustion equation becomes
CH, +08 x 203 + 1.6% 3.76N, => XCO + (l - X)CO; +210 + 6.016;
x
Xaiexet of X=08
By oxygenbalance: 16
“The combustion equation becomes
CH, + 1.60; + 6016s > 08C0 + 0.260, + 2110 + 6016N
Has Sai? + 07 Fo
= 11-7887 + 52234 (600 ~ 298) x 10") + 1.600 + 9.267) + 6.01600 + 8.891)
= 9.188 MI
El,
= 08-1052 + AR) + 02-9352 AR)
+AC24182 + AÑ) + 601600 + af)
BAR + 02h, + 2A} + 6016, - 65076
00K
8656739) + 0291.45) + 2(72.689) + 6,016(56.141) - 650.76
10336 MI < He
Inerease the temperature, Tey 7 = 2400 K.
Hp = 081134) + 02015788) + 209.604) + 60160651) ~ 65076
1.21 NO Hg
mer
ede he tempera. T= 2300 K
ip 0861.61) + 030096) + 2(88295) + 6016(67.007~ 65076
5019 <a
‘The required temperature therefore lies between 2300 K and 2400 K.
‘By linear interpolation,
T-2300 91885019
2400-2906 © 41710-5019
72300 4 616% 100 2300 + 114
36691
(Note thatthe adiebaic Mame temperacure obtained with exces air and les air are les han those
obtained with stoichiometsc air as obtained in Example 3.15, T= 2550 K.)
“The loss of thermal energy due o incomplete combustion isthe enthalpy of combustion ofthe
combustible constituents in the products.
“The only combustible substance is CO and from Table 34, AR? for CO is 283.022 MI/
Kmol.
“Thermal energy loss = 0.8 x 283,022 = [2264 NME] Ans.
3.9 DISSOCIATION
Athigh temporaates, products dissociate into smaller constituents. For example, CO, disseciares
into CO and Oy with absorption of heat energy. When CO and Os combine to form CO), heat
energy is liberated and when CO, dissociates into CO and O, heat energy is absorbed and
therefore the temperature ofthe products decreases. When chemical equilibrium is reached,
the reaction proceeds in both directions, so there is no net change ia ether the reactants or the
_ race Syms 93
ot Ag + 112848 + A
For constant pressure adiabatic combustion, Hp = Hp
= 77.16 MI
+ 28h60 + 1128408 à ARS = 877.16 + 68.936 = 946.096 MI
"To guess the required temperature, assume
946.096
946096
1128
y LO is, we have 7 2800 K.
= 8387 Miko!
"The ediabtic combustion temperature is much below this value due tothe presence of other
‘constituents in the product.
my 2000 K
1.45 + 2072689) + 11.28(56.141) + 59.199 - 877,16
2.137 MI < Ha
Increase the temperature. Try, 7 = 2100 K
E 7.5 + 2(77831) + 11.28(59:748) + 62.986 - 877.16
1295 MI > Ha
“The required temperature therefore lies between 2000 K and 2100 K.
By linear interpolation,
+ 1609x100 — 2090 +276 = [HIRE] Ans.
(0) For incomplete combustion with 20% fess air, Le. with 80% of chemically correct ar.
For 1 kiol.of fuel the combustion equation becomes
CH, +08 x 203 + 1.6% 3.76N, => XCO + (l - X)CO; +210 + 6.016;
x
Xaiexet of X=08
By oxygenbalance: 16
“The combustion equation becomes
CH, + 1.60; + 6016s > 08C0 + 0.260, + 2110 + 6016N
Has Sai? + 07 Fo
= 11-7887 + 52234 (600 ~ 298) x 10") + 1.600 + 9.267) + 6.01600 + 8.891)
= 9.188 MI
El,
= 08-1052 + AR) + 02-9352 AR)
+AC24182 + AÑ) + 601600 + af)
BAR + 02h, + 2A} + 6016, - 65076
00K
8656739) + 0291.45) + 2(72.689) + 6,016(56.141) - 650.76
10336 MI < He
Inerease the temperature, Tey 7 = 2400 K.
Hp = 081134) + 02015788) + 209.604) + 60160651) ~ 65076
1.21 NO Hg
mer
ede he tempera. T= 2300 K
ip 0861.61) + 030096) + 2(88295) + 6016(67.007~ 65076
5019 <a
‘The required temperature therefore lies between 2300 K and 2400 K.
‘By linear interpolation,
T-2300 91885019
2400-2906 © 41710-5019
72300 4 616% 100 2300 + 114
36691
(Note thatthe adiebaic Mame temperacure obtained with exces air and les air are les han those
obtained with stoichiometsc air as obtained in Example 3.15, T= 2550 K.)
“The loss of thermal energy due o incomplete combustion isthe enthalpy of combustion ofthe
combustible constituents in the products.
“The only combustible substance is CO and from Table 34, AR? for CO is 283.022 MI/
Kmol.
“Thermal energy loss = 0.8 x 283,022 = [2264 NME] Ans.
3.9 DISSOCIATION
Athigh temporaates, products dissociate into smaller constituents. For example, CO, disseciares
into CO and Oy with absorption of heat energy. When CO and Os combine to form CO), heat
energy is liberated and when CO, dissociates into CO and O, heat energy is absorbed and
therefore the temperature ofthe products decreases. When chemical equilibrium is reached,
the reaction proceeds in both directions, so there is no net change ia ether the reactants or the
Recire Sptema_95
products, The equilibrium equation is writen as
Loge
CO + $0; cor
1 propanion of CO, Op and CO} exists in the eqilirium mixture at each temperature. At
higher temperatures, he amount of CO and Op increases and that of CO; decrease. Because of
this, the theoretical temperature calculated on the assumption that al the carbon present in th fuel
has been converted into CO, (if sufiient oxygen is presen) cannot be obtained.
Conside a weak mixture of CO and O The Final composicion of he mixture at equilibrium
an be obtained as follows:
If is the numberof excess moles of oxygen inthe mixture, hen the original mixture will be
à
co+(den) 0,
Resin wih iin at is
:
c0~(Lox)0.-» 0140 om
His ce of iin CO, an CD il ii ls.
000, aco + 20,
(U = @CO; isnot dissociated
‘The final produets will be:
= 00: 000+ £0,004
‘The overall nacion can be writen as
+(Lenlor+ 0-0xc0,+000+ (n+
©0+($+n)0,+ (1-0x00,+ aco+ (n+£)o, 630)
Consiter archi of CO and Os The fs
be obained as flows
Let beth number of moles of xces CO in the mie, then th origina! mintre wil be
a +ncos 40,
Reaction witout isociaion can be writen as
U 42900 + 30, > nCO+ CO, 030
composition ofthe mixture at equilibrium can
Let exbe the degree of dissociation of CO,, then @CO; will dissociate as follows.
200, aco + LO,
(U -@)CO; is not dissociated
Tie final products wie: (I a0, + aC0 + Lo, + CO
‘The overall recon canbe writen es
(NICO + 30, (1~ ICO) + (n+ ICO + ZO, 03)
‘Determine the final composition of the mixture at equilibrium and write the
overall reaction, when the comact mixture of octane (Cay) and oxygen bara and a and care
the degrees of dissection of CO; und HO respectively. Assume hat CO is sociated into CO
and Os and HO i disocited into Hy and Os.
Sotation: Reaction without dissociation
City + 1250, 800; + 9840
Conside ie dissociation of CO:
900, > C0 + SO
Has motes of CO, will dissociate as
10/00, 80400 + 400,
and BCE ~ 6400) wil not dissociate and will remain in the product.
‘Consider the dissociation of HO,
HO 9 H+
390 moles of HO will dissociate as
DasH,0 > 90,8: 4 450202
(1 - a3) 1,0 will not disoeiae and remain in tbe products
‘The final composition willbe:
BL 00, + 80,00 + 40:03 + 90 - HO + D + 45,05
(I~ 04)CO, + 80100 + 9(1 - DIO + POH, + (Aou +4.50J0, Ans.
“The overall reaction willbe:
Citi + 1250, > 80 - CO; + 80,CO + KI — op) H¿O + 9ugh + dam + 45@)O Ans.
3.10 CHEMICAL EQUILIBRIUM
“Tocvaluat the degree of dissociation its necessary to study chemical equilibrium inthe chemical
‘reactions. As a reaction proceeds, some ofthe products dissociate, When chemical equilibrium is
reached, the reaction proceeds in both directions so there is mo net change in eter the reactants
or the products.
products, The equilibrium equation is writen as
Loge
CO + $0; cor
1 propanion of CO, Op and CO} exists in the eqilirium mixture at each temperature. At
higher temperatures, he amount of CO and Op increases and that of CO; decrease. Because of
this, the theoretical temperature calculated on the assumption that al the carbon present in th fuel
has been converted into CO, (if sufiient oxygen is presen) cannot be obtained.
Conside a weak mixture of CO and O The Final composicion of he mixture at equilibrium
an be obtained as follows:
If is the numberof excess moles of oxygen inthe mixture, hen the original mixture will be
à
co+(den) 0,
Resin wih iin at is
:
c0~(Lox)0.-» 0140 om
His ce of iin CO, an CD il ii ls.
000, aco + 20,
(U = @CO; isnot dissociated
‘The final produets will be:
= 00: 000+ £0,004
‘The overall nacion can be writen as
+(Lenlor+ 0-0xc0,+000+ (n+
©0+($+n)0,+ (1-0x00,+ aco+ (n+£)o, 630)
Consiter archi of CO and Os The fs
be obained as flows
Let beth number of moles of xces CO in the mie, then th origina! mintre wil be
a +ncos 40,
Reaction witout isociaion can be writen as
U 42900 + 30, > nCO+ CO, 030
composition ofthe mixture at equilibrium can
Let exbe the degree of dissociation of CO,, then @CO; will dissociate as follows.
200, aco + LO,
(U -@)CO; is not dissociated
Tie final products wie: (I a0, + aC0 + Lo, + CO
‘The overall recon canbe writen es
(NICO + 30, (1~ ICO) + (n+ ICO + ZO, 03)
‘Determine the final composition of the mixture at equilibrium and write the
overall reaction, when the comact mixture of octane (Cay) and oxygen bara and a and care
the degrees of dissection of CO; und HO respectively. Assume hat CO is sociated into CO
and Os and HO i disocited into Hy and Os.
Sotation: Reaction without dissociation
City + 1250, 800; + 9840
Conside ie dissociation of CO:
900, > C0 + SO
Has motes of CO, will dissociate as
10/00, 80400 + 400,
and BCE ~ 6400) wil not dissociate and will remain in the product.
‘Consider the dissociation of HO,
HO 9 H+
390 moles of HO will dissociate as
DasH,0 > 90,8: 4 450202
(1 - a3) 1,0 will not disoeiae and remain in tbe products
‘The final composition willbe:
BL 00, + 80,00 + 40:03 + 90 - HO + D + 45,05
(I~ 04)CO, + 80100 + 9(1 - DIO + POH, + (Aou +4.50J0, Ans.
“The overall reaction willbe:
Citi + 1250, > 80 - CO; + 80,CO + KI — op) H¿O + 9ugh + dam + 45@)O Ans.
3.10 CHEMICAL EQUILIBRIUM
“Tocvaluat the degree of dissociation its necessary to study chemical equilibrium inthe chemical
‘reactions. As a reaction proceeds, some ofthe products dissociate, When chemical equilibrium is
reached, the reaction proceeds in both directions so there is mo net change in eter the reactants
or the products.
Re sens 97
Ann er _ |
Consider à general case of a stoichiometric chemical equilibrium reaction: | 2 FE
NME Dem pers yan 639 LISRRSERSENSERSRENNESSSE
where, A. B, Cand D are ih individual species in ie burned gases that react together, produce | ZIERTTTHTTRTITITTTTTITTT
nd move each see a qua rca. Na ner hänge in specs compo ea E
and vo preste soieomei coefficient bleed chema eu | & o
The enulionum cosa ys defined as | i
i £ 3
Le om SIBSBESBRSSERSSSESERIERAIE
CEE PEP EEE ER EES Fes H
where Pa, Pp, Pc and pp are the partial pressures of the constituents, These cou)d be expressed in g ' 3
ies af male ing and ot pressure s = ]
pane am 3||s A E
ere a the patil pressure ofthe Ah constan, ss mole ro he Ah specie and El |Elsgggeggaageegegagggesale
is tbe toll pour E
= So tap er 6.36) APE 3
Ga us) a 2 El
In this expression Va, Yo, Ve and vo are the stoichiometric coefficients obtained from the | lis E
soichiomeuie balanced equilibrium equation, whereas the mole fractions xy xa, Xe and xp are Eliltleses alg
taken from the seal chemical reaction staining equilibrium, where the reactants may not be the leidos El s
stoichiometric mixture, The equilibrium constant X, is not really a constant but is only a constant 312115795 E
Jara given ener for an al | AE 3
The iy does ol depend on the amount of e varios consten nally present in he | 3 ME
mixture. The X, fora given reaction can be measured at various temperatures by analyzing the | llalegsa ssl
«guie gas mixture. The vales for he manual logar of the quin constant As or | ilesas E
several ideal gas reactions are given in Table 3.5, Wheu Une temperature of a gas is increased, there i Blaejensr 2
is atendency forthe gasto dissociate. Soat any temperature, there is an equilibrium mixture of the ! 2 = lt
ths and te did product Te ini process eaother, and as such tend lo alllalages sell
reus the tral energy ol system o amino vaa ora even enpertere The dicos MER E
reduces the adiabatic flame temperature as some of the chemical energy is used in the dissociation ces 3
Process ntc si te mal energy mE
The vaue of K, forthe equilibrium equation Slssss ass
1 sé a
+40, c0, 2/3995 $
bereit vahe ak, fr de opin 5 2 :
000430, Langa sas
to x GO + 10,000, mil be for COs N i j
Ann er _ |
Consider à general case of a stoichiometric chemical equilibrium reaction: | 2 FE
NME Dem pers yan 639 LISRRSERSENSERSRENNESSSE
where, A. B, Cand D are ih individual species in ie burned gases that react together, produce | ZIERTTTHTTRTITITTTTTITTT
nd move each see a qua rca. Na ner hänge in specs compo ea E
and vo preste soieomei coefficient bleed chema eu | & o
The enulionum cosa ys defined as | i
i £ 3
Le om SIBSBESBRSSERSSSESERIERAIE
CEE PEP EEE ER EES Fes H
where Pa, Pp, Pc and pp are the partial pressures of the constituents, These cou)d be expressed in g ' 3
ies af male ing and ot pressure s = ]
pane am 3||s A E
ere a the patil pressure ofthe Ah constan, ss mole ro he Ah specie and El |Elsgggeggaageegegagggesale
is tbe toll pour E
= So tap er 6.36) APE 3
Ga us) a 2 El
In this expression Va, Yo, Ve and vo are the stoichiometric coefficients obtained from the | lis E
soichiomeuie balanced equilibrium equation, whereas the mole fractions xy xa, Xe and xp are Eliltleses alg
taken from the seal chemical reaction staining equilibrium, where the reactants may not be the leidos El s
stoichiometric mixture, The equilibrium constant X, is not really a constant but is only a constant 312115795 E
Jara given ener for an al | AE 3
The iy does ol depend on the amount of e varios consten nally present in he | 3 ME
mixture. The X, fora given reaction can be measured at various temperatures by analyzing the | llalegsa ssl
«guie gas mixture. The vales for he manual logar of the quin constant As or | ilesas E
several ideal gas reactions are given in Table 3.5, Wheu Une temperature of a gas is increased, there i Blaejensr 2
is atendency forthe gasto dissociate. Soat any temperature, there is an equilibrium mixture of the ! 2 = lt
ths and te did product Te ini process eaother, and as such tend lo alllalages sell
reus the tral energy ol system o amino vaa ora even enpertere The dicos MER E
reduces the adiabatic flame temperature as some of the chemical energy is used in the dissociation ces 3
Process ntc si te mal energy mE
The vaue of K, forthe equilibrium equation Slssss ass
1 sé a
+40, c0, 2/3995 $
bereit vahe ak, fr de opin 5 2 :
000430, Langa sas
to x GO + 10,000, mil be for COs N i j
ET ——
98_Fundamentale of nera Combustion Engines
Rate items 99
Determine he percent dissociation of carbon dioxide into carbon monoxide
“and oxygen at 3000 K and 4000 K and at 1 atm pressure
Solution: From Table 33, for the chemical equilibrium equation CO, == CO + 10;
2000 Tour, = 1.171130 K for 0+ 20, m CO, La a
deso isn | mole CO The gum again becomes
ACO + $03 == (1 - C0;
Inky == 1117
‘The total mumber of moles present at equilibrium is
«Esque. EE
arta) AS
‘The partial pressure of each constituent may be expressed in terms of mole fraction and total
Pressure p as follows:
=e," mere?
FE Go Go 7
Since, p= 1 atm. and In K, = 1-117 at 3000 K,
(=a) +a)"
at
‘This equation can be solved for æ by a wial-and-ceror method,
.056
05-04”
a= 043
At 3000 K, [333%] of CO, vil dissociate Ans.
(A more accurate value is 43.4% obtained by ra and error)
‘4 K, fom Tee 35h gon CO, CO + LO) weave ny = 41558
|
|
Forth quon O + 40, ms COs nk «138,
K,= 02093
or aero” „on
By ial and error,
a= 09, K,=01995
42039, K,=02227
did 0199502227
03984
At 4000 K, [898%] of CO, will dissociate. Ans.
is thus observed that asthe temperature increases, the dissociation of CO; increases
A stoichiometric mixture of carbon monoxide and oxygen is burned in a
closed vessel, initially at | atm and 300 K. Calculate the mole fraction ofthe products of combus-
tion at 2400 K and the pressure ofthe product mixture.
866 (from Table 3.5)
Selten: For me 006 10, 4240010
Fox CO 4.10, = COS at 2400 K, laK, = 3866.
à Ken
Ie asthe degre of iseision of CO, eau equation becomes,
AGO + £0, (1 = 290045 Al consent ar preset in he ode.
‘The total number of moles present at equilibrio in the product is mp = a+ $ + (1 a =
ar2
2
Mole fractions:
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98_Fundamentale of nera Combustion Engines
Rate items 99
Determine he percent dissociation of carbon dioxide into carbon monoxide
“and oxygen at 3000 K and 4000 K and at 1 atm pressure
Solution: From Table 33, for the chemical equilibrium equation CO, == CO + 10;
2000 Tour, = 1.171130 K for 0+ 20, m CO, La a
deso isn | mole CO The gum again becomes
ACO + $03 == (1 - C0;
Inky == 1117
‘The total mumber of moles present at equilibrium is
«Esque. EE
arta) AS
‘The partial pressure of each constituent may be expressed in terms of mole fraction and total
Pressure p as follows:
=e," mere?
FE Go Go 7
Since, p= 1 atm. and In K, = 1-117 at 3000 K,
(=a) +a)"
at
‘This equation can be solved for æ by a wial-and-ceror method,
.056
05-04”
a= 043
At 3000 K, [333%] of CO, vil dissociate Ans.
(A more accurate value is 43.4% obtained by ra and error)
‘4 K, fom Tee 35h gon CO, CO + LO) weave ny = 41558
|
|
Forth quon O + 40, ms COs nk «138,
K,= 02093
or aero” „on
By ial and error,
a= 09, K,=01995
42039, K,=02227
did 0199502227
03984
At 4000 K, [898%] of CO, will dissociate. Ans.
is thus observed that asthe temperature increases, the dissociation of CO; increases
A stoichiometric mixture of carbon monoxide and oxygen is burned in a
closed vessel, initially at | atm and 300 K. Calculate the mole fraction ofthe products of combus-
tion at 2400 K and the pressure ofthe product mixture.
866 (from Table 3.5)
Selten: For me 006 10, 4240010
Fox CO 4.10, = COS at 2400 K, laK, = 3866.
à Ken
Ie asthe degre of iseision of CO, eau equation becomes,
AGO + £0, (1 = 290045 Al consent ar preset in he ode.
‘The total number of moles present at equilibrio in the product is mp = a+ $ + (1 a =
ar2
2
Mole fractions:
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00 fundamenta of Interna! Combustion Engines
A
Reste Stems 101
From the ideal gas Pav,
Eu ne
Vel” hele
Le Bale, 1200 5555 ima
CS RC ee
Now, % meee ppt? mans
aa +2) ‚ie
or O 15.398 x (4 292) = 47.75
Bar Dana a" ee
or as
‘The above equation can be solved by wia-and-emror method, and thus aris found approximately
equal 0 0.098. Therefore,
a+2 _ 009842
m7 2
20-0098)
ony
xo
Yo,
Pressure of the product, ps
5 398np = 5.333 x 1.049
CSS] Ans.
Hydrogen is stc burned wih chemical conset sc at 25°C and 1 sim
Deere the aia flame emperaure aking isociaia ito account.
For Hz a 2200 K,
ie Fi = 59.86 Mimo
and at 2400 K,
65915 Miikmol
Solution: The stoichiometric equation without dissociation is
+lo+ 1 > HO0+
Has 20,4 20708 > HO + 180,
Let abe the degee of dissociation of HO, Le.
ar
ano a+ &
“The chemical equation with dissociation is
1 Lo,
Hy 405+ 1.4804 (U HO + atts + LO, + LEE
As}, = 0, since all the reactants are elements and
Ha = Dati + 298K.
Be = Son +t Ra
0167125", o ad, + FAR, +186 aR
(Guess any temperature, and at his temperate, determine and then calculate Mp from the
above expression.
If Hp= Hg =0, then the solution is obtained. Otherwise we have to guess another temperature
viles condition is satisfied.
Guss 7230 K Aiea os cin 1,0 w= B+ O
em
Now, Kr
No of moles of ros a gum = (1a) + a+ + 188
#288 +050
Bari riss
1a
Pao = FR +03.
Tae 05a
05e
84037
x, MET 0001143
(es +050)
By ial-and-eror method, the above equation can be solved for c= 0.02
A
Reste Stems 101
From the ideal gas Pav,
Eu ne
Vel” hele
Le Bale, 1200 5555 ima
CS RC ee
Now, % meee ppt? mans
aa +2) ‚ie
or O 15.398 x (4 292) = 47.75
Bar Dana a" ee
or as
‘The above equation can be solved by wia-and-emror method, and thus aris found approximately
equal 0 0.098. Therefore,
a+2 _ 009842
m7 2
20-0098)
ony
xo
Yo,
Pressure of the product, ps
5 398np = 5.333 x 1.049
CSS] Ans.
Hydrogen is stc burned wih chemical conset sc at 25°C and 1 sim
Deere the aia flame emperaure aking isociaia ito account.
For Hz a 2200 K,
ie Fi = 59.86 Mimo
and at 2400 K,
65915 Miikmol
Solution: The stoichiometric equation without dissociation is
+lo+ 1 > HO0+
Has 20,4 20708 > HO + 180,
Let abe the degee of dissociation of HO, Le.
ar
ano a+ &
“The chemical equation with dissociation is
1 Lo,
Hy 405+ 1.4804 (U HO + atts + LO, + LEE
As}, = 0, since all the reactants are elements and
Ha = Dati + 298K.
Be = Son +t Ra
0167125", o ad, + FAR, +186 aR
(Guess any temperature, and at his temperate, determine and then calculate Mp from the
above expression.
If Hp= Hg =0, then the solution is obtained. Otherwise we have to guess another temperature
viles condition is satisfied.
Guss 7230 K Aiea os cin 1,0 w= B+ O
em
Now, Kr
No of moles of ros a gum = (1a) + a+ + 188
#288 +050
Bari riss
1a
Pao = FR +03.
Tae 05a
05e
84037
x, MET 0001143
(es +050)
By ial-and-eror method, the above equation can be solved for c= 0.02
102 fundamental of ternal Combos Engines
“The product side ofthe combustion equation is
098,0 + 0.028, + 0.010) + 1.88N;
Hy = 0 98-241.82 + 83036) + 002930) + 001065802) + 185063371)
346 Mk}
Guess T=2400K, In Ky 5425
K, = 0.0036
or MN 036
=a) (288+ 030)
By trial-and-ertor method, we obtain a = 0,04,
He = 0.96(-241.82 + 93.604) + 0.04(66:915) + 0.02(74.492) + 1.88(70.651)
=-53 Mikmole
we have, Ho = Hy = 346 Miikmol at 2200 K
and Hp Hg =-53 Mifkmo! at 2400 K, and
we have to find he temperature for which
Hp~Hg=0
is can be obtained by linea extrapolation (Figure
34) as
py (est)
HER] Ans Figura Enter Pare 220
REVIEW QUESTIONS
1. Define the exothermic and endothermic chemical reactions, What type of chemical reace
‘ion is carried out in the combustion of internal combustion engines?
2. Give a brief account ofthe properties of air in atmosphere. What isthe ratio of moles of
nitrogen to moles of oxy
3. Write the stoichiometric equation for combustion of fuel, having the general formula
CH, Op ith ae
44. What do you understand by the minimum allowable oxygen content in the reactants per
mole of fel?
5. Determine the number of moles ofthe product for the combustion of CAHLO, with aie
under the following conditions: (8) Y 2 Yn and (b) Yo SY S You where Y's the moles of
oxygen actually supplicd, Yi the chemically correct oxygen and Ya isthe minimum
allowable oxygen per mole of fel
6. Define the equivalence ratio and the relative ainfuel rato
Reacove Spramt 103
7. Define the enthalpy of formation. Whatis the reference state forthe enhalpy of formation?
Give the justification for taking his as a reference sat.
8. In writing enthalpy as fi”, what do the superscript (7 and bar over represent?
9. Write an expression for the first aw ofa steady-state steady-flow chemical reaction.
10. Define enthalpy of combustion and write an expression to caleulte it, Determine the
enthalpy of combustion for methane, when water in the producti liquid and also when it
is in gaseous form
1. Define internal energy of combustion, Write an expression o calculate the intemal energy
of combustion,
12, Define the higher heating value and the lower heating value ofa fuel. Give the relation
between them,
13, Explain he term adiabatic Mame temperature. How does this temperature change ifthe
‘combustion is incomplete, when excess air I used and when dissociation takes place?
14, Write an expression to calculate the adiabatic fame temperature. Draw the H-T diagram
{or the steady-flow adiabatic combustion.
15. What do you understand by dissociation ofa substance? Explain the term with the help of
an example,
16, Explainthe term chemical equilibrium, Weit expressions fo the equilibrium constant Kin
terms of paral pressures and mole fractions of the constituents,
PROBLEMS
Caleuat the theoretical acfuel and fuel/air ratios forthe complete combustion of ethanol
(COM). Ifthe air is supplied at 1 bar and 25°C, calculate the volume of air required for
complete combustion of fuel per kg and per kg mole of fuel
32 A fuel oil CHa is bured with 30% excess ar Determine the equivalence ratio, volumet-
Fic analysis ofthe products of combustion in percentage, molecular weight of the rescants
and products and the dew point of the product, if the pressure i bar
3.3 Fuetoil Cis used in a compression-igniton engine having bore of 100 mm and stoke
Length of 120 zum. The compression ratio is 16, The percentage composition of dry prod
uct of combustion by volume is CO; = 12.5%, O, = 3.8%, CO = 0.5% and N; = 832%.
‘Write the combustion equation. Calculat the arfel rato, the pr cent theoretial sr and
the mass of the residual gases left in the cylinder atthe end ofthe exhaust stoke. The
pressure and temperature ofthe exhaust gas ace 1.08 bar and 397°C respectively,
3.4 An IC engine fuel has the following composition by weight: Carbon 85%, hyérogen 10%.
‘oxygen 3% and the rests nitrogen. Determine the chemically correct arfuel aio. 130%
excess air is supplied, find the percentage of dry products of combustion by weight and by
volume,
3.5 A hydrocarbon fuel has the following composition of dry products of combustion by
volume:
33
CO, = 115%, CO=1%, 0,=325%, No = 84258
‘White the chemical equation for 100 moles of dry products. Determine the arfue rai
‘equivalence ratio and the fuel composition onthe mass bass
he
“The product side ofthe combustion equation is
098,0 + 0.028, + 0.010) + 1.88N;
Hy = 0 98-241.82 + 83036) + 002930) + 001065802) + 185063371)
346 Mk}
Guess T=2400K, In Ky 5425
K, = 0.0036
or MN 036
=a) (288+ 030)
By trial-and-ertor method, we obtain a = 0,04,
He = 0.96(-241.82 + 93.604) + 0.04(66:915) + 0.02(74.492) + 1.88(70.651)
=-53 Mikmole
we have, Ho = Hy = 346 Miikmol at 2200 K
and Hp Hg =-53 Mifkmo! at 2400 K, and
we have to find he temperature for which
Hp~Hg=0
is can be obtained by linea extrapolation (Figure
34) as
py (est)
HER] Ans Figura Enter Pare 220
REVIEW QUESTIONS
1. Define the exothermic and endothermic chemical reactions, What type of chemical reace
‘ion is carried out in the combustion of internal combustion engines?
2. Give a brief account ofthe properties of air in atmosphere. What isthe ratio of moles of
nitrogen to moles of oxy
3. Write the stoichiometric equation for combustion of fuel, having the general formula
CH, Op ith ae
44. What do you understand by the minimum allowable oxygen content in the reactants per
mole of fel?
5. Determine the number of moles ofthe product for the combustion of CAHLO, with aie
under the following conditions: (8) Y 2 Yn and (b) Yo SY S You where Y's the moles of
oxygen actually supplicd, Yi the chemically correct oxygen and Ya isthe minimum
allowable oxygen per mole of fel
6. Define the equivalence ratio and the relative ainfuel rato
Reacove Spramt 103
7. Define the enthalpy of formation. Whatis the reference state forthe enhalpy of formation?
Give the justification for taking his as a reference sat.
8. In writing enthalpy as fi”, what do the superscript (7 and bar over represent?
9. Write an expression for the first aw ofa steady-state steady-flow chemical reaction.
10. Define enthalpy of combustion and write an expression to caleulte it, Determine the
enthalpy of combustion for methane, when water in the producti liquid and also when it
is in gaseous form
1. Define internal energy of combustion, Write an expression o calculate the intemal energy
of combustion,
12, Define the higher heating value and the lower heating value ofa fuel. Give the relation
between them,
13, Explain he term adiabatic Mame temperature. How does this temperature change ifthe
‘combustion is incomplete, when excess air I used and when dissociation takes place?
14, Write an expression to calculate the adiabatic fame temperature. Draw the H-T diagram
{or the steady-flow adiabatic combustion.
15. What do you understand by dissociation ofa substance? Explain the term with the help of
an example,
16, Explainthe term chemical equilibrium, Weit expressions fo the equilibrium constant Kin
terms of paral pressures and mole fractions of the constituents,
PROBLEMS
Caleuat the theoretical acfuel and fuel/air ratios forthe complete combustion of ethanol
(COM). Ifthe air is supplied at 1 bar and 25°C, calculate the volume of air required for
complete combustion of fuel per kg and per kg mole of fuel
32 A fuel oil CHa is bured with 30% excess ar Determine the equivalence ratio, volumet-
Fic analysis ofthe products of combustion in percentage, molecular weight of the rescants
and products and the dew point of the product, if the pressure i bar
3.3 Fuetoil Cis used in a compression-igniton engine having bore of 100 mm and stoke
Length of 120 zum. The compression ratio is 16, The percentage composition of dry prod
uct of combustion by volume is CO; = 12.5%, O, = 3.8%, CO = 0.5% and N; = 832%.
‘Write the combustion equation. Calculat the arfel rato, the pr cent theoretial sr and
the mass of the residual gases left in the cylinder atthe end ofthe exhaust stoke. The
pressure and temperature ofthe exhaust gas ace 1.08 bar and 397°C respectively,
3.4 An IC engine fuel has the following composition by weight: Carbon 85%, hyérogen 10%.
‘oxygen 3% and the rests nitrogen. Determine the chemically correct arfuel aio. 130%
excess air is supplied, find the percentage of dry products of combustion by weight and by
volume,
3.5 A hydrocarbon fuel has the following composition of dry products of combustion by
volume:
33
CO, = 115%, CO=1%, 0,=325%, No = 84258
‘White the chemical equation for 100 moles of dry products. Determine the arfue rai
‘equivalence ratio and the fuel composition onthe mass bass
he
104 Fandarentt of buena Comburien Engines
105
3.6 A petro! has a composition of carbon 86% and hydrogen 14% by weight The ai supplied
ls 85% of that theoceticallyrequited for complete combustion. Assure tht al the hydro-
en i burnt and tha he carbon buras1o CO and CO, 5 that there is no fie carbon left
Calevtate the percentage analysis of dry exhaust gases by volume.
37 A fuel mixture of 50% CıHiyand SO% CH by volume is oxidized with 20% excess ar.
Determine the mass of at required for 100 kg of fuel and volumetric analysis of dry
products of combustion.
38 A gaseous fuel normal octane (CyHy) undergoes a steady-state steady-fow reaction with
tut Determine the heat vansfr per mole of fuel when the reactants and products are both
125°C and 1 atm pressure.
39 An engine produces 750 kW power and uses gaseous Cialis as a fuel at 25°C: 200%
theoretical ars used and ir enters at 500 K. The products of combustion leave a 800 K.
‘The heat Lo from the engine is 175 KW. Determine the fuel consumption for complete
combustion.
3.20 A mixture of liquid iséoctane and oxygen in the proper rato forthe complete combustion
and at 25°C and 1 atm reats in constant volume bomb calorimeter. Heat is ransfered
until the products of combustion ae at 600 K. Determine the heat transfer per mole of fel
3.11 Determine the amount of heat transfer per Kg of fuel during the complete combustion of
methane in an open stead-flow system with 50% excess air Methane enters at 400 K and
Air at $00 K and the products leave at 1000 K. The specific heat at constant pressure can be
‘obtained from the relation
ear rare
nord een + dr ert
= 450, b= -8965x107, e
3649108, = 1222x107
3.12 Propane bums in the presence of theoretical air. Calculate the standard enthalpy of com-
ustion and standard internal energy of combustion, when Wie water inthe products of
combustion appear (a) as a ligeid and (9) as a gas.
3.13 The lower calorific value of aliquid ful at constant pressure is 40,000 Kg, The analysis
‘of fl by mass i 85% carbon and 15% hydrogen. Determine the higher calorific vale at
constant pressure andthe lower and higher calorific values at constant volume.
3:14 Gaseous methane is burned with 200% theoretical air, Determine the adiabatic flame
temperature for th steady-state, steady-flow proces
3:15 Calculate the adiabatic flame temperature, when a chemically comect mixture of propane
and air initially at 600 K and 1 atm burs at (a) constant pressure process and () constant
volume process. The specific heat at constant pressure can be obtained fromthe relation,
®
Forpropane: a=-D486, b= 3663% 10%,
1891x10% d=3818x 10%, e=0.
3738 10%,
Ter dr vert
3.16 Calculate the adísbatic flame temperature when propane bums in the presence of air at
(Constant pressure process a 600 K and 1 atm having (a) 50% excess air and (9) 20% less
air leading to incomplete combustion, Calculate the Los of thermal energy due to incom:
plete combustion, The value ofc, ean be obtained from the data given in Problem 3.15.
3.17 Determine th percentage dissoistion of water into hydrogen and oxygen at 3000 K and at
1 atm pressure
105
3.6 A petro! has a composition of carbon 86% and hydrogen 14% by weight The ai supplied
ls 85% of that theoceticallyrequited for complete combustion. Assure tht al the hydro-
en i burnt and tha he carbon buras1o CO and CO, 5 that there is no fie carbon left
Calevtate the percentage analysis of dry exhaust gases by volume.
37 A fuel mixture of 50% CıHiyand SO% CH by volume is oxidized with 20% excess ar.
Determine the mass of at required for 100 kg of fuel and volumetric analysis of dry
products of combustion.
38 A gaseous fuel normal octane (CyHy) undergoes a steady-state steady-fow reaction with
tut Determine the heat vansfr per mole of fuel when the reactants and products are both
125°C and 1 atm pressure.
39 An engine produces 750 kW power and uses gaseous Cialis as a fuel at 25°C: 200%
theoretical ars used and ir enters at 500 K. The products of combustion leave a 800 K.
‘The heat Lo from the engine is 175 KW. Determine the fuel consumption for complete
combustion.
3.20 A mixture of liquid iséoctane and oxygen in the proper rato forthe complete combustion
and at 25°C and 1 atm reats in constant volume bomb calorimeter. Heat is ransfered
until the products of combustion ae at 600 K. Determine the heat transfer per mole of fel
3.11 Determine the amount of heat transfer per Kg of fuel during the complete combustion of
methane in an open stead-flow system with 50% excess air Methane enters at 400 K and
Air at $00 K and the products leave at 1000 K. The specific heat at constant pressure can be
‘obtained from the relation
ear rare
nord een + dr ert
= 450, b= -8965x107, e
3649108, = 1222x107
3.12 Propane bums in the presence of theoretical air. Calculate the standard enthalpy of com-
ustion and standard internal energy of combustion, when Wie water inthe products of
combustion appear (a) as a ligeid and (9) as a gas.
3.13 The lower calorific value of aliquid ful at constant pressure is 40,000 Kg, The analysis
‘of fl by mass i 85% carbon and 15% hydrogen. Determine the higher calorific vale at
constant pressure andthe lower and higher calorific values at constant volume.
3:14 Gaseous methane is burned with 200% theoretical air, Determine the adiabatic flame
temperature for th steady-state, steady-flow proces
3:15 Calculate the adiabatic flame temperature, when a chemically comect mixture of propane
and air initially at 600 K and 1 atm burs at (a) constant pressure process and () constant
volume process. The specific heat at constant pressure can be obtained fromthe relation,
®
Forpropane: a=-D486, b= 3663% 10%,
1891x10% d=3818x 10%, e=0.
3738 10%,
Ter dr vert
3.16 Calculate the adísbatic flame temperature when propane bums in the presence of air at
(Constant pressure process a 600 K and 1 atm having (a) 50% excess air and (9) 20% less
air leading to incomplete combustion, Calculate the Los of thermal energy due to incom:
plete combustion, The value ofc, ean be obtained from the data given in Problem 3.15.
3.17 Determine th percentage dissoistion of water into hydrogen and oxygen at 3000 K and at
1 atm pressure
Fuel-Air Cycles
and Their Analysis
4.1 INTRODUCTION
In the analysis of the air-standard cycle as discussed in Chapter 2 it was assumed that the working,
substance was only air and the air was a perfect gas and had a constant specific heat. The heat
was added from the extemal source andthe engine rejected heat tothe surrounding, Compression
and expansion were assumed 0 be fitloles adtbati proceses. Since this analysis is based on
2 highly simplified ssumpions, he estimated engine perfonnance is on the higher side compared
Lo the actual performance. The actual indicated thermal efficiency for a peral engine with com
pression rato of 8 is nearly 30%, whereas tat for the estandard cycle is 56.47%. This large
eviation is due to many reasons, such as non instantancous burning, incomplete combustion,
dissociation of the products of combustion at high temperature, variation of specific heats of
gases with temperature, heat transfer, friction, valve timings, pressure drop across the valve
during intake and exhaust, etc. The working substance in the actual cycle is not only air but is
also a mixtare of air, feel and residual gases left in the clearance space from the previous cycle
‘The analysis of the actual cycle is thus very complicated and the best method of approach
Lo the real cycle is through several approximations, starting with the ai-standard cycle and
‘modifying it step-by-step. The next step is to consider theoretical cycle, called the ful-ir cycle.
‘The results obtained from the analysis ofthis cole are much closer to the results obtained from
the actual engine.
‘The analysis of the air-standard cycle shows the effec of compression ratio on thermal
efficiency. The analysis ofthe fuere cycle, on the other hand, is able to predie the effect ofthe
siv/uel ratio on thermal efficiency. This is ot posible to be analysed with the air standard cycle
as the working substance is only ar, The fuel-ar cycle can also predict closely the peak pressure
‘and the peak temperature during the cycle with differnt aefvel ratios. Both te peak pressure and
the peak temperature affect dhe engine design end material selection,
42 FUEL-AIR CYCLE
‘The fuel air cycle calculations can take into consideration the following Factors, which are not
possible to be considered inthe analysis of the air-standard cycle,
1. The actual composition of the cylinder gases: The working fd is considered 10 be a
mixture of ar, fuel and residual gases.
Fuel Cels and Ther Anis 107
2. The voriovion of specific heat of the cylinder gases with temperature: Both the specific
at at constan pressure c, andthe specific heat at constant volume c, inerease with the
increase in temperature except in the case of monoatomie gases. Their difference is
‘constant and equal to but the ratio ofthe specific heats y changes with temperature
3. The dissociation of gases ar high remperarure: At higher temperatures, the products of
combustion dissocate into smaller eonsituens
4. The variation in the number of molecules: The number of molecules present in the
cylinder, after combustion, depends upon the Fier ratio and upon the temperature and
pressure existing in the cylinder
Besides taking the above factor into consideration, he following assumptions are also rad
forsimpliciy:
1. The fuel is completely vaporized and adiabatically mixed with ae and residual gases.
2. There is no change in the composition of charge during compresion. Compresion is
assumed to be reversible adiabat
3. Combustion is assumed 10 be complete without any heat loss at constant volume oF con-
stan pressure or limited pressure
4. Expansion of the burned pases is assumed tobe reversible adiebatc.
5, The law of mass action (chemical equilibrium) is obeyed a cemperaires above 1600 Kand
species concentration is frozen (fixed) at and below 1600 K.
6, Exhaust blowdow during exhausts assumed to be ideal adiabatic and the exhaust gases
ae frozen in composition.
7. Piston displacement is assumed tobe fectionles.
8. There is no heat exchange between the gases and the cylinder walls during the complete
cycle.
9. Inside the engine eylinder the velocity of gases is negligibly small
Briefly, he fue-air cycle consists of compression, combustion, expansion and blowdown
processes similar o the ar-standard cycle, There is no ition and no heat transfer between the
cylinder wal and the gases. Variation of specific heat and dissociation of gases at high tempera
tures are considered, With these considerations it has been Found thatthe indicated thermal efi
ciency ofthe fuel ai cycle is about 15% higher than tha obtained forthe actual engine,
43 FACTORS AFFECTING THE FUEL-AIR CYCLE
‘The following factors affect the analysis ofthe fuir cycle
43.1 Composition of Cylinder Gases
In an actual operation of an engine, the i/ful ratio may vary fr different operating conditions
This affects the composition ofthe cylinder gases before and after combustion. Before combut-
tion the cylinder gases are a mixture of air fuel and residual gases inthe clearance space from the
previous cycle. The products of combustion may be CO), CO, HO, Oj, and N The amount of
‘exhaust gases inthe clearance volume varies withthe speed andthe load on the engine. In order to
avoid laborious and time-consuming calculations by hand, he foel-ai cycles are analysed with he
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and Their Analysis
4.1 INTRODUCTION
In the analysis of the air-standard cycle as discussed in Chapter 2 it was assumed that the working,
substance was only air and the air was a perfect gas and had a constant specific heat. The heat
was added from the extemal source andthe engine rejected heat tothe surrounding, Compression
and expansion were assumed 0 be fitloles adtbati proceses. Since this analysis is based on
2 highly simplified ssumpions, he estimated engine perfonnance is on the higher side compared
Lo the actual performance. The actual indicated thermal efficiency for a peral engine with com
pression rato of 8 is nearly 30%, whereas tat for the estandard cycle is 56.47%. This large
eviation is due to many reasons, such as non instantancous burning, incomplete combustion,
dissociation of the products of combustion at high temperature, variation of specific heats of
gases with temperature, heat transfer, friction, valve timings, pressure drop across the valve
during intake and exhaust, etc. The working substance in the actual cycle is not only air but is
also a mixtare of air, feel and residual gases left in the clearance space from the previous cycle
‘The analysis of the actual cycle is thus very complicated and the best method of approach
Lo the real cycle is through several approximations, starting with the ai-standard cycle and
‘modifying it step-by-step. The next step is to consider theoretical cycle, called the ful-ir cycle.
‘The results obtained from the analysis ofthis cole are much closer to the results obtained from
the actual engine.
‘The analysis of the air-standard cycle shows the effec of compression ratio on thermal
efficiency. The analysis ofthe fuere cycle, on the other hand, is able to predie the effect ofthe
siv/uel ratio on thermal efficiency. This is ot posible to be analysed with the air standard cycle
as the working substance is only ar, The fuel-ar cycle can also predict closely the peak pressure
‘and the peak temperature during the cycle with differnt aefvel ratios. Both te peak pressure and
the peak temperature affect dhe engine design end material selection,
42 FUEL-AIR CYCLE
‘The fuel air cycle calculations can take into consideration the following Factors, which are not
possible to be considered inthe analysis of the air-standard cycle,
1. The actual composition of the cylinder gases: The working fd is considered 10 be a
mixture of ar, fuel and residual gases.
Fuel Cels and Ther Anis 107
2. The voriovion of specific heat of the cylinder gases with temperature: Both the specific
at at constan pressure c, andthe specific heat at constant volume c, inerease with the
increase in temperature except in the case of monoatomie gases. Their difference is
‘constant and equal to but the ratio ofthe specific heats y changes with temperature
3. The dissociation of gases ar high remperarure: At higher temperatures, the products of
combustion dissocate into smaller eonsituens
4. The variation in the number of molecules: The number of molecules present in the
cylinder, after combustion, depends upon the Fier ratio and upon the temperature and
pressure existing in the cylinder
Besides taking the above factor into consideration, he following assumptions are also rad
forsimpliciy:
1. The fuel is completely vaporized and adiabatically mixed with ae and residual gases.
2. There is no change in the composition of charge during compresion. Compresion is
assumed to be reversible adiabat
3. Combustion is assumed 10 be complete without any heat loss at constant volume oF con-
stan pressure or limited pressure
4. Expansion of the burned pases is assumed tobe reversible adiebatc.
5, The law of mass action (chemical equilibrium) is obeyed a cemperaires above 1600 Kand
species concentration is frozen (fixed) at and below 1600 K.
6, Exhaust blowdow during exhausts assumed to be ideal adiabatic and the exhaust gases
ae frozen in composition.
7. Piston displacement is assumed tobe fectionles.
8. There is no heat exchange between the gases and the cylinder walls during the complete
cycle.
9. Inside the engine eylinder the velocity of gases is negligibly small
Briefly, he fue-air cycle consists of compression, combustion, expansion and blowdown
processes similar o the ar-standard cycle, There is no ition and no heat transfer between the
cylinder wal and the gases. Variation of specific heat and dissociation of gases at high tempera
tures are considered, With these considerations it has been Found thatthe indicated thermal efi
ciency ofthe fuel ai cycle is about 15% higher than tha obtained forthe actual engine,
43 FACTORS AFFECTING THE FUEL-AIR CYCLE
‘The following factors affect the analysis ofthe fuir cycle
43.1 Composition of Cylinder Gases
In an actual operation of an engine, the i/ful ratio may vary fr different operating conditions
This affects the composition ofthe cylinder gases before and after combustion. Before combut-
tion the cylinder gases are a mixture of air fuel and residual gases inthe clearance space from the
previous cycle. The products of combustion may be CO), CO, HO, Oj, and N The amount of
‘exhaust gases inthe clearance volume varies withthe speed andthe load on the engine. In order to
avoid laborious and time-consuming calculations by hand, he foel-ai cycles are analysed with he
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108 Fndimenta of neral Cenbution Engines
FuchAle Cte and Thee Aragón 109
help of combustion cars. Suite chats re Led for unbumed and ured mixes fr ech ble 4.1_ Polynomial coetcionts to evaluate cy
fue aio of interes. However, with the availablity of fst digital computers its now posit SR rs a gi
{mans ie tai ce by means of able numerique, wich may produc fas ane Cor ©) «
Air Sn m 4 ms os
432. Variation of Specific Heats 10020 BAS GS az
AN gases, except monatomic gases, show an increase in specific hets with increase in temp oe ee À
degre. As the temperature is ase, lager factions ofthe input heat o to produce mation othe o A m m 7
‘toms within the molecules, Since temperature isthe result of motion ofthe molecaes the energy es ee
which goes into moving the atoms does not conrbue tothe temperature ie, s th Aal tee CORRE
‘erature and pressure ar lowered. Since at High temperatures, a given amount of heat results ina E 3640
smaller increase in temperature, therefore the specific eats increase with temperature, 100-300 OZ 28 106
The vacation of specific heats with temperature does not follow any specific law. Figure 41 cath a 36658181 En
shows he vration of specific heat a constant pressure c versus temperature fr a fe Hal Ma 8 864
gate. Specific hat at constant volume e, an be Obtained from the la. c= cp = R whee À 10002000 A ET 028
me N SA
14 1 A Oo
et E E]
a ns 1000-3000 SI 18 a
o E 8209 1
1000-3000 2798249305392 0001783 dam
É Ai ans pci et
ig with vale pect et
Process 3-4 ers epson with
úl constant pei eus.
CRE E UE
Temperatur)
Pawo Lt 6 lorsome idea pass,
Table 4.1 shows he polynomial coefficients for different gases, which may be used to evalu
tec, from the relation
Ba Beartrsct ear sert an
‚The value ofthe ratio of specific heats (c/c) für monatomic gases is constant and for all
exer dee ih ns pc
‘The effect of variation of pei het wi temperature on Ot eye is shown in
Figure 4,2, Es i ó
v
Figur 2. En on a opc hes on toc,
FuchAle Cte and Thee Aragón 109
help of combustion cars. Suite chats re Led for unbumed and ured mixes fr ech ble 4.1_ Polynomial coetcionts to evaluate cy
fue aio of interes. However, with the availablity of fst digital computers its now posit SR rs a gi
{mans ie tai ce by means of able numerique, wich may produc fas ane Cor ©) «
Air Sn m 4 ms os
432. Variation of Specific Heats 10020 BAS GS az
AN gases, except monatomic gases, show an increase in specific hets with increase in temp oe ee À
degre. As the temperature is ase, lager factions ofthe input heat o to produce mation othe o A m m 7
‘toms within the molecules, Since temperature isthe result of motion ofthe molecaes the energy es ee
which goes into moving the atoms does not conrbue tothe temperature ie, s th Aal tee CORRE
‘erature and pressure ar lowered. Since at High temperatures, a given amount of heat results ina E 3640
smaller increase in temperature, therefore the specific eats increase with temperature, 100-300 OZ 28 106
The vacation of specific heats with temperature does not follow any specific law. Figure 41 cath a 36658181 En
shows he vration of specific heat a constant pressure c versus temperature fr a fe Hal Ma 8 864
gate. Specific hat at constant volume e, an be Obtained from the la. c= cp = R whee À 10002000 A ET 028
me N SA
14 1 A Oo
et E E]
a ns 1000-3000 SI 18 a
o E 8209 1
1000-3000 2798249305392 0001783 dam
É Ai ans pci et
ig with vale pect et
Process 3-4 ers epson with
úl constant pei eus.
CRE E UE
Temperatur)
Pawo Lt 6 lorsome idea pass,
Table 4.1 shows he polynomial coefficients for different gases, which may be used to evalu
tec, from the relation
Ba Beartrsct ear sert an
‚The value ofthe ratio of specific heats (c/c) für monatomic gases is constant and for all
exer dee ih ns pc
‘The effect of variation of pei het wi temperature on Ot eye is shown in
Figure 4,2, Es i ó
v
Figur 2. En on a opc hes on toc,
10. fundamente of nc Combusten Engines
Fusbhir Cycles and Thee Aras LL
AF the variation of specific het is considered during the compresion stroke, the vals of
temperature and pressure atthe end of compresion would be lower han the values obtained hy
taking the fred value of specifi ese
‘With variable specific heats he state pont atthe end of compression wil be 2 instead of 2
With constant specifi heats, he temperature Ty ater compression can be obsied from the
relation 7; = 71 1°", whee y ls the compression aio and yis the ca o specific eas, ce,
‘With variable specific heals, he temperature 73 at te end of compression can be Gba
‘only by step-by-step calculatiors. For hs, he compression process is divided into a number of
male steps and assuming constant specific heats fr he smaller ste, the temperatures the
dof each ste are cvaluxed and filly Tis obtained. The larger the number of steps the more
accurate will be the result
For the combustion process, with constant specific heats, the process is represented by 2-3.
wheceas with variable specific heats the process is represented by 2-9. As the tunpcaire
increases during the combustion proces, he specifi eats aso increase, so the se in tempera:
ture with variable specific heat will be smaller thn the risen temperature without conideing the
variation in speci hen, ie
G-19<h-79
During the expansion process, the lemperatre decreases, therefore the specific heats also
decrease. Due to decrease in specifi heat, the temperaar atthe end of the expansion stoke
Ty’ would be higher than the temperature 7,” obtained without considering the variation in specific.
hen
Tecan be observed fom Figure 42 tha: by considering the variation in specific best, the area
enclosed by the cyte 1-2"-2'-4 reduces and hence te work done also redues In comparison fo
the area of standard ai eyele 1-2-3-4, where constar specific heats ae taken.
A sep-byesep procedures ls required to evaluate the propres a state pins 3° and a
explained during the compression process
433 Effect of Dissociation
Dissociation is a process of disintegration of combustion products at high temperatures. If a
mistere of a hydrocarbon fuel and excess air is ignited and the temperature does not exceed
1600 K under certain conditions, the reaction will be completed and the products of combustion
‘wil contain COs, HO, On and Np, However, in IC engines the temperatures ofthe products are
very high. Even though excess ar is present, incomplete combustion of fuel results because of
dissocirion, which may result in the formation of HO, Ha OH, H, Np, NO, N, CO, CO, Oj, O,
A (argon), hydrocarbons, ete. In other words, an equilibrium is established between the
‘encombined fel, ai, and the combustion produets, The incomplete combustion of fuel and air a
"high temperatures results in lower values of temperature and pressure afte the combustion pro-
cess than would otherwise be expected, since during combustion heat is liberated and whereas
during dissociation het is absorbed.
Figure 4.3 shows the effect of dissociation on temperature with different mixture strength
From the figure, iis observed that with no dissociation the maximum temperature obtained is at
the chemically coeet ai/fuel ratio, where the equivalence ato 4 s one. With dissociation, the
maximum temperature is obtained when the mixture is slightly rich. Dissociation reduces the
Temperate
Tan vi Kar
Equivalence ratio
aes Et ckdssctonon pert,
maximum temperature by about 300°C. The presence of CO in the products of combustion tends
10 reduce the dissociation of CO, This can be noted in a rich mixture which produces more CO
and suppresses dissociation of CO. On the lean sde 10, the cissocation is suppressed because
of lower temperature.
Figure 4.4 shows the effect of dissociation on power. If there is no dissociation, the brake
power (bp is maximum when the mixture strength i chemically correct. With dissociation, the
bp is maximum when the mixture is slightly rch. The difference in he ordinates between the two
curves of bp shows the power lost atthe given mixture strength
"The effec of dissociation is gencraly small compared with the effect of variation in specific
heat.
Fusbhir Cycles and Thee Aras LL
AF the variation of specific het is considered during the compresion stroke, the vals of
temperature and pressure atthe end of compresion would be lower han the values obtained hy
taking the fred value of specifi ese
‘With variable specific heats he state pont atthe end of compression wil be 2 instead of 2
With constant specifi heats, he temperature Ty ater compression can be obsied from the
relation 7; = 71 1°", whee y ls the compression aio and yis the ca o specific eas, ce,
‘With variable specific heals, he temperature 73 at te end of compression can be Gba
‘only by step-by-step calculatiors. For hs, he compression process is divided into a number of
male steps and assuming constant specific heats fr he smaller ste, the temperatures the
dof each ste are cvaluxed and filly Tis obtained. The larger the number of steps the more
accurate will be the result
For the combustion process, with constant specific heats, the process is represented by 2-3.
wheceas with variable specific heats the process is represented by 2-9. As the tunpcaire
increases during the combustion proces, he specifi eats aso increase, so the se in tempera:
ture with variable specific heat will be smaller thn the risen temperature without conideing the
variation in speci hen, ie
G-19<h-79
During the expansion process, the lemperatre decreases, therefore the specific heats also
decrease. Due to decrease in specifi heat, the temperaar atthe end of the expansion stoke
Ty’ would be higher than the temperature 7,” obtained without considering the variation in specific.
hen
Tecan be observed fom Figure 42 tha: by considering the variation in specific best, the area
enclosed by the cyte 1-2"-2'-4 reduces and hence te work done also redues In comparison fo
the area of standard ai eyele 1-2-3-4, where constar specific heats ae taken.
A sep-byesep procedures ls required to evaluate the propres a state pins 3° and a
explained during the compression process
433 Effect of Dissociation
Dissociation is a process of disintegration of combustion products at high temperatures. If a
mistere of a hydrocarbon fuel and excess air is ignited and the temperature does not exceed
1600 K under certain conditions, the reaction will be completed and the products of combustion
‘wil contain COs, HO, On and Np, However, in IC engines the temperatures ofthe products are
very high. Even though excess ar is present, incomplete combustion of fuel results because of
dissocirion, which may result in the formation of HO, Ha OH, H, Np, NO, N, CO, CO, Oj, O,
A (argon), hydrocarbons, ete. In other words, an equilibrium is established between the
‘encombined fel, ai, and the combustion produets, The incomplete combustion of fuel and air a
"high temperatures results in lower values of temperature and pressure afte the combustion pro-
cess than would otherwise be expected, since during combustion heat is liberated and whereas
during dissociation het is absorbed.
Figure 4.3 shows the effect of dissociation on temperature with different mixture strength
From the figure, iis observed that with no dissociation the maximum temperature obtained is at
the chemically coeet ai/fuel ratio, where the equivalence ato 4 s one. With dissociation, the
maximum temperature is obtained when the mixture is slightly rich. Dissociation reduces the
Temperate
Tan vi Kar
Equivalence ratio
aes Et ckdssctonon pert,
maximum temperature by about 300°C. The presence of CO in the products of combustion tends
10 reduce the dissociation of CO, This can be noted in a rich mixture which produces more CO
and suppresses dissociation of CO. On the lean sde 10, the cissocation is suppressed because
of lower temperature.
Figure 4.4 shows the effect of dissociation on power. If there is no dissociation, the brake
power (bp is maximum when the mixture strength i chemically correct. With dissociation, the
bp is maximum when the mixture is slightly rch. The difference in he ordinates between the two
curves of bp shows the power lost atthe given mixture strength
"The effec of dissociation is gencraly small compared with the effect of variation in specific
heat.
112 Fundmeng of Int! Combustion Engines
Figure 4.5 shows the effect of dissociation onthe p-V diagram of Ono eyele. As the dissocia-
tion lowers the maximum temperature, the maximum pressure of he cycle also reduces and the
state of the gas after combustion is shown by point 3 instead of 3, If there is no association
ring expansion, the expansion follows the path 34”, but there is always some reassociation due
10 fall in temperature during the expansion proces, so the expansion follows the path 44". By
comparing with te isentropic expansion 3-4, ii observed that the efect of dissociation is to
reduce the temperature and pressure a the beginning of the expansion stroke. This causes toss of
power and efficiency. Although during resssocatin the heat i released butt becomes 100 late Lo
contribute any significant ireease to the power ouput ofthe engine and mostly the beat i lost in
exhaust
Figure as: Erection en On yl.
43.4 Effect of Number of Molecules
The number of molecules present in the cylinder after combustion depends upon the fuer ratio,
and upon the pressure and temperature existing in the cylinder Por a given temperature from the
gas law pV = nT. the pressure varies with the number of moles present in he cylinder, This has
direc effect upon the amount of work which the cylinder gases do on the piston.
Since the composition of the working substance changes substantially during the combustion
process, the number of molecules also changes, For example, consider the complete reaction of
propane and oxygen,
Call, +50, > 300, + 4,0 a2)
The numberof moles before combustion is six and after combustion this number is seven, an
increase of 16.7%.
In he actual case, the reaction does not proceed to completion and the change may be still
greater. Let us assume, for example, that the two atoms of carbon bum to CO. the chemical
reaction then becomes
Hy + 50; >2C0 + CO, + 4H,0 +0; as
Fuel Ar Cycles and Their Anas 113
¡ox he total number of moles in the product is eight, an increase of 33.38 over the mixture
before combustion
Itisevidemt thatthe change in the number of molecules is dependent on the composition ofthe
fuel, the fuer ratio, and on the completeness of the reaction. The number of molecules is
realestate high temperature where the chemical equilibrium involves considerable amount of
(OH, NO, O;, H and CO. As the temperature falls, the number of molecules decreases, but even
if combustion were complete most fuels would give a larger total number of molecules after
combustion than the number contained inthe original mixture of fuel and ai
44 EFFECT OF ENGINE VARIABLES ON THE PERFORMANCE OF
FUEL-AIR CYCLES.
Puelair cycles have been calculated for constant inlet pressure and inlet temperature, but for
varying fuer ratios and compression ratios. These two parameter are engine variables for fuel
air eycle analysis.
Figure 4.6 shows the effet of compression ratio and equivalence ratio on thermal efficiency
ofthe constant volume fue-ar eyele using octene a fuel with initial pressure, py >] atm initial
temperature, 7 = 388 K and residual gas fraction, f= 0,05. The thermal efficiency is the ratio
‘of the work done fo the energy content of dhe fuel supplied, itis observed from the fig
as the compression rato increases the thermal efficiency increases (oo, in the same manner
as the aircycle efficiency.
Poet octen (Hy)
vs bys Lar
ET
gel 1005
‘Teenal ses, y
0H RE ur Bar à
Compression at,
Figure 46. Etampes brand clone slo gon ral acer neh conato utc.
Figure 4.5 shows the effect of dissociation onthe p-V diagram of Ono eyele. As the dissocia-
tion lowers the maximum temperature, the maximum pressure of he cycle also reduces and the
state of the gas after combustion is shown by point 3 instead of 3, If there is no association
ring expansion, the expansion follows the path 34”, but there is always some reassociation due
10 fall in temperature during the expansion proces, so the expansion follows the path 44". By
comparing with te isentropic expansion 3-4, ii observed that the efect of dissociation is to
reduce the temperature and pressure a the beginning of the expansion stroke. This causes toss of
power and efficiency. Although during resssocatin the heat i released butt becomes 100 late Lo
contribute any significant ireease to the power ouput ofthe engine and mostly the beat i lost in
exhaust
Figure as: Erection en On yl.
43.4 Effect of Number of Molecules
The number of molecules present in the cylinder after combustion depends upon the fuer ratio,
and upon the pressure and temperature existing in the cylinder Por a given temperature from the
gas law pV = nT. the pressure varies with the number of moles present in he cylinder, This has
direc effect upon the amount of work which the cylinder gases do on the piston.
Since the composition of the working substance changes substantially during the combustion
process, the number of molecules also changes, For example, consider the complete reaction of
propane and oxygen,
Call, +50, > 300, + 4,0 a2)
The numberof moles before combustion is six and after combustion this number is seven, an
increase of 16.7%.
In he actual case, the reaction does not proceed to completion and the change may be still
greater. Let us assume, for example, that the two atoms of carbon bum to CO. the chemical
reaction then becomes
Hy + 50; >2C0 + CO, + 4H,0 +0; as
Fuel Ar Cycles and Their Anas 113
¡ox he total number of moles in the product is eight, an increase of 33.38 over the mixture
before combustion
Itisevidemt thatthe change in the number of molecules is dependent on the composition ofthe
fuel, the fuer ratio, and on the completeness of the reaction. The number of molecules is
realestate high temperature where the chemical equilibrium involves considerable amount of
(OH, NO, O;, H and CO. As the temperature falls, the number of molecules decreases, but even
if combustion were complete most fuels would give a larger total number of molecules after
combustion than the number contained inthe original mixture of fuel and ai
44 EFFECT OF ENGINE VARIABLES ON THE PERFORMANCE OF
FUEL-AIR CYCLES.
Puelair cycles have been calculated for constant inlet pressure and inlet temperature, but for
varying fuer ratios and compression ratios. These two parameter are engine variables for fuel
air eycle analysis.
Figure 4.6 shows the effet of compression ratio and equivalence ratio on thermal efficiency
ofthe constant volume fue-ar eyele using octene a fuel with initial pressure, py >] atm initial
temperature, 7 = 388 K and residual gas fraction, f= 0,05. The thermal efficiency is the ratio
‘of the work done fo the energy content of dhe fuel supplied, itis observed from the fig
as the compression rato increases the thermal efficiency increases (oo, in the same manner
as the aircycle efficiency.
Poet octen (Hy)
vs bys Lar
ET
gel 1005
‘Teenal ses, y
0H RE ur Bar à
Compression at,
Figure 46. Etampes brand clone slo gon ral acer neh conato utc.
114 fundamental of neral Combustion Engines
Fue Cycles and Their Ansi 115
Figure 4.7 shows the efect of compression ratio and equivalence ratio on the ratio of fel-ir
cycle efficiency to air-sandard cycle efficiency of the constant volume fuelair cycle under the
similar condition as before. It is observed thatthe ratio ofthese efficiencies slightly increases
increase in compression ratio ata given equivalence ratio but deeeases as the amount of fuel
is increased.
Fuei—ocene (CH
El 10am
peed
08s 7005
om
En
E
fon
E
Eos
050
SUIS 262 20
Compression eo,»
Figure 7 ctl capessin a rand anale a on ro ai ja aan ye
fers male onsale tse,
Figure 48 shows the effet of equivalence ratio and compression to on thermal efficiency
of constant volume fuel ai cycle under the similar conditions as before. Ar a given compression
ratio, as the mixture is made lean (9 <1), he temperature rise between points 2 and 3 willbe less
as the energy input is less. Under these conditions, the specific heats of the gases wil be nearly
(Constant, Also atthe lower temperature, more of the fuel will combine with al at top dead centre,
ie. the combustion reaction will come to equilibrium at point 3 with a large faction of te fuel
energy inthe form of sensible energy. With lower specific heats and lower chemical equilibrium
losses, he efficiency is higher and approaches the air cycle efficiency as limits the fuer aio
is reduced.
‘On the rch side of the chemically correct fuel aio (6> 1) the efficiency falls even more
rapidly with increasing fueai ratio. This is because, in addition tothe effets noted above, there
is insufficient sir to completely utilize al the fuel present, egardless of the chemical equilibrium.
“The exhaust gases of rich mixtores will contain combusúbles in the form of CO and Hl, which
represent a direct waste of ful,
>
one
a peau
fe
as
= ;
iv y
i eas »
Ë ve À
4
035] 4
ex :
:
sal
CE ER BE E
queen $
Figure 48. Stet eqn aa ad cares ron ama ein of cosant ve rod
Apart from the effect of compression ratio and equivalence ratio on thermal efficiency, other
performances, such as maximum temperature Ts, maximum pressure py, temperature Ty and
mean effective pressure are also important for the analysis of fuel-ai cycles
Figure 49 shows the effect of equivalence ratio and compression ratio on maximum tempera:
ture 7) and maximum pressure p of the constant volume fuekair eyle with py = 1 atm, Ti =
288 K using isooctane a a fel In the region of weak mixture (6< 1), as the equivalence ratio is
“increased, more sensible energy is produced. This will result in increase in temperature Ty, At the
‘stoichiometric condition (9 = D), there is just enough fuel present to use up all the oxygen, but
‘because of chemical equilibrium both fuel and oxygen willbe present in the engine cylinder. The
se of additional fuel (9 > 1) will affect chemical equilibrium in such a way as to cause more
‘complete combustion at pont 3, and therefore more fuel will combine with oxygen. 3 continues
to ise because of ths effect until an equivalence ratio of about 1.065 is reached. A the riche fue
air ratios the incomplete combustion causes a decrease in the value of 7.
rom the gas law, pV = nT, the pressure ofa gas inside the given volume of an engine
cylinder depends upon the number of moles and its temperature. The curve of p vs. tends,
therefore, to follow the curve of 7 vs. $, except that more molecules are formed bythe combus-
tion of rich mixtures. Because of increasing mumber of roles, p does not start to decrease until
‘the mixture is somewhat richer than that for maximum 7;. Maximum ph occurs a the equivalence
ratio of about 1.2, Le. about 20% rich.
‘With the increase in compression rato, both py and 7, will increase because p and 7 are
higher at higher compresion ratios,
Fue Cycles and Their Ansi 115
Figure 4.7 shows the efect of compression ratio and equivalence ratio on the ratio of fel-ir
cycle efficiency to air-sandard cycle efficiency of the constant volume fuelair cycle under the
similar condition as before. It is observed thatthe ratio ofthese efficiencies slightly increases
increase in compression ratio ata given equivalence ratio but deeeases as the amount of fuel
is increased.
Fuei—ocene (CH
El 10am
peed
08s 7005
om
En
E
fon
E
Eos
050
SUIS 262 20
Compression eo,»
Figure 7 ctl capessin a rand anale a on ro ai ja aan ye
fers male onsale tse,
Figure 48 shows the effet of equivalence ratio and compression to on thermal efficiency
of constant volume fuel ai cycle under the similar conditions as before. Ar a given compression
ratio, as the mixture is made lean (9 <1), he temperature rise between points 2 and 3 willbe less
as the energy input is less. Under these conditions, the specific heats of the gases wil be nearly
(Constant, Also atthe lower temperature, more of the fuel will combine with al at top dead centre,
ie. the combustion reaction will come to equilibrium at point 3 with a large faction of te fuel
energy inthe form of sensible energy. With lower specific heats and lower chemical equilibrium
losses, he efficiency is higher and approaches the air cycle efficiency as limits the fuer aio
is reduced.
‘On the rch side of the chemically correct fuel aio (6> 1) the efficiency falls even more
rapidly with increasing fueai ratio. This is because, in addition tothe effets noted above, there
is insufficient sir to completely utilize al the fuel present, egardless of the chemical equilibrium.
“The exhaust gases of rich mixtores will contain combusúbles in the form of CO and Hl, which
represent a direct waste of ful,
>
one
a peau
fe
as
= ;
iv y
i eas »
Ë ve À
4
035] 4
ex :
:
sal
CE ER BE E
queen $
Figure 48. Stet eqn aa ad cares ron ama ein of cosant ve rod
Apart from the effect of compression ratio and equivalence ratio on thermal efficiency, other
performances, such as maximum temperature Ts, maximum pressure py, temperature Ty and
mean effective pressure are also important for the analysis of fuel-ai cycles
Figure 49 shows the effect of equivalence ratio and compression ratio on maximum tempera:
ture 7) and maximum pressure p of the constant volume fuekair eyle with py = 1 atm, Ti =
288 K using isooctane a a fel In the region of weak mixture (6< 1), as the equivalence ratio is
“increased, more sensible energy is produced. This will result in increase in temperature Ty, At the
‘stoichiometric condition (9 = D), there is just enough fuel present to use up all the oxygen, but
‘because of chemical equilibrium both fuel and oxygen willbe present in the engine cylinder. The
se of additional fuel (9 > 1) will affect chemical equilibrium in such a way as to cause more
‘complete combustion at pont 3, and therefore more fuel will combine with oxygen. 3 continues
to ise because of ths effect until an equivalence ratio of about 1.065 is reached. A the riche fue
air ratios the incomplete combustion causes a decrease in the value of 7.
rom the gas law, pV = nT, the pressure ofa gas inside the given volume of an engine
cylinder depends upon the number of moles and its temperature. The curve of p vs. tends,
therefore, to follow the curve of 7 vs. $, except that more molecules are formed bythe combus-
tion of rich mixtures. Because of increasing mumber of roles, p does not start to decrease until
‘the mixture is somewhat richer than that for maximum 7;. Maximum ph occurs a the equivalence
ratio of about 1.2, Le. about 20% rich.
‘With the increase in compression rato, both py and 7, will increase because p and 7 are
higher at higher compresion ratios,
116_fundamenale of neral Combustion Engines
mo) rece (Hh)
Dam
a0 1-208
200)
Tempest, 7,00
200)
Prem, (0)
2
oa IZA
Esivalnce ao, $
Figur 49 Ecol gare ao gandcopresso ño ron T und pl constant voue race.
Figure 4.10 shows the effect of equivalence ratio and compression ratio on temperature Ty It
is observed from the figure that the maximum value of Ty is obtained atthe chemically correct,
fuelair rato ($ = 1). After expansion, the temperature of he gases is low enough to shift the
chemical equilibrium in such a way that both fuel and oxygen will be completly used up atthe
cherricall comect fue rato.
Pr}
Iso (Cy)
pers
gro Teer
Em N
i 4
Eo 7
a
N to
1309,
‘os 08 ECN
nun ato, $
tect ogirtanes ra ax compression a on Te costar ote ati ee,
Figura,
“At point 4, the temperature of th gases is low, therefore he effect of chemical equilibrium is
not important a this point. The use of weak mixture ($ < 1) means that Jess fuel s burned and
therefor the temperature rie wil be smaller. The use of a ich mixture results in the formation of
more CO instead of COs, with less sensible energy developed and again there will be a small
"temperature rise. As the compression ratio increases, Ty decreases. This is because by increasing
the compression rato the expansion process is also increased, which causes the gas to do more
‘work on the piston, leaving less heat to be rejected at the end ofthe expansion stroke
Figure 4.11 shows the effect of the equivalence ratio and the compression ratio on mean
fective pressure (mep) ofthe constant volume fuelsir cycle with p= 1 tr, and 7; = 288 K.
tis observed from the figure that the mean effective pressure ofthe fack-ir cycle is maximum a
slightly richer than the chemically correct mitre. This Is because the average pressure during the
expansion stoke would be affected by the same factors that influence ps and pa. With the increase
in compression rato, the mean effective pressure also increases because ofthe higher thermal
eliiency at high compression ratios.
ss
is ,
ose (it)
5" Pop
IT: Mask
II:
Ea
a
HE
ur
2
a a
oe 08 10 11 14 16
Esuivalnce ati, à
Fue it Elcoternieor lo pandoomposcn alo cp cote crt volun tl y.
‘The results obtained from the analysis of fue-ar cycle are close to the experimental results
obtained from the actual engine. The main difference between the two is that in an actual engine,
‘combustion is not instantaneous bu it takes some time to complete. The time required for com
‘ustion (ie, the combustion duration} causes the acral efficiency 1 fall considerably below the
fuelair eycle efficiency.
[SEITHER] wear will be the percentage change in efficiency of an Otto cycle having a
‘compression ratio of 8.5, when the specific hea a constant volume increases by 1.4%?
mo) rece (Hh)
Dam
a0 1-208
200)
Tempest, 7,00
200)
Prem, (0)
2
oa IZA
Esivalnce ao, $
Figur 49 Ecol gare ao gandcopresso ño ron T und pl constant voue race.
Figure 4.10 shows the effect of equivalence ratio and compression ratio on temperature Ty It
is observed from the figure that the maximum value of Ty is obtained atthe chemically correct,
fuelair rato ($ = 1). After expansion, the temperature of he gases is low enough to shift the
chemical equilibrium in such a way that both fuel and oxygen will be completly used up atthe
cherricall comect fue rato.
Pr}
Iso (Cy)
pers
gro Teer
Em N
i 4
Eo 7
a
N to
1309,
‘os 08 ECN
nun ato, $
tect ogirtanes ra ax compression a on Te costar ote ati ee,
Figura,
“At point 4, the temperature of th gases is low, therefore he effect of chemical equilibrium is
not important a this point. The use of weak mixture ($ < 1) means that Jess fuel s burned and
therefor the temperature rie wil be smaller. The use of a ich mixture results in the formation of
more CO instead of COs, with less sensible energy developed and again there will be a small
"temperature rise. As the compression ratio increases, Ty decreases. This is because by increasing
the compression rato the expansion process is also increased, which causes the gas to do more
‘work on the piston, leaving less heat to be rejected at the end ofthe expansion stroke
Figure 4.11 shows the effect of the equivalence ratio and the compression ratio on mean
fective pressure (mep) ofthe constant volume fuelsir cycle with p= 1 tr, and 7; = 288 K.
tis observed from the figure that the mean effective pressure ofthe fack-ir cycle is maximum a
slightly richer than the chemically correct mitre. This Is because the average pressure during the
expansion stoke would be affected by the same factors that influence ps and pa. With the increase
in compression rato, the mean effective pressure also increases because ofthe higher thermal
eliiency at high compression ratios.
ss
is ,
ose (it)
5" Pop
IT: Mask
II:
Ea
a
HE
ur
2
a a
oe 08 10 11 14 16
Esuivalnce ati, à
Fue it Elcoternieor lo pandoomposcn alo cp cote crt volun tl y.
‘The results obtained from the analysis of fue-ar cycle are close to the experimental results
obtained from the actual engine. The main difference between the two is that in an actual engine,
‘combustion is not instantaneous bu it takes some time to complete. The time required for com
‘ustion (ie, the combustion duration} causes the acral efficiency 1 fall considerably below the
fuelair eycle efficiency.
[SEITHER] wear will be the percentage change in efficiency of an Otto cycle having a
‘compression ratio of 8.5, when the specific hea a constant volume increases by 1.4%?
118 Fandamen of ternal Combustion Engines
FuehAle Cycles and Ther Aria 119
Solution: The efficiency of the Oto cycle is given by
Now,
Taking log on both sides,
Differentiating the above relation keeping the compression ratio r constant, and where Risa gas
constant, we get
Benne,
Mn
7
1-0575
aso (14)
0575
=-886x 10%
an
4 x 100 =-0886%
7
‘Therefore, he efficiency decreases by [ORES] Ams
METIA What wil be the percentage change in efficiency of a Diesel cycle having a
compression ratio of 18 and eut-of taking place at 6% ofthe stoke, when the specifi heat at
‘constant volume increases by 2%? Take c, = 0.717 KI/(kg K) and R = 0287 KE K)
The efficiency of he Diesel cycle is given by
anon
Solution:
ica lll €
where ris the compression rato and is the cut-off rato.
OM
“Taking log on bot sides,
IQ =m) == Darin D) In y in (D)
Differentiating the above equation with espect toy Keeping rand constant,
da
4] a
Bu,
Differentiating the shove equation,
Edo,
®
Soni tera ia
a m FR Le In, ne
yr AaB 1
8 (Refer to Figure 4:12)
Compresion ato, # =
Mey,
CET
Ya = 006,
Vs = 0.06 x 19¥5 + Va= 2.020,
F
gure 412. Example.
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FuehAle Cycles and Ther Aria 119
Solution: The efficiency of the Oto cycle is given by
Now,
Taking log on both sides,
Differentiating the above relation keeping the compression ratio r constant, and where Risa gas
constant, we get
Benne,
Mn
7
1-0575
aso (14)
0575
=-886x 10%
an
4 x 100 =-0886%
7
‘Therefore, he efficiency decreases by [ORES] Ams
METIA What wil be the percentage change in efficiency of a Diesel cycle having a
compression ratio of 18 and eut-of taking place at 6% ofthe stoke, when the specifi heat at
‘constant volume increases by 2%? Take c, = 0.717 KI/(kg K) and R = 0287 KE K)
The efficiency of he Diesel cycle is given by
anon
Solution:
ica lll €
where ris the compression rato and is the cut-off rato.
OM
“Taking log on bot sides,
IQ =m) == Darin D) In y in (D)
Differentiating the above equation with espect toy Keeping rand constant,
da
4] a
Bu,
Differentiating the shove equation,
Edo,
®
Soni tera ia
a m FR Le In, ne
yr AaB 1
8 (Refer to Figure 4:12)
Compresion ato, # =
Mey,
CET
Ya = 006,
Vs = 0.06 x 19¥5 + Va= 2.020,
F
gure 412. Example.
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120 fundamental of nea! Combustion Engines
Fade Gyles and Ther Amps 121
some =|
ee]
2 (252 oe 2
7
0.6306
06306 202
=-001163
EM 2100 = 1.163%
”
Therefore, the efficiency decreases by [L163%] Ans.
‘The compression ratio of an engine working on an Oto cycle is 8 and the ai
fuel ratios 15:2, he pressure and temperature at de beginning ola compression sro being 1
bar and 60°C respectively, The calorific value of the fu 4,000 ki/kg. Determine the maximum
temperature and pressure in he cylinder, ifthe index of compression is 1.32 and the specific heat
st constant volume of he products of combustion is given by cy = (1678 + 0.000137) KI KI.
‘where Ts the temperature in Kelvin. Compare tis value with that of constant specific heat
= 0.217 Kg X)
Solution: Refer o Figure 4.13
Come. r= Yen
py =1 bas 7) = 60 42732 333K
2-13
Consider the compression process 1-2
TAN
gue 413. Empl 42,
m fi) = 1G)! = 15.56 bar
33 GE = 647.8 K
Since the iu rato is 15: 1,1 kg of mixtas has kg of fuel and 13 kg of ai
Heat transfer during process 2-3 per kg of mixture, 923
4.000. 2750 kg
i, an far
Í (0678 + o0o0tsnar
750
or O.G78(T) - 647.8) + 0.000065(73 ~ 647.8%) = 2750
or 0,00006573 + 0.6787) - 3216 = 0
or 73 + 1043075 ~ 494.8 x 10° = 0
10.430 + 00,430)? + 4x 4948 x10"
ñ
> [STK] Ans.
ñ
ts
xix ES Jar ins.
neben SB cas = i] A
With constant value of €,
AT ~ Ta) = 2750
“ omer, = 178) arm
15 = [WK] ane
ws py MB ax (TE) Am
Maxime pressure and maximum temperature decrease while considering the variation of
specific eat with temperature.
‘The compression ratio of an engine working on Diesel cycle is 21 andthe air?
{uct ratio is 29: 1. The temperature atthe end of compression is 1000 K. The caloriic value of fue
542,000 Kg and the specific heat at constant volume ofthe products of combustion is given by
A à 28 10°7 ekg 9 and R= 0287 ER). Determine the percer of sr
al which combustion is complete
‚Solution: Refer to Figure 4.14
‘Tne aitful ratio is 29: 1, therefore, I Kg mixture has
1
J keor ue
Gp 2G +R=071 + 28% 104+ 0.287
0.997 + 28 x 107
Heat tante during process 2-3, per hg of mixe,
2200
2-22
ook
Ais, ass | oar
ñ
Fade Gyles and Ther Amps 121
some =|
ee]
2 (252 oe 2
7
0.6306
06306 202
=-001163
EM 2100 = 1.163%
”
Therefore, the efficiency decreases by [L163%] Ans.
‘The compression ratio of an engine working on an Oto cycle is 8 and the ai
fuel ratios 15:2, he pressure and temperature at de beginning ola compression sro being 1
bar and 60°C respectively, The calorific value of the fu 4,000 ki/kg. Determine the maximum
temperature and pressure in he cylinder, ifthe index of compression is 1.32 and the specific heat
st constant volume of he products of combustion is given by cy = (1678 + 0.000137) KI KI.
‘where Ts the temperature in Kelvin. Compare tis value with that of constant specific heat
= 0.217 Kg X)
Solution: Refer o Figure 4.13
Come. r= Yen
py =1 bas 7) = 60 42732 333K
2-13
Consider the compression process 1-2
TAN
gue 413. Empl 42,
m fi) = 1G)! = 15.56 bar
33 GE = 647.8 K
Since the iu rato is 15: 1,1 kg of mixtas has kg of fuel and 13 kg of ai
Heat transfer during process 2-3 per kg of mixture, 923
4.000. 2750 kg
i, an far
Í (0678 + o0o0tsnar
750
or O.G78(T) - 647.8) + 0.000065(73 ~ 647.8%) = 2750
or 0,00006573 + 0.6787) - 3216 = 0
or 73 + 1043075 ~ 494.8 x 10° = 0
10.430 + 00,430)? + 4x 4948 x10"
ñ
> [STK] Ans.
ñ
ts
xix ES Jar ins.
neben SB cas = i] A
With constant value of €,
AT ~ Ta) = 2750
“ omer, = 178) arm
15 = [WK] ane
ws py MB ax (TE) Am
Maxime pressure and maximum temperature decrease while considering the variation of
specific eat with temperature.
‘The compression ratio of an engine working on Diesel cycle is 21 andthe air?
{uct ratio is 29: 1. The temperature atthe end of compression is 1000 K. The caloriic value of fue
542,000 Kg and the specific heat at constant volume ofthe products of combustion is given by
A à 28 10°7 ekg 9 and R= 0287 ER). Determine the percer of sr
al which combustion is complete
‚Solution: Refer to Figure 4.14
‘Tne aitful ratio is 29: 1, therefore, I Kg mixture has
1
J keor ue
Gp 2G +R=071 + 28% 104+ 0.287
0.997 + 28 x 107
Heat tante during process 2-3, per hg of mixe,
2200
2-22
ook
Ais, ass | oar
ñ
122 fundamental of Ice! Combustion Enger
Fuel Crees md Their Anais 123
(0997 + 28 x 10-74 = 1400
or (0.997(7, ~ 1000) + 14 x 10 (7} — 1000) = 1400
or 14x 107} 409997, - 2411 = 0
y DI TRA y y
EXT:
For constant pressure process 2-3,
Ve
Va = Vas 2341V = Vy = 13410;
Percentage stroke during which the combustion is completed,
% [Er
HU 100 = SET 10 = [SE] ans
“An oil engine working on a dual combustion cycle, has a compression ratio of
16: 1 and the cut-off takes place at 6% of the stoke. The maximum pressure obtained is 70 har
“The pressure and temperature atthe beginning of compression ae 1 bar and 100°C respectively.
Determine the pressure and teperature at al the important points ofthe cycle, Assume À =
0287 eg K) and e, = (0.716 + 125 x 107) tke K).
Solution: Refer to Figure 4.5.
Y
ers
Va= Vi = 006,
0 bar
Given: Compression ratio
287 3/0 KO
(0.716 + 125 x 107) ke K)
varies with temperature, so the value of 6, and 7 also vary. For compression and expansion
processes, the mean value of y willbe diferent and itis not known.
gu 416 Exang ss,
ler process 1-2: Assume y= 1.4, but its validity has tobe checked,
Tye TT! = 37316)" 11 K
Mean value of e, forthe temperature range 373 K to 1131 Kis
Con
= am 64 125% 10*nar
1-373) + 625x107 130 373)
Ta = 373 ia
181 40287 = 1.097
“The assumed value of is therefore not correct
Now, assume y= 1.354.
Ta = TN = 37306)! = 995 K
1
ste [C076 + 12510 mar
cp =0,+R=08015 + 0.287 = 1.0885
8015
Les is value is very close to the assumed value.)
Le = HERTS = 1358 Oi vale i ery 2
‘Thos the mean vale fis ken as 1.358 during compresion.
Tee HO = 37369 = TIER] An
BM yp, M 16010
A a bal
ia Conan volume pres, Le. Va = Vy
21006 = [TER] Ans.
Va~ Y = 0067,
= Vs = 0.06(¥; ~
os) zoo
=1 =006(r=
or 00S(=1)+1=006(16-1)+1=19
Fuel Crees md Their Anais 123
(0997 + 28 x 10-74 = 1400
or (0.997(7, ~ 1000) + 14 x 10 (7} — 1000) = 1400
or 14x 107} 409997, - 2411 = 0
y DI TRA y y
EXT:
For constant pressure process 2-3,
Ve
Va = Vas 2341V = Vy = 13410;
Percentage stroke during which the combustion is completed,
% [Er
HU 100 = SET 10 = [SE] ans
“An oil engine working on a dual combustion cycle, has a compression ratio of
16: 1 and the cut-off takes place at 6% of the stoke. The maximum pressure obtained is 70 har
“The pressure and temperature atthe beginning of compression ae 1 bar and 100°C respectively.
Determine the pressure and teperature at al the important points ofthe cycle, Assume À =
0287 eg K) and e, = (0.716 + 125 x 107) tke K).
Solution: Refer to Figure 4.5.
Y
ers
Va= Vi = 006,
0 bar
Given: Compression ratio
287 3/0 KO
(0.716 + 125 x 107) ke K)
varies with temperature, so the value of 6, and 7 also vary. For compression and expansion
processes, the mean value of y willbe diferent and itis not known.
gu 416 Exang ss,
ler process 1-2: Assume y= 1.4, but its validity has tobe checked,
Tye TT! = 37316)" 11 K
Mean value of e, forthe temperature range 373 K to 1131 Kis
Con
= am 64 125% 10*nar
1-373) + 625x107 130 373)
Ta = 373 ia
181 40287 = 1.097
“The assumed value of is therefore not correct
Now, assume y= 1.354.
Ta = TN = 37306)! = 995 K
1
ste [C076 + 12510 mar
cp =0,+R=08015 + 0.287 = 1.0885
8015
Les is value is very close to the assumed value.)
Le = HERTS = 1358 Oi vale i ery 2
‘Thos the mean vale fis ken as 1.358 during compresion.
Tee HO = 37369 = TIER] An
BM yp, M 16010
A a bal
ia Conan volume pres, Le. Va = Vy
21006 = [TER] Ans.
Va~ Y = 0067,
= Vs = 0.06(¥; ~
os) zoo
=1 =006(r=
or 00S(=1)+1=006(16-1)+1=19
124 _Fundamanale of lnaral Comburson Engnes
Fete Cyoet and Thee Ans 125
Consider process 3-4: It is constant pressure proces
LT, = 19% 1631
Consider process 4-5: Lisa reversible adiabatic expansion process. The value of Y i nt the
same as that for Ihe compression process. At higher temperatures, decreases
“Assume y = 1.3 and check its alii.
GG)
(ata)
pom
Pl 076 + 125 wenur
da gs 2 16385
agg (071619099 - 1635) + 625 x 103099" 163591
1299. 1.288 (The assumed value of is therefore aot correct)
= 1.283 (The assumed value of yls therefore correct)
J” = [EER] Ane
An engine working on an Otto cycle, having a compression ratio of 8, uses
à fuel, The lower healing value ofthe felis 44,000 Lg. The stl ro is
15:1. Determine the maximum pressure and temperature reached in th cycle (a) without consid
ing the molecular expansion and (b) with molecular expansion. Assume c, = 0.71 Kg K).
‘compression follows the aw p¥ = constant, he pressure and temperature of the mixture atthe
beginning of compression bring | bar and °C respectively. Determine the percentage molecular
expansion
Solution: Refer to Figure 4.16,
‘Compression ratio, r= 8
‘The solchiometi equation can be writen as
Cala + 12.50; + 3.76N;) > 8CO; + 98:0 + 478
= 1250247628160,
Suichiomenie aire = 1253293764201
21512
‘With the given afl ratio as 15, the mixtue is rich in fuel. F@wet6 Expo
‘Therefore the combustion willbe incomplete.
The chemical equation becomes:
By oxygen balance: red +6-2+45
or sens
2202
The chemical equnion now becomes:
Cilia + 1240, + 3768) > 02C0 + 7.800; + 9,0 + 46.624,
No. of moles before combustion =1 + 124 + (124 X 376) = 60.024
No. of moles after combustion =02 + 7.8 +9 + 46.624 = 63.624
Molecular expansion =
Fete Cyoet and Thee Ans 125
Consider process 3-4: It is constant pressure proces
LT, = 19% 1631
Consider process 4-5: Lisa reversible adiabatic expansion process. The value of Y i nt the
same as that for Ihe compression process. At higher temperatures, decreases
“Assume y = 1.3 and check its alii.
GG)
(ata)
pom
Pl 076 + 125 wenur
da gs 2 16385
agg (071619099 - 1635) + 625 x 103099" 163591
1299. 1.288 (The assumed value of is therefore aot correct)
= 1.283 (The assumed value of yls therefore correct)
J” = [EER] Ane
An engine working on an Otto cycle, having a compression ratio of 8, uses
à fuel, The lower healing value ofthe felis 44,000 Lg. The stl ro is
15:1. Determine the maximum pressure and temperature reached in th cycle (a) without consid
ing the molecular expansion and (b) with molecular expansion. Assume c, = 0.71 Kg K).
‘compression follows the aw p¥ = constant, he pressure and temperature of the mixture atthe
beginning of compression bring | bar and °C respectively. Determine the percentage molecular
expansion
Solution: Refer to Figure 4.16,
‘Compression ratio, r= 8
‘The solchiometi equation can be writen as
Cala + 12.50; + 3.76N;) > 8CO; + 98:0 + 478
= 1250247628160,
Suichiomenie aire = 1253293764201
21512
‘With the given afl ratio as 15, the mixtue is rich in fuel. F@wet6 Expo
‘Therefore the combustion willbe incomplete.
The chemical equation becomes:
By oxygen balance: red +6-2+45
or sens
2202
The chemical equnion now becomes:
Cilia + 1240, + 3768) > 02C0 + 7.800; + 9,0 + 46.624,
No. of moles before combustion =1 + 124 + (124 X 376) = 60.024
No. of moles after combustion =02 + 7.8 +9 + 46.624 = 63.624
Molecular expansion =
126 _Fndamene e Intra! Combarion Enger
Fuchair Cies and Their Anat 127
o Bilden Tr660+ = 335K,
T= Tyo" = 3338) = 6214K
eel 79
2100
or ER or ema)
he
CH] Am.
(9) Since the mass of he reactants and products f the same and specific heats are assumed same,
the temperature of he products with molecular expansion will remain the same as withoct mo.
Lecular expansion. Only the pressure will chang
[HSK] Ans
ART
Be
Ben
nr
Where is the number of moles of products without molecular expansion and xs ihe number of
moles of products with molecular expansion
45 EQUILIBRIUM CHARTS
‘To avoid laboious calculations, the fuel ale cycles are analyzed with the help of thermodynamic
chars. LB. Heywood developed a new set of charts in SI unis, following the approach of
[Newhall and Starkman. Nowadays, these chart are not much used and have been replaced by
computer models. However, these charts are useful to analyze the fuel-air cycles where a limited
number of calcalacion are required.
‘Two 1ypes of charts ae developed foreach fuel:
1. Unbumed mixture charts forthe properties of gases before combustion.
2. Bumed mixture chars for he properties of bumed gases after combustion under chemical
équibriun.
4,51. Unburned Mixture Charts
“The properties ofthe gases depend upon he air/fuel ratio and the residual gases in the mixture. For
diferent operating conditions ofthe engine the alv(uel rato and the amount of residual gases
change, therefore an ifiite number of chats would theoretically be required. However, limited
number of chats are used to cover the range of mixtures normally used in SI engines. The
thermodynamic charts developed for unburned mixtures are designed specifically for application
te intemal combustion engine eycle processes. The thermodynamic properties of each ofthe fuel
air mixtures considered are represented completely by a set of two charts, The first is indeed for
use in the determination of mixture temperature, pressure and volume atthe beginning and end of
(© compression process, and the other is for ıhe determination of the corresponding internal
energy and enthalpy values.
“The construction and use of the unbumed mixture chan are described here forthe case of
isooetane reacting with chemically correct amount of air (4 = 1)
Cats + 1250, + 47N -> 8CO, + 91,0 + AN 6a)
4 kg Coie +400 ke Op + 1324 kg No => 352 kg CO, + 162 kp HO + 1324 kg Na
or 1 kg Collie + 3.51 kg O; + 11.6 kg N > 309 kg CO, + 1.42 kg HO + 11.6 kg Nz (4.5)
For 1 kg of atthe chemi
(0.0662 ke Calla + Y kp air > 0.204 kg CO; +0.094 kg H¿O +0768 kN; (4.6)
“The total mass on both sides will be equal o (1+) kg, where 1 kg is air and F = 0.0662 kg
is the fuel
‘The charts are based upon (I + F) kg of mixture or 1 kg of air, both are equivalen
In terms of kmoles, the chemical reaction becomes
0.00058CyHis + 0.007250; + 0.0273N =» 0.00464C0, + 0.00522H0 + 0.0273Nz (4.7)
‘The tota number of kanoles of reactants = 0.0351, and the total number of kmoles of prod
wets = 09371. Ñ
nan engine, a mass fraction fof products remains in te clearance space and mixes withthe
mass fraction of (1 —f) of fresh charge. So, the engine cylinder contains:
(1 -NO.0662 kg Cain +1 Kg sit) + (02204 kg CO; + 0.094 kg HO + 0.768 kg Ny)
‘The total number of moles in the cylinder willbe
(1 = #9000351 + 0.03717 = 0.0351 + 0.002 using 1 Kg air.
‘These calculations can be repeated for other equivalence ratios such as for $ = 0.8 and 12.
The cesulis are shown in Table 42.
“The basis ofthe chart is as follows:
Fis the fueVair ratio and fis the fraction of mass of the residual gas in chart tothe total mass
of char contents or chart quantity
‘The total mass of chart content = (1 + F kg: here 1 kg is ai and F kg is fuel
Mass of residual gas in chart = A +)
F=0.0662,
Fuchair Cies and Their Anat 127
o Bilden Tr660+ = 335K,
T= Tyo" = 3338) = 6214K
eel 79
2100
or ER or ema)
he
CH] Am.
(9) Since the mass of he reactants and products f the same and specific heats are assumed same,
the temperature of he products with molecular expansion will remain the same as withoct mo.
Lecular expansion. Only the pressure will chang
[HSK] Ans
ART
Be
Ben
nr
Where is the number of moles of products without molecular expansion and xs ihe number of
moles of products with molecular expansion
45 EQUILIBRIUM CHARTS
‘To avoid laboious calculations, the fuel ale cycles are analyzed with the help of thermodynamic
chars. LB. Heywood developed a new set of charts in SI unis, following the approach of
[Newhall and Starkman. Nowadays, these chart are not much used and have been replaced by
computer models. However, these charts are useful to analyze the fuel-air cycles where a limited
number of calcalacion are required.
‘Two 1ypes of charts ae developed foreach fuel:
1. Unbumed mixture charts forthe properties of gases before combustion.
2. Bumed mixture chars for he properties of bumed gases after combustion under chemical
équibriun.
4,51. Unburned Mixture Charts
“The properties ofthe gases depend upon he air/fuel ratio and the residual gases in the mixture. For
diferent operating conditions ofthe engine the alv(uel rato and the amount of residual gases
change, therefore an ifiite number of chats would theoretically be required. However, limited
number of chats are used to cover the range of mixtures normally used in SI engines. The
thermodynamic charts developed for unburned mixtures are designed specifically for application
te intemal combustion engine eycle processes. The thermodynamic properties of each ofthe fuel
air mixtures considered are represented completely by a set of two charts, The first is indeed for
use in the determination of mixture temperature, pressure and volume atthe beginning and end of
(© compression process, and the other is for ıhe determination of the corresponding internal
energy and enthalpy values.
“The construction and use of the unbumed mixture chan are described here forthe case of
isooetane reacting with chemically correct amount of air (4 = 1)
Cats + 1250, + 47N -> 8CO, + 91,0 + AN 6a)
4 kg Coie +400 ke Op + 1324 kg No => 352 kg CO, + 162 kp HO + 1324 kg Na
or 1 kg Collie + 3.51 kg O; + 11.6 kg N > 309 kg CO, + 1.42 kg HO + 11.6 kg Nz (4.5)
For 1 kg of atthe chemi
(0.0662 ke Calla + Y kp air > 0.204 kg CO; +0.094 kg H¿O +0768 kN; (4.6)
“The total mass on both sides will be equal o (1+) kg, where 1 kg is air and F = 0.0662 kg
is the fuel
‘The charts are based upon (I + F) kg of mixture or 1 kg of air, both are equivalen
In terms of kmoles, the chemical reaction becomes
0.00058CyHis + 0.007250; + 0.0273N =» 0.00464C0, + 0.00522H0 + 0.0273Nz (4.7)
‘The tota number of kanoles of reactants = 0.0351, and the total number of kmoles of prod
wets = 09371. Ñ
nan engine, a mass fraction fof products remains in te clearance space and mixes withthe
mass fraction of (1 —f) of fresh charge. So, the engine cylinder contains:
(1 -NO.0662 kg Cain +1 Kg sit) + (02204 kg CO; + 0.094 kg HO + 0.768 kg Ny)
‘The total number of moles in the cylinder willbe
(1 = #9000351 + 0.03717 = 0.0351 + 0.002 using 1 Kg air.
‘These calculations can be repeated for other equivalence ratios such as for $ = 0.8 and 12.
The cesulis are shown in Table 42.
“The basis ofthe chart is as follows:
Fis the fueVair ratio and fis the fraction of mass of the residual gas in chart tothe total mass
of char contents or chart quantity
‘The total mass of chart content = (1 + F kg: here 1 kg is ai and F kg is fuel
Mass of residual gas in chart = A +)
F=0.0662,
128 fundamen of Ineral Combuscen Engines
Fuse Gyles and Their Ans 129
Table 4.2 Chartcompositon par kgo air
Bguivalence Percent Mass Rao ‘unburned mixture a
rai Ahmet ar QD [ER | ar man Um
“ 1 Toso | aas | 189 | oossosamisy7 21
10 109 im | oo | 151 | oassivoony 29
12 EN sos | nos | 126 | oos2w009J 2%
Mass of fresh charg
mass of total charge ~ mass of residual gas
LSO OS
(U + F) kg of fresh charge contains 1 kg of fresh ar,
(1+ PV =) ke of fret charge contains =f kg fresh ar,
1 kg is total air therefore, fk air is from residual
Now, since (1 + F) kg of fresh charge contains F kg of fresh fue,
F
oA
‘Total fuel is F kg therefore Y.) kg is from resido,
& + PA =D kg of fresh charge contain
emp
FC =P) kg of fresh fut,
[RMEWSIDAGERE An engine has a residual fraction of 0.03 and burns a mixture having equivalence
ratio of 1.2. How much fresh air and ful were inducted? How much residual ac and fuel are used?
Solution: From Table 4.2 for 9 = 12,
Total mass = 1 + F = 1.0795 kg
(0795 kg, where Fis the fueVsic ratio,
-003 = [057k] Ans.
10795 097 = [OOFFÜIERE] Ans.
Alin esidea f= [OK] Ans.
Fuel in residual f-F = 003 x 00795 = [DOORS] Ans.
Calculate te sensible intemal energy and sensible enthalpy pe kg of at
at 800 K for ooctane and ai mure having an equivalence rato 0010 |
Solution: tapes fisc above 298 (AF? ay), a erent temperate given
in Table 4.3. 2
rom th bia 00 K, Ay ay = 154723 Mil.
Sensible enthalpy for isooctane at 800 K = Ah, = 154.723 Ml/kmol
ces
¿
a
i
From Table 3.3, at 800 K for oxygen, A4, = 15.841 MJ/kmol, and that for nitrogen, i 15.046
Mikal
Table 4.3 Enthalpy of isooctane, &R ey.
7 Ahern When,
En]
0
oo
su
oo
mo 16851
so 13473
e 195260,
1000 239508
1.0, the number of kmoles of CH, O, and Na are 0.00058, 0.00725 and 0.0273
respectively for I kg ar
‘Total sensible enthalpy of reactants,
AH, = 0.00088 x 154.723 + 0.00725 x 15.841 + 0.0273 x 15.046
= 06153 MI per kg of air = [ETES Pig] Ans.
Sensible internal energy of reactants,
AU, = 4H, ~ n¥& (600-298)
(0.6153 ~ 0.0351 x 4314 x 10” (800 - 298)
0.6153 - 0.1465 = 0.4688 MI per kg of air
= [RETO] Ans.
‘At 298 K, Hy and U, are arbitrarily taken as zero, hence Un = 468.8 Kö ar and Haag =
(615.3 keg ar. These values agree withthe chart given in Figure 4.17. Te above example clearly
shows the method by which the chart can be drawn, The chan is very useful in obtaining the
values of sensible internal energy and sensible enthalpy for unburned air-fuel mixture at diferent
temperatures and equivalence ratios.
Inthe above calculations the burned gas faction fis taken as zero. This assumption ito
duces negligible error during the compression process. However, during the combustion proces,
this must be included,
Wie ae interested in the difference of internal energy and enthalpy so the abitary selection of
datum as 298 K imposes no problem. The itemal energy and enthalpy ofthe unbamed mixtre
tue called sensible internal energy U, and sensible enthalpy H,, because neither chemical reaction
‘or phase changes tke place and therefore the change in U, and A, is elected by the correspond
ing changes in temperature.
RR RAR RRR ARR AAA RR AAA AR AA RR RR RR RR An
Fuse Gyles and Their Ans 129
Table 4.2 Chartcompositon par kgo air
Bguivalence Percent Mass Rao ‘unburned mixture a
rai Ahmet ar QD [ER | ar man Um
“ 1 Toso | aas | 189 | oossosamisy7 21
10 109 im | oo | 151 | oassivoony 29
12 EN sos | nos | 126 | oos2w009J 2%
Mass of fresh charg
mass of total charge ~ mass of residual gas
LSO OS
(U + F) kg of fresh charge contains 1 kg of fresh ar,
(1+ PV =) ke of fret charge contains =f kg fresh ar,
1 kg is total air therefore, fk air is from residual
Now, since (1 + F) kg of fresh charge contains F kg of fresh fue,
F
oA
‘Total fuel is F kg therefore Y.) kg is from resido,
& + PA =D kg of fresh charge contain
emp
FC =P) kg of fresh fut,
[RMEWSIDAGERE An engine has a residual fraction of 0.03 and burns a mixture having equivalence
ratio of 1.2. How much fresh air and ful were inducted? How much residual ac and fuel are used?
Solution: From Table 4.2 for 9 = 12,
Total mass = 1 + F = 1.0795 kg
(0795 kg, where Fis the fueVsic ratio,
-003 = [057k] Ans.
10795 097 = [OOFFÜIERE] Ans.
Alin esidea f= [OK] Ans.
Fuel in residual f-F = 003 x 00795 = [DOORS] Ans.
Calculate te sensible intemal energy and sensible enthalpy pe kg of at
at 800 K for ooctane and ai mure having an equivalence rato 0010 |
Solution: tapes fisc above 298 (AF? ay), a erent temperate given
in Table 4.3. 2
rom th bia 00 K, Ay ay = 154723 Mil.
Sensible enthalpy for isooctane at 800 K = Ah, = 154.723 Ml/kmol
ces
¿
a
i
From Table 3.3, at 800 K for oxygen, A4, = 15.841 MJ/kmol, and that for nitrogen, i 15.046
Mikal
Table 4.3 Enthalpy of isooctane, &R ey.
7 Ahern When,
En]
0
oo
su
oo
mo 16851
so 13473
e 195260,
1000 239508
1.0, the number of kmoles of CH, O, and Na are 0.00058, 0.00725 and 0.0273
respectively for I kg ar
‘Total sensible enthalpy of reactants,
AH, = 0.00088 x 154.723 + 0.00725 x 15.841 + 0.0273 x 15.046
= 06153 MI per kg of air = [ETES Pig] Ans.
Sensible internal energy of reactants,
AU, = 4H, ~ n¥& (600-298)
(0.6153 ~ 0.0351 x 4314 x 10” (800 - 298)
0.6153 - 0.1465 = 0.4688 MI per kg of air
= [RETO] Ans.
‘At 298 K, Hy and U, are arbitrarily taken as zero, hence Un = 468.8 Kö ar and Haag =
(615.3 keg ar. These values agree withthe chart given in Figure 4.17. Te above example clearly
shows the method by which the chart can be drawn, The chan is very useful in obtaining the
values of sensible internal energy and sensible enthalpy for unburned air-fuel mixture at diferent
temperatures and equivalence ratios.
Inthe above calculations the burned gas faction fis taken as zero. This assumption ito
duces negligible error during the compression process. However, during the combustion proces,
this must be included,
Wie ae interested in the difference of internal energy and enthalpy so the abitary selection of
datum as 298 K imposes no problem. The itemal energy and enthalpy ofthe unbamed mixtre
tue called sensible internal energy U, and sensible enthalpy H,, because neither chemical reaction
‘or phase changes tke place and therefore the change in U, and A, is elected by the correspond
ing changes in temperature.
RR RAR RRR ARR AAA RR AAA AR AA RR RR RR RR An
130_Fontamenat of nr! Combunton Engines
Fuel Cees and Their Aras 131
1500
100
100 À ——
1200
uno
1000
0
so AA
mo
oo
«0
300
o
20 EJ pa EJ
Tengen fk)
1000
no
100
Fure17. Vian ctsssbe ay andtoneleng lurour coca ines topar.
“The entropy SUP») or S(T, p) of ideal gases of amount nKilomoles is given by
u eo Enns
where venfe $
sfr
The entropy change between he states (Ti, py) and (Ty p) is
A5= (6-6-0 m(2)
‘The entropy change between the states (7), vj) and (Ta, va) is
AS = (a= yen w(22)
aa)
a9)
4.0)
ay
412)
CRE)
|
|
i
1
!
For an isenteopic process, the change in entropy is zero.
CALE) on
and Gern v2) CE)
Figure 4.18 shows the variation of isentropic compression functions y and with tempera
ture for unburned isooctare-air mixes
Example 49 shows the method of obuining Y and & at a particular temperature and explains
the method of obtaining the corves by epeating he procedure at different temperatures. These
pot are then used fr analyzing he compression process ofthe feta eycle in a ister way
Determine the ientropic compression functions & and y at 500 X for the
Anbumed isoociane-air mixture with equivalence ratio 1.0. The approximate relation of c, for
isooctane is (0.44 4 3.67 x 1097) Meg K) and that for ir is (0.921 + 2:31 107) IME).
Equivalence ratio, 9 = 1.0, therefore, the air-foel mixture is stoichiometric. Under
ton for 1 kg air, isooctane is 0.0662 kp.
Fox mixture of sooctane and
12 at ar
A A | (osm ES
à cala 500 231010 (500 —
«occa aie 29 sans» m] +[asztn BE 42310020]
2 00202277 + 0.7419) + (04766 +0086)
= 0.5874 I = [STE] Ans.
10729 dk KO.
cp R = 044 + 3.76 x 10°F - 0.0729
cp R= 08921 + 231 x 10T-0287
Fuel Cees and Their Aras 131
1500
100
100 À ——
1200
uno
1000
0
so AA
mo
oo
«0
300
o
20 EJ pa EJ
Tengen fk)
1000
no
100
Fure17. Vian ctsssbe ay andtoneleng lurour coca ines topar.
“The entropy SUP») or S(T, p) of ideal gases of amount nKilomoles is given by
u eo Enns
where venfe $
sfr
The entropy change between he states (Ti, py) and (Ty p) is
A5= (6-6-0 m(2)
‘The entropy change between the states (7), vj) and (Ta, va) is
AS = (a= yen w(22)
aa)
a9)
4.0)
ay
412)
CRE)
|
|
i
1
!
For an isenteopic process, the change in entropy is zero.
CALE) on
and Gern v2) CE)
Figure 4.18 shows the variation of isentropic compression functions y and with tempera
ture for unburned isooctare-air mixes
Example 49 shows the method of obuining Y and & at a particular temperature and explains
the method of obtaining the corves by epeating he procedure at different temperatures. These
pot are then used fr analyzing he compression process ofthe feta eycle in a ister way
Determine the ientropic compression functions & and y at 500 X for the
Anbumed isoociane-air mixture with equivalence ratio 1.0. The approximate relation of c, for
isooctane is (0.44 4 3.67 x 1097) Meg K) and that for ir is (0.921 + 2:31 107) IME).
Equivalence ratio, 9 = 1.0, therefore, the air-foel mixture is stoichiometric. Under
ton for 1 kg air, isooctane is 0.0662 kp.
Fox mixture of sooctane and
12 at ar
A A | (osm ES
à cala 500 231010 (500 —
«occa aie 29 sans» m] +[asztn BE 42310020]
2 00202277 + 0.7419) + (04766 +0086)
= 0.5874 I = [STE] Ans.
10729 dk KO.
cp R = 044 + 3.76 x 10°F - 0.0729
cp R= 08921 + 231 x 10T-0287
132 Fundamentals of Internal Comburion Engines
Fuel Oper and Ther Anos 133
El
an ae = 2
À Ab
8
oe
AN
aN
E Ne R
AN]
Wo
Ñ
mm 2 a
= ANN
N
3
|
8
3
= 8
38 3 8 8 8 8 8
(atea score on ore]
8
Tempe)
Figure AIR oral compartas cn leer ruta nose an,
cosmos [oem - Font
03874 -0662 x in 320 _ 9.287 in 500
= 05874 0662 x 0.0729 In 300 0.287 In SP
= 0.5874 - 0.002498 ~ 0.1485 = 0.4364 LI
Boag aie] Ans.
A sparkignition engine with a compression ratio of 7.8 operates with a
stoichiometric fuel-sir mixture. The pressure and temperature athe str of compression are 1 atm.
and 335 K respectively. Find the temperature, the pressure and the volume per unit mas of sir at
the end ofthe compression stoke. Calculate also the work input during compression. Assume
isentropie compression using iso-ortane as a fuel.
Solution: Given: Ti = 335 K
T, can be obtained by using the isentropic compression char
From Fur 48, fr 7 2335 Ky 10 KE
(2) = 100-292 (2
mure (5) 0
From Figure 4.18, comesponding to y = 700 U air-K and $= 1.0, T= 645 K
700 eg air-K
Tz [GSK] Ans.
piv =nRT,
Orem] Ans.
a can ai be obtained by using the equation,
2648 in 2)
Beer (2
For Ti = 335 K, from Figure 4.18, & = 120
For Ta = 645 K, from Figure 418, = 910
Fuel Oper and Ther Anos 133
El
an ae = 2
À Ab
8
oe
AN
aN
E Ne R
AN]
Wo
Ñ
mm 2 a
= ANN
N
3
|
8
3
= 8
38 3 8 8 8 8 8
(atea score on ore]
8
Tempe)
Figure AIR oral compartas cn leer ruta nose an,
cosmos [oem - Font
03874 -0662 x in 320 _ 9.287 in 500
= 05874 0662 x 0.0729 In 300 0.287 In SP
= 0.5874 - 0.002498 ~ 0.1485 = 0.4364 LI
Boag aie] Ans.
A sparkignition engine with a compression ratio of 7.8 operates with a
stoichiometric fuel-sir mixture. The pressure and temperature athe str of compression are 1 atm.
and 335 K respectively. Find the temperature, the pressure and the volume per unit mas of sir at
the end ofthe compression stoke. Calculate also the work input during compression. Assume
isentropie compression using iso-ortane as a fuel.
Solution: Given: Ti = 335 K
T, can be obtained by using the isentropic compression char
From Fur 48, fr 7 2335 Ky 10 KE
(2) = 100-292 (2
mure (5) 0
From Figure 4.18, comesponding to y = 700 U air-K and $= 1.0, T= 645 K
700 eg air-K
Tz [GSK] Ans.
piv =nRT,
Orem] Ans.
a can ai be obtained by using the equation,
2648 in 2)
Beer (2
For Ti = 335 K, from Figure 4.18, & = 120
For Ta = 645 K, from Figure 418, = 910
134 Fandimen of Inemal Combustion Engines Fuel Cels and Ther Anais 13
10~ 120 = 790
7
a
Pr = [Bam] Ans.
Compression work, W = = (Uz = Un) = = (UAT) = UT
Using Figure 4.17, UTA) = 310 and UT) = 35 Kg air
Wa G10~35) == 275 Kg air
cats work input
‘Tae negative signi
Work input during compress
FR) Ans.
45.2 Bumed Mixture Charts
A tsa Uli ras
deca tan ier nse vel
“i Da ape nv soto ars in ca AMA
aul Stan, ich art PS tem Specs ah mix wer coc wn Kl
Thy I me eum a rats stow OK dh ite on
sens bee es Bid engin ten PO Tuas st nce gd on
De os of de coma al igo ve tec mp ef Th rout
osu compu ws cor mind. HeO, OH CO,COy NM 0,0, and NO
Sie bons Someta dee Sill tr goes sto ore ara ace se
hy an vo va for el de ores over el ene of empraes
onic ts st cmo of elie ede compare toon.
cig of equ cnt for ech ofthe cao actos Te dan Seed mer
ial nel fom he JANAP Um mae da les pte y te Ay
Navy air Fors on en em
‘ee chu reli fom fe cla sn omiteaions cutis above ae propery | |
cow fre high emm ed ps ch pt fern etsy en ty lr |
Fe o eyes or
Unum nc hart ur 49 show ve of here ar wong looane al Wid
depa nome sets hee of are
Ent, ge
US 33 90 92 94 96 98 100 102 104 106 TOR
ame gus propres
‘st ocn Cy
geleert: 1.0
1
"a 16 78 80 82 84
Temps: TK.
Source: Hape JB: oral Carducion Engine Furia, raw Hi, New Yo 158,
‘Figur 18 Ilmalorerg veros erry chat lor equi bed gs ma ccoo lance ño 10.
l
EXANP ‘The pressure in the cylinder of a spaigntion engine a top dead centre pene
mediately afer te completion of combustion is 65 ba. The compression aio i 10, he volume 8
per unit mass or tb ato expansions 0.1 mfg air Fuel used is isooctane ad the mature
À stichiometricDetemine the pressure, the temperatur and he volume atthe end of te expan
so stroke. Estos te wa during the expansion stroke. Assume that he proces i bai
ao)
1200
1600
aol
10~ 120 = 790
7
a
Pr = [Bam] Ans.
Compression work, W = = (Uz = Un) = = (UAT) = UT
Using Figure 4.17, UTA) = 310 and UT) = 35 Kg air
Wa G10~35) == 275 Kg air
cats work input
‘Tae negative signi
Work input during compress
FR) Ans.
45.2 Bumed Mixture Charts
A tsa Uli ras
deca tan ier nse vel
“i Da ape nv soto ars in ca AMA
aul Stan, ich art PS tem Specs ah mix wer coc wn Kl
Thy I me eum a rats stow OK dh ite on
sens bee es Bid engin ten PO Tuas st nce gd on
De os of de coma al igo ve tec mp ef Th rout
osu compu ws cor mind. HeO, OH CO,COy NM 0,0, and NO
Sie bons Someta dee Sill tr goes sto ore ara ace se
hy an vo va for el de ores over el ene of empraes
onic ts st cmo of elie ede compare toon.
cig of equ cnt for ech ofthe cao actos Te dan Seed mer
ial nel fom he JANAP Um mae da les pte y te Ay
Navy air Fors on en em
‘ee chu reli fom fe cla sn omiteaions cutis above ae propery | |
cow fre high emm ed ps ch pt fern etsy en ty lr |
Fe o eyes or
Unum nc hart ur 49 show ve of here ar wong looane al Wid
depa nome sets hee of are
Ent, ge
US 33 90 92 94 96 98 100 102 104 106 TOR
ame gus propres
‘st ocn Cy
geleert: 1.0
1
"a 16 78 80 82 84
Temps: TK.
Source: Hape JB: oral Carducion Engine Furia, raw Hi, New Yo 158,
‘Figur 18 Ilmalorerg veros erry chat lor equi bed gs ma ccoo lance ño 10.
l
EXANP ‘The pressure in the cylinder of a spaigntion engine a top dead centre pene
mediately afer te completion of combustion is 65 ba. The compression aio i 10, he volume 8
per unit mass or tb ato expansions 0.1 mfg air Fuel used is isooctane ad the mature
À stichiometricDetemine the pressure, the temperatur and he volume atthe end of te expan
so stroke. Estos te wa during the expansion stroke. Assume that he proces i bai
ao)
1200
1600
aol
136_Fundamenas of ners! Comburion Engines
Fur Cyees and Ther Avast 137
Solution: Refer to Figure 420,
Giver Ps = 65 bar = 6500 KV?
and vs 201 mig air
Corresponding to ps = 6500 KN/m?
and 2 mg ale,
from the chart given in Figure 4.19,
Ts =240K
a = 1040 Kg air Foue420 Exit
and 87 King sie: K
Process 3-4 is isentropic,
5425) = 887 Kg eK
Compression ratio, r « Fi = Mu
rv 210% 0.1 = 10 mg air
Corresponding to 887 Kk air-K and ve= 1.0 mga,
rom the chart 180K ardua 2220 Ig ir
and pa = 425 KNIm? = 4.25 bar
Pu = (SEE) 7, = [1280] and v = [10 mg
= (ty ty)
Am
=-(-2220 4 1040
4.5.3 Relation between Unburned and Burned Mixtures
‘The combustion in an intemal combustion engine takes place either at constant volume or at
constant pressure. The propetcs of gases after combustion can be estimated i he properties of
the unburned mixture before combustion are known,
HE}, is the enthalpy of formation of the unbumed mixture at 298.15 K, per kg of ai in the
original mixture, then
‘Work of expansion
Whe By 4.16)
Where is the numberof kilooles of species i perkg of stand fi,
species it 298.15 K, per klomole
For a reversible adiabati constant pressure combustion process,
Bes he gy ain
‘here fs is the bumed mixture enthalpy, A, is the unbumed mixture enthalpy and h, is tbe
sensible enthalpy of the unbumed mixture,
isthe enthalpy of formation of
3
al
Similarly for the reversible adiabatic constant volume combustion proces, he imemal energy
‘of the bumed mixture is given by
My Se ee ta a)
419)
were DEEE
‘The following example explain the procede of cbtaning the enthalpy of forman and the
intra energy of formation of te bed mitre. The vals of sandardontlp ad émet
ner of formation for gaseous isooctane (Cs), CO, CO and HO ae given in Table 4,
Tables,
ergy of formation
EZ
‘Standard enthapy andintomal
Hj Oana
En 2003
Species
Eee)
co, na 99
co 11052 Em
HO (299) 8 206
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unbumed mixture for gaseous isooctane (CeH1s) and air mixture with equivalence ratio 1.0 and
‘bumed gas fraction f Take the values of standard enthalpy and internal energy of formation from (
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Solution: The chemical equation with $= 1.0 can be wütten as
Colla + 1250; + 47%
(1324 kg)
> 800, + 950
G52 kg)
+ am
(114 kg) (162 kg) 4324 kg)
For 1 kg ai,
00661 kg Calli, + 0232 kg O + 0.768N, -> 0.204 kg CO, + 0.094 kg H,0 + 0.768N
Dividing the mass by molecular weight of species to convert to kmole,
5.198 x 10% GH + 7.25 x 10° Os + 2.73 x 10 Ny
> 464x107 CO, + 5:22 x 10° HO 42.73 10°,
fis the bumed gas fraction present with the fresh mixture, the numberof kilomoles of each
species per kg of air wil be
No. of kmoles of Cal
No. of kmoles of O
No. of kmoles of Nz
No. of kmoles of CO, =
No. of kmoles of HO
(400 Kg)
Fur Cyees and Ther Avast 137
Solution: Refer to Figure 420,
Giver Ps = 65 bar = 6500 KV?
and vs 201 mig air
Corresponding to ps = 6500 KN/m?
and 2 mg ale,
from the chart given in Figure 4.19,
Ts =240K
a = 1040 Kg air Foue420 Exit
and 87 King sie: K
Process 3-4 is isentropic,
5425) = 887 Kg eK
Compression ratio, r « Fi = Mu
rv 210% 0.1 = 10 mg air
Corresponding to 887 Kk air-K and ve= 1.0 mga,
rom the chart 180K ardua 2220 Ig ir
and pa = 425 KNIm? = 4.25 bar
Pu = (SEE) 7, = [1280] and v = [10 mg
= (ty ty)
Am
=-(-2220 4 1040
4.5.3 Relation between Unburned and Burned Mixtures
‘The combustion in an intemal combustion engine takes place either at constant volume or at
constant pressure. The propetcs of gases after combustion can be estimated i he properties of
the unburned mixture before combustion are known,
HE}, is the enthalpy of formation of the unbumed mixture at 298.15 K, per kg of ai in the
original mixture, then
‘Work of expansion
Whe By 4.16)
Where is the numberof kilooles of species i perkg of stand fi,
species it 298.15 K, per klomole
For a reversible adiabati constant pressure combustion process,
Bes he gy ain
‘here fs is the bumed mixture enthalpy, A, is the unbumed mixture enthalpy and h, is tbe
sensible enthalpy of the unbumed mixture,
isthe enthalpy of formation of
3
al
Similarly for the reversible adiabatic constant volume combustion proces, he imemal energy
‘of the bumed mixture is given by
My Se ee ta a)
419)
were DEEE
‘The following example explain the procede of cbtaning the enthalpy of forman and the
intra energy of formation of te bed mitre. The vals of sandardontlp ad émet
ner of formation for gaseous isooctane (Cs), CO, CO and HO ae given in Table 4,
Tables,
ergy of formation
EZ
‘Standard enthapy andintomal
Hj Oana
En 2003
Species
Eee)
co, na 99
co 11052 Em
HO (299) 8 206
€
(
€
€
€
€
¢
€
{
€
(
€
€
Cutter À
unbumed mixture for gaseous isooctane (CeH1s) and air mixture with equivalence ratio 1.0 and
‘bumed gas fraction f Take the values of standard enthalpy and internal energy of formation from (
€
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L
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€
€
€
€
¢
€
€
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Solution: The chemical equation with $= 1.0 can be wütten as
Colla + 1250; + 47%
(1324 kg)
> 800, + 950
G52 kg)
+ am
(114 kg) (162 kg) 4324 kg)
For 1 kg ai,
00661 kg Calli, + 0232 kg O + 0.768N, -> 0.204 kg CO, + 0.094 kg H,0 + 0.768N
Dividing the mass by molecular weight of species to convert to kmole,
5.198 x 10% GH + 7.25 x 10° Os + 2.73 x 10 Ny
> 464x107 CO, + 5:22 x 10° HO 42.73 10°,
fis the bumed gas fraction present with the fresh mixture, the numberof kilomoles of each
species per kg of air wil be
No. of kmoles of Cal
No. of kmoles of O
No. of kmoles of Nz
No. of kmoles of CO, =
No. of kmoles of HO
(400 Kg)
138 _Funduments of neral Combusien Engines
Fu Cycles and Their Amis 139
Mz E nj
= 5798 x
“a
Phe RAA 10°) + 464 x 10% (2393.52 x 10)
+ 522 x 10° fC24182 x 109
CDI PERE) Ans.
n= E a
= 5.098 1040 = 96-2043 109 + 460 1039852 x 10
+522 «1097-24063 10)
= [CUP ar] Ans.
‘Similacly, fr the otter equivalence ratios, these values an be calculated. The results are shown in
‘Table 4.5, which can be used to analyze the fuel air cycle.
Table 4.5 Enthalpy of formation A, and Internal energy of formation 4%, of the unburned.
mixtura for gaseous isooctane and air mixture.
Equivalence rao, $ CAEN Wp, (kg a)
os Tons 23617 946-2365
10 1299-2587 183-2068
12 1356-297 1419-2694
EDITE The stato of the unbumed mixture of isooctane and sr at the end of the
‘compression process is: temperature = 645 K, internal energy = 310 Kg ar, pressure = 154
“tm, and volume = 0.124 mg ait Calculate the temperature and the pressure ater constant
volume adiabatic combustion and constant pressure adiabatic combustion of the unburned mix
ture having equivalence ratio 1.0 and the burned gas fraction 0.065,
Solution: Given: T,=645K, 4
and va = 0.128 mig ait,
For constant volume adiabatic combustion,
154% 1013
= at de
For 9210, pam 1185-29637 Table 45)
= 1185-296 0.065 = BU. Kg sc
= 10-311 =— LL ig ie
Ao, da == 0.124 mg se
Locating ue on the Du as ch (Figur 4.19) 7s and cun e approximately obtained as
TER] and p= [SORA] Ans.
For constant pressure adiabatic combustion,
5 he = han 9 Hu
For@= 10, Mu =—1299—2958f (Table 45)
129.9 2958 x 0.068 = - 322 kirk air
ALT, = 645 K, from chan (Figure 4.17), gg = 440 Kg at
140-322 = 118 KI sic
= 156 bar = [TRON] Ans.
ype 118 15600,
18-4,
15
A il and-eror solution for v and long the p= 1560 KN? lin on Figure 4.19 gives
TOUR sit, = 052 msg a, T= [220K] Ans
‘An ieatized Oxo engine with a compression rato of 8 operates with a
stoichiometric guscous isooctane and air mixture which is ac 350 K and atm, at the star of
compresion. Te exhaust resido! fraction is 0.08, Th scie value ofthe ues $6,000 Kg
Determine th pressure and the emperaur at the alien points nd ales the indicated thermal
eficeney the indicated mean effective pressure and Ge volumeuic efficiency ofthe fuel
cycle. Use of combustion charts (Figures 4.17 4.18 and 4.19) and Tables (Tables 42 and 4.5 is
allowed. Atmospheric temperature is 25°C.
Rte Sade spn, GT
Ba we, BER
went 2) =150-2m ($)
nT, __ 292%350
Li
CTE
a) Ein] Ans.
125 mg air
Now, "
From Figure 4.1 50 Kg air
and 1 =40 KIN air
— |—
—— —————
Fu Cycles and Their Amis 139
Mz E nj
= 5798 x
“a
Phe RAA 10°) + 464 x 10% (2393.52 x 10)
+ 522 x 10° fC24182 x 109
CDI PERE) Ans.
n= E a
= 5.098 1040 = 96-2043 109 + 460 1039852 x 10
+522 «1097-24063 10)
= [CUP ar] Ans.
‘Similacly, fr the otter equivalence ratios, these values an be calculated. The results are shown in
‘Table 4.5, which can be used to analyze the fuel air cycle.
Table 4.5 Enthalpy of formation A, and Internal energy of formation 4%, of the unburned.
mixtura for gaseous isooctane and air mixture.
Equivalence rao, $ CAEN Wp, (kg a)
os Tons 23617 946-2365
10 1299-2587 183-2068
12 1356-297 1419-2694
EDITE The stato of the unbumed mixture of isooctane and sr at the end of the
‘compression process is: temperature = 645 K, internal energy = 310 Kg ar, pressure = 154
“tm, and volume = 0.124 mg ait Calculate the temperature and the pressure ater constant
volume adiabatic combustion and constant pressure adiabatic combustion of the unburned mix
ture having equivalence ratio 1.0 and the burned gas fraction 0.065,
Solution: Given: T,=645K, 4
and va = 0.128 mig ait,
For constant volume adiabatic combustion,
154% 1013
= at de
For 9210, pam 1185-29637 Table 45)
= 1185-296 0.065 = BU. Kg sc
= 10-311 =— LL ig ie
Ao, da == 0.124 mg se
Locating ue on the Du as ch (Figur 4.19) 7s and cun e approximately obtained as
TER] and p= [SORA] Ans.
For constant pressure adiabatic combustion,
5 he = han 9 Hu
For@= 10, Mu =—1299—2958f (Table 45)
129.9 2958 x 0.068 = - 322 kirk air
ALT, = 645 K, from chan (Figure 4.17), gg = 440 Kg at
140-322 = 118 KI sic
= 156 bar = [TRON] Ans.
ype 118 15600,
18-4,
15
A il and-eror solution for v and long the p= 1560 KN? lin on Figure 4.19 gives
TOUR sit, = 052 msg a, T= [220K] Ans
‘An ieatized Oxo engine with a compression rato of 8 operates with a
stoichiometric guscous isooctane and air mixture which is ac 350 K and atm, at the star of
compresion. Te exhaust resido! fraction is 0.08, Th scie value ofthe ues $6,000 Kg
Determine th pressure and the emperaur at the alien points nd ales the indicated thermal
eficeney the indicated mean effective pressure and Ge volumeuic efficiency ofthe fuel
cycle. Use of combustion charts (Figures 4.17 4.18 and 4.19) and Tables (Tables 42 and 4.5 is
allowed. Atmospheric temperature is 25°C.
Rte Sade spn, GT
Ba we, BER
went 2) =150-2m ($)
nT, __ 292%350
Li
CTE
a) Ein] Ans.
125 mg air
Now, "
From Figure 4.1 50 Kg air
and 1 =40 KIN air
— |—
—— —————
140 Fandumensats of Interno Comburion Engine
sebas Cels and Thee Aras 141
Adiabatic compression work = u, ~ u), = 350-- 40 = 310 Kl
For process 2-3 constant volume adiabatic combustion:
da y= thy pe
For = 10, why =-1185~2963/ (from Table 4.5)
118.5 ~2963 x 0.08 = -355: KR air
2 19 = 350 - 355.5 == 5.5 klk air
ae vy = = 0.125 mg air
Locating (us. v) on the burned gas char, Figure 4.19, gives
TR) m
and 55 = 9.33 Kg aie K
Ans.
For process 3-4 adiabatic expansion
Following a constant entropy process from sate 3 10 4,
33 Wig aie K
tg air
PER
Also,
Locating (vw 5) onthe bumed gas chan, Figure 4.19, gives
y= “ASO Wag ait, um SON and Ty = [OK] Ans.
Expansion work = us ~ ug = 5.5 + 1540 = 15345 Kg air
[Net work output = Expansion work ~ Compression work
Wo 1534.5 - 310 = 1224, Ag air
Indicated thermal efficiency,
w w
EEE
12245
x 100% = [57%] Ans.
EE
Indicated mean effective pressure,
pe E |
PAS
10125
Volumetric efficiency forte chart conditions is
4 x 10° Nm?
Titer} Ans.
nm.
2.
1.
14.
1
16,
m
ass of theoretical ai that would eocupy the displacement volume
at po and Ta of the atmosphere
00% 257298 «gay [BEER] am.
1013 10°(1= 0125)
REVIEW QUESTIONS
. Why isthe thermal efficiency of an air-standard cycle much higher than that of an actual
engine?
‘Why is he analysis ofthe fel-ir eye important?
What are the differences between the analysis ofthe arstandard cycle and that ofthe fuel
air eyele?
‘What ae the assum
s made in the analysis ofthe ful-ar cycle?
. How does the composition of cylinder gases afec he Ali cycle analysis?
5. How do the specific heats vary with temperature? Whats the physical explanation for this
variation? What will be its effect on an Quo cycle?
Explain the phenomenon of dissociation. Under what conditions isthe dissociation of prod-
"cts more prorounced? How does the presence of CO affect dissociation?
3. Show the effect of dissociation on temperature and power of different equivalence ratios.
. Show the effect of dissoca
). Explain the effect of change in number of moles during combustion on the maximum.
a on the Otto eje,
pressure in an Oto cycle.
How do the compression ratio and the equivalence rai affect the thermal efficiency and
the efficiency rato (he ratio of fuel-ireycle efficiency to atstandard cycle efficiency) oF
a Constant volume fuel a eye?
How do the equivalence ratio and the compression rro afec the maximum pressure and
the reaximum temperature of a fulair cycle?
How do the equivalence rato and the compression ratio affect the temperature atthe end of
the expansion stroke?
How do the equivalence ratio and the compression ratio affect the mean effective pressure
of fuel-air cycle?
‘Prove thatthe change in thecal efficiency with respect tothe change in specific het at a
‘constant volume of an Ono cycle having compression rato r is given by
an
aan de
Derive an expression to determine the change inefficiency ofa Diesel sele with respect to
change in specific heat at constant volume having compression ratio r and eut-of ratio A.
‘What are the two different types of combustion charts? Describe these chars withthe help
of simple curves without showing values. Explain the procedure co us these chats fr he
analysis ofa foe ir cycle.
How are the properties of bumed gases obtained, starting with the proper of the un
‘burned mixture just before combustion in the case of (a) a constant volume adiabatic
‘combustion and (b) a constant pressure adiabatic combustion?
sd
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sebas Cels and Thee Aras 141
Adiabatic compression work = u, ~ u), = 350-- 40 = 310 Kl
For process 2-3 constant volume adiabatic combustion:
da y= thy pe
For = 10, why =-1185~2963/ (from Table 4.5)
118.5 ~2963 x 0.08 = -355: KR air
2 19 = 350 - 355.5 == 5.5 klk air
ae vy = = 0.125 mg air
Locating (us. v) on the burned gas char, Figure 4.19, gives
TR) m
and 55 = 9.33 Kg aie K
Ans.
For process 3-4 adiabatic expansion
Following a constant entropy process from sate 3 10 4,
33 Wig aie K
tg air
PER
Also,
Locating (vw 5) onthe bumed gas chan, Figure 4.19, gives
y= “ASO Wag ait, um SON and Ty = [OK] Ans.
Expansion work = us ~ ug = 5.5 + 1540 = 15345 Kg air
[Net work output = Expansion work ~ Compression work
Wo 1534.5 - 310 = 1224, Ag air
Indicated thermal efficiency,
w w
EEE
12245
x 100% = [57%] Ans.
EE
Indicated mean effective pressure,
pe E |
PAS
10125
Volumetric efficiency forte chart conditions is
4 x 10° Nm?
Titer} Ans.
nm.
2.
1.
14.
1
16,
m
ass of theoretical ai that would eocupy the displacement volume
at po and Ta of the atmosphere
00% 257298 «gay [BEER] am.
1013 10°(1= 0125)
REVIEW QUESTIONS
. Why isthe thermal efficiency of an air-standard cycle much higher than that of an actual
engine?
‘Why is he analysis ofthe fel-ir eye important?
What are the differences between the analysis ofthe arstandard cycle and that ofthe fuel
air eyele?
‘What ae the assum
s made in the analysis ofthe ful-ar cycle?
. How does the composition of cylinder gases afec he Ali cycle analysis?
5. How do the specific heats vary with temperature? Whats the physical explanation for this
variation? What will be its effect on an Quo cycle?
Explain the phenomenon of dissociation. Under what conditions isthe dissociation of prod-
"cts more prorounced? How does the presence of CO affect dissociation?
3. Show the effect of dissociation on temperature and power of different equivalence ratios.
. Show the effect of dissoca
). Explain the effect of change in number of moles during combustion on the maximum.
a on the Otto eje,
pressure in an Oto cycle.
How do the compression ratio and the equivalence rai affect the thermal efficiency and
the efficiency rato (he ratio of fuel-ireycle efficiency to atstandard cycle efficiency) oF
a Constant volume fuel a eye?
How do the equivalence ratio and the compression rro afec the maximum pressure and
the reaximum temperature of a fulair cycle?
How do the equivalence rato and the compression ratio affect the temperature atthe end of
the expansion stroke?
How do the equivalence ratio and the compression ratio affect the mean effective pressure
of fuel-air cycle?
‘Prove thatthe change in thecal efficiency with respect tothe change in specific het at a
‘constant volume of an Ono cycle having compression rato r is given by
an
aan de
Derive an expression to determine the change inefficiency ofa Diesel sele with respect to
change in specific heat at constant volume having compression ratio r and eut-of ratio A.
‘What are the two different types of combustion charts? Describe these chars withthe help
of simple curves without showing values. Explain the procedure co us these chats fr he
analysis ofa foe ir cycle.
How are the properties of bumed gases obtained, starting with the proper of the un
‘burned mixture just before combustion in the case of (a) a constant volume adiabatic
‘combustion and (b) a constant pressure adiabatic combustion?
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142_Fanéamena of neral Comburdon Engines
PROBLEMS
ratio 10, when the specific heat at constant volume increases by 1.5%?
by 1897
specific heat at constant volume in Mk K) is given by €,
is the temperature in kelvin. Determine the compression ratio of the engine.
specific heat at constant pressure of the products of combustion is given by cp
aire ati.
Assume R = 0.287 KJ/Kg K) and c, = (0716 + 125 x 10% 7) KI K).
eyele (a) without cons
respectively.
cline per of ir wi
products remains inthe clearance space and mixes with the fresh charge.
are used? Obtain the composition for } kg of air
of compression. The exhaust residual fraction is 0.05. The calor
“Atmospheric temperature is 25°
42 What willbe the percentage change in the efficiency of an Otto cycle having a compression
42 What wil be the percentage change in the efficiency ofa Diesel cycle having a compres
sion ratio 20 and a cut-ofP ratio 2.62, when the specific heat at constant volume increases.
43 An engine working on Ono cycle has the al/ful ratio as 15 : 1. The temperature a the
beginning of a compression stroke is 57°C, The calorific valu of fe! is 44,000 Kg. The
maximum temperature in the cylinder is 3550 K. The index of compression is 1.33 andthe
(678 + 0.000137, where 7
44 The compression ratio of an engine working on Diesel cycle is 20. The temperature at
the end of compresion is 1050 K. The calorific value of fuel is 42,000 Kg and the
28 x 107) Kg KO. Combustion is completed at 6.5% of the stoke, Determine the
4.5 An engine working on Dual combustion cycle, has a compression ratio of 18 and the cut-
of takes place at 6.5% of the stoke. The maximum pressure of the eyele is 75 ba. The
Pressure and the temperature a the beginning of compression are I bar and 67°C respec-
tively. Determine the pressure andthe temperature a all the salient points of the cycle.
‘An engine working on Onto cycle with a compression ratio 10, uses Cali a a fel, The
‘alrifc value of fuel is 44,000 KV. The arfulctiois 16: 1. Determine the percentage
molecular expansion. Compute the maximum pressure and the temperature seached inthe
ing molecular expansion and (9) with molecular expansion,
‘Assume €, = 0.71 U/kg K), compression follows th law pVIS «constan, The pressure
and the temperature of the mixture at the beginning of compression are 1 bar and 57°C
47 Determine the number of élomoles of ar unbumed mixture of isooctane and air inthe
‘equivalence ratio (2) 0.8 and (b) 1.2. A mass faction fof the
4.8 An engine as a reidual fraction of 0.05 and burns a mixture having an equivalence ratio
‘of 08 How much fresh air and fuel were inducted? How much residu air and fuel
49 Calculat the sensible intemal energy and the sensible enthalpy pet kg of sr at 1000 K
Für an isooctane and air mixture having an equivatence ratio 1.0, Use Tables 3.3 and 4.3
410 A constant volume fut-a cycle with a compresion rato of 10 operates with a stich
metre gaseous isooctane and air mixture which is at 1 atm. and 67°C at the start
fe value of the fuel
is 44,000 Kg. Determine the pressure and he temperature a the salient points, the work
‘of compression the work of expansion, the indicated thermal efficiency, the indicated
mean effective pressure and the volumetric efficiency of the fuel cycle. Use of com-
pression charts (Figures 4.17, 4.18 and 4.19) and tables (Tables 4.2 and 4.5) is allowed.
The Actual Cycle
5.1 INTRODUCTION
An engine operating on the air eyele convert input heat into useful work. The remainder hear is
‘ejected atthe end of power stroke and represents the energy fost inthe hot exhaust gases, Air
cycle analysis predicts higher efficiency ofthe engine than what is actually obtainable, because of
very simplified approach adopted,
‘When the losses due to chemical equilibrium, variable specifi hea and the effect of increase
in the number of molecules after combustion are added to the exhaust heat loss, the fhel-air
cycle results. The analysis of the fuel air cycle predits better results but sill not so close as
desire.
‘The actual cycle analysis considers other losses in addition t the above losses. This analysis.
predicts very close results compared to the resus obtained actually by running the engine and
taking measurements by sophisticated instruments. An estimate ofthe losses ean be made from
previous experience and from simple tests performed on the engines, Iis now possible to analyse
‘he actual cycle with the help of computer programs developed for this purpose.
52 DIFFERENCE BETWEEN THE ACTUAL CYCLE AND THE
FUEL-AIR CYCLE
The possible causes of the observed differences between the actual cycle and he fuel cycle
include the following losses that are taken into account for the analysis of the actual cycle, and
Which are not considered inthe analysis ofthe fue-ar cycle.
1. Leakage
Imperfectmixing of fuel and aie
Progressive burning
Burning time loses, due tothe motion ofthe piston during combustion,
Heat losses tothe cylinder walls
Exhaust blowdovin oes
Fluid fiction
Gas exchange or pumping loss
—_
eR ———
PROBLEMS
ratio 10, when the specific heat at constant volume increases by 1.5%?
by 1897
specific heat at constant volume in Mk K) is given by €,
is the temperature in kelvin. Determine the compression ratio of the engine.
specific heat at constant pressure of the products of combustion is given by cp
aire ati.
Assume R = 0.287 KJ/Kg K) and c, = (0716 + 125 x 10% 7) KI K).
eyele (a) without cons
respectively.
cline per of ir wi
products remains inthe clearance space and mixes with the fresh charge.
are used? Obtain the composition for } kg of air
of compression. The exhaust residual fraction is 0.05. The calor
“Atmospheric temperature is 25°
42 What willbe the percentage change in the efficiency of an Otto cycle having a compression
42 What wil be the percentage change in the efficiency ofa Diesel cycle having a compres
sion ratio 20 and a cut-ofP ratio 2.62, when the specific heat at constant volume increases.
43 An engine working on Ono cycle has the al/ful ratio as 15 : 1. The temperature a the
beginning of a compression stroke is 57°C, The calorific valu of fe! is 44,000 Kg. The
maximum temperature in the cylinder is 3550 K. The index of compression is 1.33 andthe
(678 + 0.000137, where 7
44 The compression ratio of an engine working on Diesel cycle is 20. The temperature at
the end of compresion is 1050 K. The calorific value of fuel is 42,000 Kg and the
28 x 107) Kg KO. Combustion is completed at 6.5% of the stoke, Determine the
4.5 An engine working on Dual combustion cycle, has a compression ratio of 18 and the cut-
of takes place at 6.5% of the stoke. The maximum pressure of the eyele is 75 ba. The
Pressure and the temperature a the beginning of compression are I bar and 67°C respec-
tively. Determine the pressure andthe temperature a all the salient points of the cycle.
‘An engine working on Onto cycle with a compression ratio 10, uses Cali a a fel, The
‘alrifc value of fuel is 44,000 KV. The arfulctiois 16: 1. Determine the percentage
molecular expansion. Compute the maximum pressure and the temperature seached inthe
ing molecular expansion and (9) with molecular expansion,
‘Assume €, = 0.71 U/kg K), compression follows th law pVIS «constan, The pressure
and the temperature of the mixture at the beginning of compression are 1 bar and 57°C
47 Determine the number of élomoles of ar unbumed mixture of isooctane and air inthe
‘equivalence ratio (2) 0.8 and (b) 1.2. A mass faction fof the
4.8 An engine as a reidual fraction of 0.05 and burns a mixture having an equivalence ratio
‘of 08 How much fresh air and fuel were inducted? How much residu air and fuel
49 Calculat the sensible intemal energy and the sensible enthalpy pet kg of sr at 1000 K
Für an isooctane and air mixture having an equivatence ratio 1.0, Use Tables 3.3 and 4.3
410 A constant volume fut-a cycle with a compresion rato of 10 operates with a stich
metre gaseous isooctane and air mixture which is at 1 atm. and 67°C at the start
fe value of the fuel
is 44,000 Kg. Determine the pressure and he temperature a the salient points, the work
‘of compression the work of expansion, the indicated thermal efficiency, the indicated
mean effective pressure and the volumetric efficiency of the fuel cycle. Use of com-
pression charts (Figures 4.17, 4.18 and 4.19) and tables (Tables 4.2 and 4.5) is allowed.
The Actual Cycle
5.1 INTRODUCTION
An engine operating on the air eyele convert input heat into useful work. The remainder hear is
‘ejected atthe end of power stroke and represents the energy fost inthe hot exhaust gases, Air
cycle analysis predicts higher efficiency ofthe engine than what is actually obtainable, because of
very simplified approach adopted,
‘When the losses due to chemical equilibrium, variable specifi hea and the effect of increase
in the number of molecules after combustion are added to the exhaust heat loss, the fhel-air
cycle results. The analysis of the fuel air cycle predits better results but sill not so close as
desire.
‘The actual cycle analysis considers other losses in addition t the above losses. This analysis.
predicts very close results compared to the resus obtained actually by running the engine and
taking measurements by sophisticated instruments. An estimate ofthe losses ean be made from
previous experience and from simple tests performed on the engines, Iis now possible to analyse
‘he actual cycle with the help of computer programs developed for this purpose.
52 DIFFERENCE BETWEEN THE ACTUAL CYCLE AND THE
FUEL-AIR CYCLE
The possible causes of the observed differences between the actual cycle and he fuel cycle
include the following losses that are taken into account for the analysis of the actual cycle, and
Which are not considered inthe analysis ofthe fue-ar cycle.
1. Leakage
Imperfectmixing of fuel and aie
Progressive burning
Burning time loses, due tothe motion ofthe piston during combustion,
Heat losses tothe cylinder walls
Exhaust blowdovin oes
Fluid fiction
Gas exchange or pumping loss
—_
eR ———
144_ Funsumenalı of neral Combustion Engines
521 Leakage
At higher piston speeds, leakage usually insignificant in a well adjusted engine. However, alow
piston speeds and high gas pressure, the gas flows into the regions between the piston, piston
rings and cylinder walls and gets cooled by heat transfer through cylinder walls. These regions are
called crevice regions. The gases flowing int these regions usually remain unburned and some of
the gases retum o he cylinder during the iter part ofthe expansion stroke andthe remaining ges
eaks past the piston rings tothe crank case. Leakage canbe estimated by measuring blow by, that
is. the mass ofthe gases flowing out fom the erank case breather. This leakage los reduces the
cylinder pressure during combustion and ducing the edly par of the expansion stroke, thus reduce
ing the net power output ofthe engine
5.2.2 Imperfect Mixing of Fuel and Air
In practice, i is not possible to obtain a perfect homogencous mixture of fuel, air and residual
gases in the eylinder before the igition takes place, because of insufficient turbulence. In one par
of the cylinder, there may be excess oxygen and in another part excess fuel may be presen. The
excess fuel may not find enough oxygen for completo combustion, which may resul ia the
appearance of CO, Hy and unburned fel inthe exhaust, Tae efficiency ofthe engine will decrease
because ofthe wastage of fuel. Figure 5.1 shows the composition of exhaust gases of atypical
een
EE RES ET nee
i
2,
I
à
!
a
a
gue Ss Compost losas gases a pl ans egin aro eco,
Even ifthe unbumed fuel and oxygen combine later during the expansion stoke, resulting in
o loss of fuel in the exhaust, sill there will be a loss in efficiency, since the sensible energy
present with the combustion of this par of fuel is not utilized at top dead centre and hence does
ot contribute 16 the pressure rise at tht point.
A carburetor produces a wet, non-homogeneous mixture and fuel is unevenly distributed
between the inlet manifold branches of a muli-eyinder engine. Thus, some cylindes receive a
r
The Aust Gye 145
much leaner mixture than others. This madistibution of fuel in a mult-cylinder engine does not
permit to run the engine withthe most economical feVair ratio, With such mixture, the mixture
in some cylinders may be 100 lean. This may cause slow burning of fuel or the fue) may not burn
ral
‘The effect of imperfect mixing of fuel and air on engine efficiency isnot much, provided ihe
inte system is designed properly andthe inlet manifol placed over the exhaust manifold to heat
the charge for beses mixing.
52.3 Progressive Burning
Inthe analysis of constant volume fuel-air cycle its assumed thatthe ignition takes place at top
‘ead centre and combustion is instantaneous. In an actual SI engine, combustion stars a a certain
point and continues by moving the flame rom. Combustion is complete when the flame front has
passed through the entire charge. I takes some time in doing so, The time required fortis varies
‘wth the fuel composition, the combustion chamber shape and size including the number and
postion of the igntion point and engine operating conditions. Different amounts of charge bura at
different ümes even if he piston is neary stationery during combustion, The spark ignites a very
small ponion of the charge immediately adjacent to it, The flame then spreads progressively
throughout the mixture. This phenomenon of burning is called progressive burning.
‚The calculations of fuetair cycles with progressive barning show thatthe mean effective
pressure and efficiency ofthe cycles are almost the same as those for similar fuel eyees with
‘instantaneous burning. For such cycles, th piston is assumed to remain at top dead centre during
burning of all pars of the charge
‘The lasses due to Jeakage, imperfect mixing and progressive burning are 100 small and cannot
be evident on the p-V diagram. The remaiaing losses, namely the time loss, he heat los, the
exhaust blowdown loss are significan and can be shown on the p-V diagram,
524 Burning Time Losses
The crankshaft nomall rates trough 40” or more between the ime the sparks produced and
thetime the charg is completely burned. The time In degre rank angle (CA) depende upon the
“ame speed andthe distance between the poston of pak plug and the Farhest ie of combus
ti chamber. The fame tave distance can be reduced by locating the spark plug atthe centre of
the cylinder head or by using more than one spark pag. A temisphercal combustion chamber
often uses two spark logs mounted on the einer head on opposite sides to reduce the Tame
travel distance. The motion ofthe flame foot depends upon how fast the hat sransferd from
the ame font wo the unbumedmintur jun ahead ofthe late fon, Heats generated by the
chemical reaction a he fame font
As te eranksaft rotates, the piston moves and ifthe piston mation during combustion is
taken into account the burning time loses are determine, which reel in los of work and
esficiency. However, she buming ime losses are quite lage,
(a) The fuer ratios made to lean, or to ih
(©) The role is pay close, reducing the suetion pressure
(©) The point of ignition is aot propel set
521 Leakage
At higher piston speeds, leakage usually insignificant in a well adjusted engine. However, alow
piston speeds and high gas pressure, the gas flows into the regions between the piston, piston
rings and cylinder walls and gets cooled by heat transfer through cylinder walls. These regions are
called crevice regions. The gases flowing int these regions usually remain unburned and some of
the gases retum o he cylinder during the iter part ofthe expansion stroke andthe remaining ges
eaks past the piston rings tothe crank case. Leakage canbe estimated by measuring blow by, that
is. the mass ofthe gases flowing out fom the erank case breather. This leakage los reduces the
cylinder pressure during combustion and ducing the edly par of the expansion stroke, thus reduce
ing the net power output ofthe engine
5.2.2 Imperfect Mixing of Fuel and Air
In practice, i is not possible to obtain a perfect homogencous mixture of fuel, air and residual
gases in the eylinder before the igition takes place, because of insufficient turbulence. In one par
of the cylinder, there may be excess oxygen and in another part excess fuel may be presen. The
excess fuel may not find enough oxygen for completo combustion, which may resul ia the
appearance of CO, Hy and unburned fel inthe exhaust, Tae efficiency ofthe engine will decrease
because ofthe wastage of fuel. Figure 5.1 shows the composition of exhaust gases of atypical
een
EE RES ET nee
i
2,
I
à
!
a
a
gue Ss Compost losas gases a pl ans egin aro eco,
Even ifthe unbumed fuel and oxygen combine later during the expansion stoke, resulting in
o loss of fuel in the exhaust, sill there will be a loss in efficiency, since the sensible energy
present with the combustion of this par of fuel is not utilized at top dead centre and hence does
ot contribute 16 the pressure rise at tht point.
A carburetor produces a wet, non-homogeneous mixture and fuel is unevenly distributed
between the inlet manifold branches of a muli-eyinder engine. Thus, some cylindes receive a
r
The Aust Gye 145
much leaner mixture than others. This madistibution of fuel in a mult-cylinder engine does not
permit to run the engine withthe most economical feVair ratio, With such mixture, the mixture
in some cylinders may be 100 lean. This may cause slow burning of fuel or the fue) may not burn
ral
‘The effect of imperfect mixing of fuel and air on engine efficiency isnot much, provided ihe
inte system is designed properly andthe inlet manifol placed over the exhaust manifold to heat
the charge for beses mixing.
52.3 Progressive Burning
Inthe analysis of constant volume fuel-air cycle its assumed thatthe ignition takes place at top
‘ead centre and combustion is instantaneous. In an actual SI engine, combustion stars a a certain
point and continues by moving the flame rom. Combustion is complete when the flame front has
passed through the entire charge. I takes some time in doing so, The time required fortis varies
‘wth the fuel composition, the combustion chamber shape and size including the number and
postion of the igntion point and engine operating conditions. Different amounts of charge bura at
different ümes even if he piston is neary stationery during combustion, The spark ignites a very
small ponion of the charge immediately adjacent to it, The flame then spreads progressively
throughout the mixture. This phenomenon of burning is called progressive burning.
‚The calculations of fuetair cycles with progressive barning show thatthe mean effective
pressure and efficiency ofthe cycles are almost the same as those for similar fuel eyees with
‘instantaneous burning. For such cycles, th piston is assumed to remain at top dead centre during
burning of all pars of the charge
‘The lasses due to Jeakage, imperfect mixing and progressive burning are 100 small and cannot
be evident on the p-V diagram. The remaiaing losses, namely the time loss, he heat los, the
exhaust blowdown loss are significan and can be shown on the p-V diagram,
524 Burning Time Losses
The crankshaft nomall rates trough 40” or more between the ime the sparks produced and
thetime the charg is completely burned. The time In degre rank angle (CA) depende upon the
“ame speed andthe distance between the poston of pak plug and the Farhest ie of combus
ti chamber. The fame tave distance can be reduced by locating the spark plug atthe centre of
the cylinder head or by using more than one spark pag. A temisphercal combustion chamber
often uses two spark logs mounted on the einer head on opposite sides to reduce the Tame
travel distance. The motion ofthe flame foot depends upon how fast the hat sransferd from
the ame font wo the unbumedmintur jun ahead ofthe late fon, Heats generated by the
chemical reaction a he fame font
As te eranksaft rotates, the piston moves and ifthe piston mation during combustion is
taken into account the burning time loses are determine, which reel in los of work and
esficiency. However, she buming ime losses are quite lage,
(a) The fuer ratios made to lean, or to ih
(©) The role is pay close, reducing the suetion pressure
(©) The point of ignition is aot propel set
146_Funtamenal of Item Combustion Engines
5.25 Heat Losses to the Cylinder Walls
Heat transfer between ie cylinder gases and the cylinder walls during he compression stoke, up
10 the point of ignition at which combustion stats, appears 10 be negligible, owing to the gas
temperature being not high. During combustion and early pas ofthe expansion stroke, he tem
perature of the cylinder gases is high and a considerable amount of heat flows from the hot gases
through the cylinder walls and cylinder head into the water jacket in water-cooled engines or
cooling fins in at-cooled engines. Some heat enters into the piston head, and from there it flows to
‘the piston rings. As the piston rings are in contact with the clindes walls, so the heat flows tothe
cylinder walls. Out ofthis het, some teat is taken away by the engine oil present between the
piston rings and the cylinde wall for lubricaion, The rest ofthe heat goes 0 the cooling media,
As a result of loss of heat to the cylinder walls the work and efficiency of the cycle are
reduced because some of the heat energy liberated by combustion is not uilized foe producing
work during expansion. However, he loss of heat during combustion reduces the maximum
temperature and the dissociation of CO; and HO is also reduced, which results in complete
combustion, but the improvement in work and efficiency is only marginal,
5.2.6 Exhaust Blowdown Loss
‘The pressure at the end ofthe expansion stroke is much higher than the atmospheric pressure, If
the exhaust valve is opened at bottom dead entre, the piston would have to doa large amount of
‘work in order to expe the high pressure exhaust gases during the exhaust stoke. If the exhaust
valve is opened 100 easly, ar of the expansion work is lost. The best postion is to open the
“exhaust valve 40° to 70° before BDC. In this case 100, some expansion work is lost but the work
‘spent by the piston during the exhaust stoke is reduced. The ne result wil be the gain in some
work. The early opening of the exhaust valve releases the pressure of the gas before the piston
reaches BDC. This process is called exhaust blowdown, Figure 5.2 shows the effect of exhaust
valve opening time on exhaus Blowdown loss. With proper designing and timing ofthe exhaust
valve opening, the blowdovn los is not much,
Figure 5.2 Efecto east ave opening (EVO) ma on aha iondon ls.
The Aral Crée 147
Figure 5.3 shows the comparison ofthe constant volume fuel air cycle withthe actual cycle,
indicating the burning time loss, heat loss and exhaust loss. It is a power cycle and does not
include gas exchanges.
ring times
Figures. Compaizon constant volar ly vo ata o cn oder
Loss ratio
Rs the rato ofthe Joss area 1 the fuel-air cycle ara, Tes used for the sake of comparison of
diferent losses. The following loss ratios are defined:
(6) Time toss ratio: ‘The rato ofthe baring time loss area to te area of the fuer cycle
diagram is called the time Joss ratio.
(i) Heat loss ratio: The ratio of the heat loss area to the ares of fuel-air cycle diagram is
called the heat los ratio.
(iy Blowdown loss ratio: The rato of the exhaust blowdown aca tothe area ofthe fuel: air
cycle diagram is called the Blowdown lass ra
Gv) Lost work ratio: Tt can be expressed asthe ratio of he difference of area of fuckair
cycle and area of actual eycle to the area of fuel air eyes, ie.
„area of actual eyele
Tost work rao = of fuel aie cycle
For a well adjusted ana good condition typical ST engine, the ratio of the work of the
cual cycle to that of the ful lr cycle can be safely assumed as 0.8, Total lost work is therefore
20% of the fuckair eyele work, Let us assume based on experience that out of this lost work
30% goes tothe time loss, 60% goes to the heat loss and 10% goes 10 the exhaust blowdown
loss.
For the above example, the time loss comes out to be 6%, heat loss 12% and the Blowdown
loss comes out to be 2% of the ful-air cycle work
5.25 Heat Losses to the Cylinder Walls
Heat transfer between ie cylinder gases and the cylinder walls during he compression stoke, up
10 the point of ignition at which combustion stats, appears 10 be negligible, owing to the gas
temperature being not high. During combustion and early pas ofthe expansion stroke, he tem
perature of the cylinder gases is high and a considerable amount of heat flows from the hot gases
through the cylinder walls and cylinder head into the water jacket in water-cooled engines or
cooling fins in at-cooled engines. Some heat enters into the piston head, and from there it flows to
‘the piston rings. As the piston rings are in contact with the clindes walls, so the heat flows tothe
cylinder walls. Out ofthis het, some teat is taken away by the engine oil present between the
piston rings and the cylinde wall for lubricaion, The rest ofthe heat goes 0 the cooling media,
As a result of loss of heat to the cylinder walls the work and efficiency of the cycle are
reduced because some of the heat energy liberated by combustion is not uilized foe producing
work during expansion. However, he loss of heat during combustion reduces the maximum
temperature and the dissociation of CO; and HO is also reduced, which results in complete
combustion, but the improvement in work and efficiency is only marginal,
5.2.6 Exhaust Blowdown Loss
‘The pressure at the end ofthe expansion stroke is much higher than the atmospheric pressure, If
the exhaust valve is opened at bottom dead entre, the piston would have to doa large amount of
‘work in order to expe the high pressure exhaust gases during the exhaust stoke. If the exhaust
valve is opened 100 easly, ar of the expansion work is lost. The best postion is to open the
“exhaust valve 40° to 70° before BDC. In this case 100, some expansion work is lost but the work
‘spent by the piston during the exhaust stoke is reduced. The ne result wil be the gain in some
work. The early opening of the exhaust valve releases the pressure of the gas before the piston
reaches BDC. This process is called exhaust blowdown, Figure 5.2 shows the effect of exhaust
valve opening time on exhaus Blowdown loss. With proper designing and timing ofthe exhaust
valve opening, the blowdovn los is not much,
Figure 5.2 Efecto east ave opening (EVO) ma on aha iondon ls.
The Aral Crée 147
Figure 5.3 shows the comparison ofthe constant volume fuel air cycle withthe actual cycle,
indicating the burning time loss, heat loss and exhaust loss. It is a power cycle and does not
include gas exchanges.
ring times
Figures. Compaizon constant volar ly vo ata o cn oder
Loss ratio
Rs the rato ofthe Joss area 1 the fuel-air cycle ara, Tes used for the sake of comparison of
diferent losses. The following loss ratios are defined:
(6) Time toss ratio: ‘The rato ofthe baring time loss area to te area of the fuer cycle
diagram is called the time Joss ratio.
(i) Heat loss ratio: The ratio of the heat loss area to the ares of fuel-air cycle diagram is
called the heat los ratio.
(iy Blowdown loss ratio: The rato of the exhaust blowdown aca tothe area ofthe fuel: air
cycle diagram is called the Blowdown lass ra
Gv) Lost work ratio: Tt can be expressed asthe ratio of he difference of area of fuckair
cycle and area of actual eycle to the area of fuel air eyes, ie.
„area of actual eyele
Tost work rao = of fuel aie cycle
For a well adjusted ana good condition typical ST engine, the ratio of the work of the
cual cycle to that of the ful lr cycle can be safely assumed as 0.8, Total lost work is therefore
20% of the fuckair eyele work, Let us assume based on experience that out of this lost work
30% goes tothe time loss, 60% goes to the heat loss and 10% goes 10 the exhaust blowdown
loss.
For the above example, the time loss comes out to be 6%, heat loss 12% and the Blowdown
loss comes out to be 2% of the ful-air cycle work
148_Fondamentals of nara! Comburdon Engines
The Aewal pe 149
5.2.7. Fluld Friction
“At high engine speeds, urbulenee inside the engine cylinder causes fection between fluid paces.
During suction and exhaust processes, fd friction is appreciable, Near the end of the compres
sion process and during the inital par of the expansion process, fluid ition is high because of
higher pressure between the fluid panicles. During combustion, flame speed ie turbulent, which
causes more fluid friction. The overall effect of fui friction onthe actual cycle is very litle,
5.2.8 Gas Exchange or Pumping Loss
‘The purpose of he gas exchange proces is 10 admit the fresh charge during the suction stoke
‘and remove the burned gases atthe end of che expansion stroke. During the induction process,
pressure loses occur at the charge passes through che ar filer, the carburettor and the intake
(manifod, There i additional pressure drop across the inlet valve. The drop in pressure along the
intake system also depends on the engine speed. The pressure during the suction stroke is below
atmospheric, The exhaust system consists of an exhaust manifold, an exhaust pipe, and often a
catalytic converter for emission contol, and a mufRer or silencer. The bumed cylinder gases get
expelled because ofthe pressure difference between the cylinder and the exhaust system. The
pressure during the exhaust stroke is much higher than the atmospheric,
Figure 5.4 shows the gus exchange processes in a conventional SI engine, The difference of
work done in expelling the exhaust gases and the work done by he fresh charge during the sition
stroke is called the pumping work and he loop formed is called the pumping loop. The arca of the
pumping loop indicates negative work and represents pumpin losses. The term pumping is sed
as the gas from the lower inlet pressure is pumped 1 the higher exhaust pressure, The pumping
loss Intense a at ote because thing reduces the sion presse, The pumpin Ins
also increases with speed,
»
5.3 EFFECT OF ENGINE VARIABLES ON FLAME SPEED
Flame speed is a very important parameter which affects the actual cycle diagram and hence the
‘work output from the engine. The flame speed depends upon certain engine variables as explained
inthe following subsections.
634 Fuel/Air Ratio
“The flame speed is highly dependent upon tempera. At higher temperatures, the flame speed
increases. Figure 49 shows thatthe maximum temperature is obtained with a slightly rich mixture
and hence che lame speed is maximum. I is obvious that for a lean mixture, less chemical energy
‘converted ito heat energy, and hence the flame temperature i low. A very rich mixture cess
incomplets combustion producing lees heat. A slightly ich mixture results in maximum fame
temperate during combustion and therefore gives the maximun flame sped.
532 Inlet Pr
Foc a given engine speed, the inlet pressure can be changed either by throttling or by supercharg
ing the engine. When the throttle valve is partially closed, the nls pressure educes causing lower
maximum temperature, hus resulting in reduction of the flame speed: On the other hand, ifthe
engine is supercharged the inlet pressure increases, causing higher maximum temperature end
resulting in increase in the lame speed.
5.3.3 Engine Speed
At higher engine speeds, the mean piston speed increases, which causes a Higher nt velocity of
the mixture inthe cylinder through the inlet valve, This forms voices and hence turbulence in be
incoming charge. The mébulence persists during buming, causing relative motion between the
flame front andthe unburned mixture. This motion increases the heat transfer between them and
therefore the Name speed increases.
53.4 Engine Size
‘The flame speed does not depend upon the engine size of engines of si y Engines of
similar design wil have he same mean piston speed (S) and the same ratio of are of piston hend
to the effective acen of the inlet valve (A/A, )regaedles oftheir size.
‘Mean piston speed, S = ZEN, where Lis be stroke length and N is the engine speed in
revolutions er uit ie.
In order to keep the mean piston speed almost the same, the larger engines having longer
stroke lengths run at lower engine speeds and he smaller engines having shorter stoke lenghs
run at higher engine speeds ú
‘Assuming the density constant of entering mixture through valve and applying the continuity
‘equation,
Inet velocity af the charge = 5(4,/A,)
Since forthe similar designed engines, Sand A,/A, are the same, therefore, the inlet velocity
ofthe charge, the trbulence and flame speed will approximately be the same. With the same fame
Speed, the time taken for completing the combustion process inthe larger engine will be more
because the distance across the combustion space is greater. The speed (revolutions per minute
(pm) ofthe larger engine is low, so the crank takes longer to complete a revolution, The result is
{hat the crank angle required for burning willbe almost the same regardless of the sizeof the
—
The Aewal pe 149
5.2.7. Fluld Friction
“At high engine speeds, urbulenee inside the engine cylinder causes fection between fluid paces.
During suction and exhaust processes, fd friction is appreciable, Near the end of the compres
sion process and during the inital par of the expansion process, fluid ition is high because of
higher pressure between the fluid panicles. During combustion, flame speed ie turbulent, which
causes more fluid friction. The overall effect of fui friction onthe actual cycle is very litle,
5.2.8 Gas Exchange or Pumping Loss
‘The purpose of he gas exchange proces is 10 admit the fresh charge during the suction stoke
‘and remove the burned gases atthe end of che expansion stroke. During the induction process,
pressure loses occur at the charge passes through che ar filer, the carburettor and the intake
(manifod, There i additional pressure drop across the inlet valve. The drop in pressure along the
intake system also depends on the engine speed. The pressure during the suction stroke is below
atmospheric, The exhaust system consists of an exhaust manifold, an exhaust pipe, and often a
catalytic converter for emission contol, and a mufRer or silencer. The bumed cylinder gases get
expelled because ofthe pressure difference between the cylinder and the exhaust system. The
pressure during the exhaust stroke is much higher than the atmospheric,
Figure 5.4 shows the gus exchange processes in a conventional SI engine, The difference of
work done in expelling the exhaust gases and the work done by he fresh charge during the sition
stroke is called the pumping work and he loop formed is called the pumping loop. The arca of the
pumping loop indicates negative work and represents pumpin losses. The term pumping is sed
as the gas from the lower inlet pressure is pumped 1 the higher exhaust pressure, The pumping
loss Intense a at ote because thing reduces the sion presse, The pumpin Ins
also increases with speed,
»
5.3 EFFECT OF ENGINE VARIABLES ON FLAME SPEED
Flame speed is a very important parameter which affects the actual cycle diagram and hence the
‘work output from the engine. The flame speed depends upon certain engine variables as explained
inthe following subsections.
634 Fuel/Air Ratio
“The flame speed is highly dependent upon tempera. At higher temperatures, the flame speed
increases. Figure 49 shows thatthe maximum temperature is obtained with a slightly rich mixture
and hence che lame speed is maximum. I is obvious that for a lean mixture, less chemical energy
‘converted ito heat energy, and hence the flame temperature i low. A very rich mixture cess
incomplets combustion producing lees heat. A slightly ich mixture results in maximum fame
temperate during combustion and therefore gives the maximun flame sped.
532 Inlet Pr
Foc a given engine speed, the inlet pressure can be changed either by throttling or by supercharg
ing the engine. When the throttle valve is partially closed, the nls pressure educes causing lower
maximum temperature, hus resulting in reduction of the flame speed: On the other hand, ifthe
engine is supercharged the inlet pressure increases, causing higher maximum temperature end
resulting in increase in the lame speed.
5.3.3 Engine Speed
At higher engine speeds, the mean piston speed increases, which causes a Higher nt velocity of
the mixture inthe cylinder through the inlet valve, This forms voices and hence turbulence in be
incoming charge. The mébulence persists during buming, causing relative motion between the
flame front andthe unburned mixture. This motion increases the heat transfer between them and
therefore the Name speed increases.
53.4 Engine Size
‘The flame speed does not depend upon the engine size of engines of si y Engines of
similar design wil have he same mean piston speed (S) and the same ratio of are of piston hend
to the effective acen of the inlet valve (A/A, )regaedles oftheir size.
‘Mean piston speed, S = ZEN, where Lis be stroke length and N is the engine speed in
revolutions er uit ie.
In order to keep the mean piston speed almost the same, the larger engines having longer
stroke lengths run at lower engine speeds and he smaller engines having shorter stoke lenghs
run at higher engine speeds ú
‘Assuming the density constant of entering mixture through valve and applying the continuity
‘equation,
Inet velocity af the charge = 5(4,/A,)
Since forthe similar designed engines, Sand A,/A, are the same, therefore, the inlet velocity
ofthe charge, the trbulence and flame speed will approximately be the same. With the same fame
Speed, the time taken for completing the combustion process inthe larger engine will be more
because the distance across the combustion space is greater. The speed (revolutions per minute
(pm) ofthe larger engine is low, so the crank takes longer to complete a revolution, The result is
{hat the crank angle required for burning willbe almost the same regardless of the sizeof the
—
150 Funéarenas of Inara! Combustion Enga
engine. The optimum ignition advance wil therefore be approximately the same and "he burning
‘ine losses willbe almost the same percentage of the energy input
535 Residual Gas
he residual gas is more, the fresh charge is diluted. I will cause fame speed to duce and the
burning time losses will be mare, The amount of residual gas present depends upor the sizeof the
learance space and the exhaust pressure. The smaller th size of clearance space and lower the
‘exhaust pressure, the les will be the amount ofthe residual gas present, which can be achieved
with a higher compression rato, The higher the inet pressure, the more will be the fresh charge
‘The flame speed increases with more fresh charge and les residual gas.
54 EFFECT OF SPARK-ADVANCE ON THE ACTUAL
CYCLE OF SI ENGINES
Suppose the spark timing is set in such a way that as the piston reaches the TDC position, the
spark is strike and the combustion of fuel kes place. Combustion is completed only after the
piston has traveled a considerable distance from the TDC on expansion stoke, Figure 5.5 shows
the actual indicator diagram with ignition at TDC and also shows the corresponding fuer cycle
indicator diagram. Lis observed that tbe maximum pressure is considerably reduced a compar
son tothe maximum pressure obtained with the fuel-ar cycle. A considerable aes ofthe diagram
is lost and thus the actual power and efficiency are low.
»
S--Pont of spark
Fake
Acta ele
me Boe
gres. Shows tn ac naar gr vol TDC and ala howe coeur util dto
den.
te spark timing is much advanced, he ignition takes place early on the compression stoke.
‘kis possible o get complete combustion in his case just asthe piston reaches TDC, but addtional
work is required to compress the working gases, so that once again the work area i ess, and thus
‘the power and efficiency are low. Figure 5.6 shows the actual indicator diagram with early ignition
and also shows the corresponding fuel air cycle indicator diagram.
The Act! Cyeto_151
»
Sino pur
Faire
ei ele
i _
3 [73
Figo. Shows al ner gr wh a nad hs among ka pc nr
San
‘A moderate ignition advance gives the best result. There will be small loses on both the
‘compression and expansion strokes, thus giving maximum power and efieeney. Figure 5.7 shows
an actual indicaor diagram with Optimum ignition advance (15* to 30° BTDC) and also shows the
corresponding fuel-ai eye indicator diagram.
Poi of apa
Fuca cyte
Arale
RE woe
guns, Shows alu ara u piano sare aso shoe rang ul yo
Fo dagan.
The timing of the spark highly depends upon the speed and the load. The centrifugal and
‘vacuum advance mechanisms ae wed to provide pracically perfect spark timing foc all operating
conditions. The vacuum unit produces greater advance when the engine is running under part
Uhrotle and the centrifuga uit produces greater advance when Ihe engine speed is increased,
‘Table 5.1 compares the resulis ofthe engine performance, such as maximum cycle pressure,
mean effective pressure and efficiency, considering the analysis ofthe actual cycle for various
ignition timings with respect to the fuer eyel performance. The results are for Cooperative Fuel
Research (CFR) engine. The specifications and the operating conditions ae mentioned in the able.
engine. The optimum ignition advance wil therefore be approximately the same and "he burning
‘ine losses willbe almost the same percentage of the energy input
535 Residual Gas
he residual gas is more, the fresh charge is diluted. I will cause fame speed to duce and the
burning time losses will be mare, The amount of residual gas present depends upor the sizeof the
learance space and the exhaust pressure. The smaller th size of clearance space and lower the
‘exhaust pressure, the les will be the amount ofthe residual gas present, which can be achieved
with a higher compression rato, The higher the inet pressure, the more will be the fresh charge
‘The flame speed increases with more fresh charge and les residual gas.
54 EFFECT OF SPARK-ADVANCE ON THE ACTUAL
CYCLE OF SI ENGINES
Suppose the spark timing is set in such a way that as the piston reaches the TDC position, the
spark is strike and the combustion of fuel kes place. Combustion is completed only after the
piston has traveled a considerable distance from the TDC on expansion stoke, Figure 5.5 shows
the actual indicator diagram with ignition at TDC and also shows the corresponding fuer cycle
indicator diagram. Lis observed that tbe maximum pressure is considerably reduced a compar
son tothe maximum pressure obtained with the fuel-ar cycle. A considerable aes ofthe diagram
is lost and thus the actual power and efficiency are low.
»
S--Pont of spark
Fake
Acta ele
me Boe
gres. Shows tn ac naar gr vol TDC and ala howe coeur util dto
den.
te spark timing is much advanced, he ignition takes place early on the compression stoke.
‘kis possible o get complete combustion in his case just asthe piston reaches TDC, but addtional
work is required to compress the working gases, so that once again the work area i ess, and thus
‘the power and efficiency are low. Figure 5.6 shows the actual indicator diagram with early ignition
and also shows the corresponding fuel air cycle indicator diagram.
The Act! Cyeto_151
»
Sino pur
Faire
ei ele
i _
3 [73
Figo. Shows al ner gr wh a nad hs among ka pc nr
San
‘A moderate ignition advance gives the best result. There will be small loses on both the
‘compression and expansion strokes, thus giving maximum power and efieeney. Figure 5.7 shows
an actual indicaor diagram with Optimum ignition advance (15* to 30° BTDC) and also shows the
corresponding fuel-ai eye indicator diagram.
Poi of apa
Fuca cyte
Arale
RE woe
guns, Shows alu ara u piano sare aso shoe rang ul yo
Fo dagan.
The timing of the spark highly depends upon the speed and the load. The centrifugal and
‘vacuum advance mechanisms ae wed to provide pracically perfect spark timing foc all operating
conditions. The vacuum unit produces greater advance when the engine is running under part
Uhrotle and the centrifuga uit produces greater advance when Ihe engine speed is increased,
‘Table 5.1 compares the resulis ofthe engine performance, such as maximum cycle pressure,
mean effective pressure and efficiency, considering the analysis ofthe actual cycle for various
ignition timings with respect to the fuer eyel performance. The results are for Cooperative Fuel
Research (CFR) engine. The specifications and the operating conditions ae mentioned in the able.
152 Fundamental of Interna! Combustion Engines
he Actual Cree 153,
Table 5.1. Cycle performance for various ignition timings
ion Mama id EGSA jan
advance coco presure (ot) power) ta) “pega
caco m ao
CN E AT]
A
a
E EA
Soares” Rogen AR, lemons of renal Combai Bish, Neti i Bok Co, New Vor 1953
(d= 826 mm, Lu 1143 mm, rm Nw 1500p, 4118, 9,2091 bar Fe 310K, p= 1.0? a, coli ab of
foal = 44000 EIRE)
Figure 5.8 shows the effect of spark-advance on the p-V diagram, The cycles are superim-
posed for comparison. The indicated power (ip) and efficiency (n) are marked at diferent angles
‘of ignition advance. Its clear rom th diagram tht for given specifications and operating condi
ions a certain value of ignition advance is required foroptimum results. A greater than or ess than
this value will result in reduced power and poor efficiency
Posh pce: 00% jp = 666, 9 = 32.2%
Acta epee
8-0 pe 4.99 AW, 9 241%
Bu 17 pe 539 kW, y = 263%,
035% jp An
Figures Theaecttspak-otanceonttep Vegan.
Figure 53 shows the effect of deviating spark timing from optimum on the relative indicted
mean effective pressure (imep). With optimum spark timing the relative imep is taken as unity
‘As the ignition advance is increased or decreased from the optimum value, there is a reduction a
the imep, and aga result there is a loss of power, In actual practice, sometime deliberate spark
Degres ae angle om optimum spring
gue. devatig pa in rom opr tive idas msan ce presu
retardation from optimum may be necessary in oder to avoid knocking and to simultaneously
reduce exhaust emission of hydcocarbons and carbon monoxide.
55 POWER AND EFFICIENCY OF THE ACTUAL CYCLE
“The power and efficiency of the actual engine depend upon many factors, Here, the effects of
compression ratio and fuelir ratio ae considered
5.5.1 Effect of Compression Ratio
‘The effect of compression ratio on the indicated thermal efficiency ofthe actual cycle of spark-
ignition engine is shown in Figure 5.10. For the sake of comparison, the ai-cyce efficiency is
also shown, The nature ofthe two curves isthe same, but the efficiency of the actual cycle is
2d
& soe
fa as
a4 Acute
po ani a
i
im
al
S48 67 8 9 Ww
Compresion sio,
Pause Treelecttcorpecionaiccn to fines lai ard cale.
he Actual Cree 153,
Table 5.1. Cycle performance for various ignition timings
ion Mama id EGSA jan
advance coco presure (ot) power) ta) “pega
caco m ao
CN E AT]
A
a
E EA
Soares” Rogen AR, lemons of renal Combai Bish, Neti i Bok Co, New Vor 1953
(d= 826 mm, Lu 1143 mm, rm Nw 1500p, 4118, 9,2091 bar Fe 310K, p= 1.0? a, coli ab of
foal = 44000 EIRE)
Figure 5.8 shows the effect of spark-advance on the p-V diagram, The cycles are superim-
posed for comparison. The indicated power (ip) and efficiency (n) are marked at diferent angles
‘of ignition advance. Its clear rom th diagram tht for given specifications and operating condi
ions a certain value of ignition advance is required foroptimum results. A greater than or ess than
this value will result in reduced power and poor efficiency
Posh pce: 00% jp = 666, 9 = 32.2%
Acta epee
8-0 pe 4.99 AW, 9 241%
Bu 17 pe 539 kW, y = 263%,
035% jp An
Figures Theaecttspak-otanceonttep Vegan.
Figure 53 shows the effect of deviating spark timing from optimum on the relative indicted
mean effective pressure (imep). With optimum spark timing the relative imep is taken as unity
‘As the ignition advance is increased or decreased from the optimum value, there is a reduction a
the imep, and aga result there is a loss of power, In actual practice, sometime deliberate spark
Degres ae angle om optimum spring
gue. devatig pa in rom opr tive idas msan ce presu
retardation from optimum may be necessary in oder to avoid knocking and to simultaneously
reduce exhaust emission of hydcocarbons and carbon monoxide.
55 POWER AND EFFICIENCY OF THE ACTUAL CYCLE
“The power and efficiency of the actual engine depend upon many factors, Here, the effects of
compression ratio and fuelir ratio ae considered
5.5.1 Effect of Compression Ratio
‘The effect of compression ratio on the indicated thermal efficiency ofthe actual cycle of spark-
ignition engine is shown in Figure 5.10. For the sake of comparison, the ai-cyce efficiency is
also shown, The nature ofthe two curves isthe same, but the efficiency of the actual cycle is
2d
& soe
fa as
a4 Acute
po ani a
i
im
al
S48 67 8 9 Ww
Compresion sio,
Pause Treelecttcorpecionaiccn to fines lai ard cale.
154_ Fundament of er! Combuton Engnes
lower. The efficiency of the ele increases withthe increase in compression ratio, As the efi
ciency increases, the indicated power also increases
5.5.2 Effect of Fue/Alr Ratio
‘The effect of fueVai ratio on the indicated mean effective pressure (imep) and the indicated
‘thermal efficiency (1) is shown in Figure 5.1.
COR AN ET]
sr ro
Fur. Eterno cand Bema crc} (1) area nest aan cie presi).
Very ich and very lean mixtures lower the burning rates of the fuel, and thus increase the
burning time losses, The effect ofthese loses is 1 lower the efficiency atthe ich as well atthe
Jean end. The efficiency ofthe actual engine is maximum at a fuelair ato somewhat leaner than
the stoichiometric mixture.
‘A typical curve of the mean effective pressure (mep) vs, the fueV/ir ratio for an actual cycle
is similar o that forthe fuel air cycle (Figure 4.1). The actual eure is modified mainly for
‘burning timo loses and poor mechanical mixing of fuel and ar. The maximum indicated mean
effective pressure, and hence the maximum indicated power, is obtained witha slighty rch mixture
"Near the peak a small change inthe fuel ratio will not affect the indicated power asthe curve is
usually flat inthis region, However, the efficiency is greatly affected.
5.5 FRICTIONAL LOSSES
The curves of Figure 5.1 ar for indicated power and i
power and efficiency developed inside the engine cy
cated thermal efficiency. These are the
er The power developed atthe engine
A
Te Aci Cycle 155
shaft will be less than the power developed on the piston, owing to the fictional losses between
(he various engine pars, such a friction between the piston and cylinder walls, friction in bear
{ngs and fection in aunliary equipment like cooling water pump, lubricating pump, fuel pomp,
valves, ignition system, fans, etc. The shaft power is called the brake power (bp). Similey, the
‘ermal efficiency ofthe engine based upon the shaft output will always be less than the indicated
thermal efficiency. This efficiency is called te brake thermal efficiency my, and is calculated as
shown in Table 52. With the increase in engine speed, the frictions losses increase rapidly.
“Table 5.2 Typicallosses in SI engine (r= 8)
F Arnd,
- Fall load | Mefiond
e a]
Krsanda eee efficiency. Me 565 565
(0 Lower due o vrai of specific het and chemical
equilibrium mo 1o
G2) Los due to progressive burning 40 40
(i) Loss due to bering ine 30 30
(i) Heat tos 40 50
(0) Exhaun blondowa ous as os
(oi) Pumping loss 05 15
(vi) Fiona osses 30 60
Fue air yee efceney (ne ~ 0) 35 es
Gros indicated termal efficiency (gs 320 310
a 16 + 0 +65 +) +09)
Ne indeed thermal eficieny, (Mb = (gs = (40 sus ws
Brake thermal eficiccy, ms = (ma = (i 285 25
5:7 THE ACTUAL CYCLE OF COMPRESSION-IGNITION ENGINES
The combustion process of a compression-igition engine is completed in the following thee
stages:
1. The frst stage isa delay period. is the time period between the start of fuel injection and
the appearance of a flame or measurable pressure rise due 10 combustion.
2. The second stage of combustion i a rapid rise in pressure, Ifthe delay period is long or
longer than the injection pe-iod, most of te fuel burns during the period of rapid pressure
3. The tied stage is a relatively slow combustion. The remaining unburned fuel finds the
limited oxygen to bum slowly. This slow combustion extends over a considerable part of
the expansion stoke.
‘The crank angles during the above tree stages of combustion vary with design and operating
‘onions. Ata given spoe these timings can be controlled by means of injection timing, spray
‘characterises and fuel composition,
fe wegen ne EAN EN ee we Nate
lower. The efficiency of the ele increases withthe increase in compression ratio, As the efi
ciency increases, the indicated power also increases
5.5.2 Effect of Fue/Alr Ratio
‘The effect of fueVai ratio on the indicated mean effective pressure (imep) and the indicated
‘thermal efficiency (1) is shown in Figure 5.1.
COR AN ET]
sr ro
Fur. Eterno cand Bema crc} (1) area nest aan cie presi).
Very ich and very lean mixtures lower the burning rates of the fuel, and thus increase the
burning time losses, The effect ofthese loses is 1 lower the efficiency atthe ich as well atthe
Jean end. The efficiency ofthe actual engine is maximum at a fuelair ato somewhat leaner than
the stoichiometric mixture.
‘A typical curve of the mean effective pressure (mep) vs, the fueV/ir ratio for an actual cycle
is similar o that forthe fuel air cycle (Figure 4.1). The actual eure is modified mainly for
‘burning timo loses and poor mechanical mixing of fuel and ar. The maximum indicated mean
effective pressure, and hence the maximum indicated power, is obtained witha slighty rch mixture
"Near the peak a small change inthe fuel ratio will not affect the indicated power asthe curve is
usually flat inthis region, However, the efficiency is greatly affected.
5.5 FRICTIONAL LOSSES
The curves of Figure 5.1 ar for indicated power and i
power and efficiency developed inside the engine cy
cated thermal efficiency. These are the
er The power developed atthe engine
A
Te Aci Cycle 155
shaft will be less than the power developed on the piston, owing to the fictional losses between
(he various engine pars, such a friction between the piston and cylinder walls, friction in bear
{ngs and fection in aunliary equipment like cooling water pump, lubricating pump, fuel pomp,
valves, ignition system, fans, etc. The shaft power is called the brake power (bp). Similey, the
‘ermal efficiency ofthe engine based upon the shaft output will always be less than the indicated
thermal efficiency. This efficiency is called te brake thermal efficiency my, and is calculated as
shown in Table 52. With the increase in engine speed, the frictions losses increase rapidly.
“Table 5.2 Typicallosses in SI engine (r= 8)
F Arnd,
- Fall load | Mefiond
e a]
Krsanda eee efficiency. Me 565 565
(0 Lower due o vrai of specific het and chemical
equilibrium mo 1o
G2) Los due to progressive burning 40 40
(i) Loss due to bering ine 30 30
(i) Heat tos 40 50
(0) Exhaun blondowa ous as os
(oi) Pumping loss 05 15
(vi) Fiona osses 30 60
Fue air yee efceney (ne ~ 0) 35 es
Gros indicated termal efficiency (gs 320 310
a 16 + 0 +65 +) +09)
Ne indeed thermal eficieny, (Mb = (gs = (40 sus ws
Brake thermal eficiccy, ms = (ma = (i 285 25
5:7 THE ACTUAL CYCLE OF COMPRESSION-IGNITION ENGINES
The combustion process of a compression-igition engine is completed in the following thee
stages:
1. The frst stage isa delay period. is the time period between the start of fuel injection and
the appearance of a flame or measurable pressure rise due 10 combustion.
2. The second stage of combustion i a rapid rise in pressure, Ifthe delay period is long or
longer than the injection pe-iod, most of te fuel burns during the period of rapid pressure
3. The tied stage is a relatively slow combustion. The remaining unburned fuel finds the
limited oxygen to bum slowly. This slow combustion extends over a considerable part of
the expansion stoke.
‘The crank angles during the above tree stages of combustion vary with design and operating
‘onions. Ata given spoe these timings can be controlled by means of injection timing, spray
‘characterises and fuel composition,
fe wegen ne EAN EN ee we Nate
156. Fundamenals of Ineral Comburden Enger
The Aal Cycle 157
(A longer delay period is undesirable because of the resultant high maximum pressure and high
rates of pressure rte causing engine knocking. The limited pressure fuel ir cycle i used as the
basis of evaluating the actual compression-gnition engine cyele. The losses of the actal CI
engine cycle in addition 10 those of limited pressure fuir cycle are:
Leakage
Heat losses
Time losses
Exhaust losses
Fluid fection
Gas exchange or pumping los.
In SIengines, incomplete mixing of fuel and at and progressive burning ae also included, In
(Cl engines, these loses may be large, but since burning occurs during the mixing proces, such
losses cannot be separated from the time losses. The description of all other losses mentioned
above for CI engines are the same as those described for SI engines
In spark-ignition engines, the rat of buring starts slowly and accelerates tot highest veloc-
y near the end ofthe process. In CLengines, the reverse is true, Iis because the available supply
of oxygen decreases as buming progresses, the mixing process, hence the burning
process, tend o slow down in the later stages of combustion.
5.8 ACTUAL AND FUEL-AIR CYCLES OF Cl ENGINES
Ina Diesel cycle the losses ar less in comparison tothe losses in an Otto cycle The main loss is
ue to incomplete combustion and itis the cause of he main difference between the fuelai cycle
and the actual cycle of a Cl engine. Figure 5.12 shows the p-V diagram forthe actual Diese cycle
and the limited pressure fuel air cycle. The two cycles are shown on te same diagram forthe sake
‘of comparison. A ratio between the actual and fue-ar cycle efficiency of 0.85-0,90 is stainable
BD
Puebinjción
‘Acta cyte
y
Figur S12 Compare ac odie presa cha eye comprenne.
1
2
a
a.
15.
16.
1.
2.
REVIEW QUESTIONS
What are the losses considered in the analysis of the aceval cycle in addition to those
considered inthe analysis ofthe fuel-ai eye?
‘What do you understand by crevice regions? Discuss leakage losses in the actual ST engine
cycle
. Why is perfect mixing of ue and aie not possible? Show the composition of exhaust gases
fora typical gasoline engine at various equivalence ratios.
‘What sa maldisibution of fuel in a multi<ylinder engine? What will be its effect?
Wa do you mean by progressive buming? What are the factors on which the time of
progressive burning depends?
‘What do you understand by burning time Tosses? How can such losses be reduced? What
ace the causes ofa large burning tie?
During which pet of the cycle the heat losses are significant? Where does the beat disi-
pate?
What do you understand by exhaust blowdowa loss? Show the effect of exhaust valve
‘opening time on exhaust blowdown los.
Define the time loss rato, the heat loss ratio, the blowdown los ratio and the lost work
ratio. Compare the actual cycle ofan ST engine with the constant volume fuel-air cycle on
P-V diagram, showing the different losses
During which processes ofthe actual cycle isthe fluid fiction appreciable?
‘What do you understand by pumpia losses during gas exchange? Explain with the hep of
ap-V diagram, What willbe the effect of toting and speed on pumping losses?
How does the flame speed vary with respect tothe following engine variables?
(a) Fuel ratio, () Inet pressure, () Engine speed, () Engine size, and (e) Residual gas
‘Show the actual indicator diagram with (a ignion at TDC, (> early ignition advance, and
(& optimum ignition advance. Als, show the corresponding fuel-air cycle In each case.
‘Comment on actual power and efficiency
‘What are the two important factors on which spark timing depends? How cana practically
perfect spark timing be achieved for al opéráting conditions?
‘Show and compare the effect of spark advance on a single p-V diagram.
‘Show the effect of deviating spark timing from the optimum on relative indicated mean
efectivo pressure.
‘What will be the effect of compression rato on the indicated thermal efficiency ofthe
actual cycle? Compare the efficiency ofthe acual cycle with that ofthe ir cycle with the
help of a diagram.
Describe with the help of a diagram the effect of fueVaie ratio on indicated mean effective
pressure and indicated thermal efficiency ofan actual cycle ofa sparkignition engine.
‘What are the thre stages of combustion in acompression-igition engine? What willbe the
effect ofa longer delay period? What are the losses considered in the evaluation ofan actual
cycle of a Cl engine?
For a CI engine, compare with the help of a
pressure fuel air cycle.
‚ram the actual cycle with e limited
The Aal Cycle 157
(A longer delay period is undesirable because of the resultant high maximum pressure and high
rates of pressure rte causing engine knocking. The limited pressure fuel ir cycle i used as the
basis of evaluating the actual compression-gnition engine cyele. The losses of the actal CI
engine cycle in addition 10 those of limited pressure fuir cycle are:
Leakage
Heat losses
Time losses
Exhaust losses
Fluid fection
Gas exchange or pumping los.
In SIengines, incomplete mixing of fuel and at and progressive burning ae also included, In
(Cl engines, these loses may be large, but since burning occurs during the mixing proces, such
losses cannot be separated from the time losses. The description of all other losses mentioned
above for CI engines are the same as those described for SI engines
In spark-ignition engines, the rat of buring starts slowly and accelerates tot highest veloc-
y near the end ofthe process. In CLengines, the reverse is true, Iis because the available supply
of oxygen decreases as buming progresses, the mixing process, hence the burning
process, tend o slow down in the later stages of combustion.
5.8 ACTUAL AND FUEL-AIR CYCLES OF Cl ENGINES
Ina Diesel cycle the losses ar less in comparison tothe losses in an Otto cycle The main loss is
ue to incomplete combustion and itis the cause of he main difference between the fuelai cycle
and the actual cycle of a Cl engine. Figure 5.12 shows the p-V diagram forthe actual Diese cycle
and the limited pressure fuel air cycle. The two cycles are shown on te same diagram forthe sake
‘of comparison. A ratio between the actual and fue-ar cycle efficiency of 0.85-0,90 is stainable
BD
Puebinjción
‘Acta cyte
y
Figur S12 Compare ac odie presa cha eye comprenne.
1
2
a
a.
15.
16.
1.
2.
REVIEW QUESTIONS
What are the losses considered in the analysis of the aceval cycle in addition to those
considered inthe analysis ofthe fuel-ai eye?
‘What do you understand by crevice regions? Discuss leakage losses in the actual ST engine
cycle
. Why is perfect mixing of ue and aie not possible? Show the composition of exhaust gases
fora typical gasoline engine at various equivalence ratios.
‘What sa maldisibution of fuel in a multi<ylinder engine? What will be its effect?
Wa do you mean by progressive buming? What are the factors on which the time of
progressive burning depends?
‘What do you understand by burning time Tosses? How can such losses be reduced? What
ace the causes ofa large burning tie?
During which pet of the cycle the heat losses are significant? Where does the beat disi-
pate?
What do you understand by exhaust blowdowa loss? Show the effect of exhaust valve
‘opening time on exhaust blowdown los.
Define the time loss rato, the heat loss ratio, the blowdown los ratio and the lost work
ratio. Compare the actual cycle ofan ST engine with the constant volume fuel-air cycle on
P-V diagram, showing the different losses
During which processes ofthe actual cycle isthe fluid fiction appreciable?
‘What do you understand by pumpia losses during gas exchange? Explain with the hep of
ap-V diagram, What willbe the effect of toting and speed on pumping losses?
How does the flame speed vary with respect tothe following engine variables?
(a) Fuel ratio, () Inet pressure, () Engine speed, () Engine size, and (e) Residual gas
‘Show the actual indicator diagram with (a ignion at TDC, (> early ignition advance, and
(& optimum ignition advance. Als, show the corresponding fuel-air cycle In each case.
‘Comment on actual power and efficiency
‘What are the two important factors on which spark timing depends? How cana practically
perfect spark timing be achieved for al opéráting conditions?
‘Show and compare the effect of spark advance on a single p-V diagram.
‘Show the effect of deviating spark timing from the optimum on relative indicated mean
efectivo pressure.
‘What will be the effect of compression rato on the indicated thermal efficiency ofthe
actual cycle? Compare the efficiency ofthe acual cycle with that ofthe ir cycle with the
help of a diagram.
Describe with the help of a diagram the effect of fueVaie ratio on indicated mean effective
pressure and indicated thermal efficiency ofan actual cycle ofa sparkignition engine.
‘What are the thre stages of combustion in acompression-igition engine? What willbe the
effect ofa longer delay period? What are the losses considered in the evaluation ofan actual
cycle of a Cl engine?
For a CI engine, compare with the help of a
pressure fuel air cycle.
‚ram the actual cycle with e limited
Combustion in
Spark-Ignition Engines
6.1 INTRODUCTION
In a conventional sparkgniion engine a homogeneous mixture of fuel and air is supplied. The
mbuition in a gaseous fuel-ar mixture ignited by a spark is characterized by a rapid develop-
ment of a flame that starts from the point of ignition and spreads outwards in a continuous
manner, When the flame spread continues to tke end of the combustion chamber without any
abrupt change in its speed and shape, combustion is called normal. When the unburned mixture
ahead of the flame ignites and burns before the flame reaches it, the phenomenon is called
auoignition. When there is u sudden increase inthe reaction rate, accompanied by a sudden
pressure rise forming pressure waves, the phenomenon is called detonation which causes engine
Knock,
‘When combustion siniiated by a spac, iis called controlled combustion and when combas-
tion is initiated by a hot spot, ts called uncontrolled combustion. Under normal combustion
conditions, the combustion is controlled and this is a designer's objective. Uncontrlled combus-
tion is associated with preigntion and running-on. Autoignition and detonation come under the
category of abnormal combustion. In this ease the fuel-air mixture ignites spontaneously without
an ignition source,
‘The combustion of fue-ar mixture depends on chain reactions. Fist only afew highly active
constituents surrounding the ignition point cause reactions. These in tum generate additional
active constituents to cause reactions. Soon a point is reached where the chain breaking reactions
dominate the chain forming reactions. In the flame front, the chain forming rescions can only
reach a certain distance into a relatively cool, unbumed charge before they are broken and thos à
definite Name boundary is established. However, ifthe unburned gases become hot enough to
sustain chain reactions the remaining gas will suddenly autoignite.
62 NORMAL COMBUSTION
‘Towards the end of the compression stroke the cylinder contains more or les a homogencoss
‘mixture of vaporized fuel, air and residual gases. A single intense and high temperature spark is.
produced between the spark plug electrodes and as it passes from one electrode 1 the other it
leaves a thn thread of flame. Combustion spreads fo the envelope of the mixture containing the
thread a arate depending primarily on the temperature ofthe flame front and secondarily onthe
A — — +
)
CComburton in Sparkiniion Engines 159
= a
a
[2 nr Tor
we
Crank ange, @
Figur. Thre pssurys rr e ag
However in an acta sargnion engine, combusion does nt ocur instantancousy. is
iit O opr prot before TDG a ett ine an he Dane ls ite neo
tel arts e easton hamber, ring he charge ad sing e nde press as
trove Te heal enc wil be ihr the combardon approaches the constant volume
proce however he reune ma ad qui engine operon pores the resin
6.24 Stages of Combustion in SI Engine
Fu 62 sow he presu cn ne 9-9) dam inca o ge conan
ones Ter led mpi A tpt pronase oun be
ne gi shove in aro pase pa Dinas
D care Combos pure Ip dg fr mug che bene
i at ing is AB repent ei ape Be sont so sno CD RO
Combos :
u Tt is important to understand the two terms, Le. combustion and burning. Combustion pro
cet cathe qian sesh noha tiga art
seer od wb cl of fame fat sche ld
Spark-Ignition Engines
6.1 INTRODUCTION
In a conventional sparkgniion engine a homogeneous mixture of fuel and air is supplied. The
mbuition in a gaseous fuel-ar mixture ignited by a spark is characterized by a rapid develop-
ment of a flame that starts from the point of ignition and spreads outwards in a continuous
manner, When the flame spread continues to tke end of the combustion chamber without any
abrupt change in its speed and shape, combustion is called normal. When the unburned mixture
ahead of the flame ignites and burns before the flame reaches it, the phenomenon is called
auoignition. When there is u sudden increase inthe reaction rate, accompanied by a sudden
pressure rise forming pressure waves, the phenomenon is called detonation which causes engine
Knock,
‘When combustion siniiated by a spac, iis called controlled combustion and when combas-
tion is initiated by a hot spot, ts called uncontrolled combustion. Under normal combustion
conditions, the combustion is controlled and this is a designer's objective. Uncontrlled combus-
tion is associated with preigntion and running-on. Autoignition and detonation come under the
category of abnormal combustion. In this ease the fuel-air mixture ignites spontaneously without
an ignition source,
‘The combustion of fue-ar mixture depends on chain reactions. Fist only afew highly active
constituents surrounding the ignition point cause reactions. These in tum generate additional
active constituents to cause reactions. Soon a point is reached where the chain breaking reactions
dominate the chain forming reactions. In the flame front, the chain forming rescions can only
reach a certain distance into a relatively cool, unbumed charge before they are broken and thos à
definite Name boundary is established. However, ifthe unburned gases become hot enough to
sustain chain reactions the remaining gas will suddenly autoignite.
62 NORMAL COMBUSTION
‘Towards the end of the compression stroke the cylinder contains more or les a homogencoss
‘mixture of vaporized fuel, air and residual gases. A single intense and high temperature spark is.
produced between the spark plug electrodes and as it passes from one electrode 1 the other it
leaves a thn thread of flame. Combustion spreads fo the envelope of the mixture containing the
thread a arate depending primarily on the temperature ofthe flame front and secondarily onthe
A — — +
)
CComburton in Sparkiniion Engines 159
= a
a
[2 nr Tor
we
Crank ange, @
Figur. Thre pssurys rr e ag
However in an acta sargnion engine, combusion does nt ocur instantancousy. is
iit O opr prot before TDG a ett ine an he Dane ls ite neo
tel arts e easton hamber, ring he charge ad sing e nde press as
trove Te heal enc wil be ihr the combardon approaches the constant volume
proce however he reune ma ad qui engine operon pores the resin
6.24 Stages of Combustion in SI Engine
Fu 62 sow he presu cn ne 9-9) dam inca o ge conan
ones Ter led mpi A tpt pronase oun be
ne gi shove in aro pase pa Dinas
D care Combos pure Ip dg fr mug che bene
i at ing is AB repent ei ape Be sont so sno CD RO
Combos :
u Tt is important to understand the two terms, Le. combustion and burning. Combustion pro
cet cathe qian sesh noha tiga art
seer od wb cl of fame fat sche ld
160 fondumensl of Itemal Combustion Engine
Comburien in Sparktniion Engines 161.
300090
res
oh ite
50 |
i i
g }
i EA sagem
>
ee,
FE] CEE ur
me Be ibe
Cal, (ce)
Fgue6.2 Prsurecanarge agan hong ages lorient a,
When the flame reaches the far end of the cylinder, the charge is all bumed and the buming
post over The cmbusion ofthe fe wl be incomplete because of he igh terne
‘enusing dissociation,
‘The frst stago (AB)
‘This tage scaled gain lg or preparation phase. compost te mo fr he growth
and development of ase propagating mclus o the flame. Th tating point ofthe Re sage it
the point A, wher th sparks produced andthe nd of he singe is marked Wi pl B wher
the Fist measurable pressures agin the mooring carves served Te fast Sage malay
a chemical proces and depends on the atte of he fl, temperate and pets ofthe fala
mixture, he cooeutation frei fom te previous cycle preset In he cline and he
Chemical ection at. Lt al eme by loca unter,
‘Aloogh the fist stage of combo elle th non ag sis nalogns tothe delay
period of compressioigidos engine, and actully the mice of combustion appear instante
recu} ea the puk pag ecos inal he Mamo spreads very slowly and a acon of
the bumed mixture ls very il, zo there eo apte preste ss again he motoring
‘The second stage (BC)
‘This stage is called the main stage. It corresponds tothe propagation ofthe lame practically at a
constant speed. The stating point ofthe second stage is taken as point B, where the first measur-
able pressure rise against the motoring curve is observe, The end ofthe second stage is marked
‘with point C, where the maximum pressure is attained. This sage is both a physical and a chemi-
cal process. The heat release depends on the chemical composition and onthe prevailing tempera
{ures and pressures and the degree of turbulence inthe cylinder. During this stage heat transfer 10
the cylinder wall is low, since the burning mixture comes in contact with a small par of the
cylinder wall. The rate of pressure ie is almost proportional tothe rate of ea release because
during this stage, the combustion chamber volume does not change much
“The third stage (CD)
“This stags called aftrburning. Although the point Cingicates the completion ofthe Name travel
ii does ot follow thatthe whole of the heat ofthe fuel hasbeen liberated at this point, Even alter
the passage of the flame, during expansion some ofthe constituents re-assoiate and liberate heat
‘The staring point of the third stage is usually taken atthe instant when maximum pressure is
‘reached on he indicator diagram (like the point C). The end of his stage is marked with point D.
‘This point corresponds to the point where equilibrium is reached and after which the products of
combustion are assumed tobe frozen. During this stage the Mane speed decreases and the rate of
‘combustion is slow, Since the expansion stroke starts before ths stage with the piston moving
‘vay from TDC, there will be pressure fall during this stage.
6.2.2 Flame Speed Pattern
“The flame speed across the chamber follows a parer similar to thet shown in Figure 63. le
shows the relation between the relative distance travelled by the flame across the chamber with
respecto the relative time taken by the flame to travel across the chamber. The slope ofthe curve
indicate the flare speed.
10
os
Le,
Suge
CC a
Relative tie
Fu Rae dan camelias be chant. ltvnecttanotveacess te ctm
o
Comburien in Sparktniion Engines 161.
300090
res
oh ite
50 |
i i
g }
i EA sagem
>
ee,
FE] CEE ur
me Be ibe
Cal, (ce)
Fgue6.2 Prsurecanarge agan hong ages lorient a,
When the flame reaches the far end of the cylinder, the charge is all bumed and the buming
post over The cmbusion ofthe fe wl be incomplete because of he igh terne
‘enusing dissociation,
‘The frst stago (AB)
‘This tage scaled gain lg or preparation phase. compost te mo fr he growth
and development of ase propagating mclus o the flame. Th tating point ofthe Re sage it
the point A, wher th sparks produced andthe nd of he singe is marked Wi pl B wher
the Fist measurable pressures agin the mooring carves served Te fast Sage malay
a chemical proces and depends on the atte of he fl, temperate and pets ofthe fala
mixture, he cooeutation frei fom te previous cycle preset In he cline and he
Chemical ection at. Lt al eme by loca unter,
‘Aloogh the fist stage of combo elle th non ag sis nalogns tothe delay
period of compressioigidos engine, and actully the mice of combustion appear instante
recu} ea the puk pag ecos inal he Mamo spreads very slowly and a acon of
the bumed mixture ls very il, zo there eo apte preste ss again he motoring
‘The second stage (BC)
‘This stage is called the main stage. It corresponds tothe propagation ofthe lame practically at a
constant speed. The stating point ofthe second stage is taken as point B, where the first measur-
able pressure rise against the motoring curve is observe, The end ofthe second stage is marked
‘with point C, where the maximum pressure is attained. This sage is both a physical and a chemi-
cal process. The heat release depends on the chemical composition and onthe prevailing tempera
{ures and pressures and the degree of turbulence inthe cylinder. During this stage heat transfer 10
the cylinder wall is low, since the burning mixture comes in contact with a small par of the
cylinder wall. The rate of pressure ie is almost proportional tothe rate of ea release because
during this stage, the combustion chamber volume does not change much
“The third stage (CD)
“This stags called aftrburning. Although the point Cingicates the completion ofthe Name travel
ii does ot follow thatthe whole of the heat ofthe fuel hasbeen liberated at this point, Even alter
the passage of the flame, during expansion some ofthe constituents re-assoiate and liberate heat
‘The staring point of the third stage is usually taken atthe instant when maximum pressure is
‘reached on he indicator diagram (like the point C). The end of his stage is marked with point D.
‘This point corresponds to the point where equilibrium is reached and after which the products of
combustion are assumed tobe frozen. During this stage the Mane speed decreases and the rate of
‘combustion is slow, Since the expansion stroke starts before ths stage with the piston moving
‘vay from TDC, there will be pressure fall during this stage.
6.2.2 Flame Speed Pattern
“The flame speed across the chamber follows a parer similar to thet shown in Figure 63. le
shows the relation between the relative distance travelled by the flame across the chamber with
respecto the relative time taken by the flame to travel across the chamber. The slope ofthe curve
indicate the flare speed.
10
os
Le,
Suge
CC a
Relative tie
Fu Rae dan camelias be chant. ltvnecttanotveacess te ctm
o
162 Fundameyot of neral Combustion Engins
ie Mane wave app pas ng ine sages, During ge he ame oat
progres soni comas oft apoco at and low ln. Se eich ren
Sal nas of rebel ate shia very Ie easton ote Rome en eg
ths propaga simon ently y the acon ae eng an Sor advance. Te at
Hered bythe bring portion oe ame fe pep tue pon ey
charg othe combustion warn. Als sce De spa nt no qua ren
Gas he eye val he ck ofen es easton me snd era
Krane ment
Ash ame on peso more tlt regio ving he que or and
mens une» gs: mus subo it pres mor py nd
Alma constant es thaw sage Te average spec of eae e
feel emo she fe speed. 12 Rane ne
“ovate en of nee tag eve of te nbumad huge ced
apor ados ie panbecomeseglgbe,Deey an ns
"ion refer date sie te fame ona in fly ara
Ths the Rane ve pan cee como pou ow dn pee
1. Spain
2. Bi fae eet
À Fame pompe
À ameter
‘The factors affecting he flame speed have already been discussed in Chapter 5,
62.3 Fraction of Bumed Mass
Figure 64 shows the mas facionbumed" in al pain engine a a fncion of he
‘crank angle. = ”
1
02
47 E ee
Te 2
Crank angle (dep)
Fieve Nasstactonbunedscalnctend mane
Cembundon in Sprkien Engines 163
m.
Mass fraction bummed, x
where my is the mass ofthe bumed charge and m is the mass of the unbumed charge
"The "mass fraction bumned' follows the same pattem asthe flame speed. Initially the flame
speed stow, so the ‘mas fraction bummed is also tes. As he flame speed during the second stage
increases, the “mass fraction burned’ also increases rapidly. The major portion of the mass is
burned during this stage. During the Ist stage the flame speed reduces again, so the remainder of
the unburned charge which is very lle gets burned 100.
6.2.4 Pressure and Temperature Variation as a Function of
Crank Angle
Figure 65 shows the variation of pressure and temperature with respect tthe erank angle. The
flame ceaches the cylinder wal farthest from the sparkplug about 15° after TDC. Aris pont the
maximum pressure Pau is reached, but the combustion is not completed; it continues around
paris of the chamber periphery for another few degrees of crank angle, so the maximum tempera-
fue Ty is Obtained about 10° after the maximum pressure is reached. Both pressure and tem-
perature decrease a the cylinder volume continues o increase during the remainder ofthe expan
sion sioke,
me
E E à
Co agle (668)
agan. Valero spa epoca
62.5 Effect of Spark Timing on Indicator Diagram
Figure 6.6 shows the effect of spark timing on cylinder pressure versus the erank angle. Ifthe
spark timing is over advanced; th combustion proces stats while te piston is moving towards
‘TDG, so the compression work (negative work) increases. Ifthe spark timing is too much re-
tarded, the combustion process is progressively delayed, he peak cylinder pressure oceurs later in
ie Mane wave app pas ng ine sages, During ge he ame oat
progres soni comas oft apoco at and low ln. Se eich ren
Sal nas of rebel ate shia very Ie easton ote Rome en eg
ths propaga simon ently y the acon ae eng an Sor advance. Te at
Hered bythe bring portion oe ame fe pep tue pon ey
charg othe combustion warn. Als sce De spa nt no qua ren
Gas he eye val he ck ofen es easton me snd era
Krane ment
Ash ame on peso more tlt regio ving he que or and
mens une» gs: mus subo it pres mor py nd
Alma constant es thaw sage Te average spec of eae e
feel emo she fe speed. 12 Rane ne
“ovate en of nee tag eve of te nbumad huge ced
apor ados ie panbecomeseglgbe,Deey an ns
"ion refer date sie te fame ona in fly ara
Ths the Rane ve pan cee como pou ow dn pee
1. Spain
2. Bi fae eet
À Fame pompe
À ameter
‘The factors affecting he flame speed have already been discussed in Chapter 5,
62.3 Fraction of Bumed Mass
Figure 64 shows the mas facionbumed" in al pain engine a a fncion of he
‘crank angle. = ”
1
02
47 E ee
Te 2
Crank angle (dep)
Fieve Nasstactonbunedscalnctend mane
Cembundon in Sprkien Engines 163
m.
Mass fraction bummed, x
where my is the mass ofthe bumed charge and m is the mass of the unbumed charge
"The "mass fraction bumned' follows the same pattem asthe flame speed. Initially the flame
speed stow, so the ‘mas fraction bummed is also tes. As he flame speed during the second stage
increases, the “mass fraction burned’ also increases rapidly. The major portion of the mass is
burned during this stage. During the Ist stage the flame speed reduces again, so the remainder of
the unburned charge which is very lle gets burned 100.
6.2.4 Pressure and Temperature Variation as a Function of
Crank Angle
Figure 65 shows the variation of pressure and temperature with respect tthe erank angle. The
flame ceaches the cylinder wal farthest from the sparkplug about 15° after TDC. Aris pont the
maximum pressure Pau is reached, but the combustion is not completed; it continues around
paris of the chamber periphery for another few degrees of crank angle, so the maximum tempera-
fue Ty is Obtained about 10° after the maximum pressure is reached. Both pressure and tem-
perature decrease a the cylinder volume continues o increase during the remainder ofthe expan
sion sioke,
me
E E à
Co agle (668)
agan. Valero spa epoca
62.5 Effect of Spark Timing on Indicator Diagram
Figure 6.6 shows the effect of spark timing on cylinder pressure versus the erank angle. Ifthe
spark timing is over advanced; th combustion proces stats while te piston is moving towards
‘TDG, so the compression work (negative work) increases. Ifthe spark timing is too much re-
tarded, the combustion process is progressively delayed, he peak cylinder pressure oceurs later in
164, Funder of bernal Combustion Engines
«
spa ignition
Fa rev
260 0 20 TOC 20 do ENT
Cr ange (de)
Figure Press una rer arcadas ig (50, MET ing (andre ig (10,
as nano st ani gern Te
cr wot ea e a nd De
ei
nn E ra D ou hse de
AT tulo Me sp ting ud à
ron MS ia plas TT À
Snag dep cn ee of fe E
8
Propagation and termination. It also depends on the
distance of the flame tavel path across the combus-
tion chamber
Figure 6.7 shows the effect of spark advance on
brake torque at constant speed and air/fuel ratio at
wide open throtle. With optimum spark timing the
maximum pressure occur a about 15° after TDC and
Hal the charge is bumed at about 10° after TDC.
CNE |
Spa advance en)
ques? Ele adri enden.
626 Effect of Fuel/Air Ratio on Indicator Diagram
Figure 6.8 shows the effect of mixture strength on indicator diagrams. The fveVair rato ofthe
‘charg influences the rate of combustion and the amount of heat evolved. The maximum flame
speed occurs when the mixture strength for hydrocarbon fuels is about 10% rich. When the
mixture is made leaner or further enriched, the flame speed deceases. Lean mixtures release less
thermal energy, resulting in lower flame temperature and hence lower flame speed. Very rich
mixtures suffer incomplete combustion, hence release less thermal energy resulting in low flame
speed, Indicator diagrams for sich, stoichiometric and weak mixture correspond to equivalence
‘tio 1.1, 1.0, and 09 respectively
pS EE Loe u Se 2
A
Soichiomenic
Wee
Crank angle, 8
Fans. Etecolmituesreghonp-vandp-@ game,
63 FACTORS AFFECTING IGNITION LAG
“The frst phase ofa combustion process is called the ignition lag. This is the period between spark
inition nd flame development, Iisa chemical process. The ignition ag in terms of crank angle
is 10° to 20° and ofthe order of miliseconds. As the ignition lag decreases, the rate of pressure
ise andthe maximum pressure achieved increase. Th factor affecting the period of ignition lag
“aro discussed inthe following subsections.
63.1 Nature of Fuel and Air/Fuel Ratio
Ignition ag depends on the nature ofthe Fel. I the selfigniion temperature of the fucl is higher,
itis dico wo buen che fuel and therefore the ignition ag will be longer. Ras been found tha the
‘nition lag isthe shortest fora mixture sight richer than the stoichiometric as shown in
69. The inition lag becomes longer asthe mixture becomes lean or very ich,
Agen sg m)
im ES
mo
Mix reg Gnome)
agus, Eee ave Aca
Ho do Ho
64.2. Initial Temperature and Pressure
‘The rate of chemical reaction depends toa greater extent on temperature but toa smaller extent on
«
spa ignition
Fa rev
260 0 20 TOC 20 do ENT
Cr ange (de)
Figure Press una rer arcadas ig (50, MET ing (andre ig (10,
as nano st ani gern Te
cr wot ea e a nd De
ei
nn E ra D ou hse de
AT tulo Me sp ting ud à
ron MS ia plas TT À
Snag dep cn ee of fe E
8
Propagation and termination. It also depends on the
distance of the flame tavel path across the combus-
tion chamber
Figure 6.7 shows the effect of spark advance on
brake torque at constant speed and air/fuel ratio at
wide open throtle. With optimum spark timing the
maximum pressure occur a about 15° after TDC and
Hal the charge is bumed at about 10° after TDC.
CNE |
Spa advance en)
ques? Ele adri enden.
626 Effect of Fuel/Air Ratio on Indicator Diagram
Figure 6.8 shows the effect of mixture strength on indicator diagrams. The fveVair rato ofthe
‘charg influences the rate of combustion and the amount of heat evolved. The maximum flame
speed occurs when the mixture strength for hydrocarbon fuels is about 10% rich. When the
mixture is made leaner or further enriched, the flame speed deceases. Lean mixtures release less
thermal energy, resulting in lower flame temperature and hence lower flame speed. Very rich
mixtures suffer incomplete combustion, hence release less thermal energy resulting in low flame
speed, Indicator diagrams for sich, stoichiometric and weak mixture correspond to equivalence
‘tio 1.1, 1.0, and 09 respectively
pS EE Loe u Se 2
A
Soichiomenic
Wee
Crank angle, 8
Fans. Etecolmituesreghonp-vandp-@ game,
63 FACTORS AFFECTING IGNITION LAG
“The frst phase ofa combustion process is called the ignition lag. This is the period between spark
inition nd flame development, Iisa chemical process. The ignition ag in terms of crank angle
is 10° to 20° and ofthe order of miliseconds. As the ignition lag decreases, the rate of pressure
ise andthe maximum pressure achieved increase. Th factor affecting the period of ignition lag
“aro discussed inthe following subsections.
63.1 Nature of Fuel and Air/Fuel Ratio
Ignition ag depends on the nature ofthe Fel. I the selfigniion temperature of the fucl is higher,
itis dico wo buen che fuel and therefore the ignition ag will be longer. Ras been found tha the
‘nition lag isthe shortest fora mixture sight richer than the stoichiometric as shown in
69. The inition lag becomes longer asthe mixture becomes lean or very ich,
Agen sg m)
im ES
mo
Mix reg Gnome)
agus, Eee ave Aca
Ho do Ho
64.2. Initial Temperature and Pressure
‘The rate of chemical reaction depends toa greater extent on temperature but toa smaller extent on
166 Funeamenats of neral Combustion Engines
Combustion In Spark tion Engines 167
pressure, Increasing the inital temperature and pressure increase the temperature and pressure at
(he point of ignition, therefore the igition lag decreas.
63.3 Compression Ratio
‘The temperature and pressure at the point ofigation increase with the increase in compresion
‘allo, therefore the ignition lag reduces. High compression ratios also reduce the concentration of
the residual gas and therefore the inition lag is father reduced,
63.4 Spark Timing
As the spark timing is retarded, je, when the spark is produced towards the TDC, the compres-
sion process at the point of ignition is covered more resulting in an increase in temperature and
pressure, and therefore the ignition lg reduces. Advancing the spark timing increases the inition
lg.
6.3.5 Turbulence and Engine Speed
Ignition ag isnot much affected by the intensity of turbulence, Turbulence is directly proportional
to the engine speed. Therefore, the engine speed doesnot affect the ignition lag much in terms of
müliseconds. However, s he engine speed increases and Keeping he time in milliseconds almost
fixed, the erank angle in degrees increases linearly with the speed. For this reason it becomes
necessary to advance the spark timing at higher speeds by using the ignition advance mechanisms,
Excessive ubulence ofthe charge inthe vicinity ofthe spark plug causes flame quenching,
sine it increases the rate of heat transfer from the combustion zone and leads to unstable devel.
‘opment of the Mame nucteus. That is why the spark plug is usual located in a small ecess in the
al ofthe combustion chamber.
15
6.3.6 Electrode Gap of Spark Plug 10
A suitable spark plog electrode gap is necessay 1016 EE
establish the Mame nucleus. Ifthe gap i 10 small, HA
‘venching ofthe flame meleus may real and ifthe
gap is oo large, the spark intensity is reduced, Inboch § 14
the cases the range of the fuel/air rato is reduced for E [ (
the development ofthe flame nucleus.
Figure 6.10 shows the range of equivalence ratios,
ich coud be sed for fre runde gas and |
for different compression ratios of the engine. As the 10 |
competion ato 5 meray th Tage af m
gene al ao ia fr gt mie | =
a CN
th fome compression o. Fr an engine hm oi o om
Compression vto 90, te spark Peg electrode gap
Here ee FP cout Eta teo
08 fom 08 mm 09 mm is quite ita A campus,
6.4 FACTORS AFFECTING COMBUSTION IN SPARK-IGNITION
ENGINES
‘The combustion process of the spark-ignition eng
following subsections.
As affected bythe factors as i
64.1, Composition of the Mixture
‘Tye composition of the mixture affects the rate of combustion and the amount of heat evelved,
and changes the pressure and temperature of the gases in an engine cylinder. Figure 6.8 shows the
effet of mixture strength oo indicator diagrams. The angle of igaiton @, is set for the maximum
brake torque (MBT) condition, For a rich mixture wih the equivalence ratio between 1.1 and 1.2,
the duration of the first rage of combustion, te ignition lag and the duration ofthe main phase ae
all minimum, resulting in the maximum rate of pressure rise (dp/4@). The flame speed, the heat
liberation and consequently the power developed by the engine are the maximum, When the
equivalence rato is less than 1.1, the energy content is reduced, hence the duration of the frst
phase of combustion increases. The duration ofthe main phase of combustion inthe second stage
changes slighty, resulting in reduction in maximum pressure and also reduction in the rate of
pressure rise (dp/d0), These could be Improved by slightly advancing the spark timiog.
For a lean mixture withthe equivalence ratio between 0.85 and 09, the power output is
reduced but this range of equivalence ratio corresponds to the minimum bake specific fuel con-
‘sumption and represents the most economical range.
642 Load
‘When the load is reduced, the power of an engines reduced by hrotling. Tae initial pressure and
ide pressure at the point of ignition decrease and the residual gases in the mixture increase. The
first phase of combustion prolongs and the combustion process loses its stability and frequently
cannot be resummed in some cycles, causing eyelic variations. To overcome this dificult to some
‘extent, a rich mixture is used which may ensure proper combustion, bu the combustion process
may continue during e substantial portion of the expansion stoke. Tis is because of interrupted
inition at large advance angles when the compresion pressures are sil very low.
‘At par load the combustion of fuel in the sparkigniion engine is poor, causing a large
amount of products of incomplete combustion inthe exhaust including carbon monoxide, oxides
of niogen and hydrocarbons which are responsible fr air pollution. Pat load combustion is
improved by using a rich mixture but it causes wastage of fuel. These are the main shortcomings
of spark-gniton engines,
64.3 Compression Ratio
Figure 6.1 shows the effect of compression ratio on he indicator diagram.
A higher compression rato increases the pressure and temperature ofthe mixture atthe pot
of ignition and decreases the amount of residual gas inthe mixture. These ae favourable condi
ons forthe ignition of the mixture. The duration of ignition lag in the first phase decreases and the
rate of pressure rise inthe main phase increases. A high compresion rato increases the surface-
(o-volume rato ofthe combustion chamber, thus increasing he relative amount of mixture near
Combustion In Spark tion Engines 167
pressure, Increasing the inital temperature and pressure increase the temperature and pressure at
(he point of ignition, therefore the igition lag decreas.
63.3 Compression Ratio
‘The temperature and pressure at the point ofigation increase with the increase in compresion
‘allo, therefore the ignition lag reduces. High compression ratios also reduce the concentration of
the residual gas and therefore the inition lag is father reduced,
63.4 Spark Timing
As the spark timing is retarded, je, when the spark is produced towards the TDC, the compres-
sion process at the point of ignition is covered more resulting in an increase in temperature and
pressure, and therefore the ignition lg reduces. Advancing the spark timing increases the inition
lg.
6.3.5 Turbulence and Engine Speed
Ignition ag isnot much affected by the intensity of turbulence, Turbulence is directly proportional
to the engine speed. Therefore, the engine speed doesnot affect the ignition lag much in terms of
müliseconds. However, s he engine speed increases and Keeping he time in milliseconds almost
fixed, the erank angle in degrees increases linearly with the speed. For this reason it becomes
necessary to advance the spark timing at higher speeds by using the ignition advance mechanisms,
Excessive ubulence ofthe charge inthe vicinity ofthe spark plug causes flame quenching,
sine it increases the rate of heat transfer from the combustion zone and leads to unstable devel.
‘opment of the Mame nucteus. That is why the spark plug is usual located in a small ecess in the
al ofthe combustion chamber.
15
6.3.6 Electrode Gap of Spark Plug 10
A suitable spark plog electrode gap is necessay 1016 EE
establish the Mame nucleus. Ifthe gap i 10 small, HA
‘venching ofthe flame meleus may real and ifthe
gap is oo large, the spark intensity is reduced, Inboch § 14
the cases the range of the fuel/air rato is reduced for E [ (
the development ofthe flame nucleus.
Figure 6.10 shows the range of equivalence ratios,
ich coud be sed for fre runde gas and |
for different compression ratios of the engine. As the 10 |
competion ato 5 meray th Tage af m
gene al ao ia fr gt mie | =
a CN
th fome compression o. Fr an engine hm oi o om
Compression vto 90, te spark Peg electrode gap
Here ee FP cout Eta teo
08 fom 08 mm 09 mm is quite ita A campus,
6.4 FACTORS AFFECTING COMBUSTION IN SPARK-IGNITION
ENGINES
‘The combustion process of the spark-ignition eng
following subsections.
As affected bythe factors as i
64.1, Composition of the Mixture
‘Tye composition of the mixture affects the rate of combustion and the amount of heat evelved,
and changes the pressure and temperature of the gases in an engine cylinder. Figure 6.8 shows the
effet of mixture strength oo indicator diagrams. The angle of igaiton @, is set for the maximum
brake torque (MBT) condition, For a rich mixture wih the equivalence ratio between 1.1 and 1.2,
the duration of the first rage of combustion, te ignition lag and the duration ofthe main phase ae
all minimum, resulting in the maximum rate of pressure rise (dp/4@). The flame speed, the heat
liberation and consequently the power developed by the engine are the maximum, When the
equivalence rato is less than 1.1, the energy content is reduced, hence the duration of the frst
phase of combustion increases. The duration ofthe main phase of combustion inthe second stage
changes slighty, resulting in reduction in maximum pressure and also reduction in the rate of
pressure rise (dp/d0), These could be Improved by slightly advancing the spark timiog.
For a lean mixture withthe equivalence ratio between 0.85 and 09, the power output is
reduced but this range of equivalence ratio corresponds to the minimum bake specific fuel con-
‘sumption and represents the most economical range.
642 Load
‘When the load is reduced, the power of an engines reduced by hrotling. Tae initial pressure and
ide pressure at the point of ignition decrease and the residual gases in the mixture increase. The
first phase of combustion prolongs and the combustion process loses its stability and frequently
cannot be resummed in some cycles, causing eyelic variations. To overcome this dificult to some
‘extent, a rich mixture is used which may ensure proper combustion, bu the combustion process
may continue during e substantial portion of the expansion stoke. Tis is because of interrupted
inition at large advance angles when the compresion pressures are sil very low.
‘At par load the combustion of fuel in the sparkigniion engine is poor, causing a large
amount of products of incomplete combustion inthe exhaust including carbon monoxide, oxides
of niogen and hydrocarbons which are responsible fr air pollution. Pat load combustion is
improved by using a rich mixture but it causes wastage of fuel. These are the main shortcomings
of spark-gniton engines,
64.3 Compression Ratio
Figure 6.1 shows the effect of compression ratio on he indicator diagram.
A higher compression rato increases the pressure and temperature ofthe mixture atthe pot
of ignition and decreases the amount of residual gas inthe mixture. These ae favourable condi
ons forthe ignition of the mixture. The duration of ignition lag in the first phase decreases and the
rate of pressure rise inthe main phase increases. A high compresion rato increases the surface-
(o-volume rato ofthe combustion chamber, thus increasing he relative amount of mixture near
168_Fandarenais of interns! Combuston Engines
a
Combustion in Sarkigiion Engines 169
‘he walls, This par of the mixture aferburns in
the third phase. AU his retards the MBT timing
at higher compression ratos. The combustion
duration up to the point of maximum pressure
also decreases. The maximum pressure
approaches TDC. Heat liberated up to the point
of maximum pressure is reduced and the im-
portance of the afterburming process in the tid
phase increases,
644 Speed
Wen he speed increases, the time in terms of
milliseconds required for the development of 40 40 20 TDC 20 40 u M
the fame in the frst phase of combustion is not eg)
affected much and the turbulence ofthe charge guest. Etectceamoesson rot p- pam.
increases. The lame speed in the main phase of
‘combustion increase with the increase in speed, while the duration of the main phase expressed
in degrees of crank angle (05) remains practically he same. The duration ofthe frst phase of
‘combustion (0) in degrees o rank angle increases wth the increase in speed.
If the engine speed is increased witht changing the angle o ignition Oj, the duration ofthe
development of flame in the fist phase increases as shown in Figure 6.12(a). Ifthe angle of
‘ignition 6 is advanced at higher speeds, he pressure rise inthe main phase of combustion can be
practically made to coincide at diferen speeds as shown in Figure 6.1209. The duration ofthe
afterbuming phase increases withthe speed,
Figur 8.12, Efe otengespeedenndcatr sagan,
6.4.5 Turbulence and Shape of Combustion Chamber
Turbulence ofthe charge stats asi enters into he cylinder through arrow sections of inet pipes
and intake valve, Turbulence can be intensified by using a properly shaped combustion chamber
and recesses in the form of gaps between the lover surface ofthe eylinder head and the pitos
‘rowa, These recesses are so arranged as 10 creme an additional swing motion in those parts of
the charge which burn during the afterbuning phase and thus cause rapid aterbuming,
6.4.6 Spark Plug Position
ken the spark plug is mounted at the centre ofthe cylinder head, the distance travelled by the
flame from to the most distant part is the shortest. The central position of the spark plug eso
endures the maximum flame front surface. Asa resul, he rate of heat evolution and the rate of
pressure rise ae higher than those witha sie-mounted spark plug
“The flame speed is increased if the spark plug is located more towards the hotter exhaust
valve than in the direction ofthe cooler inlet valve. As the spark plug is moved away from the
central postion, the combustion period is increased and the ignition requires to be advanced
accordingly, in order to bain the best resus for the new plug location.
‘The two spark plugs suitably located reduce the lame travel path and give a higher rate
of pressure rise. This requires that ignition advance be reduced. The use of two spark plogs
‘with syachronized sparks is standard on aircraft engines. tt provides reliability and improved
performance, The thermal efficiency is increased and the specific fuel consumption is reduced.
‘With large diameter oylinders the use of two plugs gives bener performance results, whereas In
small eylinders a single plug will give satisfactory result, owing to th reduced flame travel path.
6.8 CYCLIC VARIATION
(One of the prominent characteristics ofthe sparkignition engine combustion proces is a wide
‘variation from cycle 0 cycle ofthe pressure-crank angle diagram. Tis variation increases grealy
asthe mixture strength approaches either the weak end or the rich end of the range.
Figure 6.13 shows the superimposed indicator diagrams of a number of consecutive cycles
‘with stoichiometric and lean composition ofthe mixtures. Ignition advance angles correspond in
both cases 10 maximum power of the engine
‘When the mixture is made leaner above cerain limit ($ < 0.9) depending upon the dei
features of the engine, its load and compression ratio, the rate of combustion Is different in
NA
ae me
(Sun Lane
gue 6.13. Presta dagas tig ye o) ina cure rd nan.
a
Combustion in Sarkigiion Engines 169
‘he walls, This par of the mixture aferburns in
the third phase. AU his retards the MBT timing
at higher compression ratos. The combustion
duration up to the point of maximum pressure
also decreases. The maximum pressure
approaches TDC. Heat liberated up to the point
of maximum pressure is reduced and the im-
portance of the afterburming process in the tid
phase increases,
644 Speed
Wen he speed increases, the time in terms of
milliseconds required for the development of 40 40 20 TDC 20 40 u M
the fame in the frst phase of combustion is not eg)
affected much and the turbulence ofthe charge guest. Etectceamoesson rot p- pam.
increases. The lame speed in the main phase of
‘combustion increase with the increase in speed, while the duration of the main phase expressed
in degrees of crank angle (05) remains practically he same. The duration ofthe frst phase of
‘combustion (0) in degrees o rank angle increases wth the increase in speed.
If the engine speed is increased witht changing the angle o ignition Oj, the duration ofthe
development of flame in the fist phase increases as shown in Figure 6.12(a). Ifthe angle of
‘ignition 6 is advanced at higher speeds, he pressure rise inthe main phase of combustion can be
practically made to coincide at diferen speeds as shown in Figure 6.1209. The duration ofthe
afterbuming phase increases withthe speed,
Figur 8.12, Efe otengespeedenndcatr sagan,
6.4.5 Turbulence and Shape of Combustion Chamber
Turbulence ofthe charge stats asi enters into he cylinder through arrow sections of inet pipes
and intake valve, Turbulence can be intensified by using a properly shaped combustion chamber
and recesses in the form of gaps between the lover surface ofthe eylinder head and the pitos
‘rowa, These recesses are so arranged as 10 creme an additional swing motion in those parts of
the charge which burn during the afterbuning phase and thus cause rapid aterbuming,
6.4.6 Spark Plug Position
ken the spark plug is mounted at the centre ofthe cylinder head, the distance travelled by the
flame from to the most distant part is the shortest. The central position of the spark plug eso
endures the maximum flame front surface. Asa resul, he rate of heat evolution and the rate of
pressure rise ae higher than those witha sie-mounted spark plug
“The flame speed is increased if the spark plug is located more towards the hotter exhaust
valve than in the direction ofthe cooler inlet valve. As the spark plug is moved away from the
central postion, the combustion period is increased and the ignition requires to be advanced
accordingly, in order to bain the best resus for the new plug location.
‘The two spark plugs suitably located reduce the lame travel path and give a higher rate
of pressure rise. This requires that ignition advance be reduced. The use of two spark plogs
‘with syachronized sparks is standard on aircraft engines. tt provides reliability and improved
performance, The thermal efficiency is increased and the specific fuel consumption is reduced.
‘With large diameter oylinders the use of two plugs gives bener performance results, whereas In
small eylinders a single plug will give satisfactory result, owing to th reduced flame travel path.
6.8 CYCLIC VARIATION
(One of the prominent characteristics ofthe sparkignition engine combustion proces is a wide
‘variation from cycle 0 cycle ofthe pressure-crank angle diagram. Tis variation increases grealy
asthe mixture strength approaches either the weak end or the rich end of the range.
Figure 6.13 shows the superimposed indicator diagrams of a number of consecutive cycles
‘with stoichiometric and lean composition ofthe mixtures. Ignition advance angles correspond in
both cases 10 maximum power of the engine
‘When the mixture is made leaner above cerain limit ($ < 0.9) depending upon the dei
features of the engine, its load and compression ratio, the rate of combustion Is different in
NA
ae me
(Sun Lane
gue 6.13. Presta dagas tig ye o) ina cure rd nan.
wee wee ee ee ee ee ee ee eee CR
170 Fundament of nera! Combustion Engines
consecutive cycles, The reasons for cyli variation are due to incomplete mixing o fuel air and
residual gas, andthe variation of mixture velocity that exists within the cylinder near the spark
plog. Since à large amount of random turbulent motion exists inside the cylinder, ii evident that
in presence of incomplete mixing, she spark may occur in mixtures of varying fuel/air ratios,
resulting in different rates of flame development. There Isa possibility of misting as well in some
cyeles where the lame may not develop at al. The cyclic variation is greater when the resida
exhaust gs inthe móxtre is more The residual gas will end to influence the ile lame tempera
ture and therefore will sffect the Mame speed. I is observed that the cycle variation is more at
lower compresion ratios and at reduced loads for which the residual gas i the mistue is more,
Elimination of eycle-to-eycle variation is important for obtaining improved engine perfor.
‘mance. If al cycles were like and equal o the average cycle, the maximum cylinder pressure
‘would be low, the efficiency would be greater and the detonation limit would be higher.
Cycle variation can be reduced by using mulipl ignition points, by increasing the engine
speed and turbulence. Cycle variation is greatly reduced by a tangentially-oviented swie created
by a shrouded inlet valve. À spark of extended duration alo reduces yet variation
6.6 RATE OF PRESSURE RISE
‘The rate of pressure rise during tbe combustion process influences the peak pressure, the power
produced and the smoothness with which the forces ase transmitted from the gas tothe piston.
‘The rate of pressure rise depends on the mass rate of combustion ofthe mixture inthe cylinder.
Figure 6.14 shows the pressure-crank angle diagrams for a high, normal and a low rate of
combustion. I is observed from te figure thatthe low rate of combustion requires more ignition
advance because ofthe longer time required to complete combustion. A higher rate of combustion
increases the rte of pressure rise and generally produces peak pressures at a point closer to TDC,
High eae
Normal te
Low mie
Sacar
pre rae
a 0 D OO © 6 O OO
Crank angle (de)
gua. Prsie-canang aga o eno loba
Coman in Spurcticon Engines 171
A higher peak pressure closer to TDC is generally desirable because it produces greater force on
the piston acting through a larger ponion of the power stoke, and hence increases the power
‘output Thee isa practical init on the ate of pressure rise, The higher rate of pressure rise may
result in rough running ofthe engine because of vibrations and jerks, If the rate of pressure rise is
‘excessively high, it may result in abnormal combustion called detonation. A compromise between
these two opposing factors is necessary. This can be achieved by designing and operating the
engine in such a way that approximately one-half ofthe pressure rise takes place as the piston
reaches the TDC, thus ensuring peak pressure to be reasonably close to the beginning of the
power stoke, while maintaining smooth engine operation
6.7 ABNORMAL COMBUSTION—AUTOIGNITION AND
DETONATION
In normal combustion, as shown in Figure 6.15(a), after the Name is initiated by the spark, the
flame front avels with a fairy uniform speed across the combustion chamber compressing die
‘unbumed gas ahead of it. The gas ahead ofthe flame front sealed the end: gas. This is de last
part of the charge to bum. The end-gas receives heat due to compression by expanding the bumed
gases and by radiation from the advancing flame front. Ifthe temperature and pressure are below
cenain critical values, the flame front moves across the combustion chamber through the
unburned cha.ge to the fanhest point of the chamber in the normal manner, thus burning the
mixture completely. The pressure-crank angle diagram is a smooth curve as shown in Figure
615).
If the temperature and pressure of the end-gas are high enough, it will ignite spontaneously
‘before the lame front reaches it Under this abnormal condition, the cue stages of combustion
Spuk} Spar
Cine 7
sae Y
ame artnet
LR A re
o o
Norma baston
AA
o @
Normal combustion Combustion with detonation
Figures Contstonwthpa ion eng
170 Fundament of nera! Combustion Engines
consecutive cycles, The reasons for cyli variation are due to incomplete mixing o fuel air and
residual gas, andthe variation of mixture velocity that exists within the cylinder near the spark
plog. Since à large amount of random turbulent motion exists inside the cylinder, ii evident that
in presence of incomplete mixing, she spark may occur in mixtures of varying fuel/air ratios,
resulting in different rates of flame development. There Isa possibility of misting as well in some
cyeles where the lame may not develop at al. The cyclic variation is greater when the resida
exhaust gs inthe móxtre is more The residual gas will end to influence the ile lame tempera
ture and therefore will sffect the Mame speed. I is observed that the cycle variation is more at
lower compresion ratios and at reduced loads for which the residual gas i the mistue is more,
Elimination of eycle-to-eycle variation is important for obtaining improved engine perfor.
‘mance. If al cycles were like and equal o the average cycle, the maximum cylinder pressure
‘would be low, the efficiency would be greater and the detonation limit would be higher.
Cycle variation can be reduced by using mulipl ignition points, by increasing the engine
speed and turbulence. Cycle variation is greatly reduced by a tangentially-oviented swie created
by a shrouded inlet valve. À spark of extended duration alo reduces yet variation
6.6 RATE OF PRESSURE RISE
‘The rate of pressure rise during tbe combustion process influences the peak pressure, the power
produced and the smoothness with which the forces ase transmitted from the gas tothe piston.
‘The rate of pressure rise depends on the mass rate of combustion ofthe mixture inthe cylinder.
Figure 6.14 shows the pressure-crank angle diagrams for a high, normal and a low rate of
combustion. I is observed from te figure thatthe low rate of combustion requires more ignition
advance because ofthe longer time required to complete combustion. A higher rate of combustion
increases the rte of pressure rise and generally produces peak pressures at a point closer to TDC,
High eae
Normal te
Low mie
Sacar
pre rae
a 0 D OO © 6 O OO
Crank angle (de)
gua. Prsie-canang aga o eno loba
Coman in Spurcticon Engines 171
A higher peak pressure closer to TDC is generally desirable because it produces greater force on
the piston acting through a larger ponion of the power stoke, and hence increases the power
‘output Thee isa practical init on the ate of pressure rise, The higher rate of pressure rise may
result in rough running ofthe engine because of vibrations and jerks, If the rate of pressure rise is
‘excessively high, it may result in abnormal combustion called detonation. A compromise between
these two opposing factors is necessary. This can be achieved by designing and operating the
engine in such a way that approximately one-half ofthe pressure rise takes place as the piston
reaches the TDC, thus ensuring peak pressure to be reasonably close to the beginning of the
power stoke, while maintaining smooth engine operation
6.7 ABNORMAL COMBUSTION—AUTOIGNITION AND
DETONATION
In normal combustion, as shown in Figure 6.15(a), after the Name is initiated by the spark, the
flame front avels with a fairy uniform speed across the combustion chamber compressing die
‘unbumed gas ahead of it. The gas ahead ofthe flame front sealed the end: gas. This is de last
part of the charge to bum. The end-gas receives heat due to compression by expanding the bumed
gases and by radiation from the advancing flame front. Ifthe temperature and pressure are below
cenain critical values, the flame front moves across the combustion chamber through the
unburned cha.ge to the fanhest point of the chamber in the normal manner, thus burning the
mixture completely. The pressure-crank angle diagram is a smooth curve as shown in Figure
615).
If the temperature and pressure of the end-gas are high enough, it will ignite spontaneously
‘before the lame front reaches it Under this abnormal condition, the cue stages of combustion
Spuk} Spar
Cine 7
sae Y
ame artnet
LR A re
o o
Norma baston
AA
o @
Normal combustion Combustion with detonation
Figures Contstonwthpa ion eng
172 Fundamental of lesen Combos Engines
[Combustion in Sparkignkon Engines 173
are normal, bu towards the end of combustion, namely at about the last 25% ofthe flame travel
distance, sudden inflammation ofthe remaining portion ofthe end-gas occurs. The end-gas i said
10 be auto-ignited (Figure 6.15(),
In autoignition, the charge must remain above a certain critical temperature for à certain
length of time. During this period certain chemical reactions take place which prepare the charge
for autoigntion. The time required for this preparation phase is called ignition delay or delay
«period.
Im autoignition the rate of reaction is very high and the burning is almost instantaneous
‘hich results in an extremely rapid release of energy causing pressure Auctuations as shown
in Figure 615(8), and causing pressure of the end-gas 10 increase almost 3 to 4 times from
about 90 bar to 150-200 bar The pressure rise for most of the charge is around 50 bar but
because of autoignition the pressure of the last part of the charge goes to 150-200 bar. This
large pressure difference gives rise 1 severe pressure waves which ste the eylinder wall and
set it to vibrate, giving rise to a characteristic high pitched metallic ringing sound. This
‘phenomenon is therefore known as knocking or detonation, The flame speed during detonation
ls of the order of 300 10 1000 m.
A may be noted that knocking in diesel engines is a different phenomenon. Knocking or
‘detonation in a spark-ignition engine always oecurs near the end of combustion, whereas in a
diesel engine it occurs in the beginning of combustion
‘Knock or detonation is a characteristic audible noise which is transmitted through the engine
stmctre because of spontaneous autoignition of a portion ofthe end-gas ahead ofthe propagating
‘ame. When this abnormal combustion takes place, a very high local pressure, far in excess of the
average pressure in the cylinder, and pressure waves of substantial amplitude across the combus-
tion chamber are created. A ringing metalic knocking sound clearly indicates detonation caused
by shock waves formed inthe gases and repeatedly reflected from the walls of the combustion
chamber. The frequency ofthese pressure ofillatons isthe same as the fundamental frequency
of the audible knocks. depends on the velocity of the shock waves and dhei path between
‘consecutive refletions from the walls
Intensive detonation causes loud knocks with a higher Frequency that artes in each cycle, the
power ofthe engine drops and black smoke appears intermittently in the exhaust ases. I causes
‘mechanical damage to the engine
6.8 DETRIMENTAL EFFECTS OF DETONATION
‘An engine should never be allowed 1 operate for along time with knocking. The impact of knock
will depend on ss duration and intensity, Ifthe knock duration is shor, i is unlikely to cause
damage, but a heavy constant knock can easily lead 10 severe damaging effects as explained
below.
Noise and vibration: | À violet pressure rise inkates a wave at the point of detonation, which is
reflected back and forth across the combustion chamber, causing an audible knock. The pitch of
this sound depends upon the size and shape ofthe combustion space andthe velocity ofthe wave,
which is propagated at he speed of sound in the cylinder gases. A knocking engine thus produces
‘aloud and pulsating noise annoying human ears and is very objectionable in automobile engines
Detonation also causes vibration of engine pars,
er
Increase In heat transfer: Detonation increases the rate of heat transfer to the combustion
(chamber wall. The increase in the rate of heat wansfer is because of higher temperature of the
gas in detorating engine due to rapid completion of combustion, Under detonating condition he
pressure waves scour away he protective layer of inactive stagnant gas on the cylinder walls and
this increases the rate of heat transfer. Te increased heat transfer is responsible forthe damage to
the engine.
Mechanical damage: The extremely rapid combustion increases the impact pressure, casing
fractures of aluminium alloy pistons, and aso increases the temperature, causing overbeating and
burning ofthe gaskets between the cylinder and its head, electrodes and insulators of spark plug.
piston crowns and th heads ofthe valves. In severe cases of detonation, increased cylinder and
piston temperatures cause collapsing of the piston crowns and sometimes buming ofthe cylinder
Hend Prolonged rang ofthe engineer detonating conditions causes loseningof valve inet
rings in the cylinder head, buming of he sides of piston due to blow-by ofthe very hot gases and
tumming ofthe piston rings in ther grooves which seizes the piston and the rings in the bore.
Yreigniion: Ignition ofthe mixture by some hot surface within the combustion space, before
{he normal spark ignition occur is called preignition. The detonation wave crossing and recross-
ing the cylinder causes a flow of hot gases in and out of the spark plug cavity. The hot gases
rely increase the amount of heat picked up by the sparkplug. Overheating ofthe spark plug
may be to such an extent thatthe plug electrodes may become incandescent and ignite the fresh
charge long before the ignition is supposed to occur. Thus, overheating of the spack-plg elec-
totes due tothe effets of detonation can lead to preignition. The effec: of preignition i similar to
the effect of early ignition advance, shown in Figure 5.6, The buming time losses are generally
increased, and the power and efficiency are reduced,
Power and efficiency: One ofthe principal detrimental effects of detonation is that of reduced
power ouput. I is because ofthe fact that detonation is associated with an increase in the heat
losses tothe cylinder walls and piston. I also results in he loss of thermal efcieney.
Carbon in the exhaust: Over a long period of running the engine, a large amount of carbon
gels deposited in the combustion chamber. As a result ofthe violet pressure luctaations under
‚detonation, some of the deposited carbon is not only blown out of the exhaust but alo leaves the
surface ofthe combustion chamber and the top ofthe piston becomes rough and pited
Under detonating conditions, puffs of gray smoke in the exhaust can usualy be seen against
light background. At night, these pufís are seen as bight yellow flashes. Without detonation, the
exhaust is of blue colour with occasional splashes of yellow and orange. Apart from deposited
carbon, some fice carbon is also present as one of the exhaust products under the detonating
condition. Puffs of black exhaust smoke representing free carbon in the exhaust gases also
indicate detonation; these puffs occur imtermitenly and are diferent from the black smoke of
Ovewich mixtures
6.9 THEORIES OF DETONATION
‘There is no compete explanation forthe origin of knock over the fll range of engine operating
conditions at which knock oocurs. The fundamental explanation of the knocking phenomenon
[Combustion in Sparkignkon Engines 173
are normal, bu towards the end of combustion, namely at about the last 25% ofthe flame travel
distance, sudden inflammation ofthe remaining portion ofthe end-gas occurs. The end-gas i said
10 be auto-ignited (Figure 6.15(),
In autoignition, the charge must remain above a certain critical temperature for à certain
length of time. During this period certain chemical reactions take place which prepare the charge
for autoigntion. The time required for this preparation phase is called ignition delay or delay
«period.
Im autoignition the rate of reaction is very high and the burning is almost instantaneous
‘hich results in an extremely rapid release of energy causing pressure Auctuations as shown
in Figure 615(8), and causing pressure of the end-gas 10 increase almost 3 to 4 times from
about 90 bar to 150-200 bar The pressure rise for most of the charge is around 50 bar but
because of autoignition the pressure of the last part of the charge goes to 150-200 bar. This
large pressure difference gives rise 1 severe pressure waves which ste the eylinder wall and
set it to vibrate, giving rise to a characteristic high pitched metallic ringing sound. This
‘phenomenon is therefore known as knocking or detonation, The flame speed during detonation
ls of the order of 300 10 1000 m.
A may be noted that knocking in diesel engines is a different phenomenon. Knocking or
‘detonation in a spark-ignition engine always oecurs near the end of combustion, whereas in a
diesel engine it occurs in the beginning of combustion
‘Knock or detonation is a characteristic audible noise which is transmitted through the engine
stmctre because of spontaneous autoignition of a portion ofthe end-gas ahead ofthe propagating
‘ame. When this abnormal combustion takes place, a very high local pressure, far in excess of the
average pressure in the cylinder, and pressure waves of substantial amplitude across the combus-
tion chamber are created. A ringing metalic knocking sound clearly indicates detonation caused
by shock waves formed inthe gases and repeatedly reflected from the walls of the combustion
chamber. The frequency ofthese pressure ofillatons isthe same as the fundamental frequency
of the audible knocks. depends on the velocity of the shock waves and dhei path between
‘consecutive refletions from the walls
Intensive detonation causes loud knocks with a higher Frequency that artes in each cycle, the
power ofthe engine drops and black smoke appears intermittently in the exhaust ases. I causes
‘mechanical damage to the engine
6.8 DETRIMENTAL EFFECTS OF DETONATION
‘An engine should never be allowed 1 operate for along time with knocking. The impact of knock
will depend on ss duration and intensity, Ifthe knock duration is shor, i is unlikely to cause
damage, but a heavy constant knock can easily lead 10 severe damaging effects as explained
below.
Noise and vibration: | À violet pressure rise inkates a wave at the point of detonation, which is
reflected back and forth across the combustion chamber, causing an audible knock. The pitch of
this sound depends upon the size and shape ofthe combustion space andthe velocity ofthe wave,
which is propagated at he speed of sound in the cylinder gases. A knocking engine thus produces
‘aloud and pulsating noise annoying human ears and is very objectionable in automobile engines
Detonation also causes vibration of engine pars,
er
Increase In heat transfer: Detonation increases the rate of heat transfer to the combustion
(chamber wall. The increase in the rate of heat wansfer is because of higher temperature of the
gas in detorating engine due to rapid completion of combustion, Under detonating condition he
pressure waves scour away he protective layer of inactive stagnant gas on the cylinder walls and
this increases the rate of heat transfer. Te increased heat transfer is responsible forthe damage to
the engine.
Mechanical damage: The extremely rapid combustion increases the impact pressure, casing
fractures of aluminium alloy pistons, and aso increases the temperature, causing overbeating and
burning ofthe gaskets between the cylinder and its head, electrodes and insulators of spark plug.
piston crowns and th heads ofthe valves. In severe cases of detonation, increased cylinder and
piston temperatures cause collapsing of the piston crowns and sometimes buming ofthe cylinder
Hend Prolonged rang ofthe engineer detonating conditions causes loseningof valve inet
rings in the cylinder head, buming of he sides of piston due to blow-by ofthe very hot gases and
tumming ofthe piston rings in ther grooves which seizes the piston and the rings in the bore.
Yreigniion: Ignition ofthe mixture by some hot surface within the combustion space, before
{he normal spark ignition occur is called preignition. The detonation wave crossing and recross-
ing the cylinder causes a flow of hot gases in and out of the spark plug cavity. The hot gases
rely increase the amount of heat picked up by the sparkplug. Overheating ofthe spark plug
may be to such an extent thatthe plug electrodes may become incandescent and ignite the fresh
charge long before the ignition is supposed to occur. Thus, overheating of the spack-plg elec-
totes due tothe effets of detonation can lead to preignition. The effec: of preignition i similar to
the effect of early ignition advance, shown in Figure 5.6, The buming time losses are generally
increased, and the power and efficiency are reduced,
Power and efficiency: One ofthe principal detrimental effects of detonation is that of reduced
power ouput. I is because ofthe fact that detonation is associated with an increase in the heat
losses tothe cylinder walls and piston. I also results in he loss of thermal efcieney.
Carbon in the exhaust: Over a long period of running the engine, a large amount of carbon
gels deposited in the combustion chamber. As a result ofthe violet pressure luctaations under
‚detonation, some of the deposited carbon is not only blown out of the exhaust but alo leaves the
surface ofthe combustion chamber and the top ofthe piston becomes rough and pited
Under detonating conditions, puffs of gray smoke in the exhaust can usualy be seen against
light background. At night, these pufís are seen as bight yellow flashes. Without detonation, the
exhaust is of blue colour with occasional splashes of yellow and orange. Apart from deposited
carbon, some fice carbon is also present as one of the exhaust products under the detonating
condition. Puffs of black exhaust smoke representing free carbon in the exhaust gases also
indicate detonation; these puffs occur imtermitenly and are diferent from the black smoke of
Ovewich mixtures
6.9 THEORIES OF DETONATION
‘There is no compete explanation forthe origin of knock over the fll range of engine operating
conditions at which knock oocurs. The fundamental explanation of the knocking phenomenon
We we sv es eee ee ee ee eee
174 Fundamentals of tens! Combustion Engner
hi
Combustion in Spuricleion Engines 175.
given by high speed cinsmatography tests led 10 (wo general theories of knocking-—the
autoigrition theory and the detonation theory.
toigntion theory: According to this theory when the ful-ae mixture In the end-gas region
is compressed to suficenly high pressures and above the self ignition temperatures ofthe fuel
before the flame front reaches it, th preflame reactions take place in the parts or all ofthe end:
as. During the preflame reactions, extensive decomposition of he mixture takes place producing
2idehydes, nitrogen peroxide, hydrogen peroxide and free radicals. The energy released by these
reactions and the presence of active chemical species and free radicals greatly accelerate the
chemical reaction, producing a very high pressure locally in the end-gas region and leading to
sutoigiton, Strong pressure waves propagate across the combustion chamber, and also knock
ing sound due to the acoustic vibration of the gases at the appropriate resonant frequency is
‘uansmited through the engine structure.
In autoigaition theory its assumed thatthe Flame front propagates with a normal sped before
Le start of autoigrition.
Detonation theory: According to this theory under the knocking conditions, the advancing
flame font, called detonating waves, accelerates to sonic velocity, and consumes the end-gas ata
rate much faster than would occur with normal lame speeds. Here als, there isa rapid release of
‘chemical energy in the end-gas which create a high pressure inthe end-gas region, propagates
strong pressure waves and produces knocking.
‘There is much less evidence to support the detonation theory compared to the evidence to
suppor the autoignition theory asthe knock initiating process. Most recent evidence indicates that
the knock originates with the autogniion of one or more local regions within the end-gas. The est
of the regions then ignite until the end-gas is completely reacted. This sequence of operations
oceurs extremely rapidly. Thus, the autoignition theory is most widely accepted. Therefore, the
more general term “knock is preferred to detonation to describe this phenomenon.
610 EFFECT OF ENGINE VARIABLES ON KNOCK
“To prevent knock in the SI engine the end-pas should have low temperature, pressure and density,
2 long ignition delay and a non-reactive composition. Thus the major factors that appear to be
involved in producing and preventing knocking ae: temperature, pressure, density, im, he com-
position of the unburned charge and engine design.
‘When engine conditions are changed, the effect of the change may be reflected by more than
one of the variables mentioned above. Since the effects of temperature, pressure and density are
closely elated with one another, these are grouped together in subsection 6.10.1
6.10.1 Temperature, Pressure and Density Factors
‘As the temperature of the charge is increased, the flame speed increases and he possibility ofthe
fend-gas to reach its critical temperature for autoigition also increases. This increases the
tendency o knock. An increase in pressure reduces the delay period ofthe lst par of the charge
a this par of the charge is subjected 10 a high pressure. Increase in density of the charge tends to
increase the possibilty of knocking by increasing the preflame reactions in the ends, thus
releasing higher energy. The following factors 100 tend to affct the tendency to knock:
‘The compression ratio: As the compression ratio is inereased, he pressure, the temperature
and the overall density of the charge increase. Therefore, an increase in compression ratio
increases the knocking tendency of the engine. Fora given engine seing and a fue, there is à
erica! compression ratio above which knock would occur, This compression ratio is called the
highest useful compression ratio (HUCR). Materials with high conductivity such as aluminium
alloys are used for cylindes head, since a coo! combustion chamber wall s required for an engine
10 have a high compression ratio without knock
The mass of inducted charge: The mass of the induced charge can be increased by super-
charging the engine. The charge density will be increased which in um will increase the tendency
Lo knock. The mass of the inducted charge can also be increased by opening the throtle from the
idling (othe full power output postion, so that both the charge pressure and temperaure are
increased during compression and subsequent combustion. The knock tendency will therefore
Increase withthe opening ofthe those and reach a maximum a fll tuoule position,
‘The inlet temperature of the mixture: An increase in the inet temperature ofthe mixture
increases the temperature at the end of compression, which in tum increases the temperature of
the last part of the charge to bum, thas shortening the delay period and grealy increasing the
tendency to Knock. The volumetric efficiency ofthe engine is also reduced asthe inlet temperature
isaised. Therefore, itis preferred to keep the inlet temperature low but not 100 low so as 10 cause
stating and vaporization problems.
‘The temperature of the combustion chamber walls: An increase in the temperature of the
combustion chamber walls increases the tendency to knock. To avoid knocking, the end-gas
should not be compressed against the spark plug and exhaust valve as these ae the (wo hotest
pars in the combustion chamber,
Spark timing: An increase in spark advance from the optimized timing increases the peak
pressuce of he cycle and therefore increases the pressure and temperature to which the las part
(ofthe charge is subjected. This shortens the delay period and increases the tendency to knock
‘The coolant temperature: An increase in the coolant temperature increases the temperature of
the end gas. This increase in temperatur is due to reduced heat transfer cat from the gasto the
coolant. It results in shortening the delay period of the end-gas and therefore Knocking is
increased,
Power output: An increase in the power output ofthe engine increases the temperatures ofthe
cylinder and combustion charnber walls and lso increases the temperature and pressure ofthe
endeges, thus reducing the delay period. Therefor, the tendency to knock increases.
Exhaust back pressure: Increasing the exhaust back pressure, increases the compression
temperature, increases the residual fraction and lowers che maximum pressure, The first efect
teads to increase the knocking, while the others tend to reduce it Increasing the exhaust back
Pressure has only a small effect on the knocking tendency, the opposing factor tend to balance it
out in this case
174 Fundamentals of tens! Combustion Engner
hi
Combustion in Spuricleion Engines 175.
given by high speed cinsmatography tests led 10 (wo general theories of knocking-—the
autoigrition theory and the detonation theory.
toigntion theory: According to this theory when the ful-ae mixture In the end-gas region
is compressed to suficenly high pressures and above the self ignition temperatures ofthe fuel
before the flame front reaches it, th preflame reactions take place in the parts or all ofthe end:
as. During the preflame reactions, extensive decomposition of he mixture takes place producing
2idehydes, nitrogen peroxide, hydrogen peroxide and free radicals. The energy released by these
reactions and the presence of active chemical species and free radicals greatly accelerate the
chemical reaction, producing a very high pressure locally in the end-gas region and leading to
sutoigiton, Strong pressure waves propagate across the combustion chamber, and also knock
ing sound due to the acoustic vibration of the gases at the appropriate resonant frequency is
‘uansmited through the engine structure.
In autoigaition theory its assumed thatthe Flame front propagates with a normal sped before
Le start of autoigrition.
Detonation theory: According to this theory under the knocking conditions, the advancing
flame font, called detonating waves, accelerates to sonic velocity, and consumes the end-gas ata
rate much faster than would occur with normal lame speeds. Here als, there isa rapid release of
‘chemical energy in the end-gas which create a high pressure inthe end-gas region, propagates
strong pressure waves and produces knocking.
‘There is much less evidence to support the detonation theory compared to the evidence to
suppor the autoignition theory asthe knock initiating process. Most recent evidence indicates that
the knock originates with the autogniion of one or more local regions within the end-gas. The est
of the regions then ignite until the end-gas is completely reacted. This sequence of operations
oceurs extremely rapidly. Thus, the autoignition theory is most widely accepted. Therefore, the
more general term “knock is preferred to detonation to describe this phenomenon.
610 EFFECT OF ENGINE VARIABLES ON KNOCK
“To prevent knock in the SI engine the end-pas should have low temperature, pressure and density,
2 long ignition delay and a non-reactive composition. Thus the major factors that appear to be
involved in producing and preventing knocking ae: temperature, pressure, density, im, he com-
position of the unburned charge and engine design.
‘When engine conditions are changed, the effect of the change may be reflected by more than
one of the variables mentioned above. Since the effects of temperature, pressure and density are
closely elated with one another, these are grouped together in subsection 6.10.1
6.10.1 Temperature, Pressure and Density Factors
‘As the temperature of the charge is increased, the flame speed increases and he possibility ofthe
fend-gas to reach its critical temperature for autoigition also increases. This increases the
tendency o knock. An increase in pressure reduces the delay period ofthe lst par of the charge
a this par of the charge is subjected 10 a high pressure. Increase in density of the charge tends to
increase the possibilty of knocking by increasing the preflame reactions in the ends, thus
releasing higher energy. The following factors 100 tend to affct the tendency to knock:
‘The compression ratio: As the compression ratio is inereased, he pressure, the temperature
and the overall density of the charge increase. Therefore, an increase in compression ratio
increases the knocking tendency of the engine. Fora given engine seing and a fue, there is à
erica! compression ratio above which knock would occur, This compression ratio is called the
highest useful compression ratio (HUCR). Materials with high conductivity such as aluminium
alloys are used for cylindes head, since a coo! combustion chamber wall s required for an engine
10 have a high compression ratio without knock
The mass of inducted charge: The mass of the induced charge can be increased by super-
charging the engine. The charge density will be increased which in um will increase the tendency
Lo knock. The mass of the inducted charge can also be increased by opening the throtle from the
idling (othe full power output postion, so that both the charge pressure and temperaure are
increased during compression and subsequent combustion. The knock tendency will therefore
Increase withthe opening ofthe those and reach a maximum a fll tuoule position,
‘The inlet temperature of the mixture: An increase in the inet temperature ofthe mixture
increases the temperature at the end of compression, which in tum increases the temperature of
the last part of the charge to bum, thas shortening the delay period and grealy increasing the
tendency to Knock. The volumetric efficiency ofthe engine is also reduced asthe inlet temperature
isaised. Therefore, itis preferred to keep the inlet temperature low but not 100 low so as 10 cause
stating and vaporization problems.
‘The temperature of the combustion chamber walls: An increase in the temperature of the
combustion chamber walls increases the tendency to knock. To avoid knocking, the end-gas
should not be compressed against the spark plug and exhaust valve as these ae the (wo hotest
pars in the combustion chamber,
Spark timing: An increase in spark advance from the optimized timing increases the peak
pressuce of he cycle and therefore increases the pressure and temperature to which the las part
(ofthe charge is subjected. This shortens the delay period and increases the tendency to knock
‘The coolant temperature: An increase in the coolant temperature increases the temperature of
the end gas. This increase in temperatur is due to reduced heat transfer cat from the gasto the
coolant. It results in shortening the delay period of the end-gas and therefore Knocking is
increased,
Power output: An increase in the power output ofthe engine increases the temperatures ofthe
cylinder and combustion charnber walls and lso increases the temperature and pressure ofthe
endeges, thus reducing the delay period. Therefor, the tendency to knock increases.
Exhaust back pressure: Increasing the exhaust back pressure, increases the compression
temperature, increases the residual fraction and lowers che maximum pressure, The first efect
teads to increase the knocking, while the others tend to reduce it Increasing the exhaust back
Pressure has only a small effect on the knocking tendency, the opposing factor tend to balance it
out in this case
176 _Fundamenale of era Combustion Engines
Combustion In Sprkigie
Engines 177
Cyele-to.eyele variation: Due to eyclie variation, he cycles with lower peak pressure may not
Knock, while he eyeles with higher peak pressure will knoek. A serie of cycles with lle cycle
variation will show a higher knock-Limited indicated mean effective pressure than a series with of
large eyelie variation, th average peak pressure being the same in both the cases
Carbon deposits: Incomplete combustion of fel causes carbon deposits on combustion char
ber walls, valve head and piston crown. A part of the heat released by combustion of foe is,
absorbed by these deposits due to the relatively poor thermal conduedvity and this heat i rans
ferred back tothe fresh charge which is elatively cool. Thus the temperature ofthe fresh charge
is increased and the tendency to knock inereases. Apart from this the clearance volume is alo
reduced because of the deposits on the combustion chamber walls and therefore the compression
‘ati is increased, causing an increase inthe knocking tendency.
Cylinder deposits can be reduced by using a proper grade of lubricating ol. I is found that
naphthenic ol is much superior oa paraffinic olin keeping down the cylinder deposits
6.10.2 Time Factors
In general, any ation which ends 10 decrease the normal flame speed or shortens the igition
delay period, will tend to increase Kzocking. Such an action will autignite he end-gas before the
flame front reaches it. The following factors tend 0 affect the tendency to knock:
‘Turbulence: Turbulence depends on the engine speed and the design of the combustion
chamber Decreasing trbulence decreases the Name speed and increases dhe time available forthe
end-gas to atain avroigaition conditions easily. Thus, knocking increases withthe decrease in
turbulence,
Engine speed: A decrease in engine speed decreases the turbulence within the cylinder and
therefore decreases the Name speed and increases the time available for preflame reactions. The
Jength of the delay period is not greatly affected by engine speed. Therefore, the knocking
increases with the decrease in engine sped.
Flame travel distance: The fame travel distance can be increased by increasing the size of the
‘engine and the combustion chamber. can also be increase by locating the sparkplug away from,
the centre, Increasing the lame travel distance increases the time tsken by the flame front to travel
‘across the combustion chamber. This gives more time for the end-gas to auoignte and, therefore,
knocking increases. The following feciors affect the Mame travel distance.
Combustion chamber shape: In a compact combustion chamber, the normal flame can be
‘ade to reach the last part of the charge more quickly, so the combustion time willbe shorter.
Further if the combustion chamber is highly turbulent, the combustion ete is high and the com
bastion time is further reduced. Thus a compact combustion chamber reduces knockin.
Engine sie: Large engines operate at ow pm, while he small engines operate a high pr.
‘Thus the piston speed, turbulence and the flame speed are almost the same in similar engines,
regardless ofthe size, Therefore, the time required for the flame to travel across the combustion
space would be longer in the larger engines, The delay period is not much affected by size. The
larger eylinders will therefore be more likely to Knock.
“Location of spark plug: sparkplug which is centrally located in the head ofthe combus
tion chamber has the minimum tendency to knock, since the flame travel distance is minimum.
‘The fame travel distance can further be reduced by using two or more spark plugs.
Location of exhaust valve: The exhaust valve should be located close to the spark plug
The flame stas from the spark plug, therefore the end-gas is far away from it. Locating the
exhaust valve near the spark plug means that the exhaust valve is also not situated near the
end-s region. So, the temperatute of the end-gas will not increase due to hot exhaust valve,
andthe delay period will also remain long. À long delay period means that her sa Jess chance of
knocking,
6.10.3 Composition Factors
Once the compression ratio and the engine dimensions are selected, the fuer ratio and the
properties ofthe Fuel play an importan roe in controlling the engine knock. The following compo.
son factors affect the knock.
‘Octane rating of the fuel: The tendency of an engine to knock depends on the properties of
the fel used, A lower sel igniion temperature ofthe fuel and a high preflame reactiviy would
increase the tendency of knocking. The octane number i the measure of resistance to knock. A
higher octane number ofthe fuel reduces the tendeney to knock. In general, the hydrocazbons of
the paraffin series have the maximum tendency to knock while those inthe aromatic seres have
the minimum tendency to knock. The naphihene series comes in between these wo.
‘The knock tendency of paraffins depends on the molecular sucture indicated by the follow
ing general relationships:
(2) Increasing he length of the carbon chain increases the knocking tendency.
(6) Centalizng the carbon atoms decreases the knocking tendency
(6) Adding methyl groups (CH; to the side ofthe carbon chain in the 2, or centre position
‘decreases the knocking tendency.
‘The unsaturated aliphatic hydrocarbons show les knöcking tendeney than the corresponding
saturated hydrocarbons with exceptions of ethylene, acetylene and propylene, Thus acetylene
‘knocks much more easly han elbane,
‘aphthenes and aromatics show the following relationships between the molecular structure
and the knocking tendency:
(a) The napluhenes have greater knocking tendency than the corresponding aromates, Thus,
ycloherane (C2) knocks much more easily than benzene (CH)
seal) vo 0 tree double bonds have les Knocking enone, wherest one dole bond
rocks easily.
(6) Lengtbening the side chain increases the knocking tendency in both groups of fuel,
whereas branching ofthe side chain decreases the knocking tendency.
In general, for most hydrocarbons the increased compactness of the molecular structure
reduces the knocking tendency
Combustion In Sprkigie
Engines 177
Cyele-to.eyele variation: Due to eyclie variation, he cycles with lower peak pressure may not
Knock, while he eyeles with higher peak pressure will knoek. A serie of cycles with lle cycle
variation will show a higher knock-Limited indicated mean effective pressure than a series with of
large eyelie variation, th average peak pressure being the same in both the cases
Carbon deposits: Incomplete combustion of fel causes carbon deposits on combustion char
ber walls, valve head and piston crown. A part of the heat released by combustion of foe is,
absorbed by these deposits due to the relatively poor thermal conduedvity and this heat i rans
ferred back tothe fresh charge which is elatively cool. Thus the temperature ofthe fresh charge
is increased and the tendency to knock inereases. Apart from this the clearance volume is alo
reduced because of the deposits on the combustion chamber walls and therefore the compression
‘ati is increased, causing an increase inthe knocking tendency.
Cylinder deposits can be reduced by using a proper grade of lubricating ol. I is found that
naphthenic ol is much superior oa paraffinic olin keeping down the cylinder deposits
6.10.2 Time Factors
In general, any ation which ends 10 decrease the normal flame speed or shortens the igition
delay period, will tend to increase Kzocking. Such an action will autignite he end-gas before the
flame front reaches it. The following factors tend 0 affect the tendency to knock:
‘Turbulence: Turbulence depends on the engine speed and the design of the combustion
chamber Decreasing trbulence decreases the Name speed and increases dhe time available forthe
end-gas to atain avroigaition conditions easily. Thus, knocking increases withthe decrease in
turbulence,
Engine speed: A decrease in engine speed decreases the turbulence within the cylinder and
therefore decreases the Name speed and increases the time available for preflame reactions. The
Jength of the delay period is not greatly affected by engine speed. Therefore, the knocking
increases with the decrease in engine sped.
Flame travel distance: The fame travel distance can be increased by increasing the size of the
‘engine and the combustion chamber. can also be increase by locating the sparkplug away from,
the centre, Increasing the lame travel distance increases the time tsken by the flame front to travel
‘across the combustion chamber. This gives more time for the end-gas to auoignte and, therefore,
knocking increases. The following feciors affect the Mame travel distance.
Combustion chamber shape: In a compact combustion chamber, the normal flame can be
‘ade to reach the last part of the charge more quickly, so the combustion time willbe shorter.
Further if the combustion chamber is highly turbulent, the combustion ete is high and the com
bastion time is further reduced. Thus a compact combustion chamber reduces knockin.
Engine sie: Large engines operate at ow pm, while he small engines operate a high pr.
‘Thus the piston speed, turbulence and the flame speed are almost the same in similar engines,
regardless ofthe size, Therefore, the time required for the flame to travel across the combustion
space would be longer in the larger engines, The delay period is not much affected by size. The
larger eylinders will therefore be more likely to Knock.
“Location of spark plug: sparkplug which is centrally located in the head ofthe combus
tion chamber has the minimum tendency to knock, since the flame travel distance is minimum.
‘The fame travel distance can further be reduced by using two or more spark plugs.
Location of exhaust valve: The exhaust valve should be located close to the spark plug
The flame stas from the spark plug, therefore the end-gas is far away from it. Locating the
exhaust valve near the spark plug means that the exhaust valve is also not situated near the
end-s region. So, the temperatute of the end-gas will not increase due to hot exhaust valve,
andthe delay period will also remain long. À long delay period means that her sa Jess chance of
knocking,
6.10.3 Composition Factors
Once the compression ratio and the engine dimensions are selected, the fuer ratio and the
properties ofthe Fuel play an importan roe in controlling the engine knock. The following compo.
son factors affect the knock.
‘Octane rating of the fuel: The tendency of an engine to knock depends on the properties of
the fel used, A lower sel igniion temperature ofthe fuel and a high preflame reactiviy would
increase the tendency of knocking. The octane number i the measure of resistance to knock. A
higher octane number ofthe fuel reduces the tendeney to knock. In general, the hydrocazbons of
the paraffin series have the maximum tendency to knock while those inthe aromatic seres have
the minimum tendency to knock. The naphihene series comes in between these wo.
‘The knock tendency of paraffins depends on the molecular sucture indicated by the follow
ing general relationships:
(2) Increasing he length of the carbon chain increases the knocking tendency.
(6) Centalizng the carbon atoms decreases the knocking tendency
(6) Adding methyl groups (CH; to the side ofthe carbon chain in the 2, or centre position
‘decreases the knocking tendency.
‘The unsaturated aliphatic hydrocarbons show les knöcking tendeney than the corresponding
saturated hydrocarbons with exceptions of ethylene, acetylene and propylene, Thus acetylene
‘knocks much more easly han elbane,
‘aphthenes and aromatics show the following relationships between the molecular structure
and the knocking tendency:
(a) The napluhenes have greater knocking tendency than the corresponding aromates, Thus,
ycloherane (C2) knocks much more easily than benzene (CH)
seal) vo 0 tree double bonds have les Knocking enone, wherest one dole bond
rocks easily.
(6) Lengtbening the side chain increases the knocking tendency in both groups of fuel,
whereas branching ofthe side chain decreases the knocking tendency.
In general, for most hydrocarbons the increased compactness of the molecular structure
reduces the knocking tendency
we RN IR NN SINN www wei
178 _Fundamenals of Intern Combundon Engines
Fuelair ratio: For slightly ich fuel-air mixture for which the best power is obtained, the
flame temperature is maximum resulting in maximum flame speed and minimum delay period
These two effects counteract each other regarding knocking. However, the short delay isthe
predominating factor and therefore even by using the best power fue ratio (9 =1.1-1.2) the
knock is maximum, The length of the delay period increases asthe mixture is made richer or
leaner than this and the tendency of knocking wil be reduced. For weaker mixtures the octane
requirement will increase contineousy since the reaction rate and temperature are continuously
reduced asthe foe! proportions are reduced. For richer mixtures the knock is reduced by the
cooling due tothe latent heat o the fuel and the lower flame temperature.
Humidity of air: Increasing the humidity of the entering si tends to reduce knocking by
reducing the reaction time (the time between the end of the compression stoke and the end of the
sppeeciable pressure rise due to reaction),
‘Stratifying the mixtare: The probability pf knock is decreased by stratifying the mixture,
Which makes the end-ga less reactive.
Maldistributlon: The unequal distibution of air and fuel between the various eylinder in a
mols-cylinder engine i called maldistbation, which may result in different knocking tendencies
in different cylinders because of change in the aicfel:atio locally. Usually some retardacion of
tin timing or enrichment ofthe mixture is required to reduce the knocking tendeney in those
cylinders which have the greater tendency to knock. Such adjustments may reduce the power
‘culpa and will increase the specific fuel consumption.
Dilution ef the charge: The dilution ofthe charge wilh the inet gases increases the reaction
time and ceduces the flame speed. Therefore, by intoducing cooled exhaust gas withthe inlet ai,
the tendency 10 knock can be reduced
"Water or water-alcohol infection: Injection of water or water-alcoho! mixtures ino the inlet
system of the engine reduces knocking by reducing the reaction time and increasing the flame
speed, Thus the combustion process is improved.
Fuel additives: Several substances have been found which have a pronounced ant-knock ef.
feet and increase the octane ratings when added to pero in a very small proportion, called dope,
‘Typical examples ofthese include benzole, ethanol, methanol, acetone, nitrebenzene and ter.
ethyl lead, etc. The most important ofthese is era ethyl lead Pb{C;Hs], which is soluble in petrol
and enables high compression ratios to be used compared to those with the petrol alone. A propor
tion of ethylene dibromide is added to tera ethyl lead in order to prevent the deposition of lead
inside the engine. The lead and bromine (expelled with the exhaust ga as lead bromide) combi
and greatly reduce the amount of the deposit but some par ofthe deposit may stil be found in he
cooler part ofthe exhaust system,
In recent years, the use of leaded fuel hasbeen restricted, since it pollutes the atmosphere and
estoys the effectiveness ofthe noble metal catalysts of catalytic converters, used for contol
{Ge air pollution from the exhaust of the engine. The olber drawbacks, associated with the
prolonged use of eaded fuels, ae the deposition of lad ealts upon the spark plugs, exhaust valves
and combustion chambers.
Combustion in Sporkigucon Engines 179
6.10.4 Effect of Design
“The knocking tendency of the engine is affected by the following design considerations
Effet of shrouded inlet valve: Plain valves and shrouded inlet valves are shown in Figure
6.16(a) and Figure 6.160) respectively. The use of a shrouded inlet valve provides the flow of
charge in a definite direction, so that the combustion time is reduced, This will reduce the ten
dency to knock. The shrouded valve also tends 1 reduce the cycle-to-eyele variation, especially
‘wen oriented so as to give tangential flow inc the cylinder.
tn OF
@ 10) ot
gure. (a) Pao an) oud vo (Wr ve, EV Esa)
[Effect of piston shape: Plain piston with fat top and squish piston are shown in Figure 6.179)
and Figure 6.170) respectively. In squish piston, the charge is squeezed radially invards, near the
{op dead centre and the tendency to knock is less. The thin space above the piston in the combus-
tion chamber is called the quench space. Near the end ofthe flame rave the end-ga s located in
a thin space where it makes good contact with the eylinder walls, which ae at a lower temper
ture than the end-gas. Thus the quench space is cooled which ceduces the possibility of
autigaitior and hence the knocking. Because of the reduced space above the squish piston, the
combustion chamber becomes effectively more compact and the possibility of turbulence in-
creases. Both of these factors tend to decease she knocking tendency.
è
®
Fur. (alain suspen,
Effect of cylinder bore: When engines of similar design but of increased bore cun at the
same piston speed and with the same inet conditions, fueVar ratio and exhaust back pressure,
the combustion time increases and the temperature of the inner surface ofthe eylinder also in
‘teases, Both of these factors tend to increase the knocking tendency. The octane requirement of
‘the fuel increases withthe increase in Bore even though the compression ratio and the engine rpm
remain the same,
178 _Fundamenals of Intern Combundon Engines
Fuelair ratio: For slightly ich fuel-air mixture for which the best power is obtained, the
flame temperature is maximum resulting in maximum flame speed and minimum delay period
These two effects counteract each other regarding knocking. However, the short delay isthe
predominating factor and therefore even by using the best power fue ratio (9 =1.1-1.2) the
knock is maximum, The length of the delay period increases asthe mixture is made richer or
leaner than this and the tendency of knocking wil be reduced. For weaker mixtures the octane
requirement will increase contineousy since the reaction rate and temperature are continuously
reduced asthe foe! proportions are reduced. For richer mixtures the knock is reduced by the
cooling due tothe latent heat o the fuel and the lower flame temperature.
Humidity of air: Increasing the humidity of the entering si tends to reduce knocking by
reducing the reaction time (the time between the end of the compression stoke and the end of the
sppeeciable pressure rise due to reaction),
‘Stratifying the mixtare: The probability pf knock is decreased by stratifying the mixture,
Which makes the end-ga less reactive.
Maldistributlon: The unequal distibution of air and fuel between the various eylinder in a
mols-cylinder engine i called maldistbation, which may result in different knocking tendencies
in different cylinders because of change in the aicfel:atio locally. Usually some retardacion of
tin timing or enrichment ofthe mixture is required to reduce the knocking tendeney in those
cylinders which have the greater tendency to knock. Such adjustments may reduce the power
‘culpa and will increase the specific fuel consumption.
Dilution ef the charge: The dilution ofthe charge wilh the inet gases increases the reaction
time and ceduces the flame speed. Therefore, by intoducing cooled exhaust gas withthe inlet ai,
the tendency 10 knock can be reduced
"Water or water-alcohol infection: Injection of water or water-alcoho! mixtures ino the inlet
system of the engine reduces knocking by reducing the reaction time and increasing the flame
speed, Thus the combustion process is improved.
Fuel additives: Several substances have been found which have a pronounced ant-knock ef.
feet and increase the octane ratings when added to pero in a very small proportion, called dope,
‘Typical examples ofthese include benzole, ethanol, methanol, acetone, nitrebenzene and ter.
ethyl lead, etc. The most important ofthese is era ethyl lead Pb{C;Hs], which is soluble in petrol
and enables high compression ratios to be used compared to those with the petrol alone. A propor
tion of ethylene dibromide is added to tera ethyl lead in order to prevent the deposition of lead
inside the engine. The lead and bromine (expelled with the exhaust ga as lead bromide) combi
and greatly reduce the amount of the deposit but some par ofthe deposit may stil be found in he
cooler part ofthe exhaust system,
In recent years, the use of leaded fuel hasbeen restricted, since it pollutes the atmosphere and
estoys the effectiveness ofthe noble metal catalysts of catalytic converters, used for contol
{Ge air pollution from the exhaust of the engine. The olber drawbacks, associated with the
prolonged use of eaded fuels, ae the deposition of lad ealts upon the spark plugs, exhaust valves
and combustion chambers.
Combustion in Sporkigucon Engines 179
6.10.4 Effect of Design
“The knocking tendency of the engine is affected by the following design considerations
Effet of shrouded inlet valve: Plain valves and shrouded inlet valves are shown in Figure
6.16(a) and Figure 6.160) respectively. The use of a shrouded inlet valve provides the flow of
charge in a definite direction, so that the combustion time is reduced, This will reduce the ten
dency to knock. The shrouded valve also tends 1 reduce the cycle-to-eyele variation, especially
‘wen oriented so as to give tangential flow inc the cylinder.
tn OF
@ 10) ot
gure. (a) Pao an) oud vo (Wr ve, EV Esa)
[Effect of piston shape: Plain piston with fat top and squish piston are shown in Figure 6.179)
and Figure 6.170) respectively. In squish piston, the charge is squeezed radially invards, near the
{op dead centre and the tendency to knock is less. The thin space above the piston in the combus-
tion chamber is called the quench space. Near the end ofthe flame rave the end-ga s located in
a thin space where it makes good contact with the eylinder walls, which ae at a lower temper
ture than the end-gas. Thus the quench space is cooled which ceduces the possibility of
autigaitior and hence the knocking. Because of the reduced space above the squish piston, the
combustion chamber becomes effectively more compact and the possibility of turbulence in-
creases. Both of these factors tend to decease she knocking tendency.
è
®
Fur. (alain suspen,
Effect of cylinder bore: When engines of similar design but of increased bore cun at the
same piston speed and with the same inet conditions, fueVar ratio and exhaust back pressure,
the combustion time increases and the temperature of the inner surface ofthe eylinder also in
‘teases, Both of these factors tend to increase the knocking tendency. The octane requirement of
‘the fuel increases withthe increase in Bore even though the compression ratio and the engine rpm
remain the same,
180. Fundament of ours! Comborion Engines
Combustion in Spin Engines 181
a summary of the factors that influence the tendency to knock in SI
‘Table 6.1 Summary ofthe factor influencing tendency to knock in I engines.
Variable Mejor dec on ‘ation 1 De taken Can the operator
unburned charge lo reduce knocking _ control?
Compression male ‘Temperate, pre Reduce Ne
and density Can be controled
ina VCR engine
Mass of inducted Presse and density Reduce Yes, by cti
che
Inlet temperature Temperature Reduce
Combestion chamber Temperature Reduce
wall tempecaure
Spark timing Pressure and temperature Retard Yes
Coolant temperature Temperstre Reduce Yes
Load (power output) Temperate and demsiy Reduce Yes
Cyeli vation Pressure Reduce No
Carton deposit Temperature Reduce In ome cases
Turbulence Time Increase Yes, by engine
‘speed,
Engine speed Tine crease Yes
Flame travel distance Time Reduce No
Octane rating of fuel Selfipniion temperature, High In tome cases
refine reactivity by additives.
Fuel rio “Temperature sod ime Ueveyrehoe Yes
lean tae
Hominy Reaction ime Increase No
Mal-distibution ‘Temperature and time Reduce Ne
Dituion of charge Reaction time More Yes, in some eases
6:11 DETECTION OF KNOCKING
Detection of knocking is very importan. Once knocking is recognized contol measures can be
applied before the damage is done, The following simple methods can be used to detect knocking:
1. Knocking sound can be heard in engine ited withthe silencer in the exhaust pipe. Under
Youd exhaust or Propeller pose, it soften impossible to detect knocking.
2. The temperature measurement of a spark-plug gasket by a thermocouple embedded in
it can indicate he knocking. A sudden or abnormal temperature rise under steady operating con-
ditions shows the presence of possible knock. Steady operating conditions are necessary since the
spark plug gasket temperature may also be affected by changing the ail ratio, the engine
speed, the manifold pressure, andthe rate of cooling, ee.
El
3. Knock intensity can be detected by a pressure transducer which is Mush mounted in the
combustion chamber. is a pressure sensitive unit in which the diaphragm is exposed othe gases
in the cylinder and the pressure signals ae converted 1o electrical signals. This electrical signal is
amplified and recorded ona knock mete. With increasing amplitude of he signs, the scale reading
of the knock meter increases and a relative measure of knock intensity is obtained. This nit can
be used to apply knocking control measures automatically.
4. Lis often possible to detect knocking by the presence of intermitten: puffs of gray smoke
inthe exhaust, which appear bright yellow flashes when the testi camied out in dark
6.12 UNCONTROLLED COMBUSTION
Under certain conditions, the fuera mixture is ignited by a hot spot in the cylinder. Initiation of
a flame front by a hot surface ober than the spark is called surface ignition. It comes under
the category of uncontrolled combustion. The hot surface might be the sparkplug insulator or
electrode, the exhaust valve head, the carbon deposits on the combustion chamber surfaces,
ec. Surface ignition occurring before the spark is called prefgnition and that occuring after the
spare is called postigition. Run-on, un-away, wild ping and rumble are caused by surface ¡gn
tion which are harmful
6.12.1 Preignition
is uncontrolled inflammation ofthe combustible mixture in an engine by aot surface before the
spark occurs. This is the most severe form of uncontrolled combustion. Under severe operating
conditions, some part ofthe cylinder surface may be hot enough (nearly 1100°C) to ignite the
charge before the spark does so. This is equivalent to advancing the ignition, but sine the hot spot
surface is larger than the spark, the combustion rae would be faster than that ofthe normal
combustion, creating very high eylinder pressures and temperatures and thus resulting in exces-
sive negative compression work and increased hea: loss t the wall, The overall effect wil be the
loss in power,
Preignition will also cause higher temperatures and pressures in the end-gas than those caused
by normal ignition because of its earlier occurrence onthe compression stoke. Thus pregnition
leads 10 autoignition and hence knock, and autoigrition encourages preigition. Knock and
preigniton ae different phenomena. Knock is due to the rapid combustion ofthe last par of the
‘mixture following the initiation of flame by the spark, whereas preignition isthe ignition ofthe
‘charge by a ot body Before he spark occurs.
The results of preigniion are 0 increase the work of the compression stroke, decrease the et
work of the cycle, increase the engine pressures, increase the heat loss from the engine and
decrease th efficiency. Preignition if not checked gets progressively worse, culminating in severe
engine damage.
Preignition can be detected by switching off the ignition when regular fing might occur for
2 few strokes before the engine speed drops. The sudden loss of power with no evidence of
‘mechanical malfunctioning may als indicate preigniton. The bet proof of peignitio is to take
te indicator diagram with a high speed indicator end analyse for pregnition
Combustion in Spin Engines 181
a summary of the factors that influence the tendency to knock in SI
‘Table 6.1 Summary ofthe factor influencing tendency to knock in I engines.
Variable Mejor dec on ‘ation 1 De taken Can the operator
unburned charge lo reduce knocking _ control?
Compression male ‘Temperate, pre Reduce Ne
and density Can be controled
ina VCR engine
Mass of inducted Presse and density Reduce Yes, by cti
che
Inlet temperature Temperature Reduce
Combestion chamber Temperature Reduce
wall tempecaure
Spark timing Pressure and temperature Retard Yes
Coolant temperature Temperstre Reduce Yes
Load (power output) Temperate and demsiy Reduce Yes
Cyeli vation Pressure Reduce No
Carton deposit Temperature Reduce In ome cases
Turbulence Time Increase Yes, by engine
‘speed,
Engine speed Tine crease Yes
Flame travel distance Time Reduce No
Octane rating of fuel Selfipniion temperature, High In tome cases
refine reactivity by additives.
Fuel rio “Temperature sod ime Ueveyrehoe Yes
lean tae
Hominy Reaction ime Increase No
Mal-distibution ‘Temperature and time Reduce Ne
Dituion of charge Reaction time More Yes, in some eases
6:11 DETECTION OF KNOCKING
Detection of knocking is very importan. Once knocking is recognized contol measures can be
applied before the damage is done, The following simple methods can be used to detect knocking:
1. Knocking sound can be heard in engine ited withthe silencer in the exhaust pipe. Under
Youd exhaust or Propeller pose, it soften impossible to detect knocking.
2. The temperature measurement of a spark-plug gasket by a thermocouple embedded in
it can indicate he knocking. A sudden or abnormal temperature rise under steady operating con-
ditions shows the presence of possible knock. Steady operating conditions are necessary since the
spark plug gasket temperature may also be affected by changing the ail ratio, the engine
speed, the manifold pressure, andthe rate of cooling, ee.
El
3. Knock intensity can be detected by a pressure transducer which is Mush mounted in the
combustion chamber. is a pressure sensitive unit in which the diaphragm is exposed othe gases
in the cylinder and the pressure signals ae converted 1o electrical signals. This electrical signal is
amplified and recorded ona knock mete. With increasing amplitude of he signs, the scale reading
of the knock meter increases and a relative measure of knock intensity is obtained. This nit can
be used to apply knocking control measures automatically.
4. Lis often possible to detect knocking by the presence of intermitten: puffs of gray smoke
inthe exhaust, which appear bright yellow flashes when the testi camied out in dark
6.12 UNCONTROLLED COMBUSTION
Under certain conditions, the fuera mixture is ignited by a hot spot in the cylinder. Initiation of
a flame front by a hot surface ober than the spark is called surface ignition. It comes under
the category of uncontrolled combustion. The hot surface might be the sparkplug insulator or
electrode, the exhaust valve head, the carbon deposits on the combustion chamber surfaces,
ec. Surface ignition occurring before the spark is called prefgnition and that occuring after the
spare is called postigition. Run-on, un-away, wild ping and rumble are caused by surface ¡gn
tion which are harmful
6.12.1 Preignition
is uncontrolled inflammation ofthe combustible mixture in an engine by aot surface before the
spark occurs. This is the most severe form of uncontrolled combustion. Under severe operating
conditions, some part ofthe cylinder surface may be hot enough (nearly 1100°C) to ignite the
charge before the spark does so. This is equivalent to advancing the ignition, but sine the hot spot
surface is larger than the spark, the combustion rae would be faster than that ofthe normal
combustion, creating very high eylinder pressures and temperatures and thus resulting in exces-
sive negative compression work and increased hea: loss t the wall, The overall effect wil be the
loss in power,
Preignition will also cause higher temperatures and pressures in the end-gas than those caused
by normal ignition because of its earlier occurrence onthe compression stoke. Thus pregnition
leads 10 autoignition and hence knock, and autoigrition encourages preigition. Knock and
preigniton ae different phenomena. Knock is due to the rapid combustion ofthe last par of the
‘mixture following the initiation of flame by the spark, whereas preignition isthe ignition ofthe
‘charge by a ot body Before he spark occurs.
The results of preigniion are 0 increase the work of the compression stroke, decrease the et
work of the cycle, increase the engine pressures, increase the heat loss from the engine and
decrease th efficiency. Preignition if not checked gets progressively worse, culminating in severe
engine damage.
Preignition can be detected by switching off the ignition when regular fing might occur for
2 few strokes before the engine speed drops. The sudden loss of power with no evidence of
‘mechanical malfunctioning may als indicate preigniton. The bet proof of peignitio is to take
te indicator diagram with a high speed indicator end analyse for pregnition
Sn A
182. Fandimental of Inter! Combustion Engine
Combusion ln Sparkigniion Engoes 183
ter sa very effective inhibitor of preignition. A small proportion of water is always added
in commerial alcohol to avoid preignitin.
6.122. Run-on Surface Ignition
‘When the ignition i switched off and he throttles closed (fue-air mixture is supplied through the
{alin jet) the condition in which the engine continues to Fie is called cun-o, I might be due 10 à
hot sure inte cylinder, but the major cause i spontaneous ignition ofthe fuelair mixure. The
physical factors influencing spontaneous ignition re (a) an elevated temperature of the inlet mix-
ture, ( poor cooling of the combustion chamber surface, (€) duration ofthe valve overlap, and
(& a high compression ratio. The inlet temperature is elevated atthe low speed condition bythe
Tow rte of ai flow through the induction system, often in close proximity to the hot erbaut. At
idling speed, the combustion chamber surface is not properly cooled due to poor coolant circulation,
6.12.3 Run-away Surface Ignition
In severe cases of surface ignition, the un-away surface ignition develops. Surface ignition in one
‘ele heat the surface ignition source to still higher temperatures in consecutive cycles and à
series of earier preignition is set up. The run-away surface ignition results in considerable
damage o pistons and other engine parts. Engine may cach ie as the preigntion advances to the
time when the intake valve is open and fuel-ar mixture is entering,
‘The sun away surface ignition is usually caused by an overheated park plug, exhaust valve or
piston head.
6124 Wild Ping
Wile ping is one or several regular but very sharp, combustion knocks caused by early surface
‘goition from deposit panicles aftr the inet valve is closed. Knock oecurs in an erratic way.
A probable reason for wild ping is that some glowing carbon particles attached lightly to the
combustion chamber surface break fre, and then floating erzatically through the chamber ignite
the charge until they are finally carried away past the exhaust valve.
6125 Rumble
Rumble isthe name asigoed t termite roughness caused by combustion chamber deposits
which create secondary flame fronts. is a low pitched noise distinctly different from spark
‘knock. 1 follows thatthe rate of pressure rise and the maximum pressure become very high.
‘Rumble develops early and at multiple points.
‘Rumble is avoided or minimized by eliminating deposits usually by fuel additives. The type
of lubrcating oil and gasoline without tera ethyl lead can also reduce deposits and therefore
rumble
Rumble causes vibrations of the crank shaft arising from a high ace of pressure rise with
consequent deflection of mechanical pats
‘The combustion phenomena in a sparkignition engine ae suramarized in Figure 6.18.
Aa
es IE 1
NORMAL COMBUSTION UNCONTROLLED |[ ABNORMAL COMBUSTION
ee ‘COMBUSTION (Spark Keoek)
CONTROLLED COMBUSTION |] (Surface non)
Combusioeis Inn of ame fet bya || End ga ignites syonancousty
‘defame tot hot suas att he
[cos te combaten chamber na | su e may osu re
info manner at oma speed || the park prog) or
Before ih Mam ont rec
A 0€ a process in which some
pastoral ofthe hae maybe
ste Sel ey AA
m] —
OS ]
Roues ENT
suce Nownnocxnig
age site
‘ron ng cen i sli SN
O | LS Miet | Serapio
Etes Mae
nic nt D
= RNA sua CE
‘cnr
Satis pin co
Ph period
ome ti rete
“atone Soca
waLD FN mama
tami ey | ow pene
ray ‘aay dos
Fee og ig
Er En
fre a
in nant
met
Fee Sirmayclcortstonphnemorana spin ng.
6.13 COMBUSTION CHAMBERS FOR SPARK-GNITION
ENGINES
À proper design ofthe combustion chamber forthe spark-ignition engine is important s it affects
‘he engine performance, its knocking tendencies and exhaust pollutants, The design involves the
shape ofthe eyliner head an piston crown, the location of the spark plug, and location, siz and
number of nle and exhaust valves, The design ofthe intake por als influences the tubalence
182. Fandimental of Inter! Combustion Engine
Combusion ln Sparkigniion Engoes 183
ter sa very effective inhibitor of preignition. A small proportion of water is always added
in commerial alcohol to avoid preignitin.
6.122. Run-on Surface Ignition
‘When the ignition i switched off and he throttles closed (fue-air mixture is supplied through the
{alin jet) the condition in which the engine continues to Fie is called cun-o, I might be due 10 à
hot sure inte cylinder, but the major cause i spontaneous ignition ofthe fuelair mixure. The
physical factors influencing spontaneous ignition re (a) an elevated temperature of the inlet mix-
ture, ( poor cooling of the combustion chamber surface, (€) duration ofthe valve overlap, and
(& a high compression ratio. The inlet temperature is elevated atthe low speed condition bythe
Tow rte of ai flow through the induction system, often in close proximity to the hot erbaut. At
idling speed, the combustion chamber surface is not properly cooled due to poor coolant circulation,
6.12.3 Run-away Surface Ignition
In severe cases of surface ignition, the un-away surface ignition develops. Surface ignition in one
‘ele heat the surface ignition source to still higher temperatures in consecutive cycles and à
series of earier preignition is set up. The run-away surface ignition results in considerable
damage o pistons and other engine parts. Engine may cach ie as the preigntion advances to the
time when the intake valve is open and fuel-ar mixture is entering,
‘The sun away surface ignition is usually caused by an overheated park plug, exhaust valve or
piston head.
6124 Wild Ping
Wile ping is one or several regular but very sharp, combustion knocks caused by early surface
‘goition from deposit panicles aftr the inet valve is closed. Knock oecurs in an erratic way.
A probable reason for wild ping is that some glowing carbon particles attached lightly to the
combustion chamber surface break fre, and then floating erzatically through the chamber ignite
the charge until they are finally carried away past the exhaust valve.
6125 Rumble
Rumble isthe name asigoed t termite roughness caused by combustion chamber deposits
which create secondary flame fronts. is a low pitched noise distinctly different from spark
‘knock. 1 follows thatthe rate of pressure rise and the maximum pressure become very high.
‘Rumble develops early and at multiple points.
‘Rumble is avoided or minimized by eliminating deposits usually by fuel additives. The type
of lubrcating oil and gasoline without tera ethyl lead can also reduce deposits and therefore
rumble
Rumble causes vibrations of the crank shaft arising from a high ace of pressure rise with
consequent deflection of mechanical pats
‘The combustion phenomena in a sparkignition engine ae suramarized in Figure 6.18.
Aa
es IE 1
NORMAL COMBUSTION UNCONTROLLED |[ ABNORMAL COMBUSTION
ee ‘COMBUSTION (Spark Keoek)
CONTROLLED COMBUSTION |] (Surface non)
Combusioeis Inn of ame fet bya || End ga ignites syonancousty
‘defame tot hot suas att he
[cos te combaten chamber na | su e may osu re
info manner at oma speed || the park prog) or
Before ih Mam ont rec
A 0€ a process in which some
pastoral ofthe hae maybe
ste Sel ey AA
m] —
OS ]
Roues ENT
suce Nownnocxnig
age site
‘ron ng cen i sli SN
O | LS Miet | Serapio
Etes Mae
nic nt D
= RNA sua CE
‘cnr
Satis pin co
Ph period
ome ti rete
“atone Soca
waLD FN mama
tami ey | ow pene
ray ‘aay dos
Fee og ig
Er En
fre a
in nant
met
Fee Sirmayclcortstonphnemorana spin ng.
6.13 COMBUSTION CHAMBERS FOR SPARK-GNITION
ENGINES
À proper design ofthe combustion chamber forthe spark-ignition engine is important s it affects
‘he engine performance, its knocking tendencies and exhaust pollutants, The design involves the
shape ofthe eyliner head an piston crown, the location of the spark plug, and location, siz and
number of nle and exhaust valves, The design ofthe intake por als influences the tubalence
184_Fandamanuie of vera Canon Enger
and flow pattern of the charge inthe combustion chamber. The optimum design of a combustion
‘chamber isa subject of research and development During the days of development ofthe engine,
the compression ratio used was only 4 and row itis possible to rise the compression ratio to
above 10 without knock.
6.13.1 Basic Requirements of a Good Combustion Chamber
‘The basi requirements ofa good combustion chamber are to provide
1. High power ouput
2. High thermal efficiency and low specific fuel consumption
3. Smooth engine operation
4, Reduced exhaust pollutants
High power output: For producing a high power output, a combustion chamber requires the
following:
(a) A high compression ratio
(6) A lil rich mixta.
(©) Good turbulence
(8) Large inlet valve to obtain a higher volumetre efficieney
(6) Streamline flow in order to reduce the pressure drop and 10 increase futher volumetric
efficiency.
High thermal eMicieney and low specific fuel consumption: In order to achieve high thermal
efficiency and low specifi fuel consumption he following are the requirements:
(a) A high compression ratio
(o) A sonal heat loss during combustion, which means a small surface-to-volume ratio and a
compact shape.
(©) Faster fuel burning process
(@) litle lean mixture.
‘Smooth engine operation: Smooth engine operation, with the
pression ratio to use fora fuel of given octane cating, requires the
(a) A moderate rate of pressure rise during combustion.
(0) Absence of knock, which in tum means:
(® A compact combustion chamber to reduce the flame travel distance.
Gi) Proper location of spark plug and exhaust valve, and their coo
Reduced exhaust pollutants: Exhaust pollutants can be reduced by designing a combustion
‚chamber that produces a faster buming rte of fue. A faster burning chamber with its shorter
baming time permits operation with substantially higher amounts of Exhaust Gas Recirculation
(EGR), which reduces the oxides of nitrogen (NO,) in the exhaust gas without substantial inv
esse in the hydrocarbon emissions. It can also bum very lean mixtures within the normal con-
Saints of engine smoothness and response. À faster burning chamber exhibits much les cylic
variations, permiting the normal combustion at par oad to have greater dilation ofthe charge.
Cemburien in Sprkiicen Enger 185
“Methods of using a fast burn” combustion chamber include the following:
(a) Locating the sparkplug to a more central position within a compact combustion chamber
(0) Using two spark plugs.
(6) Uncressing the inylinder gas motion by creating swi during the induction process or
ducing the later stages of compresion.
6.14 COMBUSTION CHAMBER DESIGN PRINCIPLES
principles governing an efficient combustion chamber design may be enumerated as
High volumetric eMicieney: High volumeti efficiency means more charge per stroke and a
proportionate increase in the power output. Effective valve open ara, which depends on valve
diameter and lift, directly affects the volumetric effcieney. To obtain maximum performance and
to reduce pumping loses, the size of the valve heads should be large. The valve sizes hat can be
ccommodated depend on the cylinder head geometry
Minimum path of flame travel: The flame travel path is determined by the location ofthe
sparkplug and by the shape ofthe combustion chamber. A compact combustion chamber reduces
the flame travel distance oa minimum. With given turbulence, this reduces the te of combus-
‘ign and minimizes the burning time loss. The minimum path of flame travel reduces the possibility
of knock. SI engines are generally imited up to 100 mm cylinder bore because of short flame
travel distance, There are no such limits on CI engines.
Provision of minimum heat loss zone around the spark plug: It ensures good initial com
baston conditions, The sparkplug is placed near the exhaust valve to prevent hat loss in the first,
‘phase of combustion. The surfsce-o-volume ratio should be minimum here.
Reduced rate of pressure rise: The second phase of the combustion zone or shock zone
should be designed t give a reduced rte of pressure rset avoid knocking and to avoid excessive
shocks on the crankshaft
Provision ofa suitable quench region: ‘The queach region in a combustion chamber is pro-
vided at he farthest distance ofthe flame travel, so thal there wil be increased cooling ofthe
combustion gases during the most likely knocking period. This condition is obtained by making
the surface-o-volume ratio maximum in this region. Ifthe relatively cool let valve is located in
this region, then cooling of he ead-gases will be improved.
‘Maximum thermal efficiency: Maximum thermal efficiency for the given grade of fuel ean be
obtained by employing the highest compression ratio for smooth engine operation, without knock:
ing tendency, unde all operating conditions.
‘Short combustion time or fast burn: ts an important consideration in combustion chamber
design of spark-ignition engine. Fast bum results from properly creating irbulence. It improves
the possibilty of lean burn’, thus reducing ai pollution. Proper turbulence may be created by
Positioning the inte valve suitably, designing the inet passage to create wil inthe induction
and flow pattern of the charge inthe combustion chamber. The optimum design of a combustion
‘chamber isa subject of research and development During the days of development ofthe engine,
the compression ratio used was only 4 and row itis possible to rise the compression ratio to
above 10 without knock.
6.13.1 Basic Requirements of a Good Combustion Chamber
‘The basi requirements ofa good combustion chamber are to provide
1. High power ouput
2. High thermal efficiency and low specific fuel consumption
3. Smooth engine operation
4, Reduced exhaust pollutants
High power output: For producing a high power output, a combustion chamber requires the
following:
(a) A high compression ratio
(6) A lil rich mixta.
(©) Good turbulence
(8) Large inlet valve to obtain a higher volumetre efficieney
(6) Streamline flow in order to reduce the pressure drop and 10 increase futher volumetric
efficiency.
High thermal eMicieney and low specific fuel consumption: In order to achieve high thermal
efficiency and low specifi fuel consumption he following are the requirements:
(a) A high compression ratio
(o) A sonal heat loss during combustion, which means a small surface-to-volume ratio and a
compact shape.
(©) Faster fuel burning process
(@) litle lean mixture.
‘Smooth engine operation: Smooth engine operation, with the
pression ratio to use fora fuel of given octane cating, requires the
(a) A moderate rate of pressure rise during combustion.
(0) Absence of knock, which in tum means:
(® A compact combustion chamber to reduce the flame travel distance.
Gi) Proper location of spark plug and exhaust valve, and their coo
Reduced exhaust pollutants: Exhaust pollutants can be reduced by designing a combustion
‚chamber that produces a faster buming rte of fue. A faster burning chamber with its shorter
baming time permits operation with substantially higher amounts of Exhaust Gas Recirculation
(EGR), which reduces the oxides of nitrogen (NO,) in the exhaust gas without substantial inv
esse in the hydrocarbon emissions. It can also bum very lean mixtures within the normal con-
Saints of engine smoothness and response. À faster burning chamber exhibits much les cylic
variations, permiting the normal combustion at par oad to have greater dilation ofthe charge.
Cemburien in Sprkiicen Enger 185
“Methods of using a fast burn” combustion chamber include the following:
(a) Locating the sparkplug to a more central position within a compact combustion chamber
(0) Using two spark plugs.
(6) Uncressing the inylinder gas motion by creating swi during the induction process or
ducing the later stages of compresion.
6.14 COMBUSTION CHAMBER DESIGN PRINCIPLES
principles governing an efficient combustion chamber design may be enumerated as
High volumetric eMicieney: High volumeti efficiency means more charge per stroke and a
proportionate increase in the power output. Effective valve open ara, which depends on valve
diameter and lift, directly affects the volumetric effcieney. To obtain maximum performance and
to reduce pumping loses, the size of the valve heads should be large. The valve sizes hat can be
ccommodated depend on the cylinder head geometry
Minimum path of flame travel: The flame travel path is determined by the location ofthe
sparkplug and by the shape ofthe combustion chamber. A compact combustion chamber reduces
the flame travel distance oa minimum. With given turbulence, this reduces the te of combus-
‘ign and minimizes the burning time loss. The minimum path of flame travel reduces the possibility
of knock. SI engines are generally imited up to 100 mm cylinder bore because of short flame
travel distance, There are no such limits on CI engines.
Provision of minimum heat loss zone around the spark plug: It ensures good initial com
baston conditions, The sparkplug is placed near the exhaust valve to prevent hat loss in the first,
‘phase of combustion. The surfsce-o-volume ratio should be minimum here.
Reduced rate of pressure rise: The second phase of the combustion zone or shock zone
should be designed t give a reduced rte of pressure rset avoid knocking and to avoid excessive
shocks on the crankshaft
Provision ofa suitable quench region: ‘The queach region in a combustion chamber is pro-
vided at he farthest distance ofthe flame travel, so thal there wil be increased cooling ofthe
combustion gases during the most likely knocking period. This condition is obtained by making
the surface-o-volume ratio maximum in this region. Ifthe relatively cool let valve is located in
this region, then cooling of he ead-gases will be improved.
‘Maximum thermal efficiency: Maximum thermal efficiency for the given grade of fuel ean be
obtained by employing the highest compression ratio for smooth engine operation, without knock:
ing tendency, unde all operating conditions.
‘Short combustion time or fast burn: ts an important consideration in combustion chamber
design of spark-ignition engine. Fast bum results from properly creating irbulence. It improves
the possibilty of lean burn’, thus reducing ai pollution. Proper turbulence may be created by
Positioning the inte valve suitably, designing the inet passage to create wil inthe induction
le en ww A NPN DA wie wiesen
186, Fundamenue of letra! Cambon Engines
Combustion In Sparkignion Engines 187
process and sreamlining the combustion chamber. Turbulence may also be created by ui‘,
Which is better as it does not adversely affect he volumetric efficiency.
Exhaust valve location: To reduce the possibility of knock, thee should not bea bot surface in
the end: gas region. Exhaust valve being a very hot surface should noë be placed in this region. The
‘exhaust valve should be located near the spark plug. In order to reduce the hot surface area, the
‘exhaust valve head diameter is kept small and to avoid flow cesurictons, a high I is employed.
“The exhaust valve head should be cooled 0 he desired exten.
Maximum output: For maximum output, two inlet and two exhaust valves are used per cylinder
Engines of high output usually ave intake valves in one ine and exhaust valves in another, The
valve-ia-head type of combustion chamber is usually domed. The sparkplug i located in the top
‘of the dome, which makes a compact combustion chamber. The lame front area increases rapidly
‘with this type of chamber, the length of flame travel is short and the combustion rate is high
‘Cooling of spark plug points: Sufficient cooling of the sparkplug points s required to avoid
preigition effects, a the wider throttle openings.
Scavenging of the exhaust gas: A good scavenging of the exhaust gas is require.
Materials for cylinder head: Aluminium-alloy heads are mostly used. Some heads have been
le of copper or copper alloys, and others had copper inserts located to contact the last par of
the charge to be burned. These are materials of hgh heat conductivity, which conduct heat away
From the hot spots
6.15 COMBUSTION CHAMBER OPTIMIZATION PROCEDURE
‘The sequence of steps described in the following subsections constitutes the process of develop-
ment of a good combustion chamber.
6.15.1 Geometric Considerations
‘These involve the considerations of the shape of cylinder head and piston crown, the spark plug
location, and the inlet and exhaust valves location and size. Open Chambers, such asthe hemi-
spherical wit almost central spark plug location, give close to the maximum flame front surface
area ensuring faster burn and provide the lowest chamber surface area in contact with the burned
gases ensuring the lowest heat transfer More compact combustion chamber shapes other than che
‘open chambers, such as the bow)-in-piston, do produce a somewhat faster bum but suffer from
lower volumetic efficiency and higher heat loses.
‘With almost central positioning ofthe spark plug and providing some squish area the bum sate
is improved.
6.18.2 Considerations for Cyclic Variations
‘Cyclic variations can be reduced by taking care of the following:
1. Improving the uniformity of the How of air, fuel and residual gases mixture during the
intake process.
Delivery of equal amounts of constituents o etch cylinder o avoid maldisinbution,
Provision for good mixing between constituents inthe intake manifold,
‘Accurate control of mixture composition during engine transients.
. Achicving nearly similar flow pateras within each engine cylinder 10 obtain equal burn
rates in all lingers.
6.15.3 Consideration for Proper Turbulence
‘The higher turbulence levels during combustion are required which can usually be best done
by creating swirl during the induction process, Higher than necessary gas veleities within the
cylinder result in excessive eat losses and low volumen efficiency
6.16 TYPES OF COMBUSTION CHAMBER
Brief descriptions of a few important types of combustion chambers,
sparkplug, showing their developments are given below:
Locations of valves and
6.16.1. Thead Type Combustion Chamber
Figure 6.19 shows the T-head type of combustion chamber. This was the earliest type used by
Ford Motor Corporation during early stages of engine development in 1908, The T-head design
suffers fom the following disadvantages:
(4) The distance across the combustion chamber is very long. The spark plug i located near
the exhaust valve, so the Name travel distance fom the spark plug to the end-gas (near the
inet valve) increases. Therefore, knocking tendency is increased,
(©) The configuration provides two valves on either side ofthe combustion chamber, requiring
two camshafts.
‘There was a violent knocking even at compression ratio 4:1. This was also because of the low
‘octane number of petol available at tha time, which varied from 45 to 50,
6.162 L-headType or Side Valve Combustion
Chamber
Figure 620 shows the L-head type of combustion chamber In this, the combustion chamber sin
{he form of a more or less lt slab, extending over the piston. The disadvantages of the T-head
type of combustion chamber forced the development of L-head, in which the two valves are
placed on the same side ofthe combustion chamber, thus educing the flame travel distance, and
the valves are operated by a single camshaft
During he period 1910-1930, the side valve combustion chambers were commonly used in
SLengines. In such an engine the valves are placed side by sie na detachable block. Manufactur
{ng and maintenance of this type of combustion chamber ae both easy. The valve mechanism can
‘ensily be enclosed and lubricated The detachable head can easly be removed for decarbonising
without disturbing either the valve gear or the main pipe work,
186, Fundamenue of letra! Cambon Engines
Combustion In Sparkignion Engines 187
process and sreamlining the combustion chamber. Turbulence may also be created by ui‘,
Which is better as it does not adversely affect he volumetric efficiency.
Exhaust valve location: To reduce the possibility of knock, thee should not bea bot surface in
the end: gas region. Exhaust valve being a very hot surface should noë be placed in this region. The
‘exhaust valve should be located near the spark plug. In order to reduce the hot surface area, the
‘exhaust valve head diameter is kept small and to avoid flow cesurictons, a high I is employed.
“The exhaust valve head should be cooled 0 he desired exten.
Maximum output: For maximum output, two inlet and two exhaust valves are used per cylinder
Engines of high output usually ave intake valves in one ine and exhaust valves in another, The
valve-ia-head type of combustion chamber is usually domed. The sparkplug i located in the top
‘of the dome, which makes a compact combustion chamber. The lame front area increases rapidly
‘with this type of chamber, the length of flame travel is short and the combustion rate is high
‘Cooling of spark plug points: Sufficient cooling of the sparkplug points s required to avoid
preigition effects, a the wider throttle openings.
Scavenging of the exhaust gas: A good scavenging of the exhaust gas is require.
Materials for cylinder head: Aluminium-alloy heads are mostly used. Some heads have been
le of copper or copper alloys, and others had copper inserts located to contact the last par of
the charge to be burned. These are materials of hgh heat conductivity, which conduct heat away
From the hot spots
6.15 COMBUSTION CHAMBER OPTIMIZATION PROCEDURE
‘The sequence of steps described in the following subsections constitutes the process of develop-
ment of a good combustion chamber.
6.15.1 Geometric Considerations
‘These involve the considerations of the shape of cylinder head and piston crown, the spark plug
location, and the inlet and exhaust valves location and size. Open Chambers, such asthe hemi-
spherical wit almost central spark plug location, give close to the maximum flame front surface
area ensuring faster burn and provide the lowest chamber surface area in contact with the burned
gases ensuring the lowest heat transfer More compact combustion chamber shapes other than che
‘open chambers, such as the bow)-in-piston, do produce a somewhat faster bum but suffer from
lower volumetic efficiency and higher heat loses.
‘With almost central positioning ofthe spark plug and providing some squish area the bum sate
is improved.
6.18.2 Considerations for Cyclic Variations
‘Cyclic variations can be reduced by taking care of the following:
1. Improving the uniformity of the How of air, fuel and residual gases mixture during the
intake process.
Delivery of equal amounts of constituents o etch cylinder o avoid maldisinbution,
Provision for good mixing between constituents inthe intake manifold,
‘Accurate control of mixture composition during engine transients.
. Achicving nearly similar flow pateras within each engine cylinder 10 obtain equal burn
rates in all lingers.
6.15.3 Consideration for Proper Turbulence
‘The higher turbulence levels during combustion are required which can usually be best done
by creating swirl during the induction process, Higher than necessary gas veleities within the
cylinder result in excessive eat losses and low volumen efficiency
6.16 TYPES OF COMBUSTION CHAMBER
Brief descriptions of a few important types of combustion chambers,
sparkplug, showing their developments are given below:
Locations of valves and
6.16.1. Thead Type Combustion Chamber
Figure 6.19 shows the T-head type of combustion chamber. This was the earliest type used by
Ford Motor Corporation during early stages of engine development in 1908, The T-head design
suffers fom the following disadvantages:
(4) The distance across the combustion chamber is very long. The spark plug i located near
the exhaust valve, so the Name travel distance fom the spark plug to the end-gas (near the
inet valve) increases. Therefore, knocking tendency is increased,
(©) The configuration provides two valves on either side ofthe combustion chamber, requiring
two camshafts.
‘There was a violent knocking even at compression ratio 4:1. This was also because of the low
‘octane number of petol available at tha time, which varied from 45 to 50,
6.162 L-headType or Side Valve Combustion
Chamber
Figure 620 shows the L-head type of combustion chamber In this, the combustion chamber sin
{he form of a more or less lt slab, extending over the piston. The disadvantages of the T-head
type of combustion chamber forced the development of L-head, in which the two valves are
placed on the same side ofthe combustion chamber, thus educing the flame travel distance, and
the valves are operated by a single camshaft
During he period 1910-1930, the side valve combustion chambers were commonly used in
SLengines. In such an engine the valves are placed side by sie na detachable block. Manufactur
{ng and maintenance of this type of combustion chamber ae both easy. The valve mechanism can
‘ensily be enclosed and lubricated The detachable head can easly be removed for decarbonising
without disturbing either the valve gear or the main pipe work,
Fundament 91 inarmal Combustion Engines
Comunion in Spriciiten Engines 189
2
ee
[KE rin cere
Faunia Tinstombictondamer Fgue620 LHoadorsd aa cousin chamber
In its original form, this type of engine gave poor performance because of the following
lisitatons
(@) Lack of turbulence as he charge had 0 take two right angle tus to enter into the cylinder
snd in doing s te inital velocity of he charge got reduced,
(0) Extremely prone to knock due to Lack of turbulence, resulting in alow flame speed. The
flame travel distance was also lage, and it therefore caused Knock.
(©) Exuremely sensitive to ignition timing due to lower rate of burning and slow combustion,
‘The side valve engines are not preferred for higher compression ratios on account of
inadequate voluneti efficiency, noncompactness and additional requirement of cooling, These
engines do not compare well with the overhead valve engines which were developed later to give
more power and higher efficiency.
6.16.3 Ricardo Turbulent Head Side Valve Combustion Chamber
Figure 621 shows the arrangement ofthis type of combustion chamber developed in 1919. The
main objective ofthis design wast increase turbulence in order to obtain a higher flame speed and
19 reduce the knocking tendency ofthe engine.
‘A greater volume of the space of combustion chamber was available over the valves and was
called the main body ofthe combustion chamber. A slightly restricted passage-way was provided
‘over the cylinder. During the compression suoke the gases were forced back to the main body
de
Pion
ine
to: Inlet msi
Ex: Belated
guest Ast une ber (151,
through the rsticted passago-way tat created additional tubulence. By varying the throat area
of the restricted passage it was possible to achieve any desired degree of urbulence within the
main body of the combustion chamber. The ate of combustion during the second stage of com>
baston was improved considerably and this resulted in improved performance.
In order to reduce the knockin tendency o a minimum, the distance of effective lame travel
was shortened by forming a very thio layer of entrapped gas between the piston crown and the
portion of combustion chamber at the end-gas region, when the piston was at TDC. The surface.
to-volume ratio in this region was high, which belped in rejecting enough het from the end-gas to
prevent knocking. The flame travel distance was further reduced by placing the spark plugin the
centre ofthe effective combustion space with a slight shift towards the exhaust valve.
‘At the time the turbulent head was developed, the octane number of the perol was inthe
region of 45-50. With this fuel the compression rato of the engine was raised from 4:1 10 48:1
and the power and efficiency ofthe engine got substanaly improved
As the octane number of petrol improved with time, by about 1935, it was possible to un the
engine with a compression ratio 6:1. A his ratio the flame speed was increased tothe extent tht
the rate of pressure rise was observed more than 2.5 bar per degree of crank angle exceeding the
‘optimum rate of pressure rise, namely about 2-2. bar per degree of crank angle. To combat this
problem, the area of the passageway was increased progressively
‘With the relatively high octane petrol available today, the Compression ratio has been in-
‘reased, resulting in Lack of space to accommodate the valves in L-head or sie-valve design. I
appears tat the side-valve engine can no longer compete with Ihe overhead design. Nowadays a
Comunion in Spriciiten Engines 189
2
ee
[KE rin cere
Faunia Tinstombictondamer Fgue620 LHoadorsd aa cousin chamber
In its original form, this type of engine gave poor performance because of the following
lisitatons
(@) Lack of turbulence as he charge had 0 take two right angle tus to enter into the cylinder
snd in doing s te inital velocity of he charge got reduced,
(0) Extremely prone to knock due to Lack of turbulence, resulting in alow flame speed. The
flame travel distance was also lage, and it therefore caused Knock.
(©) Exuremely sensitive to ignition timing due to lower rate of burning and slow combustion,
‘The side valve engines are not preferred for higher compression ratios on account of
inadequate voluneti efficiency, noncompactness and additional requirement of cooling, These
engines do not compare well with the overhead valve engines which were developed later to give
more power and higher efficiency.
6.16.3 Ricardo Turbulent Head Side Valve Combustion Chamber
Figure 621 shows the arrangement ofthis type of combustion chamber developed in 1919. The
main objective ofthis design wast increase turbulence in order to obtain a higher flame speed and
19 reduce the knocking tendency ofthe engine.
‘A greater volume of the space of combustion chamber was available over the valves and was
called the main body ofthe combustion chamber. A slightly restricted passage-way was provided
‘over the cylinder. During the compression suoke the gases were forced back to the main body
de
Pion
ine
to: Inlet msi
Ex: Belated
guest Ast une ber (151,
through the rsticted passago-way tat created additional tubulence. By varying the throat area
of the restricted passage it was possible to achieve any desired degree of urbulence within the
main body of the combustion chamber. The ate of combustion during the second stage of com>
baston was improved considerably and this resulted in improved performance.
In order to reduce the knockin tendency o a minimum, the distance of effective lame travel
was shortened by forming a very thio layer of entrapped gas between the piston crown and the
portion of combustion chamber at the end-gas region, when the piston was at TDC. The surface.
to-volume ratio in this region was high, which belped in rejecting enough het from the end-gas to
prevent knocking. The flame travel distance was further reduced by placing the spark plugin the
centre ofthe effective combustion space with a slight shift towards the exhaust valve.
‘At the time the turbulent head was developed, the octane number of the perol was inthe
region of 45-50. With this fuel the compression rato of the engine was raised from 4:1 10 48:1
and the power and efficiency ofthe engine got substanaly improved
As the octane number of petrol improved with time, by about 1935, it was possible to un the
engine with a compression ratio 6:1. A his ratio the flame speed was increased tothe extent tht
the rate of pressure rise was observed more than 2.5 bar per degree of crank angle exceeding the
‘optimum rate of pressure rise, namely about 2-2. bar per degree of crank angle. To combat this
problem, the area of the passageway was increased progressively
‘With the relatively high octane petrol available today, the Compression ratio has been in-
‘reased, resulting in Lack of space to accommodate the valves in L-head or sie-valve design. I
appears tat the side-valve engine can no longer compete with Ihe overhead design. Nowadays a
=
190 Ranma of nara! Corban gt Cantin Spee gs 191
corptsin tio of 8:1 is coral anda up 105: even I: seus ve High ut y—~«Wdge-shaped combustion chamber,
‘engines and sports ca engines. It is shown in Figure 6.22(b). The combustion chamber is wedge shaped with slightly inclined
‘At compression ratios over 8, the normal turbulence created by the entry ofthe gases through valves, Tais type has also given very satisactory performance.
In il va Ira stn Asal Inc tl can slays be oi D
md a. SU ie rad on ua app veces pach tnd some fay
sponding turin einer ead
6.164 Ovorheadwalve or Ehand Type Combustion Chamber
"e ova valve combustion chamberi lso calle the head yp in whic bh be inet and un
a de D D de e El oca oe agi meets lars tn
era care hither comprosión ños Polo ar de aan O fhe oven
ee
(a) The volumen fieieny ihr because ofthe beer eating of he engine om
larger vanes ar a lian he png oss ts boone af he de De
‘ops pond Où de as exchange pres wi Is peste ops tough tale. o.
(9) The average flan nel ice redved and erre engin ls ros to © ©
D pets
(© The surfe -volum iis erase, href, he eut loses tough be our one E
son Sumber wns m Brad gue cola en ets vances fs
thermal efficiency of the engine. I also provides more complete combustion of fuel, thus produc- i Lj
Ine more over ad rain a pollen, =
(4) Hot exhaust vals laced over the head instead of in the cylinder block, tht finit wre ie
exhaust valves plc over BeBe instead of inte pd lock, ds fing
heel ares ale ir head wich ut ely te ere and opc Ti. Onde snr,
(e) The possibility of leakage of compression gases and jacket water is reduced as in this type. 7
of sangemen Be elder Beh ar nl fe 6.165 F-hoad Type Combustion Chamber
: ‘yp en saber an lil ne nes nie
(fhe FARINE ponce is cate, His ain to reduction Im cost block is known as the F-head combustion chamber. Figute 6.23 shows one of the most perfect
The wo import aragones of he ehe eambusion chamber ar era Fed Wodye ype cortas chambers wed 1) e Rover company I ha wel sped
icone ion cowa il à corespoodngly matches ping do ad eet an als vas
decimos Theta ane po dean cs alo lesa Topp
Bathtub ype of combustion chamber fesse Joie bes wate ce Te fr tee cr o ge eat
‘The bab ype of combustion chamber is th most single nd convene frm consis of init ton ecu bs Ely ote ge pr e lc aes oad
an oval-shaped combustion chamber boked over the main cylinder in such a way that some par of
the oval portion overhangs the cylinder. This part may be used for ‘squish’. Both the valves are
‘mounted venically overhead, with the spark plug at the side, as shown in Figure 6 224).
‘The main disadvantage ofthis type of combustion chamber is thatthe valves are placed in
2 single row along the cylirder block, resulting in Less space to locate valves of larger diameter
reduces the volumes efficiency. More space for valves within the bore diameter can be made
available if the stroke/bore ratio is kept unity or less,
=
The flame travel distance is short and the end-gas is reduced to.2 thin layer, so the knocking
tendency is reduced. The operation of the valves involves a complex mechanism.
6.16.6 Hemispherical Combustion Chamber
Figure 624 shows the hemispherical head with domed piston uted in Jaguar racing car engines
‘A hemispherical chamber with inclined valves isthe best design to use where the maximum
specific output is required, involving piston speeds exceeding 15 mvs, Nearly al racing cars have.
‘used the hemispherical eylinder head with domed piston
190 Ranma of nara! Corban gt Cantin Spee gs 191
corptsin tio of 8:1 is coral anda up 105: even I: seus ve High ut y—~«Wdge-shaped combustion chamber,
‘engines and sports ca engines. It is shown in Figure 6.22(b). The combustion chamber is wedge shaped with slightly inclined
‘At compression ratios over 8, the normal turbulence created by the entry ofthe gases through valves, Tais type has also given very satisactory performance.
In il va Ira stn Asal Inc tl can slays be oi D
md a. SU ie rad on ua app veces pach tnd some fay
sponding turin einer ead
6.164 Ovorheadwalve or Ehand Type Combustion Chamber
"e ova valve combustion chamberi lso calle the head yp in whic bh be inet and un
a de D D de e El oca oe agi meets lars tn
era care hither comprosión ños Polo ar de aan O fhe oven
ee
(a) The volumen fieieny ihr because ofthe beer eating of he engine om
larger vanes ar a lian he png oss ts boone af he de De
‘ops pond Où de as exchange pres wi Is peste ops tough tale. o.
(9) The average flan nel ice redved and erre engin ls ros to © ©
D pets
(© The surfe -volum iis erase, href, he eut loses tough be our one E
son Sumber wns m Brad gue cola en ets vances fs
thermal efficiency of the engine. I also provides more complete combustion of fuel, thus produc- i Lj
Ine more over ad rain a pollen, =
(4) Hot exhaust vals laced over the head instead of in the cylinder block, tht finit wre ie
exhaust valves plc over BeBe instead of inte pd lock, ds fing
heel ares ale ir head wich ut ely te ere and opc Ti. Onde snr,
(e) The possibility of leakage of compression gases and jacket water is reduced as in this type. 7
of sangemen Be elder Beh ar nl fe 6.165 F-hoad Type Combustion Chamber
: ‘yp en saber an lil ne nes nie
(fhe FARINE ponce is cate, His ain to reduction Im cost block is known as the F-head combustion chamber. Figute 6.23 shows one of the most perfect
The wo import aragones of he ehe eambusion chamber ar era Fed Wodye ype cortas chambers wed 1) e Rover company I ha wel sped
icone ion cowa il à corespoodngly matches ping do ad eet an als vas
decimos Theta ane po dean cs alo lesa Topp
Bathtub ype of combustion chamber fesse Joie bes wate ce Te fr tee cr o ge eat
‘The bab ype of combustion chamber is th most single nd convene frm consis of init ton ecu bs Ely ote ge pr e lc aes oad
an oval-shaped combustion chamber boked over the main cylinder in such a way that some par of
the oval portion overhangs the cylinder. This part may be used for ‘squish’. Both the valves are
‘mounted venically overhead, with the spark plug at the side, as shown in Figure 6 224).
‘The main disadvantage ofthis type of combustion chamber is thatthe valves are placed in
2 single row along the cylirder block, resulting in Less space to locate valves of larger diameter
reduces the volumes efficiency. More space for valves within the bore diameter can be made
available if the stroke/bore ratio is kept unity or less,
=
The flame travel distance is short and the end-gas is reduced to.2 thin layer, so the knocking
tendency is reduced. The operation of the valves involves a complex mechanism.
6.16.6 Hemispherical Combustion Chamber
Figure 624 shows the hemispherical head with domed piston uted in Jaguar racing car engines
‘A hemispherical chamber with inclined valves isthe best design to use where the maximum
specific output is required, involving piston speeds exceeding 15 mvs, Nearly al racing cars have.
‘used the hemispherical eylinder head with domed piston
192 fundamente of Inema! Comburion Engines
Comision in Spain Engines _ 193
To ermano
Ex: Externa
CE
ote
Forest Henépter pe dep one cher
Following are the advantages ofthe hemispherical head
(2) The combustion chamber is very compact
(6) The surface-10-volume ratio is small which reduces the heat loss to the cylinder wall during
combustion, thus providing a higher thermal efficiency.
(€) The luger diameter valves can be employed which may increase the volumetric efficiency.
However, the operation ofthe valves and placing of te spark plugs in a mult-eylinder engine
present dificukies unless a twin overhead camshaft mechanism i used,
6.167. Piston Cavity Combustion Chamber
“The combustion chamber comprises a bow inthe piston crown in conjunction with a fat cylinder
‘ead. The rover piston cavit type combustion chamber is shown in Figure 6.25. This resembles
Spark
Pig
Cention
chamber
Fro 8.25 Pte avy o Ravel canbe
(he combustion chamber ofthe normal direc-injecion compression ignition engine. Here an al-
most ideal chamber shape is provided with all surfaces machined o give an accurately defined
volume. Such a design was not possible in he past when Long strokes nd low compression ratios
were used, but now with the use of higher compression ratios and stroke/bore mis near one or
Jess, this configuration has become practical and likely 10 appear more inthe future,
6.16.8 Combustion Chamber with a Pre-chamber for Lean
Burn Engine
Lean combustion in an engine is one of the most promising methods or reducing the exbaust
emission and improving the fuel economy. The problems associated with lean burn are:
(@) Tis impossible o operate an engine with arbre laze than an af ato f 19 due to
deteriorated igiabiiy.
(b) The fuel consumption tends o increase because ofthe lower combustion speed andthe
deterioration ofthe lame propagation in a combustion with a ean mixture.
(6) Increased vation of combustion from cycle to cyel causes Auctions in torpe, thus
resulingín poor diva.
Toyota lean bum engine wih a prechamber bas been developed taking care ofthe above
problems. Figure 626 shows the configuration of the lean bum combustion chamber. A fresh
Intros iso the pre-chambe rough an orifice during th compresion stoke, resulting in
strong eddies of mixture within the rechamber. A spack plug located atthe wie ignites and
produces alae kernel inthe mixture flow. This ame kernel lows into the prechamber with he
‘mixture flow and causes rapid combustion in the prechamber. Asa result, an optimum jt ame
Spots ino the main combustion chamber. This je lame increases the combustion speed of the
can mixture ths improving the combustion. The pechambe s named the Turbulence Gert“
ing Pot (TOP), since its fonction iso gereraotubulenc in he main combustion chamber. In
dition othe TR, the carburetor andthe exhaust manifold ar also modified forse nthe fan
|
Comision in Spain Engines _ 193
To ermano
Ex: Externa
CE
ote
Forest Henépter pe dep one cher
Following are the advantages ofthe hemispherical head
(2) The combustion chamber is very compact
(6) The surface-10-volume ratio is small which reduces the heat loss to the cylinder wall during
combustion, thus providing a higher thermal efficiency.
(€) The luger diameter valves can be employed which may increase the volumetric efficiency.
However, the operation ofthe valves and placing of te spark plugs in a mult-eylinder engine
present dificukies unless a twin overhead camshaft mechanism i used,
6.167. Piston Cavity Combustion Chamber
“The combustion chamber comprises a bow inthe piston crown in conjunction with a fat cylinder
‘ead. The rover piston cavit type combustion chamber is shown in Figure 6.25. This resembles
Spark
Pig
Cention
chamber
Fro 8.25 Pte avy o Ravel canbe
(he combustion chamber ofthe normal direc-injecion compression ignition engine. Here an al-
most ideal chamber shape is provided with all surfaces machined o give an accurately defined
volume. Such a design was not possible in he past when Long strokes nd low compression ratios
were used, but now with the use of higher compression ratios and stroke/bore mis near one or
Jess, this configuration has become practical and likely 10 appear more inthe future,
6.16.8 Combustion Chamber with a Pre-chamber for Lean
Burn Engine
Lean combustion in an engine is one of the most promising methods or reducing the exbaust
emission and improving the fuel economy. The problems associated with lean burn are:
(@) Tis impossible o operate an engine with arbre laze than an af ato f 19 due to
deteriorated igiabiiy.
(b) The fuel consumption tends o increase because ofthe lower combustion speed andthe
deterioration ofthe lame propagation in a combustion with a ean mixture.
(6) Increased vation of combustion from cycle to cyel causes Auctions in torpe, thus
resulingín poor diva.
Toyota lean bum engine wih a prechamber bas been developed taking care ofthe above
problems. Figure 626 shows the configuration of the lean bum combustion chamber. A fresh
Intros iso the pre-chambe rough an orifice during th compresion stoke, resulting in
strong eddies of mixture within the rechamber. A spack plug located atthe wie ignites and
produces alae kernel inthe mixture flow. This ame kernel lows into the prechamber with he
‘mixture flow and causes rapid combustion in the prechamber. Asa result, an optimum jt ame
Spots ino the main combustion chamber. This je lame increases the combustion speed of the
can mixture ths improving the combustion. The pechambe s named the Turbulence Gert“
ing Pot (TOP), since its fonction iso gereraotubulenc in he main combustion chamber. In
dition othe TR, the carburetor andthe exhaust manifold ar also modified forse nthe fan
|
194 Fundarencis of Inara! Combustion Engine
Spuk plug
guess. Teydalntemerghe wit apestan
burn engine. The TGP improves the combustion ofthe lean mixture. The fuel consumption and
torque fluctuations of te lean mixture combustion are reduced. Lean misfire limit i extended
remarkably by toating the spark lug in the orifice of the TGP. Both the ignition lag and combus-
tion noise are reduced due to ths location ofthe sparkplug.
6168 Futuro Trends
The design of the future combust
increasing amounts of air pollution.
burning is important and in order to complete the burning fas, the flame travel distance should be
short. requires a smaller bore than the stoke, Le. a reversal of the modem trend and ali
‘quench area in the combustion chamber.
6.17 OCTANE REQUIREMENT
‘The compression ratio, the performance and the efficiency of an engine are limited by knock,
Knock in an engine depends onthe antiknock quality of fue called the octane number. I deter-
‘mines whether or nota fuel will knockin a given engine under the given operating conditions. A
higher octane number will have a higher resistance to knock. The octane number requirement of
is defined as the minimum fuel octane number that will resist knock throughout the
engine's speed and load range. The following factors affect the octane requirement of an engine:
(2) Composition of the fuel
(9) Combustion chamber geometry
(©) Charge motion
Combustion in Sparklgtion Enger 195
(A) Sparktiming
(e) Inlet ir, intake manifold and water jacket temperatures
© Aivfuet aio
(8) Ambient conditions pressure, temperature and relative humidity,
‘The octane number requirement tends to go down when
(2) the ignition timing is retarded,
(0) the engine is operated at higher altitudes or smaller drole openings or lower ambient
pressures.
(6) the humidity ofthe air increases.
(&) the inlet air temperature is decreased
(6) (he fuer ratio is richer or leaner than that required for producing maximum knock,
CD) {he exhaust gas recycle (EGR) system operates a part thot.
(8) the engine loa is reduced.
REVIEW QUESTIONS
What do you understand by normal combustion?
2. Explain the ters controlled uncontrolled, and abnormal combustion.
3. How do the combustion reactions proceed and how does a definite flame boundary get
‘established?
4. How does the nucleus of a flame grow and how does the combustion proceed?
5. Draw and explain theoretical p- diagram.
6. Distinguish between combustion and burning.
7. Explain the stages of combustion in he ST engine with the help of a p-8 diagram.
8. Define the terms: ignition ag and afterburning.
9. Show the flame speed pattern wih the help of a diagram, How does the lame rave) pattem
divide the combustion process into distinct phases?
10. Describe, withthe help ofa diagram, the altem of the burned mass fection in atypical ST
engine as a funcion of the erank angle.
11. Show and explain with reasons the variation of pressure and temperature in th ST engine
as a funcion ofthe crank angle
12. Show and explain the effect of spark timing on an indicator diagram. What do you under-
stand by the lerms MBT, overadvanced and retarded timing?
13, Show the effect of spark advance on brake torque.
14. Show and explain the effect of mixture strengths on p-» and p-8 diagrams
15, Discuss the effect ofthe following variables on ignition lag
(a) Nature of fuel and ai/fue ration
(0) Initial temperaure and pressure
(€) Compression ratio
(4) Spark iming
(c) Turbulence and engine speed
(D Gap between electrodes of the spark plug
Spuk plug
guess. Teydalntemerghe wit apestan
burn engine. The TGP improves the combustion ofthe lean mixture. The fuel consumption and
torque fluctuations of te lean mixture combustion are reduced. Lean misfire limit i extended
remarkably by toating the spark lug in the orifice of the TGP. Both the ignition lag and combus-
tion noise are reduced due to ths location ofthe sparkplug.
6168 Futuro Trends
The design of the future combust
increasing amounts of air pollution.
burning is important and in order to complete the burning fas, the flame travel distance should be
short. requires a smaller bore than the stoke, Le. a reversal of the modem trend and ali
‘quench area in the combustion chamber.
6.17 OCTANE REQUIREMENT
‘The compression ratio, the performance and the efficiency of an engine are limited by knock,
Knock in an engine depends onthe antiknock quality of fue called the octane number. I deter-
‘mines whether or nota fuel will knockin a given engine under the given operating conditions. A
higher octane number will have a higher resistance to knock. The octane number requirement of
is defined as the minimum fuel octane number that will resist knock throughout the
engine's speed and load range. The following factors affect the octane requirement of an engine:
(2) Composition of the fuel
(9) Combustion chamber geometry
(©) Charge motion
Combustion in Sparklgtion Enger 195
(A) Sparktiming
(e) Inlet ir, intake manifold and water jacket temperatures
© Aivfuet aio
(8) Ambient conditions pressure, temperature and relative humidity,
‘The octane number requirement tends to go down when
(2) the ignition timing is retarded,
(0) the engine is operated at higher altitudes or smaller drole openings or lower ambient
pressures.
(6) the humidity ofthe air increases.
(&) the inlet air temperature is decreased
(6) (he fuer ratio is richer or leaner than that required for producing maximum knock,
CD) {he exhaust gas recycle (EGR) system operates a part thot.
(8) the engine loa is reduced.
REVIEW QUESTIONS
What do you understand by normal combustion?
2. Explain the ters controlled uncontrolled, and abnormal combustion.
3. How do the combustion reactions proceed and how does a definite flame boundary get
‘established?
4. How does the nucleus of a flame grow and how does the combustion proceed?
5. Draw and explain theoretical p- diagram.
6. Distinguish between combustion and burning.
7. Explain the stages of combustion in he ST engine with the help of a p-8 diagram.
8. Define the terms: ignition ag and afterburning.
9. Show the flame speed pattern wih the help of a diagram, How does the lame rave) pattem
divide the combustion process into distinct phases?
10. Describe, withthe help ofa diagram, the altem of the burned mass fection in atypical ST
engine as a funcion of the erank angle.
11. Show and explain with reasons the variation of pressure and temperature in th ST engine
as a funcion ofthe crank angle
12. Show and explain the effect of spark timing on an indicator diagram. What do you under-
stand by the lerms MBT, overadvanced and retarded timing?
13, Show the effect of spark advance on brake torque.
14. Show and explain the effect of mixture strengths on p-» and p-8 diagrams
15, Discuss the effect ofthe following variables on ignition lag
(a) Nature of fuel and ai/fue ration
(0) Initial temperaure and pressure
(€) Compression ratio
(4) Spark iming
(c) Turbulence and engine speed
(D Gap between electrodes of the spark plug
196 _Fundamenais of neral Conbusson Engines
Combustion in Sparkigtion Engmes 197
16. Discuss the effect ofthe following factors on the combustion process ofthe SI engine,
(a) Composition of the mixture
(0) Load
(€) Compression ratio
(a) Speed
(€) Turbulence and shape ofthe combustion chamber
(8) Spark plug location.
17. What do you understand by cyelic variation? What are the reasons for it? How does it
depend on the mixture strength, the compression ratio and the load? How can it be re.
duced?
18. On the p-0 diagram, show the efect of rate of pressure rise during the combustion pro.
cess of an ST engine. How does the ignition timing vary with the rate of combustion? At
‘what point inthe cycle sit desirable 10 locate te peak pressure?
19, How does anormal combustion take place in the Sl engine? What do you understand by te
term ‘end-gas"? Show the p-0 diagram with normal combustion,
20. What do you understand bythe term autigniion? Define the ignition delay perio,
21. What do you understand by knock or detonation in SI engines? Explain this phenomenon,
How docs the Knock in SI engines differ from the knock in CI engines?
22. Expiain the auoigntion theory and detonation theory of knocking in SI engine,
23. What are the detrimental effects of detonation?
24. What are the major factors involved in preveating knock in SI engines?
25. Discuss the effect of the following engine variables on knock in SI engines:
(0) Compression ratio
(0) The mass ofthe inducted charge
(6) Inle temperature
(d) Temperature of the combustion chamber wall
(©) Spark timing.
(0 Coolant temperature
(2) Power ouput
0h) Exhaust back pressure
@ Cycle-1o-cyce variation
0) Carbon deposit
26. Briefly explain the time factors that affect knockin SI engines.
27. Enumerate the factors that affect the flame travel distance,
28. Briefly explain the composition factors that affect knockin SI engines.
29. Discuss the influence ofthe following design considerations on knock in SI engines:
(a) Effect of shrouded inet valve
(0) Effet of piston shape
(©) Bite of eyinder bore
30. What are the methods of detecting knock?
31. What is surface ignition? How does it occur?
ablar
EE
32. Explain the following terms coated to surface ignition;
€) Peesignition
€) Rur-on
(6) Runaway
€) Wilaping
(©) Rumble
33. What are the basic requirements of
achieved?
34. Briefly explain the design principles underying a good combustion chamber of a spark-
leniion engine.
35. Discuss the sequence of steps generally followed in the opt
chamber of SI engines?
36. Describe with the help of simple diagrams the Type, the Lype and the type of come
bustion chamber heads
31. What are the shortcomings of the T-head type of combustion chamber? What are the
advantages ofthe L-head type over the T-bead type? What ae the limitations of the Lead.
pe combustion chamber?
38, How isthe desired degree of turbulence obtained in a Ricardo turbulent combustion cham-
ber? How is the effective flame travel distance reduced in this typeof combustion cham-
ber?
39. What are the advantages of the overbead valve combustion chamber? Describe the bath-
tub type and the wedge-ype of combustion chambers withthe help of diagrams.
40. Describe the F-ype of combustion chamber withthe help of a simple diagram. How ie the
knocking tendency reduced inthis type of combustion chamber?
A1. Describe the hemispherical type combustion chamber. What ae is advantages?
42. Describe he piston cavity type combustion chamber. Whit are is advantages?
43. With the help of a simple diagram, describe the combustion chamber witha pre-chamber
used forthe Toyota Jean bum engine.
44. Define the octane number requirement. Name the Factors that affect the octane require-
‘ment ofan engine? How does the octane number requiremeat go down in SI engines?
400d combustion chamber? How can these be
zation of a combustion
Combustion in Sparkigtion Engmes 197
16. Discuss the effect ofthe following factors on the combustion process ofthe SI engine,
(a) Composition of the mixture
(0) Load
(€) Compression ratio
(a) Speed
(€) Turbulence and shape ofthe combustion chamber
(8) Spark plug location.
17. What do you understand by cyelic variation? What are the reasons for it? How does it
depend on the mixture strength, the compression ratio and the load? How can it be re.
duced?
18. On the p-0 diagram, show the efect of rate of pressure rise during the combustion pro.
cess of an ST engine. How does the ignition timing vary with the rate of combustion? At
‘what point inthe cycle sit desirable 10 locate te peak pressure?
19, How does anormal combustion take place in the Sl engine? What do you understand by te
term ‘end-gas"? Show the p-0 diagram with normal combustion,
20. What do you understand bythe term autigniion? Define the ignition delay perio,
21. What do you understand by knock or detonation in SI engines? Explain this phenomenon,
How docs the Knock in SI engines differ from the knock in CI engines?
22. Expiain the auoigntion theory and detonation theory of knocking in SI engine,
23. What are the detrimental effects of detonation?
24. What are the major factors involved in preveating knock in SI engines?
25. Discuss the effect of the following engine variables on knock in SI engines:
(0) Compression ratio
(0) The mass ofthe inducted charge
(6) Inle temperature
(d) Temperature of the combustion chamber wall
(©) Spark timing.
(0 Coolant temperature
(2) Power ouput
0h) Exhaust back pressure
@ Cycle-1o-cyce variation
0) Carbon deposit
26. Briefly explain the time factors that affect knockin SI engines.
27. Enumerate the factors that affect the flame travel distance,
28. Briefly explain the composition factors that affect knockin SI engines.
29. Discuss the influence ofthe following design considerations on knock in SI engines:
(a) Effect of shrouded inet valve
(0) Effet of piston shape
(©) Bite of eyinder bore
30. What are the methods of detecting knock?
31. What is surface ignition? How does it occur?
ablar
EE
32. Explain the following terms coated to surface ignition;
€) Peesignition
€) Rur-on
(6) Runaway
€) Wilaping
(©) Rumble
33. What are the basic requirements of
achieved?
34. Briefly explain the design principles underying a good combustion chamber of a spark-
leniion engine.
35. Discuss the sequence of steps generally followed in the opt
chamber of SI engines?
36. Describe with the help of simple diagrams the Type, the Lype and the type of come
bustion chamber heads
31. What are the shortcomings of the T-head type of combustion chamber? What are the
advantages ofthe L-head type over the T-bead type? What ae the limitations of the Lead.
pe combustion chamber?
38, How isthe desired degree of turbulence obtained in a Ricardo turbulent combustion cham-
ber? How is the effective flame travel distance reduced in this typeof combustion cham-
ber?
39. What are the advantages of the overbead valve combustion chamber? Describe the bath-
tub type and the wedge-ype of combustion chambers withthe help of diagrams.
40. Describe the F-ype of combustion chamber withthe help of a simple diagram. How ie the
knocking tendency reduced inthis type of combustion chamber?
A1. Describe the hemispherical type combustion chamber. What ae is advantages?
42. Describe he piston cavity type combustion chamber. Whit are is advantages?
43. With the help of a simple diagram, describe the combustion chamber witha pre-chamber
used forthe Toyota Jean bum engine.
44. Define the octane number requirement. Name the Factors that affect the octane require-
‘ment ofan engine? How does the octane number requiremeat go down in SI engines?
400d combustion chamber? How can these be
zation of a combustion
Combustion in Compression-
Ignition Engines
7.1 INTRODUCTION
‘The diesel engine is compression ignition (CD engine and the typical compression ratio are in
(be range of 14:1 10 22:1. In order to achieve spontaneous ignition, the compression stoke must
rise the ar to a much higher temperature than that in (he SI engine, and this requires a high
‘compression ratio, Diesel engines have considerable advantages in commercial applications, for
‘example, for continuous heavy-duty operation such as that required in locomotives, heavy road
transport and marine engines, and where robustess is at a premium as in tractors and carth-
moving vehicles, These engines are also used for stationary industrial applications, such as in
pumping ses, small and medium electric power generators, et,
The thermal efficiency ofthe CI engine is higher than that of the SI engine because of the
higher compression ratio. The Cl engine fuels (diesel or crude il) ae less expensive than the SI
‘engine fuels (peto! or gasoline). Moreover, the CI engine fuels have higher specific gravity han.
that of perol and since the fuel is sold on volume bass, more kilograms of ful per lie are
‘obtained in purchasing Cl engine fuels. Most ofthe time engines are run at part load andthe supply
of fl through the fuel injeetors can be controlled in CLengines, thus reducing the fueair ratio at
par load. In S engines, the fuir ratio prepared in the carburetor remains almost constant at al
Toads. These factors reduce the running cost of CI engines. However, de CI engines are not
favoured in passenger cas, where the use i limited, because of certain drawbacks compared 19
ST engines, such as heavier weight for the same power output. It is because of the fect that
heterogeneous mixture is used in CI engines, and the compression ratio is high as wel. It increases
the initial cos ofthe engine. The CT engines produce more nose and vibrations because of heavier
par, The exhaust emissions from CL engines with heterogeneous mixture are unburned hydro-
‘carbons, oxides of nitrogen, aldehydes, carbon monoxide, smoke particulates and the odour con
stituents. The major pollstns from SI engines are unburned hydrocarbons, oxides of nitrogen
and carbon, monoxide.
Smoke and odour re the most noticeable emissions of diesel engines. White smoke i emitted
when the engine is old and consists largely of unbumed or parially burned fuel droplets, White
smoke may be accompanied by carbonyl compounds and other partial oxidation products. Black
smoke is emitted when the engine is operating at a high load. This smoke consists of catbon-
aceous particles produced by the pyrolyic reactions that occur in th core ofthe fue spray where
large amounts of fuel are injected into the combustion chamber.
Combunien in Compresiontmiion Engnes_199
Diesel engines come in many configueations: wo stoke and four stoke engines, open and
closed (prechamber) combustion chamber types and with especially shaped pistons and inle valve
configurations to provide chamber turbulence and swt.
The combustion proces in a Cl engine is very complex and its detailed mechanisms are not
well understood. Autoignition occurs a several locations in he combustion chamber where there
is a combustible mixture, Meanwhile in some other locations the fuel may sill be inthe liquid
phase. Under most engine operating conditions, ignition stats while some portion of the fue} may
til not have been injected, The proportion of fuel present in the combustion chamber atthe start
‘of combustion to the total amount of fuel injected gready affects the combustion process. Also.
the distribution of the fuel within the combustion chamber has a great effect onthe mechanisms of
combustion and emission formation. Tis distribution depends mainly on the injection process and
the air motion,
7.2 AIR MOTION IN CI ENGINES
In open chamber CI engines the fuel is injected inthe bulk of the ir, so the turbulence of ir in the
combustion chamber atthe time of fuel injection and during the combustion process is very
important, The air velocity in the combustion chamber has two components: (a) air wir (spiral
ox) and (b) ale radial flow (sqist.
‘Air swir i eeated during the intake swoke by inducing the air into the eylinder through a.
shaped intake port which is tangential o the piston as showin in Figure 7.1. The induced swil
an be increased during compresion by transferring the acto the recess in te piston or in the
cylinder head. As the piston approaches TDC, the air flows cadially inwards, i.e. cowards
(ie combustion chamber recess. Tis shown in Figure 72, The radial streams coming from the
garza. Arata ect.
Ignition Engines
7.1 INTRODUCTION
‘The diesel engine is compression ignition (CD engine and the typical compression ratio are in
(be range of 14:1 10 22:1. In order to achieve spontaneous ignition, the compression stoke must
rise the ar to a much higher temperature than that in (he SI engine, and this requires a high
‘compression ratio, Diesel engines have considerable advantages in commercial applications, for
‘example, for continuous heavy-duty operation such as that required in locomotives, heavy road
transport and marine engines, and where robustess is at a premium as in tractors and carth-
moving vehicles, These engines are also used for stationary industrial applications, such as in
pumping ses, small and medium electric power generators, et,
The thermal efficiency ofthe CI engine is higher than that of the SI engine because of the
higher compression ratio. The Cl engine fuels (diesel or crude il) ae less expensive than the SI
‘engine fuels (peto! or gasoline). Moreover, the CI engine fuels have higher specific gravity han.
that of perol and since the fuel is sold on volume bass, more kilograms of ful per lie are
‘obtained in purchasing Cl engine fuels. Most ofthe time engines are run at part load andthe supply
of fl through the fuel injeetors can be controlled in CLengines, thus reducing the fueair ratio at
par load. In S engines, the fuir ratio prepared in the carburetor remains almost constant at al
Toads. These factors reduce the running cost of CI engines. However, de CI engines are not
favoured in passenger cas, where the use i limited, because of certain drawbacks compared 19
ST engines, such as heavier weight for the same power output. It is because of the fect that
heterogeneous mixture is used in CI engines, and the compression ratio is high as wel. It increases
the initial cos ofthe engine. The CT engines produce more nose and vibrations because of heavier
par, The exhaust emissions from CL engines with heterogeneous mixture are unburned hydro-
‘carbons, oxides of nitrogen, aldehydes, carbon monoxide, smoke particulates and the odour con
stituents. The major pollstns from SI engines are unburned hydrocarbons, oxides of nitrogen
and carbon, monoxide.
Smoke and odour re the most noticeable emissions of diesel engines. White smoke i emitted
when the engine is old and consists largely of unbumed or parially burned fuel droplets, White
smoke may be accompanied by carbonyl compounds and other partial oxidation products. Black
smoke is emitted when the engine is operating at a high load. This smoke consists of catbon-
aceous particles produced by the pyrolyic reactions that occur in th core ofthe fue spray where
large amounts of fuel are injected into the combustion chamber.
Combunien in Compresiontmiion Engnes_199
Diesel engines come in many configueations: wo stoke and four stoke engines, open and
closed (prechamber) combustion chamber types and with especially shaped pistons and inle valve
configurations to provide chamber turbulence and swt.
The combustion proces in a Cl engine is very complex and its detailed mechanisms are not
well understood. Autoignition occurs a several locations in he combustion chamber where there
is a combustible mixture, Meanwhile in some other locations the fuel may sill be inthe liquid
phase. Under most engine operating conditions, ignition stats while some portion of the fue} may
til not have been injected, The proportion of fuel present in the combustion chamber atthe start
‘of combustion to the total amount of fuel injected gready affects the combustion process. Also.
the distribution of the fuel within the combustion chamber has a great effect onthe mechanisms of
combustion and emission formation. Tis distribution depends mainly on the injection process and
the air motion,
7.2 AIR MOTION IN CI ENGINES
In open chamber CI engines the fuel is injected inthe bulk of the ir, so the turbulence of ir in the
combustion chamber atthe time of fuel injection and during the combustion process is very
important, The air velocity in the combustion chamber has two components: (a) air wir (spiral
ox) and (b) ale radial flow (sqist.
‘Air swir i eeated during the intake swoke by inducing the air into the eylinder through a.
shaped intake port which is tangential o the piston as showin in Figure 7.1. The induced swil
an be increased during compresion by transferring the acto the recess in te piston or in the
cylinder head. As the piston approaches TDC, the air flows cadially inwards, i.e. cowards
(ie combustion chamber recess. Tis shown in Figure 72, The radial streams coming from the
garza. Arata ect.
200, Fandamentl of Internal Combustion Engines
Combustion In Conpresson‘gntion Engines 201
‘opposite sides meet and get deflected upwards into the chamber. After reaching the end of
the chamber, the air lows radially outwards, Le. towards the outer walls, then downwards,
ice towards the open end. Here the aris met by air flowing radially inwards from between the
cylinder and piston, and is caried around agai, producing a toroidal movement within the
‘combustion chamber
‘The effect of the squish component on the spray formation is very small compared 10 the
effect ofthe switl component,
7.8 SPRAY STRUCTURE
A schematic of the spray pattern which results when a fuel jet is injected radially odtwards into à
swiring flow is shown in Figure 73, The structure ofthe jt is complex because there is relative
‘motion in both the radial and tangential directions between the inital jet and the ar. The small
dropiets are carried away withthe air and fore the leading edge ofthe spray. The relatively large
droplets are concentcated in the core and the trailing edge of the spray. The average distance
‘between the droplets changes withthe location in the spray, being the greatest in the leading edge
of the spray.
Neale bole
‘aii
gun? Fusspoy pool rogar
‘A plot of the local fuer ratio on a mass basis versus the angle from the centre ine of the
injector hole is also shown in Figure 73. The fuel-air distribution varies with the radial distance
from the nozzle hole. The leading edge ofthe spray always contains the smallest droplets, which
a the first to evaporate.
The smaller the doplet diameter the farther it willbe carried away from the core, by the
‘swirling ai, Thus the mixture near the leading edge ofthe spray may be assumed 19 consis of
premixed fuel-vapour and air before ignition. In. the core the big droplets are concentrated, and
they are expected tobe inthe liquid phase at he start of ignition.
‘The spray may be divided ino several regions depending upon the clair distribution end
‘mechanism of combustion in exch region. These regions ace: (2) the lean flame region, () the lean
flameou region, (©) the spray core, (d) the spray al, (e) the afer injection, and () the fuel
deposited on the walls.
Lean flame region
‘The concentration of the fuel in the sir between the core and the leading edge ofthe spray is
Heterogeneaus and de local fur ratio may vary from zero to infinity. Ignition nuclei will be
formed at several locations where the mixture is most suitable fr autoignition. Ignition starts near
the leading edge of the spray as shown in Figure 74. Once the ignition stars, small independent
nonluminous flame fronts propagate from the ignition nuclei and ignite the combustible mixture
around them. This mixture i leaner than the stoichiometric mixture and the region is called the
*lean flame region’. In ths region combustion is complete andthe nc oxide may be formed at
high local concentrations, Under very light loads, the temperature may not be high enough to
produce high rire oxide concentrations a this early stage of the combustion process.
Ales
prit
Fa T4 Mocharans clesnbusion lat ar eecedin eninge
Loan flame-autreglon
"Near the far leading edge of the spray, the mixture is oo Lean 1 gaie or support combastion. This
egioniscaled the ‘ea flame-out region. Within this region some fue decomposition and patal
‘oxidation take place. The decomposition products consist of lighter hydrocarbon molecules and
{his region is believed to be the main contributor tothe unbumed hydrocarbons in the exhaust. The
peral oxidation products may contain aldehydes and other oxygenats.
_ —
Combustion In Conpresson‘gntion Engines 201
‘opposite sides meet and get deflected upwards into the chamber. After reaching the end of
the chamber, the air lows radially outwards, Le. towards the outer walls, then downwards,
ice towards the open end. Here the aris met by air flowing radially inwards from between the
cylinder and piston, and is caried around agai, producing a toroidal movement within the
‘combustion chamber
‘The effect of the squish component on the spray formation is very small compared 10 the
effect ofthe switl component,
7.8 SPRAY STRUCTURE
A schematic of the spray pattern which results when a fuel jet is injected radially odtwards into à
swiring flow is shown in Figure 73, The structure ofthe jt is complex because there is relative
‘motion in both the radial and tangential directions between the inital jet and the ar. The small
dropiets are carried away withthe air and fore the leading edge ofthe spray. The relatively large
droplets are concentcated in the core and the trailing edge of the spray. The average distance
‘between the droplets changes withthe location in the spray, being the greatest in the leading edge
of the spray.
Neale bole
‘aii
gun? Fusspoy pool rogar
‘A plot of the local fuer ratio on a mass basis versus the angle from the centre ine of the
injector hole is also shown in Figure 73. The fuel-air distribution varies with the radial distance
from the nozzle hole. The leading edge ofthe spray always contains the smallest droplets, which
a the first to evaporate.
The smaller the doplet diameter the farther it willbe carried away from the core, by the
‘swirling ai, Thus the mixture near the leading edge ofthe spray may be assumed 19 consis of
premixed fuel-vapour and air before ignition. In. the core the big droplets are concentrated, and
they are expected tobe inthe liquid phase at he start of ignition.
‘The spray may be divided ino several regions depending upon the clair distribution end
‘mechanism of combustion in exch region. These regions ace: (2) the lean flame region, () the lean
flameou region, (©) the spray core, (d) the spray al, (e) the afer injection, and () the fuel
deposited on the walls.
Lean flame region
‘The concentration of the fuel in the sir between the core and the leading edge ofthe spray is
Heterogeneaus and de local fur ratio may vary from zero to infinity. Ignition nuclei will be
formed at several locations where the mixture is most suitable fr autoignition. Ignition starts near
the leading edge of the spray as shown in Figure 74. Once the ignition stars, small independent
nonluminous flame fronts propagate from the ignition nuclei and ignite the combustible mixture
around them. This mixture i leaner than the stoichiometric mixture and the region is called the
*lean flame region’. In ths region combustion is complete andthe nc oxide may be formed at
high local concentrations, Under very light loads, the temperature may not be high enough to
produce high rire oxide concentrations a this early stage of the combustion process.
Ales
prit
Fa T4 Mocharans clesnbusion lat ar eecedin eninge
Loan flame-autreglon
"Near the far leading edge of the spray, the mixture is oo Lean 1 gaie or support combastion. This
egioniscaled the ‘ea flame-out region. Within this region some fue decomposition and patal
‘oxidation take place. The decomposition products consist of lighter hydrocarbon molecules and
{his region is believed to be the main contributor tothe unbumed hydrocarbons in the exhaust. The
peral oxidation products may contain aldehydes and other oxygenats.
_ —
wee weve we we ee eww EEE EE CEE CEE CE
202 Fundamental of Itemal Combustion Engines
_ Combustion in Compressonignkion Engines 203
‘Spray core
Following ignition and combustion inthe lan flame region, he flame propagates towards the core
of the spray. Between these two regions he fuel droplets are larger. They give eat by radiation
from the already established fares and evaporate at a higher rate. The increase in temperaare
also increases the rate of vapour difusion. These droplets may get completely or patally evapo-
‘ated, Ifthey ae completely evaporated, the Name will burn al he mixto with the ich ignition
limit. The droplets which do not get completely evaporated will be surounded by a
diffusion typeof flame. The combustion inthe core of he jet depends mainly upon the local Fuel
air ato. Under part load operation, his region contains adequate oxygen and combustion is ex-
pected tobe complete and result in the production of high oxides of nitrogen (NO,). Near the fll
load conditions, incomplete combustion occurs in many locations inthe fuel-rich core resulting in
unburned hydrocarbons, carbon monoxide, oxygenated compounds and carbon in the exhaust
NO, are formed at low concentration under these conditions.
Spray tall
‘The las pax ofthe fuel to be injected usally forms large droplets because of the relatively less
pressure difference acting on the fuel near he end of the injection process. Tis is caused by a
decreased fue injection pressure and increased cylinder gas pressure. The penetration of this part
ofthe fuel is usually poor. This portion is known asthe spray til Under high load conditions, the
spray tal bas lite chance to get into regions with adequate oxygen concentration. However,
the temperature of the surrounding gases is high and the rate of heat transfer o these droplets is
fairly high. These droplets therefore, tend to evaporate quickly and decompose into undumed
hydrocarbons and a high percentage of carbon molecules. Partial oxidation products include
carbon monoxide and aldehydes
Atorinfection
Wen the injector valve remains open for a short time after the end of the main injection, a
‘small amount of ue is further injected, called ‘aferinjecton’, especially under medium a
High load conditions. I is injected ate in the expansion stroke with very litle atomization ard
penetration. This fuel is quickly evaporated and gets decomposed, resulting in the formation
‘of carbon monoxide, carbon particles (smoke), unbumed hydrocarbons and oxygenated
Iydrocarbons
Fuel deposited on the walls
Some fuel sprays impinge on the walls. Because of the shorter spray path and the limited number
Of sprays, this is expecially the case in small, high speed direct injected CI engines I
‘surrounding gas basa high relative velocity and contains enough oxygen, che flame will propagate
from wall 0 a small distance within the chamber, Combustion ofthe rest ofthe fuel on the walls
will depend upon the rate of evaporation and mixing of fuel and oxygen Ifthe surounding gas has
2 low oxygen concentration or the mixing is not appropriate, evaporation will occur without
complete combustion. Under this condition, the fuel vapour will decompose and form unburned
hhyerocarbons, paral oxidation products and carbon paces.
7.4 STAGES OF COMBUSTION
‘The combustion process which continually tes place in an operating diesel engine is basically
represented by the pressure vs. crank angle disgram shown in Figure 7.5
ES
Crankange, à
Fu Prasneys.caskargedagam claC org stoning Steen sage of contusion.
(Gnanac/p-€tagam aon em energie, e dry pora pour ando ar
gos aro sito dera)
At oia, jets tarso jet (int th combustion canbe. A ine time elapse,
ing process AB, before the fuel role each the grin temperature, although wen dis
‘pene mos fhe el jste dona he st stage ites spomaneusy. Cog ab
presu ss ot B and also during the proc BC (econ sao) The rest he fe injected
din ae am on act conti ham
vet cups coll y meten the mount of njeted fc resting in very ood
load efficiency, “ peca pan
The classical del compresion and combustion peste diagram shown in Figure 75 has
ten prove be a acc de and ca De au divided Io four broad sages
(3) Teton period
(0) Rapid or unconoled combesion
(©) Miigcconvoncecombwrton puse
{@) Late combustion phase or acu
‘Thotirststage—Ignition delay period (Process A to B)
During this stage no noticeable deviation ofthe pressure diagram from the pure air compression
‘curve is observed. The processes that tke place ducing he ignition delay can be divided into the
following physical and chemical processes.
202 Fundamental of Itemal Combustion Engines
_ Combustion in Compressonignkion Engines 203
‘Spray core
Following ignition and combustion inthe lan flame region, he flame propagates towards the core
of the spray. Between these two regions he fuel droplets are larger. They give eat by radiation
from the already established fares and evaporate at a higher rate. The increase in temperaare
also increases the rate of vapour difusion. These droplets may get completely or patally evapo-
‘ated, Ifthey ae completely evaporated, the Name will burn al he mixto with the ich ignition
limit. The droplets which do not get completely evaporated will be surounded by a
diffusion typeof flame. The combustion inthe core of he jet depends mainly upon the local Fuel
air ato. Under part load operation, his region contains adequate oxygen and combustion is ex-
pected tobe complete and result in the production of high oxides of nitrogen (NO,). Near the fll
load conditions, incomplete combustion occurs in many locations inthe fuel-rich core resulting in
unburned hydrocarbons, carbon monoxide, oxygenated compounds and carbon in the exhaust
NO, are formed at low concentration under these conditions.
Spray tall
‘The las pax ofthe fuel to be injected usally forms large droplets because of the relatively less
pressure difference acting on the fuel near he end of the injection process. Tis is caused by a
decreased fue injection pressure and increased cylinder gas pressure. The penetration of this part
ofthe fuel is usually poor. This portion is known asthe spray til Under high load conditions, the
spray tal bas lite chance to get into regions with adequate oxygen concentration. However,
the temperature of the surrounding gases is high and the rate of heat transfer o these droplets is
fairly high. These droplets therefore, tend to evaporate quickly and decompose into undumed
hydrocarbons and a high percentage of carbon molecules. Partial oxidation products include
carbon monoxide and aldehydes
Atorinfection
Wen the injector valve remains open for a short time after the end of the main injection, a
‘small amount of ue is further injected, called ‘aferinjecton’, especially under medium a
High load conditions. I is injected ate in the expansion stroke with very litle atomization ard
penetration. This fuel is quickly evaporated and gets decomposed, resulting in the formation
‘of carbon monoxide, carbon particles (smoke), unbumed hydrocarbons and oxygenated
Iydrocarbons
Fuel deposited on the walls
Some fuel sprays impinge on the walls. Because of the shorter spray path and the limited number
Of sprays, this is expecially the case in small, high speed direct injected CI engines I
‘surrounding gas basa high relative velocity and contains enough oxygen, che flame will propagate
from wall 0 a small distance within the chamber, Combustion ofthe rest ofthe fuel on the walls
will depend upon the rate of evaporation and mixing of fuel and oxygen Ifthe surounding gas has
2 low oxygen concentration or the mixing is not appropriate, evaporation will occur without
complete combustion. Under this condition, the fuel vapour will decompose and form unburned
hhyerocarbons, paral oxidation products and carbon paces.
7.4 STAGES OF COMBUSTION
‘The combustion process which continually tes place in an operating diesel engine is basically
represented by the pressure vs. crank angle disgram shown in Figure 7.5
ES
Crankange, à
Fu Prasneys.caskargedagam claC org stoning Steen sage of contusion.
(Gnanac/p-€tagam aon em energie, e dry pora pour ando ar
gos aro sito dera)
At oia, jets tarso jet (int th combustion canbe. A ine time elapse,
ing process AB, before the fuel role each the grin temperature, although wen dis
‘pene mos fhe el jste dona he st stage ites spomaneusy. Cog ab
presu ss ot B and also during the proc BC (econ sao) The rest he fe injected
din ae am on act conti ham
vet cups coll y meten the mount of njeted fc resting in very ood
load efficiency, “ peca pan
The classical del compresion and combustion peste diagram shown in Figure 75 has
ten prove be a acc de and ca De au divided Io four broad sages
(3) Teton period
(0) Rapid or unconoled combesion
(©) Miigcconvoncecombwrton puse
{@) Late combustion phase or acu
‘Thotirststage—Ignition delay period (Process A to B)
During this stage no noticeable deviation ofthe pressure diagram from the pure air compression
‘curve is observed. The processes that tke place ducing he ignition delay can be divided into the
following physical and chemical processes.
204 Fandamen of Ines Comborcen Engine
E]
Cembuston in Compreniondenzion Enges_205
The physical processes are
1. Spray disintegration and droplet formation
2. Heating ofthe liquid fuel and evaporation
3. Diffusion ofthe vaporized fuel into the seo form an ignitable mixture
“The chemical procestes are
1. Decomposition ofthe heavy hydrocarbons into lighter components
2. Preignition chemical reactions between the decomposed components and oxygen.
During this period, the chemical reactions proceed so slowly that no effects discernible. Lis
‘incorrect to think ofthese two delays—the physical and the chemical—as additive. They overlap,
and the rate of chemical cesetion increases as the fuel and sir become intimately mixed, Therefore,
the first par ofthe ignition delay is considered to be dominated by the physical processes which
resul inthe formation of a combustible mixture, The second par of the ignition delay is consid
cred tobe dominated by the chemical changes whic lead to autoigaition,
‘The second stage—rapld or uncontrolled combustion (Process BtoC)
In his phase, combustion ofthe fuel, which has mixed wit arto within flammability limits during
ion delay period, occurs rapidly in a few crank angle degrees. Ignition in one place is
ion elsewhere, so rapid combustion ofthe prepared fuel follows the first
‘The rate and quantity of combustion in the second phase is thus dependent onthe duration of the
delay period and the rate of preparation of ful during this period. The speed ofthis reaction deter
ines the rate of pressure rise (p40) In the cylinder. high ate of pressure rise means a sudden
cation of load tothe engine structure, which often resus in fatigue damage tothe parts. A high
rate of pressure rise also produces a violen pounding noise whichis known as "diesel knock’
‘The magnitude ofthe pressure rise during the second period may determine the value of the
peak pressure ofthe cycle. For structural reasons, to reduce mechanical stresses itis important 0
limit the peak pressure as wel a he rat of pressure cise. As the peak pressure increases, the peak
temperature also increases, which increases (a) the NO, emission, (b) the thermal loads oa the
cooling system, and (c) the temperature and thermal stressing ofthe combustion chamber walls
‘Therefore, to limit he pressure and temperature rise during the second period, iti important to
Keep the delay period as short as possible.
‘The third stage—controtled combustion phase (Process Cto D)
Once the fuel and air which premixed during the ignition delay have been consumed atthe end of
the period of rapid combustion, the temperatures within the cylindec are so high that any fuel
Injected aftr this time will burn soon as it finds oxygen, and any furher rise in pressure is
controlled by the injection rate as well as by the mixing and diffusion processes. Engines running
at low rpm should be designed 0 secure rapid mixing of fuel and air during the third stage in order
10 complete the combustion process as early as possible in the expansion stroke.
‘The fourth stage—late combustion phase or afterbumning (Process D to E)
A very low rate of combustion, sometimes refered toas the tail of combustion, occurs well down
the expansion stoke ofthe engine. There are several reasons for (his. A small faction of Fuel may
not yet have bumed. The cylinder charge is nonaniform and mixing during this period promotes
more complete combustion and less dissociated product gases. The kinetics of the final bamou.
processes become slower asthe temperature of the cylinder gases fall during expansion.
‘The late combustion phase is undesirable because i reduces the power output and produces
smoky exhaust. This canbe eliminated by supplying more excess ar and eresting more turbulence.
À flow disgram of the entice process of combustion in CI engines i shown in Figure 7.6,
Mis
wt pu pronta ms |
Le
ne
Es ‘se
nb ai
pe
RE sh
AER
PEA
I ]
sea] | Fee]
iene
Ed
À
En
| lien ve
| rye deny (ites sve Focal
Soret wie, O "sms
ei are Ft me) (mai
Fur 76 tow Gaga alta conbsionprosein len.
7.5 HEAT RELEASE RATE
Atypical heatreleas rate diagram ofa dire injection compression ignition engine, identifying the
feet diesel combustion phases is shown in Figure 77.
“The period a-b represents the ignition delay. No hea is released during this period. The period
be represents he rapid combustion phase. The high heat release rate isthe characteisti ofthis
————————
E]
Cembuston in Compreniondenzion Enges_205
The physical processes are
1. Spray disintegration and droplet formation
2. Heating ofthe liquid fuel and evaporation
3. Diffusion ofthe vaporized fuel into the seo form an ignitable mixture
“The chemical procestes are
1. Decomposition ofthe heavy hydrocarbons into lighter components
2. Preignition chemical reactions between the decomposed components and oxygen.
During this period, the chemical reactions proceed so slowly that no effects discernible. Lis
‘incorrect to think ofthese two delays—the physical and the chemical—as additive. They overlap,
and the rate of chemical cesetion increases as the fuel and sir become intimately mixed, Therefore,
the first par ofthe ignition delay is considered to be dominated by the physical processes which
resul inthe formation of a combustible mixture, The second par of the ignition delay is consid
cred tobe dominated by the chemical changes whic lead to autoigaition,
‘The second stage—rapld or uncontrolled combustion (Process BtoC)
In his phase, combustion ofthe fuel, which has mixed wit arto within flammability limits during
ion delay period, occurs rapidly in a few crank angle degrees. Ignition in one place is
ion elsewhere, so rapid combustion ofthe prepared fuel follows the first
‘The rate and quantity of combustion in the second phase is thus dependent onthe duration of the
delay period and the rate of preparation of ful during this period. The speed ofthis reaction deter
ines the rate of pressure rise (p40) In the cylinder. high ate of pressure rise means a sudden
cation of load tothe engine structure, which often resus in fatigue damage tothe parts. A high
rate of pressure rise also produces a violen pounding noise whichis known as "diesel knock’
‘The magnitude ofthe pressure rise during the second period may determine the value of the
peak pressure ofthe cycle. For structural reasons, to reduce mechanical stresses itis important 0
limit the peak pressure as wel a he rat of pressure cise. As the peak pressure increases, the peak
temperature also increases, which increases (a) the NO, emission, (b) the thermal loads oa the
cooling system, and (c) the temperature and thermal stressing ofthe combustion chamber walls
‘Therefore, to limit he pressure and temperature rise during the second period, iti important to
Keep the delay period as short as possible.
‘The third stage—controtled combustion phase (Process Cto D)
Once the fuel and air which premixed during the ignition delay have been consumed atthe end of
the period of rapid combustion, the temperatures within the cylindec are so high that any fuel
Injected aftr this time will burn soon as it finds oxygen, and any furher rise in pressure is
controlled by the injection rate as well as by the mixing and diffusion processes. Engines running
at low rpm should be designed 0 secure rapid mixing of fuel and air during the third stage in order
10 complete the combustion process as early as possible in the expansion stroke.
‘The fourth stage—late combustion phase or afterbumning (Process D to E)
A very low rate of combustion, sometimes refered toas the tail of combustion, occurs well down
the expansion stoke ofthe engine. There are several reasons for (his. A small faction of Fuel may
not yet have bumed. The cylinder charge is nonaniform and mixing during this period promotes
more complete combustion and less dissociated product gases. The kinetics of the final bamou.
processes become slower asthe temperature of the cylinder gases fall during expansion.
‘The late combustion phase is undesirable because i reduces the power output and produces
smoky exhaust. This canbe eliminated by supplying more excess ar and eresting more turbulence.
À flow disgram of the entice process of combustion in CI engines i shown in Figure 7.6,
Mis
wt pu pronta ms |
Le
ne
Es ‘se
nb ai
pe
RE sh
AER
PEA
I ]
sea] | Fee]
iene
Ed
À
En
| lien ve
| rye deny (ites sve Focal
Soret wie, O "sms
ei are Ft me) (mai
Fur 76 tow Gaga alta conbsionprosein len.
7.5 HEAT RELEASE RATE
Atypical heatreleas rate diagram ofa dire injection compression ignition engine, identifying the
feet diesel combustion phases is shown in Figure 77.
“The period a-b represents the ignition delay. No hea is released during this period. The period
be represents he rapid combustion phase. The high heat release rate isthe characteisti ofthis
————————
1206 Fundamento nera! Combustion Engines
Combuuon in Compreson-gniioo Enger 207
S01 —Sam tnt
FOI Enot mien
A
5 \:
if | m wo
soi .
CE CC o
Crank angle (es)
Fu encens ga,
phase, The period cd represents the controlled combustion phase. During this period the heat
release rate may or may not reach a second (usually lower) peak. I decreases as this phase
progresses, The period d-e represents the late combustion phase, the heat release rate decreases
further and continues at a lower rate well into the expansion stroke,
7.8 AIR/FUEL RATIO IN CI ENGINES
For a given engine speed, the supply of it in a CI engine i almost constant and doesnot depend
‘upon the engine lod. This engine may be termed a constant air supply engine. With he change in
Toad the qusntty of fus is changed, which alters the arfuel ato. As the load increases, more fuel
is used. The overall ei/fuel ratio may very from 100:1 at no-load to 20:1 at ful-toxd. Inthe SI
engine, the joel ratio remains almost tonstant rear to stoichiometric from no-lod to full-oad
conditions. The inflammability mit of hydrocarbon fuel ranges from 8:1 10 30:1. The question
arises that how does the combustion of fuel occur in Cl engines when the overall mintur is much
leaner tha this limi? From the study of spray structure i is clear that there is a heterogeneous
mixture in the combuscon chamber. The local aifuel ratio may vary from zero to infinity in
different parts. Ia the regions of very ich or very lean mixtures, o definite flame front can be
established, There would also be some regions whece te local airful ratio is within the combus-
file limits, and ignition would occur under Favourable conditions of temperature. Ignition nuclei
ate formed at severa locations, and multiple flame front travel to burn the remaining charge (tis
in contrast 1 Ihe SI engine where a definite flame front travels
“At fultlosd, the ST engines sun with a slighty rich mixture (say 13.5 to 14:1) but the CI
engines sil un witha lean mixture (say 20:1).
‘With leaner mixture the indicated thermal efficiency ofthe CI engines will be higher but the
mean effective pressure and power ouput will be decreased. Therefore, the size ofthe CI engine
compared tothe SE engine willbe larger fora given power output.
“Theoretically, the maximum mean effective pressure and power output can be obtained with
newly stoichiometric mixture but the nor-homogencous intermixing of fuel withthe ai results in
objectionable smoke under this condition. Hence, the C engines must always operte with lean
mixture
Figure 7.8 shows the effect of the irfuel aio on the power output of a Cl engine. As he ai
fuel ratio reduces because of injection of more fue, the power output inereses, but then comes a
limit of reducing the airfue ratio further, as it leads to production of an undesirable quantity of
smoke, Thus the power output of the diesel engine by increasing the quantity of fuel is limited to
the point where objectionable quantity of smoke begins to be produced. Incomplete utilization of
air in Cl engines during the combustion process increases the size ofthe engine for the same
power output compared to SI engines where almost complete utilization of air due to homoge-
neous mixing takes place.
Obetionable
mole ron
Power ut
ETE Er à
Aire! ado
guna, Et al ac por up laCiengo.
7.7 INFLUENCE OF VARIOUS FACTORS ON DELAY PERIOD
“The factors described in the following subsections affect he delay period.
Ignition quality of fuel
‘The selfiguition temperature of a fuel is a very important igaition quality. Ifthe selfignition
temperature of a fuel is low, the delay period is reduced. Cetane number is a scale used for
comparing the ignition quality of fuels By using a fuel witha higher cetare number, all other
conditions being the same, the delay period can be reduced and the engine operation made
smoother. The dependence of cetane number on fuel molecular structure is as follows: Staight-
chain paraffinic compounds (normal alkanes) have the highest ignition quality, which improves as
the chain length increases. Aromatic compounds have poor inition quality as do the alcohols.
Hence, dfficulies are associated with he use of methanol and ethanol as possible allernative Fuels
inClengines. The effec of cetane number oa the indicator diagram when the ignition timing is the
same is shown in Figure 79.
‘The ignition quality ofthe fuel may be affected by volatility, latent heat, viscosity and surface
tension. Volailiy and latent heat affect the time taken to form an envelop of the vapour, The
Viscosity and surface tension influence the Fineness of atomization of fuel
Combuuon in Compreson-gniioo Enger 207
S01 —Sam tnt
FOI Enot mien
A
5 \:
if | m wo
soi .
CE CC o
Crank angle (es)
Fu encens ga,
phase, The period cd represents the controlled combustion phase. During this period the heat
release rate may or may not reach a second (usually lower) peak. I decreases as this phase
progresses, The period d-e represents the late combustion phase, the heat release rate decreases
further and continues at a lower rate well into the expansion stroke,
7.8 AIR/FUEL RATIO IN CI ENGINES
For a given engine speed, the supply of it in a CI engine i almost constant and doesnot depend
‘upon the engine lod. This engine may be termed a constant air supply engine. With he change in
Toad the qusntty of fus is changed, which alters the arfuel ato. As the load increases, more fuel
is used. The overall ei/fuel ratio may very from 100:1 at no-load to 20:1 at ful-toxd. Inthe SI
engine, the joel ratio remains almost tonstant rear to stoichiometric from no-lod to full-oad
conditions. The inflammability mit of hydrocarbon fuel ranges from 8:1 10 30:1. The question
arises that how does the combustion of fuel occur in Cl engines when the overall mintur is much
leaner tha this limi? From the study of spray structure i is clear that there is a heterogeneous
mixture in the combuscon chamber. The local aifuel ratio may vary from zero to infinity in
different parts. Ia the regions of very ich or very lean mixtures, o definite flame front can be
established, There would also be some regions whece te local airful ratio is within the combus-
file limits, and ignition would occur under Favourable conditions of temperature. Ignition nuclei
ate formed at severa locations, and multiple flame front travel to burn the remaining charge (tis
in contrast 1 Ihe SI engine where a definite flame front travels
“At fultlosd, the ST engines sun with a slighty rich mixture (say 13.5 to 14:1) but the CI
engines sil un witha lean mixture (say 20:1).
‘With leaner mixture the indicated thermal efficiency ofthe CI engines will be higher but the
mean effective pressure and power ouput will be decreased. Therefore, the size ofthe CI engine
compared tothe SE engine willbe larger fora given power output.
“Theoretically, the maximum mean effective pressure and power output can be obtained with
newly stoichiometric mixture but the nor-homogencous intermixing of fuel withthe ai results in
objectionable smoke under this condition. Hence, the C engines must always operte with lean
mixture
Figure 7.8 shows the effect of the irfuel aio on the power output of a Cl engine. As he ai
fuel ratio reduces because of injection of more fue, the power output inereses, but then comes a
limit of reducing the airfue ratio further, as it leads to production of an undesirable quantity of
smoke, Thus the power output of the diesel engine by increasing the quantity of fuel is limited to
the point where objectionable quantity of smoke begins to be produced. Incomplete utilization of
air in Cl engines during the combustion process increases the size ofthe engine for the same
power output compared to SI engines where almost complete utilization of air due to homoge-
neous mixing takes place.
Obetionable
mole ron
Power ut
ETE Er à
Aire! ado
guna, Et al ac por up laCiengo.
7.7 INFLUENCE OF VARIOUS FACTORS ON DELAY PERIOD
“The factors described in the following subsections affect he delay period.
Ignition quality of fuel
‘The selfiguition temperature of a fuel is a very important igaition quality. Ifthe selfignition
temperature of a fuel is low, the delay period is reduced. Cetane number is a scale used for
comparing the ignition quality of fuels By using a fuel witha higher cetare number, all other
conditions being the same, the delay period can be reduced and the engine operation made
smoother. The dependence of cetane number on fuel molecular structure is as follows: Staight-
chain paraffinic compounds (normal alkanes) have the highest ignition quality, which improves as
the chain length increases. Aromatic compounds have poor inition quality as do the alcohols.
Hence, dfficulies are associated with he use of methanol and ethanol as possible allernative Fuels
inClengines. The effec of cetane number oa the indicator diagram when the ignition timing is the
same is shown in Figure 79.
‘The ignition quality ofthe fuel may be affected by volatility, latent heat, viscosity and surface
tension. Volailiy and latent heat affect the time taken to form an envelop of the vapour, The
Viscosity and surface tension influence the Fineness of atomization of fuel
208 Fundamental of internal Combustion Engines
7
Comburion in Comprerondgniion Engines 209
ou
SOI Sun ofineton
Cranage, 8
guna Electo Cmenundor (Conte p-0dayran
Infection timing |
A age injection advance increases the delay period since th presure ad temperature ofthe ir
are lower when the injection begins. he injection start later, i. closer to TDC, the temperature
and pressure are initially slightly higher but then decrease due tothe increased heat Loss as the
delay proceeds, Both advancing and retarding ofthe injection increase the delay period, The most
favourable conditions for ignition le in between these two conditions,
Figure 7.10 shows the indicator diagrams taken at various angles of injection advance at a
‘constant duration of injection, the most advantageous angle at which the injection begins is about
20° before TDC. The optimum angie of injection advance depends on various factors such a the
‘compression rato, the pressure and the temperature ofthe al at the inlet to the eyliner, the
injection characteristics, the load and the engine speed, ete
Faura Inner dran sarna, y
Compression ratio
A ig compression rato increases the temperature and pressure of the era the beginning of
injection. This reduces the delay period and the operation ofthe engine becames sruooter Oving
(6 ih higher pressures in the cylinder at high compression ratos, however the erank gear pare
have to be stronger and heavier, which leads to an increase in the mechanical losses
In practice, the higher the compression ratio, the higher will be the engine fiction, the leak-
‘age, and the torque required for starting. Thus, the diesel engine designers use the lowest come
Pression rato. also makes the cold sing ofthe engine easier. The design practico is ust he
“poste ofthat adopted in SI engine desig, where the highest possible compression ratios sed
hich is limite only by knocking.
‘The maximum pressure ofthe cycle is not much affected by varying the compression ratio,
‚because withthe increase in compression ratio the delay period is reduced and, therefore, the rate
of pressure rise decresses which controls the maximum pressure reached fa the eye,
igure 7.11 shows the typical effect of compression ratio on the p-8 diagram when the
injection timing, he speed andthe fuel quality are held consta. The delay period reduces by
increasing the compression ratio
Sa injection TIC
De
Crank angle, 0
Furet Eat pro rat on -9 gen.
‘The selFignition temperature alo reduces wilh the increase in compression ratio, This is
apparenty due to the increased density ofthe compressed air, resulting in loser contact of the
‘molecules which thereby reduces the me of reaction when the fuel is injected
Injection pressure, rate of injection and drop size.
[None ofthese factors has a significant efect on the delay period. At normal operating conditions,
increasing the injection pressure produces only a modest decrease inthe delay period. Inreasing,
the nozzle hole diameter at constant injection pressure 10 increase the rate of fel injection and
rep size have no significant effect on jhe delay period, These can be explained as follows: I
spears that in order to reduce the delay period, the fuel should be injecte in small droplets to
increase the surface arca of inflammation but the rate of combustion mainly depends upon tie
relative motion between the fuel droplets and the swing ait. The smaller droplets wi! have less
|
7
Comburion in Comprerondgniion Engines 209
ou
SOI Sun ofineton
Cranage, 8
guna Electo Cmenundor (Conte p-0dayran
Infection timing |
A age injection advance increases the delay period since th presure ad temperature ofthe ir
are lower when the injection begins. he injection start later, i. closer to TDC, the temperature
and pressure are initially slightly higher but then decrease due tothe increased heat Loss as the
delay proceeds, Both advancing and retarding ofthe injection increase the delay period, The most
favourable conditions for ignition le in between these two conditions,
Figure 7.10 shows the indicator diagrams taken at various angles of injection advance at a
‘constant duration of injection, the most advantageous angle at which the injection begins is about
20° before TDC. The optimum angie of injection advance depends on various factors such a the
‘compression rato, the pressure and the temperature ofthe al at the inlet to the eyliner, the
injection characteristics, the load and the engine speed, ete
Faura Inner dran sarna, y
Compression ratio
A ig compression rato increases the temperature and pressure of the era the beginning of
injection. This reduces the delay period and the operation ofthe engine becames sruooter Oving
(6 ih higher pressures in the cylinder at high compression ratos, however the erank gear pare
have to be stronger and heavier, which leads to an increase in the mechanical losses
In practice, the higher the compression ratio, the higher will be the engine fiction, the leak-
‘age, and the torque required for starting. Thus, the diesel engine designers use the lowest come
Pression rato. also makes the cold sing ofthe engine easier. The design practico is ust he
“poste ofthat adopted in SI engine desig, where the highest possible compression ratios sed
hich is limite only by knocking.
‘The maximum pressure ofthe cycle is not much affected by varying the compression ratio,
‚because withthe increase in compression ratio the delay period is reduced and, therefore, the rate
of pressure rise decresses which controls the maximum pressure reached fa the eye,
igure 7.11 shows the typical effect of compression ratio on the p-8 diagram when the
injection timing, he speed andthe fuel quality are held consta. The delay period reduces by
increasing the compression ratio
Sa injection TIC
De
Crank angle, 0
Furet Eat pro rat on -9 gen.
‘The selFignition temperature alo reduces wilh the increase in compression ratio, This is
apparenty due to the increased density ofthe compressed air, resulting in loser contact of the
‘molecules which thereby reduces the me of reaction when the fuel is injected
Injection pressure, rate of injection and drop size.
[None ofthese factors has a significant efect on the delay period. At normal operating conditions,
increasing the injection pressure produces only a modest decrease inthe delay period. Inreasing,
the nozzle hole diameter at constant injection pressure 10 increase the rate of fel injection and
rep size have no significant effect on jhe delay period, These can be explained as follows: I
spears that in order to reduce the delay period, the fuel should be injecte in small droplets to
increase the surface arca of inflammation but the rate of combustion mainly depends upon tie
relative motion between the fuel droplets and the swing ait. The smaller droplets wi! have less
|
210 Fundaentals of mem Combustion Engines
omen ar en ie ae voi ring al salon y o
ca o omnia, ah thus giving ce à gr Sly period As these wo reasons
roa tah er prt the con peso, the ate fection nd the io ie 69
oui aes the de pr ‘
Ino, jacket water andueltempoatres
! rennais
Any rein te lee he cong wate tempera oh eee
ao he tempora of te charge hemmen! of ection and Be aes à
ase nth ay pros,
eier emperaturbypreheaing nari udescabe as teducs the deso
air and hence reduces the volumetio efficiency and power output
Intake pressure ‘nema
oy ras nak a press or sapecharging eens he day pro The mats
dudes contusion ao decrease and gies oth perio ol te cgi Sic
Dean pucca il nee wih e peta, ds peak pressure wil bight. At
Pn mor tl be ose net mor feo ban more poner Te
gc Censo mon compared he unspechaged engine.
Engine speed e .
ihe cgi splices te [ss of het ding compression desees, eng in in
Ao eee at rs of de comp se Ths he day period in meando
Ca are vue in ges of rank are ness. The amount ffs! net during be
Ei era spn o Sacer nd nn bere ei he u pr
aon ee tine at high sends wl be fel presen the yids tak pat
congo combat, lng in higher ates of resue san ihe
the con ot TA nr a cused cls the develpent of hgh speed CI en
aa Ph seed CI engine. erre, eg a greater ange fection aban, igh
lan gai a spec den for combustion chanbe.
Aruelrato
As ie aile ratio is increased, the cylinder wall temperature and combustion temperatures are
qowered and hence the delay period is increased. There is very line reduction in the maximum rate
Of pressure se encep al the very High are ais, On te or had, the manimum pressure
fal steadily with increasing fuel ratios. A practical limit on the minimum a/fuel ratio, how
ther is setby incomplete combustion accompanied by a smoky exhaust—called the smoke limit
Load m
As ie load is increased, the residual gas temperature and the wal temperature increase. This
‘ull in a higher charge temperature at injection, thus shortening the delay period
Engine size e
ae engines ore low pm ec ones tans. Lar engines a mal
Lg rr wb onen ls Ds loss during compres, ré in Mah
Combustion In Compresion guion Engines 211
temperatures of the compressed ar. e shortens the delay period and improves the combustion
‘conditions. The design of a CI engine of larger size operating at a lower speed is therefore less
difficult
Combustion chamber wall effects
‘The impingement ofthe fuel jeton the combustion chamber wall affects the Fuel evaporation end
mixing processes. The impingement occur almost inal smaller sie and higher speed engines. 1
the pressure and temperature inside the cylinder are low, the presence of wall reduces the delay
period, but most diesel engines running under normal operating conditions have higher pressure
and temperature inside the cyliade ad the fuel jet impingement onthe wall surface hs no signifi
‘can effect on he delay period. However, the initial ate of buming increases because of increased
‘evaporation and fuel ie mixing rats.
‘Swirl rate
‘The air swir rate affects fuel evaporation, the fue-ar mixing processes andthe wall heat transfer
during compression and hence the charge temperature at injection. Under engine starting condi-
tions, the engine speed and compression temperature are low and a good ar sw would reduce
the ignition delay. At normal operating engine speeds, the air swid rte has very litle effect on
‘delay period
8 recirculation (EGR)
‘The oxygen concentration in the charge into which the fue is injected, influences the delay period,
‘The oxygen concentration is changed when the exhaust gas is recyeled to the intake for the
‘control of oxides of nitrogen emissions. As the oxygen concentration is decreased, the ignition
delay period becomes longer.
‘Type of combustion chamber
‘The pre-combustion chamber because of its compactness, produces a shorter delay period com.
pared to an open type of combustion chamber à
‘A summary of the influence of various factors on delay period is presénted in Table 7.1.
7.8 COMBUSTION KNOCK IN CI ENGINES
Combustion knock in Cl engines is associated with an extremely high rte of pressure rise during
the second phase of combustion (apid or uncontrolled combustion) and aso with heavy vibration
accompanied by a knocking sound, thus causing overheating of the piston and the cylinder head,
drop in power, damage to bearings and possible piston seizure.
‘The injection process of a fue takes place over a definite period of time in terms of degree
crank angle. AS a result, the frst few drops which are injected into the chamber passthrough the
Ignition delay while the additional droples are being injected into the chamber. Normal, he fuel
injected period is more than the delay period. Ifthe delay period of the injected fuel is shor, the
fist few droplets will commence the buming phase in a relativel shor time ate injection, and a
relatively small amount of fuel will be accumulated in the chamber when actual burning com:
omen ar en ie ae voi ring al salon y o
ca o omnia, ah thus giving ce à gr Sly period As these wo reasons
roa tah er prt the con peso, the ate fection nd the io ie 69
oui aes the de pr ‘
Ino, jacket water andueltempoatres
! rennais
Any rein te lee he cong wate tempera oh eee
ao he tempora of te charge hemmen! of ection and Be aes à
ase nth ay pros,
eier emperaturbypreheaing nari udescabe as teducs the deso
air and hence reduces the volumetio efficiency and power output
Intake pressure ‘nema
oy ras nak a press or sapecharging eens he day pro The mats
dudes contusion ao decrease and gies oth perio ol te cgi Sic
Dean pucca il nee wih e peta, ds peak pressure wil bight. At
Pn mor tl be ose net mor feo ban more poner Te
gc Censo mon compared he unspechaged engine.
Engine speed e .
ihe cgi splices te [ss of het ding compression desees, eng in in
Ao eee at rs of de comp se Ths he day period in meando
Ca are vue in ges of rank are ness. The amount ffs! net during be
Ei era spn o Sacer nd nn bere ei he u pr
aon ee tine at high sends wl be fel presen the yids tak pat
congo combat, lng in higher ates of resue san ihe
the con ot TA nr a cused cls the develpent of hgh speed CI en
aa Ph seed CI engine. erre, eg a greater ange fection aban, igh
lan gai a spec den for combustion chanbe.
Aruelrato
As ie aile ratio is increased, the cylinder wall temperature and combustion temperatures are
qowered and hence the delay period is increased. There is very line reduction in the maximum rate
Of pressure se encep al the very High are ais, On te or had, the manimum pressure
fal steadily with increasing fuel ratios. A practical limit on the minimum a/fuel ratio, how
ther is setby incomplete combustion accompanied by a smoky exhaust—called the smoke limit
Load m
As ie load is increased, the residual gas temperature and the wal temperature increase. This
‘ull in a higher charge temperature at injection, thus shortening the delay period
Engine size e
ae engines ore low pm ec ones tans. Lar engines a mal
Lg rr wb onen ls Ds loss during compres, ré in Mah
Combustion In Compresion guion Engines 211
temperatures of the compressed ar. e shortens the delay period and improves the combustion
‘conditions. The design of a CI engine of larger size operating at a lower speed is therefore less
difficult
Combustion chamber wall effects
‘The impingement ofthe fuel jeton the combustion chamber wall affects the Fuel evaporation end
mixing processes. The impingement occur almost inal smaller sie and higher speed engines. 1
the pressure and temperature inside the cylinder are low, the presence of wall reduces the delay
period, but most diesel engines running under normal operating conditions have higher pressure
and temperature inside the cyliade ad the fuel jet impingement onthe wall surface hs no signifi
‘can effect on he delay period. However, the initial ate of buming increases because of increased
‘evaporation and fuel ie mixing rats.
‘Swirl rate
‘The air swir rate affects fuel evaporation, the fue-ar mixing processes andthe wall heat transfer
during compression and hence the charge temperature at injection. Under engine starting condi-
tions, the engine speed and compression temperature are low and a good ar sw would reduce
the ignition delay. At normal operating engine speeds, the air swid rte has very litle effect on
‘delay period
8 recirculation (EGR)
‘The oxygen concentration in the charge into which the fue is injected, influences the delay period,
‘The oxygen concentration is changed when the exhaust gas is recyeled to the intake for the
‘control of oxides of nitrogen emissions. As the oxygen concentration is decreased, the ignition
delay period becomes longer.
‘Type of combustion chamber
‘The pre-combustion chamber because of its compactness, produces a shorter delay period com.
pared to an open type of combustion chamber à
‘A summary of the influence of various factors on delay period is presénted in Table 7.1.
7.8 COMBUSTION KNOCK IN CI ENGINES
Combustion knock in Cl engines is associated with an extremely high rte of pressure rise during
the second phase of combustion (apid or uncontrolled combustion) and aso with heavy vibration
accompanied by a knocking sound, thus causing overheating of the piston and the cylinder head,
drop in power, damage to bearings and possible piston seizure.
‘The injection process of a fue takes place over a definite period of time in terms of degree
crank angle. AS a result, the frst few drops which are injected into the chamber passthrough the
Ignition delay while the additional droples are being injected into the chamber. Normal, he fuel
injected period is more than the delay period. Ifthe delay period of the injected fuel is shor, the
fist few droplets will commence the buming phase in a relativel shor time ate injection, and a
relatively small amount of fuel will be accumulated in the chamber when actual burning com:
212 Fundamenats of neral Corbunion Engnes
Cotusion in Compresonigntion Engines 213
Table 71 Effect of various factors on delay period
Increase in variable Effect on delay period Reason
Tenition quality of fk
6) Seirigniion Increases Diff ignite
temperature
(i) Cetane number Decreases Reduces the selfigntion temperature,
Injetion timing:
@ advancing Increases AX injection point the pressure and
temperature of ar are lower
@ retarding Increases Increased heat los
Compression io Decreases Increases the temperature and pressure of
ie Reduces the signo temperate,
Injection pressure, rate Decreases a litle, but no Surco arc increases, this tends 10 reduce
of injection ad deop significant change delay. Momentum reduce, this tends fo
sue increase delay
‘Temperature:
© Take Decreases Increases the ae temperate
©) Jacket water Decrenses Increase the wall temperstte and hence
that of
Gi) Poet Decreases Beter vaporization, inereates rection
ake pressure Dectea Compression pressure increases
Engine speed Decreases in milliseconds Heu loss dereates during compression
Increases in “CA,
Art ri Toereases Wall and combustion temperatures a lowered
Load Decreases Residual gas and wall temperature increase
Engine ss Decreases Smaller sufae-1-volume rai, les heat
loss resulting in higher temperature of
compressed ie
Flr Jet impingement Decresss a ite, ot no Increse in ful evaporation and mixing
‘onthe wall significan effect process
Swit rate Decreases. Inereues cvapoaton and mixing reduces
heat transfer, incas the charge temperature
Exhaust Gas Recycle Increares Less concentration of oxygen.
CS
“Type of combustion
chamber
Decreases for engines
‘with pre-combustion
chamber
Compactness of the chamber causing
increased temperature and presse of
the charge.
‘mences. As a result, the rate of burn mass of fuel wil be such as to produce a rate of presse
rise that will exert smooth force onthe piston, as shown in Figure 7.12) I, on the other hand
the delay period is longer, the burning ofthe first few droples is delayed and therefore a greater
‘quantity of fuel droplets will accumulate in the chamber. When the actual burning commences, the
|
|
ya
additional fuel may cause rapid rate of pressure rice (Figure 7.1205) resulting in rough engine
‘operation. Ifthe delay period 10 long, much fuel willbe accumulated resulting in instantaneous
rise in pressure (Figure 7.12(c). Such a situation produces pressure waves striking on cylinder
walls piston crown and cylinder head, producing knock and vibrations. In fact, che combustion
mechanism of diese engin is based on the auoigniion ofthe charge and hence, mild knock may
always be present. When it exceeds a certain limi, the engine is said to be knocking,
a
se Bos
aii
shi
ii 3 3
o
\ Sarefinisien
©
Sarto sombre
S.ofcomb,
Delay prod
q ser.
o
San ofinjeion À Stat finest
Tet ofconbustioe
—À
Fqwe712_ Dira nro cto lin a rire in Clg.
‘Though the long ignition delay improves the mixing process of fuel and air and makes the
mixture more homogeneous, it helps the process of autoignition and makes the engine more prone
te knock.
Cotusion in Compresonigntion Engines 213
Table 71 Effect of various factors on delay period
Increase in variable Effect on delay period Reason
Tenition quality of fk
6) Seirigniion Increases Diff ignite
temperature
(i) Cetane number Decreases Reduces the selfigntion temperature,
Injetion timing:
@ advancing Increases AX injection point the pressure and
temperature of ar are lower
@ retarding Increases Increased heat los
Compression io Decreases Increases the temperature and pressure of
ie Reduces the signo temperate,
Injection pressure, rate Decreases a litle, but no Surco arc increases, this tends 10 reduce
of injection ad deop significant change delay. Momentum reduce, this tends fo
sue increase delay
‘Temperature:
© Take Decreases Increases the ae temperate
©) Jacket water Decrenses Increase the wall temperstte and hence
that of
Gi) Poet Decreases Beter vaporization, inereates rection
ake pressure Dectea Compression pressure increases
Engine speed Decreases in milliseconds Heu loss dereates during compression
Increases in “CA,
Art ri Toereases Wall and combustion temperatures a lowered
Load Decreases Residual gas and wall temperature increase
Engine ss Decreases Smaller sufae-1-volume rai, les heat
loss resulting in higher temperature of
compressed ie
Flr Jet impingement Decresss a ite, ot no Increse in ful evaporation and mixing
‘onthe wall significan effect process
Swit rate Decreases. Inereues cvapoaton and mixing reduces
heat transfer, incas the charge temperature
Exhaust Gas Recycle Increares Less concentration of oxygen.
CS
“Type of combustion
chamber
Decreases for engines
‘with pre-combustion
chamber
Compactness of the chamber causing
increased temperature and presse of
the charge.
‘mences. As a result, the rate of burn mass of fuel wil be such as to produce a rate of presse
rise that will exert smooth force onthe piston, as shown in Figure 7.12) I, on the other hand
the delay period is longer, the burning ofthe first few droples is delayed and therefore a greater
‘quantity of fuel droplets will accumulate in the chamber. When the actual burning commences, the
|
|
ya
additional fuel may cause rapid rate of pressure rice (Figure 7.1205) resulting in rough engine
‘operation. Ifthe delay period 10 long, much fuel willbe accumulated resulting in instantaneous
rise in pressure (Figure 7.12(c). Such a situation produces pressure waves striking on cylinder
walls piston crown and cylinder head, producing knock and vibrations. In fact, che combustion
mechanism of diese engin is based on the auoigniion ofthe charge and hence, mild knock may
always be present. When it exceeds a certain limi, the engine is said to be knocking,
a
se Bos
aii
shi
ii 3 3
o
\ Sarefinisien
©
Sarto sombre
S.ofcomb,
Delay prod
q ser.
o
San ofinjeion À Stat finest
Tet ofconbustioe
—À
Fqwe712_ Dira nro cto lin a rire in Clg.
‘Though the long ignition delay improves the mixing process of fuel and air and makes the
mixture more homogeneous, it helps the process of autoignition and makes the engine more prone
te knock.
214 Funtamens of irae! Combustion Engines
Comturion in Compressontpnidon Engines 215
7.9. COMPARISON OF KNOCK IN SI AND Cl ENGINES
IL is now possible to make an interesting comparison between knocking in SI and CI engines
‘While koocking in the SI engine and in CI engine have essentially the same basic cause, ie
autoignition followed by a rapid pressure rise iti important 1 note the following differences:
(&) In the St engine, knocking occurs due 10 autoigntion ofthe last part ofthe charge (end-
gas) Le. a the end of combustion, while in the Cl engine knocking oscurs inthe fist pan,
at the str of combustion (Figure 7.13),
a an me 6 4
Crank angl (de)
ua? Conpañsenoinakin land eng.
(6) In the ST engine, its the homogencous charge that autoigaites and causes knocking,
resulting in a very high ate of pressure rise ard high peak pressure In the CT engine the
fuel and air are not homogeneously mixed and hence the rate of pressure rise is normally
Lower than that in the knocking part of the charge in the SI engine. However, the peak
Pressure is higher due o a igh compression ratio.
(e) Inthe Cl engine only the ais compressed during the compression stroke and te inition
can take place only after the fue is injected just before TDC. Therefore, there is no ques-
tion of preignition occurring in he CI engine, whereas preignition may occur in the SI
engine due tothe presence of both fuel and ai during compression.
(@) Inthe St engine, knocking can easily be detected by human car but inthe CI engine there
isno clear distinction between knocking and normal combustion, since normal combustion
in the CI engine is itself by autoigition and a mild koock may always be present. I is
therefore a persona judgment that i involved here. When such noise becomes excessive
and these is excessive vibration inthe engine structure, in te opinion of the observer, the
engine is said tobe knocking,
“Those factors which tend to prevent knock in SI engines, the same very factors promote
‘knock in Cl engines. To prevent knock in S engines, the autoignition ofthe last pat ofthe charge
should not ike place; this requis a long delay period and a high sel-ignition temperature, To
prevent knock in Cl engines, the autoigntion ofthe First part ofthe charge should be achieved as
{nly as possible and therefore i requires a short delay period and alow sel-ioition temperature.
Te may alo be noted that a good SI engine fue is a bad CI engine fuel and vice-versa
Table 72 presents a comparative statement of the various factors o be varied in order 10
reduce knock in SI and CI engines
‘Table 7.2 Factors tending to reduce knockin SI and Cl engines
actor engines
SelFigntion temperature High
“Time lag o delay period of fet Long
Compression ratio Low
In temperature Low
Inet pressure Low
‘Combustion chamber wall temperature Low
Engine speed, rpm High
yiner size Seal
7.10 METHODS OF CONTROLLING KNOCK
IN CI ENGINES
“The methods to eliminate knockin Clengines ar those which were discussed in conjunction with
the decrease ofthe delay period. Apart from the operating variables discussed above, the knockin
Cl engines can be controlled by the following methods:
1. Certain fuel cause knocking in a given Cl engine, others do not, Thus, fuels of high cetane
number are obtained by adding chemical dopes, called ignition accelerators. The two,
common chemical dopes are ethy nitrate and amy] nitrate in concentrations of 8.8 g/l and
7. gf respectively. The chemical dopes increase the preflame reactions and reduce the
{ash point. The celane number of the diesel fuel is increased and the Fuel autoigites at
lower temperature, However, these dopes are expensive and produce more oxides of
nitogen emissions ia the exhaust as they contain nitrogen.
2. The turbulent ai-cell method of combustion generally gives knockless running of the
engine and ifthe amount of fuel injected is not excessive, a smokeless exhaust is emite.
3. Two-stage injection is used to avoid knocking in CI engines. In order to reduce diesel
banca peeps aie qero lores peleen
is delivered to the injector. I is known as pilo injection. The use of two-stage injection
gives a beter control of the rate of pressure rise ater the main delivery of fuel has taken
place and avoids a sudden pressure rie in the cylinder. Special types of fuel injection
props have been developed to give this initial delivery of a small fuel charge before the
Comturion in Compressontpnidon Engines 215
7.9. COMPARISON OF KNOCK IN SI AND Cl ENGINES
IL is now possible to make an interesting comparison between knocking in SI and CI engines
‘While koocking in the SI engine and in CI engine have essentially the same basic cause, ie
autoignition followed by a rapid pressure rise iti important 1 note the following differences:
(&) In the St engine, knocking occurs due 10 autoigntion ofthe last part ofthe charge (end-
gas) Le. a the end of combustion, while in the Cl engine knocking oscurs inthe fist pan,
at the str of combustion (Figure 7.13),
a an me 6 4
Crank angl (de)
ua? Conpañsenoinakin land eng.
(6) In the ST engine, its the homogencous charge that autoigaites and causes knocking,
resulting in a very high ate of pressure rise ard high peak pressure In the CT engine the
fuel and air are not homogeneously mixed and hence the rate of pressure rise is normally
Lower than that in the knocking part of the charge in the SI engine. However, the peak
Pressure is higher due o a igh compression ratio.
(e) Inthe Cl engine only the ais compressed during the compression stroke and te inition
can take place only after the fue is injected just before TDC. Therefore, there is no ques-
tion of preignition occurring in he CI engine, whereas preignition may occur in the SI
engine due tothe presence of both fuel and ai during compression.
(@) Inthe St engine, knocking can easily be detected by human car but inthe CI engine there
isno clear distinction between knocking and normal combustion, since normal combustion
in the CI engine is itself by autoigition and a mild koock may always be present. I is
therefore a persona judgment that i involved here. When such noise becomes excessive
and these is excessive vibration inthe engine structure, in te opinion of the observer, the
engine is said tobe knocking,
“Those factors which tend to prevent knock in SI engines, the same very factors promote
‘knock in Cl engines. To prevent knock in S engines, the autoignition ofthe last pat ofthe charge
should not ike place; this requis a long delay period and a high sel-ignition temperature, To
prevent knock in Cl engines, the autoigntion ofthe First part ofthe charge should be achieved as
{nly as possible and therefore i requires a short delay period and alow sel-ioition temperature.
Te may alo be noted that a good SI engine fue is a bad CI engine fuel and vice-versa
Table 72 presents a comparative statement of the various factors o be varied in order 10
reduce knock in SI and CI engines
‘Table 7.2 Factors tending to reduce knockin SI and Cl engines
actor engines
SelFigntion temperature High
“Time lag o delay period of fet Long
Compression ratio Low
In temperature Low
Inet pressure Low
‘Combustion chamber wall temperature Low
Engine speed, rpm High
yiner size Seal
7.10 METHODS OF CONTROLLING KNOCK
IN CI ENGINES
“The methods to eliminate knockin Clengines ar those which were discussed in conjunction with
the decrease ofthe delay period. Apart from the operating variables discussed above, the knockin
Cl engines can be controlled by the following methods:
1. Certain fuel cause knocking in a given Cl engine, others do not, Thus, fuels of high cetane
number are obtained by adding chemical dopes, called ignition accelerators. The two,
common chemical dopes are ethy nitrate and amy] nitrate in concentrations of 8.8 g/l and
7. gf respectively. The chemical dopes increase the preflame reactions and reduce the
{ash point. The celane number of the diesel fuel is increased and the Fuel autoigites at
lower temperature, However, these dopes are expensive and produce more oxides of
nitogen emissions ia the exhaust as they contain nitrogen.
2. The turbulent ai-cell method of combustion generally gives knockless running of the
engine and ifthe amount of fuel injected is not excessive, a smokeless exhaust is emite.
3. Two-stage injection is used to avoid knocking in CI engines. In order to reduce diesel
banca peeps aie qero lores peleen
is delivered to the injector. I is known as pilo injection. The use of two-stage injection
gives a beter control of the rate of pressure rise ater the main delivery of fuel has taken
place and avoids a sudden pressure rie in the cylinder. Special types of fuel injection
props have been developed to give this initial delivery of a small fuel charge before the
216_Fondimenals of Internal Combustion Enger
Combustion ln Compresion gion Engines 217
7.11. COMBUSTION CHAMBER FOR CI ENGINES
7.11.1, Combustion Chamber Characteristics
‘The proper design of a combustion chamber is very important. In a CI engine the fuel is injected
«tin period of some 20 to 35 degrees of crank angle. In this shot period of time an efficient
preparation ofthe fuelair charge is required, which means:
(2) An even disuibution of the injected fuel throughout the combustion space, for which it
requires a directed flow or swit of the ir.
(6) A thorough mixing of the fuel with the air 10 ensure complete combustion withthe
‘minimum excess ai, for which it requires an air swir or squish of high intensity.
‘An efficient smooth combustion depends upon:
(4) A sufficiently high temperature to initiate ignition,
proper compression ratio.
(6) A small delay period or ignition ag
(e) A moderate rate of pressure rise during the second stage of combustion.
(2) A controlled, even burning during the third stage: it's governed by the rate of injection.
€) À minimum ofafierdurning.
(© Minimum eat losses 1 Ihe walls, These osses ean be controlled by reducing the surface.
to-volume ratio,
“The main characteristics of an injection system that ink it with a given combustion chamber
are atomization, penetration, fuel distribution, and the shape ofthe fuel spray.
is controlled by the selection of the
7.112 Classification of CI Engine Combustion Chambers.
In order t attain the above objectives, the CLengines are divided into two basic categories accord
ing to their combustion chamber design: (a) direct injection (DI) engines, which have a single
‘open combustion chamber into which fuel is injected directly; (9) indirect injection (IDD) engines,
‘where the chamber is divided into two regions and the fuel is injected into the prechamber which
is situated above the piston crown and is connected tothe main chamber via a nozzle or one or
more orifices. The IDI engine designs are only used in the smallest engine sizes. Within each
category thee are different chamber geometries, ar flow, and fuel injection arrangements.
Figure 7.14 shows the classification of CI engine combustion chamber.
Engine Combusion Chambers
Dire Injetion (DD Tadiet nection (DI)
Open chamber Divided amber
1 |
i T 1 [ 1 1
Semiqiessen Medium Highswi Sud Preombusion Ale
a Mae or ‘ember ‘ed
tow wid cun nergy ells
canter
Fiwe7.1¢ CusalatonelClergeacarbustoncambars,
T
|
|
7.12 DIRECT INJECTION (DI) ENGINES OR OPEN
COMBUSTION CHAMBER ENGINES
An open chamber hs ie ere compresion sola in which the combustion aes place in
Chamber formed been he stn an teen en, The shape fie comicios
ray crete si or calme o ss ful a a Sl denne Flay an he a
(ie chamber nore or es abou the chamber ns, Turbulence ante ships mene an
ee,
Ins combi chamber he ming of ul and ir pends emily on he spay cae
tess an on ur motion, ait sante torso Inte
ol est, de sr) chats mt be ely range oka mpd sing Pa
ijt thigh necio pressure ard mixing is ual assed by as, da bl
the inlet tangential or bya sus whieh des main cased y sal ea ae
‘over pr ofthese, The open under design can ced u fl
(a) Semtisecen ow sn open chamber
(©) Medi sat open clambee
(©) High sit open chamber CM pe.
7121 Semigulescent or Low Suit 0)
Chamber pen
rein
men
Bene
BETT
TE
ee
een
Sen
en
ann
Se
en
Be er it
a
BE dc a se
menace ict e mn
sees eta AE
reduce heat loss to the coolant, = ES -
Figure Dion lenge aries
abe ina mar
Combustion ln Compresion gion Engines 217
7.11. COMBUSTION CHAMBER FOR CI ENGINES
7.11.1, Combustion Chamber Characteristics
‘The proper design of a combustion chamber is very important. In a CI engine the fuel is injected
«tin period of some 20 to 35 degrees of crank angle. In this shot period of time an efficient
preparation ofthe fuelair charge is required, which means:
(2) An even disuibution of the injected fuel throughout the combustion space, for which it
requires a directed flow or swit of the ir.
(6) A thorough mixing of the fuel with the air 10 ensure complete combustion withthe
‘minimum excess ai, for which it requires an air swir or squish of high intensity.
‘An efficient smooth combustion depends upon:
(4) A sufficiently high temperature to initiate ignition,
proper compression ratio.
(6) A small delay period or ignition ag
(e) A moderate rate of pressure rise during the second stage of combustion.
(2) A controlled, even burning during the third stage: it's governed by the rate of injection.
€) À minimum ofafierdurning.
(© Minimum eat losses 1 Ihe walls, These osses ean be controlled by reducing the surface.
to-volume ratio,
“The main characteristics of an injection system that ink it with a given combustion chamber
are atomization, penetration, fuel distribution, and the shape ofthe fuel spray.
is controlled by the selection of the
7.112 Classification of CI Engine Combustion Chambers.
In order t attain the above objectives, the CLengines are divided into two basic categories accord
ing to their combustion chamber design: (a) direct injection (DI) engines, which have a single
‘open combustion chamber into which fuel is injected directly; (9) indirect injection (IDD) engines,
‘where the chamber is divided into two regions and the fuel is injected into the prechamber which
is situated above the piston crown and is connected tothe main chamber via a nozzle or one or
more orifices. The IDI engine designs are only used in the smallest engine sizes. Within each
category thee are different chamber geometries, ar flow, and fuel injection arrangements.
Figure 7.14 shows the classification of CI engine combustion chamber.
Engine Combusion Chambers
Dire Injetion (DD Tadiet nection (DI)
Open chamber Divided amber
1 |
i T 1 [ 1 1
Semiqiessen Medium Highswi Sud Preombusion Ale
a Mae or ‘ember ‘ed
tow wid cun nergy ells
canter
Fiwe7.1¢ CusalatonelClergeacarbustoncambars,
T
|
|
7.12 DIRECT INJECTION (DI) ENGINES OR OPEN
COMBUSTION CHAMBER ENGINES
An open chamber hs ie ere compresion sola in which the combustion aes place in
Chamber formed been he stn an teen en, The shape fie comicios
ray crete si or calme o ss ful a a Sl denne Flay an he a
(ie chamber nore or es abou the chamber ns, Turbulence ante ships mene an
ee,
Ins combi chamber he ming of ul and ir pends emily on he spay cae
tess an on ur motion, ait sante torso Inte
ol est, de sr) chats mt be ely range oka mpd sing Pa
ijt thigh necio pressure ard mixing is ual assed by as, da bl
the inlet tangential or bya sus whieh des main cased y sal ea ae
‘over pr ofthese, The open under design can ced u fl
(a) Semtisecen ow sn open chamber
(©) Medi sat open clambee
(©) High sit open chamber CM pe.
7121 Semigulescent or Low Suit 0)
Chamber pen
rein
men
Bene
BETT
TE
ee
een
Sen
en
ann
Se
en
Be er it
a
BE dc a se
menace ict e mn
sees eta AE
reduce heat loss to the coolant, = ES -
Figure Dion lenge aries
abe ina mar
218 fundamental of Inem! Combustion Engines
Combustion in Comprenant Engines 219
“The advantages of the open chamber design with a slow speed engine ae as follows:
1. The specific fuel consumption i less, because of the following reasons:
(a) The fuel i burned close to TDC because the time in degree crank angle is long. tis an
approach towards achieving the Oto cyce efficiency
(6) The an/uel ratios igh, therefore, combustion shouldbe relatively complete with an
approach towards the air standard efficiency.
(&) Percentage het loss is reduced. It i an approach towards adiabatic combustion. Fol-
lowing are the possible reasons
(i) Either low swit or Jow turbulence
(6) Low surfaceto-volume rato of an undivided chamber
Gi) Low overall combustion temperatures.
2. Starting is relatively easier. I Is because of low beat losses
3. Less heat is rejected othe coolant and tothe exhaust gases. requires smaller radiator and
Pumps. The life ofthe exhaust valve is increased
4, The engine is quiet and provides relative freedom from combustion noise,
5. The residual fuels can be burned. It favours the operation of two-stroke engines.
7.122. Medium Swirl Open Chamber
As th engine size decreases ad the speed increases, the
‘quantity of fuel injected per cycle is reduced and the nur
Ber of holes in the nozzle is necessarily les (usually 4)
{Asa resul, the injected fuel needs help in finding sufí
«ientairina short tine, Fase fve-air mixing rates can be
achieved by increasing the amount of air swirl. Air sil
is generated by a suitable design ofthe in‘et port. The air
Swic rte can be increased as the piston approaches TDC
by forcing the air towards the cylinder axis. Figure 7.16
shows a bowl-in-piston type of medium swirl open
chamber with a centrally located multihole injector
‘orale. The amount of liquid fuel which impinges onthe
Piston cap walls is kept minimum. This type is used in
medium size (10 to 15 em bore) diesel engines.
Poets
Figueras a 1
(pson tanberwihrnaiun wlan arattle
pee
7.123. High Swirl Open Chamber (‘M type)
Spiral intake ports produce a high speed rotary air motion in the cylinder during the induction
stroke, Here, a single coarse spray i injected from a pie nozzle in the direction ofthe air sue,
and tangential to the spherical wall of the combustion chamber in the piston. The fuel stokes
‘against the wall o the sphexcal combustion chamber where it spreads to form a tin film which
will evaporate under controlled conditions, The air sw in the sphericlly shaped combustion
chamber i quite high which sweeps Over the fue film, peeling it from the wall layer by layer for
progressive and complete combustion. The flame spirals slowly inwards and around the boul.
‘with the rate of combustion conwolled by the rate of vaporization
igure 7.17 shows the “M, ‘MAN! Meurer
wall buming combustion system, optimized to give
greater swirl and mixing for complete combustion,
This combustion system was developed around
1954 by the Maschin-enfabrik Augsburg Númborg
(MAN) AG of Germany for small, high speed
‘engines. Ithassinge-hole fue injection, so oriented
hat mos ofthe felis deposited an the piston bowl
all. In practice, this engine gives good perfor.
mance even with fuels of exceedingly poor ignition
‘quality. Is fuel economy appears to be extremely.
good for an engine of small size. Because of the Flue 717 Diveiqeston bon ten arbor
vaporization and mixing processes, the "M engines WI and a sing ha nora, May.
ideally sited as à mulüfuel engine
7.13 INDIRECTINJECTION (IDI) ENGINES OR DIVIDED
COMBUSTION CHAMBER ENGINES
For small high speed diesel engines such as those used in automobile, the inlet generated air swiel
for high fue-ar mixing rate isnot sufficient. Indiret injection (IDI) or divided chamber engine
systems have been used to generate vigocous charge motion during the compression stroke. The
divided combustion chamber can be classified as;
(a) Swirl or turbulent chamber
(6) Precombustion chamber
(6) Airand energy cells.
743.1. Swirl or Turbulent Chamber
The wir chamber design is shown in Figure 7.18, The spherically shaped swirl chamber contains
about 50 percent of the clearance volume and is connected to the main chamber by «tangential
thzoat offering mild restriction. Because ofthe tangential passageway, the air flowing into the
chamber on the compression stoke sets up a high swe.
During compression the upward moving piston forces a flow of air from the main chamber
above the piston into the small antechamber, called the swirl chamber, through the nozzle or
rice. Thus, towards the end of compression, a vigorous flow inthe antechamber is set up. The
‘connecting passage and chamber are shaped so thatthe aie flow within the antechamber rotates
rapidly. Fuel is usually injected into the antechamber through a pinle nozzle as a single spray. In
some cases sufficient air may be present in the atechamber to burn completely all but the ove
load quanüties of the fue! injected. The pressure built up inthe antechamber by the expanding,
burning gases forces the burning and the unburned fuel and air mixtures back into the main
chamber, where the je issuing from the nozzle entrains and mixes with the main chamber ar,
‘imparting high turbulence and therefore further assisting combustion. The glow plug shown on
the right of the antechamber in Figur 7.18 is a colé starting ai,
Combustion in Comprenant Engines 219
“The advantages of the open chamber design with a slow speed engine ae as follows:
1. The specific fuel consumption i less, because of the following reasons:
(a) The fuel i burned close to TDC because the time in degree crank angle is long. tis an
approach towards achieving the Oto cyce efficiency
(6) The an/uel ratios igh, therefore, combustion shouldbe relatively complete with an
approach towards the air standard efficiency.
(&) Percentage het loss is reduced. It i an approach towards adiabatic combustion. Fol-
lowing are the possible reasons
(i) Either low swit or Jow turbulence
(6) Low surfaceto-volume rato of an undivided chamber
Gi) Low overall combustion temperatures.
2. Starting is relatively easier. I Is because of low beat losses
3. Less heat is rejected othe coolant and tothe exhaust gases. requires smaller radiator and
Pumps. The life ofthe exhaust valve is increased
4, The engine is quiet and provides relative freedom from combustion noise,
5. The residual fuels can be burned. It favours the operation of two-stroke engines.
7.122. Medium Swirl Open Chamber
As th engine size decreases ad the speed increases, the
‘quantity of fuel injected per cycle is reduced and the nur
Ber of holes in the nozzle is necessarily les (usually 4)
{Asa resul, the injected fuel needs help in finding sufí
«ientairina short tine, Fase fve-air mixing rates can be
achieved by increasing the amount of air swirl. Air sil
is generated by a suitable design ofthe in‘et port. The air
Swic rte can be increased as the piston approaches TDC
by forcing the air towards the cylinder axis. Figure 7.16
shows a bowl-in-piston type of medium swirl open
chamber with a centrally located multihole injector
‘orale. The amount of liquid fuel which impinges onthe
Piston cap walls is kept minimum. This type is used in
medium size (10 to 15 em bore) diesel engines.
Poets
Figueras a 1
(pson tanberwihrnaiun wlan arattle
pee
7.123. High Swirl Open Chamber (‘M type)
Spiral intake ports produce a high speed rotary air motion in the cylinder during the induction
stroke, Here, a single coarse spray i injected from a pie nozzle in the direction ofthe air sue,
and tangential to the spherical wall of the combustion chamber in the piston. The fuel stokes
‘against the wall o the sphexcal combustion chamber where it spreads to form a tin film which
will evaporate under controlled conditions, The air sw in the sphericlly shaped combustion
chamber i quite high which sweeps Over the fue film, peeling it from the wall layer by layer for
progressive and complete combustion. The flame spirals slowly inwards and around the boul.
‘with the rate of combustion conwolled by the rate of vaporization
igure 7.17 shows the “M, ‘MAN! Meurer
wall buming combustion system, optimized to give
greater swirl and mixing for complete combustion,
This combustion system was developed around
1954 by the Maschin-enfabrik Augsburg Númborg
(MAN) AG of Germany for small, high speed
‘engines. Ithassinge-hole fue injection, so oriented
hat mos ofthe felis deposited an the piston bowl
all. In practice, this engine gives good perfor.
mance even with fuels of exceedingly poor ignition
‘quality. Is fuel economy appears to be extremely.
good for an engine of small size. Because of the Flue 717 Diveiqeston bon ten arbor
vaporization and mixing processes, the "M engines WI and a sing ha nora, May.
ideally sited as à mulüfuel engine
7.13 INDIRECTINJECTION (IDI) ENGINES OR DIVIDED
COMBUSTION CHAMBER ENGINES
For small high speed diesel engines such as those used in automobile, the inlet generated air swiel
for high fue-ar mixing rate isnot sufficient. Indiret injection (IDI) or divided chamber engine
systems have been used to generate vigocous charge motion during the compression stroke. The
divided combustion chamber can be classified as;
(a) Swirl or turbulent chamber
(6) Precombustion chamber
(6) Airand energy cells.
743.1. Swirl or Turbulent Chamber
The wir chamber design is shown in Figure 7.18, The spherically shaped swirl chamber contains
about 50 percent of the clearance volume and is connected to the main chamber by «tangential
thzoat offering mild restriction. Because ofthe tangential passageway, the air flowing into the
chamber on the compression stoke sets up a high swe.
During compression the upward moving piston forces a flow of air from the main chamber
above the piston into the small antechamber, called the swirl chamber, through the nozzle or
rice. Thus, towards the end of compression, a vigorous flow inthe antechamber is set up. The
‘connecting passage and chamber are shaped so thatthe aie flow within the antechamber rotates
rapidly. Fuel is usually injected into the antechamber through a pinle nozzle as a single spray. In
some cases sufficient air may be present in the atechamber to burn completely all but the ove
load quanüties of the fue! injected. The pressure built up inthe antechamber by the expanding,
burning gases forces the burning and the unburned fuel and air mixtures back into the main
chamber, where the je issuing from the nozzle entrains and mixes with the main chamber ar,
‘imparting high turbulence and therefore further assisting combustion. The glow plug shown on
the right of the antechamber in Figur 7.18 is a colé starting ai,
220 Fundamentals of Inemal Combuiion Engines LL Combustion in Compresionigrion Engines 221
Nowe - 5. Higher secondary swirl decreases the lube-oi ie, and piston and ring life
6. Cold string is more difficult because of greater heat loss through the throst
7.132. Precombustion Chamber
Here also the chambers are divided into two parts, one between the piston and the cylinder head
(Ge. the main chamber) are the other, smaller one, in the cylinder hend (ie, precombustion cham-
ber) as shown in Figure 7.19. Comparatively small passageways, made more restricted than those
in a swirl chamber, connects the two chambers. Fue is injected into the precombustion chamber,
‘and under fl-toad conditions sufficient ar for complete combustion is ot present in tis cham
ber, The precombustion chamber is used to create a high secondary turbulence for mixing and
bbuming the major part of the fuel and air, Paral combustion of the fuel discharges the burning
mixture through te small passageways into the arin various parts ofthe main chamber where he
combustion is completed,
Since the antechamber is small, deep penetration of the spray is not required. Sines the
is high single hole nozzle is sufficient, though a well atomized fuel spray is desirable. A inte
type nozae offers ese qualities.
‘The advantages ofthe indirect injection swirl chamber over the open chamber ar as follows: Pe
1. Higher speed, bruke mean effective pressure and power with less smoke are feasible, I is ‘ore
because of
(a) Higher volumeuic efficiency—since the nozzle is at th sie, there is more room for
the larger intake and exhaust valves.
(b) Shorter delay period —since the antechamber is compact and the ai swirl in the cham
er is very high, 1 Gr”
2. Less mechanical stress and noise. I is because of the lower rate of pressure rise and the 1
lower maximum pressure in the main chamber due tothe throting effec of throat. 1
3. Less maintenance—since the pince nozzle is self cleaing and the mechanical stress is less,
4. Wider range of fuels can be used. can serve as a multi fuel engine with minimal changes.
5. Smoother and quicteridting—since matching of mal air supply with the small fuel supply
is possible
6. Cleaner exhaust resulting i les air pollution. ‘The precharmber contains 20 to 30 per cent ofthe clearance volume (versus SD percent and
was vi asc Ges WSS ce aaa ete higher in the swirl chamber), with one or more outlets leading t the main chamber. The passage-
‘The disadvantages of he IDI wi chamber over the open chamber are as follows: ways may be oriemed wo create primary tubulence inthe prechamber.Puel is injected by single
1. Higher specific fuel consumption resulting in poorer fuel economy. is because of greater
open nozzle with one lrg orifice o ain a je with a concentrated cor.
heat losses and pressure loses through he teoat which result in lower thermal ficiency This typeof combustion chamber produce a smh combustion proces but has high Mid
and higher pumping losses
fiction and heat wansfer losses. The advantages and disadvantages ofthe precombustion chamber
2. The flow of combusion gases through the thoat leads to thermal cracks in the elinder relative to open chamber type are, in general, the same as those described for the swirl chamber,
head and oretes sealing problems.
3. Cinder comio smo expe | aa 7133 Air Celle
4. More thermal energy i lost 10 the exhaust gases. may decreas the i st . o
valve which will un hotter and increase cracking and sealing problems ofthe exhaust The sr cell type of combustion chamber does not depend upon the oxganized sir-wit tke the
‘manifold precombustion chamber. The ar cel is a separate chamber used to communicate with the main
Nowe - 5. Higher secondary swirl decreases the lube-oi ie, and piston and ring life
6. Cold string is more difficult because of greater heat loss through the throst
7.132. Precombustion Chamber
Here also the chambers are divided into two parts, one between the piston and the cylinder head
(Ge. the main chamber) are the other, smaller one, in the cylinder hend (ie, precombustion cham-
ber) as shown in Figure 7.19. Comparatively small passageways, made more restricted than those
in a swirl chamber, connects the two chambers. Fue is injected into the precombustion chamber,
‘and under fl-toad conditions sufficient ar for complete combustion is ot present in tis cham
ber, The precombustion chamber is used to create a high secondary turbulence for mixing and
bbuming the major part of the fuel and air, Paral combustion of the fuel discharges the burning
mixture through te small passageways into the arin various parts ofthe main chamber where he
combustion is completed,
Since the antechamber is small, deep penetration of the spray is not required. Sines the
is high single hole nozzle is sufficient, though a well atomized fuel spray is desirable. A inte
type nozae offers ese qualities.
‘The advantages ofthe indirect injection swirl chamber over the open chamber ar as follows: Pe
1. Higher speed, bruke mean effective pressure and power with less smoke are feasible, I is ‘ore
because of
(a) Higher volumeuic efficiency—since the nozzle is at th sie, there is more room for
the larger intake and exhaust valves.
(b) Shorter delay period —since the antechamber is compact and the ai swirl in the cham
er is very high, 1 Gr”
2. Less mechanical stress and noise. I is because of the lower rate of pressure rise and the 1
lower maximum pressure in the main chamber due tothe throting effec of throat. 1
3. Less maintenance—since the pince nozzle is self cleaing and the mechanical stress is less,
4. Wider range of fuels can be used. can serve as a multi fuel engine with minimal changes.
5. Smoother and quicteridting—since matching of mal air supply with the small fuel supply
is possible
6. Cleaner exhaust resulting i les air pollution. ‘The precharmber contains 20 to 30 per cent ofthe clearance volume (versus SD percent and
was vi asc Ges WSS ce aaa ete higher in the swirl chamber), with one or more outlets leading t the main chamber. The passage-
‘The disadvantages of he IDI wi chamber over the open chamber are as follows: ways may be oriemed wo create primary tubulence inthe prechamber.Puel is injected by single
1. Higher specific fuel consumption resulting in poorer fuel economy. is because of greater
open nozzle with one lrg orifice o ain a je with a concentrated cor.
heat losses and pressure loses through he teoat which result in lower thermal ficiency This typeof combustion chamber produce a smh combustion proces but has high Mid
and higher pumping losses
fiction and heat wansfer losses. The advantages and disadvantages ofthe precombustion chamber
2. The flow of combusion gases through the thoat leads to thermal cracks in the elinder relative to open chamber type are, in general, the same as those described for the swirl chamber,
head and oretes sealing problems.
3. Cinder comio smo expe | aa 7133 Air Celle
4. More thermal energy i lost 10 the exhaust gases. may decreas the i st . o
valve which will un hotter and increase cracking and sealing problems ofthe exhaust The sr cell type of combustion chamber does not depend upon the oxganized sir-wit tke the
‘manifold precombustion chamber. The ar cel is a separate chamber used to communicate with the main
222_Fundımena of Inem Combustion Engines
Semburdon in Compresiontgntion Engines_223
chamber through a narrow restricted neck. The ir cell contain 5 to 15 per cent of tbe clearance
‘volume. Fuel is injected ito the main combustion space and ejects in a jet across this space tothe
‘open neck ofthe ar cll, as shown in Figure 7.20. Some fuel enters and ignites in the ar cel. This
rises the pressure in ch ar ell and the burning mixtur is discharged into the main chamber.
Some combustion alo takes place in the main combustion chamber. Combustion is completed on
the downstroke ofthe piston while the aris discharged from the air cell into the partly bursed
mistue, The effective expansion ralo is curtailed and both the efficiency and he power output
ar reduced, but easy starting and reasonably smooth running ue obtained with fairly low mani
um pressures, I is best stated for small engines of medium duty where a relatively high fuel
‘consumption can be tolerated. The air cell was considered unnecessary after it became possible 10
[generate swi in open chamber and therefore he air eel types of combustion chambers are now
=
=
Aires
LYN
Figon720 Arce Clenge,
7.134 Energy Cells
Inthe precombustion chamber, fuel injected into the arsccam entrin the prechamber during
¡be compression stroke. As a result, ts not possible o inject the main body ofthe fuel spray is
the most important place for buming. In the air cells, unbumed fuel in the main chamber may
ot find enough tubulence, These drawbacks can be overcome in the energy cells, eis a hybrid
(sign between the precombustion chamber and the ait cel, The energy cell contains about 10-15%
ofthe clearance volume, It has two cells, major and minor, which are separated from each other
by a restrictive orifice. The energy cells Separated from the main chamber by a narrow restricted
neck (Figure 721).
‘As the piston moves up onthe compression toke, some of th ar is forced into the major
and minor chambers ofthe energy cell. When the fuel is injected through the pil type nozzle,
pan of the fuel pastes across the main combustion chamber and enters the minor cell, where it is
mixed with te ai entering during compression from the main chamber. Combustion fist com-
‘ences inthe main chamber where the temperature is higher, but the rate of buming is slower in
this location due to insufficient mixing ofthe fuel and ai. Tue buming inthe minor cells slower
atte star, but due to better mixing, progresses at a more rapid ate. The pressures built up in
the minor cell, create added turbulence and produce beter combustion in this chamber. In the
= =
ay Main
cobain
‘chamber
Fous T21 rorya henge,
meantme, the pressure built up in the major cll prolongs the action ofthe jet stream entering the
‘main chamber, thus continuing to induce turbulence inthe main chamber
In this type of engine the fue! consumption is higher and more energy is cried away in the
‘exhaust and inthe cooling water. Thus, the life ofthe exhaust valve is reduced and this type of
engine requires a larger cadíator and fan.
7.14 COMPARISON OF CHARACTERISTICS OF COMBUSTION
CHAMBERS OF CI ENGINE
‘The characteristics of Cl engine combustion chambers including the advantages and disadvantages
of all different types of combustion chambers may be deduced from the various remarks made
above and ftom general thermodynamic and gas dynamic principles, These characteristics are
‘summarized in Table 73. The remarks made for different combustion chambers are only the
generalizations and may not all be tre for any particular engine, The tabulated dimensions and
‘operating characteristics are indicative of only the typical ranges for exch different type of CI
‘engine and its combustion system.
7.15. STARTING METHODS AND AIDS
Before the CI engine canbe stated, some extemal means must be provided to roate the erank-
shaft ofthe engine until combustion starts. The engine can be rolated by any one of the following
1. Hand starting: Single cylinder small engines can be cranked mancally by rotating the
crankshaft with the help of a handle. For easy rotation of the crank, a decompression valve
is provided. Inialy this valve is kept open, so tat asthe long as rotating air isnot com-
Semburdon in Compresiontgntion Engines_223
chamber through a narrow restricted neck. The ir cell contain 5 to 15 per cent of tbe clearance
‘volume. Fuel is injected ito the main combustion space and ejects in a jet across this space tothe
‘open neck ofthe ar cll, as shown in Figure 7.20. Some fuel enters and ignites in the ar cel. This
rises the pressure in ch ar ell and the burning mixtur is discharged into the main chamber.
Some combustion alo takes place in the main combustion chamber. Combustion is completed on
the downstroke ofthe piston while the aris discharged from the air cell into the partly bursed
mistue, The effective expansion ralo is curtailed and both the efficiency and he power output
ar reduced, but easy starting and reasonably smooth running ue obtained with fairly low mani
um pressures, I is best stated for small engines of medium duty where a relatively high fuel
‘consumption can be tolerated. The air cell was considered unnecessary after it became possible 10
[generate swi in open chamber and therefore he air eel types of combustion chambers are now
=
=
Aires
LYN
Figon720 Arce Clenge,
7.134 Energy Cells
Inthe precombustion chamber, fuel injected into the arsccam entrin the prechamber during
¡be compression stroke. As a result, ts not possible o inject the main body ofthe fuel spray is
the most important place for buming. In the air cells, unbumed fuel in the main chamber may
ot find enough tubulence, These drawbacks can be overcome in the energy cells, eis a hybrid
(sign between the precombustion chamber and the ait cel, The energy cell contains about 10-15%
ofthe clearance volume, It has two cells, major and minor, which are separated from each other
by a restrictive orifice. The energy cells Separated from the main chamber by a narrow restricted
neck (Figure 721).
‘As the piston moves up onthe compression toke, some of th ar is forced into the major
and minor chambers ofthe energy cell. When the fuel is injected through the pil type nozzle,
pan of the fuel pastes across the main combustion chamber and enters the minor cell, where it is
mixed with te ai entering during compression from the main chamber. Combustion fist com-
‘ences inthe main chamber where the temperature is higher, but the rate of buming is slower in
this location due to insufficient mixing ofthe fuel and ai. Tue buming inthe minor cells slower
atte star, but due to better mixing, progresses at a more rapid ate. The pressures built up in
the minor cell, create added turbulence and produce beter combustion in this chamber. In the
= =
ay Main
cobain
‘chamber
Fous T21 rorya henge,
meantme, the pressure built up in the major cll prolongs the action ofthe jet stream entering the
‘main chamber, thus continuing to induce turbulence inthe main chamber
In this type of engine the fue! consumption is higher and more energy is cried away in the
‘exhaust and inthe cooling water. Thus, the life ofthe exhaust valve is reduced and this type of
engine requires a larger cadíator and fan.
7.14 COMPARISON OF CHARACTERISTICS OF COMBUSTION
CHAMBERS OF CI ENGINE
‘The characteristics of Cl engine combustion chambers including the advantages and disadvantages
of all different types of combustion chambers may be deduced from the various remarks made
above and ftom general thermodynamic and gas dynamic principles, These characteristics are
‘summarized in Table 73. The remarks made for different combustion chambers are only the
generalizations and may not all be tre for any particular engine, The tabulated dimensions and
‘operating characteristics are indicative of only the typical ranges for exch different type of CI
‘engine and its combustion system.
7.15. STARTING METHODS AND AIDS
Before the CI engine canbe stated, some extemal means must be provided to roate the erank-
shaft ofthe engine until combustion starts. The engine can be rolated by any one of the following
1. Hand starting: Single cylinder small engines can be cranked mancally by rotating the
crankshaft with the help of a handle. For easy rotation of the crank, a decompression valve
is provided. Inialy this valve is kept open, so tat asthe long as rotating air isnot com-
224 Fundamentals of vera! Combstvon Engines
Combision in Compresiontgition Engines 225
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pressed, the free rotation is possible. When the engine gets momentum, is valve closed
and the airs compressed 1 ignite the fuel by compression,
2. Electrie motor: It is used for eranking small engioes. It needs a 12 vot battery.
3. An auxiliary SI engine: It can be cranked by hand or ese by an electro motor,
4. Airpressure: Large Cl engines are normally started by ale pressure I require a storage
tank for the compressed air and a compresor. On the expansion sroke of the engine,
‘compressed air enters the cylinder through the air valve and cranks the engine.
Cold staring of a CI engine in some caes is avery serious problem, The problem is aggra-
vated furtber ifthe weather is extremely cold, he cylinder line is worn or the valves ae leaky. In
order to start ignition, the temperature must sufficiently exceed the sefgniion temperature ofthe
fuel. The pressure must also be high enough to ensure good contact and hence rapid het transfer
from hot airto the surface ofthe fiquid fuel
‘At very low speed during compression the het loss tothe walls will be more. The tempera:
ture and pressure ofthe air may not be enough to ignite the Fuel. At very high speed allbough the
‘emperanire and pressure will be high enough but the time for vaporization and mixing will ot be
enough to ignite the fuel. Therefore, for a CI engine there will be an optimum stating speed in
between these two limits. The optimum speed will depend upon:
1. Surface-to-volume ratio: The larger the size ofthe cylinder, the less wil be the surface-
to-volume rato and hence less will be the rate of loss of heat during compression.
2. The intensity of airswirl: Xt determines the rate of loss of heat by convection during
‘compression.
3. The physical conditions: Such as weather, leakage ete,
Its evident thatthe open-chamber directnjection engine will give the easiest cold starting,
since it will have both the smallest surface-to-volume ratio and the lowest intensity of ar wil
However, sometime physical conditions may not be favourable and cold staring may not be
possible without the vse of some aid o ignition.
“The majority of high speed engines require some starting aids, A few of them are mentioned
below:
1. Electric glow plugs in the combustion chamber: A glow plug can get damaged by
combustion over a period of time.
2, Pintaux mozzle: It is a combination of pin with the auxiliary spray. AC lower rpm, the
‘cede valve lifts small and hence less fuels supplied. To increase the supply of uel, the
auxiliay orifice delivers more fuel which helps in cold starting. As the speed picks up the
increased lit of the needle valve supplies more fuel through the main jet. The aurliay
orifice then delivers Less fuel.
3. Intake manifold heater: I ignites a small fed of fuel.
4. Injection of diethyl ether into the intake in a controlled amount: Esher has a very low
selFigniion temperature.
Combision in Compresiontgition Engines 225
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epitelio PRÉ a
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Sl din dissii iles 35
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¡INE = 33
si oi ida. 8 3 3
ali aa Tigh 23223 153
E
i
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pressed, the free rotation is possible. When the engine gets momentum, is valve closed
and the airs compressed 1 ignite the fuel by compression,
2. Electrie motor: It is used for eranking small engioes. It needs a 12 vot battery.
3. An auxiliary SI engine: It can be cranked by hand or ese by an electro motor,
4. Airpressure: Large Cl engines are normally started by ale pressure I require a storage
tank for the compressed air and a compresor. On the expansion sroke of the engine,
‘compressed air enters the cylinder through the air valve and cranks the engine.
Cold staring of a CI engine in some caes is avery serious problem, The problem is aggra-
vated furtber ifthe weather is extremely cold, he cylinder line is worn or the valves ae leaky. In
order to start ignition, the temperature must sufficiently exceed the sefgniion temperature ofthe
fuel. The pressure must also be high enough to ensure good contact and hence rapid het transfer
from hot airto the surface ofthe fiquid fuel
‘At very low speed during compression the het loss tothe walls will be more. The tempera:
ture and pressure ofthe air may not be enough to ignite the Fuel. At very high speed allbough the
‘emperanire and pressure will be high enough but the time for vaporization and mixing will ot be
enough to ignite the fuel. Therefore, for a CI engine there will be an optimum stating speed in
between these two limits. The optimum speed will depend upon:
1. Surface-to-volume ratio: The larger the size ofthe cylinder, the less wil be the surface-
to-volume rato and hence less will be the rate of loss of heat during compression.
2. The intensity of airswirl: Xt determines the rate of loss of heat by convection during
‘compression.
3. The physical conditions: Such as weather, leakage ete,
Its evident thatthe open-chamber directnjection engine will give the easiest cold starting,
since it will have both the smallest surface-to-volume ratio and the lowest intensity of ar wil
However, sometime physical conditions may not be favourable and cold staring may not be
possible without the vse of some aid o ignition.
“The majority of high speed engines require some starting aids, A few of them are mentioned
below:
1. Electric glow plugs in the combustion chamber: A glow plug can get damaged by
combustion over a period of time.
2, Pintaux mozzle: It is a combination of pin with the auxiliary spray. AC lower rpm, the
‘cede valve lifts small and hence less fuels supplied. To increase the supply of uel, the
auxiliay orifice delivers more fuel which helps in cold starting. As the speed picks up the
increased lit of the needle valve supplies more fuel through the main jet. The aurliay
orifice then delivers Less fuel.
3. Intake manifold heater: I ignites a small fed of fuel.
4. Injection of diethyl ether into the intake in a controlled amount: Esher has a very low
selFigniion temperature.
Wee ee wee ee IIA
226 Fundunenu of Intel Combustion Engines
Combutton In Compessionignion Engneı 227
5. Injection of a small amount of lubricating oll or fuel o
‘compression ratio and seals both he piston sings and valves.
la raises temporarily the
REVIEW QUESTIONS
Whats the typical range ofthe compresion rato in CI engines?
What ae the advantages and disadvantages of the CI engine over the SI engine? Where
does the Cl engine find its application?
Describe with the help of diagrams the
chamber.
4. Draw and describe the spray pattem when ful is injected into swirling al. Show a plot of
‘equivalence ratio on the spray pattem.
. Describe the mechanisms of combustion of fuel spray injected in swirling ai.
Describe the different stages of combustion ina Cl engine.
‘What is meant by a delay period? Describe it, indicating its importance.
Deseribe the heat release rate patter of a CI engine during the different stages of
combustion
9. What isthe inflamreabilty mit ofa diesel fuel? How does the combustion ofa fuel occur
ina Cl engine, when the overall mixture is much leaner than this limit? How does the act
fuel aio in a Cl engine change withthe change in load?
10, Show the effect ofthe au ro on power output from a CL engine. What isthe limit of
using rich fuel?
A1. Describe the influence ofthe Following factors on delay period:
(a) Ignition quality of fuel and cane number: show the effect of cetane number onthe
-O diagram.
(6) Injection timing: show the effet of injection timing on the p-@ diagram.
(€) Compression ratio: show the effect of compresion ratio on the p-@ diagram,
(8) Injection pressure, rate of injection and drop size
(&) Intake, jacke water and fuel temperatures
(0) Intake pressure
(4) Engine speed
(5) Aleve ratio
6) Load
© Enginesize
(6) Combustion chamber wal effect
(Swirl eate
GES
(a) Type of combustion chamber.
12. Summarize in a tabular form the effect of various factors on the Cl engine delay period
13. Describe the phenomenon of knock in CI engines,
14, Hlustrte and describe the effect o ignition delay onthe rate of pressure rise in a CI engine.
15. Compare the knocking phenomena in SI and Cl engines. Explain clearly that the factors
hich tend to prevent knock in SI engines in fet promote knock in CI engines.
it swirl and squish inthe Cl engine combustion
16. Give a comparative statement of the various factors Lo be increased or decreased, which
tend to reduce knock in SI and Cl engines
17. Briefly describe the different methods used to contro knockin CI engines.
18, What are che requirements of good combustion chamber of a Ch engine?
19. Give the classifications of different types of combustion chambers of a CI engine.
20. What is directinjecion (DI) type combustion chamber for a CL engine? What are the
different types ofthis combustion chamber?
21. Briefy describe with the help of simple diagrams the following types of directinjection
combustion chambers for CT engines
(a) Semiquiescent (6) Medium Swirl () M° type.
22. What ae the advantages of the open chamber design of combustion chamber for a CI
engine?
23. What i indirect-injection (IDD type combustion chamber for a CI engine? What are the
Afferent types ofthis combustion chamber?
24, Describe with the help of a diagram the sie! chamber IDI type combustion chamber fora
Clengine.
25. What are the advantages and disadvantages of the IDI swirl chamber over the open
chamber?
126. Deserbe withthe help ofa diagram the IDI presombusion chamber fora engine. What
are the advantages and disadvantages ofthis type of combustion chamber compared 10 the
‘open chamber type.
27. Describe the ar cel type of combustion chamber with the help of a diagram.
28. Describe the energy cell ype of combustion chamber with the help of a diagram, What are
its advantages over the air cell type?
29. Briefly compare the characteristics of different types of combustion chambers in a tabular
form.
30. What are the diferen methods of stating a diesel engine?
31: Why is it not possible to sarı an engine at a very low or ata very high speed? On what
factors does the optimum starting speed depend?
32. Why are the open chamber direct injection engines easy to cold sar?
33. What ae cold starting aids? Deserbe them brit
226 Fundunenu of Intel Combustion Engines
Combutton In Compessionignion Engneı 227
5. Injection of a small amount of lubricating oll or fuel o
‘compression ratio and seals both he piston sings and valves.
la raises temporarily the
REVIEW QUESTIONS
Whats the typical range ofthe compresion rato in CI engines?
What ae the advantages and disadvantages of the CI engine over the SI engine? Where
does the Cl engine find its application?
Describe with the help of diagrams the
chamber.
4. Draw and describe the spray pattem when ful is injected into swirling al. Show a plot of
‘equivalence ratio on the spray pattem.
. Describe the mechanisms of combustion of fuel spray injected in swirling ai.
Describe the different stages of combustion ina Cl engine.
‘What is meant by a delay period? Describe it, indicating its importance.
Deseribe the heat release rate patter of a CI engine during the different stages of
combustion
9. What isthe inflamreabilty mit ofa diesel fuel? How does the combustion ofa fuel occur
ina Cl engine, when the overall mixture is much leaner than this limit? How does the act
fuel aio in a Cl engine change withthe change in load?
10, Show the effect ofthe au ro on power output from a CL engine. What isthe limit of
using rich fuel?
A1. Describe the influence ofthe Following factors on delay period:
(a) Ignition quality of fuel and cane number: show the effect of cetane number onthe
-O diagram.
(6) Injection timing: show the effet of injection timing on the p-@ diagram.
(€) Compression ratio: show the effect of compresion ratio on the p-@ diagram,
(8) Injection pressure, rate of injection and drop size
(&) Intake, jacke water and fuel temperatures
(0) Intake pressure
(4) Engine speed
(5) Aleve ratio
6) Load
© Enginesize
(6) Combustion chamber wal effect
(Swirl eate
GES
(a) Type of combustion chamber.
12. Summarize in a tabular form the effect of various factors on the Cl engine delay period
13. Describe the phenomenon of knock in CI engines,
14, Hlustrte and describe the effect o ignition delay onthe rate of pressure rise in a CI engine.
15. Compare the knocking phenomena in SI and Cl engines. Explain clearly that the factors
hich tend to prevent knock in SI engines in fet promote knock in CI engines.
it swirl and squish inthe Cl engine combustion
16. Give a comparative statement of the various factors Lo be increased or decreased, which
tend to reduce knock in SI and Cl engines
17. Briefly describe the different methods used to contro knockin CI engines.
18, What are che requirements of good combustion chamber of a Ch engine?
19. Give the classifications of different types of combustion chambers of a CI engine.
20. What is directinjecion (DI) type combustion chamber for a CL engine? What are the
different types ofthis combustion chamber?
21. Briefy describe with the help of simple diagrams the following types of directinjection
combustion chambers for CT engines
(a) Semiquiescent (6) Medium Swirl () M° type.
22. What ae the advantages of the open chamber design of combustion chamber for a CI
engine?
23. What i indirect-injection (IDD type combustion chamber for a CI engine? What are the
Afferent types ofthis combustion chamber?
24, Describe with the help of a diagram the sie! chamber IDI type combustion chamber fora
Clengine.
25. What are the advantages and disadvantages of the IDI swirl chamber over the open
chamber?
126. Deserbe withthe help ofa diagram the IDI presombusion chamber fora engine. What
are the advantages and disadvantages ofthis type of combustion chamber compared 10 the
‘open chamber type.
27. Describe the ar cel type of combustion chamber with the help of a diagram.
28. Describe the energy cell ype of combustion chamber with the help of a diagram, What are
its advantages over the air cell type?
29. Briefly compare the characteristics of different types of combustion chambers in a tabular
form.
30. What are the diferen methods of stating a diesel engine?
31: Why is it not possible to sarı an engine at a very low or ata very high speed? On what
factors does the optimum starting speed depend?
32. Why are the open chamber direct injection engines easy to cold sar?
33. What ae cold starting aids? Deserbe them brit
Fuels for Internal
Combustion Engines
8.1 INTRODUCTION
Fuelis a substance which participates easily with oxygen ina self-sustaining exothermic reaction
‘The subject of fuels for IC engines has been studied ever since the engines have been in existence.
Engine performance depends upon the fuel characteristics. I is therefore essential to study the
‘characteristics of different types of fuels to understand the combustion phenomenon. The charac-
ter ofthe fuel used may have considerable fluence on the design, the output, the efficiency, the
fuel consumption, the air pollution and in many cases on the reliability and dozabiliy ofthe engine.
‘The characteristics of the IC engine fuel: must be such thatthe following requirements a
‘The fuel should get effectively atomized, vaporized and well mixed withthe ar.
‘The combustion process must be fas
Starting ofthe engine shouldbe quick and reliable at any ambient condition.
‘The surface of the combustion chamber should remain free from carbon and other
deposits.
The cylinder face, the piston and the piston rings should not get subjected to excessive
wear and corrosion.
6. The basic elements of the engine should remain free from thermal stresses due to
temperature gradient developed during combustion.
7. Combustion shouldbe complete without the evolution of harmful exhaust gases.
The IC engines can be operated on many different kinds of fuels, including liquid, gaseous,
and even solid. The selection of a fuel fora particular use in engines is mainly govemed by (a) the
‘ype ofthe equipment required to store, supply and bum the fuel in the engine, (b) the heating valve
Per unit volume of he fel, and () he availability and cos ofthe fuel at the site of he engine.
8.2 CLASSIFICATION OF FUELS
‘The principal constituents of any fuel are carbon and hydrogen. Fuels may be classified as
Primary or secondary according to whether they occur in nature or are prepared, Fuels can
be in soli, liquid or gaseous state. The classification of important fuels can be summarized a
follows
Fes for Internal Conbunion Engines 229
1. Solid fuels
‘Natural (Primary): Wood; Pet, Col, he major ranks of cal from the lowest 0 the highest
ar: ()Lignite (i) Subbituminoss, (i) Bituminous, (iv) Semianthacite, and (4) Antracte
Prepared Secondary): Charcoal; Coke; Briquetted cou; Pulverized col,
2. Liquid fuels
Natural: Petroleum
Prepared: (i) Petroleum based: gaslin, kerosene, diese il, fu oil, bricating il
Gi) Nor-petroleum based: benzo, alcohol
3. Gaseous fuels
Naturals” Natural gas
Prepared: Liqufied petroleum gas (LPG), producer gas, coal gas, hydrogen,
83 SOLID FUELS
8.3.1 Brief Description of Solid Fuels
Wood: Iris anaturally available solid fue. is not generally uted asa commercial fuel exceptin
industries where a large amount of waste wood is available
Peat: Iris a mixture of decayed vegetable matter with water. It is dried with air. I contains a
high percentage of moisture. is used asa feel in gas producer plant.
Coal: This includes al rypes of natural sold fuels from lignite to anthracite. Pat no col but
represents the first stage in he formation of coal I the early stages of transformation, varying
amounts of wate, methane and carbon dioxide got gradually eliminated by increased pressure and
temperature. Peat was changed to lignite and then o bimminous coal. The volale matter of the
fuel was reduced further o form the anthracite coals. Lignites have a wood or clay like appear
ance associated witha high amount of moisture and it has low heat content. Lignies are usualy
amorphous in character and pose transportation dificulis as they break easily. Anthracite is very
hard and has shining black lustre. The moisture contents very low. The heating value of ths fuel
is high. The quality of coal improves gradually from lignite to anthracite.
Charcoal: Iris prepared by destructive distillation of wood. The by-prodaci resulting from
<isilation ave methy alcohol, acetic acid, acetone, gaseous compounds, and ta It absorbs 12 to
15 percent rmoistre from atmosphere and this lowers its heating value.
Coke: It isthe solid residue left after the destructive distillation of certain sft coals. It consists
of carbon, mineral matter with about 2% sulphue and small quantities of hydrogen, nivogen and
phosphorous. Iti mainly used in blast furnaces
Briquetted coal: It is a block of compressed coal dst. The blocks are prepared from fine coal
and slacks of all types produced in mining by eompressing the material under higb pressure. It
gives satisfactory strong briquettes bricks) without the addition of a binder.
Pulverized coal: Reducing the coal to powder or dus is called pulverized coal Low grade fuel
is efficiently burnt by pulverzing-
Combustion Engines
8.1 INTRODUCTION
Fuelis a substance which participates easily with oxygen ina self-sustaining exothermic reaction
‘The subject of fuels for IC engines has been studied ever since the engines have been in existence.
Engine performance depends upon the fuel characteristics. I is therefore essential to study the
‘characteristics of different types of fuels to understand the combustion phenomenon. The charac-
ter ofthe fuel used may have considerable fluence on the design, the output, the efficiency, the
fuel consumption, the air pollution and in many cases on the reliability and dozabiliy ofthe engine.
‘The characteristics of the IC engine fuel: must be such thatthe following requirements a
‘The fuel should get effectively atomized, vaporized and well mixed withthe ar.
‘The combustion process must be fas
Starting ofthe engine shouldbe quick and reliable at any ambient condition.
‘The surface of the combustion chamber should remain free from carbon and other
deposits.
The cylinder face, the piston and the piston rings should not get subjected to excessive
wear and corrosion.
6. The basic elements of the engine should remain free from thermal stresses due to
temperature gradient developed during combustion.
7. Combustion shouldbe complete without the evolution of harmful exhaust gases.
The IC engines can be operated on many different kinds of fuels, including liquid, gaseous,
and even solid. The selection of a fuel fora particular use in engines is mainly govemed by (a) the
‘ype ofthe equipment required to store, supply and bum the fuel in the engine, (b) the heating valve
Per unit volume of he fel, and () he availability and cos ofthe fuel at the site of he engine.
8.2 CLASSIFICATION OF FUELS
‘The principal constituents of any fuel are carbon and hydrogen. Fuels may be classified as
Primary or secondary according to whether they occur in nature or are prepared, Fuels can
be in soli, liquid or gaseous state. The classification of important fuels can be summarized a
follows
Fes for Internal Conbunion Engines 229
1. Solid fuels
‘Natural (Primary): Wood; Pet, Col, he major ranks of cal from the lowest 0 the highest
ar: ()Lignite (i) Subbituminoss, (i) Bituminous, (iv) Semianthacite, and (4) Antracte
Prepared Secondary): Charcoal; Coke; Briquetted cou; Pulverized col,
2. Liquid fuels
Natural: Petroleum
Prepared: (i) Petroleum based: gaslin, kerosene, diese il, fu oil, bricating il
Gi) Nor-petroleum based: benzo, alcohol
3. Gaseous fuels
Naturals” Natural gas
Prepared: Liqufied petroleum gas (LPG), producer gas, coal gas, hydrogen,
83 SOLID FUELS
8.3.1 Brief Description of Solid Fuels
Wood: Iris anaturally available solid fue. is not generally uted asa commercial fuel exceptin
industries where a large amount of waste wood is available
Peat: Iris a mixture of decayed vegetable matter with water. It is dried with air. I contains a
high percentage of moisture. is used asa feel in gas producer plant.
Coal: This includes al rypes of natural sold fuels from lignite to anthracite. Pat no col but
represents the first stage in he formation of coal I the early stages of transformation, varying
amounts of wate, methane and carbon dioxide got gradually eliminated by increased pressure and
temperature. Peat was changed to lignite and then o bimminous coal. The volale matter of the
fuel was reduced further o form the anthracite coals. Lignites have a wood or clay like appear
ance associated witha high amount of moisture and it has low heat content. Lignies are usualy
amorphous in character and pose transportation dificulis as they break easily. Anthracite is very
hard and has shining black lustre. The moisture contents very low. The heating value of ths fuel
is high. The quality of coal improves gradually from lignite to anthracite.
Charcoal: Iris prepared by destructive distillation of wood. The by-prodaci resulting from
<isilation ave methy alcohol, acetic acid, acetone, gaseous compounds, and ta It absorbs 12 to
15 percent rmoistre from atmosphere and this lowers its heating value.
Coke: It isthe solid residue left after the destructive distillation of certain sft coals. It consists
of carbon, mineral matter with about 2% sulphue and small quantities of hydrogen, nivogen and
phosphorous. Iti mainly used in blast furnaces
Briquetted coal: It is a block of compressed coal dst. The blocks are prepared from fine coal
and slacks of all types produced in mining by eompressing the material under higb pressure. It
gives satisfactory strong briquettes bricks) without the addition of a binder.
Pulverized coal: Reducing the coal to powder or dus is called pulverized coal Low grade fuel
is efficiently burnt by pulverzing-
DeLee eee ee ee ee SIT UT ev ee ee eee
230_ Fundamental of Internal Combustion Engasr
Fals for Internal Combustion Engines 231
8.3.2 Use of Solid Fuels in IC Engines
‘The use of solid fuels leads 1 problems of complicated injection systems as well as difficulties
associated with solid residue or ash. Attempts have been made to use pulverized coal in CI
engines, but these has been very litle development ofthe use of fuel in this form. Solid els
consequently find litle practic! application at present. The problem of using coal directly by
pulverizing it and burning ina Cl engines being brought nearer toa practical solution but the main
‘obstacle isthe excessive wear ofthe cylinder liners and te piston rings,
Since coal is our most abundant fuel, considerable esearch is underway on methods that in
the future will produce ether gasoline or gs from coal. A number of processes have been devel
‘oped far converting coal into liquid fuels. Basically, he process involves the forming of a synthe
sis ges by partially burning cost with insufficient ai. This yields a product high in CO and Hy
content, The synthesis gas is then passed dhrough a synthesis reactor where, in the presence of a
catalyst andthe proper temperature and pressure, the CO and Hace reformed o produce hydro
(arbons ofthe paraffin, olefia, and alcohol families. These products are further refined to form.
suitable liquid fuels.
8.4 LIQUID FUELS
8.4.1 Petroleum Fuels (Petra = rock + oleum = oil)
The most widely accepted theory is thatthe il was formed by the decomposition of dead animals
and plants at high temperature and under high pressure which brought about a type of semi
destractve diaillaion, This along with other metamorphic processes resulted in the formation of
peoleum. After a period of many centuris, the oil was forced trough layers of porous rock
‘era until it finally became entrapped under a domed shaped hart rock (Figure 8.1). This made it
impossible forthe gas and oi to escape, and the water kept the pool of ol under pressure
In drilling for oi, the doise-shaped har rock i penetrated, and the existing pressure forces
the oil, gos, and some water to the surface. As the petroleum is removed from the underground
deposit the water moves into take its place. Eventually, he natural pressure decreases tothe point
‘where it will aot be possible to force the oil and gas 10 the surface, When this occurs, the gas or
‘water may be pumped back into the well to increase the pressure and hence force the crudo cil
from the pool tothe surface.
Petroleum isa mixture of many diferent hydrocarbons, with some sulphor and other impuri
lies. Hydrocarbons present in fuel may be classified into four different groups: (a) Parafis.
(0) Olefins, (+) Naphthenes, and (d) Aromatics.
Paraffins (Alkanes)
[Normal or straight-chain paraffins are sable, saturated compounds having the general chemical
formula CH. The compounds in his group have a name ending in =ane, The first four ment
bers of his series (n = 1 to 4) are gases. The members from n = 6 to 18 are liquids and then
‘gradually the transformation takes place from n = 18 10 21, after which they are solids, The
‘molecalarstrctures of three ofthe members ofthe normal paaffin family with n= 1,3 and 8 are
ES
LOUE Hu
Hr CHAT
i FRET
EA We
the ie na mu om
sen cen Ay en fr le ey ras mr
ee ee re ma à
mp
wooctan 22,4 timethypentane)
Isooctane isa very smooth burning fuel in aspark-ignition engine and has been chosen as the
standard for 100 octane gasoline.
In contrast, normal octane is a rather poor engine fuel and has a ow octane rating
úOlefins (Alkenes)
Olefins are also straight chain compounds similar to parafins but they are unsaturated as they
‘contain one or more double bonds between the carbon atoms, Their general chemical formula is
Calis. The double bond of the olefins may appear between any (wo carbon atoms, the position
being designated by a number indicating the smaller numberof carbon atoms at one side of the
(double bond, The members of this family have names similar to paraffins except thatthe suffix
ene is used. The structure of 3-Heptene (CH) is shown below:
— —_ __—_____ ____
230_ Fundamental of Internal Combustion Engasr
Fals for Internal Combustion Engines 231
8.3.2 Use of Solid Fuels in IC Engines
‘The use of solid fuels leads 1 problems of complicated injection systems as well as difficulties
associated with solid residue or ash. Attempts have been made to use pulverized coal in CI
engines, but these has been very litle development ofthe use of fuel in this form. Solid els
consequently find litle practic! application at present. The problem of using coal directly by
pulverizing it and burning ina Cl engines being brought nearer toa practical solution but the main
‘obstacle isthe excessive wear ofthe cylinder liners and te piston rings,
Since coal is our most abundant fuel, considerable esearch is underway on methods that in
the future will produce ether gasoline or gs from coal. A number of processes have been devel
‘oped far converting coal into liquid fuels. Basically, he process involves the forming of a synthe
sis ges by partially burning cost with insufficient ai. This yields a product high in CO and Hy
content, The synthesis gas is then passed dhrough a synthesis reactor where, in the presence of a
catalyst andthe proper temperature and pressure, the CO and Hace reformed o produce hydro
(arbons ofthe paraffin, olefia, and alcohol families. These products are further refined to form.
suitable liquid fuels.
8.4 LIQUID FUELS
8.4.1 Petroleum Fuels (Petra = rock + oleum = oil)
The most widely accepted theory is thatthe il was formed by the decomposition of dead animals
and plants at high temperature and under high pressure which brought about a type of semi
destractve diaillaion, This along with other metamorphic processes resulted in the formation of
peoleum. After a period of many centuris, the oil was forced trough layers of porous rock
‘era until it finally became entrapped under a domed shaped hart rock (Figure 8.1). This made it
impossible forthe gas and oi to escape, and the water kept the pool of ol under pressure
In drilling for oi, the doise-shaped har rock i penetrated, and the existing pressure forces
the oil, gos, and some water to the surface. As the petroleum is removed from the underground
deposit the water moves into take its place. Eventually, he natural pressure decreases tothe point
‘where it will aot be possible to force the oil and gas 10 the surface, When this occurs, the gas or
‘water may be pumped back into the well to increase the pressure and hence force the crudo cil
from the pool tothe surface.
Petroleum isa mixture of many diferent hydrocarbons, with some sulphor and other impuri
lies. Hydrocarbons present in fuel may be classified into four different groups: (a) Parafis.
(0) Olefins, (+) Naphthenes, and (d) Aromatics.
Paraffins (Alkanes)
[Normal or straight-chain paraffins are sable, saturated compounds having the general chemical
formula CH. The compounds in his group have a name ending in =ane, The first four ment
bers of his series (n = 1 to 4) are gases. The members from n = 6 to 18 are liquids and then
‘gradually the transformation takes place from n = 18 10 21, after which they are solids, The
‘molecalarstrctures of three ofthe members ofthe normal paaffin family with n= 1,3 and 8 are
ES
LOUE Hu
Hr CHAT
i FRET
EA We
the ie na mu om
sen cen Ay en fr le ey ras mr
ee ee re ma à
mp
wooctan 22,4 timethypentane)
Isooctane isa very smooth burning fuel in aspark-ignition engine and has been chosen as the
standard for 100 octane gasoline.
In contrast, normal octane is a rather poor engine fuel and has a ow octane rating
úOlefins (Alkenes)
Olefins are also straight chain compounds similar to parafins but they are unsaturated as they
‘contain one or more double bonds between the carbon atoms, Their general chemical formula is
Calis. The double bond of the olefins may appear between any (wo carbon atoms, the position
being designated by a number indicating the smaller numberof carbon atoms at one side of the
(double bond, The members of this family have names similar to paraffins except thatthe suffix
ene is used. The structure of 3-Heptene (CH) is shown below:
— —_ __—_____ ____
ton Expres
vr
weer?
tete (Ch
ne eins (Cy) an suce ilar dt of eins bt veo dole bonds
inthe open stand sure” oe.
y
DEE
Feine
Te olefins andthe till more unsaturated olefins ar unstable compounds and ar ought to
be the cause of mach gum formation in gasoline. However, since they possess very good ignition
characteristics, substantial quantities of thece compounds appear in modem high octane gasoline.
Naphthenes (Cyelanes)
Naphthenes are saturated, stable compounds with a ring structure. The molecular structure of
‘eyelopentane is shown below:
‘The naphthenes are saturated compounds eventhough the geera chemical formula is CHa
the same as forthe unsaturated olefins. The names ofthe members of his family are the same
as those of the corresponding paraffin excep thatthe prefix cyclo= is added to denote the sing
structure ofthe raphhenes.
“The physical propetes of this group are similar to those of the normal paraffins but the
‘combustion properties are more like those of isoparafins.
Aromatics (Benzene derivatives) |
‘The aromatics are unsaturated but able ing compounds. The general chemical formula or his
i
oca
ec Jon
i
toco
unis for IneraCombordon Ergines_233
group is Cyt. Benzene (Col) isthe most characteristic member of the group, and all other
aromates consist of some variation of the benzene ring. Various aromatic compounds are formed
by replacing one or more ofthe hydrogen atoms ofthe benzene molecules with an organi radical.
By adding a methyl group (CH) tolune is formed.
This group has very desirable combustion characteristics for use in SI engines, and the
members of this group ar often added to gasoline to produce high ocane fuels
8.4.2. Refining Process of Petroleum
‘Crude il coming out from the oil wells is aliquid consisting mally of hydrocarbons with traces
of sulphur nitrogen, oxygen and a few impurities such as water and sediment. Crude petroleum is
rarely used as a fuel. I is refined so as to produce desirable commercial products, Cre petto-
Tem has different hydrocarbon constituents that have different boiling points, The boiling points
Of the various constituents increase more or less regularly with the increase in molar mass. This
facts used inthe refining process to separate crude oil into more desirable products by fractional
itilation,
Fractional distillation
‘The distillation of petroleum is amd ou in a tubular fumace with a tal steel frctionating column,
The crude oil is pumped continuously throngh a heated pipe and flashed into the fractonating
column, The vapours of the oi as they rise up the factionating coların become cooler and condense
0% the shelves at various heights. The heavier compounds have a high boiling point and, as the
‘vapours rise inthe tower and are cooked, the heavy fractions precipitate fs and are removed
from the tower. Te light hydrocarbons rise 0 the top of the column before condensing, while the
‘compounds with intermediate boiling points are removed atthe intermediate stages, Outlets are
provided in the side of the column at suitable heights for withdrawal of several fractions.
Dred al)
Mol sian gs ot
L Cabra)
Mol — teary ga
/
—— Rese
Fgue82_ Franc mortadela ros.
vr
weer?
tete (Ch
ne eins (Cy) an suce ilar dt of eins bt veo dole bonds
inthe open stand sure” oe.
y
DEE
Feine
Te olefins andthe till more unsaturated olefins ar unstable compounds and ar ought to
be the cause of mach gum formation in gasoline. However, since they possess very good ignition
characteristics, substantial quantities of thece compounds appear in modem high octane gasoline.
Naphthenes (Cyelanes)
Naphthenes are saturated, stable compounds with a ring structure. The molecular structure of
‘eyelopentane is shown below:
‘The naphthenes are saturated compounds eventhough the geera chemical formula is CHa
the same as forthe unsaturated olefins. The names ofthe members of his family are the same
as those of the corresponding paraffin excep thatthe prefix cyclo= is added to denote the sing
structure ofthe raphhenes.
“The physical propetes of this group are similar to those of the normal paraffins but the
‘combustion properties are more like those of isoparafins.
Aromatics (Benzene derivatives) |
‘The aromatics are unsaturated but able ing compounds. The general chemical formula or his
i
oca
ec Jon
i
toco
unis for IneraCombordon Ergines_233
group is Cyt. Benzene (Col) isthe most characteristic member of the group, and all other
aromates consist of some variation of the benzene ring. Various aromatic compounds are formed
by replacing one or more ofthe hydrogen atoms ofthe benzene molecules with an organi radical.
By adding a methyl group (CH) tolune is formed.
This group has very desirable combustion characteristics for use in SI engines, and the
members of this group ar often added to gasoline to produce high ocane fuels
8.4.2. Refining Process of Petroleum
‘Crude il coming out from the oil wells is aliquid consisting mally of hydrocarbons with traces
of sulphur nitrogen, oxygen and a few impurities such as water and sediment. Crude petroleum is
rarely used as a fuel. I is refined so as to produce desirable commercial products, Cre petto-
Tem has different hydrocarbon constituents that have different boiling points, The boiling points
Of the various constituents increase more or less regularly with the increase in molar mass. This
facts used inthe refining process to separate crude oil into more desirable products by fractional
itilation,
Fractional distillation
‘The distillation of petroleum is amd ou in a tubular fumace with a tal steel frctionating column,
The crude oil is pumped continuously throngh a heated pipe and flashed into the fractonating
column, The vapours of the oi as they rise up the factionating coların become cooler and condense
0% the shelves at various heights. The heavier compounds have a high boiling point and, as the
‘vapours rise inthe tower and are cooked, the heavy fractions precipitate fs and are removed
from the tower. Te light hydrocarbons rise 0 the top of the column before condensing, while the
‘compounds with intermediate boiling points are removed atthe intermediate stages, Outlets are
provided in the side of the column at suitable heights for withdrawal of several fractions.
Dred al)
Mol sian gs ot
L Cabra)
Mol — teary ga
/
—— Rese
Fgue82_ Franc mortadela ros.
Vee ee ee o ee ee ee ee eee
1234 Fundamentals of Inerra! Combustion Engines
Fu for ItemakCambusten Engines 235
Figure 82 shows he prima ction, chaine rom a actonting to andthe oder in
sti ty cur rm ep tem fe atoning oer he cone a u
cio) bus, propane nd lan. Nest ome te gals, apa, Kerosene deel ol
Fobia os heavy ga ol in at order Aer dilaton, a ese of arin wax or spl
ister opening on he base of theo 1, whether pin or nphe.
The dena ato of cra spore, such as gua o be peoleum component,
fac ences he natal oecuing rol alv fund incre This has le othe devel
apr ener processo ‘ck age molccls ino smaller meleules an ‘polymer.
122 “bla sal moles it lage moeclos to get he bailing point of teresting,
compare inthe gasoline range. Some of such processes are bel desorbed hee
Cracking: isthe process of breaking down the large and complex molecules ito lighter and
simpler compounds, Cracking reactions may be thermal or eaaltic. In thermal cracking the heavy
hydrocarbons are subjected to high temperature and pressure. AC high temperature, the kinetic
‘energy of the molecules increases and asa result they move faster and strike harder. Thus, some
‘of the chemical bonds holding the carbon atoms together break away and the molecules split into
lighter and smaller compounds, In catalyde cracking, somewhat lower pressure and temperature
‘are required and the smaller molecules ate found to be isomeric rater than normal hydcocarbons.
‘This is Gesrable because the isomeric compounds have better atiknock characteristics.
‘An example of a eracking reaction isthe breaking off the chain-ike structure of parafin,
rtetradecane into two smaller constiuents, one being a paraffin, Cpl. andthe other an olefin,
Chis.
Cube Hyg + Colla av
Hydrogenation: it may be described as a cracking process which occurs in an atmosphere of
hydrogen. Here, certain unsaturted compounds pick up mare hydrogen to become saturated, and
the yield and quality of gasoline ae increased. This process gives a high-octane product with a
high boiling point and high flash pom, Lis especially suited for aviation gasoline. The bydrogena-
tion process is also used to produce liquid fuel from cual and other similar materials,
Absorption: The gases leaving the refiner processes may contain some heavier hydrocarbons
inthe vapour stale, which may fall into the gasoline range. The absorption process is used to
recover these vapours, In this process the gases come into contact with a kerosene or light il
‘which absorbs the heavy hydrocarbon vapours. The vapours are then driven out from the oi by
heating, Final, the vapours ae cooled to obtain gasoline,
Polymerization: It isthe process of combining the unsaturated products of one family (wo or
more olefinic molecules) to form heavier and stable compounds tht have a high aniknock rating.
‘Atypical chemical reaction is givea below:
a engen aan
ey œ 62
Gwomsleofiveduylen) (One moe af tabuyens)
Alkylation: It is the process of combining light undesirable hydrocarbons of one chemical
family with another family to form a larger molecule. An isoparafin (usually isobutane) combines
a
with an olefin (usually butene or propene) 10 form a larger isopaatfin (usually isooctane or
isoheplane that has a very high oclane number.
Isomerization: Iris the process of changing tbe relative position of atoms within the molecule
of a tyérocarbon without changing its molecular formula. I produces isomers ofthe original
hydrocarbons.
Cyclization: Is a process of joining together the ends ofa sralght chain molecule 10 form a
‘ing compound ofthe naphihene Fami.
Aromatization: Ibis a process of joining togeter the ends of a sai chain molecule to form
an sromatie compound.
Reforming: Itis used to convert low antiknock quality gasoline into high antiknock quality. It
does not ineresse the total gasoline volume asin polymerization and alkylation
Finished blended products: It isa process of mixing certain products o obtain a commercial
product of desired quality. The producs from the various refinery processes are blended together
Lo form liquid fuels withthe proper physical characteristics to give high quality gasoline, fuel oil,
kerosene, diesel fuel, ete. These liquid products are then pur through the various finishing
processes to duce the sulphur and wax contents.
2.4.3. Petroleum-based Liquid Fuels
‘Some pevoleum-based liquid fuels of importance ae discussed below:
Gasoline
consists of a mixture of liquid hydrocarbons having four to ten carbon atoms, small amounts of
lighter and heavier hydrocarbons, minute quantities of crude petroleum impurities such as sulphur
and nitrogen. Some addiivos in very low percentages are used 0 impart performance benefits.
Gasoline is the lightest petroleum fraction in the liquid form. The boiling range of gasoline lis
‘between 30°C and 200°C. The specific gravity lies between 0.70 and 0.78. The chemical compo-
sition ofits constituents vares widely, depending on he base crude and the process of refining.
‘The heating value of a typical gasoline is 44,000 KK It is widely used in spark-ignition engines
Kerosene
kis the next fraction heavier than gasoline It is widely used in lamps, heaters, stoves and similar
appliances. It may also be used in Cl engines and gas turbines. The specific gravity of kerosene
between 0.78 10085,
Diesel otis
These are petroleum feactions heavier than Kerosene, These oils cover a wide
range of specific gravity and a very wide distillaion range. Their composition is controlled to
make them suitable for use in various types of CI engines. The heating value of typical diesel oil
is 42,000 Ku.
Fuel os
‘The range of specific gravity andthe distillation range are similar co those of diesel oils. Their
composition does not require accurate control as is required inthe case of diesel oils, These fuels
we used in continuous bumers
1234 Fundamentals of Inerra! Combustion Engines
Fu for ItemakCambusten Engines 235
Figure 82 shows he prima ction, chaine rom a actonting to andthe oder in
sti ty cur rm ep tem fe atoning oer he cone a u
cio) bus, propane nd lan. Nest ome te gals, apa, Kerosene deel ol
Fobia os heavy ga ol in at order Aer dilaton, a ese of arin wax or spl
ister opening on he base of theo 1, whether pin or nphe.
The dena ato of cra spore, such as gua o be peoleum component,
fac ences he natal oecuing rol alv fund incre This has le othe devel
apr ener processo ‘ck age molccls ino smaller meleules an ‘polymer.
122 “bla sal moles it lage moeclos to get he bailing point of teresting,
compare inthe gasoline range. Some of such processes are bel desorbed hee
Cracking: isthe process of breaking down the large and complex molecules ito lighter and
simpler compounds, Cracking reactions may be thermal or eaaltic. In thermal cracking the heavy
hydrocarbons are subjected to high temperature and pressure. AC high temperature, the kinetic
‘energy of the molecules increases and asa result they move faster and strike harder. Thus, some
‘of the chemical bonds holding the carbon atoms together break away and the molecules split into
lighter and smaller compounds, In catalyde cracking, somewhat lower pressure and temperature
‘are required and the smaller molecules ate found to be isomeric rater than normal hydcocarbons.
‘This is Gesrable because the isomeric compounds have better atiknock characteristics.
‘An example of a eracking reaction isthe breaking off the chain-ike structure of parafin,
rtetradecane into two smaller constiuents, one being a paraffin, Cpl. andthe other an olefin,
Chis.
Cube Hyg + Colla av
Hydrogenation: it may be described as a cracking process which occurs in an atmosphere of
hydrogen. Here, certain unsaturted compounds pick up mare hydrogen to become saturated, and
the yield and quality of gasoline ae increased. This process gives a high-octane product with a
high boiling point and high flash pom, Lis especially suited for aviation gasoline. The bydrogena-
tion process is also used to produce liquid fuel from cual and other similar materials,
Absorption: The gases leaving the refiner processes may contain some heavier hydrocarbons
inthe vapour stale, which may fall into the gasoline range. The absorption process is used to
recover these vapours, In this process the gases come into contact with a kerosene or light il
‘which absorbs the heavy hydrocarbon vapours. The vapours are then driven out from the oi by
heating, Final, the vapours ae cooled to obtain gasoline,
Polymerization: It isthe process of combining the unsaturated products of one family (wo or
more olefinic molecules) to form heavier and stable compounds tht have a high aniknock rating.
‘Atypical chemical reaction is givea below:
a engen aan
ey œ 62
Gwomsleofiveduylen) (One moe af tabuyens)
Alkylation: It is the process of combining light undesirable hydrocarbons of one chemical
family with another family to form a larger molecule. An isoparafin (usually isobutane) combines
a
with an olefin (usually butene or propene) 10 form a larger isopaatfin (usually isooctane or
isoheplane that has a very high oclane number.
Isomerization: Iris the process of changing tbe relative position of atoms within the molecule
of a tyérocarbon without changing its molecular formula. I produces isomers ofthe original
hydrocarbons.
Cyclization: Is a process of joining together the ends ofa sralght chain molecule 10 form a
‘ing compound ofthe naphihene Fami.
Aromatization: Ibis a process of joining togeter the ends of a sai chain molecule to form
an sromatie compound.
Reforming: Itis used to convert low antiknock quality gasoline into high antiknock quality. It
does not ineresse the total gasoline volume asin polymerization and alkylation
Finished blended products: It isa process of mixing certain products o obtain a commercial
product of desired quality. The producs from the various refinery processes are blended together
Lo form liquid fuels withthe proper physical characteristics to give high quality gasoline, fuel oil,
kerosene, diesel fuel, ete. These liquid products are then pur through the various finishing
processes to duce the sulphur and wax contents.
2.4.3. Petroleum-based Liquid Fuels
‘Some pevoleum-based liquid fuels of importance ae discussed below:
Gasoline
consists of a mixture of liquid hydrocarbons having four to ten carbon atoms, small amounts of
lighter and heavier hydrocarbons, minute quantities of crude petroleum impurities such as sulphur
and nitrogen. Some addiivos in very low percentages are used 0 impart performance benefits.
Gasoline is the lightest petroleum fraction in the liquid form. The boiling range of gasoline lis
‘between 30°C and 200°C. The specific gravity lies between 0.70 and 0.78. The chemical compo-
sition ofits constituents vares widely, depending on he base crude and the process of refining.
‘The heating value of a typical gasoline is 44,000 KK It is widely used in spark-ignition engines
Kerosene
kis the next fraction heavier than gasoline It is widely used in lamps, heaters, stoves and similar
appliances. It may also be used in Cl engines and gas turbines. The specific gravity of kerosene
between 0.78 10085,
Diesel otis
These are petroleum feactions heavier than Kerosene, These oils cover a wide
range of specific gravity and a very wide distillaion range. Their composition is controlled to
make them suitable for use in various types of CI engines. The heating value of typical diesel oil
is 42,000 Ku.
Fuel os
‘The range of specific gravity andthe distillation range are similar co those of diesel oils. Their
composition does not require accurate control as is required inthe case of diesel oils, These fuels
we used in continuous bumers
a
236 Fundamentals of erat Combustion Engines Fuel for nemalComburton Enpres_237
Lubricating ots Table 8.1. Important properties ot mathanal, ethanol and gasoline
‘These are made up in pa fom heavy disiltio of peroleum and in par from residual ois that = o
remain after istlaton, These ae used for ubeeating purposes. Propeny Methanol Ethanol Gasoline
‘Chemical formula enon Son CH
8.4.4. Non-petroleum Based Liquid Fuels Molecular ui “3204 206 19
Various liquid fuels have been used as substitutes for gasoline. The principal feels are benzo, Coron by weight (er cen)
alcohol and ther blends with gasoline, Acton and ciethy-ther may also be used or bending in avon ms 22 mo
fuel Hydrogen us 150 1600
Oven 500 ss NL.
Benzol Specie sity om oms 07-078
lis a isis of coal a. contains about 70% benzene (CH), 20% tole (CH), 10% xylene Boiling poin (°C) 650 38-205
(Cot) and traces of sulphur compounds. ha the high antiknock character It has a free: ‘Late hea of vporzion Oe) us 290-420
ing pont of .6°C and therefore it is nota suitable fuel to be used in a old climate, Because ofits Vapour pressure at 311 K Qu) es 048-105
High antiknock characteristic, it can be bended with gasoline to be us as à fuel in SLemgies. | ‘Lower cloro valve (M2) 40
or i Soichiomeañ el rio 147
pee Be ae ehe | Tandem, ail aio 35-170 10-20
os of organic origin and can be produced from a wide range of abundantly available mw | pion tempera = -
ee tony ee en es
natually and abundantly in some plats like sugarcane and can also be produced from starchy ous ae m a
‘materials lke com, potatoes, maize and barley. The starchy material fist converted into sugar pa
Which is then fermented by yeast ©) Motor % =
Forte lrge-sale production of methanol (CHSOH), the following meihods are commonly Coco camber a El su
employed: (1) destuctive disiltion of wood, (3) synthesis fom water gas () from narra gas
but its petroleum based, (d) from coal, a relatively abundant fosil fue. e |
Aleohols have high amknock characteristics which permi spark-gntion engines to un at lisa very volle fuel. is used wi othe ues to increase the vola ofthe blend.
higher compression ratios. À len mixtar will bim andthe exhaust gas temperature wil be lower.
Alcohol, therefore, will reduce CO and NO, in the exhaust. The alcohol fueled SI engines can GASEOUS FUELS
produce a slighty higher power output. y
‘Methanol is considered to be one of the most likely alternative automotive fuel, However, \Ghscous feel pen ao Sly cogne mizing wth ar, ieriburing homogeneous wisn
several major technical difioltes must be resolved before 100% methanol can became a com. ONE e pas fuck Coun probit of sores ad
mercially aceptable fel for use in vices, The most commonly mentioned difficulties are cold handling large volumes especial in automobile. Consequently, gaseous fuel find applications in
start (no start below 15°C), safety (explosive mixture in the fuel tanks, invisible flame), and ‘sationtay power plants located near an abundant apply of te fuel. Sams gaseows fuels can bo
corrosion and wear of engine and fe system materials. In addon, the vehicle range (distance Je coder esate AE 118 Bay nad Case Fa AB aa ak ollo. Ue of
covered) wil also be reduced substaialy, unless the size ofthe fel tank is greatly increased, ea es aa Bgl prie ge LO) I reg O eo ee OS
because the olumeti energy density of methanol is only about one-alf ofthat of gasoline, Most in IC engines are in progres.
ofthese problems may be resolved by using a mediar concentration (30-70% by volume) blend
of methanol and gasoline, However, the use of such blends may compromise some of metñanol' EST Natural Gas
ey technical advantages, namely increased engine efficiency and power, and decreased NO, Natural gas is mixture of several different gases. The primary constituent is methane, which
emissions, | typically makes up 85-99 % ofthe total volume. The othe contents include other hydrocurbans,
‘The physical properties of methanol ethanol and gasoline are compared in Tabl 8.1. | imet gases such as nitrogen, helium and carbon dioxide, and traces of hydrogen sulphide and
water. Toe non-methane hydrocarbons present in natural gas consist primarily of ethane. The
Acetone ‘remainder is made up mostly of propane and butane, with some traces of Cs and higher species.
‘Acetone is more volatile than methanol is antiknock quality is higher than that of butanol, and [Natural gas is an excellent fuel for SI engines. As a gas under nomma conditions, it mises
‘consequently its a destabe fel 10 blend with butanol, readily with arin any proportion. Unlike liquid fuel it does not need 10 vaporize before burning.
|
— _
—
236 Fundamentals of erat Combustion Engines Fuel for nemalComburton Enpres_237
Lubricating ots Table 8.1. Important properties ot mathanal, ethanol and gasoline
‘These are made up in pa fom heavy disiltio of peroleum and in par from residual ois that = o
remain after istlaton, These ae used for ubeeating purposes. Propeny Methanol Ethanol Gasoline
‘Chemical formula enon Son CH
8.4.4. Non-petroleum Based Liquid Fuels Molecular ui “3204 206 19
Various liquid fuels have been used as substitutes for gasoline. The principal feels are benzo, Coron by weight (er cen)
alcohol and ther blends with gasoline, Acton and ciethy-ther may also be used or bending in avon ms 22 mo
fuel Hydrogen us 150 1600
Oven 500 ss NL.
Benzol Specie sity om oms 07-078
lis a isis of coal a. contains about 70% benzene (CH), 20% tole (CH), 10% xylene Boiling poin (°C) 650 38-205
(Cot) and traces of sulphur compounds. ha the high antiknock character It has a free: ‘Late hea of vporzion Oe) us 290-420
ing pont of .6°C and therefore it is nota suitable fuel to be used in a old climate, Because ofits Vapour pressure at 311 K Qu) es 048-105
High antiknock characteristic, it can be bended with gasoline to be us as à fuel in SLemgies. | ‘Lower cloro valve (M2) 40
or i Soichiomeañ el rio 147
pee Be ae ehe | Tandem, ail aio 35-170 10-20
os of organic origin and can be produced from a wide range of abundantly available mw | pion tempera = -
ee tony ee en es
natually and abundantly in some plats like sugarcane and can also be produced from starchy ous ae m a
‘materials lke com, potatoes, maize and barley. The starchy material fist converted into sugar pa
Which is then fermented by yeast ©) Motor % =
Forte lrge-sale production of methanol (CHSOH), the following meihods are commonly Coco camber a El su
employed: (1) destuctive disiltion of wood, (3) synthesis fom water gas () from narra gas
but its petroleum based, (d) from coal, a relatively abundant fosil fue. e |
Aleohols have high amknock characteristics which permi spark-gntion engines to un at lisa very volle fuel. is used wi othe ues to increase the vola ofthe blend.
higher compression ratios. À len mixtar will bim andthe exhaust gas temperature wil be lower.
Alcohol, therefore, will reduce CO and NO, in the exhaust. The alcohol fueled SI engines can GASEOUS FUELS
produce a slighty higher power output. y
‘Methanol is considered to be one of the most likely alternative automotive fuel, However, \Ghscous feel pen ao Sly cogne mizing wth ar, ieriburing homogeneous wisn
several major technical difioltes must be resolved before 100% methanol can became a com. ONE e pas fuck Coun probit of sores ad
mercially aceptable fel for use in vices, The most commonly mentioned difficulties are cold handling large volumes especial in automobile. Consequently, gaseous fuel find applications in
start (no start below 15°C), safety (explosive mixture in the fuel tanks, invisible flame), and ‘sationtay power plants located near an abundant apply of te fuel. Sams gaseows fuels can bo
corrosion and wear of engine and fe system materials. In addon, the vehicle range (distance Je coder esate AE 118 Bay nad Case Fa AB aa ak ollo. Ue of
covered) wil also be reduced substaialy, unless the size ofthe fel tank is greatly increased, ea es aa Bgl prie ge LO) I reg O eo ee OS
because the olumeti energy density of methanol is only about one-alf ofthat of gasoline, Most in IC engines are in progres.
ofthese problems may be resolved by using a mediar concentration (30-70% by volume) blend
of methanol and gasoline, However, the use of such blends may compromise some of metñanol' EST Natural Gas
ey technical advantages, namely increased engine efficiency and power, and decreased NO, Natural gas is mixture of several different gases. The primary constituent is methane, which
emissions, | typically makes up 85-99 % ofthe total volume. The othe contents include other hydrocurbans,
‘The physical properties of methanol ethanol and gasoline are compared in Tabl 8.1. | imet gases such as nitrogen, helium and carbon dioxide, and traces of hydrogen sulphide and
water. Toe non-methane hydrocarbons present in natural gas consist primarily of ethane. The
Acetone ‘remainder is made up mostly of propane and butane, with some traces of Cs and higher species.
‘Acetone is more volatile than methanol is antiknock quality is higher than that of butanol, and [Natural gas is an excellent fuel for SI engines. As a gas under nomma conditions, it mises
‘consequently its a destabe fel 10 blend with butanol, readily with arin any proportion. Unlike liquid fuel it does not need 10 vaporize before burning.
|
— _
—
www. Cw ee er ee Oe SRS à
238_Fundamensls of Internal Combustion Engines
Fuels for mtemalCombunion Engines 239
“Thus cold engine starting is easier especialy at low temperatures, ard cold-start enrichments not.
required Cold-sart enrichment is a major source of CO emissions and emissions-related prob-
lems in eacline-uelled SI engines.
"Natural gas has a high fition temperature, and is resistant to sel-ignition. Tt has excellent
antknock properties, Pure methane bas an equivalent research octane number (RON) of 130, the
highest of any commonly used fuel, Because of its antiknock properties, natural gas can saely be
used with engine compression ratio a high as 15:1 (compared to 8-10:1 for 91 octane gasoline).
Natural gas engines using these higher compression ratios can reach significantly higher efficien-
cies than are possible with gasoline.
8.5.2 Liquified Petroleum Gas (LPG) E
Liguified Petroleum Gas (LPG) is a product of petroleunt gases, principally propane (C3H),
propylene (CH) and butane (Ca). These gases can be liquificd at normal temperatures by
subjecting Ihem to a moderate pressure. Owing tothe demand from industry for butane deriva-
tives, LPG sold as a foe is made up largely of propane. Liqified peroleum gases are used as fuels
for stoves, trucks, buses and tractors in many pars of the world. The LPG has higher heating
value compared to gasoline. Since propane and butane are heavier than ir, the escaping gas will
{end to settle and collet in pockets thus creating an explosion hazard. The LPG is suitable for IC
‘engines because of is avllabilty and low carbon content, ths resulting in drastic reduction in
“exhaust emissions, The LPG has a high sel-igniion temperature and a high octane number, which
makes it more suitable for S engines.
Engines with natura gas and LPG can run lean because of their beter distribution and
higher misfire limit. Also, ter higher octane numbers, allow an increase in the compression ratio
in ST engines, which consequently improves the thermal efficiency and reduces the exhaust emis-
85.3 Producer Gas
I is made by buming carbonaceous material (coal, wood, charcosl, coke, etc) with a large
deficiency of air and treating wth steam. The products ofthis partial combustion contain CO and
Ha in suficent quantities, o that they can be used in an engine asa fuel. The producer gas has a
high percentage of N since ai is used. Thus, it has alow heat value.
854 Coal Gas
Coals heated to temperatures up to 1500°C in the presence of very lite air. The complex organic
compounds of the coal decompose a the high temperature and form simpler, volatile products
and coke.
85.5 Hydrogen
‘With he imposition of stringent emission standards along withthe decreasing availabilty of petro-
eum products, itis imperative that a search fr low pollting alternative fuels be made, Hydrogen,
as an Sl engine fuel acquices special significance in view of its unlimited supply potential and
‘almost non polluting characterises. Even though with eurent economics hydrogen would be a
costly aroma fe based on longer considerations env os standing may improve
deb. As and when cheap metodo ydrgen production becomes aval etd
Suse o sra marine veal ways andro veils
Hydrogen hs emerged» penal fe fo intemal combusion engines. is generally
considere to he non poliing bes hydrogen coma no carton Species sch eon
monoxide and wubumed hydrocarbon, which are non lourd in gasoline fueled enla,
‘ould be viral lininated i exhaust Hydrogen sound in abundant quanies in vars
forms and can be considered o e an lineal felt cn be edd 2 fal
cates witout majo design changes
The problems general experienc na yérogen full engin ete Dackfrng pri
Son, ing and rapid at of rs ui e combuton process case ft her
fare sped Backfhngis mail de os go energy ray arme Laced
tot ons chambre theemperatre of he estat gs sometimes nent anse
backing
Hydrogen fled engines canbe run ata much aer equivalence at than a gasoline
nti shou an operons of hydrogel engine ener ee NO, enon and
Show prod ermal efiieney robles asi wi 10 ean mixes increase te
Son delay and eave severe yee vais. Te hykogen proxies preset in he exaust
[roduc of hydrogen cl engine operating wi ey Ian mixes,
Compare with ydrocaon Fl, drogen has cain vantages de tit high chemical
fact. (9) a higher ane propagan see, denon i, and (lowes ol
caer Te high fame propagation sped of hydrogen extant benefit the temod pam
Eine) 0 the engine the combustion pres ls ser the optimum Lorca om
Gon corsa ale. The mide pio ts provide pos lore tee ean
tres lower ¡un nergy i favourable or nin oa mies in Sis bt hat
Be dsadvatage o sulin nomma combustion (ck and surface nio) espec nar
oichiomecy.
Because Socie must be avoided at al co, ts necessary to voi ka and surface
igo. This can be doe ylang th mint. Since hs eee the salle poe a ue
Soule ie cig ado of ur so o cons y rc oe
travel sane, Ti canbe don y losing he spark poy eee pic) away fom
the centre of the cylinder head. E nn Prison away
Omar storage o hydagen remis a major technical challenge. As a gs, drogen hs a
very low ne ds. This as to age tank ie even wit high presu soe and shot
‘eb range Sevinghydogeninlgud fom sss probate ast gus 233 0 Songe
oftyerogen may be shieved by sold state bade rage mae, ui tyes, copes
sphere tage, storage arte, sage oles, an sir sch rage
“he prope of hyogen, sta go (metan) and sole ar Come in Table 82.
8.6 FUELS FOR SI ENGINES
‘The performance of the spack-ignition engine depends upon the following fuel characterises,
which are of importance: (a) volatility, () sulphur contents, () gum deposits, (d) carburettor
detergent additives, and (e) antknock quality.
238_Fundamensls of Internal Combustion Engines
Fuels for mtemalCombunion Engines 239
“Thus cold engine starting is easier especialy at low temperatures, ard cold-start enrichments not.
required Cold-sart enrichment is a major source of CO emissions and emissions-related prob-
lems in eacline-uelled SI engines.
"Natural gas has a high fition temperature, and is resistant to sel-ignition. Tt has excellent
antknock properties, Pure methane bas an equivalent research octane number (RON) of 130, the
highest of any commonly used fuel, Because of its antiknock properties, natural gas can saely be
used with engine compression ratio a high as 15:1 (compared to 8-10:1 for 91 octane gasoline).
Natural gas engines using these higher compression ratios can reach significantly higher efficien-
cies than are possible with gasoline.
8.5.2 Liquified Petroleum Gas (LPG) E
Liguified Petroleum Gas (LPG) is a product of petroleunt gases, principally propane (C3H),
propylene (CH) and butane (Ca). These gases can be liquificd at normal temperatures by
subjecting Ihem to a moderate pressure. Owing tothe demand from industry for butane deriva-
tives, LPG sold as a foe is made up largely of propane. Liqified peroleum gases are used as fuels
for stoves, trucks, buses and tractors in many pars of the world. The LPG has higher heating
value compared to gasoline. Since propane and butane are heavier than ir, the escaping gas will
{end to settle and collet in pockets thus creating an explosion hazard. The LPG is suitable for IC
‘engines because of is avllabilty and low carbon content, ths resulting in drastic reduction in
“exhaust emissions, The LPG has a high sel-igniion temperature and a high octane number, which
makes it more suitable for S engines.
Engines with natura gas and LPG can run lean because of their beter distribution and
higher misfire limit. Also, ter higher octane numbers, allow an increase in the compression ratio
in ST engines, which consequently improves the thermal efficiency and reduces the exhaust emis-
85.3 Producer Gas
I is made by buming carbonaceous material (coal, wood, charcosl, coke, etc) with a large
deficiency of air and treating wth steam. The products ofthis partial combustion contain CO and
Ha in suficent quantities, o that they can be used in an engine asa fuel. The producer gas has a
high percentage of N since ai is used. Thus, it has alow heat value.
854 Coal Gas
Coals heated to temperatures up to 1500°C in the presence of very lite air. The complex organic
compounds of the coal decompose a the high temperature and form simpler, volatile products
and coke.
85.5 Hydrogen
‘With he imposition of stringent emission standards along withthe decreasing availabilty of petro-
eum products, itis imperative that a search fr low pollting alternative fuels be made, Hydrogen,
as an Sl engine fuel acquices special significance in view of its unlimited supply potential and
‘almost non polluting characterises. Even though with eurent economics hydrogen would be a
costly aroma fe based on longer considerations env os standing may improve
deb. As and when cheap metodo ydrgen production becomes aval etd
Suse o sra marine veal ways andro veils
Hydrogen hs emerged» penal fe fo intemal combusion engines. is generally
considere to he non poliing bes hydrogen coma no carton Species sch eon
monoxide and wubumed hydrocarbon, which are non lourd in gasoline fueled enla,
‘ould be viral lininated i exhaust Hydrogen sound in abundant quanies in vars
forms and can be considered o e an lineal felt cn be edd 2 fal
cates witout majo design changes
The problems general experienc na yérogen full engin ete Dackfrng pri
Son, ing and rapid at of rs ui e combuton process case ft her
fare sped Backfhngis mail de os go energy ray arme Laced
tot ons chambre theemperatre of he estat gs sometimes nent anse
backing
Hydrogen fled engines canbe run ata much aer equivalence at than a gasoline
nti shou an operons of hydrogel engine ener ee NO, enon and
Show prod ermal efiieney robles asi wi 10 ean mixes increase te
Son delay and eave severe yee vais. Te hykogen proxies preset in he exaust
[roduc of hydrogen cl engine operating wi ey Ian mixes,
Compare with ydrocaon Fl, drogen has cain vantages de tit high chemical
fact. (9) a higher ane propagan see, denon i, and (lowes ol
caer Te high fame propagation sped of hydrogen extant benefit the temod pam
Eine) 0 the engine the combustion pres ls ser the optimum Lorca om
Gon corsa ale. The mide pio ts provide pos lore tee ean
tres lower ¡un nergy i favourable or nin oa mies in Sis bt hat
Be dsadvatage o sulin nomma combustion (ck and surface nio) espec nar
oichiomecy.
Because Socie must be avoided at al co, ts necessary to voi ka and surface
igo. This can be doe ylang th mint. Since hs eee the salle poe a ue
Soule ie cig ado of ur so o cons y rc oe
travel sane, Ti canbe don y losing he spark poy eee pic) away fom
the centre of the cylinder head. E nn Prison away
Omar storage o hydagen remis a major technical challenge. As a gs, drogen hs a
very low ne ds. This as to age tank ie even wit high presu soe and shot
‘eb range Sevinghydogeninlgud fom sss probate ast gus 233 0 Songe
oftyerogen may be shieved by sold state bade rage mae, ui tyes, copes
sphere tage, storage arte, sage oles, an sir sch rage
“he prope of hyogen, sta go (metan) and sole ar Come in Table 82.
8.6 FUELS FOR SI ENGINES
‘The performance of the spack-ignition engine depends upon the following fuel characterises,
which are of importance: (a) volatility, () sulphur contents, () gum deposits, (d) carburettor
detergent additives, and (e) antknock quality.
1240_ Fandamenal of Internal Comborion Engine
Fuel for IternalCombunion Engines 241
Table
Properties of hydrogen, methane and gasoline
Property Hydrogen Methane
Molecular weight 2016 1608
Heat of combustion (low), Mg 11993 sam
Specific ea, cy at NTP, Kg R) 1489 22
Viscosiy at NTR, gen =? 00000875 00011
Specific het rato at NTP 1389 1308 105
Gas constant R, 2908 KD an os oom
Difusion coefficient in ai, emt os 016 oo
Lit of fammabity inal, vol % 400750 536150 10076
Stoichiometric composition in ai, vol % BS 948 126
Minimum energy for ignition ar oo 0 0%
‘Autoignition temperature, K se a um
Flame tempertar init, K Et zu 270
Burning velocity in air at NTP, em. 26510325, 371045 331047
TICENG (compres aa 9) as in snout fm tas component, e burg voii
ower ta a fo piste. None of be Ber proper asic depende o he nat oro
ts atar a LNG (hued uta) a ce meee.
8.6.1 Volatility of Liquid Fuels
Volt is the tendency of liquid o evaporate at given conditions. Petroleum fuels consist of à
Large numberof different hydrocarbons, each having a diferent boiling paint. Hence, upon heating
a gasoline of fuel ol, it is observed that all ofthe Liquid does not pas to the vapour phase atone
temperanic, as isthe case when water is heated a constant pressure, Instead, a small percentage
of te fuel will vaporize at a low temperature, and a much higher temperature must be reached
before the fuel completely vaporizes. Volatility characteristics of fuels can be obtained by the
following tests
ASTM distillation test
“The relative volatility of fuels is ordinarily measured by means ofthe ASTM (American Society for
“Testing Materials) distillation test. The apparatus used is shown in Figure 8.3. Heat is supplied 10
the flask, which contains 100 ml of the fuel. The vapours pass through the condenser mabe, which
is surrounded by cracked ice, and the condensate drips into the graduated receiver where the
‘quantity of condensed fuel is measured
on the thermometer is taken atthe time the first drop of the condensate appears.
‘This temperature i known asthe inl boiling point of the fuel. Subsequent temperature read
ings are taken as each additional 10% ofthe fuel is evaporated. The final temperatur required to
evaporate the liquid completely is called the end point temperature.
However, itis found that not al ofthe fuel is really driven from the Mask, even though the flask
appears tobe empty, anda residue will condense upon cooling Its also found that a portion ofthe
fuel has unavoidably escaped. Since the sum ofthe condensed portion andthe residue will noc total
ee
hu
Fume ASTM taa,
the original amount, the portion of ie fuel hat has unavoidably escaped is called as. His abi-
‘warily assumed that the loss represents the most volatile pat of the fuel and therefore occurs at the
very start ofthe distilstion. Typical resus ofthe ASTM distltion test of several products of
petroleum refining are given in Figure 84,
a IE
cc empre
Posta, “ips cts Pm ds rer ss
fon gesoine; 7, alcohol 8, banzene, i
|
Fuel for IternalCombunion Engines 241
Table
Properties of hydrogen, methane and gasoline
Property Hydrogen Methane
Molecular weight 2016 1608
Heat of combustion (low), Mg 11993 sam
Specific ea, cy at NTP, Kg R) 1489 22
Viscosiy at NTR, gen =? 00000875 00011
Specific het rato at NTP 1389 1308 105
Gas constant R, 2908 KD an os oom
Difusion coefficient in ai, emt os 016 oo
Lit of fammabity inal, vol % 400750 536150 10076
Stoichiometric composition in ai, vol % BS 948 126
Minimum energy for ignition ar oo 0 0%
‘Autoignition temperature, K se a um
Flame tempertar init, K Et zu 270
Burning velocity in air at NTP, em. 26510325, 371045 331047
TICENG (compres aa 9) as in snout fm tas component, e burg voii
ower ta a fo piste. None of be Ber proper asic depende o he nat oro
ts atar a LNG (hued uta) a ce meee.
8.6.1 Volatility of Liquid Fuels
Volt is the tendency of liquid o evaporate at given conditions. Petroleum fuels consist of à
Large numberof different hydrocarbons, each having a diferent boiling paint. Hence, upon heating
a gasoline of fuel ol, it is observed that all ofthe Liquid does not pas to the vapour phase atone
temperanic, as isthe case when water is heated a constant pressure, Instead, a small percentage
of te fuel will vaporize at a low temperature, and a much higher temperature must be reached
before the fuel completely vaporizes. Volatility characteristics of fuels can be obtained by the
following tests
ASTM distillation test
“The relative volatility of fuels is ordinarily measured by means ofthe ASTM (American Society for
“Testing Materials) distillation test. The apparatus used is shown in Figure 8.3. Heat is supplied 10
the flask, which contains 100 ml of the fuel. The vapours pass through the condenser mabe, which
is surrounded by cracked ice, and the condensate drips into the graduated receiver where the
‘quantity of condensed fuel is measured
on the thermometer is taken atthe time the first drop of the condensate appears.
‘This temperature i known asthe inl boiling point of the fuel. Subsequent temperature read
ings are taken as each additional 10% ofthe fuel is evaporated. The final temperatur required to
evaporate the liquid completely is called the end point temperature.
However, itis found that not al ofthe fuel is really driven from the Mask, even though the flask
appears tobe empty, anda residue will condense upon cooling Its also found that a portion ofthe
fuel has unavoidably escaped. Since the sum ofthe condensed portion andthe residue will noc total
ee
hu
Fume ASTM taa,
the original amount, the portion of ie fuel hat has unavoidably escaped is called as. His abi-
‘warily assumed that the loss represents the most volatile pat of the fuel and therefore occurs at the
very start ofthe distilstion. Typical resus ofthe ASTM distltion test of several products of
petroleum refining are given in Figure 84,
a IE
cc empre
Posta, “ips cts Pm ds rer ss
fon gesoine; 7, alcohol 8, banzene, i
|
242 Fundamanalsof internal Combustion Engines
Fels fr ItemalCombuion Engnes 243
Equilibrium air distillation (EAD) test
lu the ASTM disiltion test the liquid ful evaporates in the presence of fuel vapour. In IC
engines, the fuel s evaporaed in the presence of at, and a greater percentage of the fel wll be
vaporatd a given temperature then is indicated by th standard ASTM results. The EAD test
nay be used to obtain more secure information concerning the actual volatility characteristics of
the foes in use. o Ñ
Comparisons of characteristics of average summer and winter premium gasoline, as
determined by the ASTM distillation test and the BAD test for 16:1 airfuel ratos, are made in
Figure 8. It is easier and quicker to conduct tke ASTM test, hence itis performed more often
‘andthe EAD temperatures are computed from the ASTM data with the help of suitable chars,
200
ASTM tien —/
sp Sure
Wiser:
E
Temper °C)
s= 3
a
CAC
Parcent evaponted
‘gut Ss Company chro ene serma an ita prism gasses atomic y he ATH
aEADss,
Reld vapour prossure bomb
A affords another method for measuring the volalicy characteristic of a fuel. Figure 86 shows
the Reid vapour pressure bomb. In conducting this test, a sample of 100 ml of fuel is sealed inthe
bomb and the instrumentisimmersed in a 38°C water bath, A
potion ofthe fuel, which vapories, rise into the ar cham-
ber above the fuel. The increas in pressure in the ar ham
bes is measured by a pressure gauge. The vapour pressure in
{he air chamber is reported as Ihe Reid vapour pressure ofthe
fuel,
862 Effect of Vol
SI Engines
ity on the Performance of
Disilltion curves shown in Figure 85 can be divided into
three portions (a) Front-end volatility: it covers 0 ta 20% of
volatility of fuel, (9) mid-range: 1 covers 20 10 80% of vola-
‘ity, and (e) til-end:iveovers 8010 100% of volatility.
Frontend volatility
‘The following important performance characteristics are
affected by he first part of volatility
Cold starting: Inthe winter and in the cold climate, an ai
vapour mixture of about 13:1 is required for easy starting in
less than 10 revolutions). This ratio can be obtained in the
engine by choking the carburetor and so restectng the inet.
flow of air. the carburetor delivers a 1.3: aefuel aio and
10% of the fue vapories, the desired 13:1 airvapour ratio
willbe obtained, Hs therefore desirable to have a relatively
low evaporation temperature of the front-end of he fuel, so — POWEBS, Pldvapourpracien tomb,
that almost 10% of the total fuel evaporates as quickly as posible,
Hot starting: Ifthe engine is stated immediately after a hot shutdown, the amount of fuel
vapours entering the intake manifold will be high, andthe mixture formed in the combustion
chamber wil be 100 rich to ignite. create the problem of hot starting. In order to avoid tis ot
ing problem especially on hor days, volatility temperature ofthe fist portion of the fue should
be high. This requicement is opposite to the equirement of cold starting. Therefore, iis a normal
practice to use less volatile gasoline in summer than that used in winter. The problem of hot
Starting can be avoided by proper design and proper placement of the fuel system. The fuel system
should be placed away from the hot engine pans. The use of an electrical pump helps in piscing
‘the pump andthe fuel lines away from the hot engine pars and thus in reducing the problem of hot
starting.
Vapour lock: Vapour lock is the restriction of the fue supply to the engine caused by exces-
sively rapid formation of vapour in the fuel supply system or earburttor The vapour will occupy
A greater volume than Ue liquid and therefore, che amount of fuel Bow to the engine will be
reduced, causing los in power or else complete stoppage ofthe engine. The possibilty of vapour
Lock increases with highly volatile fuels related ro the front-end volatility and by the exposure of
the fuel to either high temperatures or low pressures in the fuel system
Fels fr ItemalCombuion Engnes 243
Equilibrium air distillation (EAD) test
lu the ASTM disiltion test the liquid ful evaporates in the presence of fuel vapour. In IC
engines, the fuel s evaporaed in the presence of at, and a greater percentage of the fel wll be
vaporatd a given temperature then is indicated by th standard ASTM results. The EAD test
nay be used to obtain more secure information concerning the actual volatility characteristics of
the foes in use. o Ñ
Comparisons of characteristics of average summer and winter premium gasoline, as
determined by the ASTM distillation test and the BAD test for 16:1 airfuel ratos, are made in
Figure 8. It is easier and quicker to conduct tke ASTM test, hence itis performed more often
‘andthe EAD temperatures are computed from the ASTM data with the help of suitable chars,
200
ASTM tien —/
sp Sure
Wiser:
E
Temper °C)
s= 3
a
CAC
Parcent evaponted
‘gut Ss Company chro ene serma an ita prism gasses atomic y he ATH
aEADss,
Reld vapour prossure bomb
A affords another method for measuring the volalicy characteristic of a fuel. Figure 86 shows
the Reid vapour pressure bomb. In conducting this test, a sample of 100 ml of fuel is sealed inthe
bomb and the instrumentisimmersed in a 38°C water bath, A
potion ofthe fuel, which vapories, rise into the ar cham-
ber above the fuel. The increas in pressure in the ar ham
bes is measured by a pressure gauge. The vapour pressure in
{he air chamber is reported as Ihe Reid vapour pressure ofthe
fuel,
862 Effect of Vol
SI Engines
ity on the Performance of
Disilltion curves shown in Figure 85 can be divided into
three portions (a) Front-end volatility: it covers 0 ta 20% of
volatility of fuel, (9) mid-range: 1 covers 20 10 80% of vola-
‘ity, and (e) til-end:iveovers 8010 100% of volatility.
Frontend volatility
‘The following important performance characteristics are
affected by he first part of volatility
Cold starting: Inthe winter and in the cold climate, an ai
vapour mixture of about 13:1 is required for easy starting in
less than 10 revolutions). This ratio can be obtained in the
engine by choking the carburetor and so restectng the inet.
flow of air. the carburetor delivers a 1.3: aefuel aio and
10% of the fue vapories, the desired 13:1 airvapour ratio
willbe obtained, Hs therefore desirable to have a relatively
low evaporation temperature of the front-end of he fuel, so — POWEBS, Pldvapourpracien tomb,
that almost 10% of the total fuel evaporates as quickly as posible,
Hot starting: Ifthe engine is stated immediately after a hot shutdown, the amount of fuel
vapours entering the intake manifold will be high, andthe mixture formed in the combustion
chamber wil be 100 rich to ignite. create the problem of hot starting. In order to avoid tis ot
ing problem especially on hor days, volatility temperature ofthe fist portion of the fue should
be high. This requicement is opposite to the equirement of cold starting. Therefore, iis a normal
practice to use less volatile gasoline in summer than that used in winter. The problem of hot
Starting can be avoided by proper design and proper placement of the fuel system. The fuel system
should be placed away from the hot engine pans. The use of an electrical pump helps in piscing
‘the pump andthe fuel lines away from the hot engine pars and thus in reducing the problem of hot
starting.
Vapour lock: Vapour lock is the restriction of the fue supply to the engine caused by exces-
sively rapid formation of vapour in the fuel supply system or earburttor The vapour will occupy
A greater volume than Ue liquid and therefore, che amount of fuel Bow to the engine will be
reduced, causing los in power or else complete stoppage ofthe engine. The possibilty of vapour
Lock increases with highly volatile fuels related ro the front-end volatility and by the exposure of
the fuel to either high temperatures or low pressures in the fuel system
244_ Fundamentals of Internal Combustion Engines
us for mark Combustion Engnes 245
In orderto avoid vapour lock, he fuel lines, the pump and he carburettor shouldbe placed in
relatively cool regions and not exposed o radiated heat rom the engine and exhaus pipes. These
par should be cooled by the flow of air from the fan
Evaporation loss: Vaporization and loss of te lighter fractions of gasoline from the fuel tank
and the carburetor occur a all mes. The evaporation loss depends onthe vapour pressure ofthe
fuel a the storage temperature. I decreases the fuel economy and the anti-Enock quality of the
fue, since te lighter fractions have higher anirknoek properties. The evaporation los is related
10 10% ASTM distillation temperature. The front-end volatility temperature should be higher 10
reduce evaporation in order 1 reduce evaporation loss and vapour lock
‘Mid-range volatility
‘Warm-up and acceleration: After the engine has been started, a warm-up period of the engine
begins. Daring this period, engine temperatures gradually increase to those of normal operation at
which engine accelerates smoothly from a given speed. The warm-up period is ofcourse influ-
‘enced by the design ofthe engine in quickly securing a minimum mixture temperature but the ease
‘of relatively warming-up the given designed engine depends upon the volasicy ofthe fl. War
vp performance is controlled 1 a large extent bythe mid-range of tke distillation curve (S0-70%
portion and to a esse extent by the front and tail end. The warm-up period wil be shorter if the
‘whole range of temperatures on the ASTM curve is lower,
Carburettor icing: Carburetor icing is formed due tothe vaporization of gasline into the sr
‘containing water vapour. This results in a rapid drop in temperature of the srfvel mixture and that of
the carburetor parts, and consequently, under some condition, ie is formed on the ero blade,
Under ling conditions the ie slides down the throne biade and resricts the passage, preventing
the flow of mixture past the thot, thereby causing the engine to run slower and to sl.
Carburetor icing can be prevented by the use of less volatile fuels. Kean also be reduced
by using ani-icing additives with Volatile gasolnes. Two types of antiicing additives have been
‘used: frezing-poict depressans, such as isopropyl alcohol or methyl alcohol (1 10 2%), and
surface-active materials, which coat the meal surface with à il, thus minimizing the tendency
of ice to edhere Lo the surfaces
Short and long trip economy: In short driving the warm-up period is quite significant, For
‘efficient operation and greater economy, it require a fuel having relatively more volatility in the
mid-range section of distillation. In Jong-tp driving the warm-up period is insigifiant compared to
{otal deving. A gasoline having higher density wil give more kilometres per linen warm-upengine.
Talend volatility
Crankcase dilution: Liquid gasoline in the cylinder is undesirable, since it washes away the
lubricating ol from the cylinder walls. le reduces lubrication and tends to increase the fiction
between the piston rings and the cylinder, thus causing damage to the engine. The degree of
crankcase oil dilution is direct related tothe ti-ead volatliy temperatures of the mixture. The
90% temperatures of the ASTM and EAD distilations evaluate the dilution tendency ofthe fuel;
the lower the temperature ofthe 90% point (the more volatile the tier portion of Fel, theless
willbe the dilution ofthe crankcase oil, assuming that almost ll ofthe gasoline inthe eyinder will
be vaporized.
Engines using heavy fuels, such as kerosene, being les volatile, may suffer from poor lubri-
cation because of excessive dilation.
Sludge deposits: Certain types of hydrocarbons present in gasoline may not evaporate even
during the taitend evaporation, due to very high evaporation temperature and may leave slide
‘deposits inside the engine. These deposits may cause sticking of piston sings and valves, thus
resulting in poor operation, It may also cauce spark plug fouling. The lower the tai-cnd volaity
temperature, the less willbe the chance of sludge deposits,
86.3 Sulphur Content
High sulphur content in gasoline in the form of fee sulphur, hydrogen sulphide and other sulphur
‘compounds is undesiabie because of the formation of SO, whose combination wth water vapour
forms HSO,, whichis a very corosive substance that may atack varios parts ofthe engine
Aus affecting engine performance and life. Since sulphur has a low ignition temperature, the
presence of sulphur can reduce the sel-igition temperature of the fuel, an thus promote knock
in Sl engines, Consequently, the gasoline specifications limit the permisible quantity of sulphur
which may be present. Sulphur contents les than 0,1% are demanded for gasolines used in St
engines
864 Gum Deposits
Reactive hydrocarbons and impurities inthe fuel have a tendency to oxidize and form viscous
liquids and solid called gum. I deteriorates the gasoline during the long period of storage at high
ambient temperatures, The pure stable hydrocarbons of the paraffin, naphthene, and aromatic
families form inte gum, while racked gasolines form considerable amount of gum. A gasoline
with high gum content will cause operating dificuldes, such as sticking valves and piston rings,
carbon deposits in the engine, gum deposits in the manifold, clogging of carburetor jets and
Incquering (varnish appearing residue) of the valve stems, the eylinders and pistons. Sticking of
‘he inlet valve and formation of gum deposis in he intake manifold reduce volumetic efficiency
great.
‘The amount of gum increases with increased concentrations of oxygen, with the rise in
temperature, with exposure 10 sunlight and also on contact with metals, In storing fuels, these
factors should be kept in mind,
Inhibitors of gum deposits are almost invariably added to thermally cracked gasoline in order
to ensure stbili Cetin dyes can be added to colour the gasoline, and alo to inhibit the formation
of gum, Such inhibitors have preference for oxidization over gasoline and he activity ofthe inhibitor
decreases. This fades the colour of the gasoline, Thus, the loss of colour ofthe gasoline may be an
indication of the age or exposure ofthe fuel to gum-forming conditions. Gasoline specifications
(&erefore limit both the gum content ofthe fuel and is tendency to form gum during storage.
86.5 Carburettor Detergont Additives
‘The intake manifold and carburetor deposit may result from irbome contaminants, from gums
content in the gasoline, from incomplete combustion products and crankease vapours, These
deposit restrict the flow of charge past the throtle plate, especialy inthe ile postion, thus
‘causing rough idling and stating.
us for mark Combustion Engnes 245
In orderto avoid vapour lock, he fuel lines, the pump and he carburettor shouldbe placed in
relatively cool regions and not exposed o radiated heat rom the engine and exhaus pipes. These
par should be cooled by the flow of air from the fan
Evaporation loss: Vaporization and loss of te lighter fractions of gasoline from the fuel tank
and the carburetor occur a all mes. The evaporation loss depends onthe vapour pressure ofthe
fuel a the storage temperature. I decreases the fuel economy and the anti-Enock quality of the
fue, since te lighter fractions have higher anirknoek properties. The evaporation los is related
10 10% ASTM distillation temperature. The front-end volatility temperature should be higher 10
reduce evaporation in order 1 reduce evaporation loss and vapour lock
‘Mid-range volatility
‘Warm-up and acceleration: After the engine has been started, a warm-up period of the engine
begins. Daring this period, engine temperatures gradually increase to those of normal operation at
which engine accelerates smoothly from a given speed. The warm-up period is ofcourse influ-
‘enced by the design ofthe engine in quickly securing a minimum mixture temperature but the ease
‘of relatively warming-up the given designed engine depends upon the volasicy ofthe fl. War
vp performance is controlled 1 a large extent bythe mid-range of tke distillation curve (S0-70%
portion and to a esse extent by the front and tail end. The warm-up period wil be shorter if the
‘whole range of temperatures on the ASTM curve is lower,
Carburettor icing: Carburetor icing is formed due tothe vaporization of gasline into the sr
‘containing water vapour. This results in a rapid drop in temperature of the srfvel mixture and that of
the carburetor parts, and consequently, under some condition, ie is formed on the ero blade,
Under ling conditions the ie slides down the throne biade and resricts the passage, preventing
the flow of mixture past the thot, thereby causing the engine to run slower and to sl.
Carburetor icing can be prevented by the use of less volatile fuels. Kean also be reduced
by using ani-icing additives with Volatile gasolnes. Two types of antiicing additives have been
‘used: frezing-poict depressans, such as isopropyl alcohol or methyl alcohol (1 10 2%), and
surface-active materials, which coat the meal surface with à il, thus minimizing the tendency
of ice to edhere Lo the surfaces
Short and long trip economy: In short driving the warm-up period is quite significant, For
‘efficient operation and greater economy, it require a fuel having relatively more volatility in the
mid-range section of distillation. In Jong-tp driving the warm-up period is insigifiant compared to
{otal deving. A gasoline having higher density wil give more kilometres per linen warm-upengine.
Talend volatility
Crankcase dilution: Liquid gasoline in the cylinder is undesirable, since it washes away the
lubricating ol from the cylinder walls. le reduces lubrication and tends to increase the fiction
between the piston rings and the cylinder, thus causing damage to the engine. The degree of
crankcase oil dilution is direct related tothe ti-ead volatliy temperatures of the mixture. The
90% temperatures of the ASTM and EAD distilations evaluate the dilution tendency ofthe fuel;
the lower the temperature ofthe 90% point (the more volatile the tier portion of Fel, theless
willbe the dilution ofthe crankcase oil, assuming that almost ll ofthe gasoline inthe eyinder will
be vaporized.
Engines using heavy fuels, such as kerosene, being les volatile, may suffer from poor lubri-
cation because of excessive dilation.
Sludge deposits: Certain types of hydrocarbons present in gasoline may not evaporate even
during the taitend evaporation, due to very high evaporation temperature and may leave slide
‘deposits inside the engine. These deposits may cause sticking of piston sings and valves, thus
resulting in poor operation, It may also cauce spark plug fouling. The lower the tai-cnd volaity
temperature, the less willbe the chance of sludge deposits,
86.3 Sulphur Content
High sulphur content in gasoline in the form of fee sulphur, hydrogen sulphide and other sulphur
‘compounds is undesiabie because of the formation of SO, whose combination wth water vapour
forms HSO,, whichis a very corosive substance that may atack varios parts ofthe engine
Aus affecting engine performance and life. Since sulphur has a low ignition temperature, the
presence of sulphur can reduce the sel-igition temperature of the fuel, an thus promote knock
in Sl engines, Consequently, the gasoline specifications limit the permisible quantity of sulphur
which may be present. Sulphur contents les than 0,1% are demanded for gasolines used in St
engines
864 Gum Deposits
Reactive hydrocarbons and impurities inthe fuel have a tendency to oxidize and form viscous
liquids and solid called gum. I deteriorates the gasoline during the long period of storage at high
ambient temperatures, The pure stable hydrocarbons of the paraffin, naphthene, and aromatic
families form inte gum, while racked gasolines form considerable amount of gum. A gasoline
with high gum content will cause operating dificuldes, such as sticking valves and piston rings,
carbon deposits in the engine, gum deposits in the manifold, clogging of carburetor jets and
Incquering (varnish appearing residue) of the valve stems, the eylinders and pistons. Sticking of
‘he inlet valve and formation of gum deposis in he intake manifold reduce volumetic efficiency
great.
‘The amount of gum increases with increased concentrations of oxygen, with the rise in
temperature, with exposure 10 sunlight and also on contact with metals, In storing fuels, these
factors should be kept in mind,
Inhibitors of gum deposits are almost invariably added to thermally cracked gasoline in order
to ensure stbili Cetin dyes can be added to colour the gasoline, and alo to inhibit the formation
of gum, Such inhibitors have preference for oxidization over gasoline and he activity ofthe inhibitor
decreases. This fades the colour of the gasoline, Thus, the loss of colour ofthe gasoline may be an
indication of the age or exposure ofthe fuel to gum-forming conditions. Gasoline specifications
(&erefore limit both the gum content ofthe fuel and is tendency to form gum during storage.
86.5 Carburettor Detergont Additives
‘The intake manifold and carburetor deposit may result from irbome contaminants, from gums
content in the gasoline, from incomplete combustion products and crankease vapours, These
deposit restrict the flow of charge past the throtle plate, especialy inthe ile postion, thus
‘causing rough idling and stating.
1246. Fundamentals of cereal Combustion Engines
Fl for Iyer Cambastion Engines 247.
Many gasolines now contain detergent additives to prevent the formation of these deposits
and to remove the existing deposits. Alphanaphihol is used asantoxidant additive to control the
‘oxidation of fuels
86.6 Anti-knock Quality ÿ
Detonation in SL engine causes à very rapid and uncontrolled burning ofthe fuel and ai mixture in
cylinder and his results in an abnormally rapid pressure rise. This sets up vibrations of the gases,
the cylinder walls, and other metalic surfaces giving a distinct krack or noise, Therefore, the
‘hazacterstic ofthe fuel shouldbe such thatthe knocking tendeney is resisted, and this property
fuel called the anti-knock quality. The ami Knock quality ofa el depends onthe selFignition
temperature of the fel andthe chain reaction mechanisms by wäjch the fuel bums. À liquid such
ds isooctane exhibits very smooth buming characteristics. In contrast with this, the longer chain
Compound, normal heptane displays a very strong, tendency towards detonation, In general, the
est St engine fuel willbe that which has the highest ant-knock property, since this permits the
tse of higher compression ratios, resulting in higher thermal efficiency and power output.
8.7 FUELS FOR CI ENGINES
Most CI engine fuels are obtained in the fractions of crudo peoleur near kerosene and gas o
“These fuels are heavier and more viscous than the gasoline used in the SI engine. Some of the
imporant characteristics of CI engine fuels are: (2) ignition quality, (2) volatility () viscosity,
(8) gravity, (6) comosion and wear, (9 handling ease, () safety, and (9) cleaniness
874 Ignition Quality
“The ignition quality of a fuel is one ofthe most important characteristics. I Is a measure of ability
‘of fuel to ignite promptly ater injection, thus ensuring a progressive smooth buraing and easy
‘tating. The ignition quality is measured in terms of he delay period, which is the apse of time
between the beginning of injection and the ignition ofthe fuel showing the appearance of an
sppreciale pressure rise. The ignition quality is beter wih a shorter delay period. In lager, low
Speed engines the delay is not so noticeable and the usual fuels give a satisfactory performance. In
smaller, high-speed engines short delay is very imposant.
"A fuel vith a lower self ignition temperature vil igite more quickly when injected into the
combustion chamber than the one with a higher self-gnition temperature, The desired chemical
Structure for Cl engine fuels is opposite to that desirable for SU engine. The best fuels fr the CI
‘engine ee swraighechain paraffins with average molecular weights greater than those of the
fusolines. The rating of diesel fuels is given by the ceane number. À fuel with a higher cetane
Arabes gives better ignition quality in CT engines. The ignition quality of CI engine fuels can be
{proved by certain additives. Te ignition quality ofa CI engine fuel has a marked influence on
cold staring, engine roughness, and compression ratio.
Cold starting
Diesel fuels are les volatile und more viscous then gasoline. Because of these properties the
formation of a combustible mixture daring cold stating becomes difficult I order tat the fuel
should star the cold engine easily, high eetane cating of the fuel is required, Tt reduces the sel
ignition teraperatre.
‘Volatile fuels, such as ether, have been found to reduce the delay period and cold starting
becomes easier when a small amount of itis introduced with the itake air
Engine roughness
ie nes of ren of varios engine pani the meas of
a esse of engine rones, which
cad mph tof pes in de combs cant As ete Pte cee
the maxim rato of pesos rie decrees, cine in reduced engines fons À high
(sine numbers sly ss Imporan ode vided combuson chamber pe of Cl engine ten
ttt open chamber pe The cun number salvo ls porn fo fw sped large ind,
since only a small fraction ofthe fuel is bored during the rapid pressure rise period compared to
ati thigh sped mat ender
‘Compression ato
The rai is normally ket low inondr o avi excessive rs
119 aid excesvely high oder press,
which vil fact easy string, WA he res n scan numberof he Al, non
ana improves ad o compresion ato can be lowered without fing de kocking problem
inClengines.
17.2 Volatility
ecole ful usd CI engines cover a ide range vol, The ange of olay o
Enge el er lower olay compare othe ange ol vol LS ne ul High
‘olay its are general ot wen CI eninen, pay Because of te ig demand for high
volt fel for engine us in als and party becas of poration qualit.
Nellis as se spy shanties and
may affect both power and efficiency. Increase in 40,
Ni nes te rate of emporio fe
And enc the ae of ising of fel and sie Te 0
fol sold be sie volt inthe opting
Temperatur rango to produc good mixin and
<ombusion and hus reduce obetoabe eke
Sd don isthe ems gases, The salle Re
Speed engines require rai evaporation ofthe
tnd onen shoul ave fs wi move of 200
the ow bling and es of de igh boli con
rien compared wi the wie Comet e 59
Ste by te lng Tow-pecd engines, The
ASTM lian con of «pa ese fas
presen in Figure 8
300
20
Tenpastr °C)
(mr Tu ur E
Per centre
Figure ASTM pl dst
8.73 Viscosity
sony ef the ado o ering sess ina Md othe ra of shear gala efoma.
tion, nd mess of te estan ad on an inponanı haare at
the mization of fst end operation al de high pres eel pumps
Fl for Iyer Cambastion Engines 247.
Many gasolines now contain detergent additives to prevent the formation of these deposits
and to remove the existing deposits. Alphanaphihol is used asantoxidant additive to control the
‘oxidation of fuels
86.6 Anti-knock Quality ÿ
Detonation in SL engine causes à very rapid and uncontrolled burning ofthe fuel and ai mixture in
cylinder and his results in an abnormally rapid pressure rise. This sets up vibrations of the gases,
the cylinder walls, and other metalic surfaces giving a distinct krack or noise, Therefore, the
‘hazacterstic ofthe fuel shouldbe such thatthe knocking tendeney is resisted, and this property
fuel called the anti-knock quality. The ami Knock quality ofa el depends onthe selFignition
temperature of the fel andthe chain reaction mechanisms by wäjch the fuel bums. À liquid such
ds isooctane exhibits very smooth buming characteristics. In contrast with this, the longer chain
Compound, normal heptane displays a very strong, tendency towards detonation, In general, the
est St engine fuel willbe that which has the highest ant-knock property, since this permits the
tse of higher compression ratios, resulting in higher thermal efficiency and power output.
8.7 FUELS FOR CI ENGINES
Most CI engine fuels are obtained in the fractions of crudo peoleur near kerosene and gas o
“These fuels are heavier and more viscous than the gasoline used in the SI engine. Some of the
imporant characteristics of CI engine fuels are: (2) ignition quality, (2) volatility () viscosity,
(8) gravity, (6) comosion and wear, (9 handling ease, () safety, and (9) cleaniness
874 Ignition Quality
“The ignition quality of a fuel is one ofthe most important characteristics. I Is a measure of ability
‘of fuel to ignite promptly ater injection, thus ensuring a progressive smooth buraing and easy
‘tating. The ignition quality is measured in terms of he delay period, which is the apse of time
between the beginning of injection and the ignition ofthe fuel showing the appearance of an
sppreciale pressure rise. The ignition quality is beter wih a shorter delay period. In lager, low
Speed engines the delay is not so noticeable and the usual fuels give a satisfactory performance. In
smaller, high-speed engines short delay is very imposant.
"A fuel vith a lower self ignition temperature vil igite more quickly when injected into the
combustion chamber than the one with a higher self-gnition temperature, The desired chemical
Structure for Cl engine fuels is opposite to that desirable for SU engine. The best fuels fr the CI
‘engine ee swraighechain paraffins with average molecular weights greater than those of the
fusolines. The rating of diesel fuels is given by the ceane number. À fuel with a higher cetane
Arabes gives better ignition quality in CT engines. The ignition quality of CI engine fuels can be
{proved by certain additives. Te ignition quality ofa CI engine fuel has a marked influence on
cold staring, engine roughness, and compression ratio.
Cold starting
Diesel fuels are les volatile und more viscous then gasoline. Because of these properties the
formation of a combustible mixture daring cold stating becomes difficult I order tat the fuel
should star the cold engine easily, high eetane cating of the fuel is required, Tt reduces the sel
ignition teraperatre.
‘Volatile fuels, such as ether, have been found to reduce the delay period and cold starting
becomes easier when a small amount of itis introduced with the itake air
Engine roughness
ie nes of ren of varios engine pani the meas of
a esse of engine rones, which
cad mph tof pes in de combs cant As ete Pte cee
the maxim rato of pesos rie decrees, cine in reduced engines fons À high
(sine numbers sly ss Imporan ode vided combuson chamber pe of Cl engine ten
ttt open chamber pe The cun number salvo ls porn fo fw sped large ind,
since only a small fraction ofthe fuel is bored during the rapid pressure rise period compared to
ati thigh sped mat ender
‘Compression ato
The rai is normally ket low inondr o avi excessive rs
119 aid excesvely high oder press,
which vil fact easy string, WA he res n scan numberof he Al, non
ana improves ad o compresion ato can be lowered without fing de kocking problem
inClengines.
17.2 Volatility
ecole ful usd CI engines cover a ide range vol, The ange of olay o
Enge el er lower olay compare othe ange ol vol LS ne ul High
‘olay its are general ot wen CI eninen, pay Because of te ig demand for high
volt fel for engine us in als and party becas of poration qualit.
Nellis as se spy shanties and
may affect both power and efficiency. Increase in 40,
Ni nes te rate of emporio fe
And enc the ae of ising of fel and sie Te 0
fol sold be sie volt inthe opting
Temperatur rango to produc good mixin and
<ombusion and hus reduce obetoabe eke
Sd don isthe ems gases, The salle Re
Speed engines require rai evaporation ofthe
tnd onen shoul ave fs wi move of 200
the ow bling and es of de igh boli con
rien compared wi the wie Comet e 59
Ste by te lng Tow-pecd engines, The
ASTM lian con of «pa ese fas
presen in Figure 8
300
20
Tenpastr °C)
(mr Tu ur E
Per centre
Figure ASTM pl dst
8.73 Viscosity
sony ef the ado o ering sess ina Md othe ra of shear gala efoma.
tion, nd mess of te estan ad on an inponanı haare at
the mization of fst end operation al de high pres eel pumps
248. Fundamental of nera! Comberton Engines
ul for Inena.Combunden Engines 249
‘The si eins wih be ners in he nambe o carbon som in e dere
are emo numberof carbon sons In wo hydrocarbons, the one with th ower number of
Iago content wi have a higher vico, The ii el où decease ply wi te
“oe time en forthe fw of a ive on of i sgh andar ce under he
acia of gravity is th ease of de OM fh il Te standar est pp sd 10
Sstermine the vacant a ol ithe Sabo Univeral (SU) coser À rein of
Say viscosity tx aparatos show in Figure 88, The viscosity soporte as Supt
Universal Seconds (SUS) at the temps he st The vicaıy in SUS may Become o
Shoe or nema viscosity y als ale for pupa.
ES
Fgue8# Cs sedonel Sebo viscose appara
‘The scsi) ff rat Ines he yy caracteres. High vino cases ow
stomization (large-sized droplets and high penetration of he spray je. In small combustion cham-
bers, the effect of viscosity is cnica, hence the maximum and minimum values suitable forthe
engine should be specified. In cold engines, a high viscous oil may cause starting problems and
also a smoky exhaust may appear. Ifthe viscosity ofthe fue slow, eakage past the piston in he
pump will be increased. The Inbricating qualities of low-viscosity fuels are poor, hus resulting in
‘The SU viscosity required for most high-speed engines ranges between 35 and 70 at 37.8°C
(QOO"F). As viscosity changes rapidly with temperature, just a numerical value of viscosity has no
significance unless he temperatur is specified
87.4 Specific Gravity
‘The specific gravity is defined as the mass ofa unit volume of Aid to that of the same volume of
water preferably atthe same temperature (say 156"C). It is commonly designated as "spa.
15.6/15.6°C", indicating that both the ol and the water are weighed and measured ats temperature
of 15.6°C (60°F)
‘The oil industry uses a scale adopted by the American Petroleum Institute (APD for measur-
ing the relative density of fuels, giving eadings in degrees API. The relation between the specific
gravity and the API gravity is given by
1a
pr
API gravity in degrees) 1315
‘Thus a light fuel, which has a tow specific gravity, has a higher API gravity. Limiinions
imposed by viscosity limits on CI engines more or less confine the limits of specific gravity to
about 083 10.090 or 39° 10 26° APL
2.7.5 Corrosion and Wear
‘The fuel shouldbe such tha it should nor cause corrosion and wear before and after combus
In order o avoid corrosion and wear, te fuel shoulé not contain much sulphur, ash and carbon
residue,
‘Sulphur
‘The percentage of sulphur in diesel il is higher than that in gasoline, The wear and fouling tat
«arise from sulphur in he fuel result fom the formation of SO), during the combustion process,
‘ue t combination of sulphur with tage amount of excess ar. The SO, may attack the lubricating
oil on the cylinder walls to form resinous materials which harden to form varnish and carbon. It
‘may also react with wate to form sulphuric acid. Wear is caused due to acidic comosion and due
to abrasion withthe carbonaceous material, This condition is expecially bad whea the combustion
Products are cooled enough to condense some ofthe Water vapour. In ths case excessive coro.
sion of the combustion equipment and exhaust passages will resul.
‘The amount of sulphur in the diesel il can be greatly reduced by expensive refining pro-
esses. Sulphur contents over 1,0% are harmful, while amounts of 0.5% are economic
feasible.
Carbon residue
‘When a felis burned with a limited amouat of oxygen, carton residue is usually left. The heavier
ends of the liquid fuel suffer from the incomplete combustion and therefore yield carbon in the
‘combustion chamber. High carbon residues increase the deposit in the combustion chamber and
‘around the nozzle tps, thus adversely affecting the spray characters,
Ash
‘The ash content of a fuel is he solid material which remains after complete combustion ofthe
fuel. This measure of abrasiveness ofthe products of combustion that could cause wear in he
ul for Inena.Combunden Engines 249
‘The si eins wih be ners in he nambe o carbon som in e dere
are emo numberof carbon sons In wo hydrocarbons, the one with th ower number of
Iago content wi have a higher vico, The ii el où decease ply wi te
“oe time en forthe fw of a ive on of i sgh andar ce under he
acia of gravity is th ease of de OM fh il Te standar est pp sd 10
Sstermine the vacant a ol ithe Sabo Univeral (SU) coser À rein of
Say viscosity tx aparatos show in Figure 88, The viscosity soporte as Supt
Universal Seconds (SUS) at the temps he st The vicaıy in SUS may Become o
Shoe or nema viscosity y als ale for pupa.
ES
Fgue8# Cs sedonel Sebo viscose appara
‘The scsi) ff rat Ines he yy caracteres. High vino cases ow
stomization (large-sized droplets and high penetration of he spray je. In small combustion cham-
bers, the effect of viscosity is cnica, hence the maximum and minimum values suitable forthe
engine should be specified. In cold engines, a high viscous oil may cause starting problems and
also a smoky exhaust may appear. Ifthe viscosity ofthe fue slow, eakage past the piston in he
pump will be increased. The Inbricating qualities of low-viscosity fuels are poor, hus resulting in
‘The SU viscosity required for most high-speed engines ranges between 35 and 70 at 37.8°C
(QOO"F). As viscosity changes rapidly with temperature, just a numerical value of viscosity has no
significance unless he temperatur is specified
87.4 Specific Gravity
‘The specific gravity is defined as the mass ofa unit volume of Aid to that of the same volume of
water preferably atthe same temperature (say 156"C). It is commonly designated as "spa.
15.6/15.6°C", indicating that both the ol and the water are weighed and measured ats temperature
of 15.6°C (60°F)
‘The oil industry uses a scale adopted by the American Petroleum Institute (APD for measur-
ing the relative density of fuels, giving eadings in degrees API. The relation between the specific
gravity and the API gravity is given by
1a
pr
API gravity in degrees) 1315
‘Thus a light fuel, which has a tow specific gravity, has a higher API gravity. Limiinions
imposed by viscosity limits on CI engines more or less confine the limits of specific gravity to
about 083 10.090 or 39° 10 26° APL
2.7.5 Corrosion and Wear
‘The fuel shouldbe such tha it should nor cause corrosion and wear before and after combus
In order o avoid corrosion and wear, te fuel shoulé not contain much sulphur, ash and carbon
residue,
‘Sulphur
‘The percentage of sulphur in diesel il is higher than that in gasoline, The wear and fouling tat
«arise from sulphur in he fuel result fom the formation of SO), during the combustion process,
‘ue t combination of sulphur with tage amount of excess ar. The SO, may attack the lubricating
oil on the cylinder walls to form resinous materials which harden to form varnish and carbon. It
‘may also react with wate to form sulphuric acid. Wear is caused due to acidic comosion and due
to abrasion withthe carbonaceous material, This condition is expecially bad whea the combustion
Products are cooled enough to condense some ofthe Water vapour. In ths case excessive coro.
sion of the combustion equipment and exhaust passages will resul.
‘The amount of sulphur in the diesel il can be greatly reduced by expensive refining pro-
esses. Sulphur contents over 1,0% are harmful, while amounts of 0.5% are economic
feasible.
Carbon residue
‘When a felis burned with a limited amouat of oxygen, carton residue is usually left. The heavier
ends of the liquid fuel suffer from the incomplete combustion and therefore yield carbon in the
‘combustion chamber. High carbon residues increase the deposit in the combustion chamber and
‘around the nozzle tps, thus adversely affecting the spray characters,
Ash
‘The ash content of a fuel is he solid material which remains after complete combustion ofthe
fuel. This measure of abrasiveness ofthe products of combustion that could cause wear in he
250 Funtumencale of Ural Combustion Engines
Fuels for Ineral-Comburien Engnes 251
engine. The ash content should not exceed 0.12% by weight for the heaviest fel and should be
0.01% fo ig fuels used in high speed engines.
87.6. Handling Ease
“The fuel oil ved in CLengines is liquid that wil readily flow under all conditions. This requie-
ment is measured by the cloud point and the pour pint of the fuel.
Cloud point
Lis the temperature below which the wax content ofthe petroleum ol separates out inthe form
fa solid The wany solid may clog the fue lines and fuel filters,
Pour point
“The pour point of an oi is found by cooling a sample in a test tube until no movement of the il
‘occurs for $ seconds after te tube is tilted from the vertical to the horizontal position. The pour
point is important only when the engine has to run at low temperatures. In such cases, the oil
should have a pour point 3:0 10°C below the operating temperature, The pour point indicates that
may not be possible o have gravity feeding of fuel from the reservoir to the engine below his
temperate
87.7 Satoty
‘The safety ofa diesel il is measured by ls Mash point ard fire point.
Flash point
‘The Mash point is the lowest temperature at which a fuel will vaporize suficenly to form a
combustible mixture of fuel vapour and air above the fuel. It can be determined by heating a
(quay ofthe fuel in a special container while passing a flame above the liquid 10 ignite the
‘vapours. A distinct flash of flame oceurs when the flash point temperature has been reached. The
fash point is important for safety purposes and serves asa measure of the fire hazard. A minimum.
flashpoint of 65°C is specified for safety
Fire point
‘The fre point the temperature at which enough vapours willie to produce a continuous flame
above the liquid fuel. The lame must sustain atleast for five seconds.
‘The fire hazard increases with increase in volatility. As he volatility of diesel ol is less than
that of gasoline, ii safer under most circumstances,
878 Cleanliness.
‘The cleanliness factor is very important is CI engines, because of the precisely fited parts in the
fuel pump and nozzle. Dirt and water in the oil may damage engines. Since diesel oi is more
viscous than gasoline, so thas a tendency to hold more solid particles in suspension. Is there
fore necessary to pass diesel oil through an elaborate filtering process before it enters the pipe
lines, fuel pumps and nozzles.
8.8 KNOCK RATING OF FUELS
I determines whether or nota fuel will knock in a given engine under the given operating condi
tions.
8.8.1 Knock Rating of SI Engine Fuels
A practical measure of a fuel resistance to knock in SI engines is the fuel'octane number.
‘The higher octane number (ON) indicates higher resistance to knock andthe higher compression
ratio may be used without knocking, The octane number used depends on the engine de
the operating conditions during the test. The octane number (ON) scale is based on two hydracar-
bons which define the ends of the scale. The scale has been se up in which isooctane (Cal:
2-2-4-timethyl pentane) being a very good antiknock fuel is arbitrarily asigned a rating of 100
octane number, and normal heptane (e-CH) onthe other hand, as very poor antiknock quali-
ties and is given a rating of zero octane number. These hydrocarbons were selected because ofthe
great difference in their ability to resist knock and the fact that isooctane had a higher resistance 10
Anock than any ofthe fuels available atthe time the scale was established, A gasoline is rated as a
90 octane number, fits tendency to detonate in the test engine isthe seme as tha ofa mixture of
90% isooctane and 10% normal heptane by volume. Tas, the octane number rating i an expees-
sion which indicates the ability ofa fuel t resist knockin SI engines
"There ae two common procedures for determining Ihe octane rating of Fuels—the research
method (Testing code: ASTM D 2699) and the motor method (Testing Code: ASTM D ~ 2700).
In the motor method, the engine operating conditions are more severe and thus there are more
chances of knock being produced. The engine operating conditions of the two methods are
presented in Table 8.3
Table 8.3 Engine operating conditions for research and motor methods.
Variable ‘Research method ‘Motor meihod,
Int tempera wen can,
Inet pressure Atmospheie Atmospheric
Humidy (Mg dy ain 00056-00072 00056-00072
Coolant temperature MC GIP) 100°C 12°F)
Engine speed mpm om
Spark advance LBTDC 1926" BDC
(constan) (tas with compresion rado)
Alot rato Adjusted for maximum koock __ Adjusled for maximum knock
‘The engine used inthe research and motor methods is a special CFR engine developed by the
Cooperative Fue! Reseach Commie (now the Coordinating Research Council In.) in 1931. I
as single cylinder, overhead valves, a tree boul carburetor and a variable compresion rai.
The compression ratio can be changed even withthe engine running) by raising o lowering the
entre cylinder and head assembly relativo to the crankshaft and crankcase through a worm gear
tuned by the hand rank
Fuels for Ineral-Comburien Engnes 251
engine. The ash content should not exceed 0.12% by weight for the heaviest fel and should be
0.01% fo ig fuels used in high speed engines.
87.6. Handling Ease
“The fuel oil ved in CLengines is liquid that wil readily flow under all conditions. This requie-
ment is measured by the cloud point and the pour pint of the fuel.
Cloud point
Lis the temperature below which the wax content ofthe petroleum ol separates out inthe form
fa solid The wany solid may clog the fue lines and fuel filters,
Pour point
“The pour point of an oi is found by cooling a sample in a test tube until no movement of the il
‘occurs for $ seconds after te tube is tilted from the vertical to the horizontal position. The pour
point is important only when the engine has to run at low temperatures. In such cases, the oil
should have a pour point 3:0 10°C below the operating temperature, The pour point indicates that
may not be possible o have gravity feeding of fuel from the reservoir to the engine below his
temperate
87.7 Satoty
‘The safety ofa diesel il is measured by ls Mash point ard fire point.
Flash point
‘The Mash point is the lowest temperature at which a fuel will vaporize suficenly to form a
combustible mixture of fuel vapour and air above the fuel. It can be determined by heating a
(quay ofthe fuel in a special container while passing a flame above the liquid 10 ignite the
‘vapours. A distinct flash of flame oceurs when the flash point temperature has been reached. The
fash point is important for safety purposes and serves asa measure of the fire hazard. A minimum.
flashpoint of 65°C is specified for safety
Fire point
‘The fre point the temperature at which enough vapours willie to produce a continuous flame
above the liquid fuel. The lame must sustain atleast for five seconds.
‘The fire hazard increases with increase in volatility. As he volatility of diesel ol is less than
that of gasoline, ii safer under most circumstances,
878 Cleanliness.
‘The cleanliness factor is very important is CI engines, because of the precisely fited parts in the
fuel pump and nozzle. Dirt and water in the oil may damage engines. Since diesel oi is more
viscous than gasoline, so thas a tendency to hold more solid particles in suspension. Is there
fore necessary to pass diesel oil through an elaborate filtering process before it enters the pipe
lines, fuel pumps and nozzles.
8.8 KNOCK RATING OF FUELS
I determines whether or nota fuel will knock in a given engine under the given operating condi
tions.
8.8.1 Knock Rating of SI Engine Fuels
A practical measure of a fuel resistance to knock in SI engines is the fuel'octane number.
‘The higher octane number (ON) indicates higher resistance to knock andthe higher compression
ratio may be used without knocking, The octane number used depends on the engine de
the operating conditions during the test. The octane number (ON) scale is based on two hydracar-
bons which define the ends of the scale. The scale has been se up in which isooctane (Cal:
2-2-4-timethyl pentane) being a very good antiknock fuel is arbitrarily asigned a rating of 100
octane number, and normal heptane (e-CH) onthe other hand, as very poor antiknock quali-
ties and is given a rating of zero octane number. These hydrocarbons were selected because ofthe
great difference in their ability to resist knock and the fact that isooctane had a higher resistance 10
Anock than any ofthe fuels available atthe time the scale was established, A gasoline is rated as a
90 octane number, fits tendency to detonate in the test engine isthe seme as tha ofa mixture of
90% isooctane and 10% normal heptane by volume. Tas, the octane number rating i an expees-
sion which indicates the ability ofa fuel t resist knockin SI engines
"There ae two common procedures for determining Ihe octane rating of Fuels—the research
method (Testing code: ASTM D 2699) and the motor method (Testing Code: ASTM D ~ 2700).
In the motor method, the engine operating conditions are more severe and thus there are more
chances of knock being produced. The engine operating conditions of the two methods are
presented in Table 8.3
Table 8.3 Engine operating conditions for research and motor methods.
Variable ‘Research method ‘Motor meihod,
Int tempera wen can,
Inet pressure Atmospheie Atmospheric
Humidy (Mg dy ain 00056-00072 00056-00072
Coolant temperature MC GIP) 100°C 12°F)
Engine speed mpm om
Spark advance LBTDC 1926" BDC
(constan) (tas with compresion rado)
Alot rato Adjusted for maximum koock __ Adjusled for maximum knock
‘The engine used inthe research and motor methods is a special CFR engine developed by the
Cooperative Fue! Reseach Commie (now the Coordinating Research Council In.) in 1931. I
as single cylinder, overhead valves, a tree boul carburetor and a variable compresion rai.
The compression ratio can be changed even withthe engine running) by raising o lowering the
entre cylinder and head assembly relativo to the crankshaft and crankcase through a worm gear
tuned by the hand rank
252, fundamente of ternal Combution Engines
Fuels for tar Combution Engines 253
Fuel sensitivity
Since the motor method of determining the octane number used more severe operating conditions
than the research method, the motor octane number (MON) is lower than the research octane
number (RON). The difference between these octane numbers is called the fuel sens, i,
Fuel sensitivity 2 RON - MON es
‘Sensitivity is a measure of the extent to which a gasoline is downgraded under severe cond
‘ions. The higher sensitivity indicates poor performance under severe conditions.
“The primary reference fuels—isooctane and r-heptane—ate paraffins having the same RON
and MON. In general, he paraffin are the least sensitive, while olefins, naphthenes and aromatics
are more sensitive, Therefore, the sreighterungasolines containing a high percentage of saturated
hydrocarbons have low sensitivity, while the racked gasolines containing a lago percentage of
unsaturated hydroearbons have high sensitivity
Road octane number
Automobile engines run on the road under variable speed, load and weather conditions, The
‘spark-timing also changes with speed. On the other hand, the CFR engines, to determine research
fctane number and motor octane number, re run at constant speed, fll tot, and fixed
sparktiming.
‘Therefore, the road octane number requcement differs from RON and MON. The rond
ratings of fuels usualy lie between the research and motor ratings and can be expressed as
Road ON = a(RON) + (MON) + 4)
‘where à, b, are experimentally determined constants. For most gasolines used in automobiles,
a = b = 05 ande = 0 give good agreement with the practical results.
‘The antknock index of a fuel can be expressed asthe mean of the RON and MON. tt charac-
terizes the antiknock quality
RON + MON
+ 65
Aniknock inde
Additives to improve octane number
The octane number of a gasoline can be improved by adding cerain antknock agents, such as
tevaethyl ead, (CH Pb (TEL), tetramethyl lead, (CH), Pb (IML), and methy|-<yclopentadieny!
‘manganese tricarbonyl (MMT).
‘The introduction of TML permits beter distribution of octave amongst the cylindes of an
engine because it boils in the mid-range of a gasoline (110°C), whereas TEL toils at he high end
(200°C). MMT isa supplementary aniknock agent for TEL. Engines fited with catalytic converters
for the reduction of exhaust emissions require unleaded fuel, because the catalysts used will be
poisoned by Ihe presence of lad in he fuel and will son loose their activities. Low concentrations
of MMT may be used as an aniknock additive in unleaded gasoline This also produces deposits in
the catalytic converter, which may increase the resistance to flow, developing back pressure on
the engine and thus reducing the performance of the engine. Nowadays, itis more common to use
j
|
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|
alcohols and ethers to increase the octane rating ofthe gasoline. Alcohols and ethers possess
excelent antinock qualities.
‘Fuels superior 10 isoosiane in antiknock quals have become increasingly important. For
fuels having octane numbers greater than 100, a mixture of isooctane and ttraethy lead is used,
and the octane number scale according to ASTM standards is defined as follows:
ON = 100 + (28.28 TEL/(1 + 0.736 TEL + + 1472 TEL - O03S2IGTEL))) (8.6)
3 of TEL per US gallon in isooctane.
where, TEL is
Performance number
Performance number (PN) is the measure of antiknock effectiveness, Figure 89 shows the
performance number related 1 octane number and tersethyl ead in isooctane. Ii observed that
a he amount of etraeth lea in isooctane increases, the antknock effec lso increases, but the
increase is not lineat. The antiknock effect fist increases rapidly and then with further addition of
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Fuels for tar Combution Engines 253
Fuel sensitivity
Since the motor method of determining the octane number used more severe operating conditions
than the research method, the motor octane number (MON) is lower than the research octane
number (RON). The difference between these octane numbers is called the fuel sens, i,
Fuel sensitivity 2 RON - MON es
‘Sensitivity is a measure of the extent to which a gasoline is downgraded under severe cond
‘ions. The higher sensitivity indicates poor performance under severe conditions.
“The primary reference fuels—isooctane and r-heptane—ate paraffins having the same RON
and MON. In general, he paraffin are the least sensitive, while olefins, naphthenes and aromatics
are more sensitive, Therefore, the sreighterungasolines containing a high percentage of saturated
hydrocarbons have low sensitivity, while the racked gasolines containing a lago percentage of
unsaturated hydroearbons have high sensitivity
Road octane number
Automobile engines run on the road under variable speed, load and weather conditions, The
‘spark-timing also changes with speed. On the other hand, the CFR engines, to determine research
fctane number and motor octane number, re run at constant speed, fll tot, and fixed
sparktiming.
‘Therefore, the road octane number requcement differs from RON and MON. The rond
ratings of fuels usualy lie between the research and motor ratings and can be expressed as
Road ON = a(RON) + (MON) + 4)
‘where à, b, are experimentally determined constants. For most gasolines used in automobiles,
a = b = 05 ande = 0 give good agreement with the practical results.
‘The antknock index of a fuel can be expressed asthe mean of the RON and MON. tt charac-
terizes the antiknock quality
RON + MON
+ 65
Aniknock inde
Additives to improve octane number
The octane number of a gasoline can be improved by adding cerain antknock agents, such as
tevaethyl ead, (CH Pb (TEL), tetramethyl lead, (CH), Pb (IML), and methy|-<yclopentadieny!
‘manganese tricarbonyl (MMT).
‘The introduction of TML permits beter distribution of octave amongst the cylindes of an
engine because it boils in the mid-range of a gasoline (110°C), whereas TEL toils at he high end
(200°C). MMT isa supplementary aniknock agent for TEL. Engines fited with catalytic converters
for the reduction of exhaust emissions require unleaded fuel, because the catalysts used will be
poisoned by Ihe presence of lad in he fuel and will son loose their activities. Low concentrations
of MMT may be used as an aniknock additive in unleaded gasoline This also produces deposits in
the catalytic converter, which may increase the resistance to flow, developing back pressure on
the engine and thus reducing the performance of the engine. Nowadays, itis more common to use
j
|
|
|
alcohols and ethers to increase the octane rating ofthe gasoline. Alcohols and ethers possess
excelent antinock qualities.
‘Fuels superior 10 isoosiane in antiknock quals have become increasingly important. For
fuels having octane numbers greater than 100, a mixture of isooctane and ttraethy lead is used,
and the octane number scale according to ASTM standards is defined as follows:
ON = 100 + (28.28 TEL/(1 + 0.736 TEL + + 1472 TEL - O03S2IGTEL))) (8.6)
3 of TEL per US gallon in isooctane.
where, TEL is
Performance number
Performance number (PN) is the measure of antiknock effectiveness, Figure 89 shows the
performance number related 1 octane number and tersethyl ead in isooctane. Ii observed that
a he amount of etraeth lea in isooctane increases, the antknock effec lso increases, but the
increase is not lineat. The antiknock effect fist increases rapidly and then with further addition of
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254 Funéamantl of Intel Combustion Eng
us for Intra: Combation Engines 255
“TEL the enüknock effect increases slowly. Also, as the octane number increases from 0 10 100,
the antiknock effect not linear An increase in octane number atthe higher range of octane scale
produces a greater aniknock effect compared 10 Ihe same inerease in octane number at he lower
‘end ofthe scale, For example, the increase in octane number from 80 10 90 will produce a greater
antknock effect than the inercae from 201 30. Because ofthis nonlinear variation another scale
is used, which is known as Performance Number (PN). I expresses almost the relative engine
performance,
‚The performance number is the ratio ofthe knock limited indicated mean effective pressure
(Klien) of the test fuel to the knock-limited indicated mean effective pressure (klimep) of
isooctane. That i,
limep of test fuel
* Klimap of isooetane en
Isooctane is arbitrarily assigned a PN of 100. A fuel rated at 120 PN can produce approxi-
mately 12 times the power (without knock) that it can develop with a 100 PN fuel (without
knock).
‘Octane number and performance umber can be related approximately by the following.
relation:
es
‘The above relation is given by Wiese; its an attempt to extend the octane scale beyond 100.
‘A fuel having 100 ON will have 100 PN, but fel having 120 ON will have 160 PN.
Highest useful compression ratio
‘The knock rating of a fuel ean also be expressed in terms of the highest useful compression ratio
(HUCR). 1 is obtained by carying out the test on a variable compression ratio engine under
specified operating conditions, when the pas timing and mixture strength have been adjusted to
give the maximum efficiency. The compression ratio is raised under specified conditions till the
knocking conditions are reached. Table 8.4 gives the HUCR for different fuels determined in
Ricardo B6 variable compression ratio engine.
Table 84 HUCRfor different fuels
Fuel HUCK
Trooctane 1096
heptane 375
Toluene 1500
Cyclo-herane an
8.2.2 Knock Rating of CI Engine Fuels
‘The methods for determining and measuring the ignition quality of CI engine fuels are (2) the
cetane number and () the diesel index.
Cotane number
‘The cerane number determines the ignition quality of a diesel fue, Ris the most used method. An
increase in cetane number reduces the ignition delay period and thus reduces the tendeney 10
Knock, The cetane number scale is defined by blending cetane (n-hexadecane CH) a hydro.
carbon of high igition quality that represents the top ofthe scale with a cetane number 100. An
isocetane (Hepta-methyinonane, HMN) having low ignition quality, represents the botor of the
scale with a celine number 15. I the original procedure a-methylnapthalene (C,H) with a
cetane number of zero represented the botom ofthe scale, but HMN, a more stable compound,
has replaced it
The ceiane number (CN) of a felis given by
CN = per cent metano + 0.15 x per cent HMN 6%
‘The ASTM method for rating the cetane numberof a given fuel is determined by performing the
test in a CFR engine. I is a single cylinder, variable compression ratio engine. The operating
conditions ae: engine speed 900 rpm, intake air temperature 65.6°C (150°F); coolant temperature
100°C; injection éming 13°bTDC; injection pressure 10.3 MPa (1500 vit). The cetane number
ofthe fuel to be determined is tested in Ihe above engine with the specified operating conditions,
the compression ratio of the engine is varied until the combustion stars at TDC, Le. an ignition
delay period of 13 is obtained. This compression ratio is now kept fied and he ext engine with
the specified operating conditions is run withthe diferen blends of the reference fuels vail
combustion stats once again at TDC. Knowing the percentage of both Le reference fuel in the
blend, the cetane number is calculated from Eq. (8). The recommended cetane numbers are 25
1035 for low speed, 35 to 45 for medium speed and 45 to 60 for high speed engines. Experiments
have shown that, wit a given fü), ifthe engine has a good start and operates satisfactory, sing
the cetane number may not inerease the engine performance, and it is quite possible thatthe
performance on the otber hand may somewhat deteriorate, resulting in decreased power and
increased fuel consumption.
‘The ignition quality ofa diesel fel has a nonlinear relationship with the cetane number, but it
is nota serious problem, since CI engines bum fuel in a narrow range of ectane scale.
‘The cracked fuels and fuels of other than paraffinic base have low cetane number. Certain
addiives are required to raise the cetane number o desirable values for high speed engines. Such
Additives reduce the sel-igition temperature of the fuel. Most additives for CI engine fuels are
mil explosives. Some of he Cl fuels additives are Isopropy! nitrate, ethyl nitrate, amy] nitrate,
«hy nie, buy! peroxide and methyl acetate.
"TEL is nota suitable additive for Cl engine Fels. increases the ignition delay and hence the
knocking tendency increases 100.
Diesel index
‘The diesel index depends on the fat that aromatic hydrocarbons mix completely with aniline at
comparatively low temperatures, whereas the paraffins require considerably higher temperatures
before becoming completely miscible, First, the ‘aniline point is determined. I is the lowest
temperature a which equal volumes ofthe furl and aniline become jst miscible. The anline point
is determined by heating a mixture consisting of equal volumes of the est sample and freshly
254 Funéamantl of Intel Combustion Eng
us for Intra: Combation Engines 255
“TEL the enüknock effect increases slowly. Also, as the octane number increases from 0 10 100,
the antiknock effect not linear An increase in octane number atthe higher range of octane scale
produces a greater aniknock effect compared 10 Ihe same inerease in octane number at he lower
‘end ofthe scale, For example, the increase in octane number from 80 10 90 will produce a greater
antknock effect than the inercae from 201 30. Because ofthis nonlinear variation another scale
is used, which is known as Performance Number (PN). I expresses almost the relative engine
performance,
‚The performance number is the ratio ofthe knock limited indicated mean effective pressure
(Klien) of the test fuel to the knock-limited indicated mean effective pressure (klimep) of
isooctane. That i,
limep of test fuel
* Klimap of isooetane en
Isooctane is arbitrarily assigned a PN of 100. A fuel rated at 120 PN can produce approxi-
mately 12 times the power (without knock) that it can develop with a 100 PN fuel (without
knock).
‘Octane number and performance umber can be related approximately by the following.
relation:
es
‘The above relation is given by Wiese; its an attempt to extend the octane scale beyond 100.
‘A fuel having 100 ON will have 100 PN, but fel having 120 ON will have 160 PN.
Highest useful compression ratio
‘The knock rating of a fuel ean also be expressed in terms of the highest useful compression ratio
(HUCR). 1 is obtained by carying out the test on a variable compression ratio engine under
specified operating conditions, when the pas timing and mixture strength have been adjusted to
give the maximum efficiency. The compression ratio is raised under specified conditions till the
knocking conditions are reached. Table 8.4 gives the HUCR for different fuels determined in
Ricardo B6 variable compression ratio engine.
Table 84 HUCRfor different fuels
Fuel HUCK
Trooctane 1096
heptane 375
Toluene 1500
Cyclo-herane an
8.2.2 Knock Rating of CI Engine Fuels
‘The methods for determining and measuring the ignition quality of CI engine fuels are (2) the
cetane number and () the diesel index.
Cotane number
‘The cerane number determines the ignition quality of a diesel fue, Ris the most used method. An
increase in cetane number reduces the ignition delay period and thus reduces the tendeney 10
Knock, The cetane number scale is defined by blending cetane (n-hexadecane CH) a hydro.
carbon of high igition quality that represents the top ofthe scale with a cetane number 100. An
isocetane (Hepta-methyinonane, HMN) having low ignition quality, represents the botor of the
scale with a celine number 15. I the original procedure a-methylnapthalene (C,H) with a
cetane number of zero represented the botom ofthe scale, but HMN, a more stable compound,
has replaced it
The ceiane number (CN) of a felis given by
CN = per cent metano + 0.15 x per cent HMN 6%
‘The ASTM method for rating the cetane numberof a given fuel is determined by performing the
test in a CFR engine. I is a single cylinder, variable compression ratio engine. The operating
conditions ae: engine speed 900 rpm, intake air temperature 65.6°C (150°F); coolant temperature
100°C; injection éming 13°bTDC; injection pressure 10.3 MPa (1500 vit). The cetane number
ofthe fuel to be determined is tested in Ihe above engine with the specified operating conditions,
the compression ratio of the engine is varied until the combustion stars at TDC, Le. an ignition
delay period of 13 is obtained. This compression ratio is now kept fied and he ext engine with
the specified operating conditions is run withthe diferen blends of the reference fuels vail
combustion stats once again at TDC. Knowing the percentage of both Le reference fuel in the
blend, the cetane number is calculated from Eq. (8). The recommended cetane numbers are 25
1035 for low speed, 35 to 45 for medium speed and 45 to 60 for high speed engines. Experiments
have shown that, wit a given fü), ifthe engine has a good start and operates satisfactory, sing
the cetane number may not inerease the engine performance, and it is quite possible thatthe
performance on the otber hand may somewhat deteriorate, resulting in decreased power and
increased fuel consumption.
‘The ignition quality ofa diesel fel has a nonlinear relationship with the cetane number, but it
is nota serious problem, since CI engines bum fuel in a narrow range of ectane scale.
‘The cracked fuels and fuels of other than paraffinic base have low cetane number. Certain
addiives are required to raise the cetane number o desirable values for high speed engines. Such
Additives reduce the sel-igition temperature of the fuel. Most additives for CI engine fuels are
mil explosives. Some of he Cl fuels additives are Isopropy! nitrate, ethyl nitrate, amy] nitrate,
«hy nie, buy! peroxide and methyl acetate.
"TEL is nota suitable additive for Cl engine Fels. increases the ignition delay and hence the
knocking tendency increases 100.
Diesel index
‘The diesel index depends on the fat that aromatic hydrocarbons mix completely with aniline at
comparatively low temperatures, whereas the paraffins require considerably higher temperatures
before becoming completely miscible, First, the ‘aniline point is determined. I is the lowest
temperature a which equal volumes ofthe furl and aniline become jst miscible. The anline point
is determined by heating a mixture consisting of equal volumes of the est sample and freshly
256 Fundameras of Imeral Combution Engines
Fuel for ItomalComursen Exgines_257
istled, water free aniline, Cb N, until clear solution is obained. Then, while the solution is
cooling, the temperature at which turbidity appear is noted
“The diesel index i competed from the following expression:
Aniline point °F) APL gaviy,
Dislindex = CAP aan eo
= (Anne point (26) do 32) x APL en
‚The diesel index usually gives values slightly above be cetane number. Figure 8.10 shows the
relationship between the cetane number and he diesel index number.
MÁ
El
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#6 0 EJ 60 70
Cennemumber
Faute anbeheende onaremborendhodesindecnunbet
REVIEW QUESTIONS
Define a fuel, What ar Ihe requirements of IC engine fuels?
"What ae the eitera forthe selection of IC engine fuels?
How are the fuels classified?
. Briefly describe the following types of solid fuels: wood, peat, coal lignite to amb
charcoal, coke, briqueted coal, and pulverized coal.
5. Comment on the use of solid fuel in 1C engines
6. Describe, with the help of a diagram, a typical où-pool formation. How isthe erude oil
forced out from the pool tothe surface?
7. How are the hydrocarbons present inthe fuel classified?, Briefly describe them with their
structural formulae.
8. Describe the refining proces of petroleum by the method of fractional distillation.
9. Briefly describe the following processes used afte the fractional distillation of crue o
Cracking, Hydrogenation, Absorption, Polymerization, Alkylaon, Isomerization, Cycliza-
tion, Aromutizaion, Reforming, and Finished blended product.
10. Briely describo the different petroleum based liquid fuel of importance in IC engines.
11. Briefly describe the following non-petroleum based liquid fuel used in IC engines:
"Benzol, Methyl alcohol, and Ethy alcohol.
12. What are the advantages and disadvantages of using gaseous Fuels in IC engines?
pepe
13. Deseribe the composition, properties and suitability to use the following gaseous fuels in IC
engines: Natural gas, iuified petroleum gs, and hydrogen,
14, What are the different fuel characteristics on which the performance of SI engines
depends?
15. Describe the volatility characteristics of petroleum fuels
16. Describe the ASTM distillation test procedure forthe measurement of relative volatility of
fuels
17. How does the EAD test dife from the ASTM distilaton test? Enumerat the importance
of each of these tests?
18. Describe the Reid vapour pressure bomb for measuring the volatility characteristic of a
fuel
19. Briefly describe the effect of volatility on the following performance characteristics of SI
Cold starting, Hot starting, Vapour lock, Evaporation loss, Warm-up and accel
Carburetior icing, Shor. and long tp economy, Crankcase dilution, and Sindge depos
20. Briefly describe the effect ofthe following fuel characteristics on the performance of
Slengines
Sulphur content, Gum deposits, Carburetor detergent additives, and Antiknock quali.
21. Mention the important characteristics of CI engine fuels
22, Briefly describe the effect ofthe following fuel characteristics onthe performance of CI
engines:
Ignition quality, Volatility, Viscosity, Gravity, Comosion and wear, Handling ease, Safety
and cleanliness,
13. Describe the influence of ignition que
roughness and compression rai.
24, How is Saybolt Universal Viscosimeter used to determine the viscosity of où?
25. Define API gravity.
26. Define te following tems: Cloud point, Pour point, Flash point, and Fire point of liquid
fiel.
27. How are the SI engine fuels ated in terms of octane number? Define Ih octane number
scale and give the reasons for selecting this scale
28. What are the two common procedures fr determining the octane ratings of fuels? Briefly
describe them.
29. Define fuel sensitivity. Give examples of hydrocarbons having low sensitivity and hi
sensitivity.
30. Define Road Octane Number and Antiknoc index.
31. Mention some of the addiives to increase the octane number of fuels. What are the
“advantages and disadvantages of using leaded gasolines?
32. How is the fuel superior to isooctane in aniknock quality rated?
33. Define the performance number of a fuel. Give the approximate relation between the
‘cane number and the performance number,
34. How i the rating ofa fuel expressed in terms of HUCR?
35. Describe the following methods for determining and measuring the ignition quality of CT
engine fuels: a) Ctare number (9) Diese index.
of CL engine fuels on cold starting, engine
Fuel for ItomalComursen Exgines_257
istled, water free aniline, Cb N, until clear solution is obained. Then, while the solution is
cooling, the temperature at which turbidity appear is noted
“The diesel index i competed from the following expression:
Aniline point °F) APL gaviy,
Dislindex = CAP aan eo
= (Anne point (26) do 32) x APL en
‚The diesel index usually gives values slightly above be cetane number. Figure 8.10 shows the
relationship between the cetane number and he diesel index number.
MÁ
El
oo
j |
y EZ
#6 0 EJ 60 70
Cennemumber
Faute anbeheende onaremborendhodesindecnunbet
REVIEW QUESTIONS
Define a fuel, What ar Ihe requirements of IC engine fuels?
"What ae the eitera forthe selection of IC engine fuels?
How are the fuels classified?
. Briefly describe the following types of solid fuels: wood, peat, coal lignite to amb
charcoal, coke, briqueted coal, and pulverized coal.
5. Comment on the use of solid fuel in 1C engines
6. Describe, with the help of a diagram, a typical où-pool formation. How isthe erude oil
forced out from the pool tothe surface?
7. How are the hydrocarbons present inthe fuel classified?, Briefly describe them with their
structural formulae.
8. Describe the refining proces of petroleum by the method of fractional distillation.
9. Briefly describe the following processes used afte the fractional distillation of crue o
Cracking, Hydrogenation, Absorption, Polymerization, Alkylaon, Isomerization, Cycliza-
tion, Aromutizaion, Reforming, and Finished blended product.
10. Briely describo the different petroleum based liquid fuel of importance in IC engines.
11. Briefly describe the following non-petroleum based liquid fuel used in IC engines:
"Benzol, Methyl alcohol, and Ethy alcohol.
12. What are the advantages and disadvantages of using gaseous Fuels in IC engines?
pepe
13. Deseribe the composition, properties and suitability to use the following gaseous fuels in IC
engines: Natural gas, iuified petroleum gs, and hydrogen,
14, What are the different fuel characteristics on which the performance of SI engines
depends?
15. Describe the volatility characteristics of petroleum fuels
16. Describe the ASTM distillation test procedure forthe measurement of relative volatility of
fuels
17. How does the EAD test dife from the ASTM distilaton test? Enumerat the importance
of each of these tests?
18. Describe the Reid vapour pressure bomb for measuring the volatility characteristic of a
fuel
19. Briefly describe the effect of volatility on the following performance characteristics of SI
Cold starting, Hot starting, Vapour lock, Evaporation loss, Warm-up and accel
Carburetior icing, Shor. and long tp economy, Crankcase dilution, and Sindge depos
20. Briefly describe the effect ofthe following fuel characteristics on the performance of
Slengines
Sulphur content, Gum deposits, Carburetor detergent additives, and Antiknock quali.
21. Mention the important characteristics of CI engine fuels
22, Briefly describe the effect ofthe following fuel characteristics onthe performance of CI
engines:
Ignition quality, Volatility, Viscosity, Gravity, Comosion and wear, Handling ease, Safety
and cleanliness,
13. Describe the influence of ignition que
roughness and compression rai.
24, How is Saybolt Universal Viscosimeter used to determine the viscosity of où?
25. Define API gravity.
26. Define te following tems: Cloud point, Pour point, Flash point, and Fire point of liquid
fiel.
27. How are the SI engine fuels ated in terms of octane number? Define Ih octane number
scale and give the reasons for selecting this scale
28. What are the two common procedures fr determining the octane ratings of fuels? Briefly
describe them.
29. Define fuel sensitivity. Give examples of hydrocarbons having low sensitivity and hi
sensitivity.
30. Define Road Octane Number and Antiknoc index.
31. Mention some of the addiives to increase the octane number of fuels. What are the
“advantages and disadvantages of using leaded gasolines?
32. How is the fuel superior to isooctane in aniknock quality rated?
33. Define the performance number of a fuel. Give the approximate relation between the
‘cane number and the performance number,
34. How i the rating ofa fuel expressed in terms of HUCR?
35. Describe the following methods for determining and measuring the ignition quality of CT
engine fuels: a) Ctare number (9) Diese index.
of CL engine fuels on cold starting, engine
Carburettors and Fuel
Injection in SI Engines
9.1 INTRODUCTION
Carburetors device for atomizing and vaporizing the fl and mind it wit the arin varying
Proportion to ult entire operating ange o ST engines. The process of breaking up and mixing
the fel with the aris cal carburerion. Te arbueto supplies à mixture of vaporized fuel and
ai inte proper proportion oe ina manifold and fly tothe cylinders Te intake maid
isnormalykepcoverthe exhaust manifold thea the atomized fel, which helps the vaporization
process. The opdmun actue rao fr SL engines is that which gives the required power out,
‘ith the minimum fel consumption. Te ail ao tht provide the minimum fuel consump
on, smooth and reliable engine operation and ais the emision requirements at he equred
power up, depends on engine speed ad load. The afl ratio fr maximum power is nthe
Same as these lo for maximum economy. The mitur requirements for staring, Warm-up
and acceleration are also diferent rom those for steady operation
92 LIMITS OF FLAMMABILITY
Tiere are two limits of flammability for each fl. The lower limit of flammability is the leanest
mixture (the least amount of fel in the mixture), which will support combustion. The upper limit
isthe richest mixture which can propagate aflame. At both ends ofthe ammable limits, the rate
of flame propagation isthe lowes. Since combustion engines run at various speeds and provide
varios ait velocities in the combustion chamber, the lame wil be stabilized with ai/ful rato well
within the flammability Limit. Forisooctane the rich imi, the stoichiometric and the lean Limit for
engines are 8, 15.2 and LE aiuel ratios, by weight respectively.
Various other terms, such a inflammation init explosion limit, mit of inflammability are
often used interchangeably with the terms ‘Limits of fammabilty’. The limits of lammabiity are
affected by the following factors in combustion engines.
Temperature
Temperature changes ofa few degrees atthe ime of ignition have little effect onthe Mammabiliy
limits. At temperatures considerably above th room temperature, he range of flammability us
ally increases by extending both he mis.
2
Carburetors sd Fuel Incion ia SI Engines 259
Pressure
‘The limits of flammability are not appreciably affected by normal variations of the atmospheric
pressure. Lowesing the pressure appreciably below the aumospheri usually decreases the range
of flammability. The effet of pressure above the atmospheric varies with each fuel, and no
general statement can be applied 10 the effect of flammability.
Humidity
‘A normal amount of water vapour in the mixture prior to ignition seems to have no efect on the
lower limit, since the oxygen content ofthe aris usually much more than the fuel content ofthe
mixture. However, the upper limit is lowered, because the water vapour decreases the oxygen
content of the air.
9.3 STEADY-RUNNING MIXTURE REQUIREMENTS:
‘Steady running means the continuous operation of the engine at a given speed and power output
‘with normal engine temperatures. Under the steady-ninning condition the mixture requirements
for maximum power and for minimum specific fel consumption are different.
9.3.1 Mixture requirements for maximum power
Figure 9.1 shows the effect ofthe fueVair rato on the indicated mean effective pressure at full
foule and part throtle positions. The maximum indicated mean effective presse oocurs ata
fuer ratio of about 0.08 for gasoline, Which i a lle more tan the chemically correct amount
of fuel At full rot and with a maximum indicated mean effective pressure mixture, the flame
speed is high, and the burning time losses are very small, since the piston is near the TDC and
‘moves very litle during the burning process, The effect of closing the thotle reduces the indi-
cated mean effective pressure and the indicated power by reducing both the intake manifold
pressure and the volumetric efficiency, The entire indicated mean effective pressure curve, there
<n
AZ rote
Jocs power
nets mean eco pressure
Fr
Poel rato
Fe Edel orcos fleche rss Ava a anos
Injection in SI Engines
9.1 INTRODUCTION
Carburetors device for atomizing and vaporizing the fl and mind it wit the arin varying
Proportion to ult entire operating ange o ST engines. The process of breaking up and mixing
the fel with the aris cal carburerion. Te arbueto supplies à mixture of vaporized fuel and
ai inte proper proportion oe ina manifold and fly tothe cylinders Te intake maid
isnormalykepcoverthe exhaust manifold thea the atomized fel, which helps the vaporization
process. The opdmun actue rao fr SL engines is that which gives the required power out,
‘ith the minimum fel consumption. Te ail ao tht provide the minimum fuel consump
on, smooth and reliable engine operation and ais the emision requirements at he equred
power up, depends on engine speed ad load. The afl ratio fr maximum power is nthe
Same as these lo for maximum economy. The mitur requirements for staring, Warm-up
and acceleration are also diferent rom those for steady operation
92 LIMITS OF FLAMMABILITY
Tiere are two limits of flammability for each fl. The lower limit of flammability is the leanest
mixture (the least amount of fel in the mixture), which will support combustion. The upper limit
isthe richest mixture which can propagate aflame. At both ends ofthe ammable limits, the rate
of flame propagation isthe lowes. Since combustion engines run at various speeds and provide
varios ait velocities in the combustion chamber, the lame wil be stabilized with ai/ful rato well
within the flammability Limit. Forisooctane the rich imi, the stoichiometric and the lean Limit for
engines are 8, 15.2 and LE aiuel ratios, by weight respectively.
Various other terms, such a inflammation init explosion limit, mit of inflammability are
often used interchangeably with the terms ‘Limits of fammabilty’. The limits of lammabiity are
affected by the following factors in combustion engines.
Temperature
Temperature changes ofa few degrees atthe ime of ignition have little effect onthe Mammabiliy
limits. At temperatures considerably above th room temperature, he range of flammability us
ally increases by extending both he mis.
2
Carburetors sd Fuel Incion ia SI Engines 259
Pressure
‘The limits of flammability are not appreciably affected by normal variations of the atmospheric
pressure. Lowesing the pressure appreciably below the aumospheri usually decreases the range
of flammability. The effet of pressure above the atmospheric varies with each fuel, and no
general statement can be applied 10 the effect of flammability.
Humidity
‘A normal amount of water vapour in the mixture prior to ignition seems to have no efect on the
lower limit, since the oxygen content ofthe aris usually much more than the fuel content ofthe
mixture. However, the upper limit is lowered, because the water vapour decreases the oxygen
content of the air.
9.3 STEADY-RUNNING MIXTURE REQUIREMENTS:
‘Steady running means the continuous operation of the engine at a given speed and power output
‘with normal engine temperatures. Under the steady-ninning condition the mixture requirements
for maximum power and for minimum specific fel consumption are different.
9.3.1 Mixture requirements for maximum power
Figure 9.1 shows the effect ofthe fueVair rato on the indicated mean effective pressure at full
foule and part throtle positions. The maximum indicated mean effective presse oocurs ata
fuer ratio of about 0.08 for gasoline, Which i a lle more tan the chemically correct amount
of fuel At full rot and with a maximum indicated mean effective pressure mixture, the flame
speed is high, and the burning time losses are very small, since the piston is near the TDC and
‘moves very litle during the burning process, The effect of closing the thotle reduces the indi-
cated mean effective pressure and the indicated power by reducing both the intake manifold
pressure and the volumetric efficiency, The entire indicated mean effective pressure curve, there
<n
AZ rote
Jocs power
nets mean eco pressure
Fr
Poel rato
Fe Edel orcos fleche rss Ava a anos
260 Fundamental of interna! Combasion Engnes
Carburenors ad Fun lejecóon ln SI Egoas_261
{ore towers itself patrol, however the intake manifold pressure so reduces the amo
SF whch increases the burning time losses and which further reduces the indicated nenn
Koran presse, However, he busing tine loses a fee ro 010.08 ae almost split
For any given at posion, he Indiaed mean effective pressure Wil be am ha
ratio of about 0.08,
932 Mixture Requirements for Minimum Specific Fuel
‘Consumption
cer anima m Indicated hemal efficiency occurs at feat ratio of about 006 for gasoline,
sich 3 slighty leaner han the chemically comet fuel ratio because excess ait anna
Fee combustion ofthe fuel, À lan mixture lowers the maximum temperature, which lavo
cl euro and specific heat of gases. If the mixture made 10 lean, he ame sr
era Which inereases the buming tine oes and lowes he efcieney. The indicated peta
Lia. consumption (sl) reduces as the indicted themal ficiency increases, The impor a
reduced.
| mn
z
E Y Full theottle
i
3
|
06 Gr
Peel
2. Era cd pu onu as llos ancora pm
9.3.3. Mixture Requirements for Various Outputs
In 2.3 shows e pic! cures o brake mean effective pressure (omo) andthe coesond.
Ink rae specific ful consumption fe) versus the fala tos or aa egin opera a
heit trol positions. From he figure itis observed that there is only one flair csc
Tene ti of 008. Fite equiedo reduce power by 80% of main ican dene by
‘ducing the thro with foca rato of 0.08 corresponding to point B. This will veal cy
i E
¿ =
¿ sty tt
»
e
An ir ne is
rut
A. AA
fy he bree ra rc
SR cn a crs rene
DE Dee ne em ot soe a
een
q a a as rf
ee tm Al
eee re ee ee Ti inte
phos
9.3.4 Mixture Requirements for ldling, Cruising and
High Powor
‘The mixture requirements for idling, cruising, and high power ranges are shown in Figure 94.
Idling range
“The engine is sai o dle when itis operating at o extemal load withthe throttle almost closed.
‘An idling engine requires arch mixture as shown by point A in Figure 94, I is because of he
following reasons: tte
‘The mass of the exhaust gas remaining as residual in the clearance space a he end
‘exhaust stroke remains fairly constant throughout the throte range. On the other hand, the mass
Carburenors ad Fun lejecóon ln SI Egoas_261
{ore towers itself patrol, however the intake manifold pressure so reduces the amo
SF whch increases the burning time losses and which further reduces the indicated nenn
Koran presse, However, he busing tine loses a fee ro 010.08 ae almost split
For any given at posion, he Indiaed mean effective pressure Wil be am ha
ratio of about 0.08,
932 Mixture Requirements for Minimum Specific Fuel
‘Consumption
cer anima m Indicated hemal efficiency occurs at feat ratio of about 006 for gasoline,
sich 3 slighty leaner han the chemically comet fuel ratio because excess ait anna
Fee combustion ofthe fuel, À lan mixture lowers the maximum temperature, which lavo
cl euro and specific heat of gases. If the mixture made 10 lean, he ame sr
era Which inereases the buming tine oes and lowes he efcieney. The indicated peta
Lia. consumption (sl) reduces as the indicted themal ficiency increases, The impor a
reduced.
| mn
z
E Y Full theottle
i
3
|
06 Gr
Peel
2. Era cd pu onu as llos ancora pm
9.3.3. Mixture Requirements for Various Outputs
In 2.3 shows e pic! cures o brake mean effective pressure (omo) andthe coesond.
Ink rae specific ful consumption fe) versus the fala tos or aa egin opera a
heit trol positions. From he figure itis observed that there is only one flair csc
Tene ti of 008. Fite equiedo reduce power by 80% of main ican dene by
‘ducing the thro with foca rato of 0.08 corresponding to point B. This will veal cy
i E
¿ =
¿ sty tt
»
e
An ir ne is
rut
A. AA
fy he bree ra rc
SR cn a crs rene
DE Dee ne em ot soe a
een
q a a as rf
ee tm Al
eee re ee ee Ti inte
phos
9.3.4 Mixture Requirements for ldling, Cruising and
High Powor
‘The mixture requirements for idling, cruising, and high power ranges are shown in Figure 94.
Idling range
“The engine is sai o dle when itis operating at o extemal load withthe throttle almost closed.
‘An idling engine requires arch mixture as shown by point A in Figure 94, I is because of he
following reasons: tte
‘The mass of the exhaust gas remaining as residual in the clearance space a he end
‘exhaust stroke remains fairly constant throughout the throte range. On the other hand, the mass
262. Funtimenul of noma Combustion Engines
Carburetors and fuel Injection in SI Engines 263
Rich —
_Bestponer L
Monitor?
y
| Chemialyeomer ce]
Paire
hen eco
y a
- ing range À Casing rango —À Power ange |
Low
alg E To
‘Tec opening 0%),
Figura. Matson ri cis undighpome age
ofthe fresh charge induced on cach intake stroke depends upon the manifold pressure and there-
fore it depends upon the throttle position, The manifold pressure and hence the mass ofthe fresh
charge inducted during idling are much les than those during the fll hote operation, due tothe
restricions imposed by throttle. The result sa much larger proportion of exhaust gas being mixed
‘with the fresh charge, under iling conditions causing dition of the fresh charge. The presence
‘ofthe exhaust gas reduces the intimate contact of el and air particles, resulting in poor combus-
(ion and thus causing power los. It is, therefore, necessary to provide more fuel particles for
enriching the charge. This increases the probability of contact of fuel and air particles, and thus
improves combustion.
Aste throtles gradually opened from A 10 B (Figure 94), the exhaust gas dilution of the fresh
charge diminishes. Mixture requirements then proceed along he curve AB to aleanerfueVair ato.
Cruising range
Inthe cruising range from B to C (Figure 94), the engine is operating at par throue, The main
objective isto obtain the maximum fuel economy. Consequently, inthis range, its desirable that
‘the carburetor should provide the engine withthe best economy mixture, which i slightly leaner
than the stoichiomenc.
With lean mixtures the flame speed is relatively slow, and even slower when the mixture i
iluted with exhaust gas. Hence the spark is advanced asthe manifold vacuum increases.
High powerrange
During high power operation, when the engine is operating withthe ful opened trot, the engine
requires a richer mixture as indicated by the curve CD (Figure 9.4), I has already been observed
thatthe mixtore requirement for maximum power is with a slighll richer mixture than the
stoichiometric, The carburenor has tobe set inthe vicinity ofthe best power mixture,
At high power, a wide open throttle increases the mass flow ofthe charge to the cylinder,
which incseases the demand ofthe rate of heat transfer from critical areas such as exhaust valve
‘This demand cold be reduced by enriching the mixture, which in tum reduces the flame tempera:
ture and the cylinder temperature, ths also reducing the cooling problem and the possibility of
damaging the exhaust valve, Therefor, the charge should be enriched before the rote is made
wide open. The rich mixture lowers the temperature i the combustion chamber and thus helps in
reducing he possibly of detonation and the formation of oxides of nitrogen in the exhaust,
9.4 TRANSIENT REQUIREMENTS
The transient operation include staring, warming-up, and acceleration
9.4.1 Starting and Warm-up Requirements
‘When a cold engine is started, the heavy end of gasoline is not evaporated. Although the fuer
rai atthe carburetor may be well within te flammability limits of gasoline-air mixtures, bot the
ratio of evaporated fue-o-ar in the cylinder may be far to lean to ignite. Its, therefore, neces-
to supply Sto 10 times richer fue atthe carburettor to obtain enough evaporated light ends to
ignite, until the manifold and cylinder parts become warm.
As the engine warms up, the fueVair ratio requirement atthe casbuettor must be reduced to
refrain the evaporated fuel/air ato from becoming 10 rich
9.42 Acceleration Requirement
Under steady-running conditions, there is a tendency for some non-vaporized liquid droplets
form athin iquid film and move along the inner wall of he intake manifold tothe ylinders The
and evaporated fuel mixture take much less time than the liquid streams along the wall to each the
cylinder from the carburetor. When a sudden acceleration is required and he throttle i suddenly
‘opened, the guscous charge of ar and fuel moves rapidly ino the eylindes. The liquid film, dueto
its greater inertia las behind. It causes lean mixture to move to the engine cylinder for a short,
time. This temporary lean mixture prevents the engine from developing fll power just at the time
when it is required the most.
In order to compensate for this tendency of the carburettor, during acceleration, to Fail
‘momentarily to suppl a sufiient rich mixture, a mechanical accelerating device is provided,
‘hich is directly connected tothe throtie mechanism.
95 MIXTURE REQUIREMENTS IN A MULTI-CYLINDER
ENGINE
Aire! malisbution between the eylindesisinerent ina conventional mulicylinder spark
ignition engine. Complete atomization and vaporization ofthe Fue by the carburetor i dificult
brain. Even under the best conditions, the intake manifold contains an appreciable amount of
Liquid as well as large fel droples. A thin film of liquid fuel lso adheres othe inner wall ofthe
intake manifold. These droplets have greater inertia than the gaseous mixtures, Consequently,
‘whenever the direction of flow is changed abruptly the droplets tend to continue in their original
Carburetors and fuel Injection in SI Engines 263
Rich —
_Bestponer L
Monitor?
y
| Chemialyeomer ce]
Paire
hen eco
y a
- ing range À Casing rango —À Power ange |
Low
alg E To
‘Tec opening 0%),
Figura. Matson ri cis undighpome age
ofthe fresh charge induced on cach intake stroke depends upon the manifold pressure and there-
fore it depends upon the throttle position, The manifold pressure and hence the mass ofthe fresh
charge inducted during idling are much les than those during the fll hote operation, due tothe
restricions imposed by throttle. The result sa much larger proportion of exhaust gas being mixed
‘with the fresh charge, under iling conditions causing dition of the fresh charge. The presence
‘ofthe exhaust gas reduces the intimate contact of el and air particles, resulting in poor combus-
(ion and thus causing power los. It is, therefore, necessary to provide more fuel particles for
enriching the charge. This increases the probability of contact of fuel and air particles, and thus
improves combustion.
Aste throtles gradually opened from A 10 B (Figure 94), the exhaust gas dilution of the fresh
charge diminishes. Mixture requirements then proceed along he curve AB to aleanerfueVair ato.
Cruising range
Inthe cruising range from B to C (Figure 94), the engine is operating at par throue, The main
objective isto obtain the maximum fuel economy. Consequently, inthis range, its desirable that
‘the carburetor should provide the engine withthe best economy mixture, which i slightly leaner
than the stoichiomenc.
With lean mixtures the flame speed is relatively slow, and even slower when the mixture i
iluted with exhaust gas. Hence the spark is advanced asthe manifold vacuum increases.
High powerrange
During high power operation, when the engine is operating withthe ful opened trot, the engine
requires a richer mixture as indicated by the curve CD (Figure 9.4), I has already been observed
thatthe mixtore requirement for maximum power is with a slighll richer mixture than the
stoichiometric, The carburenor has tobe set inthe vicinity ofthe best power mixture,
At high power, a wide open throttle increases the mass flow ofthe charge to the cylinder,
which incseases the demand ofthe rate of heat transfer from critical areas such as exhaust valve
‘This demand cold be reduced by enriching the mixture, which in tum reduces the flame tempera:
ture and the cylinder temperature, ths also reducing the cooling problem and the possibility of
damaging the exhaust valve, Therefor, the charge should be enriched before the rote is made
wide open. The rich mixture lowers the temperature i the combustion chamber and thus helps in
reducing he possibly of detonation and the formation of oxides of nitrogen in the exhaust,
9.4 TRANSIENT REQUIREMENTS
The transient operation include staring, warming-up, and acceleration
9.4.1 Starting and Warm-up Requirements
‘When a cold engine is started, the heavy end of gasoline is not evaporated. Although the fuer
rai atthe carburetor may be well within te flammability limits of gasoline-air mixtures, bot the
ratio of evaporated fue-o-ar in the cylinder may be far to lean to ignite. Its, therefore, neces-
to supply Sto 10 times richer fue atthe carburettor to obtain enough evaporated light ends to
ignite, until the manifold and cylinder parts become warm.
As the engine warms up, the fueVair ratio requirement atthe casbuettor must be reduced to
refrain the evaporated fuel/air ato from becoming 10 rich
9.42 Acceleration Requirement
Under steady-running conditions, there is a tendency for some non-vaporized liquid droplets
form athin iquid film and move along the inner wall of he intake manifold tothe ylinders The
and evaporated fuel mixture take much less time than the liquid streams along the wall to each the
cylinder from the carburetor. When a sudden acceleration is required and he throttle i suddenly
‘opened, the guscous charge of ar and fuel moves rapidly ino the eylindes. The liquid film, dueto
its greater inertia las behind. It causes lean mixture to move to the engine cylinder for a short,
time. This temporary lean mixture prevents the engine from developing fll power just at the time
when it is required the most.
In order to compensate for this tendency of the carburettor, during acceleration, to Fail
‘momentarily to suppl a sufiient rich mixture, a mechanical accelerating device is provided,
‘hich is directly connected tothe throtie mechanism.
95 MIXTURE REQUIREMENTS IN A MULTI-CYLINDER
ENGINE
Aire! malisbution between the eylindesisinerent ina conventional mulicylinder spark
ignition engine. Complete atomization and vaporization ofthe Fue by the carburetor i dificult
brain. Even under the best conditions, the intake manifold contains an appreciable amount of
Liquid as well as large fel droples. A thin film of liquid fuel lso adheres othe inner wall ofthe
intake manifold. These droplets have greater inertia than the gaseous mixtures, Consequently,
‘whenever the direction of flow is changed abruptly the droplets tend to continue in their original
264 Fundumenat of ternal Cantin Engines
Carburewors and Ful jection in St Engines 265
iretion of movement. As resul her isa variation in the rue ratio between the eylnders,
depending upon the cylinder location and the manifold design
For good distribution, ts important to heat the mixture in the intake manifold, causing the
less volatile part of the fuel to vaporize. Poor distribution of fuel to the cylindes of a mul.
Sylinder engine results in alos of power and efficiency. A slight enrichment ofthe overall mixture
il improve the engine performance, so that the leanesteylinder receive the required aire)
ratio. Is indicated by he curve A’B’C’ D’ in Figure 9.4.
9.6 CARBURETTOR REQUIREMENTS
‘The following are the requirements fr an ideal carburetor:
It should provide easy starting of the engine from the cold
[should provide properly atomized fuel with the correct fuer mixture at each speed
corresponding to the droit postion.
should provide the correct fue-air mixture at each trotle opening under diferent loads
and speeds.
4. It should enable the engine to run slowly during idling without hunting or missing the
engine and thus eliminating undue wastage of fl,
5. [should generate maximum acceleration when the trot is suddealy or slowly opened.
‘There should not be any flat spots (hesitation to pick up speed) throughout Ihe trode
opening range.
6. It shouldbe so designed that when the those is fully opened the maximum quantity ofthe
Correct mixture flows into the engine. Sudden bends and restrictions must be avoided
7. Itshould function corecly under diferent climatic conditions, such as temperature, baro-
‘metric or aude and atmosphere moisture changes,
8. It should enable maximum distance perlite under the above conditions
9.7 A SIMPLE CARBURETTOR
‘A simple jet type of carburetor is shown in Figure 9.5. The modem carburettor in ts various
forms has been evolved from ths elementary carburetor. An explanation o ts constuction and
‘operation will aid in understanding the basic principles underlying all carburetors.
consists of a fuel jt of small diameter placed in a constricted tube called ventur or choke
tube, and afloat chamber having a hollow in metal float provided witha conical needle valve.
‘Tac fuel pump detivers fue from the fuel tank to the float chamber. When sofficien fac!
enters the float chamber, the float is ited due 10 buoyancy and the conical needle valve engages
th a sinulaly shaped seating in the petrol pipe union, and thus shut ofthe fuel. I this way the
uel level inthe float chamber is always maintained constant, Ef the fuel level ends to al the Dost
(op and thereby opens the needle valve, bus admiting more fue, The height at which the fel
15 maintained i the float chamber is governed by the level required in the discharge jet. This level
Should stand a lite below the orifice at he ip ofthe jet 10 prevent spilling. The Moat chamber is
vented to atmosphere through a small hole in the cover, hence the pressure onthe surface ofthe
fuel remains constant and equa o that ofthe atmosphere.
Feier —t
a]
coke me
Flatchanber
Te |
ae
Toengine
Fess: Aumpecatunte.
‘The ars induced inthe venturi tube by the suction created by the descending piston ofthe
engine cylinder The Sl engine is quantity governed which means that when less power is required
ata panicular speed the amount of charge delivered o the cylinder is reduced, Tis is achieved
‘by means ofa trot valve ofthe butterfly type whichis situated athe exit ofthe ven ube. At
the throat ofthe venturi tube, the area of eross-setion is minimum, which is shaped to give the
‘minimum resistance o the ai flow. The fuel discharge jet is situated atthe throat. The pressure at
the cat is below atmospheric, since the air velocity has been increased from that atthe inlet to
the carburettor 0 a maximum athe throat. The surface ofthe fuel inthe float chamber is exposed
o atmospheric pressure, while that atthe jet opening in the ventur tube i less than this it thus
follows that the Fuel is forced out of the jr due to this pressure difference. where it mixes wit the
high velocity of air being atomized in the process, and passes with into the engine via the intake
‘manifold and intake valve. The rate of fuel low is controlled or metered by the size of the smallest
section inthe perl passage. This is provided by the main jet and the size ofthis jet is chosen 10
give the required engine performance. The pressure atthe throat at the fully open throttle condition
lies usually between 38 and 50 mm He below atmospheric
Inthe elementary carburettor described above, the choke or throat has a constant area andthe
pressure changes withthe throtle opening and engine speed. Its refered 10 as a fixed choke type
‘of carburettor It is evident that with this type of carburettor the correct fuer rato is obtained
‘only atone particular speed. As the engine speed increases the mixture is enriched and asthe speed
falls the mixture is weakened. I is usual to indicate the size of the carburetor by quoting the
‘diameter ofthe venturi tube in millimetes, nd the jt size in hundredths ofa millimete ejer
number 50 has a diameter of 0.050 mm.
The mathematical analysis ofthe performance ofa simple carburetor follows in the next
Carburewors and Ful jection in St Engines 265
iretion of movement. As resul her isa variation in the rue ratio between the eylnders,
depending upon the cylinder location and the manifold design
For good distribution, ts important to heat the mixture in the intake manifold, causing the
less volatile part of the fuel to vaporize. Poor distribution of fuel to the cylindes of a mul.
Sylinder engine results in alos of power and efficiency. A slight enrichment ofthe overall mixture
il improve the engine performance, so that the leanesteylinder receive the required aire)
ratio. Is indicated by he curve A’B’C’ D’ in Figure 9.4.
9.6 CARBURETTOR REQUIREMENTS
‘The following are the requirements fr an ideal carburetor:
It should provide easy starting of the engine from the cold
[should provide properly atomized fuel with the correct fuer mixture at each speed
corresponding to the droit postion.
should provide the correct fue-air mixture at each trotle opening under diferent loads
and speeds.
4. It should enable the engine to run slowly during idling without hunting or missing the
engine and thus eliminating undue wastage of fl,
5. [should generate maximum acceleration when the trot is suddealy or slowly opened.
‘There should not be any flat spots (hesitation to pick up speed) throughout Ihe trode
opening range.
6. It shouldbe so designed that when the those is fully opened the maximum quantity ofthe
Correct mixture flows into the engine. Sudden bends and restrictions must be avoided
7. Itshould function corecly under diferent climatic conditions, such as temperature, baro-
‘metric or aude and atmosphere moisture changes,
8. It should enable maximum distance perlite under the above conditions
9.7 A SIMPLE CARBURETTOR
‘A simple jet type of carburetor is shown in Figure 9.5. The modem carburettor in ts various
forms has been evolved from ths elementary carburetor. An explanation o ts constuction and
‘operation will aid in understanding the basic principles underlying all carburetors.
consists of a fuel jt of small diameter placed in a constricted tube called ventur or choke
tube, and afloat chamber having a hollow in metal float provided witha conical needle valve.
‘Tac fuel pump detivers fue from the fuel tank to the float chamber. When sofficien fac!
enters the float chamber, the float is ited due 10 buoyancy and the conical needle valve engages
th a sinulaly shaped seating in the petrol pipe union, and thus shut ofthe fuel. I this way the
uel level inthe float chamber is always maintained constant, Ef the fuel level ends to al the Dost
(op and thereby opens the needle valve, bus admiting more fue, The height at which the fel
15 maintained i the float chamber is governed by the level required in the discharge jet. This level
Should stand a lite below the orifice at he ip ofthe jet 10 prevent spilling. The Moat chamber is
vented to atmosphere through a small hole in the cover, hence the pressure onthe surface ofthe
fuel remains constant and equa o that ofthe atmosphere.
Feier —t
a]
coke me
Flatchanber
Te |
ae
Toengine
Fess: Aumpecatunte.
‘The ars induced inthe venturi tube by the suction created by the descending piston ofthe
engine cylinder The Sl engine is quantity governed which means that when less power is required
ata panicular speed the amount of charge delivered o the cylinder is reduced, Tis is achieved
‘by means ofa trot valve ofthe butterfly type whichis situated athe exit ofthe ven ube. At
the throat ofthe venturi tube, the area of eross-setion is minimum, which is shaped to give the
‘minimum resistance o the ai flow. The fuel discharge jet is situated atthe throat. The pressure at
the cat is below atmospheric, since the air velocity has been increased from that atthe inlet to
the carburettor 0 a maximum athe throat. The surface ofthe fuel inthe float chamber is exposed
o atmospheric pressure, while that atthe jet opening in the ventur tube i less than this it thus
follows that the Fuel is forced out of the jr due to this pressure difference. where it mixes wit the
high velocity of air being atomized in the process, and passes with into the engine via the intake
‘manifold and intake valve. The rate of fuel low is controlled or metered by the size of the smallest
section inthe perl passage. This is provided by the main jet and the size ofthis jet is chosen 10
give the required engine performance. The pressure atthe throat at the fully open throttle condition
lies usually between 38 and 50 mm He below atmospheric
Inthe elementary carburettor described above, the choke or throat has a constant area andthe
pressure changes withthe throtle opening and engine speed. Its refered 10 as a fixed choke type
‘of carburettor It is evident that with this type of carburettor the correct fuer rato is obtained
‘only atone particular speed. As the engine speed increases the mixture is enriched and asthe speed
falls the mixture is weakened. I is usual to indicate the size of the carburetor by quoting the
‘diameter ofthe venturi tube in millimetes, nd the jt size in hundredths ofa millimete ejer
number 50 has a diameter of 0.050 mm.
The mathematical analysis ofthe performance ofa simple carburetor follows in the next
DL RDA STARR en ie Nr et Sait
266 fundamen of interna! Combustion Engines
Carburetors and Fuel ljeton in St Engres 267
98 CALCULATION OF THE AIR/FUEL RATIO FOR
A SIMPLE CARBURETTOR
Figure 9.6 shows a simple carburetor where the section AA (plane 1) is taken atthe entry o he
carburetor andthe section BB (plane 2) ac the venti throat
FgureasAsinge carte shoving scion Ah BBand CC.
‘Applying the steady-flow energy equation between the sections AA and BB and considering
nit mass of aie flow, we can write
techs Sew on
Here, y and ware the heat and work tansfrs per unit mass of at flow between planes land 2 and
hand €, denote the enthalpy and velocity of air respectively.
“The flow is assumed o be reversible adiabatic Gsentropic) and there is no work transfer
between planes Land 2; therefore, q =O and w = 0. The approach velocity of air Cay is negligible
‘compared to velocity Cuz, therefore Cay may be taken as zero, Substituting these values in
Eg. (01), the velocity
Ca= TER e»
‘Assuming srt behave lke an ideal gas, therefore, taking h= 6,7, Eq. (9-2) becomes.
corra pará) e
For an isentropic process,
04)
jon
2) vr
a
Ga pa nji (22)
Me os
From ie coi equation, he mas ow of srs
iy = Pri Cas = paña Cas 0
se ae e sei ua fd oe ees of nd aan ae
‘heat voi ate arate (line D and venir thos (plane 2 respectively.
For reversible adiabatic process, pıy = pay " ae
MONO!
meal 2)” en
Paha Ca
LOC
a] on
From qui te, p =
AT
‘The actual rate of mass flow of airis given by
Now,
F
Cha = Cher
where Cs he coefficient of discharge or the vent.
Caen Cda (2) (2) | 0.0)
For the calculation of the mass rate of low of fuel the Bernoulli's theorem can be used as the
fuel is considered 10 be incompressible. Applying the Bernoulli's theorem between sections CC
e
266 fundamen of interna! Combustion Engines
Carburetors and Fuel ljeton in St Engres 267
98 CALCULATION OF THE AIR/FUEL RATIO FOR
A SIMPLE CARBURETTOR
Figure 9.6 shows a simple carburetor where the section AA (plane 1) is taken atthe entry o he
carburetor andthe section BB (plane 2) ac the venti throat
FgureasAsinge carte shoving scion Ah BBand CC.
‘Applying the steady-flow energy equation between the sections AA and BB and considering
nit mass of aie flow, we can write
techs Sew on
Here, y and ware the heat and work tansfrs per unit mass of at flow between planes land 2 and
hand €, denote the enthalpy and velocity of air respectively.
“The flow is assumed o be reversible adiabatic Gsentropic) and there is no work transfer
between planes Land 2; therefore, q =O and w = 0. The approach velocity of air Cay is negligible
‘compared to velocity Cuz, therefore Cay may be taken as zero, Substituting these values in
Eg. (01), the velocity
Ca= TER e»
‘Assuming srt behave lke an ideal gas, therefore, taking h= 6,7, Eq. (9-2) becomes.
corra pará) e
For an isentropic process,
04)
jon
2) vr
a
Ga pa nji (22)
Me os
From ie coi equation, he mas ow of srs
iy = Pri Cas = paña Cas 0
se ae e sei ua fd oe ees of nd aan ae
‘heat voi ate arate (line D and venir thos (plane 2 respectively.
For reversible adiabatic process, pıy = pay " ae
MONO!
meal 2)” en
Paha Ca
LOC
a] on
From qui te, p =
AT
‘The actual rate of mass flow of airis given by
Now,
F
Cha = Cher
where Cs he coefficient of discharge or the vent.
Caen Cda (2) (2) | 0.0)
For the calculation of the mass rate of low of fuel the Bernoulli's theorem can be used as the
fuel is considered 10 be incompressible. Applying the Bernoulli's theorem between sections CC
e
268 Fundamenas of Imaral Comborcon Engines
Carburetors and Fue Injection 1 Engines 269°
(olae3) and BB (lane2),
LA a
BG BG vez ea
CEE RSS
er, gi the deny af el Cl te fel velocity and Z se height of the none exit above
the evel Of fel ine out amor
Her, velciy fe Cj asco CC le nego sins the level of fe oes ot op
Inthe reser
“The fuel velocity atthe nozzle exit G can be obtained from Eq, (9.11), which is given by
om
Pressures at plane 1 and plane 3 are both stmosphero, therefore, ps
= ES 2) cas
7
= Fen
Ca
From ie continuity equation, the mass at of fuel is given by
Acne A JOGO eus
where A, is the area of cross-section of te fue je at the exit from the nozzle
‘The actual rate of mass flow of fuel it
Cp? Gr ANR RE 015
Gus)
‘where Cis the coefficient of discharge for Fuel nozzle.
Aivfuel ratio, A
DEC
A]
al
0.16
9.9 AIR/FUEL RATIO NEGLECTING THE COMPRESSIBILITY OF AIR
Neglecting the effect of compressibility of air, the Bernouli’s theorem can be used for flow of
air as well. Therefore, applying the Bemoulli's theorem between the section AA (plane 1) and
section BB (plane 2) and neglecting the change in potential energy (for air being very light ia
< weight) compared to the change in pressure and Kinetic energy the equation becomes,
a,
| A om
|The approach velocity Cy may be neglected
ETES)
. Ga Peral
| E CT)
Now, De = A Cape
= PET 019
Citar = Cd, Ay f2p, Sp 020
A ides
Fr
A Ge ty [pal
4.2 2
F Cay Ay Op 82) cn
= A. Ay [De
12-0 Fed om
9.10 COMMENTS ON AIR/FUEL RATIO SUPPLIED
BY A SIMPLE CARBURETTOR
‘The following points relevant othe aiduel ratio supplied by a simple carburettor are worth noting:
1. From Eq, (9.14), itis clear hat when Ap & py 2, there wil be no flow of fuel. The fuel.
flow will take place only when Ap > pyaZ. As this pressure difference increases the rate of
mass flow of fuel increases and the mixture becomes progressively richer.
2. Minimum air velocity tthe throat which may cause fuel flow can be estimated approx:
tel from Eq (9.18) a8
Æ. GE ,
Pa Pa va
3. At high rate of flow of al, pis very large compared to py 2. Hence py 87 can be
glo compared 1 pin EA (221), and Ihe ae io ee
ALS ta [ps
FT ae
02)
4. Equation (921) also reveals hat as the density of ar reduces the aifuel to als decreases,
ice. the mixture becomes richer. At high altitudes, the density of ai is Tow. The density OÙ
a atthe throat also reduces for a high ate of air flow through the carburettor,
———<
Carburetors and Fue Injection 1 Engines 269°
(olae3) and BB (lane2),
LA a
BG BG vez ea
CEE RSS
er, gi the deny af el Cl te fel velocity and Z se height of the none exit above
the evel Of fel ine out amor
Her, velciy fe Cj asco CC le nego sins the level of fe oes ot op
Inthe reser
“The fuel velocity atthe nozzle exit G can be obtained from Eq, (9.11), which is given by
om
Pressures at plane 1 and plane 3 are both stmosphero, therefore, ps
= ES 2) cas
7
= Fen
Ca
From ie continuity equation, the mass at of fuel is given by
Acne A JOGO eus
where A, is the area of cross-section of te fue je at the exit from the nozzle
‘The actual rate of mass flow of fuel it
Cp? Gr ANR RE 015
Gus)
‘where Cis the coefficient of discharge for Fuel nozzle.
Aivfuel ratio, A
DEC
A]
al
0.16
9.9 AIR/FUEL RATIO NEGLECTING THE COMPRESSIBILITY OF AIR
Neglecting the effect of compressibility of air, the Bernouli’s theorem can be used for flow of
air as well. Therefore, applying the Bemoulli's theorem between the section AA (plane 1) and
section BB (plane 2) and neglecting the change in potential energy (for air being very light ia
< weight) compared to the change in pressure and Kinetic energy the equation becomes,
a,
| A om
|The approach velocity Cy may be neglected
ETES)
. Ga Peral
| E CT)
Now, De = A Cape
= PET 019
Citar = Cd, Ay f2p, Sp 020
A ides
Fr
A Ge ty [pal
4.2 2
F Cay Ay Op 82) cn
= A. Ay [De
12-0 Fed om
9.10 COMMENTS ON AIR/FUEL RATIO SUPPLIED
BY A SIMPLE CARBURETTOR
‘The following points relevant othe aiduel ratio supplied by a simple carburettor are worth noting:
1. From Eq, (9.14), itis clear hat when Ap & py 2, there wil be no flow of fuel. The fuel.
flow will take place only when Ap > pyaZ. As this pressure difference increases the rate of
mass flow of fuel increases and the mixture becomes progressively richer.
2. Minimum air velocity tthe throat which may cause fuel flow can be estimated approx:
tel from Eq (9.18) a8
Æ. GE ,
Pa Pa va
3. At high rate of flow of al, pis very large compared to py 2. Hence py 87 can be
glo compared 1 pin EA (221), and Ihe ae io ee
ALS ta [ps
FT ae
02)
4. Equation (921) also reveals hat as the density of ar reduces the aifuel to als decreases,
ice. the mixture becomes richer. At high altitudes, the density of ai is Tow. The density OÙ
a atthe throat also reduces for a high ate of air flow through the carburettor,
———<
PS wow... uw SO Se ees
270 Fondumenae of neral Combustion Engines
Careers and Fuel jection in St Ergnes_271
9:11. DEFICIENCIES OF THE ELEMENTARY CARBURETTOR
‘The deficiencies of the elementary carburettor can be listed as follows:
1. At Tow loads the thule valve is partially open, so the mixture becomes lean whereas the
engine requires the rich mixture a low loads.
2. At intermediate loads, the equivalece ratio increases slightly because the proportionate
increase in fuel low i more than the increase in ai flow. However, he engine requires an
Almost constant equivalence ratio.
3. Nes: 10 wide open chrotl the elementary carburettor provides the maximum air low and
the equivalence rro remains constant. However, the engine requires the rich mixture with
equivalence ratio 1.1 or more to develop maximum power.
4. The elementary carburettor cannot enrich the mixture during Engine starting and warm-up
5. The elementary carburettor cannot adjust 10 changes in aude.
9.12 ESSENTIAL PARTS OF A MODERN CARBURETTOR
Modern carburetors vary considerably in design and in tbe means adopted for mixture compense
tion for speed and tros opening. The essential parts of all such modern automobile earburet-
tors, in addition to oat chamber, venturi tube, fuel nozzle and throte, are choke, main metering
system iling system, accelerating system, economizer system and power system.
9421 Choke
‘All modem carburetors are provided with a choke valve inthe air intake passage ofthe carburet-
tor It iss battery type of valve and is shown in Figure 9.7
+
To cage
Figures singe carer whateva,
‘When a cold engine is started, especially at low ambient temperatures, the starting motor
cranks the engine slowly (7010 150 rpm). This produces low manifold vacınım, which draws less
fuel from the jet causing the 100 lean fuel to ignite. The method usually employed for stating the
engine from cold is 0 shutoff most of he main air supply tothe main jes and thus produce rich
mixture necessary for col stating. The choke valve is held in à pataly closed poston by the
thermostat when the engine is being started, and is opened automatically as the engine warms up,
thus gradually supplying the leaner mixture. Some popular ears sill use a hand-operated choke
controlled through linkage by a knob on the instrument panel. Pulling the knob out clases the
choke valve partial, providing a rich mixture for staring. After te engine has started, the knob
is poste back o open che valve which creases the flow tough he carbure ths ening
mixture,
9.122. Main Metering System
‘The tendency ofa simple jet carburetors to increase the richness of the charge with increase in
To nd rl ce ta ow fe fam het ness under son
fae than des the comesponding Cow of lr To compen fr hs tedene of simple et
carburettor, several devices are used as follows: as as
An auxllary air valve
Figure 9 shows a carburetor with an auxiliary air valve, I sutomatically admits additional air
as the mixture flow increases. The valve spring is operated by the vacuum, which increases
wih inet in engine lad and inreass the air admin in proporon to the HR of ie
A
TI
Trt
Ao vive
ateos —
van?
Thole valve
Fuerte mire
Wengne
Figures Catane an aus aval
270 Fondumenae of neral Combustion Engines
Careers and Fuel jection in St Ergnes_271
9:11. DEFICIENCIES OF THE ELEMENTARY CARBURETTOR
‘The deficiencies of the elementary carburettor can be listed as follows:
1. At Tow loads the thule valve is partially open, so the mixture becomes lean whereas the
engine requires the rich mixture a low loads.
2. At intermediate loads, the equivalece ratio increases slightly because the proportionate
increase in fuel low i more than the increase in ai flow. However, he engine requires an
Almost constant equivalence ratio.
3. Nes: 10 wide open chrotl the elementary carburettor provides the maximum air low and
the equivalence rro remains constant. However, the engine requires the rich mixture with
equivalence ratio 1.1 or more to develop maximum power.
4. The elementary carburettor cannot enrich the mixture during Engine starting and warm-up
5. The elementary carburettor cannot adjust 10 changes in aude.
9.12 ESSENTIAL PARTS OF A MODERN CARBURETTOR
Modern carburetors vary considerably in design and in tbe means adopted for mixture compense
tion for speed and tros opening. The essential parts of all such modern automobile earburet-
tors, in addition to oat chamber, venturi tube, fuel nozzle and throte, are choke, main metering
system iling system, accelerating system, economizer system and power system.
9421 Choke
‘All modem carburetors are provided with a choke valve inthe air intake passage ofthe carburet-
tor It iss battery type of valve and is shown in Figure 9.7
+
To cage
Figures singe carer whateva,
‘When a cold engine is started, especially at low ambient temperatures, the starting motor
cranks the engine slowly (7010 150 rpm). This produces low manifold vacınım, which draws less
fuel from the jet causing the 100 lean fuel to ignite. The method usually employed for stating the
engine from cold is 0 shutoff most of he main air supply tothe main jes and thus produce rich
mixture necessary for col stating. The choke valve is held in à pataly closed poston by the
thermostat when the engine is being started, and is opened automatically as the engine warms up,
thus gradually supplying the leaner mixture. Some popular ears sill use a hand-operated choke
controlled through linkage by a knob on the instrument panel. Pulling the knob out clases the
choke valve partial, providing a rich mixture for staring. After te engine has started, the knob
is poste back o open che valve which creases the flow tough he carbure ths ening
mixture,
9.122. Main Metering System
‘The tendency ofa simple jet carburetors to increase the richness of the charge with increase in
To nd rl ce ta ow fe fam het ness under son
fae than des the comesponding Cow of lr To compen fr hs tedene of simple et
carburettor, several devices are used as follows: as as
An auxllary air valve
Figure 9 shows a carburetor with an auxiliary air valve, I sutomatically admits additional air
as the mixture flow increases. The valve spring is operated by the vacuum, which increases
wih inet in engine lad and inreass the air admin in proporon to the HR of ie
A
TI
Trt
Ao vive
ateos —
van?
Thole valve
Fuerte mire
Wengne
Figures Catane an aus aval
AT2_ Fundamente of neral Combustion Engines
_ Carourenors and Fuel lection In S Egin 273
Acomponsating ot
Figure 99 shows the carburettor wth a compensating et. In addition o the main je, a compen-
“ating jet is incorporated which is connected othe compensating well. The compensating well is
so vented o atmosphere and gets its fel supply fom the float chamber trough a rested
orifice, The main jet delivers a richer mixture with increase in ar low, The compensating jet
‘would give a mixture thats too Jean and which becomes sil leaner with the increases in engine
speed and load due tothe fat that more air is drawn in from the well when it is emptied and a
‘constant amount of fuel is discharged. The two jets working together, properly proportioned,
‘compensate one another and keep he ful-ir mixture almost constant as shown in Figure 9.10
Fa
Compensing
ie
Main jet —
pm
A
geo. Cotustervthacarrentnget
Ate ro
‘Aired pa
Figaro. Vator ara owner A compensation.
‘The metering pin
Figure 9.11 shows «carburetor with a metering pin inthe main fuel orifice to conto!
inthe main fuel orifice 1 contol the mixture.
ls a tapered pin, arranged to be moved in and out ofthe main fuel once, tus c
‘quantity ofthe fuel draw into the vertu tube dl
Dr
Peso!
L in ia
rs canter
Fetten
a
Fs: Cobuetawh temankeloio megs.
‘The restricted airbloed system
Figure 9.12 shows a carburetor which contains an air Bleed into the main nozzle and therefore is
into the main no refor is
called restricted sir-bleed et carburetor, Air enters the nozzle though a small ote and enters the
Figue812 Cofueterttthoreeizdhied te.
_ Carourenors and Fuel lection In S Egin 273
Acomponsating ot
Figure 99 shows the carburettor wth a compensating et. In addition o the main je, a compen-
“ating jet is incorporated which is connected othe compensating well. The compensating well is
so vented o atmosphere and gets its fel supply fom the float chamber trough a rested
orifice, The main jet delivers a richer mixture with increase in ar low, The compensating jet
‘would give a mixture thats too Jean and which becomes sil leaner with the increases in engine
speed and load due tothe fat that more air is drawn in from the well when it is emptied and a
‘constant amount of fuel is discharged. The two jets working together, properly proportioned,
‘compensate one another and keep he ful-ir mixture almost constant as shown in Figure 9.10
Fa
Compensing
ie
Main jet —
pm
A
geo. Cotustervthacarrentnget
Ate ro
‘Aired pa
Figaro. Vator ara owner A compensation.
‘The metering pin
Figure 9.11 shows «carburetor with a metering pin inthe main fuel orifice to conto!
inthe main fuel orifice 1 contol the mixture.
ls a tapered pin, arranged to be moved in and out ofthe main fuel once, tus c
‘quantity ofthe fuel draw into the vertu tube dl
Dr
Peso!
L in ia
rs canter
Fetten
a
Fs: Cobuetawh temankeloio megs.
‘The restricted airbloed system
Figure 9.12 shows a carburetor which contains an air Bleed into the main nozzle and therefore is
into the main no refor is
called restricted sir-bleed et carburetor, Air enters the nozzle though a small ote and enters the
Figue812 Cofueterttthoreeizdhied te.
www RIN CIARA RSP ES TS
214 rundum tna Conbtion Engrs
liquid stream through fe larger oles. Thus the Mud stream becomes an emulsion of ai and quid
with negligible viscosity and surface tension. As the suction increases, the influence of viscosity
(iminiches and therefore the air entering the nozzle decreases the flow rate of liquid.
Back suction control or pressure reduction method
Figure 9.13 shows the back suction control or
the pressure reduction method of controling the ae
mixture, A relatively large ven pipe containing a
‘control valve is connected to the carburettor inet Copco vate
At the top of the float chamber. Another pipe
‘conlining a small orifice is connected a he 10p |-ontee
float chamber to the ventur throat. When
the control valve is fully open, the vent pipe is „A. Fallot
‘unrestricted andthe pressure inthe float chamber
is aumospheric, say py. Let the pressure at the
venta throat be pa which is less than py. The
pressure difference acting across the orifice
becomes py = pz. Ifthe control valve is fly
closed, the pressure on both sides of the orifice
‘becomes equal to p and here wil be no pressure
difesence across the orifice and, therefore, there
will be no fuel flow. Thus by regulating the
contro! valve, any debired pressure difference
cross the orifice can be obtained to regulate the
fut flow, This method is normally employed in
large carburetior because iis easily adaptable to
tomatic contol.
‘
Fowe9.13 Cauetor nan can.
Auxilary por carburator nett
Figure 9.14 shows an auxiliary port carburetor. ware 4
“he sunny port contains à brel valve. As
the baterfly valve opens, some sie by-pases
through the aii port and reduces the mount
‘ofr posing tough the vem I eases ess
depression athe throat and rates the amount
of vel lowing ont hough the je. This metho
de used in avert carburetors for elude
compensation.
9.123 Idling System Figure. pudo patent.
Au id and light loads, (he air flow through the carburetor is low which creates insufficient
vacuum at the venturi throat to draw enough fuel into the air steam. However, the manifold
vacuum is high. For idling and low speed operation, the engines require a rch mixture. This
Carburetors and Fo! con in 5 Engnes 275,
ir supply hig system of he carburetor consisting of an ing ul asa and
the ing per. This stem comes im acto daring in, ¡gan ren rr nd
au ut athe engine seed nea. Figure 915 shows acond ing ya nets
a anal fc Sine cn rr th fa che oom eur Do enga Col he hee
The vay comal fined ing fel ote o meter he fel hes aie an
ste contol he ces of the mate tig; when dj me pea ma
Sein ec
cr
ling sc eig fee
Fo chanter
Aledo pre ie
ees ced roe
an sea
ite ie asin Se)
Maa 7
Faum15 Canon ing plan nach.
Win e oie ce be ton ow e Uco cae te el sie ine ie
te and cares he fuel though he ie has por dct in sage ae
rl Teuton so rua od ae ws o an eh
‘sia vpn ud oa wt pss rag ee eee ana
lin th idle ischage po combines wi he ar arm a aes cre a
odie acontusble mir lea proportion for peed Aste Reap es
And ir lo increases, atonal dlrs ble we condo Seen a
Addo oi fred oat of Use ok ito a Beca to poe anne CS
rai. Ae ote par open ute anal me nr a a A
el Sine de wo system coupled he a com a Ho ponds Soe ae
ih, pores aig oft miro aa flow incurs a a an ne a
Constant móxur composition when the main sytem takes over fll control of te fuel ow
214 rundum tna Conbtion Engrs
liquid stream through fe larger oles. Thus the Mud stream becomes an emulsion of ai and quid
with negligible viscosity and surface tension. As the suction increases, the influence of viscosity
(iminiches and therefore the air entering the nozzle decreases the flow rate of liquid.
Back suction control or pressure reduction method
Figure 9.13 shows the back suction control or
the pressure reduction method of controling the ae
mixture, A relatively large ven pipe containing a
‘control valve is connected to the carburettor inet Copco vate
At the top of the float chamber. Another pipe
‘conlining a small orifice is connected a he 10p |-ontee
float chamber to the ventur throat. When
the control valve is fully open, the vent pipe is „A. Fallot
‘unrestricted andthe pressure inthe float chamber
is aumospheric, say py. Let the pressure at the
venta throat be pa which is less than py. The
pressure difference acting across the orifice
becomes py = pz. Ifthe control valve is fly
closed, the pressure on both sides of the orifice
‘becomes equal to p and here wil be no pressure
difesence across the orifice and, therefore, there
will be no fuel flow. Thus by regulating the
contro! valve, any debired pressure difference
cross the orifice can be obtained to regulate the
fut flow, This method is normally employed in
large carburetior because iis easily adaptable to
tomatic contol.
‘
Fowe9.13 Cauetor nan can.
Auxilary por carburator nett
Figure 9.14 shows an auxiliary port carburetor. ware 4
“he sunny port contains à brel valve. As
the baterfly valve opens, some sie by-pases
through the aii port and reduces the mount
‘ofr posing tough the vem I eases ess
depression athe throat and rates the amount
of vel lowing ont hough the je. This metho
de used in avert carburetors for elude
compensation.
9.123 Idling System Figure. pudo patent.
Au id and light loads, (he air flow through the carburetor is low which creates insufficient
vacuum at the venturi throat to draw enough fuel into the air steam. However, the manifold
vacuum is high. For idling and low speed operation, the engines require a rch mixture. This
Carburetors and Fo! con in 5 Engnes 275,
ir supply hig system of he carburetor consisting of an ing ul asa and
the ing per. This stem comes im acto daring in, ¡gan ren rr nd
au ut athe engine seed nea. Figure 915 shows acond ing ya nets
a anal fc Sine cn rr th fa che oom eur Do enga Col he hee
The vay comal fined ing fel ote o meter he fel hes aie an
ste contol he ces of the mate tig; when dj me pea ma
Sein ec
cr
ling sc eig fee
Fo chanter
Aledo pre ie
ees ced roe
an sea
ite ie asin Se)
Maa 7
Faum15 Canon ing plan nach.
Win e oie ce be ton ow e Uco cae te el sie ine ie
te and cares he fuel though he ie has por dct in sage ae
rl Teuton so rua od ae ws o an eh
‘sia vpn ud oa wt pss rag ee eee ana
lin th idle ischage po combines wi he ar arm a aes cre a
odie acontusble mir lea proportion for peed Aste Reap es
And ir lo increases, atonal dlrs ble we condo Seen a
Addo oi fred oat of Use ok ito a Beca to poe anne CS
rai. Ae ote par open ute anal me nr a a A
el Sine de wo system coupled he a com a Ho ponds Soe ae
ih, pores aig oft miro aa flow incurs a a an ne a
Constant móxur composition when the main sytem takes over fll control of te fuel ow
276 fundamente of Inernai Comhusion Engnes
Carturecors and Fut! ection in St Engines 277
tox cercano ave peed ae Thea pot most sunt,
Her ol tis ne llas ag aye
Te acelin pun pte spies te str un of fe ht sde 1 enrich he
Re EE pon sc des e ed
ante op csm guy
‘Sot be ft barter and dav m ng ese ad in ae we
: Oe ce ncn Da a o ds ele
Spun ner eds ng il»
se pa ds unge nove vn
aan a rec cnc iva ops cage var, and charges he fc
reef ae ta Gah pa chase
hie
I
Motion ini direction
fe used opening
Ta
Pl es.
DS
guns: Acer punprecunnnacature,
‘As the throttle is allowed 1 esur to ts original postion, the plangeris lifted by the ink his
action canses a paral vacuum in the pump cylinder which opens the intake valve, coses the
discharge valve, and draws fuel from the float chamber.
9.125 Economizer System and Power System E
I as town Fg 93 ti cnica ne yore o man
ng hoe Iman powers notes he engine ote cu
ns le ur an he maximum soy ferro obtained a fl iro. Fr
Suess power totes goal closed
:Onomizer system changes the mixture from maximum power to maximum economy.
Its usually of the metering pin type. The pin in not fully withdrawa from the fuel orifice when
‘maximum economy is required at fll hroële, The economizec mixture control is usually of the
metering-pi type, shown in Figure 9.11. The pi is linked tothe thot.
Extra fuel for more power is obtained by the use of 4 vacuum contol onthe metering rod in
ion othe control by linkage tothe thon shaft
942.6 Antipercolator Valve
In hot weather the vapour pressure of the fuel increases because of its vaporization. Ths pressure
tends to free the fue ou of the discharge eto produce an overrich condition called carburetor
‘flooding, which may stall the engine. The antipercoltos valve relieves the vapour pressure by
venting the passage in the discharge nozale tothe atmosphere. The valve is naked to the torte
shaft so that when the Ihre i closed the anipercoltos valve is opened.
9.13 TYPES OF CARBURETTORS
Casburenors can be classified on several diferent basis as follows:
1. On the basi ofthe direction of flow of air:
©) up-daught (i) down-draught, and
2. On the bass of location of float chamber
() concentre type and Gi) eccenti tye,
3. On the basis of venturi pe:
(©) The fixed venturi and variable pressure type—the cross-sectional area of the venti
is constant and the depression is vared, This type of carburetor has already been
discussed.
(@ The muhi-ventar and constant presutetype—the cross-sectional ara ofthe venturi
is varied to meet the variation of au ratio, and the depression is almost constant.
(Gi) horizontal drag,
9.131 Down-draught, Up-draught and Horizontal-draught
Carburettors
Down-dravpht, up draught and ocizonal-draphtcarburetrs are shown in Figure 9.17 (0). 0)
and () respectively. The down-draught carburetor mounted above th induction pots, in such
2 manner thatthe ar forthe carburetor is dawn venically downwards past the jet. The fuel
issuing fom the jets therfore assisted by gravity o enter he engine. In the up-draught caburt-
{0¢ the aie ous in the upoar rection and che fuel entre the intake manifold agains the force
of ravi, The Borizontal-draught ype of carburetor has a uaight.ihrough passage. Such cab
‘tors ae used on streamlined cas having low bonne.
“Among these types the down-draught carburetor is more popular It is because the force of
¿xavi asis the fel ito the induction manifold. Large chokes can be used in down draught
surcar because he carburetor can operate satisfactorily with a lower depresion, owing 10
the gravity effect ofthe weight ofthe ue in etrig he induction manito cables a restr
‘eight ofthe mitre to be passed through othe engine at fll role and at igh engine seeds
(
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Carturecors and Fut! ection in St Engines 277
tox cercano ave peed ae Thea pot most sunt,
Her ol tis ne llas ag aye
Te acelin pun pte spies te str un of fe ht sde 1 enrich he
Re EE pon sc des e ed
ante op csm guy
‘Sot be ft barter and dav m ng ese ad in ae we
: Oe ce ncn Da a o ds ele
Spun ner eds ng il»
se pa ds unge nove vn
aan a rec cnc iva ops cage var, and charges he fc
reef ae ta Gah pa chase
hie
I
Motion ini direction
fe used opening
Ta
Pl es.
DS
guns: Acer punprecunnnacature,
‘As the throttle is allowed 1 esur to ts original postion, the plangeris lifted by the ink his
action canses a paral vacuum in the pump cylinder which opens the intake valve, coses the
discharge valve, and draws fuel from the float chamber.
9.125 Economizer System and Power System E
I as town Fg 93 ti cnica ne yore o man
ng hoe Iman powers notes he engine ote cu
ns le ur an he maximum soy ferro obtained a fl iro. Fr
Suess power totes goal closed
:Onomizer system changes the mixture from maximum power to maximum economy.
Its usually of the metering pin type. The pin in not fully withdrawa from the fuel orifice when
‘maximum economy is required at fll hroële, The economizec mixture control is usually of the
metering-pi type, shown in Figure 9.11. The pi is linked tothe thot.
Extra fuel for more power is obtained by the use of 4 vacuum contol onthe metering rod in
ion othe control by linkage tothe thon shaft
942.6 Antipercolator Valve
In hot weather the vapour pressure of the fuel increases because of its vaporization. Ths pressure
tends to free the fue ou of the discharge eto produce an overrich condition called carburetor
‘flooding, which may stall the engine. The antipercoltos valve relieves the vapour pressure by
venting the passage in the discharge nozale tothe atmosphere. The valve is naked to the torte
shaft so that when the Ihre i closed the anipercoltos valve is opened.
9.13 TYPES OF CARBURETTORS
Casburenors can be classified on several diferent basis as follows:
1. On the basi ofthe direction of flow of air:
©) up-daught (i) down-draught, and
2. On the bass of location of float chamber
() concentre type and Gi) eccenti tye,
3. On the basis of venturi pe:
(©) The fixed venturi and variable pressure type—the cross-sectional area of the venti
is constant and the depression is vared, This type of carburetor has already been
discussed.
(@ The muhi-ventar and constant presutetype—the cross-sectional ara ofthe venturi
is varied to meet the variation of au ratio, and the depression is almost constant.
(Gi) horizontal drag,
9.131 Down-draught, Up-draught and Horizontal-draught
Carburettors
Down-dravpht, up draught and ocizonal-draphtcarburetrs are shown in Figure 9.17 (0). 0)
and () respectively. The down-draught carburetor mounted above th induction pots, in such
2 manner thatthe ar forthe carburetor is dawn venically downwards past the jet. The fuel
issuing fom the jets therfore assisted by gravity o enter he engine. In the up-draught caburt-
{0¢ the aie ous in the upoar rection and che fuel entre the intake manifold agains the force
of ravi, The Borizontal-draught ype of carburetor has a uaight.ihrough passage. Such cab
‘tors ae used on streamlined cas having low bonne.
“Among these types the down-draught carburetor is more popular It is because the force of
¿xavi asis the fel ito the induction manifold. Large chokes can be used in down draught
surcar because he carburetor can operate satisfactorily with a lower depresion, owing 10
the gravity effect ofthe weight ofthe ue in etrig he induction manito cables a restr
‘eight ofthe mitre to be passed through othe engine at fll role and at igh engine seeds
(
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We ew Sw we eo ee TE ewe:
278 Fantamenal of Interna! Combusion Engines
Carburetors and Fuel neuen in St Engines 279
Air
o » 0
gue 317 {Doug usta, ar aan.
“The volume efficiency is therefore higher. In addition, the engine pulls beter at lower speeds
‘unde load, as the fuel is fed by gravity.
9.132 Concentric and Eccentric Carburettors.
level of fuel
In he cocentic type the float chamber is placed atthe side ofthe ventur tube, The level
inthe jet changes when the carburetor is ed as the automobile negotiates a grade. The effect of
the grades on this type of carburetor is shown in Figure. 9.18.
las
AU Se
o ® ©
Fado gas once ye lc
ee ezeszgnen
e
ee en
RSR Mer eis
TE
En nen
gg
en CES
9.13.3 Multi-venturi Carburettor
{is generally employed ina mult-cylinder engine for providing a uniform quality of mixture to
each cylinder, It results in increased volumetric efficiency and higher engine output. A mul
venturi carburetor with a concentric Nost chamber is shown in Figure. 9.19. I contains thece
ventures Va, Vo and Va in series. The outlet of smaller venturi Vs is placed inthe throat ofthe
larger venturi Va This arrangement provides better atomization of fuel particles by increasing the
air velocity a the throat. The pressure in the vicinity of jet deereases. The venturi Vis a boost
venturi and itis placed upstream of he main vent, The quantity ofthe air flowing through the
boost venturi is smal but the velocity of aris very high. As the Fuel discharge nozzle is located at
the boost venti tout, the fuel atomization will be much beter. The alcuel mixture is dí
‘charged centrally into the mein venturi where it mixes with more air and a more homogeneous
mixture is produced,
Mallo ven
FEES LE Fast
1 cone oa
Conce Nat
amb
Figue.19_ Araitvenelesbuvterwnacnccifot char:
‘An additional venturi can be used o increase the air velocity Further. In this case the overall
coefficient of discharge decreases. In order to improve the coefficient of discharge, the diameter
ofthe main venturi roti increased. Two ventures, one boost ventur and another main venus,
are also used,
A simple jet carbarettor is required to supply 5 kg of air per minute and 0.4 kg.
por minute of fuel of density 780 g/m’. The air is intially at 1.013 bar and 27°C. Calculate the
‘throat diameter of he choke for an ar low velocity of 90 m/s. Take the velocity coefficient for
the venturi 10 be 0.80 and the coefficient of discharge of the main fuel jet to be 06. Assume
isentropie low and the flow 10 be compressible. IF the pressure drop across the fuel metering
orifice is 0.75 ofthat atthe choke, calculate the orifice dir
Solution: Refer 10 Figure 920
Given: mz =5 kg/min
278 Fantamenal of Interna! Combusion Engines
Carburetors and Fuel neuen in St Engines 279
Air
o » 0
gue 317 {Doug usta, ar aan.
“The volume efficiency is therefore higher. In addition, the engine pulls beter at lower speeds
‘unde load, as the fuel is fed by gravity.
9.132 Concentric and Eccentric Carburettors.
level of fuel
In he cocentic type the float chamber is placed atthe side ofthe ventur tube, The level
inthe jet changes when the carburetor is ed as the automobile negotiates a grade. The effect of
the grades on this type of carburetor is shown in Figure. 9.18.
las
AU Se
o ® ©
Fado gas once ye lc
ee ezeszgnen
e
ee en
RSR Mer eis
TE
En nen
gg
en CES
9.13.3 Multi-venturi Carburettor
{is generally employed ina mult-cylinder engine for providing a uniform quality of mixture to
each cylinder, It results in increased volumetric efficiency and higher engine output. A mul
venturi carburetor with a concentric Nost chamber is shown in Figure. 9.19. I contains thece
ventures Va, Vo and Va in series. The outlet of smaller venturi Vs is placed inthe throat ofthe
larger venturi Va This arrangement provides better atomization of fuel particles by increasing the
air velocity a the throat. The pressure in the vicinity of jet deereases. The venturi Vis a boost
venturi and itis placed upstream of he main vent, The quantity ofthe air flowing through the
boost venturi is smal but the velocity of aris very high. As the Fuel discharge nozzle is located at
the boost venti tout, the fuel atomization will be much beter. The alcuel mixture is dí
‘charged centrally into the mein venturi where it mixes with more air and a more homogeneous
mixture is produced,
Mallo ven
FEES LE Fast
1 cone oa
Conce Nat
amb
Figue.19_ Araitvenelesbuvterwnacnccifot char:
‘An additional venturi can be used o increase the air velocity Further. In this case the overall
coefficient of discharge decreases. In order to improve the coefficient of discharge, the diameter
ofthe main venturi roti increased. Two ventures, one boost ventur and another main venus,
are also used,
A simple jet carbarettor is required to supply 5 kg of air per minute and 0.4 kg.
por minute of fuel of density 780 g/m’. The air is intially at 1.013 bar and 27°C. Calculate the
‘throat diameter of he choke for an ar low velocity of 90 m/s. Take the velocity coefficient for
the venturi 10 be 0.80 and the coefficient of discharge of the main fuel jet to be 06. Assume
isentropie low and the flow 10 be compressible. IF the pressure drop across the fuel metering
orifice is 0.75 ofthat atthe choke, calculate the orifice dir
Solution: Refer 10 Figure 920
Given: mz =5 kg/min
280 Fundamentals of neral Combustion Engines
Carburetors and Fuel Injeccon in SI Engines 281
iy >04 Kain ;
= 1.013 bat, 7; = 300 K
= ml, Ou = 08, C= 06
4
Anplying the flow enery ton between planes and 2, foire
ope ow,
+Gem+
geht
“Taking aprosch velocity, Cı +0, we have L
en Pesan Eso.
A
= HEAD = fas li-E)
a
5 ji
: Perf (2) |
Actua velocity of sr at plane,
Pa
= brli-
CN
> a
m Et,
nro
a
e m cr
ais an
= 101341 - 00209973
09405 tar
Tiros pressure, m = 09405 bar
2. _ 1013x10°
Rh 287300
pie = Pave
Density of airat inlet, py
For isentopie flow,
aii
dolina aici
vada chat
a
da A
O OS
A "nt
= 1.116 kgf?
‘To determine he throat ars, apply the coin equation Le.
ma © Poa
Ma _ 5/60
Aas See = GS = (8297 x 10-4 m2 8297 en?
3200] Ans.
Pressure drop at jet
15 X 0.0725 = 0.0544 bar
Now. (es = Cd Ep OR
Hee, z
fy ou
“ -
Ca 20,5 | os fax TRO x00se x10"
= (3,814 x 10%) m?
3.814 mm?
Raj 23818
DE]
a FE ran] am
A foursroke patrol engine of 2 li capaci is required to develop maximum
Power at 4500 rpm. The volumetric efficiency at this speed ie sumed to be 75% and the aiefuel
‘tio is 14:1. Two carburetors ae to be fitted and it is expected that at peak power the ar speed
at the choke will be 100 mvs, The coefficient of discharge forthe ventar is assumed to be 0.85
and that ofthe main petrol jet is 0.66. An allowance should be made for te emulsion tube, the
diameter of which can be taken as 0.4 ofthe ehoke diameter, The petrol surface is 6 mm below the
choke at this engine condition. Calculate the size ofa suitable choke and that ofthe main jet. The
specific gravity of pero is 0.75.
‘The atmospheric pressure and temperature are 1.013 bar and 15°C respectively.
Carburetors and Fuel Injeccon in SI Engines 281
iy >04 Kain ;
= 1.013 bat, 7; = 300 K
= ml, Ou = 08, C= 06
4
Anplying the flow enery ton between planes and 2, foire
ope ow,
+Gem+
geht
“Taking aprosch velocity, Cı +0, we have L
en Pesan Eso.
A
= HEAD = fas li-E)
a
5 ji
: Perf (2) |
Actua velocity of sr at plane,
Pa
= brli-
CN
> a
m Et,
nro
a
e m cr
ais an
= 101341 - 00209973
09405 tar
Tiros pressure, m = 09405 bar
2. _ 1013x10°
Rh 287300
pie = Pave
Density of airat inlet, py
For isentopie flow,
aii
dolina aici
vada chat
a
da A
O OS
A "nt
= 1.116 kgf?
‘To determine he throat ars, apply the coin equation Le.
ma © Poa
Ma _ 5/60
Aas See = GS = (8297 x 10-4 m2 8297 en?
3200] Ans.
Pressure drop at jet
15 X 0.0725 = 0.0544 bar
Now. (es = Cd Ep OR
Hee, z
fy ou
“ -
Ca 20,5 | os fax TRO x00se x10"
= (3,814 x 10%) m?
3.814 mm?
Raj 23818
DE]
a FE ran] am
A foursroke patrol engine of 2 li capaci is required to develop maximum
Power at 4500 rpm. The volumetric efficiency at this speed ie sumed to be 75% and the aiefuel
‘tio is 14:1. Two carburetors ae to be fitted and it is expected that at peak power the ar speed
at the choke will be 100 mvs, The coefficient of discharge forthe ventar is assumed to be 0.85
and that ofthe main petrol jet is 0.66. An allowance should be made for te emulsion tube, the
diameter of which can be taken as 0.4 ofthe ehoke diameter, The petrol surface is 6 mm below the
choke at this engine condition. Calculate the size ofa suitable choke and that ofthe main jet. The
specific gravity of pero is 0.75.
‘The atmospheric pressure and temperature are 1.013 bar and 15°C respectively.
282 Fancamenal ol Internal Combustion Engines
Carbureors and Fuel Ijecion In S Engines 283
Solution: — Swept volume, V, = 2 lite = 0.002 m?. Volume ofa
x
inducted for fourstoke engine per second = ny: Pa ÈS
‘where ny isthe volumetric efficiency and A
0.750.002 4500 dde a
2x60 id
0.05625,
ihe engine rpm.
Volume of air inducted =
= 0.028125 mvs
ach carburetor delivers an air flow of
2
Y, = 0028125 mits
|
Figure 321 Ecmglo92.
nk „ 1013x10°x0008125
ESE
Velocity athroat, Co = [26,1
03447 kgs
CS
a) |
Density of
1013105 A
2 IA 1 256
ps RE = Hs = 2256 ko
(2) = 1.2256(0.9408)"" = 1.1733 kom?
act ae,
Ags tte = pag SOE 7 (456 10 mé
27 pCa, 11733x100x085
HS mn?
gt
Zt -d) = 3456
Now. 4=04D
Ep? 01604 = 456
or 0.84 x FD? = 45.6
4 ETA
o De PESA A] ams.
y = GANT Pr 2
vig _ 003087
a
For the petrol the pressure difference aros ho main jets given y
proce = 100-095 220006290
00-095 - one
105956 bar = (0.05956 x 10°) Nm?
fy
A]
ous
© 965625750 0.05956 10°)
1.248 10% m = 1.248 mun
A four cylinder four-stroke spark ignition engine with 80 mm bore and 90 mm.
stroke runs at 4000 rpm and uses a fuel having 84% carbon and 16% hydrogen by mass. The
volumetio efficiency of the engine at that speed is 80%. The ambient conditions are: pressure
‘Oba, temperature = 25°C. The depression tthe venturi throat is 0.06 bar The actual quantity
‘of airsuppliedis 0.95 ofthe stoichiometcc value. Calculate the fuel flowrate, the air velocity atthe
bro and the throat diameter.
Take Rain) = 287 Mi K); Ruel vapour) = 98 kg K).
Solution: As the gas constant R for fuel vapour is given, instead of only volume of ar supplied
to the engine, the volume of the mixture can be considered, which is more accurate,
fy 0.002462 kgs
Area of the jet
Volume of mixture supplied 0 thee
wy
xO
Pen X No. of eylinders
(008) (0.09) (08) - ¿Pe X4
= 004825 ms
Morea)
Stoichiometicav/fuel aio
Carbureors and Fuel Ijecion In S Engines 283
Solution: — Swept volume, V, = 2 lite = 0.002 m?. Volume ofa
x
inducted for fourstoke engine per second = ny: Pa ÈS
‘where ny isthe volumetric efficiency and A
0.750.002 4500 dde a
2x60 id
0.05625,
ihe engine rpm.
Volume of air inducted =
= 0.028125 mvs
ach carburetor delivers an air flow of
2
Y, = 0028125 mits
|
Figure 321 Ecmglo92.
nk „ 1013x10°x0008125
ESE
Velocity athroat, Co = [26,1
03447 kgs
CS
a) |
Density of
1013105 A
2 IA 1 256
ps RE = Hs = 2256 ko
(2) = 1.2256(0.9408)"" = 1.1733 kom?
act ae,
Ags tte = pag SOE 7 (456 10 mé
27 pCa, 11733x100x085
HS mn?
gt
Zt -d) = 3456
Now. 4=04D
Ep? 01604 = 456
or 0.84 x FD? = 45.6
4 ETA
o De PESA A] ams.
y = GANT Pr 2
vig _ 003087
a
For the petrol the pressure difference aros ho main jets given y
proce = 100-095 220006290
00-095 - one
105956 bar = (0.05956 x 10°) Nm?
fy
A]
ous
© 965625750 0.05956 10°)
1.248 10% m = 1.248 mun
A four cylinder four-stroke spark ignition engine with 80 mm bore and 90 mm.
stroke runs at 4000 rpm and uses a fuel having 84% carbon and 16% hydrogen by mass. The
volumetio efficiency of the engine at that speed is 80%. The ambient conditions are: pressure
‘Oba, temperature = 25°C. The depression tthe venturi throat is 0.06 bar The actual quantity
‘of airsuppliedis 0.95 ofthe stoichiometcc value. Calculate the fuel flowrate, the air velocity atthe
bro and the throat diameter.
Take Rain) = 287 Mi K); Ruel vapour) = 98 kg K).
Solution: As the gas constant R for fuel vapour is given, instead of only volume of ar supplied
to the engine, the volume of the mixture can be considered, which is more accurate,
fy 0.002462 kgs
Area of the jet
Volume of mixture supplied 0 thee
wy
xO
Pen X No. of eylinders
(008) (0.09) (08) - ¿Pe X4
= 004825 ms
Morea)
Stoichiometicav/fuel aio
284 Fandamenaı of Intamal Combustion Engines
Carturenors and Fue nection in S Engines 285,
lol + 016%:
(osx 40103) =153:1
‘The actual mass of ai supplied per kg of ful
0.95 x 15.3 = 14,535 kere fuel
Actual aifuel rato = 14.535 : 1
‘The density of air at 1 bar and 298 K,
ew
E AS
3.424 kg/m!
‘The distribution of ar and fuel is usually approximated by
‘Volume flow rate of air + Volume flow rate of fue = Volume flow rate of mixture
ie, ea LL 004825
Pe’ Be
my
Also, > ss
i 1
cis nase
ña = 0.05511 kgs
) = 000025
= fay OEM = mx 10°) Kg [TORRE] Am.
‘The depen tie vst ret = 006 ba
in Sen -n one
pi 008 = 100-006 0.98 ba
or 2-09
ñ
An
Velocity of ict the hos, G = Et) |
= 2x 1005x2981 09a]
TES] Ans.
le density of ae at the rot =e
The dns fairen. pe
= 298 (0.94% = 292.8 K
94x10?
a= BOUL 1119 gm
If the coeficient of discharge forthe throat is assumed as unity, the cross-sectional area of the
vent throat,
ty __ 005511
Baby © TRS NOUS = 48905 x 10° mé
805 emt
Pen
A four-suoke four-cylinder spark-ignition engine having a bore of 100 mm
and stoke of 120 mm and running at 3000 rpm has a carburetor venturi with a 35 ma theoat
ameter. The volumeti efficiency ofthe engine at this speed is 80%, the coefficient of discharge
of air flow is 0.82. The ambient pressure and temperature are 1.013 bar and 25°C respectively,
‘Tae ail ratio is 15. The top ofthe jets 5 mm above the petrol level inthe oat chamber, The
coefficient of discharge for fuel flow is 0.7. Determine the depression at the theoat andthe dia
ter ofthe fuel jet of a simple carburetor. The specific gravity of pero is 0.75
47 om= [mm] Ans.
Soluton: Votan of inate pr second = E Lx yx x0 fetes
5 3000
= FO? «01 x08 x 208 x4
= 00754 ms
ity of ai, LO
ene ila e I ka?
Mass of aids = m= 0.0754 x 1.184 = 0.08927 Kg
‘As the throat velocity and depression are both not given, the problems solved by he approx
mate method, Le. by assuming incompressible flow of air
the = Cada TP One Pad
An = Elo 20.035) = (9621 10%) mi
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N
Carturenors and Fue nection in S Engines 285,
lol + 016%:
(osx 40103) =153:1
‘The actual mass of ai supplied per kg of ful
0.95 x 15.3 = 14,535 kere fuel
Actual aifuel rato = 14.535 : 1
‘The density of air at 1 bar and 298 K,
ew
E AS
3.424 kg/m!
‘The distribution of ar and fuel is usually approximated by
‘Volume flow rate of air + Volume flow rate of fue = Volume flow rate of mixture
ie, ea LL 004825
Pe’ Be
my
Also, > ss
i 1
cis nase
ña = 0.05511 kgs
) = 000025
= fay OEM = mx 10°) Kg [TORRE] Am.
‘The depen tie vst ret = 006 ba
in Sen -n one
pi 008 = 100-006 0.98 ba
or 2-09
ñ
An
Velocity of ict the hos, G = Et) |
= 2x 1005x2981 09a]
TES] Ans.
le density of ae at the rot =e
The dns fairen. pe
= 298 (0.94% = 292.8 K
94x10?
a= BOUL 1119 gm
If the coeficient of discharge forthe throat is assumed as unity, the cross-sectional area of the
vent throat,
ty __ 005511
Baby © TRS NOUS = 48905 x 10° mé
805 emt
Pen
A four-suoke four-cylinder spark-ignition engine having a bore of 100 mm
and stoke of 120 mm and running at 3000 rpm has a carburetor venturi with a 35 ma theoat
ameter. The volumeti efficiency ofthe engine at this speed is 80%, the coefficient of discharge
of air flow is 0.82. The ambient pressure and temperature are 1.013 bar and 25°C respectively,
‘Tae ail ratio is 15. The top ofthe jets 5 mm above the petrol level inthe oat chamber, The
coefficient of discharge for fuel flow is 0.7. Determine the depression at the theoat andthe dia
ter ofthe fuel jet of a simple carburetor. The specific gravity of pero is 0.75
47 om= [mm] Ans.
Soluton: Votan of inate pr second = E Lx yx x0 fetes
5 3000
= FO? «01 x08 x 208 x4
= 00754 ms
ity of ai, LO
ene ila e I ka?
Mass of aids = m= 0.0754 x 1.184 = 0.08927 Kg
‘As the throat velocity and depression are both not given, the problems solved by he approx
mate method, Le. by assuming incompressible flow of air
the = Cada TP One Pad
An = Elo 20.035) = (9621 10%) mi
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1286 Fundamentals of Ir Combustion Engines
Carburetors and Fue necien in S Engines 287
PORT CENT,
(008927 _
82 (9.621 x 10) (2x 1184)
GEO] Ans.
fy
on y BR à 5951 x 10° kg
Now, my = GOA Too P= BLY
n=
ae]
5951x107
ATAN ITA
2310 m=
¿- E = [ia] am
‘An engine having a single jet carburetor consumes 6.0 kg/h of fuel. The den
ty of fuel 750 kg/m. The level inthe float chamber is 3 mm below the top of the jet when the
‘engine is not running. Ambient conditions are 1.013 bar and 21°C. The jet diameters 1.2 mm and
its discharge coefficient is 0,65. The discharge coefficient of air is 0.80. The aicfuel ratio is
1534. Determine the eiical aie velocity, the depression at tbe Uroat in ram of HO and the
effective throat diameter. Neglet the compressibility of at
Solution:
Density of a, Pa =12kgm
ab
an
[Neglecting he compressibility oft, de cial air velocity at ih throat,
PILE
Cd Pee 05
CE) Ans.
Fuel flow per second,
fi = LA TOA AI)
qe e E
wm
Exa?
Given: my kes; C2065; Z
1003 m
131 mom = (1131 10% m?
Deyo. Pa SPP = aoe
57
Ca
one oe 7
AA
1
a BRD
OOP IO PERT * >
23427 + 22 = 3449 Nim? = 0.03449 bar
no 3449
Poe © 100%
349
tommot 0, = 342 - [BlEmmoriho] Ans
Ai flow per second,
In meu of water,
‘hy = CILA LATE)
Alto, x 153 = 0.0255 ky/s
Here, Des VD Keim’, pr py = 3449 Nm?
(ne) Ans.
[ESSIUHHERN A simple carburetor has a venturi throat diameter of 2 mm andthe coefficient
(of air Row is 0.82, The fuel orifice has a diameter of 1.2 mm and th coefficient of fuel flow is
(0.70. The petol surface is 4 mm below the throat, Find:
(a) The ail ratio when the nozzle li is neglected
y
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1286 Fundamentals of Ir Combustion Engines
Carburetors and Fue necien in S Engines 287
PORT CENT,
(008927 _
82 (9.621 x 10) (2x 1184)
GEO] Ans.
fy
on y BR à 5951 x 10° kg
Now, my = GOA Too P= BLY
n=
ae]
5951x107
ATAN ITA
2310 m=
¿- E = [ia] am
‘An engine having a single jet carburetor consumes 6.0 kg/h of fuel. The den
ty of fuel 750 kg/m. The level inthe float chamber is 3 mm below the top of the jet when the
‘engine is not running. Ambient conditions are 1.013 bar and 21°C. The jet diameters 1.2 mm and
its discharge coefficient is 0,65. The discharge coefficient of air is 0.80. The aicfuel ratio is
1534. Determine the eiical aie velocity, the depression at tbe Uroat in ram of HO and the
effective throat diameter. Neglet the compressibility of at
Solution:
Density of a, Pa =12kgm
ab
an
[Neglecting he compressibility oft, de cial air velocity at ih throat,
PILE
Cd Pee 05
CE) Ans.
Fuel flow per second,
fi = LA TOA AI)
qe e E
wm
Exa?
Given: my kes; C2065; Z
1003 m
131 mom = (1131 10% m?
Deyo. Pa SPP = aoe
57
Ca
one oe 7
AA
1
a BRD
OOP IO PERT * >
23427 + 22 = 3449 Nim? = 0.03449 bar
no 3449
Poe © 100%
349
tommot 0, = 342 - [BlEmmoriho] Ans
Ai flow per second,
In meu of water,
‘hy = CILA LATE)
Alto, x 153 = 0.0255 ky/s
Here, Des VD Keim’, pr py = 3449 Nm?
(ne) Ans.
[ESSIUHHERN A simple carburetor has a venturi throat diameter of 2 mm andthe coefficient
(of air Row is 0.82, The fuel orifice has a diameter of 1.2 mm and th coefficient of fuel flow is
(0.70. The petol surface is 4 mm below the throat, Find:
(a) The ail ratio when the nozzle li is neglected
288 Fundamentals of Internal Combunden Eng
[Carburetors and fue! neon in SI Engines 289°
o) The aire to fora pressure drop of 0.078 bar when the nogal lip sake int account
{© Ts minimum veya aor ic ar veo eed a fw ten
nozzle pis provided.
“Take density of air and fut a 1.2 km? and 750 kg/m? respect
) When the nozzle Hip Zi neplected
Rate of mass flow of ai, u = Cay An BP BP
Rate of mess flow of fuel, shy = GA)
Be à Coto, [Bi
By Cay, VP
= adh [pe
Ca, a Vy
082, (227
“ oa)
(0) When the nozzle lip Zis considered:
si, will remain the same
si my = GANT D
Solutio
Ai
Now, 29 = 9.81 x 0.008 x 750 = 29.43 Nim?
= 0,0002983 bar
and Ap - sZpy= 0.075 — 00002943 = 0.0747 bar
fig Cla Ay 7
my "Ca, Ay PTE)
e (2y [Tom
“07 12) V 350x078
(©) When the nozzle lip is provided, the flow of fuel wil stat only when there is sufficient
depression to overcome the nozzle ip effect. The depression is created by the critical velocity of
Alltel ratio,
1578] Ans.
Minimum velocity of uc or critical velocity atthe throat,
ca PEE
Ls
PE
Tai] Ans.
Determine the airlfuel ratio in an airplane engine carburécor st 4000 m altitude
arbureitors adjusted to give an ar/uel ratio Of 14.7; | at ea level where the ir temperature
422°C and the pressure 1.013 bar The temperature variation with altitude is given by the expresion
T= Tania = 000654,
where is the eight in metres and To
decreases wit ate as per the elation.
Solution: Given:
isthe sea level temperature in °C, The ar pressure
19200 log (1.013%p), where is in bar.
T= Treg tes = 0.0055
= 22 ~ (0.0065 x 4000)
26 =~ 470 = 269
Non, 12 fone opt 0139)
& 4000 = 19200 e0.013)
o (2)
>
sivfue rato makimde _ fp,
‘ie rio ates evel” Vas
ere Zu,
va Pas E AO «951014 ha?
„ 1013x10° B
a Pats LOTO 1.196 ten
aloe ca at alude [ORTATE
147 “Yin
sudo = 147 {81214
Aider at aitade = 14.1 [28127
is observed that with the increase in altitude the mixture becomes rich. Therefore, some
altitude compensating device should be incorporated for proper combustion of fuel.
A carburetor is sted without an ancleaner, The main metering sytem is
adjusted to give sifuel ratio of 14.5. The pressure atthe venturi throat is 0.895 bar The
sumosphere pressure is 1.013 bat The same carburo is tested again wih en alonso
reste drop 2 he arcano is found 1 be 37. mun of Hg. The ir Now is 260 ks per hom.
TAN] Ans.
[Carburetors and fue! neon in SI Engines 289°
o) The aire to fora pressure drop of 0.078 bar when the nogal lip sake int account
{© Ts minimum veya aor ic ar veo eed a fw ten
nozzle pis provided.
“Take density of air and fut a 1.2 km? and 750 kg/m? respect
) When the nozzle Hip Zi neplected
Rate of mass flow of ai, u = Cay An BP BP
Rate of mess flow of fuel, shy = GA)
Be à Coto, [Bi
By Cay, VP
= adh [pe
Ca, a Vy
082, (227
“ oa)
(0) When the nozzle lip Zis considered:
si, will remain the same
si my = GANT D
Solutio
Ai
Now, 29 = 9.81 x 0.008 x 750 = 29.43 Nim?
= 0,0002983 bar
and Ap - sZpy= 0.075 — 00002943 = 0.0747 bar
fig Cla Ay 7
my "Ca, Ay PTE)
e (2y [Tom
“07 12) V 350x078
(©) When the nozzle lip is provided, the flow of fuel wil stat only when there is sufficient
depression to overcome the nozzle ip effect. The depression is created by the critical velocity of
Alltel ratio,
1578] Ans.
Minimum velocity of uc or critical velocity atthe throat,
ca PEE
Ls
PE
Tai] Ans.
Determine the airlfuel ratio in an airplane engine carburécor st 4000 m altitude
arbureitors adjusted to give an ar/uel ratio Of 14.7; | at ea level where the ir temperature
422°C and the pressure 1.013 bar The temperature variation with altitude is given by the expresion
T= Tania = 000654,
where is the eight in metres and To
decreases wit ate as per the elation.
Solution: Given:
isthe sea level temperature in °C, The ar pressure
19200 log (1.013%p), where is in bar.
T= Treg tes = 0.0055
= 22 ~ (0.0065 x 4000)
26 =~ 470 = 269
Non, 12 fone opt 0139)
& 4000 = 19200 e0.013)
o (2)
>
sivfue rato makimde _ fp,
‘ie rio ates evel” Vas
ere Zu,
va Pas E AO «951014 ha?
„ 1013x10° B
a Pats LOTO 1.196 ten
aloe ca at alude [ORTATE
147 “Yin
sudo = 147 {81214
Aider at aitade = 14.1 [28127
is observed that with the increase in altitude the mixture becomes rich. Therefore, some
altitude compensating device should be incorporated for proper combustion of fuel.
A carburetor is sted without an ancleaner, The main metering sytem is
adjusted to give sifuel ratio of 14.5. The pressure atthe venturi throat is 0.895 bar The
sumosphere pressure is 1.013 bat The same carburo is tested again wih en alonso
reste drop 2 he arcano is found 1 be 37. mun of Hg. The ir Now is 260 ks per hom.
TAN] Ans.
A ADR D SR NON Nat ENA BE Sat PR a ASAD NR ÓN
290 _Fundumenals of Interna Combustion Eines
Carburetors and Fu jeton In SI Engines 291
Assuming zero nozzle lip and constant coefficient of flow, determine (a) the throat pressure when.
the air-cleaner is fied and (0) the ale ratio withthe ai-cleaner fited,
Solution: (2) Without the siccleanes, the depression atthe throst,
pa = 1.013 ~ 0825 = 0.188 bar
When the aircleaner is fed, let p be the throat pressure,
then,
(1019-223)
(0.963 - pa) bar
For the same ai low and constant coefficient of flow,
[SE] Ans.
(0) Without e aireleaner, Apy
‘With the sir-leane, py = 1.013 ~ 0.795 = 0238 bar
As Apyhas increased, more fel will low through, tus making the mixture richer
“The aie Now is given by
= CA, An TPE.
Since dp, and all other terms ar same in both the cases, he, with and without the ar-leaner,
remains the same.
The fuel flow without tip Z = 0).
sy = CA 878
Cy Ay and pyare the same in both the cass, but Apy is different
CARRE
Cana are
= CIA ie
A © V OP Dinar
Gig
irc ati withthe aineleaner = 14.5 [Gas
= [2B] Ans.
OP Nai ee
Oia
A pesotengiedevlops 8W bre powerhavng brake thermal efficiency of
En vodkng a ie fll oud coniuon Te caloi vale ofthe fc is 44000 ig. The
ion conditions ef the engine ar 1.01 bar and 300K. The carburetor fed on is engine has
Sate et of23 mn? andthe norte Hpi mm. Deter the vert thot dimer ofthe
rer 1 provide an ive! rat of 15. Take the following dt:
Ch =09, p= Token, — C4y=07
and vafat NTP) = 0.8 mg.
Solution: Specific volume of air at atmospheric pressure and 300 K
28300 0.8791 ming.
Ey
is 11375 kom
Brake thermal efficiency,
ew)
RESTO]
8
o 032 co
Ñ 8 ig
Os Tr Le
Fram the continuity equation,
y = Chan
Velocity of fuel, at
” EST
= 0.000606 M
ES
Nov, a en
g
or ap pps = EPL.
do
or op = LLL + pyez
2
= LAGO 759 981 x 0.008
= 1994 + $886 = 1388 Nm!
290 _Fundumenals of Interna Combustion Eines
Carburetors and Fu jeton In SI Engines 291
Assuming zero nozzle lip and constant coefficient of flow, determine (a) the throat pressure when.
the air-cleaner is fied and (0) the ale ratio withthe ai-cleaner fited,
Solution: (2) Without the siccleanes, the depression atthe throst,
pa = 1.013 ~ 0825 = 0.188 bar
When the aircleaner is fed, let p be the throat pressure,
then,
(1019-223)
(0.963 - pa) bar
For the same ai low and constant coefficient of flow,
[SE] Ans.
(0) Without e aireleaner, Apy
‘With the sir-leane, py = 1.013 ~ 0.795 = 0238 bar
As Apyhas increased, more fel will low through, tus making the mixture richer
“The aie Now is given by
= CA, An TPE.
Since dp, and all other terms ar same in both the cases, he, with and without the ar-leaner,
remains the same.
The fuel flow without tip Z = 0).
sy = CA 878
Cy Ay and pyare the same in both the cass, but Apy is different
CARRE
Cana are
= CIA ie
A © V OP Dinar
Gig
irc ati withthe aineleaner = 14.5 [Gas
= [2B] Ans.
OP Nai ee
Oia
A pesotengiedevlops 8W bre powerhavng brake thermal efficiency of
En vodkng a ie fll oud coniuon Te caloi vale ofthe fc is 44000 ig. The
ion conditions ef the engine ar 1.01 bar and 300K. The carburetor fed on is engine has
Sate et of23 mn? andthe norte Hpi mm. Deter the vert thot dimer ofthe
rer 1 provide an ive! rat of 15. Take the following dt:
Ch =09, p= Token, — C4y=07
and vafat NTP) = 0.8 mg.
Solution: Specific volume of air at atmospheric pressure and 300 K
28300 0.8791 ming.
Ey
is 11375 kom
Brake thermal efficiency,
ew)
RESTO]
8
o 032 co
Ñ 8 ig
Os Tr Le
Fram the continuity equation,
y = Chan
Velocity of fuel, at
” EST
= 0.000606 M
ES
Nov, a en
g
or ap pps = EPL.
do
or op = LLL + pyez
2
= LAGO 759 981 x 0.008
= 1994 + $886 = 1388 Nm!
292 Fundamental of Internal Combustion Eng
Carburetors and Fuel ejection in SI Eines 293
Now, velocity of air atthe throat,
G
Aix supplied 1 Ihe engine per second,
fe: Fat
a= ape age
CEA
pr = (5.684 x 10") m? = 5.684 cm
aa (5.684 x 107) m? = 5.684
do ¡ER
9.14 PROBLEMS ASSOCIATED WITH CARBURETTORS
‘Some ofthe problems associated with satisfactory running of the carburettor are discussed inthe
following subsections.
9.14.1 Ice Formation
"When a volatile liquid evaporates, the temperature around is lowered owing to the effect of latent
heat of evaporation. Applied to the fuel jet ofa carburetc this evaporation lowers the temperature
‘of the intake air and if the air contas any moisture, some of it wil be condensed. If the outside
{temperature is low, asin winter or at higher altitudes a in the case of aircraft engines, the moisture
in the air will tend to form ie on all interna surfaces exposed to the mixture stream. Moisture in
the intake ai tends to form ice onthe tote blade and on the pats ofthe carburettor barrel near
10 the blade. Inthe course of time the whole of the top edges become coated and the ac low is
restricted, therefore at low throttle openings the engine may cease to operate.
‘As this poses a serious problem, steps must be taken to overcome this difficult, The follow
ing methods may be employed:
1. Heating the intake at
2, Heating the metal surface, ie. the choke and mixture charaber by coolant from the water
Jackets or exhaust gases, on which ice is liable to form.
3. The use of ice preventives or iahibiors. alcohol such as ethanol or methanol is added to
the fue, freezing canbe avoided. An ce detector and an automatic servomechanism can be
used to deliver alcohol on o the surfaces liable to be covered with ice until the ice ls
dispersed,
9.142 Vapour Lock in Fuel Systems
‘The improved volatility of modern fuels, andthe necessity of providing heat 10 prevent icing
roubles, has le tothe occasional occurrence of caburetion difficulties, duc to vaporization ofthe
fuel in the petrol pipes, uel feed pump, carburettor flot chamber and the jet walls Apart from the
a a 5
ful volatility, excessive heating of the fuel can be due to petrol pipes being 100 near the engine and
‘due to heat conducted from the engine metal tothe fuel pump and caiburetor infer manifold
‘anges.
After a car engine has been used for a road jourey and is left to ide, the cooling system
becomes less efficient due to lack of cooling air, and therefore the bonnet temperature rises. A few
minutes after stopping he car, but withthe engine idling, the carburetor and the cooling water
temperatures usually tie considerably. Vapour lock can occur under these conditions
‘The formation of fuel vapour in the carburetor may result in a weak mixture. The vapour will
‘occupy a greater volume than the liquid and therefore the amount of fuel flow willbe reduced. The
‘eduction will cause ether a loss in power or else complete stoppage of the engine
‘The heat insulation of the fuel pump and the carburettor flanges by non-conducting type
gaskets will often prevent vapour lock.
9.14.3 Backfiring or Popping in the Carburettor
Backfring or popping inthe carburetor is an occasional wesk explosion in the inet pipe and
carburetor. It occurs due to too weak mixture or insufficient heating, The mixture isso weak
‘hat the explosion flame travels very slowly trough i with the result that inflammation occurs not
‘only during the firing and exhaust strokes, but also continues when the inlet valve opens again. Ut
often happens in cold weatber at starting. The emedy isto increase the fuel supply or reduce the
sir supply, and 10 look for extraneous sources of ai leakage.
9.15 CARBURETTOR DRAWBACKS
system in ST engines
1. The carburetor has certain wearing parts. When wear occurs, it usually operates less
efficiently.
2. There isa maldistribution of mixture quantity and quality in mui-cytinder engines, since the
induction passages are of unequal lengths and offer diferent resistances to mixture Now.
3. There is a loss of volumetic efficiency on account of restrictions of free flow passages for
‘mixture through the venue tube, the je, the thot valve, the inet pipe bend, te.
4. Freezing of moisture of air at low temperatures may take place unless some means are
provided to eliminate it.
5. When the carburetors ied, while the vehicle is negotiating a grade, surging of the fue is
caused inthe float chamber
6. There i possibility of backfire in the intake manifold and popping inthe carburettor in
cold weather, unless the flame taps ae ited, I involves an additional complication which
tends to reduce the volumeti efficiency.
7. Vapour lock inthe fuel systems may result in hot weather,
9.16 FUEL-INJECTION SYSTEMS IN SI ENGINES
In view ofthe several disadvantages of the carburettor, the fuckinjetion system in SI engines it
the right solution. This system is geting more popular on modem vehicles with mult-cylinder
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Carburetors and Fuel ejection in SI Eines 293
Now, velocity of air atthe throat,
G
Aix supplied 1 Ihe engine per second,
fe: Fat
a= ape age
CEA
pr = (5.684 x 10") m? = 5.684 cm
aa (5.684 x 107) m? = 5.684
do ¡ER
9.14 PROBLEMS ASSOCIATED WITH CARBURETTORS
‘Some ofthe problems associated with satisfactory running of the carburettor are discussed inthe
following subsections.
9.14.1 Ice Formation
"When a volatile liquid evaporates, the temperature around is lowered owing to the effect of latent
heat of evaporation. Applied to the fuel jet ofa carburetc this evaporation lowers the temperature
‘of the intake air and if the air contas any moisture, some of it wil be condensed. If the outside
{temperature is low, asin winter or at higher altitudes a in the case of aircraft engines, the moisture
in the air will tend to form ie on all interna surfaces exposed to the mixture stream. Moisture in
the intake ai tends to form ice onthe tote blade and on the pats ofthe carburettor barrel near
10 the blade. Inthe course of time the whole of the top edges become coated and the ac low is
restricted, therefore at low throttle openings the engine may cease to operate.
‘As this poses a serious problem, steps must be taken to overcome this difficult, The follow
ing methods may be employed:
1. Heating the intake at
2, Heating the metal surface, ie. the choke and mixture charaber by coolant from the water
Jackets or exhaust gases, on which ice is liable to form.
3. The use of ice preventives or iahibiors. alcohol such as ethanol or methanol is added to
the fue, freezing canbe avoided. An ce detector and an automatic servomechanism can be
used to deliver alcohol on o the surfaces liable to be covered with ice until the ice ls
dispersed,
9.142 Vapour Lock in Fuel Systems
‘The improved volatility of modern fuels, andthe necessity of providing heat 10 prevent icing
roubles, has le tothe occasional occurrence of caburetion difficulties, duc to vaporization ofthe
fuel in the petrol pipes, uel feed pump, carburettor flot chamber and the jet walls Apart from the
a a 5
ful volatility, excessive heating of the fuel can be due to petrol pipes being 100 near the engine and
‘due to heat conducted from the engine metal tothe fuel pump and caiburetor infer manifold
‘anges.
After a car engine has been used for a road jourey and is left to ide, the cooling system
becomes less efficient due to lack of cooling air, and therefore the bonnet temperature rises. A few
minutes after stopping he car, but withthe engine idling, the carburetor and the cooling water
temperatures usually tie considerably. Vapour lock can occur under these conditions
‘The formation of fuel vapour in the carburetor may result in a weak mixture. The vapour will
‘occupy a greater volume than the liquid and therefore the amount of fuel flow willbe reduced. The
‘eduction will cause ether a loss in power or else complete stoppage of the engine
‘The heat insulation of the fuel pump and the carburettor flanges by non-conducting type
gaskets will often prevent vapour lock.
9.14.3 Backfiring or Popping in the Carburettor
Backfring or popping inthe carburetor is an occasional wesk explosion in the inet pipe and
carburetor. It occurs due to too weak mixture or insufficient heating, The mixture isso weak
‘hat the explosion flame travels very slowly trough i with the result that inflammation occurs not
‘only during the firing and exhaust strokes, but also continues when the inlet valve opens again. Ut
often happens in cold weatber at starting. The emedy isto increase the fuel supply or reduce the
sir supply, and 10 look for extraneous sources of ai leakage.
9.15 CARBURETTOR DRAWBACKS
system in ST engines
1. The carburetor has certain wearing parts. When wear occurs, it usually operates less
efficiently.
2. There isa maldistribution of mixture quantity and quality in mui-cytinder engines, since the
induction passages are of unequal lengths and offer diferent resistances to mixture Now.
3. There is a loss of volumetic efficiency on account of restrictions of free flow passages for
‘mixture through the venue tube, the je, the thot valve, the inet pipe bend, te.
4. Freezing of moisture of air at low temperatures may take place unless some means are
provided to eliminate it.
5. When the carburetors ied, while the vehicle is negotiating a grade, surging of the fue is
caused inthe float chamber
6. There i possibility of backfire in the intake manifold and popping inthe carburettor in
cold weather, unless the flame taps ae ited, I involves an additional complication which
tends to reduce the volumeti efficiency.
7. Vapour lock inthe fuel systems may result in hot weather,
9.16 FUEL-INJECTION SYSTEMS IN SI ENGINES
In view ofthe several disadvantages of the carburettor, the fuckinjetion system in SI engines it
the right solution. This system is geting more popular on modem vehicles with mult-cylinder
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294 Fundamentals of nora Combustion Engines
carburecrs an Fuel econ In S Engines 295,
engines, Table 9.1 shoves the comparison beiween the carburetor mounted SI engine and the
fuebinjcction St engine. 1
Table9.1 Carburetior mounted vs. uelinfection SI engines
Description Carburetor mounted Injetormounted St
ST engine engine
Applications Sal egin Larger engines having
rmu-ylinéers.
Precision in manuienring To high degree To a much higher degree
Power ouput Usual Produces 10 1 20% more power
Nevesity of ehoke Yes No
Fuel distribution Good Very good
Detonation Possible Reduced
Compression ratio High Much higher
Fuel consumption Usual ‘Comparatively less
Engine response to hote Quick Very fast
“Tis ag between tote Short Much shorter
ovement and fel injection
Maintenance Less More
Cost Less Ben
Exhaust emissions More Lest
) 9.17 TYPES OF FUELINJECTION SYSTEMS IN SI ENGINES
> Sevea arangements are being employed or ful Injection in SL engines. Some important
) anangements ve dese ine folowing stein.
) 9.17.4 Continuous! Injection System
"Tue principle of the coniauous injection system isto introduce a steady flow of fuel at low
Pressure into the air supply. The principle of this system is illutraed in Figure 9.22. The fuel is
fawn from a fuel tank (1) by & fuel pump (2) and delivered 10 a speed sensing mechanism (3).
) which is divenby the engine. The fel at pressure round 2 bars delivered othe main metering
y 538m (8), whic sa dens bellows chamber nt or che purpose of regala te amount of
fel according Lo the inlet manifold and atmospheric pressures. The fuel then passes through an
engine iling unit (5). The acceleration purnp (6) delivers an extra supply of fuel for quick acc
‘tation purposes consists of a diaphragm which is forced upwards by the fuel pressure so as 10
I store the extra fuel for acceleration, When the accelerator pedal is depressed sharply, this fuel is
) forced ito the delivery side ofthe fuel nozzle injection system. Automatic staring requirements.
forthe engine are taken cae of by a bimetallic regulator device (7), which when actuted controls
a separate starting or iling ar valve inthe body of the trot. I also regulates the fuel flow for
9 ating andthe fel ow during the engine warsng-p period, The hole plate (8) Is asus.
)
)
>
>
Automat sr contol
Fgure9.22 Coinunishiechnen,
‘The injection nozzle (9) can be arranged under the throle body or at each of the cylinder inlet
pots. The nozzle has a spring-actuated pressure regulator which controls the fuel flow in accor-
dance withthe fuel line pressure.
9.17.2 Timed injection System
In this system there is a single pump unit which delivers fuel under pressure to a rotating distibu-
tor, the purpose of which isto deliver the metered quantity of ful at exactly the correct time 10
‘each cylinder in tum in elation to the pistons position in its compression stoke. The fuel supply
is regulated by engine speed, inlet manifold vacuum, atmospheric pressure and temperature, warm
and cold starting requirements, idling conditions and rapid acceleration. In place of the rotating
distributor, a single pump unit containing as many fuel pump plungers and barrels as there are
cylinders in the engine can alo be used. This i similar to the diesel engine Fel njecion pump.
‘The individual plunger contols the amount of fuel and its ime of injection, The controls ofthe
‘STenginefuel-injetion system differ considerably from the CI engine fuel-injction system.
Inthe method described above te fuel directly injected inside the engine cylinder during the
‘compression stroke; his method is called the direct cylinder injection method using the timed
Injection system.
‘An alternative to the above method isto deliver a measured small quantity of fue! into each
cylinder during the induction stroke at low pressure, but at definite time and over a definite
period of this stoke. The two methods of timed injection system are described below.
carburecrs an Fuel econ In S Engines 295,
engines, Table 9.1 shoves the comparison beiween the carburetor mounted SI engine and the
fuebinjcction St engine. 1
Table9.1 Carburetior mounted vs. uelinfection SI engines
Description Carburetor mounted Injetormounted St
ST engine engine
Applications Sal egin Larger engines having
rmu-ylinéers.
Precision in manuienring To high degree To a much higher degree
Power ouput Usual Produces 10 1 20% more power
Nevesity of ehoke Yes No
Fuel distribution Good Very good
Detonation Possible Reduced
Compression ratio High Much higher
Fuel consumption Usual ‘Comparatively less
Engine response to hote Quick Very fast
“Tis ag between tote Short Much shorter
ovement and fel injection
Maintenance Less More
Cost Less Ben
Exhaust emissions More Lest
) 9.17 TYPES OF FUELINJECTION SYSTEMS IN SI ENGINES
> Sevea arangements are being employed or ful Injection in SL engines. Some important
) anangements ve dese ine folowing stein.
) 9.17.4 Continuous! Injection System
"Tue principle of the coniauous injection system isto introduce a steady flow of fuel at low
Pressure into the air supply. The principle of this system is illutraed in Figure 9.22. The fuel is
fawn from a fuel tank (1) by & fuel pump (2) and delivered 10 a speed sensing mechanism (3).
) which is divenby the engine. The fel at pressure round 2 bars delivered othe main metering
y 538m (8), whic sa dens bellows chamber nt or che purpose of regala te amount of
fel according Lo the inlet manifold and atmospheric pressures. The fuel then passes through an
engine iling unit (5). The acceleration purnp (6) delivers an extra supply of fuel for quick acc
‘tation purposes consists of a diaphragm which is forced upwards by the fuel pressure so as 10
I store the extra fuel for acceleration, When the accelerator pedal is depressed sharply, this fuel is
) forced ito the delivery side ofthe fuel nozzle injection system. Automatic staring requirements.
forthe engine are taken cae of by a bimetallic regulator device (7), which when actuted controls
a separate starting or iling ar valve inthe body of the trot. I also regulates the fuel flow for
9 ating andthe fel ow during the engine warsng-p period, The hole plate (8) Is asus.
)
)
>
>
Automat sr contol
Fgure9.22 Coinunishiechnen,
‘The injection nozzle (9) can be arranged under the throle body or at each of the cylinder inlet
pots. The nozzle has a spring-actuated pressure regulator which controls the fuel flow in accor-
dance withthe fuel line pressure.
9.17.2 Timed injection System
In this system there is a single pump unit which delivers fuel under pressure to a rotating distibu-
tor, the purpose of which isto deliver the metered quantity of ful at exactly the correct time 10
‘each cylinder in tum in elation to the pistons position in its compression stoke. The fuel supply
is regulated by engine speed, inlet manifold vacuum, atmospheric pressure and temperature, warm
and cold starting requirements, idling conditions and rapid acceleration. In place of the rotating
distributor, a single pump unit containing as many fuel pump plungers and barrels as there are
cylinders in the engine can alo be used. This i similar to the diesel engine Fel njecion pump.
‘The individual plunger contols the amount of fuel and its ime of injection, The controls ofthe
‘STenginefuel-injetion system differ considerably from the CI engine fuel-injction system.
Inthe method described above te fuel directly injected inside the engine cylinder during the
‘compression stroke; his method is called the direct cylinder injection method using the timed
Injection system.
‘An alternative to the above method isto deliver a measured small quantity of fue! into each
cylinder during the induction stroke at low pressure, but at definite time and over a definite
period of this stoke. The two methods of timed injection system are described below.
296 Fundamenals of Irma! Combustion Engines
Cartureors an fue uen in St Engnes 297
Direct cylinder injection
Figure 9.23 illustrates the primary design elements of direct cylinder injection of gasoline fuel. It
consists of a transfer purop T. a filter Fa metering, distributing and timing pomp P with speed-
‘metering control (this pump is geared tothe engine) Ioa-melering control R, a mixture contol
M (a throttle valve in the ar stream), ard nozzles N (fuel injectors),
qu 923. Draco ts
‘The pump plunger raises the pressure and meters the correct amount of fuel forthe load on.
the engine, and also delivers the fuel into the cylinder over a particular interval of the cycle. The
control R isa device used roexert the manifold pressure ona diaphragm atached o he ack ofthe
pump. Thus at wide open thot, the maximum quantity of fuel per stroke will be delivered, and
‘the fuel quantity will decrease wth decrease in pressure inthe thotled manifold
Direct-injection of gasoline into the cylinder ie rarely used because of (a) the difficulty of
finding space in the head for an injector, (5) the added cooling and casting complications, (e) the
added cost, (4) the refinements hat are necessary for iin, and (e) the problems of exact meter.
ing at light Toads from cylinder to cylinder owing othe individual plungers.
Lucas potrolinjection system
Figure 9.24 shows the schematic your of the Lucas petrolinjection system. The timed port
injection of fuel is used in this system. contains a high pressure (7 bar) gear pump Pa metring
and timing distributor M (geared to be engin), a load control C, andthe atomizing injectornozzles
NGS bas
‘An lectrically driven ful pump supplies filered fuel u a pressure of neasy 7 bar 10 the
combined metering distibutor and mixture control unit mounted on, and deiven by, the engin.
From the metering distributor, the accuratelytmed and metered quantities of fuel ave delivered at
dd RE Bea
Pr
Me op
CES
Zar Ind
ina satel (©)
Inoue
~~ no 00
> Foe) File
FM Mean ning
= Ci ‘eu
Puros Shurañcdogam alone nan em.
Injector in tum. A relief valve returns excess fuel othe tank and maintains the line pressure
7 ba
9.18 ELECTRONIC FUEL-INJECTION SYSTEMS (EFls)
Barly foekinjection systems were mechanical and used complex designs. They have now been
superseded by elscronie fuelnjection systems (EFIs). The EFI systems are generally of two
pes.
9.16.1 Single-point Throttle Body Injection
In this system an elestonically controled injector meters the fuel and injes it into the ae flow
directly above the trate body It provides electronic control of fuel metering ata. cos lower than
the mulipoin port injection systems. The injector meters the Fuel in response o calibraions of aie
flow based on intake manifold pressure, ar temperature, and engine speed. This system creates
problems in obtining equal distribution of fet to all cylinders, andthe fuel particles have a ten.
dene ta deposit on the wall ofthe manifold when cold. produce about 10 per cent es power
(han à mati-point por injection,
9.18.2 Multi-point Port Injection
In this system, fue is injected into the intake port of each engine cylinder. Injectors are located
immediately before the inlet valve of each cylinder. requires one injector per ender and in
some systems, one or more injectors are used to supplement the fuel low during staring and
warm-up periods, The advantages of port fel injection are increased power and torque tough
improved volumetric efficiency and more uniform fue distribution 1 each cylinder, more rapid
engine response to changes in throule position, and more preise control ofthe equivalence ratio
during cold star and engine warm-up,
‘The combination of emission control and fuel economy gives he impact for using EFT. With
this system itis possible to operate the engine atthe stoichiometric airful ratio and to apply
losed-toop control, These features result in an appreciable fuel economy.
Cartureors an fue uen in St Engnes 297
Direct cylinder injection
Figure 9.23 illustrates the primary design elements of direct cylinder injection of gasoline fuel. It
consists of a transfer purop T. a filter Fa metering, distributing and timing pomp P with speed-
‘metering control (this pump is geared tothe engine) Ioa-melering control R, a mixture contol
M (a throttle valve in the ar stream), ard nozzles N (fuel injectors),
qu 923. Draco ts
‘The pump plunger raises the pressure and meters the correct amount of fuel forthe load on.
the engine, and also delivers the fuel into the cylinder over a particular interval of the cycle. The
control R isa device used roexert the manifold pressure ona diaphragm atached o he ack ofthe
pump. Thus at wide open thot, the maximum quantity of fuel per stroke will be delivered, and
‘the fuel quantity will decrease wth decrease in pressure inthe thotled manifold
Direct-injection of gasoline into the cylinder ie rarely used because of (a) the difficulty of
finding space in the head for an injector, (5) the added cooling and casting complications, (e) the
added cost, (4) the refinements hat are necessary for iin, and (e) the problems of exact meter.
ing at light Toads from cylinder to cylinder owing othe individual plungers.
Lucas potrolinjection system
Figure 9.24 shows the schematic your of the Lucas petrolinjection system. The timed port
injection of fuel is used in this system. contains a high pressure (7 bar) gear pump Pa metring
and timing distributor M (geared to be engin), a load control C, andthe atomizing injectornozzles
NGS bas
‘An lectrically driven ful pump supplies filered fuel u a pressure of neasy 7 bar 10 the
combined metering distibutor and mixture control unit mounted on, and deiven by, the engin.
From the metering distributor, the accuratelytmed and metered quantities of fuel ave delivered at
dd RE Bea
Pr
Me op
CES
Zar Ind
ina satel (©)
Inoue
~~ no 00
> Foe) File
FM Mean ning
= Ci ‘eu
Puros Shurañcdogam alone nan em.
Injector in tum. A relief valve returns excess fuel othe tank and maintains the line pressure
7 ba
9.18 ELECTRONIC FUEL-INJECTION SYSTEMS (EFls)
Barly foekinjection systems were mechanical and used complex designs. They have now been
superseded by elscronie fuelnjection systems (EFIs). The EFI systems are generally of two
pes.
9.16.1 Single-point Throttle Body Injection
In this system an elestonically controled injector meters the fuel and injes it into the ae flow
directly above the trate body It provides electronic control of fuel metering ata. cos lower than
the mulipoin port injection systems. The injector meters the Fuel in response o calibraions of aie
flow based on intake manifold pressure, ar temperature, and engine speed. This system creates
problems in obtining equal distribution of fet to all cylinders, andthe fuel particles have a ten.
dene ta deposit on the wall ofthe manifold when cold. produce about 10 per cent es power
(han à mati-point por injection,
9.18.2 Multi-point Port Injection
In this system, fue is injected into the intake port of each engine cylinder. Injectors are located
immediately before the inlet valve of each cylinder. requires one injector per ender and in
some systems, one or more injectors are used to supplement the fuel low during staring and
warm-up periods, The advantages of port fel injection are increased power and torque tough
improved volumetric efficiency and more uniform fue distribution 1 each cylinder, more rapid
engine response to changes in throule position, and more preise control ofthe equivalence ratio
during cold star and engine warm-up,
‘The combination of emission control and fuel economy gives he impact for using EFT. With
this system itis possible to operate the engine atthe stoichiometric airful ratio and to apply
losed-toop control, These features result in an appreciable fuel economy.
298 Fundamental of Inter Combustion Engines
Carburers and Fuel action in SI Engres 299
DxJetronle EFIsystem |
‘The Ss generation of EF at BOSCH was called D-Jeuonic, where D stand for ‘Dock’, which
means pressure, This name is derived from the fat that one of the man input signals is the
intake manifold pressure. Engine speed and air temperature are also used to control the airflow.
Figure 925 shows a schematic diagram of he D-Jetronie system. The fuel loop consists of the
fuel pump, the fuel filter and he pressure regulator, The eleciclly driven fuel pump delivers the
fuel through a filter tothe fel inc. A pressure regulator maintains the pressure around 2.7 bar in
the Tne ata fixed value, Branch lines lead to each injector. The excess fue remus tothe fuel tank
via a second line, The contol unit receives the main input signels from the pressure sensors
connected to the intake minifold and receives the speed information from the distributor, The
inducted air flows through the ae fle, past the throttle plate to Ihe intake manifold. The other
(Components, i.e the cold start valve, the thermal timing switch, the temperature sensor and
auiiay ait valve are used for cold start and warm-up control.
sg et er
CRE = Presse
pat
casa |] ‚meter
ger
ë
Hlcrenie [I
ESS
arr si
Fun 825. DICE yt ih maton pan
LuetronleEFI system
‘Tis isthe second generation EFI system developed at BOSCH. The L-Tetronie use the air flow
rate as one of the basic input signals. Its name is due to this fact: L stands for
"Lufmengenmessung’, which means ar flow measurement. A schematic diagram of the L-Jetroie
multi-point por fuel injection (MPF) system is shown in Figure. 926.
“The fuel loop is basically the same as in the D-Jetonic system, except thatthe pressure
regulator is connected through a hose to the intake manifold. Thus the fuel pressure is a function
‘Of the manifold pressure, end consequently the pressure drop across the injectors is kept constant.
“The ar flow rte is measured by the airflow meer whose movable measuring plate is opened
by the airstream against the force of a spring. The position ofthe measuring plate is sensed by a
UNH ios
ES
Faue228 Lite EA ean ith mp.
Stet ewich
potentiometer. Its voltage represents the ar flow rate, and is one of the main input signals going
to the control nit. The second one is the engine speed taken from the distributor. For cold
starting, additional fuel in the highly vapourized form is injected by the cold stan injector which is
‘mounted on the inake manifold, The col sar valve is controlled by the slater switch and the
thermo time switch. During the warm-up period, additional air bypassing the throttle plate is
‘controlled by the auxiliary ac valve. The throtle position switch is used 1 adjust the a/ac! ratio
at full- load and aiding and overun.
I tis system, the cost is reduced by using Integrated circuits in the electronic control unit,
‘which at the same tive results in higher reliability due tothe reduced number of components,
Fuslinjector
‘Anclectromagneticlly actuated fuel injection valve is shown in Figure 9.27 tis located either in
{he intake port or in he intake manifold tube of each cylinder I consists of valve housing, the
‘injector spindle, the magnetic plunger to which the spindle is connected, the elicl spring and the
solenci coil. When the solenoid is not energize, the solenoid plunger of the magnetic circuit is
forced with its seal against the valve seat by the helical spring and closes the fuel passage. When
the solenoid coll is energized, the plunger is arracted and lifts the spindle by about 0.15 mm, so
‘thatthe fuel can low through the calibrated annular passage around the valve stem. The frontend
of te injector spindle is shaped as an atomizing pitle with aground top to atomize the injected
fue. The mass ofthe fue injected per injection is controlled by varying the duration ofthe current
pale that excites the solenoid col. Typical injection times for automobile applications range fom.
about 1.510 10 ms. The appropriate col excitation pulse duration or with is se by the electronic
controlunit (ECU). The control unit also initates mixture enrichment during cold-engine operation
and during acceleration that are detected by the thot sensor.
Carburers and Fuel action in SI Engres 299
DxJetronle EFIsystem |
‘The Ss generation of EF at BOSCH was called D-Jeuonic, where D stand for ‘Dock’, which
means pressure, This name is derived from the fat that one of the man input signals is the
intake manifold pressure. Engine speed and air temperature are also used to control the airflow.
Figure 925 shows a schematic diagram of he D-Jetronie system. The fuel loop consists of the
fuel pump, the fuel filter and he pressure regulator, The eleciclly driven fuel pump delivers the
fuel through a filter tothe fel inc. A pressure regulator maintains the pressure around 2.7 bar in
the Tne ata fixed value, Branch lines lead to each injector. The excess fue remus tothe fuel tank
via a second line, The contol unit receives the main input signels from the pressure sensors
connected to the intake minifold and receives the speed information from the distributor, The
inducted air flows through the ae fle, past the throttle plate to Ihe intake manifold. The other
(Components, i.e the cold start valve, the thermal timing switch, the temperature sensor and
auiiay ait valve are used for cold start and warm-up control.
sg et er
CRE = Presse
pat
casa |] ‚meter
ger
ë
Hlcrenie [I
ESS
arr si
Fun 825. DICE yt ih maton pan
LuetronleEFI system
‘Tis isthe second generation EFI system developed at BOSCH. The L-Tetronie use the air flow
rate as one of the basic input signals. Its name is due to this fact: L stands for
"Lufmengenmessung’, which means ar flow measurement. A schematic diagram of the L-Jetroie
multi-point por fuel injection (MPF) system is shown in Figure. 926.
“The fuel loop is basically the same as in the D-Jetonic system, except thatthe pressure
regulator is connected through a hose to the intake manifold. Thus the fuel pressure is a function
‘Of the manifold pressure, end consequently the pressure drop across the injectors is kept constant.
“The ar flow rte is measured by the airflow meer whose movable measuring plate is opened
by the airstream against the force of a spring. The position ofthe measuring plate is sensed by a
UNH ios
ES
Faue228 Lite EA ean ith mp.
Stet ewich
potentiometer. Its voltage represents the ar flow rate, and is one of the main input signals going
to the control nit. The second one is the engine speed taken from the distributor. For cold
starting, additional fuel in the highly vapourized form is injected by the cold stan injector which is
‘mounted on the inake manifold, The col sar valve is controlled by the slater switch and the
thermo time switch. During the warm-up period, additional air bypassing the throttle plate is
‘controlled by the auxiliary ac valve. The throtle position switch is used 1 adjust the a/ac! ratio
at full- load and aiding and overun.
I tis system, the cost is reduced by using Integrated circuits in the electronic control unit,
‘which at the same tive results in higher reliability due tothe reduced number of components,
Fuslinjector
‘Anclectromagneticlly actuated fuel injection valve is shown in Figure 9.27 tis located either in
{he intake port or in he intake manifold tube of each cylinder I consists of valve housing, the
‘injector spindle, the magnetic plunger to which the spindle is connected, the elicl spring and the
solenci coil. When the solenoid is not energize, the solenoid plunger of the magnetic circuit is
forced with its seal against the valve seat by the helical spring and closes the fuel passage. When
the solenoid coll is energized, the plunger is arracted and lifts the spindle by about 0.15 mm, so
‘thatthe fuel can low through the calibrated annular passage around the valve stem. The frontend
of te injector spindle is shaped as an atomizing pitle with aground top to atomize the injected
fue. The mass ofthe fue injected per injection is controlled by varying the duration ofthe current
pale that excites the solenoid col. Typical injection times for automobile applications range fom.
about 1.510 10 ms. The appropriate col excitation pulse duration or with is se by the electronic
controlunit (ECU). The control unit also initates mixture enrichment during cold-engine operation
and during acceleration that are detected by the thot sensor.
300 Fundamentals of nara! Comburion Engine
Carburetor and Fuel neon in St Engines 301
Feedback control
Figure 9.28 shows the closed-loop EFI feedback control. With this control it is posible to obtain
very low exhaust emissions. The A-sensor which isa detetor for oxygen helps t run the engine
with stoichiometric icfuel ratio (A= 1). In this case the emission standards can be met with one
catalyst
EN
pes
Chen eus gs
=
9.19 ADVANTAGES OF THE SI ENGINE FUEL-INJECTION SYSTEM
‘An SI engine with Ihe fuel injection system has the following advantages Over the carburited
engine:
} 1. Increase in volumetri efficiency resulting in higher power output and torque. The
volumeti efficiency is increased because of elimination of intake manifold heating and
‘carburettor pressure los.
2. Lower specific fuel consumption since the amount of fuel injected is reduced at part
‘rot and during decceleration.
3. Faster acceleration, sine the fuel is injected into or lose 10 he cylinder and need not flow
through the masifold.
4. Less maldistrbution to each eylinder
5. Elimination of cote plate icing since the fuel s not vaporized before the throttle.
66. Basiee starting, since atomization of fuel does not depend onthe cranking speed
7. Less knocking tendency, since heat need not be supplied for better distribution. The
temperature of the mixture, therefore, is lowered. Thus, a fuel having a lower octane
number ora higher compression ratio can be used,
- The tendency of backfiring or popping in the carburetor is reduced, since the combustible
mixture is not in the intake manifold
9. Less exhaust emissions are produced. For emission control, fuelinjction exhibits the
higher accuracy of fuel metering. Ths allows a leaner adjustment of the engine with
E Acceptablediveabiliy
Fuel response is practically instantaneous, 50 the Nat spot is eliminated,
11. Engine bonnet can be appreciably lower owing o the absence ofthe usual down-daught
carburetor and owing o th fact tha the position ofthe injection unit isnot ees
Engines fied with injection systems can be used in high angles of tit the tilt may produce
«| fuel surge problems inthe float chamber of the carburetor
Figure 9.29 shows the typical performance curves forthe fuel-injection and carburettor sys
tems. is observed thatthe Power output with the fucl-injection system i higher than that with
the carburetor system. There is also a marked reduction in fuel consumption over a wide range of
‘pm wit the fue-injection system.
920 DISADVANTAGES OF THE SI ENGINE FUEL-INJECTION SYSTEM
‘The disadvantsges of the ST engine fuel-njection system compared tothe carbureted engine are
as follows:
1. "The working mechanism of the fue-injeeion equipment is much more compli
components of te injection system are of high precision workmanship and fr
for, it has much higher cost
2. The fuel injection pump continuously runs at half the speed of the crankshaft and this
‘causes wear of plungers and barels and valves and their seatings. There are no similar
‘wearing components inthe carburetor.
3. The individual fuel pipes are require from the pump to each clinder increases the risk
of breakdown,
sities
ds Wied pins
r
Carburetor and Fuel neon in St Engines 301
Feedback control
Figure 9.28 shows the closed-loop EFI feedback control. With this control it is posible to obtain
very low exhaust emissions. The A-sensor which isa detetor for oxygen helps t run the engine
with stoichiometric icfuel ratio (A= 1). In this case the emission standards can be met with one
catalyst
EN
pes
Chen eus gs
=
9.19 ADVANTAGES OF THE SI ENGINE FUEL-INJECTION SYSTEM
‘An SI engine with Ihe fuel injection system has the following advantages Over the carburited
engine:
} 1. Increase in volumetri efficiency resulting in higher power output and torque. The
volumeti efficiency is increased because of elimination of intake manifold heating and
‘carburettor pressure los.
2. Lower specific fuel consumption since the amount of fuel injected is reduced at part
‘rot and during decceleration.
3. Faster acceleration, sine the fuel is injected into or lose 10 he cylinder and need not flow
through the masifold.
4. Less maldistrbution to each eylinder
5. Elimination of cote plate icing since the fuel s not vaporized before the throttle.
66. Basiee starting, since atomization of fuel does not depend onthe cranking speed
7. Less knocking tendency, since heat need not be supplied for better distribution. The
temperature of the mixture, therefore, is lowered. Thus, a fuel having a lower octane
number ora higher compression ratio can be used,
- The tendency of backfiring or popping in the carburetor is reduced, since the combustible
mixture is not in the intake manifold
9. Less exhaust emissions are produced. For emission control, fuelinjction exhibits the
higher accuracy of fuel metering. Ths allows a leaner adjustment of the engine with
E Acceptablediveabiliy
Fuel response is practically instantaneous, 50 the Nat spot is eliminated,
11. Engine bonnet can be appreciably lower owing o the absence ofthe usual down-daught
carburetor and owing o th fact tha the position ofthe injection unit isnot ees
Engines fied with injection systems can be used in high angles of tit the tilt may produce
«| fuel surge problems inthe float chamber of the carburetor
Figure 9.29 shows the typical performance curves forthe fuel-injection and carburettor sys
tems. is observed thatthe Power output with the fucl-injection system i higher than that with
the carburetor system. There is also a marked reduction in fuel consumption over a wide range of
‘pm wit the fue-injection system.
920 DISADVANTAGES OF THE SI ENGINE FUEL-INJECTION SYSTEM
‘The disadvantsges of the ST engine fuel-njection system compared tothe carbureted engine are
as follows:
1. "The working mechanism of the fue-injeeion equipment is much more compli
components of te injection system are of high precision workmanship and fr
for, it has much higher cost
2. The fuel injection pump continuously runs at half the speed of the crankshaft and this
‘causes wear of plungers and barels and valves and their seatings. There are no similar
‘wearing components inthe carburetor.
3. The individual fuel pipes are require from the pump to each clinder increases the risk
of breakdown,
sities
ds Wied pins
r
102, Fundamentals of Inmo Combustion Engines
Cerbaretort and fuel Injection SI Engines 303
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REVIEW QUESTIONS
1. What isthe function of a crbureuoe? What is carburtion? |
2. What are the limits of flammability? What are the Factors on which the flammability limits
depend? :
3. Explain the mixture requirements for maximum power and minimum specific fuel
consumption under steady running ofthe engine.
_ he
4. Describe the mixture requirements for various power outputs withthe help of bmep and
{he corresponding bsfe curves versus the FueVair rato a different hote postions.
5. Show and explain with reasons the mixture requirements for idling, eruising and
power range at various thrortle openings
6. Explain the mixture requirements for stating, warm-up and acceleration,
7. Compare and explain with reasons the mixture requirements for a multi-cplinder engine
with a single cylinder for idling, cruising and high power range a various chroule openings,
8. What are the requirements for an ideal carburetor?
9. Explain the construction and operation ofa simple carburetor with the help ofa diagram,
10. Derive an expression to calculate the aifuel ratio for a simple carboretor taking into
account the compressibility ofa.
11. Derive an expression to calculate the ir/fuel ratio for a simple carburetor neglecting the
compressibility of ai,
12. What are the deficiencies ofan elementary carburetor?
13. What are the essential parts of à modem carburetor?
14, Describe the function, the location and the working of a choke valve with the help of a
simple diagram.
15. Whacis te fonction of main metering system?
Describe the following with the help of diagrams:
(2) Anauxiliary air valve
(b) Acompensating jet
(©) The metering pin
(d) The restricted air-bleed system
(€) Back suction control
{D Auxiliary por carbarenor
16, Describe the function and working principle of an idling system in a carburettor with the
help of a diagram.
17. Describe the purpose and working of an accelerating pump mechanism in a cazburetor
‘withthe help ofa diagram.
18. Describe with the help ofa diagram an economizer system using the metering pin. How
an it be used for more power?
19. What is the purpose of an antipercolator valve? How does it work?
20. Classify the different types of carburetors.
21. Describe down-draught, up-draught and horizontal-draught carburetors with the help of
diagrams.
22. Describe the concentric and eccentric cabureors with the help of diagrams, Which type
is mostly prefered in modern carburetors?
23. Describe the multi-ventui carburettor wth the help of a diagram. What are its advantages
‘over a single venlur carburettor?
24. How does the ice formation take place in a carburettor? What are the possible steps
required to overcome this difficulty?
25. How does the vapour lock take place In the fuel system? What ate its detrimental effects?
How can they be avoided?
igh
Cerbaretort and fuel Injection SI Engines 303
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REVIEW QUESTIONS
1. What isthe function of a crbureuoe? What is carburtion? |
2. What are the limits of flammability? What are the Factors on which the flammability limits
depend? :
3. Explain the mixture requirements for maximum power and minimum specific fuel
consumption under steady running ofthe engine.
_ he
4. Describe the mixture requirements for various power outputs withthe help of bmep and
{he corresponding bsfe curves versus the FueVair rato a different hote postions.
5. Show and explain with reasons the mixture requirements for idling, eruising and
power range at various thrortle openings
6. Explain the mixture requirements for stating, warm-up and acceleration,
7. Compare and explain with reasons the mixture requirements for a multi-cplinder engine
with a single cylinder for idling, cruising and high power range a various chroule openings,
8. What are the requirements for an ideal carburetor?
9. Explain the construction and operation ofa simple carburetor with the help ofa diagram,
10. Derive an expression to calculate the aifuel ratio for a simple carboretor taking into
account the compressibility ofa.
11. Derive an expression to calculate the ir/fuel ratio for a simple carburetor neglecting the
compressibility of ai,
12. What are the deficiencies ofan elementary carburetor?
13. What are the essential parts of à modem carburetor?
14, Describe the function, the location and the working of a choke valve with the help of a
simple diagram.
15. Whacis te fonction of main metering system?
Describe the following with the help of diagrams:
(2) Anauxiliary air valve
(b) Acompensating jet
(©) The metering pin
(d) The restricted air-bleed system
(€) Back suction control
{D Auxiliary por carbarenor
16, Describe the function and working principle of an idling system in a carburettor with the
help of a diagram.
17. Describe the purpose and working of an accelerating pump mechanism in a cazburetor
‘withthe help ofa diagram.
18. Describe with the help ofa diagram an economizer system using the metering pin. How
an it be used for more power?
19. What is the purpose of an antipercolator valve? How does it work?
20. Classify the different types of carburetors.
21. Describe down-draught, up-draught and horizontal-draught carburetors with the help of
diagrams.
22. Describe the concentric and eccentric cabureors with the help of diagrams, Which type
is mostly prefered in modern carburetors?
23. Describe the multi-ventui carburettor wth the help of a diagram. What are its advantages
‘over a single venlur carburettor?
24. How does the ice formation take place in a carburettor? What are the possible steps
required to overcome this difficulty?
25. How does the vapour lock take place In the fuel system? What ate its detrimental effects?
How can they be avoided?
igh
304 _Fundamenals of inamal Combustion Engines
Carburetors aná Fuel econ in SI Engines 305
tre he causes of this backfiring? Suggest
26. What is backficing in an intake system? W
methode for is remedy.
27. What are the main drawbacks of the carburettor which prompted the use of the fuel
injection system in SI engines?
28. Show the comparison between the carboretor-mounted SI engines and the injector.
mounted SI engines.
29. Describe the principle and working of continuous injection system with the belp of a
diagram.
30. Describe the principle of a timed injection system. What are the two methods of fuel
injection using timed injection?
31. Describe the dire eylinder injection method in SLengines with the help ofa dingram. Why
is this system rarely used in ST engines?
32. Deseribe the Lucas petrl-injection system with the help ofa diagram,
33, Describe the principle of single-point throte body EFT system,
34. Describe the principle of multi-point port EFI system.
35. Describe the working of D-Jeronic Bosch EFI system wih the help ofa diagram,
36. Describe the working ofL-Jetonic Bosch EFI system withthe help ofa diagram,
37. Describe an elecromagnetically actuated fuel injector with the help 0 a diagram.
38. Draw a schematic diagram ofa closed-loop EFT feedback control. What is its purpose?
39. What are he advantages ofthe SI engine fuel-injecton system? Compare the performance
curves ofthe fuebinjecion system in S engines with those ofthe caburetor system.
40. What are the disadvantages of the ST engine fuel-injection system?
PROBLEMS
9.1 A gasoline engine has a carburetor of 35 mm throat diameter. The ful jet diameter is
22 mm. The depression at the throat is 60 mm of Hg. The ambient pressure is 1 bar and
temperature 27°C, The coefficient of discharge for ventu is 0.8 and for fue jet 0.6. The
density of gasoline is 750 kp/m?. Neplect the nozale lip. Determine the air velocity and sir
flow, he fuel velocity and fuel flow and the arfuel rato in the following cases:
(a) Considering he compressibility of air
€) Neglecting the compressibility of ait
942 A venturi ofa simple eatburetor has a throat diameter of 30 mm. The fue je diameter is
2.0 mm. The coefficient of ai low i 0.88 and the coefficient of fuel flow is 0.65. The fuel
surface is 6 mm below the jet. The depression of pressure at the ventur throat is 0.075 bar
the denis of air and fuel are 1.2 kg/m? and 750 kg/m? respectively. Determine:
(2) The itfuel ratio when the nozzle ips neglected.
(0) The aizuel ratio when the nozzle lip is considered.
(6) The minimum velocity of ai required to star the fuel flow when the nozzle Lip is
provided
9.3 What wil be the percentage change inthe fueVair ratio if the velocity of ar atthe throat is
ince ens nly. e depen aie si hot ie rer
94 A foveswok St engine of 1100 c caps is required develop
manu power a
4000 pm Te volume ee a spec HR. Te ged ae hoben
100 mb. Te coin scr forthe venus an he fan na
The el sur is 8 nun below top ld J Determine he at dao ot
choke ue and de aul ao, te o dates 12 men Te Say RU
950 kgm ard ambien conten are LD bar and 27°:
9:5 A fee (ou eyinder Senin on 10 mon bre and Bm stoke uns 3000
‘pm and uses à fol having 54% cañon ad 16% hydrogen by mar Te sahen
Sfieney of engine's 85% The adn condone 0 at ml 27 The de
Son athe vn ors 0.65 us Teal any fap es ete
home vale, aut tefl Morte eV ane
throat diameter do
‘Take Ríair) = 287 J/(kg K), and R(fuel vapour) = 98 J/(kg K).
346 A ourotefureynter S egin hang a bare & 9 me an sok of 100 mm
Cani at 260 m has a vena nt wih 20 mm diameter The volume Han
OF te engin at is spend is 858. The coso of dcr of flow 095 Te,
ambien rss an temperate ae {Ob wn °C. The wpa ee 8 Me
ie fl el neo aber The colin o dca fil ow 03. Te
ater ofthe fc jet? mm ad the sper gray of eel 96 Doc
‘depression at the throat and the airfuel ratio ~
9:7 Deere ie fuel toin nara enge exer at 3000 mad. The col
‘ti ssa levels 151. The abn codons we 1.013 bar and 27 The op
Sara ind he FT 0048 h whe hit Seb ees
208 Ths he ea lel empero 170 Te ar prs deren al
per the relation. pe ie
À = 19200 logy (1.013/p) where pis in bar.
Carburetors aná Fuel econ in SI Engines 305
tre he causes of this backfiring? Suggest
26. What is backficing in an intake system? W
methode for is remedy.
27. What are the main drawbacks of the carburettor which prompted the use of the fuel
injection system in SI engines?
28. Show the comparison between the carboretor-mounted SI engines and the injector.
mounted SI engines.
29. Describe the principle and working of continuous injection system with the belp of a
diagram.
30. Describe the principle of a timed injection system. What are the two methods of fuel
injection using timed injection?
31. Describe the dire eylinder injection method in SLengines with the help ofa dingram. Why
is this system rarely used in ST engines?
32. Deseribe the Lucas petrl-injection system with the help ofa diagram,
33, Describe the principle of single-point throte body EFT system,
34. Describe the principle of multi-point port EFI system.
35. Describe the working of D-Jeronic Bosch EFI system wih the help ofa diagram,
36. Describe the working ofL-Jetonic Bosch EFI system withthe help ofa diagram,
37. Describe an elecromagnetically actuated fuel injector with the help 0 a diagram.
38. Draw a schematic diagram ofa closed-loop EFT feedback control. What is its purpose?
39. What are he advantages ofthe SI engine fuel-injecton system? Compare the performance
curves ofthe fuebinjecion system in S engines with those ofthe caburetor system.
40. What are the disadvantages of the ST engine fuel-injection system?
PROBLEMS
9.1 A gasoline engine has a carburetor of 35 mm throat diameter. The ful jet diameter is
22 mm. The depression at the throat is 60 mm of Hg. The ambient pressure is 1 bar and
temperature 27°C, The coefficient of discharge for ventu is 0.8 and for fue jet 0.6. The
density of gasoline is 750 kp/m?. Neplect the nozale lip. Determine the air velocity and sir
flow, he fuel velocity and fuel flow and the arfuel rato in the following cases:
(a) Considering he compressibility of air
€) Neglecting the compressibility of ait
942 A venturi ofa simple eatburetor has a throat diameter of 30 mm. The fue je diameter is
2.0 mm. The coefficient of ai low i 0.88 and the coefficient of fuel flow is 0.65. The fuel
surface is 6 mm below the jet. The depression of pressure at the ventur throat is 0.075 bar
the denis of air and fuel are 1.2 kg/m? and 750 kg/m? respectively. Determine:
(2) The itfuel ratio when the nozzle ips neglected.
(0) The aizuel ratio when the nozzle lip is considered.
(6) The minimum velocity of ai required to star the fuel flow when the nozzle Lip is
provided
9.3 What wil be the percentage change inthe fueVair ratio if the velocity of ar atthe throat is
ince ens nly. e depen aie si hot ie rer
94 A foveswok St engine of 1100 c caps is required develop
manu power a
4000 pm Te volume ee a spec HR. Te ged ae hoben
100 mb. Te coin scr forthe venus an he fan na
The el sur is 8 nun below top ld J Determine he at dao ot
choke ue and de aul ao, te o dates 12 men Te Say RU
950 kgm ard ambien conten are LD bar and 27°:
9:5 A fee (ou eyinder Senin on 10 mon bre and Bm stoke uns 3000
‘pm and uses à fol having 54% cañon ad 16% hydrogen by mar Te sahen
Sfieney of engine's 85% The adn condone 0 at ml 27 The de
Son athe vn ors 0.65 us Teal any fap es ete
home vale, aut tefl Morte eV ane
throat diameter do
‘Take Ríair) = 287 J/(kg K), and R(fuel vapour) = 98 J/(kg K).
346 A ourotefureynter S egin hang a bare & 9 me an sok of 100 mm
Cani at 260 m has a vena nt wih 20 mm diameter The volume Han
OF te engin at is spend is 858. The coso of dcr of flow 095 Te,
ambien rss an temperate ae {Ob wn °C. The wpa ee 8 Me
ie fl el neo aber The colin o dca fil ow 03. Te
ater ofthe fc jet? mm ad the sper gray of eel 96 Doc
‘depression at the throat and the airfuel ratio ~
9:7 Deere ie fuel toin nara enge exer at 3000 mad. The col
‘ti ssa levels 151. The abn codons we 1.013 bar and 27 The op
Sara ind he FT 0048 h whe hit Seb ees
208 Ths he ea lel empero 170 Te ar prs deren al
per the relation. pe ie
À = 19200 logy (1.013/p) where pis in bar.
CI Engines:
Fuel-Injection System
10
101 INTRODUCTION
in compresion itn engine, a usine sm rege inet dt quan of
cd nad. a Generate ii the combson camber The stem mus ls
orate ue an abate to he va ara of be combustion chamber, The nection
Reta esponsor iting and controling te combusion process Cosequenty, he
ns af eines nel pend pen te pod dei ofthe fe nection ae
Teens Ja the tn Sooke, i ain he engine ener, and dig te
conpuston ok is speed 10 high pressor, ds ing the epee of th cm.
See er ane tpn temp of nected fF injected ino the
Yen ner near en ofthe compression sank, ad a a te the prsae in de
‘Snes asl been 20 and br Ath combine injected a pros, be
sm epider ese eins ap 070 bar The fe is thus inte into a high pres
cum 1 ers the ition este of te fc lo be mach higher an hs
cate od za fe fel depends upon he high cio vlcies wich
Re à hgh puso diem. Thus Hg presu, cal ben 100 and 200 bs, ae
Fai for he encina
102 REQUIREMENTS OF INJECTION SYSTEMS
“The fuchinjction system of the Cl engine has w fulfil the following requirements fora proper
running and good performance of he cage:
1. Metering the quantity of fuel as required by the engine speed and load, Metering means the
Supply of the desired quantity of fuel in each injection, at an acceptable rate and over
fn accepuable crank angle Iti very ciel as even a small variation may affeet the perfor-
mance of the engine drastically.
2, The distribution ofthe metered ful in a muli-cylinder engine should be equal among the
cylinders.
3. The injection of the fuel shouldbe at the correct time in the cycle so that more power is
‘obtained withthe least amount of ful, thus ensuring clean buming,
Ci Engines relier Sytem 307
4. The fuel should be injected atthe comect at, so
Pattern during combustion
5. The füe shouldbe injected with the proper spray pattern and atomization depending upon
the design of the combustion chamber in oder to ensure proper mixing of ful and at, both
in ime and space.
6. Injection should start and stop starply o eliminate dribbling of fuel droplets into the cylinder.
7. The injection system must have the minimum weight and overall dimensions. I should be
inexpensive to manufacture, and easy to maintain and repair
8, The service life of all he elements of the fuel-igjecton system should be compatible with
that ofthe engine itself
it results inthe desired heat release
In order to accomplish the above requirements, the following components are required in a
nel-injetion system:
1. Pumping elements: Pumping elements pump the fuel from the fuel tank tothe cylinder
through pipe lines and injectors.
2. Metering elements: | Metering elements measure and supply the fuel atthe rate required by
the engine speed and Jon.
3. Metering controls: Metering controls adjust the at of the metering elements for changes
in engine speed and load
4. Distributing elements: Distibuting elements distribute the metered fucl equally among.
the cylinders.
Timing controls: Timing controls adjust the start and the stop of injection
Mixing elements: Mixing elements atomize and distribute the fuel in the combustion
chamber
103 INJECTION SYSTEMS
Based on the methods used o produce the required pressure for atomization ofthe fue, there are
basically two distinct methods of fuel injection in CT engines
1. Airinection system
2. Airles-orolidájoction system,
10.31 Alrinjection System
Alrinjection apple to systems injecting air along withthe liquid fuel, This method was first
successfully developed by Rudolf Diesel and is shown in Figure 10.1. requires an ar compressor
for supplying air at 70 bar or even a higher pressure. A camshaft diven fuel pump meters and
discharges a definite quan of fue! into the injection valve. The injection valve is mechanically
‘opened, and the high-pressure ai drives the fuel charge and some air into te combustion chamber
‘The following are the advantages of the ar-injction system:
1. Very good atomization and distribution of the fuel, resulting in comparatively high mean
effective pressures
2. High viscous fuels, which ae Less expensive than those used bythe engine having the solid
injection system, can be utilize without any problem.
mu
Fuel-Injection System
10
101 INTRODUCTION
in compresion itn engine, a usine sm rege inet dt quan of
cd nad. a Generate ii the combson camber The stem mus ls
orate ue an abate to he va ara of be combustion chamber, The nection
Reta esponsor iting and controling te combusion process Cosequenty, he
ns af eines nel pend pen te pod dei ofthe fe nection ae
Teens Ja the tn Sooke, i ain he engine ener, and dig te
conpuston ok is speed 10 high pressor, ds ing the epee of th cm.
See er ane tpn temp of nected fF injected ino the
Yen ner near en ofthe compression sank, ad a a te the prsae in de
‘Snes asl been 20 and br Ath combine injected a pros, be
sm epider ese eins ap 070 bar The fe is thus inte into a high pres
cum 1 ers the ition este of te fc lo be mach higher an hs
cate od za fe fel depends upon he high cio vlcies wich
Re à hgh puso diem. Thus Hg presu, cal ben 100 and 200 bs, ae
Fai for he encina
102 REQUIREMENTS OF INJECTION SYSTEMS
“The fuchinjction system of the Cl engine has w fulfil the following requirements fora proper
running and good performance of he cage:
1. Metering the quantity of fuel as required by the engine speed and load, Metering means the
Supply of the desired quantity of fuel in each injection, at an acceptable rate and over
fn accepuable crank angle Iti very ciel as even a small variation may affeet the perfor-
mance of the engine drastically.
2, The distribution ofthe metered ful in a muli-cylinder engine should be equal among the
cylinders.
3. The injection of the fuel shouldbe at the correct time in the cycle so that more power is
‘obtained withthe least amount of ful, thus ensuring clean buming,
Ci Engines relier Sytem 307
4. The fuel should be injected atthe comect at, so
Pattern during combustion
5. The füe shouldbe injected with the proper spray pattern and atomization depending upon
the design of the combustion chamber in oder to ensure proper mixing of ful and at, both
in ime and space.
6. Injection should start and stop starply o eliminate dribbling of fuel droplets into the cylinder.
7. The injection system must have the minimum weight and overall dimensions. I should be
inexpensive to manufacture, and easy to maintain and repair
8, The service life of all he elements of the fuel-igjecton system should be compatible with
that ofthe engine itself
it results inthe desired heat release
In order to accomplish the above requirements, the following components are required in a
nel-injetion system:
1. Pumping elements: Pumping elements pump the fuel from the fuel tank tothe cylinder
through pipe lines and injectors.
2. Metering elements: | Metering elements measure and supply the fuel atthe rate required by
the engine speed and Jon.
3. Metering controls: Metering controls adjust the at of the metering elements for changes
in engine speed and load
4. Distributing elements: Distibuting elements distribute the metered fucl equally among.
the cylinders.
Timing controls: Timing controls adjust the start and the stop of injection
Mixing elements: Mixing elements atomize and distribute the fuel in the combustion
chamber
103 INJECTION SYSTEMS
Based on the methods used o produce the required pressure for atomization ofthe fue, there are
basically two distinct methods of fuel injection in CT engines
1. Airinection system
2. Airles-orolidájoction system,
10.31 Alrinjection System
Alrinjection apple to systems injecting air along withthe liquid fuel, This method was first
successfully developed by Rudolf Diesel and is shown in Figure 10.1. requires an ar compressor
for supplying air at 70 bar or even a higher pressure. A camshaft diven fuel pump meters and
discharges a definite quan of fue! into the injection valve. The injection valve is mechanically
‘opened, and the high-pressure ai drives the fuel charge and some air into te combustion chamber
‘The following are the advantages of the ar-injction system:
1. Very good atomization and distribution of the fuel, resulting in comparatively high mean
effective pressures
2. High viscous fuels, which ae Less expensive than those used bythe engine having the solid
injection system, can be utilize without any problem.
mu
308 fundemencal of barna! Combustion Engines
_ Cl Engines: Fuerncion Siem 309
injection Inecon
‘she “he
— oma
ratte
lA
Pue pumps
Coste
Faut Ap
3. The fuel pump is required o develop es pressure than that required by the engine having
the solid injection system.
“The following are the disadvantages of the si-injection system.
1. Complex of te engine due wa mle ar compresor, which fen ia sates a
tou ad ce cor nen.
2. A separa mean lao le roque o pete ul valve athe prope ime
3. Due tothe comprar and age ng weight inca and ab ome poner
three in opting compres tnd aka te bn power reds,
4. Teen soii cam vo sde nin sore, sh my
lin oral an Dig of eel ave adhe valve set
Te fc valve seating resis ar neo o guar als any Jogo
ite fel valve sks, he system Bane: vn dango este a th presence of
Fig presa de
‘he size an cs ol ac compretir, log wit he ower equi fos operon hs
sae te necio yom lt
10.3.2. Alriess- or Solidinjection System
y witout ite
Anh yt ful jet very high este int combunion camber with
of he compressed, Hence cad ues econ oye, is a called hes
ion syuc The main pat of ts ss ae the fl pump and th injector, Deentng
ton e tacon de fe amps, te poping e mado cating te pups a e
med und to meter he felts jen systems can be sid slows
1. Invi pump yn the divided ful ed device
2. Ual ci tte unidad bet deve
|
|
3. Distributor system
4. Common ral system,
All of he above systems consis of the following components:
1. Fuel tank to sore the fuel
2. Files:
(4) A primary stage filter o remove course panicles large than 0.025 mim). Itis a metal.
edge files
(0) A secondary stage filter to remove fine particles from about 4 micros to 0.025 mm. It
is areplaceable cloth paper, or fl element.
‘The primary and secondary ler are place between the fuel tank and the taster pump.
3. A low pressure (3 bar transfer pump (gear or vane type) is used to lift the fuel fre the
tank, to overcome the pressure drops i he fiers and to charge the metering and presser,
ining unit
4. Final stage filter to remove fine particles that might have escaped th secondary stage. is
A sealed non-replaceable element. Is use to guard the high-pressure unie.
5. High-pressure foe injection pump to meter and pressurize the fuel (100 to 200 ba) for
injection.
6. Governor to ensure thatthe amount of fuel injected is in accordance with change in load,
7. Injector to receive the high-pressure fuel from the injection pump and 1 je te ft in
(he combustion chamber, and atomize it nt fine droplets.
10.3.3 Individual Pump System or the Divided Fuel-feed Device
Figure 102 shows the schematic diagram of an individual pump system. tn tht system, each
ylinder is provide with one pump and one injector. The injectors located onthe cylinder wile
the pump ison the side ofthe engine. Fach pump may be placed close to the eyinder to mic
it delivers the fuel as shown in Figure 10.3) or pumps may be arranged ina cluster, as shown
in Figure 10.30). The smaller engines combine the individual pumps into one asen. The high
Pressure pump plunger is actuated by a cam and produces the fuel pressure necessary to open fhe
spring-loaded injector valve a he correct time, This valve i a hydraulically operated um
‘The fuel pump used in this system is of reciprocating type. This requires robust and heavy
components causing the up tobe always accompanied by a jecking noise. The pump i there
fore called a jerk pump.
10.3.4 Unit Injector System or the Undivided Fuel-teed Device
‘Tie high-pressure pipe ine connecting the individual pump andthe associated injctor can be
voided by the design of a unit injector. T this system the pump and the injector nova are
combined in one housing. Each cylinder has one ofthese injector units, Fuels brought up tothe
Injector by a low-pressure pump. This system requires a push rod and a rocker arm fo actuate the
DT
_ Cl Engines: Fuerncion Siem 309
injection Inecon
‘she “he
— oma
ratte
lA
Pue pumps
Coste
Faut Ap
3. The fuel pump is required o develop es pressure than that required by the engine having
the solid injection system.
“The following are the disadvantages of the si-injection system.
1. Complex of te engine due wa mle ar compresor, which fen ia sates a
tou ad ce cor nen.
2. A separa mean lao le roque o pete ul valve athe prope ime
3. Due tothe comprar and age ng weight inca and ab ome poner
three in opting compres tnd aka te bn power reds,
4. Teen soii cam vo sde nin sore, sh my
lin oral an Dig of eel ave adhe valve set
Te fc valve seating resis ar neo o guar als any Jogo
ite fel valve sks, he system Bane: vn dango este a th presence of
Fig presa de
‘he size an cs ol ac compretir, log wit he ower equi fos operon hs
sae te necio yom lt
10.3.2. Alriess- or Solidinjection System
y witout ite
Anh yt ful jet very high este int combunion camber with
of he compressed, Hence cad ues econ oye, is a called hes
ion syuc The main pat of ts ss ae the fl pump and th injector, Deentng
ton e tacon de fe amps, te poping e mado cating te pups a e
med und to meter he felts jen systems can be sid slows
1. Invi pump yn the divided ful ed device
2. Ual ci tte unidad bet deve
|
|
3. Distributor system
4. Common ral system,
All of he above systems consis of the following components:
1. Fuel tank to sore the fuel
2. Files:
(4) A primary stage filter o remove course panicles large than 0.025 mim). Itis a metal.
edge files
(0) A secondary stage filter to remove fine particles from about 4 micros to 0.025 mm. It
is areplaceable cloth paper, or fl element.
‘The primary and secondary ler are place between the fuel tank and the taster pump.
3. A low pressure (3 bar transfer pump (gear or vane type) is used to lift the fuel fre the
tank, to overcome the pressure drops i he fiers and to charge the metering and presser,
ining unit
4. Final stage filter to remove fine particles that might have escaped th secondary stage. is
A sealed non-replaceable element. Is use to guard the high-pressure unie.
5. High-pressure foe injection pump to meter and pressurize the fuel (100 to 200 ba) for
injection.
6. Governor to ensure thatthe amount of fuel injected is in accordance with change in load,
7. Injector to receive the high-pressure fuel from the injection pump and 1 je te ft in
(he combustion chamber, and atomize it nt fine droplets.
10.3.3 Individual Pump System or the Divided Fuel-feed Device
Figure 102 shows the schematic diagram of an individual pump system. tn tht system, each
ylinder is provide with one pump and one injector. The injectors located onthe cylinder wile
the pump ison the side ofthe engine. Fach pump may be placed close to the eyinder to mic
it delivers the fuel as shown in Figure 10.3) or pumps may be arranged ina cluster, as shown
in Figure 10.30). The smaller engines combine the individual pumps into one asen. The high
Pressure pump plunger is actuated by a cam and produces the fuel pressure necessary to open fhe
spring-loaded injector valve a he correct time, This valve i a hydraulically operated um
‘The fuel pump used in this system is of reciprocating type. This requires robust and heavy
components causing the up tobe always accompanied by a jecking noise. The pump i there
fore called a jerk pump.
10.3.4 Unit Injector System or the Undivided Fuel-teed Device
‘Tie high-pressure pipe ine connecting the individual pump andthe associated injctor can be
voided by the design of a unit injector. T this system the pump and the injector nova are
combined in one housing. Each cylinder has one ofthese injector units, Fuels brought up tothe
Injector by a low-pressure pump. This system requires a push rod and a rocker arm fo actuate the
DT
Ue ee ee ee ere ee eee eee ee ee eee
310 Furdanenuls of Imernal Combustion Engines
0 pen
pe oe
Ve
opte [| onen AR
o o
| | a a avant on
mem LL, u
= ssi
DIT ue
a
Filter a
Er
ar
ae
Low reee pump
enter ump)
Fiurei02 nido pupa.
been ache
| High greso
13
High ri pues
Lores
par
Fu 109) Imrdnlpenpandnze wth stented runes.
plunger and injects the fuel ino the cylinder at the proper time. The quantity of fuel injected is
Fegulsted by the effective stroke of the plonger. The uni injector sytem is shown in Figure 104.
I is used extensively on large two-stroke cycle diesel engines
i Engines: Fue eco System 311
Se
Huge pompe presea.
gum 10.90) Iva pur andoozin vt pps nds,
niet wit big presse pur
HR
—g IT TE
Lowpresaue ine <=] Le Low-prease ios
Low pressure
Ml ooh
Fur 104 Untrieceroptem
10.3.5 The Distributor System
Figure 10.5 shows a schematic diagram of the distributor system. The individual pump system,
described earlier, requires a separate metering and compression pump for each cylinder, which
increases the cost ofthe system. Inthe disibutor system, a single pump for compressing the fuel
Mires as
Te gene
Low pes
ii te
Figure 105 Schonatedayondte dd jte.
310 Furdanenuls of Imernal Combustion Engines
0 pen
pe oe
Ve
opte [| onen AR
o o
| | a a avant on
mem LL, u
= ssi
DIT ue
a
Filter a
Er
ar
ae
Low reee pump
enter ump)
Fiurei02 nido pupa.
been ache
| High greso
13
High ri pues
Lores
par
Fu 109) Imrdnlpenpandnze wth stented runes.
plunger and injects the fuel ino the cylinder at the proper time. The quantity of fuel injected is
Fegulsted by the effective stroke of the plonger. The uni injector sytem is shown in Figure 104.
I is used extensively on large two-stroke cycle diesel engines
i Engines: Fue eco System 311
Se
Huge pompe presea.
gum 10.90) Iva pur andoozin vt pps nds,
niet wit big presse pur
HR
—g IT TE
Lowpresaue ine <=] Le Low-prease ios
Low pressure
Ml ooh
Fur 104 Untrieceroptem
10.3.5 The Distributor System
Figure 10.5 shows a schematic diagram of the distributor system. The individual pump system,
described earlier, requires a separate metering and compression pump for each cylinder, which
increases the cost ofthe system. Inthe disibutor system, a single pump for compressing the fuel
Mires as
Te gene
Low pes
ii te
Figure 105 Schonatedayondte dd jte.
312 Fundamentals of internal Camburdon Engines
© Engines: Fuebinecson Sytem 313
anda dividing device for isibating the fel tothe cylinders are used. The pump ortheisributor
may meter the quantity of fuel. Since there Isa single metering and distributing element, i is
expected tha the unit will distribute the feel uniforaly to each eylinder. The pumps ofthis type are
found on medium and small-sized (7.5 KW-75 KW per cylinder) diesel engines
10.3.6 Common-rail System
Figur 106 shows a scheme digram Fa common: system The fe fom the fuel sorge
Unk i drawn ag prima fel kes y low resus eed pump. The cae
from his pump enter the gres fe ijcion pamp Tis pump sere nl o deliver
fuel under igh pre, o common pl al ear, vis pressure ad Lot by
a peste regala valve. Ts the mani press sudar de cool and denen
problems ot handles y be igh peste pump. Te high pesen e eat ce he fu
(each ofthe nor oeste intend AL e poe ne, mechanical epee valve
by means oa push rod and a ocker ar alow the fi ene ie older ig the oe
‘The presu inthe oe! ende must he schen 10 ponte an Opos te ful in he
charge
(igh press)
bing
Nozzle spring
loaded valve
tinder
— P
tog shot.
„ un
=> Ll
(aceusmulator) toatl al
pes
>
=
ones
Pira un
combustion chamber and must be in accordance with the injector system design. The amount of
fuel supplied to the combustion chamber is regulated by varying the length ofthe pushrod stoke
‘The common-rail system tends to be self-governing, IF the engine speed falls, an increased
‘quantity of fue is automatically injected, since the üme taken forthe same erank angle rotation,
during which period the fel is supplied is increased. AS the ful pressure i maintained constant
With increases time, the ful supply will alzo be increased
Very accurate design and workmanship ae required inthis type of fue injection mechanism.
‘The Hit of the valve spindle is very small, it requires absolut rigidity ofthe operating mechanism
and freedom from vibration and temperature effects, moreover, the wear must be negligible, The
common-rai systems were, once, quite popular for arg, slow-speed engines, bu over he years,
have been replaced by the jerk-pump injection,
10.4 FUEL-INJECTION PUMPS.
‘The bighr pressure fueLnjection pump is one ofthe main and most complicated units ofthe fuel
injection system in a CI engine, It meters out the fuel in conformity withthe engine dany and
‘supplies fue tothe injector atthe proper time. Fuel pumps i which every working section delivers
fuel to individual cylinders ofthe engine ae known as multsecional pumps. These are generally
of jerk type. The other types are single or double-phuagec distributing Pumps in which one work,
ing section feeds fuel to several eylinders
10.4.1 Jerk Type Bosch Fuekinjection Pump
Figure 10.7 shows the jerk type Bosch high pressure fuel-injetion pump. consists of a bare! in
which a plunger reciprocate. The pump plunger is lifted by a cam on a camshaft eriven by the
‘engine. There isa very smal clearance between the barrel and the plunger, whichis ofthe order of
210 3thousandits of a millimere I provides perfec sealing even at very high pressures and ow
Speeds.
‘The pump barrel has two radially opposing ports. These are the inlet port and the spill ot
bypass port. The plunger moves vertically inthe bare with a constant stroke. To enable the pump
10 vary the quantity of fuel deivered per stroke the plunger is provided with a vertical channel
extending (rom its top edge to an annular groove, the upper edge of which is formed as a he.
‘The helix uns a ithe way down che plunger length. The effective stroke is varied by means ofthe
el onthe plunger which permit the by-passing of fuel a any position of the delivery stoke,
‘hereby controlling the quantity delivered. This is accomplished by means ofa contol rod or ack,
which tums a oothed control sleeve that runs he plunger tothe desired position,
Operation
‘When the plungeris atthe botiom of ts stroke, the inet pot and the spill port ae uncovered. Fuel
enters the barrel and asthe plunger rises, both the ports are covered. The trapped fuel is come
Pressed and fs the delivery valve and then the injection begins. As the phingetcontinoes to rise.
the spill port is uncovered by the helical groove on the plunger andthe high pressure ofl above the
Plunges retums o the sump. When the pressure above the plinger falls, the delivery valve is
osed by the spring and then the injection stops
|
© Engines: Fuebinecson Sytem 313
anda dividing device for isibating the fel tothe cylinders are used. The pump ortheisributor
may meter the quantity of fuel. Since there Isa single metering and distributing element, i is
expected tha the unit will distribute the feel uniforaly to each eylinder. The pumps ofthis type are
found on medium and small-sized (7.5 KW-75 KW per cylinder) diesel engines
10.3.6 Common-rail System
Figur 106 shows a scheme digram Fa common: system The fe fom the fuel sorge
Unk i drawn ag prima fel kes y low resus eed pump. The cae
from his pump enter the gres fe ijcion pamp Tis pump sere nl o deliver
fuel under igh pre, o common pl al ear, vis pressure ad Lot by
a peste regala valve. Ts the mani press sudar de cool and denen
problems ot handles y be igh peste pump. Te high pesen e eat ce he fu
(each ofthe nor oeste intend AL e poe ne, mechanical epee valve
by means oa push rod and a ocker ar alow the fi ene ie older ig the oe
‘The presu inthe oe! ende must he schen 10 ponte an Opos te ful in he
charge
(igh press)
bing
Nozzle spring
loaded valve
tinder
— P
tog shot.
„ un
=> Ll
(aceusmulator) toatl al
pes
>
=
ones
Pira un
combustion chamber and must be in accordance with the injector system design. The amount of
fuel supplied to the combustion chamber is regulated by varying the length ofthe pushrod stoke
‘The common-rail system tends to be self-governing, IF the engine speed falls, an increased
‘quantity of fue is automatically injected, since the üme taken forthe same erank angle rotation,
during which period the fel is supplied is increased. AS the ful pressure i maintained constant
With increases time, the ful supply will alzo be increased
Very accurate design and workmanship ae required inthis type of fue injection mechanism.
‘The Hit of the valve spindle is very small, it requires absolut rigidity ofthe operating mechanism
and freedom from vibration and temperature effects, moreover, the wear must be negligible, The
common-rai systems were, once, quite popular for arg, slow-speed engines, bu over he years,
have been replaced by the jerk-pump injection,
10.4 FUEL-INJECTION PUMPS.
‘The bighr pressure fueLnjection pump is one ofthe main and most complicated units ofthe fuel
injection system in a CI engine, It meters out the fuel in conformity withthe engine dany and
‘supplies fue tothe injector atthe proper time. Fuel pumps i which every working section delivers
fuel to individual cylinders ofthe engine ae known as multsecional pumps. These are generally
of jerk type. The other types are single or double-phuagec distributing Pumps in which one work,
ing section feeds fuel to several eylinders
10.4.1 Jerk Type Bosch Fuekinjection Pump
Figure 10.7 shows the jerk type Bosch high pressure fuel-injetion pump. consists of a bare! in
which a plunger reciprocate. The pump plunger is lifted by a cam on a camshaft eriven by the
‘engine. There isa very smal clearance between the barrel and the plunger, whichis ofthe order of
210 3thousandits of a millimere I provides perfec sealing even at very high pressures and ow
Speeds.
‘The pump barrel has two radially opposing ports. These are the inlet port and the spill ot
bypass port. The plunger moves vertically inthe bare with a constant stroke. To enable the pump
10 vary the quantity of fuel deivered per stroke the plunger is provided with a vertical channel
extending (rom its top edge to an annular groove, the upper edge of which is formed as a he.
‘The helix uns a ithe way down che plunger length. The effective stroke is varied by means ofthe
el onthe plunger which permit the by-passing of fuel a any position of the delivery stoke,
‘hereby controlling the quantity delivered. This is accomplished by means ofa contol rod or ack,
which tums a oothed control sleeve that runs he plunger tothe desired position,
Operation
‘When the plungeris atthe botiom of ts stroke, the inet pot and the spill port ae uncovered. Fuel
enters the barrel and asthe plunger rises, both the ports are covered. The trapped fuel is come
Pressed and fs the delivery valve and then the injection begins. As the phingetcontinoes to rise.
the spill port is uncovered by the helical groove on the plunger andthe high pressure ofl above the
Plunges retums o the sump. When the pressure above the plinger falls, the delivery valve is
osed by the spring and then the injection stops
|
314 Fundamentals of In Combustion Engines
Gt Engine: Fuakinjeten System 315
Deivey
ae flo
Rei pison ser,
Deiivery save
Fag 107_ SaciralvemolBoschjung ent
accord wit te out.
ay moving he ack, te quart of tan Be vai in coran
a he ston of epg for al ol Hor e five aves ma
aa par uncovered oy te Bel. cose o maxim ivr of fl
aaa ad gr 110) sows «shores ef tel ned y ang te
hl al da reves ie Glen ih stale fr pr nd
Fe ae sin de page ii ach he pl on. Ti poston
Ze dde
©
que 108, Psion eh oran oir.
obtained by further rotating the planger withthe help of the rack. At his position, fuel is not
trapped by the upware movement of the plunger. All te felis etumed tothe sump via the spill
port and the fuel isnot delivered. This is the stop position for shuting down the engine. Thus, the
overall displacement of the plunger remains constant at al speeds and loads but the effective ravel
is varie by he helix in accordance with the load on the engine.
‘The delivery valve maintains the high pressure in te delivery pipe and also stops the injection
‘through nozzles abruptly. When the pump is on its delivery stoke, the pressure ofthe fuel above
the plunger increases, the delivery valve is forced upwards but the flow does not begin until the
relief piston ofthe delivery valve leaves the passage. The fuel can now be delivered through the
longitudinal grooves over the valve face tothe nozzle. By the movement ofthe plunger when the
pressure falls inthe bac, the delivery valve is closed by he spring andthe reli piston returns
into its housing. The return of che relief piston increases the volume of the delivery line and
reduces the pressure. The effect ofthis isto cause the spring-loaded nozzle valve in the fuel nozzle
Gt Engine: Fuakinjeten System 315
Deivey
ae flo
Rei pison ser,
Deiivery save
Fag 107_ SaciralvemolBoschjung ent
accord wit te out.
ay moving he ack, te quart of tan Be vai in coran
a he ston of epg for al ol Hor e five aves ma
aa par uncovered oy te Bel. cose o maxim ivr of fl
aaa ad gr 110) sows «shores ef tel ned y ang te
hl al da reves ie Glen ih stale fr pr nd
Fe ae sin de page ii ach he pl on. Ti poston
Ze dde
©
que 108, Psion eh oran oir.
obtained by further rotating the planger withthe help of the rack. At his position, fuel is not
trapped by the upware movement of the plunger. All te felis etumed tothe sump via the spill
port and the fuel isnot delivered. This is the stop position for shuting down the engine. Thus, the
overall displacement of the plunger remains constant at al speeds and loads but the effective ravel
is varie by he helix in accordance with the load on the engine.
‘The delivery valve maintains the high pressure in te delivery pipe and also stops the injection
‘through nozzles abruptly. When the pump is on its delivery stoke, the pressure ofthe fuel above
the plunger increases, the delivery valve is forced upwards but the flow does not begin until the
relief piston ofthe delivery valve leaves the passage. The fuel can now be delivered through the
longitudinal grooves over the valve face tothe nozzle. By the movement ofthe plunger when the
pressure falls inthe bac, the delivery valve is closed by he spring andthe reli piston returns
into its housing. The return of che relief piston increases the volume of the delivery line and
reduces the pressure. The effect ofthis isto cause the spring-loaded nozzle valve in the fuel nozzle
316 Funsamenals of Inamal Combution Engines
I Engines: Fuliction Sptem 317
o snap on its seat, thus suddenly terminating the spray of fuel and eliminating dribbling of he fuel
‘through the nozzle holes. The action of the delivery valve is such that it does not relieve entirely the
pressure in the delivery pipe line. It helps ro increase the pressure inthe pipe line quickly, on the
next injection stroke, oa Value sufficient to open the nozzle,
‘The plunger is of constant stoke and is top edge will always cover the ports inthe pump
barrel at the same position ofthe cam rotation, so tha he fac-njection start atthe same position
‘of the crankshaft, The duration of injection in degrees crank angle wil be a maximum a full ead,
and will decrease with the reduction in load. Hence the pump has a constant beginning and à
variable ending of delivery.
‘Two more variations of plunger helix are also considered by the engine designer Figure 10.94)
shows a plunger helix for variable beginning and constant ending of injection, As the load is
increased te start of injection can be advanced while keeping he end of delivery at toastant rank
angle, This design is sometimes found in low compression SI oil engines. Figure 10.9(b) shows
a variable beginning and a variable ending design, which is sometimes specified for small CI
automotive engines.
Righetand Right-hand upper
one Land lower
Consaot end Vibe bein and
ie variable cod of eiery
@ Q
Agum109. Pangerñe
Delivery characteristics
‘The characteristic of a fuel pump related to the speed isthe relation between the delivery per
‘cycle and the camshaft speed with the goveming member (ack) in a constant position. Figure
10.10 shows the delivery characteristics ofa por-contolled displacement pump. The curve A of
Figure 10.10(2) shows the actual fuel delivery per cycle versus the pump speed. It bas rising
delivery characteristics. Here, with the increase in engine speed, the quantity of fuel
per stoke is increased. This is because of the throttling effects of the inlet and bypass por
‘Throtling appears at the beginning and end of delivery when the intake port is closed by the
plunger edge and the cutsof port is opened by the helical edge. Ata result, a pressure is bu
inthe space above the plunger which is sufficient to open the delivery valve before the geometricl
beginning of injection. Owing to throng in the relief port when iis closed, a high pressure
sufficient 10 feed fuel to the injector is retained in the space above the plunger over part ofits
=
stroke, This is why throling increases the actual delivery of he pump per cyele compared with
the theoretical vale, In C engines ences airs always needed, so th theoretical value of livery
¿sin proportion 10 the mass of air indeed by the
engine per intake stoke. Therefore, it should fl
low a pattem of volumetrc efficiency with speed
which is slightly rising and then falling charac-
teristic, as shown by curve B of Figure 10.100),
Al Tow speed, the compression ofthe ful will
‘occur only after the ports are completely covered
by the plunger. However, a higher speeds the
pressure will build up above the plunger faster
‘than the fuel can bypass through the ports, and
the delivery valve, leading the fuel tthe injector,
will open before the bypass port is completely
covered, Thus the fuel injected at higher speeds
increases, and the rising delivery characteris
as shown by curve A in Figure 10.100) is
baie.
Apart from throttling, the other factors that
fect the delivery ofthe Fuel are compres
ofthe fuel and resilience of the elements
Fuck devices like plunger barrel and delivery
pipe. These factors may cause some of the
supplied fuel to accumulate in the high-pressure
region between he delivery valve and tbe injector.
‘This par ofthe fuel does not ener into the engine
cylinder and the delivery per cycle diminishes,
Figure 10.100) shows the delivery charac-
teristics at three positions ofthe fue! pump rec.
‚Curve 1 is for ack positon corresponding to the
{ull delivery. Atths position the delivery per cycle
increases sligitly with speed. Curves 2 and 3 are
for rack positions corresponding to part delivery,
the delivery per cycle increases more intensively
with the speed. This indicats the growth in the
influence of fuel throtding inthe transition from
full t par delivery adjusted by rack position.
A constan-speed fuel pump eharacteristc,
for the same type of pump, can also be drawn,
which gives the fuel delivery per cycle with
respect to the rack postion, This characteristic is
shown in Figure 10.11. Direct proportionality
between the fuel delivery per cycle and the rack
stroke exists above a certain rack stroke, At
en
ype eye
2,
Ue,
3 <A
E
ppd om)
Figure 0104). Doro racer
me,
T
100]
#
e
40
2
Y
200 HO 5 500 Tom
Pamppecd (um)
pue 10.108) Detvey pco veras perp sped.
se)
8
Bud delivery en
Ts
Rack sooke (na)
Fu lait Det peceras
Feel ie Get)
AA
I Engines: Fuliction Sptem 317
o snap on its seat, thus suddenly terminating the spray of fuel and eliminating dribbling of he fuel
‘through the nozzle holes. The action of the delivery valve is such that it does not relieve entirely the
pressure in the delivery pipe line. It helps ro increase the pressure inthe pipe line quickly, on the
next injection stroke, oa Value sufficient to open the nozzle,
‘The plunger is of constant stoke and is top edge will always cover the ports inthe pump
barrel at the same position ofthe cam rotation, so tha he fac-njection start atthe same position
‘of the crankshaft, The duration of injection in degrees crank angle wil be a maximum a full ead,
and will decrease with the reduction in load. Hence the pump has a constant beginning and à
variable ending of delivery.
‘Two more variations of plunger helix are also considered by the engine designer Figure 10.94)
shows a plunger helix for variable beginning and constant ending of injection, As the load is
increased te start of injection can be advanced while keeping he end of delivery at toastant rank
angle, This design is sometimes found in low compression SI oil engines. Figure 10.9(b) shows
a variable beginning and a variable ending design, which is sometimes specified for small CI
automotive engines.
Righetand Right-hand upper
one Land lower
Consaot end Vibe bein and
ie variable cod of eiery
@ Q
Agum109. Pangerñe
Delivery characteristics
‘The characteristic of a fuel pump related to the speed isthe relation between the delivery per
‘cycle and the camshaft speed with the goveming member (ack) in a constant position. Figure
10.10 shows the delivery characteristics ofa por-contolled displacement pump. The curve A of
Figure 10.10(2) shows the actual fuel delivery per cycle versus the pump speed. It bas rising
delivery characteristics. Here, with the increase in engine speed, the quantity of fuel
per stoke is increased. This is because of the throttling effects of the inlet and bypass por
‘Throtling appears at the beginning and end of delivery when the intake port is closed by the
plunger edge and the cutsof port is opened by the helical edge. Ata result, a pressure is bu
inthe space above the plunger which is sufficient to open the delivery valve before the geometricl
beginning of injection. Owing to throng in the relief port when iis closed, a high pressure
sufficient 10 feed fuel to the injector is retained in the space above the plunger over part ofits
=
stroke, This is why throling increases the actual delivery of he pump per cyele compared with
the theoretical vale, In C engines ences airs always needed, so th theoretical value of livery
¿sin proportion 10 the mass of air indeed by the
engine per intake stoke. Therefore, it should fl
low a pattem of volumetrc efficiency with speed
which is slightly rising and then falling charac-
teristic, as shown by curve B of Figure 10.100),
Al Tow speed, the compression ofthe ful will
‘occur only after the ports are completely covered
by the plunger. However, a higher speeds the
pressure will build up above the plunger faster
‘than the fuel can bypass through the ports, and
the delivery valve, leading the fuel tthe injector,
will open before the bypass port is completely
covered, Thus the fuel injected at higher speeds
increases, and the rising delivery characteris
as shown by curve A in Figure 10.100) is
baie.
Apart from throttling, the other factors that
fect the delivery ofthe Fuel are compres
ofthe fuel and resilience of the elements
Fuck devices like plunger barrel and delivery
pipe. These factors may cause some of the
supplied fuel to accumulate in the high-pressure
region between he delivery valve and tbe injector.
‘This par ofthe fuel does not ener into the engine
cylinder and the delivery per cycle diminishes,
Figure 10.100) shows the delivery charac-
teristics at three positions ofthe fue! pump rec.
‚Curve 1 is for ack positon corresponding to the
{ull delivery. Atths position the delivery per cycle
increases sligitly with speed. Curves 2 and 3 are
for rack positions corresponding to part delivery,
the delivery per cycle increases more intensively
with the speed. This indicats the growth in the
influence of fuel throtding inthe transition from
full t par delivery adjusted by rack position.
A constan-speed fuel pump eharacteristc,
for the same type of pump, can also be drawn,
which gives the fuel delivery per cycle with
respect to the rack postion, This characteristic is
shown in Figure 10.11. Direct proportionality
between the fuel delivery per cycle and the rack
stroke exists above a certain rack stroke, At
en
ype eye
2,
Ue,
3 <A
E
ppd om)
Figure 0104). Doro racer
me,
T
100]
#
e
40
2
Y
200 HO 5 500 Tom
Pamppecd (um)
pue 10.108) Detvey pco veras perp sped.
se)
8
Bud delivery en
Ts
Rack sooke (na)
Fu lait Det peceras
Feel ie Get)
AA
318 Fundamentals of ier! Combusdon Engines
Engines: FuaLnjction Sem 319
shorts rack strokes, the dire proportionality between the fuel delivery and the rack stoke gets
‘more and more violated owing 1 the greater influence of rotin inthe bare! port
104.2 Unit Injector
A unitinjector and its diving mechanism are shown in Figure 10.12 Fuel enters ino the chamber
bad of the plunger through a metering orifice. When fuel is to be injected, the rocker arm
“operated by the cam pushes down the phinger. This action closes the metering orifice and com-
presse the fuel The compressed fuel flows through the check valves and discharges into the
sry te
we 1012. Unto ands eg echaron
engine cylinder through the injector nozzles or or
fices. The amount of fuel injected is controlled by the
horizontal movement of the rack, which in tem 10>
tates the plunger. It controls e spill of fuel ino the
fuel drain manifold by rotating the plunger with is he.
lil rele section via the gear
Figure 10.13 shows the unit injector delivery
characteristics. At full delivery, compressibility of the
fuel prevails over throttling, so the delivery per cycle
drops with an increase in the speed (curve 1). AS the
(llvery per cele is reduced, the influence of theot:
Ming increases (curves 2 and 3). Throling becomes
predominant at stil smaller delivery which reduces the
Injection pressure sharply, and the delivery per cycle
increases withthe speed (curve 4)
“0800 1210 Ten 200
Pop speed pn
Fur t013- Delay hacer
10.4.3 Distributor Type Fuekinjection Pump
A single plunger pump is used to inject fuel in a mull-cylinder engine, This is accomplished by
rotating the plunger by gear, which is driven at half the pump speed by he gear driven shaft. The
rotating plunger distributes the fuel to each injector and the fue is injected by the reciprocating
jon by cam. The plunger makes one rotation per engine cycle but makes as many delivery
rokes per cycle as the number of eylinders it serves.
Figure 10.14 shows the sections ofthe Bosch, asingle-plunger distributor pump. Fuel enters
the barrel at he end of the downward stoke, and the compression ofthe fuel begins asthe intake
port ae closed by the upward motion ofthe plunger. Delivery begins when the upper anoulus in
fhe plunger uncovers the high pressure duct from the delivery valve. At this time the distibating
slot connects this annulus with the dot lo the nozzle. Delivery ends when the second annulus
‘uncovers the upper edge ofthe control sleeve, The amount delivered is controlled by varying the
vertical postion of the contol sleeve. Thus, all cylinders are supplied with fuel from the same
plunger, the same delivery valve, and duct ofthe same shape and lengih.
gue 0%4 Scions tne Aron Be purga meyer og puro ead.
Engines: FuaLnjction Sem 319
shorts rack strokes, the dire proportionality between the fuel delivery and the rack stoke gets
‘more and more violated owing 1 the greater influence of rotin inthe bare! port
104.2 Unit Injector
A unitinjector and its diving mechanism are shown in Figure 10.12 Fuel enters ino the chamber
bad of the plunger through a metering orifice. When fuel is to be injected, the rocker arm
“operated by the cam pushes down the phinger. This action closes the metering orifice and com-
presse the fuel The compressed fuel flows through the check valves and discharges into the
sry te
we 1012. Unto ands eg echaron
engine cylinder through the injector nozzles or or
fices. The amount of fuel injected is controlled by the
horizontal movement of the rack, which in tem 10>
tates the plunger. It controls e spill of fuel ino the
fuel drain manifold by rotating the plunger with is he.
lil rele section via the gear
Figure 10.13 shows the unit injector delivery
characteristics. At full delivery, compressibility of the
fuel prevails over throttling, so the delivery per cycle
drops with an increase in the speed (curve 1). AS the
(llvery per cele is reduced, the influence of theot:
Ming increases (curves 2 and 3). Throling becomes
predominant at stil smaller delivery which reduces the
Injection pressure sharply, and the delivery per cycle
increases withthe speed (curve 4)
“0800 1210 Ten 200
Pop speed pn
Fur t013- Delay hacer
10.4.3 Distributor Type Fuekinjection Pump
A single plunger pump is used to inject fuel in a mull-cylinder engine, This is accomplished by
rotating the plunger by gear, which is driven at half the pump speed by he gear driven shaft. The
rotating plunger distributes the fuel to each injector and the fue is injected by the reciprocating
jon by cam. The plunger makes one rotation per engine cycle but makes as many delivery
rokes per cycle as the number of eylinders it serves.
Figure 10.14 shows the sections ofthe Bosch, asingle-plunger distributor pump. Fuel enters
the barrel at he end of the downward stoke, and the compression ofthe fuel begins asthe intake
port ae closed by the upward motion ofthe plunger. Delivery begins when the upper anoulus in
fhe plunger uncovers the high pressure duct from the delivery valve. At this time the distibating
slot connects this annulus with the dot lo the nozzle. Delivery ends when the second annulus
‘uncovers the upper edge ofthe control sleeve, The amount delivered is controlled by varying the
vertical postion of the contol sleeve. Thus, all cylinders are supplied with fuel from the same
plunger, the same delivery valve, and duct ofthe same shape and lengih.
gue 0%4 Scions tne Aron Be purga meyer og puro ead.
320_ Fundumenals of neral Combarion Engines
LI Engnes Fueiejeción Sytem 321
‘The cost ofthe Bosch pump is about 60% of an individual pump assembly with comparable
delivery characteristics and life,
10.5 FUEL INJECTOR
‘The successful operation ofa CT engine depends on the Functional efficiency of ts injector assem-
bly. The selection ofthe injection holder and nozzle depends onthe construction ofthe combus
tion chamber, the location of the holder and the nozzle assembly.
105.1. Fuokinfection Holder
‘The main purpose ofthe fuel injection holder iso position and to hold the fue-injeetionnozze in
the cylinder head. The fuel duct within the body connects he fuel inet with the injection nozale.
‘The leak-off fel, used to lubricate the nozzle valve, ills the spindle and the adjusting device area
and retums va the leak off connection to the fuel tank
105.2. Fuel-injection Nozzle
‘The fue.injection nozzle has a nozzle body and a needle valve, The design ofthe injector nozzle
must be such that the liquid fuel forced though the nozzle will get broken up into fine droplets, or
et atomized, as it enters nto the combustion chamber. This will ensure proper mixing of the fuel
And ar inthe combustion chamber during the frst phase, The fuel must then be propery dst
‘uted inthe desired areas ofthe combustion chamber. For ths, the injection pressure, the density of
arin the cylinder, the physical qualities of fuel such as viscosity the surface tension ec. and the
mozale design are the important factors. Higher injection pressure results in better disibuton and
greater penetration of the fuel into te desired locations. I also produces finer droplets which tend
Lo mix more reaily withthe air, Fuel spray most reach the air in che combustion space farthest
from the nozzle, but should not impinge the surrounding wall, as it may form gummy deposits
‘ich will cause the piston rings to sick i ther grooves and produce carbon deposits, unpleasant
‘odour, smoky exhaust and cause an increase in fuel consumption.
Injector action
Figure 10.15(a) shows the eros seetion of a Bosch fl.njector. A simplified diagram of atypical
automatic injector nozzteis shown in Figure 10.15(b). High-pressure liquid fel from the injection
[Purp pastes into the combustion chamber through the ful-injector Fuel is supplied tothe orifice
‘through a narrow fuel duct along the nozzle body which terminates in an annular gallery before the
valve sea, The nozzle orifice is usually built with one or more small hols through which the fuel
sprays int the cylinder at high velocity. Immediately behind the orifice, there isa valve which i
sated on the valve seat by means of a stiff adjustable spring. A high pressure is built up inthe
injection line by the movement of ie fuel pump plunger. The pressure acting on part ofthe valve
surface causes a force which overcomes the set spring foree, and opens the valve. The needie~
valve Lifts off ts seat and comes to cest with its upper shoulder against the face ofthe hokler Fuel
is forced out into the combustion chamber in a spray pater, which depends on the type ofthe
‘nozzle used. Thus the injection of fuel in the combustion chamber starts though the orifice thigh
velocity, which ensures good atomization and penetration of the fuel inthe combustion chamber.
12389) peg des
dope Fo Amiens
‘When te fetiejecion pump sis back by te linger movement, he delivery fom te
Bam ses and he delivery var of he pump cows, vih ness volum fe
Son ie and reduces rss, The realign dp of pesue ae ore cos te
Presse pig o sap ed al inte et andthe ze valve cloves tay. Te oe
Injection ths op scaly wihout ring
106 TYPES OF NOZZLES
‘The combustion chamber design dictates the typeof nozzle the droplet size and the spray required
10 achieve complete combustion within a given time and space, There is a wide variety of nozzle
designs to provide the spray characteristics required for each type of combustion chamber The
most common types illustrated in Figure 10.16 are:
LI Engnes Fueiejeción Sytem 321
‘The cost ofthe Bosch pump is about 60% of an individual pump assembly with comparable
delivery characteristics and life,
10.5 FUEL INJECTOR
‘The successful operation ofa CT engine depends on the Functional efficiency of ts injector assem-
bly. The selection ofthe injection holder and nozzle depends onthe construction ofthe combus
tion chamber, the location of the holder and the nozzle assembly.
105.1. Fuokinfection Holder
‘The main purpose ofthe fuel injection holder iso position and to hold the fue-injeetionnozze in
the cylinder head. The fuel duct within the body connects he fuel inet with the injection nozale.
‘The leak-off fel, used to lubricate the nozzle valve, ills the spindle and the adjusting device area
and retums va the leak off connection to the fuel tank
105.2. Fuel-injection Nozzle
‘The fue.injection nozzle has a nozzle body and a needle valve, The design ofthe injector nozzle
must be such that the liquid fuel forced though the nozzle will get broken up into fine droplets, or
et atomized, as it enters nto the combustion chamber. This will ensure proper mixing of the fuel
And ar inthe combustion chamber during the frst phase, The fuel must then be propery dst
‘uted inthe desired areas ofthe combustion chamber. For ths, the injection pressure, the density of
arin the cylinder, the physical qualities of fuel such as viscosity the surface tension ec. and the
mozale design are the important factors. Higher injection pressure results in better disibuton and
greater penetration of the fuel into te desired locations. I also produces finer droplets which tend
Lo mix more reaily withthe air, Fuel spray most reach the air in che combustion space farthest
from the nozzle, but should not impinge the surrounding wall, as it may form gummy deposits
‘ich will cause the piston rings to sick i ther grooves and produce carbon deposits, unpleasant
‘odour, smoky exhaust and cause an increase in fuel consumption.
Injector action
Figure 10.15(a) shows the eros seetion of a Bosch fl.njector. A simplified diagram of atypical
automatic injector nozzteis shown in Figure 10.15(b). High-pressure liquid fel from the injection
[Purp pastes into the combustion chamber through the ful-injector Fuel is supplied tothe orifice
‘through a narrow fuel duct along the nozzle body which terminates in an annular gallery before the
valve sea, The nozzle orifice is usually built with one or more small hols through which the fuel
sprays int the cylinder at high velocity. Immediately behind the orifice, there isa valve which i
sated on the valve seat by means of a stiff adjustable spring. A high pressure is built up inthe
injection line by the movement of ie fuel pump plunger. The pressure acting on part ofthe valve
surface causes a force which overcomes the set spring foree, and opens the valve. The needie~
valve Lifts off ts seat and comes to cest with its upper shoulder against the face ofthe hokler Fuel
is forced out into the combustion chamber in a spray pater, which depends on the type ofthe
‘nozzle used. Thus the injection of fuel in the combustion chamber starts though the orifice thigh
velocity, which ensures good atomization and penetration of the fuel inthe combustion chamber.
12389) peg des
dope Fo Amiens
‘When te fetiejecion pump sis back by te linger movement, he delivery fom te
Bam ses and he delivery var of he pump cows, vih ness volum fe
Son ie and reduces rss, The realign dp of pesue ae ore cos te
Presse pig o sap ed al inte et andthe ze valve cloves tay. Te oe
Injection ths op scaly wihout ring
106 TYPES OF NOZZLES
‘The combustion chamber design dictates the typeof nozzle the droplet size and the spray required
10 achieve complete combustion within a given time and space, There is a wide variety of nozzle
designs to provide the spray characteristics required for each type of combustion chamber The
most common types illustrated in Figure 10.16 are:
Ue eee ee eee ee eee eee eS ee ee eee
322 Fundamenls of neral Combustion Eines
Cl Engines Futjeción Sptem_323
re vo
À À
ha ~~
= er
arm eran
CO Mati tole pe
Nore ae
Norte body
Corinne re
Fe 1016 pes trs
(a) Thepinlenore
(5) The single-hole(oiice) orale
(&) The muli-hole(orfice) nozzle
(8) The pinta nozzle,
106.1 Pintle Nozzle
“The gie type nozzle is shown in Figure 10.16(8). The stem of the nozzle valve has a profiled
extension o form a pte that protrudes io the valve body orifice to form an annula spray bol,
‘The pinle shape is controlled to vary the annular orifice area as the valve lifts. Two types of
pine nozzles are shown in Figure 10.17. Figure 10.17(2) shows a standard pinle nozzle and
(9) Tirting pnt one
(0) Sunda pt orate
Four Tiger.
Figure 10.1700) shows a thronling pinte nozzle. They are quite similar except for the increased
‘office length and greater pinte protrusion ofthe throng type. Depending upon he pine profile,
the spray can be made to issue in the form of a hollow cone with an included angle as high as
60 degrees for standard pintle nozaes, or asa relatively heavy core-spray with an included angle
‘of only a few degree of theoting nozzles.
‘The throtling nozzle gives smoother combustion by reducing the intial rate of injection
‘during the ignition lag period, Figure 10.18() shows a comparison of typical rates of discharge
between the standard pinle nozzle and the rrotling nozzle. Both the beginning and ending ofthe
‘throttle nozzle ae slower.
‘The relation ofthe orifice ares to valve lift for both nozzles is shown in Figure 10.180). This
shows thatthe orifice area forthe thvotle nozzle is very small up 0 0.48 mm valve lift, whereas
‘with the standard pinle nozzle the orifice area increases rapidly above 0.10 mum valve lift
Amar oros ae (sm)
Rate o discharge (desc)
IO
Camdegrees Vale HR Gran)
‘a e
Fu 1018 Compare reso dc anderen as li and sin yar
Standard piste or throttling types are used in engines with precombustion chambers,
turbulence chambers, air or energy cell
10.6.2 Single-hole (Orifice) Nozzle
‘The singl-hole nozzle (Figure 10.16()) consists ofa single hole in he end ofthe nozzle, through
which the fuel passes ino the combustion chamber. The size ofthe hole is usually of the orde of
02 mm. Injection pressure is ofthe order of 80 to 100 bar. The hole may be delle centrally or at
an angle 10 the centre line of the nozzle, such thatthe spray cone angle is about 1°.
‘The main disadvantages of the single-hole nozzle are:
(&) The spray angle is very narrow which does not facilite good mixing unless higher sie
velocities are provide.
(6) requires high injection pressure,
(©) It has a tendency to dribble
322 Fundamenls of neral Combustion Eines
Cl Engines Futjeción Sptem_323
re vo
À À
ha ~~
= er
arm eran
CO Mati tole pe
Nore ae
Norte body
Corinne re
Fe 1016 pes trs
(a) Thepinlenore
(5) The single-hole(oiice) orale
(&) The muli-hole(orfice) nozzle
(8) The pinta nozzle,
106.1 Pintle Nozzle
“The gie type nozzle is shown in Figure 10.16(8). The stem of the nozzle valve has a profiled
extension o form a pte that protrudes io the valve body orifice to form an annula spray bol,
‘The pinle shape is controlled to vary the annular orifice area as the valve lifts. Two types of
pine nozzles are shown in Figure 10.17. Figure 10.17(2) shows a standard pinle nozzle and
(9) Tirting pnt one
(0) Sunda pt orate
Four Tiger.
Figure 10.1700) shows a thronling pinte nozzle. They are quite similar except for the increased
‘office length and greater pinte protrusion ofthe throng type. Depending upon he pine profile,
the spray can be made to issue in the form of a hollow cone with an included angle as high as
60 degrees for standard pintle nozaes, or asa relatively heavy core-spray with an included angle
‘of only a few degree of theoting nozzles.
‘The throtling nozzle gives smoother combustion by reducing the intial rate of injection
‘during the ignition lag period, Figure 10.18() shows a comparison of typical rates of discharge
between the standard pinle nozzle and the rrotling nozzle. Both the beginning and ending ofthe
‘throttle nozzle ae slower.
‘The relation ofthe orifice ares to valve lift for both nozzles is shown in Figure 10.180). This
shows thatthe orifice area forthe thvotle nozzle is very small up 0 0.48 mm valve lift, whereas
‘with the standard pinle nozzle the orifice area increases rapidly above 0.10 mum valve lift
Amar oros ae (sm)
Rate o discharge (desc)
IO
Camdegrees Vale HR Gran)
‘a e
Fu 1018 Compare reso dc anderen as li and sin yar
Standard piste or throttling types are used in engines with precombustion chambers,
turbulence chambers, air or energy cell
10.6.2 Single-hole (Orifice) Nozzle
‘The singl-hole nozzle (Figure 10.16()) consists ofa single hole in he end ofthe nozzle, through
which the fuel passes ino the combustion chamber. The size ofthe hole is usually of the orde of
02 mm. Injection pressure is ofthe order of 80 to 100 bar. The hole may be delle centrally or at
an angle 10 the centre line of the nozzle, such thatthe spray cone angle is about 1°.
‘The main disadvantages of the single-hole nozzle are:
(&) The spray angle is very narrow which does not facilite good mixing unless higher sie
velocities are provide.
(6) requires high injection pressure,
(©) It has a tendency to dribble
324 Fundamentals of Interna! Comborgen Engines
Cl Engines: Fueiieeion System 325
10.5.3. Multichole Nozzle
‘The mult-hole nozzles (Figure 10.16(c) are most suitable for open chamber engines because of
the versatility with which changes can be made to provide any desired penetration, dispersion, and
uration of injection. The orifices can be drilled as small a 0.125 mun diameter or a large as
0.85 mm, and the number of orifices varies from 410 10 depending upon the cylinder bore and air
Swirl, The use of more than 10 orifices generally results in interference between the adjacent
sprays. The nozzle opening pressure fr these nozzles varies from 165 bar to 200 bar for small
engines and 240 to 300 bar for large engines. The nozzle opening and closing pressures should be
sufficiently high to ensure thatch valve is fully seated against high combustion chamber pres.
sure after the injection has ended, otherwise the combustion gases will enter the nozzle and fou!
the orfices and the valve with carbon
In general, the singie- and mult-hole nozzles are used wich the non-trbulent typeof eombus-
tion chamber. The orifices of these nozzles are very small and are subject to clogging by carton
particles which may either intecere with the functioning of the nozzle stream, or may even com.
pietely stop the flow through some orifices. Consequendy, this type of nozzle usualy requires
greater maintenance and higher operating expenses
10.6.4 Pintaux Nozzle
Iisa throtding typeof pine nozzle with an auiliay hole Figure 10.16(9). An auxiliary 02 mm
diameter bole i driled a a 30 degree angl through the bottom of the nozzle into a space just
below the valve seat. The needle valve does nor lif enough at low speeds and most of the fuel is
injected through the auxiliary hole, but at higher speeds mot ofthe fuel is discharged normally
past he pinte as shown in Figure 10.19, The main advantage ofthe pintaux nozzle is that
provides better cold starting performance. The main disadvantage ofthis type of nozzl isthe
“| Fase A IT]
aaa
i, Eee
an i
po
2 SCA |
Two me
RE
=
Fie 018. cken arcas lo pau ar.
tendency for the ausiliary hole 10 choke. The injection characteristic of the pintaux nozale is
poorer than tat ofthe multichole nozzle
10.7 ELECTRONICALLY CONTROLLED UNIT
FUEL-INJECTION SYSTEM
Figure 10.20 shows an clectonicaly controlled unit fuel-injecion system. The technology forthis
system is now avaiable. In this system, the injection timing and metering functions are peformed
by a solenoid operated control valve in a fashion analogous othe port and helix ofthe mechanical
injector. Higher fuel injection commences asthe solenoid valve cloces, The duration of the valve
loue determines the quantity of the fuel injected. The injection terminates as soon as the sole
Termin)
=
Si
Poppet cool valve
ody foiting
Fu i020 era siedongton
Cl Engines: Fueiieeion System 325
10.5.3. Multichole Nozzle
‘The mult-hole nozzles (Figure 10.16(c) are most suitable for open chamber engines because of
the versatility with which changes can be made to provide any desired penetration, dispersion, and
uration of injection. The orifices can be drilled as small a 0.125 mun diameter or a large as
0.85 mm, and the number of orifices varies from 410 10 depending upon the cylinder bore and air
Swirl, The use of more than 10 orifices generally results in interference between the adjacent
sprays. The nozzle opening pressure fr these nozzles varies from 165 bar to 200 bar for small
engines and 240 to 300 bar for large engines. The nozzle opening and closing pressures should be
sufficiently high to ensure thatch valve is fully seated against high combustion chamber pres.
sure after the injection has ended, otherwise the combustion gases will enter the nozzle and fou!
the orfices and the valve with carbon
In general, the singie- and mult-hole nozzles are used wich the non-trbulent typeof eombus-
tion chamber. The orifices of these nozzles are very small and are subject to clogging by carton
particles which may either intecere with the functioning of the nozzle stream, or may even com.
pietely stop the flow through some orifices. Consequendy, this type of nozzle usualy requires
greater maintenance and higher operating expenses
10.6.4 Pintaux Nozzle
Iisa throtding typeof pine nozzle with an auiliay hole Figure 10.16(9). An auxiliary 02 mm
diameter bole i driled a a 30 degree angl through the bottom of the nozzle into a space just
below the valve seat. The needle valve does nor lif enough at low speeds and most of the fuel is
injected through the auxiliary hole, but at higher speeds mot ofthe fuel is discharged normally
past he pinte as shown in Figure 10.19, The main advantage ofthe pintaux nozzle is that
provides better cold starting performance. The main disadvantage ofthis type of nozzl isthe
“| Fase A IT]
aaa
i, Eee
an i
po
2 SCA |
Two me
RE
=
Fie 018. cken arcas lo pau ar.
tendency for the ausiliary hole 10 choke. The injection characteristic of the pintaux nozale is
poorer than tat ofthe multichole nozzle
10.7 ELECTRONICALLY CONTROLLED UNIT
FUEL-INJECTION SYSTEM
Figure 10.20 shows an clectonicaly controlled unit fuel-injecion system. The technology forthis
system is now avaiable. In this system, the injection timing and metering functions are peformed
by a solenoid operated control valve in a fashion analogous othe port and helix ofthe mechanical
injector. Higher fuel injection commences asthe solenoid valve cloces, The duration of the valve
loue determines the quantity of the fuel injected. The injection terminates as soon as the sole
Termin)
=
Si
Poppet cool valve
ody foiting
Fu i020 era siedongton
UG sn e e UNE er OSs POSS Sees
326_fandumenale ol ners! Combusion Engines
1 Engines: FueLnjecion Sytem 327
‘oid valve opens. The injection pressure is generated by the camshaft driven plunger, and the
needle valve nozzle is employed as usual
“The clecronically-controlled unit fue-injection system provides increased flexibility in fuel
‘metering and timing. This system has a simple mechanical design 100.
10.8 Cl ENGINE GOVERNORS
‘Thece are only a few engine applications which do not requir govemor. The passenger cars an
example of engine application without a govemor Here, the changes in engine speed and engine
Toad are sensed by the driver, There are many other applications for which governors are used to
readjust automatically to changes in load and speed, The different types of govemors are
mechanical, pneumati, hydraulic, and electronic.
Regardless of the type of govemor required o do a particular job, each must perform two
major task. A governor must serve asa sped indicator to measure the engine speed and must act
sa power mechanism to actuate the fuel contol whenever a speed change occuts. Further more,
the govemor must regulate de injected fuel to prevent the engine fom stalling or overspeeding.
‘The conventional govemor is speed sensitive control which maintaias the engine speed within
the desired limits by automatically adjusting the fuel pump delivery to meet the variations in lod.
‘Only the mechanical governor is described here. Figure 1021 shows a schematic diagram of
a simple mechanical governor. has a pair of engine driven fyweighss, working against spring,
for speed sensing, When he engine speed increases due to decreased load, he centrifugal force of
the roating Ayweights forces the weight outwards agains the spring force until both the forces
ae equal. At te same time the fuel control rack ofthe injection purap is moved towards the low
fuel postion and the governor maintains a constant engine speed. The reverse action takes place
when the engine speed decreases due to increased load, Thus the engine speed is maintained fairly
‘constant irespecive of the engine load
10.9 SPRAY CHARACTERISTICS
The efficiency and power output of Cl engines are highly dependent on the characteristics ofthe
fuel spray injected from the ndzze into the combustion chamber, The process of spraying has two
objectives. I divides the liquid fuel into a large numberof fine droplets to increase is surface area
for rapid heat transfer ard combustion, and it distributes the fuel though the combustion chamber
for intimate mixing of the fuel and air.
10.9.1 Spray Formation
Depending upon te injection pressure and visos ofthe Liquid fue, the ft poston of fol
Coming out for the nome ually appears a à clica jet. A a cerin distance from the
foal the et breaks up int fice droplets to form a conical shaped spray.
“The mos widely sed method for spraying liquid fel in CI engine i by slid or pressure
injection, Ful is fred though an orice under presse o form an unstable jet which dante:
ties as comes no contact wth he ar inthe combustion chee
109.2 Atomization
‘The uniformity and fineness ofthe droplets ina spray defines its degree of atorization. The fuel
velocity isthe most important facts that affects the degree of atomization, This depends primarily
‘upon the injection pressure, being a function of the square root of the difference between the
injection pressure and the compression pressure. Increasing the injection pressure reduces
the mean diameter of the particles as well as varies her size. The percentage of particles with
the large diameters decreases rapidly with an increase in the injection pressure. A small orifice
diameter results a large suface-1o-volume ratio for the fuel steam. This should result in beter
somnization
“The density ofthe airino which th Fuel is injected affects atomization because ofthe impor
ant part played by the ai nthe fuel jet disintegration process. As dhe air pressure is increased,
there is à consistent decrease in droplet size.
“The fuel factors that affect atomization ae viscosity, surface tension and density.
10.9.3 Penetration
‘The distance to which the tip of a fuel spray wil penetrate the arin the combustion chamber in a
given time depends primarily upon the jet velocity, the combustion chamber aie density and the
orifice size. The fuel viseosity has a small effect on penetration
"An increase in injection pressure increases the spray-ip penetration. An increase in combus-
tion chamber air density decreases the penetration. An increase in orifice diameter increases the
penetration of the spray tip. The orifice should have a high coefficient of discharge and should be
‘ofsuch length tha the fuel leaves the orifice as a team Slowing along the axis ofthe orifice ifhigh
penetration is desired. An orifice’slength-to-diameter ratio between 4 and 7 gives the highest
spray penetration.
For a given orifice and combustion chamber pressure, it
s= stip) don
i found that
— ————————————
326_fandumenale ol ners! Combusion Engines
1 Engines: FueLnjecion Sytem 327
‘oid valve opens. The injection pressure is generated by the camshaft driven plunger, and the
needle valve nozzle is employed as usual
“The clecronically-controlled unit fue-injection system provides increased flexibility in fuel
‘metering and timing. This system has a simple mechanical design 100.
10.8 Cl ENGINE GOVERNORS
‘Thece are only a few engine applications which do not requir govemor. The passenger cars an
example of engine application without a govemor Here, the changes in engine speed and engine
Toad are sensed by the driver, There are many other applications for which governors are used to
readjust automatically to changes in load and speed, The different types of govemors are
mechanical, pneumati, hydraulic, and electronic.
Regardless of the type of govemor required o do a particular job, each must perform two
major task. A governor must serve asa sped indicator to measure the engine speed and must act
sa power mechanism to actuate the fuel contol whenever a speed change occuts. Further more,
the govemor must regulate de injected fuel to prevent the engine fom stalling or overspeeding.
‘The conventional govemor is speed sensitive control which maintaias the engine speed within
the desired limits by automatically adjusting the fuel pump delivery to meet the variations in lod.
‘Only the mechanical governor is described here. Figure 1021 shows a schematic diagram of
a simple mechanical governor. has a pair of engine driven fyweighss, working against spring,
for speed sensing, When he engine speed increases due to decreased load, he centrifugal force of
the roating Ayweights forces the weight outwards agains the spring force until both the forces
ae equal. At te same time the fuel control rack ofthe injection purap is moved towards the low
fuel postion and the governor maintains a constant engine speed. The reverse action takes place
when the engine speed decreases due to increased load, Thus the engine speed is maintained fairly
‘constant irespecive of the engine load
10.9 SPRAY CHARACTERISTICS
The efficiency and power output of Cl engines are highly dependent on the characteristics ofthe
fuel spray injected from the ndzze into the combustion chamber, The process of spraying has two
objectives. I divides the liquid fuel into a large numberof fine droplets to increase is surface area
for rapid heat transfer ard combustion, and it distributes the fuel though the combustion chamber
for intimate mixing of the fuel and air.
10.9.1 Spray Formation
Depending upon te injection pressure and visos ofthe Liquid fue, the ft poston of fol
Coming out for the nome ually appears a à clica jet. A a cerin distance from the
foal the et breaks up int fice droplets to form a conical shaped spray.
“The mos widely sed method for spraying liquid fel in CI engine i by slid or pressure
injection, Ful is fred though an orice under presse o form an unstable jet which dante:
ties as comes no contact wth he ar inthe combustion chee
109.2 Atomization
‘The uniformity and fineness ofthe droplets ina spray defines its degree of atorization. The fuel
velocity isthe most important facts that affects the degree of atomization, This depends primarily
‘upon the injection pressure, being a function of the square root of the difference between the
injection pressure and the compression pressure. Increasing the injection pressure reduces
the mean diameter of the particles as well as varies her size. The percentage of particles with
the large diameters decreases rapidly with an increase in the injection pressure. A small orifice
diameter results a large suface-1o-volume ratio for the fuel steam. This should result in beter
somnization
“The density ofthe airino which th Fuel is injected affects atomization because ofthe impor
ant part played by the ai nthe fuel jet disintegration process. As dhe air pressure is increased,
there is à consistent decrease in droplet size.
“The fuel factors that affect atomization ae viscosity, surface tension and density.
10.9.3 Penetration
‘The distance to which the tip of a fuel spray wil penetrate the arin the combustion chamber in a
given time depends primarily upon the jet velocity, the combustion chamber aie density and the
orifice size. The fuel viseosity has a small effect on penetration
"An increase in injection pressure increases the spray-ip penetration. An increase in combus-
tion chamber air density decreases the penetration. An increase in orifice diameter increases the
penetration of the spray tip. The orifice should have a high coefficient of discharge and should be
‘ofsuch length tha the fuel leaves the orifice as a team Slowing along the axis ofthe orifice ifhigh
penetration is desired. An orifice’slength-to-diameter ratio between 4 and 7 gives the highest
spray penetration.
For a given orifice and combustion chamber pressure, it
s= stip) don
i found that
— ————————————
328_ Fundamentals of Interna Conburton Engines
Cl Engines Fugen Sytem 329
where £ is the time required for the spray to penetrate the distance s and Ap is the pressure
difference between the injection pressure and the combustion chamber pressure. The functional
relation (10.1) can be represented by a curve shown in Figure 10.22), With the variation of
injection pressufe the results li on a single curve, The two points | and 2on the curve satisly the
fonctions! relation, therfore,
fan) and fa) (10.2)
I he penetration sy = sy, then
nan = afán (10.3)
For the same value of penetration the above relation is satisfied, This relation may be used to
determine the time required forthe spray o penetrate the same distance when one injection pres.
Sure is known,
Teis alo found that
243) (104)
Where d is he orifice diameter. This functional relation is represented by a curve shown in
Figure 1022(b). The two points | and 2 satisfy he funcional relation, therefore
AY = a) m
Forth similar points on the penetration curve,
(10.6)
10.9.4. Dispersion
“The primary objective in fuel injection isto distibute the Fuel throughout the inducted air in the
combustion chamber. This is achieved by the spray having the required penetration and disper-
ion, which involves te atomization and spreading of the fuel. Spray dispersion has been defined
a the ratio of spray volume to fuel volume at a given phase ofthe injection interval.
‘The dispersion ofthe fuel spray depends upon the injetion-nozele design, The type of orifice
that gives a large spray cone produces better dispersion of the fuel than does a small spray con.
‘Tis indicates a small length-i-diameter ratio forthe orifice. However, an increase in spray dis.
persion decreases the penetration,
‘Spray dispersion is affected by the following factors:
1. The process of dispersion takes time, and st becomes more uniform as the distance from
the onifio is increased
2. The dispersion becomes more even asthe air density increases
3. As the oil viscosity is decreased the dispersion becomes more uniform.
4. The dispersion improves as the injection pressure is increased,
10.10 RATE OF FUEL INJECTION IN Cl ENGINES
(Consider Figure 1023, showing fuel injection into a cylinder through an injection nozzle. Take
‘bo sections 1-1 and 2-2" as shown in te diagram
La
pi = Sostinjcion pese
Pa = pressor inthe linda the time of fel
ain
= density of fue (assumed incompressible)
= veloc a section 1-1"
cs = veloc a section 2-27
From Bermauli’s egenion (negletng change in i
potential energy), e.
EIN 103)
24 29% won
[Neglecting the initial velocity offuel,c being very small Figure 1023. Fusco trohan tan
compared 10 cy, we have rod.
a Bee ao
If cgis th actual velocity of fuel, c isthe velocity coefficient forthe orifice and Bp
Pa
gaa fe 109)
6, dos)
—
Cl Engines Fugen Sytem 329
where £ is the time required for the spray to penetrate the distance s and Ap is the pressure
difference between the injection pressure and the combustion chamber pressure. The functional
relation (10.1) can be represented by a curve shown in Figure 10.22), With the variation of
injection pressufe the results li on a single curve, The two points | and 2on the curve satisly the
fonctions! relation, therfore,
fan) and fa) (10.2)
I he penetration sy = sy, then
nan = afán (10.3)
For the same value of penetration the above relation is satisfied, This relation may be used to
determine the time required forthe spray o penetrate the same distance when one injection pres.
Sure is known,
Teis alo found that
243) (104)
Where d is he orifice diameter. This functional relation is represented by a curve shown in
Figure 1022(b). The two points | and 2 satisfy he funcional relation, therefore
AY = a) m
Forth similar points on the penetration curve,
(10.6)
10.9.4. Dispersion
“The primary objective in fuel injection isto distibute the Fuel throughout the inducted air in the
combustion chamber. This is achieved by the spray having the required penetration and disper-
ion, which involves te atomization and spreading of the fuel. Spray dispersion has been defined
a the ratio of spray volume to fuel volume at a given phase ofthe injection interval.
‘The dispersion ofthe fuel spray depends upon the injetion-nozele design, The type of orifice
that gives a large spray cone produces better dispersion of the fuel than does a small spray con.
‘Tis indicates a small length-i-diameter ratio forthe orifice. However, an increase in spray dis.
persion decreases the penetration,
‘Spray dispersion is affected by the following factors:
1. The process of dispersion takes time, and st becomes more uniform as the distance from
the onifio is increased
2. The dispersion becomes more even asthe air density increases
3. As the oil viscosity is decreased the dispersion becomes more uniform.
4. The dispersion improves as the injection pressure is increased,
10.10 RATE OF FUEL INJECTION IN Cl ENGINES
(Consider Figure 1023, showing fuel injection into a cylinder through an injection nozzle. Take
‘bo sections 1-1 and 2-2" as shown in te diagram
La
pi = Sostinjcion pese
Pa = pressor inthe linda the time of fel
ain
= density of fue (assumed incompressible)
= veloc a section 1-1"
cs = veloc a section 2-27
From Bermauli’s egenion (negletng change in i
potential energy), e.
EIN 103)
24 29% won
[Neglecting the initial velocity offuel,c being very small Figure 1023. Fusco trohan tan
compared 10 cy, we have rod.
a Bee ao
If cgis th actual velocity of fuel, c isthe velocity coefficient forthe orifice and Bp
Pa
gaa fe 109)
6, dos)
—
DS Gow GS Ce wor DOSS So’
330 _Fundamenals of neral Combustion Engines
Cl Engines: Fuekineon Sytem 331
Rate of mass Now of fuel
my = pray
C7
ea of eros-section of fuel nozzle,
(10.0)
ay = area of cross-section of te fuel jet at venna-contract,
iro with C, as the coefficient of contraction
(Ca = coefficient of discharge = CC,
10.11 FUEL-LINE HYDRAULICS
Efficient combustion requires tha the fue! be injected at the proper time and rate andthe injection
Pressure must be suficenty high for adequate atomization and penetration. This requires not only
{he mechanical characteristics ofthe pump, the discharge tubing and the injector, but also the
compressibility and dynamics of he fuel flow between the pump and the nozzle,
10.11.41
Since fuel is compressible at igh pressure, thereis atime lag between the begianing of delivery by
‘the pump and the beginning o discharge from the nozzle, and the rate of delivery from the pump
is not identical with the rate of discharge from the nozzle.
‘The compressibility ofa quid isthe reciprocal of te modulos of elasticity or bulk modulus.
‘The modulus of elasticity for liquids can be expressed in he same way as forthe slid. The bulk
modulus K of a liquid is defined as the pressure required to produce unit volumetric sain.
Ko sess increase in pressure
ferain ~ Weetease in volume per uit orginal volume
Fuel Compressibility
ao
‘The bulk modulus is «funtion Of temperature and pressure but here it will be considere to
be a constant. Then with adequate accuracy, we can write
ar 10.12)
aoe 0.12)
where Apis the inresse in density and pis he density ofthe Msi,
The coefficient of compressibily kis ih reciprocal ofthe bulk modulus X, Le.
EA 0.13)
Kop
10.112. Pressure Waves In Fuel Lines
‘As uel oilis compressible fluid the movement ofthe pump plunger initiates a pressure wave and
‘propagates it through the discharge tube atthe speed of sound in the fuel oil. The pressure wave
is aus by he pesure tas built up bythe plage compressing the fe ate pump. while
acocerat the fel column towards the onze. These waves not only travel fom the Pimp 10
the noel, or re als elected towards he pump om te nz. The pressure waves ar
the designed rates o injection and presos
Consider Figure 1024 showing simplified representation x
of plunger and barrel of injection pump. Assume that the Lendl i
plunger and ll i parie re moving I the elinder at à :
Yelo and ha the plags I being accelerated and the
Nele is jesanly inresed hy. Te ud adjacent othe >
unge wl ao increase e velciy te same instant by Av, :
du section EX à ite ine wi pas before the pressure
increase is evident. The ool mass of Mui spaced in
M by the plonge because of the velociy increase Av E
would be vn, where is the consi ofthe fd and
the ara of erre section of Ue bue, This displacement
Causes a pressure wave to teve down he pipe a son
‘elocity vrand increases the density af the Aid The ations mas ofthe Mi displaced in the
Brel by the plunger because of he Inereaed velocity must be equal othe gain in mas ofthe
fluid resulting fom de inereased density: This pin in mass would e (Apr AA. Equatin these
wo expressions,
(PAvADA = (Apsand
=p 2
werd dois
where
vs = velocit of propagation of pressure isurbane inthe uid (soni velocity), ia ms
1 = density of Suid ekg?
‘Av change in velocity of langer, in més
“apa increase in density resuóng from increase pressure, in kr.
“Another expression for sonic velocity vg ean be obtained from Newton's law,
F=ma
“ men
‘where Ap is the increase in pressure in N/m? corresponding to the acceleration Avlär and m is the
ms of hd pires
Now, m= pyshiA
Opa = pra St
a
or Ap pra ous,
„18
ve (10.16)
330 _Fundamenals of neral Combustion Engines
Cl Engines: Fuekineon Sytem 331
Rate of mass Now of fuel
my = pray
C7
ea of eros-section of fuel nozzle,
(10.0)
ay = area of cross-section of te fuel jet at venna-contract,
iro with C, as the coefficient of contraction
(Ca = coefficient of discharge = CC,
10.11 FUEL-LINE HYDRAULICS
Efficient combustion requires tha the fue! be injected at the proper time and rate andthe injection
Pressure must be suficenty high for adequate atomization and penetration. This requires not only
{he mechanical characteristics ofthe pump, the discharge tubing and the injector, but also the
compressibility and dynamics of he fuel flow between the pump and the nozzle,
10.11.41
Since fuel is compressible at igh pressure, thereis atime lag between the begianing of delivery by
‘the pump and the beginning o discharge from the nozzle, and the rate of delivery from the pump
is not identical with the rate of discharge from the nozzle.
‘The compressibility ofa quid isthe reciprocal of te modulos of elasticity or bulk modulus.
‘The modulus of elasticity for liquids can be expressed in he same way as forthe slid. The bulk
modulus K of a liquid is defined as the pressure required to produce unit volumetric sain.
Ko sess increase in pressure
ferain ~ Weetease in volume per uit orginal volume
Fuel Compressibility
ao
‘The bulk modulus is «funtion Of temperature and pressure but here it will be considere to
be a constant. Then with adequate accuracy, we can write
ar 10.12)
aoe 0.12)
where Apis the inresse in density and pis he density ofthe Msi,
The coefficient of compressibily kis ih reciprocal ofthe bulk modulus X, Le.
EA 0.13)
Kop
10.112. Pressure Waves In Fuel Lines
‘As uel oilis compressible fluid the movement ofthe pump plunger initiates a pressure wave and
‘propagates it through the discharge tube atthe speed of sound in the fuel oil. The pressure wave
is aus by he pesure tas built up bythe plage compressing the fe ate pump. while
acocerat the fel column towards the onze. These waves not only travel fom the Pimp 10
the noel, or re als elected towards he pump om te nz. The pressure waves ar
the designed rates o injection and presos
Consider Figure 1024 showing simplified representation x
of plunger and barrel of injection pump. Assume that the Lendl i
plunger and ll i parie re moving I the elinder at à :
Yelo and ha the plags I being accelerated and the
Nele is jesanly inresed hy. Te ud adjacent othe >
unge wl ao increase e velciy te same instant by Av, :
du section EX à ite ine wi pas before the pressure
increase is evident. The ool mass of Mui spaced in
M by the plonge because of the velociy increase Av E
would be vn, where is the consi ofthe fd and
the ara of erre section of Ue bue, This displacement
Causes a pressure wave to teve down he pipe a son
‘elocity vrand increases the density af the Aid The ations mas ofthe Mi displaced in the
Brel by the plunger because of he Inereaed velocity must be equal othe gain in mas ofthe
fluid resulting fom de inereased density: This pin in mass would e (Apr AA. Equatin these
wo expressions,
(PAvADA = (Apsand
=p 2
werd dois
where
vs = velocit of propagation of pressure isurbane inthe uid (soni velocity), ia ms
1 = density of Suid ekg?
‘Av change in velocity of langer, in més
“apa increase in density resuóng from increase pressure, in kr.
“Another expression for sonic velocity vg ean be obtained from Newton's law,
F=ma
“ men
‘where Ap is the increase in pressure in N/m? corresponding to the acceleration Avlär and m is the
ms of hd pires
Now, m= pyshiA
Opa = pra St
a
or Ap pra ous,
„18
ve (10.16)
332 Fundamentals of Inerat Comburton Engines
‘Upon muliplying Bes. (10.14) and (10.16),
2. ae
wee de 1
(0.17)
Upon substituting Bq. (1.12) in Eq. (10.17) and simplifying,
E
ve= JE 10.18)
A aos,
By substituting this value of vein Eg. (10.16),
or 0019)
From Ba, (1018). 6 = X. subaining it in Eg. (109)
wk
wok “om,
A six-cylinder four-stroke diesel engine develops a power of 250 KW at 1500
pm. The brake specific fuel consumption is 0.3 kg/kWh. The pressures of air in the cylinder at
the beginning o injection an atthe end of injection are 30 bar and 60 bar respectively. The fuel
injection pressures a he beginning and end of injection are 220 bar and 550 bar respectively
Assume the eoefficient of discharge forte injector to be 0.5, specific gravity of ful to be 0.85
and the atmospheric pressure to be 1.013 bar. Assume the effective pressure difference 10 be the
average pressure difference over the injection period.
Determine the nozzle area required per injection if the injection takes place over 15° crank
angle. Ifthe numberof orifices used in the nozzle ae 4, find the diameter of he rice.
sag (kab)
ew)
5 kg = 1.25 kgmin
fuel consumed per min 1
“hoof cycles per min > ne.oFeylinders
125 „1.
= abs yx} = 00002778 kg
Solution
Brake specific fuel consumption, bse (ke/kWH) =
ray = fe xbp = 0.3 x250.
Fuel injected per cycle per cylinder =
ISCH contagio) hen
CL Engins: Futjción Spam 333
10. of revolutions
Duration of injection(s) = nn - aoe
= 1.667 x 107 5 = 0.001667 à
2 Mass of fuel injected per second, my = 1666 kgs
0002778
(0.001667
Pressure difference atthe beginning = 220 - 30 = 190 bar
Pressure difference a te e
Average pressure difference, A
‘The mass of fuel injected per second,
‘Area of cross-section ofthe nozzle,
tig
Choy Be
01666
Ar
* pas ax850x 100x107
Ans.
‘Now, he diameter of orifice, d, can be calculated from the relation,
(52) no: of res
or apna
A single-cylinder fr suoke diesel engine develops a owerof301W a 3000
rpm. The specific fe consumption is 028 KERN fuel of 35° APL The fel is injeted at an
average pressure of 160 ba. The duration of injection i 28" of crank rave. The pressure in ie
combustion chamber is 35 bar. The cocfficien of velocity is 092. Determino the velocity of
injection ofthe fe and ameter ofthe fel cie
ais 1915
BES APT © 1315435
Density ffl, py = 0.85 x 1000 = 850 kg/m?
‘Solution: Specific gravity = =085
‘Upon muliplying Bes. (10.14) and (10.16),
2. ae
wee de 1
(0.17)
Upon substituting Bq. (1.12) in Eq. (10.17) and simplifying,
E
ve= JE 10.18)
A aos,
By substituting this value of vein Eg. (10.16),
or 0019)
From Ba, (1018). 6 = X. subaining it in Eg. (109)
wk
wok “om,
A six-cylinder four-stroke diesel engine develops a power of 250 KW at 1500
pm. The brake specific fuel consumption is 0.3 kg/kWh. The pressures of air in the cylinder at
the beginning o injection an atthe end of injection are 30 bar and 60 bar respectively. The fuel
injection pressures a he beginning and end of injection are 220 bar and 550 bar respectively
Assume the eoefficient of discharge forte injector to be 0.5, specific gravity of ful to be 0.85
and the atmospheric pressure to be 1.013 bar. Assume the effective pressure difference 10 be the
average pressure difference over the injection period.
Determine the nozzle area required per injection if the injection takes place over 15° crank
angle. Ifthe numberof orifices used in the nozzle ae 4, find the diameter of he rice.
sag (kab)
ew)
5 kg = 1.25 kgmin
fuel consumed per min 1
“hoof cycles per min > ne.oFeylinders
125 „1.
= abs yx} = 00002778 kg
Solution
Brake specific fuel consumption, bse (ke/kWH) =
ray = fe xbp = 0.3 x250.
Fuel injected per cycle per cylinder =
ISCH contagio) hen
CL Engins: Futjción Spam 333
10. of revolutions
Duration of injection(s) = nn - aoe
= 1.667 x 107 5 = 0.001667 à
2 Mass of fuel injected per second, my = 1666 kgs
0002778
(0.001667
Pressure difference atthe beginning = 220 - 30 = 190 bar
Pressure difference a te e
Average pressure difference, A
‘The mass of fuel injected per second,
‘Area of cross-section ofthe nozzle,
tig
Choy Be
01666
Ar
* pas ax850x 100x107
Ans.
‘Now, he diameter of orifice, d, can be calculated from the relation,
(52) no: of res
or apna
A single-cylinder fr suoke diesel engine develops a owerof301W a 3000
rpm. The specific fe consumption is 028 KERN fuel of 35° APL The fel is injeted at an
average pressure of 160 ba. The duration of injection i 28" of crank rave. The pressure in ie
combustion chamber is 35 bar. The cocfficien of velocity is 092. Determino the velocity of
injection ofthe fe and ameter ofthe fel cie
ais 1915
BES APT © 1315435
Density ffl, py = 0.85 x 1000 = 850 kg/m?
‘Solution: Specific gravity = =085
Cen wu ee ieee Gar SS ES
334_ Fundumencats of Intra Combustion Engines
10. of revolutions
‘evolution per second
28/360 _ 556
BBE = 1.556% 10° s
sto kW
‘Gyles per hour
„ _028x30
= oa
Mass of ful flow per second,
dr = 2333x108
CETTE
Velocity of injection fuel,
ce
A
099 UD _ A
200 EEE 75 m
Darationof injection
Fuel consumption per cycle =
= 9.393 10 kg
=6x107
06 kgs
y = 9/XAyX (neglecting contraction ofthe jet)
473 x 107 m
CES) am
A closed injection nozzle has an orifice diameter of 0.8 mm andthe maximum
‘ros-setional area ofthe passage between the needle cone and the seat is 1.65 mn, The dis-
charge coefficient for he once is 0.9 an that for the passage is 0.85. The injection pressure is
170 bar andthe compresion pressure ofthe charge during injection is 25 bar. when the needle
valve is fully open, Determine the discharge of fue through the injector andthe jet velocity a that
instant. The density of the fuel is 850 kg/m.
Re
Pr
[Neglecting contraction of the jet, he coefficient of contraction, Cz = 1.0
Coefficient of velocity, C, = coefficient of discharge, Ca
mE
cal
Q=Axe,
Solution: Velocity of Now, ey
Discharge,
Cl Enge: Fuel injection Sytem 335
where A is the area of eross-section of the oi,
wa
= 192) ie loan
Let p be the pressure immediately before the orifice in bar. We now have the following two
equations:
Flow through passage
170 =p = q «850 Oe Dal
OOO
é 170 -p = 2.161 x 10707 [02
Fw rn ite:
se A
ET
:
P25 = 2077 x 10/07 @
aan a and vea
145 = 22.931 x 10/07
a= watt 795 x 10% mis
En
= [55%] Ans.
From Eq. @,
170 -p = 2.161 x 10? x (0.7957 x 10
p= 170 ~ 13.66 = 156.34 bar
‘Velocity of fuel flow through the once,
ES
ae F7
20565-29010
be 350
Ber] Ans.
334_ Fundumencats of Intra Combustion Engines
10. of revolutions
‘evolution per second
28/360 _ 556
BBE = 1.556% 10° s
sto kW
‘Gyles per hour
„ _028x30
= oa
Mass of ful flow per second,
dr = 2333x108
CETTE
Velocity of injection fuel,
ce
A
099 UD _ A
200 EEE 75 m
Darationof injection
Fuel consumption per cycle =
= 9.393 10 kg
=6x107
06 kgs
y = 9/XAyX (neglecting contraction ofthe jet)
473 x 107 m
CES) am
A closed injection nozzle has an orifice diameter of 0.8 mm andthe maximum
‘ros-setional area ofthe passage between the needle cone and the seat is 1.65 mn, The dis-
charge coefficient for he once is 0.9 an that for the passage is 0.85. The injection pressure is
170 bar andthe compresion pressure ofthe charge during injection is 25 bar. when the needle
valve is fully open, Determine the discharge of fue through the injector andthe jet velocity a that
instant. The density of the fuel is 850 kg/m.
Re
Pr
[Neglecting contraction of the jet, he coefficient of contraction, Cz = 1.0
Coefficient of velocity, C, = coefficient of discharge, Ca
mE
cal
Q=Axe,
Solution: Velocity of Now, ey
Discharge,
Cl Enge: Fuel injection Sytem 335
where A is the area of eross-section of the oi,
wa
= 192) ie loan
Let p be the pressure immediately before the orifice in bar. We now have the following two
equations:
Flow through passage
170 =p = q «850 Oe Dal
OOO
é 170 -p = 2.161 x 10707 [02
Fw rn ite:
se A
ET
:
P25 = 2077 x 10/07 @
aan a and vea
145 = 22.931 x 10/07
a= watt 795 x 10% mis
En
= [55%] Ans.
From Eq. @,
170 -p = 2.161 x 10? x (0.7957 x 10
p= 170 ~ 13.66 = 156.34 bar
‘Velocity of fuel flow through the once,
ES
ae F7
20565-29010
be 350
Ber] Ans.
336_Fundarenals of Inara! Combustion Engines
6) A spay pen of 20cm in 157 msi baie with an jon
[reste of SD har Detrane te tine equi forthe spray o peel ls lt wine
ion rer of 450 bri used, Tye oie an the combustion chamber deni emia
Constant Tee combustion chamber pra 5 ber
(e) The penton for an once of 03 mum diameter is 20 em in 12 m fra een
incio pressure. Detrnie à ir gt fr ae penton core fan ace having
met of 017 rm
Solution: (= Kup) and 2 = fa VB)
“These two results lie on single curve.
se then n VBR, = An
157 0-18 = 4 30-15
10) E
ala) = 2-2)
Fe oe abo on sio Th, tra mar,
Itsy
422 Anh,
ane ae
a). 017x20
n=a(2) = 022 om] Am.
nr (8) 0 „(em
= (4) 2
Ina fuckinjecion pump ofa diesel engine, th volume ofthe fuel in the pump
barrel just before the commencement of he effective stoke is 6.5 cc. The fuel pipe line is 3 mm
in diameter and 650 mm in length. Te fuel in the injection valve is 2.5 ce, Assume the coefficient
of compressibility ofthe ollo be 78,5 x 10” per bar. Take the simospherie pressure as 1 bar
Determine:
(2) The pump displacement necessary to deliver 0.1 ce of fuel at a pressure of 180 bar
(6) The effective stroke ofthe plunger which is 7.5 mm in diameter.
Solution: The coefficient of compressibili,
2 shang in voue peru volume
‘ere pos sing compresion
ate
Ace]
ds
ÿ
= Cl Engines Futfsin Sytem 337
Total initial volume, Y, = Vol of fuel in the barrel + Vol. oFfuel in the pipe ine
+ Vol of fuel in the injection valve
= 65 + OI x65 425 = 13.59 ce
Change in volume due to compression,
vn
vito po)
= 7855 x 10% x 1339(180 — 1)
191 ce
Toral displacement ofthe plunger = (Y, = Vs + 0.8
191 +01
021%] Ans.
Eat =0291
[Effective stroke of the plunger,
xt E
ost x$ xt AS
A four-cylinder four-stroke diese engine running at 2500 mpm, produces
SOKW power The specie fue consuption I 028 fh, ach esla pn es
parte fc pump, pipeline and injectr At he beginning ofthe effective plunger stoke of os
fuel pump, the fut in the bare is 3.5 es the uel nthe pipe in s 25 ce and he fel sine ie
Injector is 2 ce. The average injection pressure is 280 tar and the compression preso of ar
during injection is 30 bar. The density of fuel is 850 kg/m”, the coefficient ‘of compressibility of
fuel is 80 x 10° per bar. Fuel enters the pump barrel at 1 bar. Determine the displacement volume
‘of one plunger pe yee and the power ost in pumping the fel
bite
0.07 cycles per hour
= 02890
Tanx®
Solucion: Bud consumption per ele =
336x108
Fil consumption pe pie er ye = 338710" = 95410 reto
Westin, SIE
= 0.0988 x 104m?
0988 cm?
Coefficient of compressibility,
6) A spay pen of 20cm in 157 msi baie with an jon
[reste of SD har Detrane te tine equi forthe spray o peel ls lt wine
ion rer of 450 bri used, Tye oie an the combustion chamber deni emia
Constant Tee combustion chamber pra 5 ber
(e) The penton for an once of 03 mum diameter is 20 em in 12 m fra een
incio pressure. Detrnie à ir gt fr ae penton core fan ace having
met of 017 rm
Solution: (= Kup) and 2 = fa VB)
“These two results lie on single curve.
se then n VBR, = An
157 0-18 = 4 30-15
10) E
ala) = 2-2)
Fe oe abo on sio Th, tra mar,
Itsy
422 Anh,
ane ae
a). 017x20
n=a(2) = 022 om] Am.
nr (8) 0 „(em
= (4) 2
Ina fuckinjecion pump ofa diesel engine, th volume ofthe fuel in the pump
barrel just before the commencement of he effective stoke is 6.5 cc. The fuel pipe line is 3 mm
in diameter and 650 mm in length. Te fuel in the injection valve is 2.5 ce, Assume the coefficient
of compressibility ofthe ollo be 78,5 x 10” per bar. Take the simospherie pressure as 1 bar
Determine:
(2) The pump displacement necessary to deliver 0.1 ce of fuel at a pressure of 180 bar
(6) The effective stroke ofthe plunger which is 7.5 mm in diameter.
Solution: The coefficient of compressibili,
2 shang in voue peru volume
‘ere pos sing compresion
ate
Ace]
ds
ÿ
= Cl Engines Futfsin Sytem 337
Total initial volume, Y, = Vol of fuel in the barrel + Vol. oFfuel in the pipe ine
+ Vol of fuel in the injection valve
= 65 + OI x65 425 = 13.59 ce
Change in volume due to compression,
vn
vito po)
= 7855 x 10% x 1339(180 — 1)
191 ce
Toral displacement ofthe plunger = (Y, = Vs + 0.8
191 +01
021%] Ans.
Eat =0291
[Effective stroke of the plunger,
xt E
ost x$ xt AS
A four-cylinder four-stroke diese engine running at 2500 mpm, produces
SOKW power The specie fue consuption I 028 fh, ach esla pn es
parte fc pump, pipeline and injectr At he beginning ofthe effective plunger stoke of os
fuel pump, the fut in the bare is 3.5 es the uel nthe pipe in s 25 ce and he fel sine ie
Injector is 2 ce. The average injection pressure is 280 tar and the compression preso of ar
during injection is 30 bar. The density of fuel is 850 kg/m”, the coefficient ‘of compressibility of
fuel is 80 x 10° per bar. Fuel enters the pump barrel at 1 bar. Determine the displacement volume
‘of one plunger pe yee and the power ost in pumping the fel
bite
0.07 cycles per hour
= 02890
Tanx®
Solucion: Bud consumption per ele =
336x108
Fil consumption pe pie er ye = 338710" = 95410 reto
Westin, SIE
= 0.0988 x 104m?
0988 cm?
Coefficient of compressibility,
DI voeu sterner O orne were wie
338 fundamenale of nera! Comburion Enger
_ Cl Engines Fusnfcten Siem 339
étain volume, V = Fuel pump bare + fuel in pipe line + fuel in injector
2354254
Vi Vas kV Ap
BOX 10 8 > (280 - D
Volume displaced by plunger = + (Y — VD
= 0.0988 + 0.1786
DTA ce] Ans.
11786 ee
Pump work per cycle, W = compression work + injection work.
‘The compression of fuel may be assumed to be represented by a straight line on the p-V
iagram, as shown in Figure 10.25(a) The area enclosed represents the compression work,
Injection is a constant-volume flow process. The work during this precess is shown in
Figure 10250).
Pel 3 Pais
Corn sen
== 7 at
» f
nn nt
o o
Pains péage o acorta Peine
Pump work per cycle,
We Gps Pd = VD + (Pay Pad
= 4280- 1x 10° «0.1786 10% + 280 ~ 0) x 10 x 00988 x 10%
E
2249 4247-4961
Wow
Powe fot per elie = LED ew
4496x2500
a © 0103 KW
“Toul power lost for pumping the feel = 0.103 x4= [DATZEW] Ans.
PERA An injection system consists of a pump plunger moving with a velocity of
03 adv ee wc 075m nga ls rein a het
‘hat ofthe plunger elder. The end ofthe pipe s provided with an open nozzle having a hole
hon en ho in of he pipe. Then pres te
827.6 bar, and the compres-
sion pressure the engines 27.6 bar Ifthe ba modus of fel, K, is 17830 10° Nin and the
specif ravi of theo 30.6, determine te follow
(9) The velocity of pressure disutarcs.
(0) The time taken byte dance to vel through he pipe ine.
(©) The pesar and the velocity athe pomp end ofthe pipe In asthe plunger moves
(6) The magnitude ofthe fit relie pressure and veloc) wave
(e) The pressure ard the velocity at the ice end of te pipe lin fr the fs rein.
Solution: Refer 10 Figure 1026.
me À
a TL A
| u a
>
Fier 026. Sempdiconspaen.
(0) The velocity of pressure disturbances in ol of specific gravity 0.86 is
© _ [meo
JE PU [ros] Ans.
la 560 a
D) The ime taken by the disturbance to travel through the pipeline,
‘A = length of the pipe ine _ 0.575
5 140
(©) Let the velocity ofthe fuel athe net ofthe pipe line bey,
A= Ay
®
asısm E
3
000015] Ans.
A
1 = 20x03
%
nthe velocity ofthe fuel a he pump end ofthe pipe line
338 fundamenale of nera! Comburion Enger
_ Cl Engines Fusnfcten Siem 339
étain volume, V = Fuel pump bare + fuel in pipe line + fuel in injector
2354254
Vi Vas kV Ap
BOX 10 8 > (280 - D
Volume displaced by plunger = + (Y — VD
= 0.0988 + 0.1786
DTA ce] Ans.
11786 ee
Pump work per cycle, W = compression work + injection work.
‘The compression of fuel may be assumed to be represented by a straight line on the p-V
iagram, as shown in Figure 10.25(a) The area enclosed represents the compression work,
Injection is a constant-volume flow process. The work during this precess is shown in
Figure 10250).
Pel 3 Pais
Corn sen
== 7 at
» f
nn nt
o o
Pains péage o acorta Peine
Pump work per cycle,
We Gps Pd = VD + (Pay Pad
= 4280- 1x 10° «0.1786 10% + 280 ~ 0) x 10 x 00988 x 10%
E
2249 4247-4961
Wow
Powe fot per elie = LED ew
4496x2500
a © 0103 KW
“Toul power lost for pumping the feel = 0.103 x4= [DATZEW] Ans.
PERA An injection system consists of a pump plunger moving with a velocity of
03 adv ee wc 075m nga ls rein a het
‘hat ofthe plunger elder. The end ofthe pipe s provided with an open nozzle having a hole
hon en ho in of he pipe. Then pres te
827.6 bar, and the compres-
sion pressure the engines 27.6 bar Ifthe ba modus of fel, K, is 17830 10° Nin and the
specif ravi of theo 30.6, determine te follow
(9) The velocity of pressure disutarcs.
(0) The time taken byte dance to vel through he pipe ine.
(©) The pesar and the velocity athe pomp end ofthe pipe In asthe plunger moves
(6) The magnitude ofthe fit relie pressure and veloc) wave
(e) The pressure ard the velocity at the ice end of te pipe lin fr the fs rein.
Solution: Refer 10 Figure 1026.
me À
a TL A
| u a
>
Fier 026. Sempdiconspaen.
(0) The velocity of pressure disturbances in ol of specific gravity 0.86 is
© _ [meo
JE PU [ros] Ans.
la 560 a
D) The ime taken by the disturbance to travel through the pipeline,
‘A = length of the pipe ine _ 0.575
5 140
(©) Let the velocity ofthe fuel athe net ofthe pipe line bey,
A= Ay
®
asısm E
3
000015] Ans.
A
1 = 20x03
%
nthe velocity ofthe fuel a he pump end ofthe pipe line
340, Findimenai ol Inem Combustion Engines
Assume te initial velocity ofthe fuel at his location to be zero.
Change in velocity atte nle tothe pipe line, Av = 6 m/s
„17890 x10°x6
Te
Initial pressure in the pipe line is 27.6 bar
‘The foe is assumed to increase in velocity from zero 106 ms instantaneously;
Pressure at this instant = 743 + 27.6= [1019er] Ans.
Now, = 143 x 10° Nin? = 743 bar
(2) A pressure disturbance of 743 bar and a velocity disturbance of 6 m/s now move down
(he pipe at a speed of 1440 mis.
“The velocity y of the fluid after passing the orice willbe
ne 3
Nr
‘Velocity in he pipe jus before de oe, ,, can be obtained rom ad, = Av
lay, [Pde „1 mom)
APP BY py “WY oy
where 2 27.6 bar intial) + 74.3 bar (ring pressure istrbance) +p, (elected pressure
disturbance.
and p= compression pressure of engine = 27.6 bar.
‘The velocity of 6 m/s is propagated through the pipe from pump end ofthe line. When this
velocity reaches the orifice end ofthe line, a reduction of velocity will ake place.
‘Change in this velocity,
Av <6.
Ay =6
6-0380H3=p,
"The fist reflected pressure wave resulting fiom Av will be
papes Kos EG aan ITH)
N
yt, = SRE] Ane
Gt Engine: Funden Sytem 34
apex BS BE | -
Ara GE ETT
216474342682 [12870] Ans.
ee
El
Ans.
© Pe
REVIEW QUESTIONS
1. What ae the requirements ofa fuel-injction system of Cl engine?
2. What are the main components reguied in fuluinjetion system?
3. Describe an air.injection system with the help of a diagram. What ar the advantages and
isadvanlages of an arinjection system?
4. What do you mean by a solid injection system? Name the different types of slidiajection
systems, What are the main components of this system?
5. Describe the construction and working of an individual pump fuel-injection system with
the help ofa diagram. Draw che schematic diagrams of two arrangements of te pump in
this system,
6. Describe the construction and working of a unit injector system withthe help ofa diagram,
7. Deseribe the construction and working of a distritos foe injection system withthe help
of a diagram.
8 Describe the common-ril uel-injecion system with the help of a diagram. Why is this
system not so popular now?
9. Describe the construction ofa Jesk type fue-njetion pump.
10. Describe the working principle ofa Jerk typeof injection pump. Show the position ofthe
helix for various loed conditions.
11, Show the variation of plunger helix indicating the beginning and ending o injection
12. Draw and describe the actual and theoretical delivery characteristics of a port controlled
displacement pomp.
19. Describe and draw the injection pump delivery characteristics corresponding to full and
part delivery with respect to pump speed, Also draw the fuel pump delivery characteristics
A At constant speed versus the rack stroke.
| 14, Describe the construction of a unit injector with the help of a diagram. Show and explain
‘the unit injector fuel delivery characteristics versus the pump speed.
15. Describe the construction and working of a distributor typeof fuel-injecton pump with the
help of suitable diagrams.
4 16. Whats he function of à leak-of fuel in the fueinjection holder?
17. Describe tbe construction and working of a fuel injector nozzle with the help of a digram.
18, What are the different types of nozzles? What isthe difference between the pinl type and
the pintaux type nozzles?
|
Assume te initial velocity ofthe fuel at his location to be zero.
Change in velocity atte nle tothe pipe line, Av = 6 m/s
„17890 x10°x6
Te
Initial pressure in the pipe line is 27.6 bar
‘The foe is assumed to increase in velocity from zero 106 ms instantaneously;
Pressure at this instant = 743 + 27.6= [1019er] Ans.
Now, = 143 x 10° Nin? = 743 bar
(2) A pressure disturbance of 743 bar and a velocity disturbance of 6 m/s now move down
(he pipe at a speed of 1440 mis.
“The velocity y of the fluid after passing the orice willbe
ne 3
Nr
‘Velocity in he pipe jus before de oe, ,, can be obtained rom ad, = Av
lay, [Pde „1 mom)
APP BY py “WY oy
where 2 27.6 bar intial) + 74.3 bar (ring pressure istrbance) +p, (elected pressure
disturbance.
and p= compression pressure of engine = 27.6 bar.
‘The velocity of 6 m/s is propagated through the pipe from pump end ofthe line. When this
velocity reaches the orifice end ofthe line, a reduction of velocity will ake place.
‘Change in this velocity,
Av <6.
Ay =6
6-0380H3=p,
"The fist reflected pressure wave resulting fiom Av will be
papes Kos EG aan ITH)
N
yt, = SRE] Ane
Gt Engine: Funden Sytem 34
apex BS BE | -
Ara GE ETT
216474342682 [12870] Ans.
ee
El
Ans.
© Pe
REVIEW QUESTIONS
1. What ae the requirements ofa fuel-injction system of Cl engine?
2. What are the main components reguied in fuluinjetion system?
3. Describe an air.injection system with the help of a diagram. What ar the advantages and
isadvanlages of an arinjection system?
4. What do you mean by a solid injection system? Name the different types of slidiajection
systems, What are the main components of this system?
5. Describe the construction and working of an individual pump fuel-injection system with
the help ofa diagram. Draw che schematic diagrams of two arrangements of te pump in
this system,
6. Describe the construction and working of a unit injector system withthe help ofa diagram,
7. Deseribe the construction and working of a distritos foe injection system withthe help
of a diagram.
8 Describe the common-ril uel-injecion system with the help of a diagram. Why is this
system not so popular now?
9. Describe the construction ofa Jesk type fue-njetion pump.
10. Describe the working principle ofa Jerk typeof injection pump. Show the position ofthe
helix for various loed conditions.
11, Show the variation of plunger helix indicating the beginning and ending o injection
12. Draw and describe the actual and theoretical delivery characteristics of a port controlled
displacement pomp.
19. Describe and draw the injection pump delivery characteristics corresponding to full and
part delivery with respect to pump speed, Also draw the fuel pump delivery characteristics
A At constant speed versus the rack stroke.
| 14, Describe the construction of a unit injector with the help of a diagram. Show and explain
‘the unit injector fuel delivery characteristics versus the pump speed.
15. Describe the construction and working of a distributor typeof fuel-injecton pump with the
help of suitable diagrams.
4 16. Whats he function of à leak-of fuel in the fueinjection holder?
17. Describe tbe construction and working of a fuel injector nozzle with the help of a digram.
18, What are the different types of nozzles? What isthe difference between the pinl type and
the pintaux type nozzles?
|
342 fundamen of ural Combustion Engines
19. Describe the pi celo wth the hep ofa diagram. What she mai ference between
the sanded pn oz andthe toting pide nrae?
20. Compare Be var of ate of discharge with respect o cam dees and orice areas
Si reses valve ol silo pi ozale ana rung pe noel.
21. Deserve single hole oz wi bl of gr.
22. Decre aml hole oz wi the help of diga
23. Describe he pinta sozae with he eof alt. Show he fuel delivery charco
feof a pin orl.
24. Deere be wekngpicpl ofan ectonicalycontlldfel-jeton system
25. Desens the Simple echaeal governor wed for Cl engines
26. Dede dete lomos. Wha the Imporan factors that affect the depres of
sum?
27, Mat faces alle the peto of fein the combustion canbe ofa CL engine?
28. Define yey dispersion What are the import factors hat fest the dispersion lin
the combustion number ol Clengine?
28, Deve an expression to evaluate te of mas low of fe for the injector of a CI
40, Dan te offen o compressibility ofa quid ful Derive an expression oeraluie
the velo propagó of pressure bare inthe pipe ine, Prove th
BE
By vs
where
increase in pressure
change in velocity ofthe pump plunger
K = module of igidty
vs = velocity of propagation of pressure disturbance in Maid.
PROBLEMS
10.3 A fourauoke for cylinder Cl engine develops 100 KW at 3000 pm. Te specific fel
anse i 0223 fk Wh, Determine the mas of th fc injected by te nozzle per
Se per Her i de combustion chambet
102 X tours sbeylindee CT engine develops 240 KW when running at 1000 rpm. The
cc fc consumption i 024 Ti values of pressure of ain the ylindr at
the beginning o injection and the end of injection are a0 bar and 6O ba respectively. The
foe injection pressure tthe beginning and end of injection are 200 and 60 bar resp
tively Amume Ue effective presence tobe the average pressure difference
during he injection period, Take the coefficient of ischrge forthe injector to be 0 and
{he density of te fue to be 850 kg/m). Determine the nozzle ara required per injection if
the injection is eared ou during the 12° ration ofthe ran, Ihe number of res
‘sed in anole are two, nd the diameter of an oie.
103 Bal he diameter of he fus nie a fourstoke single-cylinder Cl engine which
dovelas «power of 20 KW at 2000 pm, The specie fel consumption i 0.25 kWh
T
|
|
ene
jection Sptom_ 343
fuel of 32° APL. The fuel is injected at an average pressure of 180 bar over a crank travel
‘of 20°. The pressure in the combustion chamber is 30 bar. The coefficient of discharge
is 088,
104 A fou-sroke four-cylinder CI engine operates on airfue ratio of 20, The bore and stoke
of the cylinder are 12 cm and 16 cm respectively The volumeti efficiency is 086. The
condition of ic atthe beginning of compresion is 1 bar and 300 K. Determine the mass of
the fuel injected in each cylinder per second. If the speed of tke engine is 1500 mm, the
injection pressure is 180 bar, the compression pressure of ai is 35 bar and the fuel injection
is cared out during the 20° of rank rotation, determine the diameter of the fuel orifice
having single-hole nozzle. Take the density of the fuel to be 850 kg/m and the coefficient
of discharge for fuel nozzle 10 be 0.5.
10.5 A close injection nozzle ofa C engine with single hole injector, has an orifice diameter
of 0.75 mm. and the maximum cross-sectional area of the passage between the needle
‘cone and the seats 1.6mun”. The felis injected at an average pressure of 180 bar andthe
average compression pressure of air during injection is 30 bar The discharge coefficient
forthe orifice i 0.85 and that forthe passage is 0.80. The density of the fuel is 850 ke/m?.
Determine the volume rate of flow per second of ful through the injector and the velocity
‘ofthe je at that instant,
10.6 From the injecior nozzl ofa Cl engine, a spray penetration of 25 cm is obtained in 18 ms
from an orfice of 0.6 mm diameter with an injection pressure of 170 bar. The combustion
chamber pressure is 20 bar, Determine:
(4) The time required forthe spray to penetrate the same distance when an injection
pressure of 250 bar is used,
CH) The penetration and time fora similar point on the penetration curve of an orifice
having a diameter of 0.4 mm.
10.7 A four cylinder four-stzoke Cl engine running at 2200 rpm, produces 85 KW power. The
specifi Fuel consumption is 0.26 kg/kWh. The volume ofthe fuel in the pump barrel just
before the commencement of the effective stoke is See, The fuel pipe line is 3.2 mm in
diameter and 700 mm in length. The fuel inside the injector is 2.5 ce. The average injection
pressuce is 200 bar and the compression pressure of aie during injection is 35 bar, The
density of fuel is 860 kg/m, andthe coefficient of compressibility of fuel is 75 x 104 per
bar Pet enters the pump barrel at 1 bar. Determine the plunger displacement pe cycle per
cylinder and the effective stroke of the plunger which is 8 mun in diameter Alo calculato
the power lost in pumping the fuel.
108 In an injection system of a CI engine, the pump plunger moves with a velocity of 025
he he eg fe pi 06. The on ae fie Loft
of plang: bare Te ed fe pipes nope cee having ole ara ich 5
i
na ofp. The ilps ane 29 brand de ompesin
pressure ofthe engine is 30 bar. Ifthe bulk modulus of the fuel is 18 x 10° Nim? and the
specific gravity of theo is 0.85, determine the following:
_ A
19. Describe the pi celo wth the hep ofa diagram. What she mai ference between
the sanded pn oz andthe toting pide nrae?
20. Compare Be var of ate of discharge with respect o cam dees and orice areas
Si reses valve ol silo pi ozale ana rung pe noel.
21. Deserve single hole oz wi bl of gr.
22. Decre aml hole oz wi the help of diga
23. Describe he pinta sozae with he eof alt. Show he fuel delivery charco
feof a pin orl.
24. Deere be wekngpicpl ofan ectonicalycontlldfel-jeton system
25. Desens the Simple echaeal governor wed for Cl engines
26. Dede dete lomos. Wha the Imporan factors that affect the depres of
sum?
27, Mat faces alle the peto of fein the combustion canbe ofa CL engine?
28. Define yey dispersion What are the import factors hat fest the dispersion lin
the combustion number ol Clengine?
28, Deve an expression to evaluate te of mas low of fe for the injector of a CI
40, Dan te offen o compressibility ofa quid ful Derive an expression oeraluie
the velo propagó of pressure bare inthe pipe ine, Prove th
BE
By vs
where
increase in pressure
change in velocity ofthe pump plunger
K = module of igidty
vs = velocity of propagation of pressure disturbance in Maid.
PROBLEMS
10.3 A fourauoke for cylinder Cl engine develops 100 KW at 3000 pm. Te specific fel
anse i 0223 fk Wh, Determine the mas of th fc injected by te nozzle per
Se per Her i de combustion chambet
102 X tours sbeylindee CT engine develops 240 KW when running at 1000 rpm. The
cc fc consumption i 024 Ti values of pressure of ain the ylindr at
the beginning o injection and the end of injection are a0 bar and 6O ba respectively. The
foe injection pressure tthe beginning and end of injection are 200 and 60 bar resp
tively Amume Ue effective presence tobe the average pressure difference
during he injection period, Take the coefficient of ischrge forthe injector to be 0 and
{he density of te fue to be 850 kg/m). Determine the nozzle ara required per injection if
the injection is eared ou during the 12° ration ofthe ran, Ihe number of res
‘sed in anole are two, nd the diameter of an oie.
103 Bal he diameter of he fus nie a fourstoke single-cylinder Cl engine which
dovelas «power of 20 KW at 2000 pm, The specie fel consumption i 0.25 kWh
T
|
|
ene
jection Sptom_ 343
fuel of 32° APL. The fuel is injected at an average pressure of 180 bar over a crank travel
‘of 20°. The pressure in the combustion chamber is 30 bar. The coefficient of discharge
is 088,
104 A fou-sroke four-cylinder CI engine operates on airfue ratio of 20, The bore and stoke
of the cylinder are 12 cm and 16 cm respectively The volumeti efficiency is 086. The
condition of ic atthe beginning of compresion is 1 bar and 300 K. Determine the mass of
the fuel injected in each cylinder per second. If the speed of tke engine is 1500 mm, the
injection pressure is 180 bar, the compression pressure of ai is 35 bar and the fuel injection
is cared out during the 20° of rank rotation, determine the diameter of the fuel orifice
having single-hole nozzle. Take the density of the fuel to be 850 kg/m and the coefficient
of discharge for fuel nozzle 10 be 0.5.
10.5 A close injection nozzle ofa C engine with single hole injector, has an orifice diameter
of 0.75 mm. and the maximum cross-sectional area of the passage between the needle
‘cone and the seats 1.6mun”. The felis injected at an average pressure of 180 bar andthe
average compression pressure of air during injection is 30 bar The discharge coefficient
forthe orifice i 0.85 and that forthe passage is 0.80. The density of the fuel is 850 ke/m?.
Determine the volume rate of flow per second of ful through the injector and the velocity
‘ofthe je at that instant,
10.6 From the injecior nozzl ofa Cl engine, a spray penetration of 25 cm is obtained in 18 ms
from an orfice of 0.6 mm diameter with an injection pressure of 170 bar. The combustion
chamber pressure is 20 bar, Determine:
(4) The time required forthe spray to penetrate the same distance when an injection
pressure of 250 bar is used,
CH) The penetration and time fora similar point on the penetration curve of an orifice
having a diameter of 0.4 mm.
10.7 A four cylinder four-stzoke Cl engine running at 2200 rpm, produces 85 KW power. The
specifi Fuel consumption is 0.26 kg/kWh. The volume ofthe fuel in the pump barrel just
before the commencement of the effective stoke is See, The fuel pipe line is 3.2 mm in
diameter and 700 mm in length. The fuel inside the injector is 2.5 ce. The average injection
pressuce is 200 bar and the compression pressure of aie during injection is 35 bar, The
density of fuel is 860 kg/m, andthe coefficient of compressibility of fuel is 75 x 104 per
bar Pet enters the pump barrel at 1 bar. Determine the plunger displacement pe cycle per
cylinder and the effective stroke of the plunger which is 8 mun in diameter Alo calculato
the power lost in pumping the fuel.
108 In an injection system of a CI engine, the pump plunger moves with a velocity of 025
he he eg fe pi 06. The on ae fie Loft
of plang: bare Te ed fe pipes nope cee having ole ara ich 5
i
na ofp. The ilps ane 29 brand de ompesin
pressure ofthe engine is 30 bar. Ifthe bulk modulus of the fuel is 18 x 10° Nim? and the
specific gravity of theo is 0.85, determine the following:
_ A
344 Fundamentals of nara Combustion Engines
(2) The velocity of pressure disturbance
(6) The time taken by the disturbance to travel through the pipe ine
(©) The pressure and velocity at the pump end ofthe pipeline as the plunger moves
(&) The magnitude o the firs reflected pressure and velocity wave
(©) The pressure and velocity a the ofice end of the pipeline after reflection.
1 Two-Stroke Engines
11.1 INTRODUCTION
In twosstsoke cycle engines the cycle of operation is completed in two stokes only and each
ouswasd stroke of the piston is a power or expansion stroke. The engine piston needs only 10
‘omnpress the fresh charge and to expand the products of combustion. Such operation is made
possible by the fact hat the pumping function isnot carried out in the working eylinders but is
accomplished either in a separate mechanism called the scavenging pump or in an enclosed
erankease withthe back of the engine piston being used as a scavenging pump. The fresh charge
is supplied to the engine cylinder at high enough pressure o displace the burned gases from the
‘previous cycle. The operation of clearing the exhaust gases from the cylinder and filing it more or
less completely with fresh charge is called scavenging. The process of scavenging includes both
the intake and the exhaust processes
Many two-stoke engines use the piston as a side valve in conjonction withthe inet and
exhaust ports on the side of the cylinder, This arrangement greatly simplifies the mechanical
construction of the engine. Very large marine engines and vey small reciprocating piston engines
ae two-stroke engines.
112 CLASSIFICATION OF TWO-STROKE ENGINES
Depending upon the methods of producing the scavenge charge for the scavenging proces, the
‘worstoke engines are classified as follows:
1. Crankcase scavenged engines
2. Separately scavenged engines
The crankcase scavenged engine isthe simplest type and has already been discussed in
Section 1.13. The engines ofthis type seldom have mean effective pressure of over 4 ar. This
‘ype of engine is not satisfactory asthe crankcase punping has avery low volumetric efficiency
and, instead of an exces ait, the engine receives les ale than ls theoretically necessary
‘The separately scavenged engines are widely used in al larger and some small engines. In his
‘ype, a separate scavenging pump such as roots blower, as shown in Figure 111, is used, whieh
is either driven from the engine crankshaft or driven using outside power. An external blower is
used for charge to enter into he cylinder through an intake port. As the piston moves down on the
(2) The velocity of pressure disturbance
(6) The time taken by the disturbance to travel through the pipe ine
(©) The pressure and velocity at the pump end ofthe pipeline as the plunger moves
(&) The magnitude o the firs reflected pressure and velocity wave
(©) The pressure and velocity a the ofice end of the pipeline after reflection.
1 Two-Stroke Engines
11.1 INTRODUCTION
In twosstsoke cycle engines the cycle of operation is completed in two stokes only and each
ouswasd stroke of the piston is a power or expansion stroke. The engine piston needs only 10
‘omnpress the fresh charge and to expand the products of combustion. Such operation is made
possible by the fact hat the pumping function isnot carried out in the working eylinders but is
accomplished either in a separate mechanism called the scavenging pump or in an enclosed
erankease withthe back of the engine piston being used as a scavenging pump. The fresh charge
is supplied to the engine cylinder at high enough pressure o displace the burned gases from the
‘previous cycle. The operation of clearing the exhaust gases from the cylinder and filing it more or
less completely with fresh charge is called scavenging. The process of scavenging includes both
the intake and the exhaust processes
Many two-stoke engines use the piston as a side valve in conjonction withthe inet and
exhaust ports on the side of the cylinder, This arrangement greatly simplifies the mechanical
construction of the engine. Very large marine engines and vey small reciprocating piston engines
ae two-stroke engines.
112 CLASSIFICATION OF TWO-STROKE ENGINES
Depending upon the methods of producing the scavenge charge for the scavenging proces, the
‘worstoke engines are classified as follows:
1. Crankcase scavenged engines
2. Separately scavenged engines
The crankcase scavenged engine isthe simplest type and has already been discussed in
Section 1.13. The engines ofthis type seldom have mean effective pressure of over 4 ar. This
‘ype of engine is not satisfactory asthe crankcase punping has avery low volumetric efficiency
and, instead of an exces ait, the engine receives les ale than ls theoretically necessary
‘The separately scavenged engines are widely used in al larger and some small engines. In his
‘ype, a separate scavenging pump such as roots blower, as shown in Figure 111, is used, whieh
is either driven from the engine crankshaft or driven using outside power. An external blower is
used for charge to enter into he cylinder through an intake port. As the piston moves down on the
346_ Fundamentals of Internal Combustion Engines
TwoSeake Einer 347
Fire 114. Sopa ucaırgodtstek enge,
‘expansion stroke, it uncovers the exhaust ports at approximately 65° crank angle before the
bottom dead centre. About 10° ltr, when the cylinder pressure is considerably lowered, the inlet
ports open andthe scavenging proces takes place, The inlet ports are shaped in such a way that
most of he charge flows tote top ofthe cylinder on the ile side and back down onthe exhaust
sie, thus expelling the bumed gases ou through the exhaust por. Tis ensures scavenging ofthe
"per par of the cylinder as wel. Piston deflectors ae not suitable as they are heavy and tend to
become overheated at high output. The scavenging process is more efficient in propery designed
separately scavenged engines than in te usual cranketse compression engines
11,3. SCAVENGING ARRANGEMENTS
Based on te scavenging arrangements te scavenging process can be classified as follows
1. Retum-flow scavenging
2. Uniflow seavenging
‘The retun-flow scavenging is applicable to single-piston engines, while uniflow engines are
of side-by-side cylinder, rin piston type. No uniflow petrl engine with valve gear or opposed
piston has achieved success.
11.3.1. Return-flow Scavenging
In eturnflow scavenging the scavenge ai is direct towards the other end of he cylinder by a
sant of the inet ports or by te shape ofthe piston head or by both and then the ai is retumed to
(be piston head pushing the burned gas out through the exhaust por. In doing so, some of the air
sixes with the bumed gases and escapes with them through the exhaust ports. The scavenging
efficiency is thus lowered, The exhaust and int port are opened and closed by the siding motion
ofthe piston,
A we ee ew
Depending on the shape and relative postion ofthe exhaust and scavenge ports the retum
flow scavengings are divided int:
(a) Cross-fow scavenging, Figure 11.2)
€) Ful-Ioop seavenging (MAN type), Figure 11.209)
(€) Tangential cop scavenging (Schnuerle type), Figure 11.2)
(8) Combination of toop- and cross-scavenging (Curiss type), Figure 1.244)
Most small engines ae cross-scavenged. This ype of engine is the simplest bu it is the least
<lfcient. The cross-flow system requires a piston with shaped crown, and it is necessary forthe
sans and exhaust posto be situated on a diametical line across the cylinder bore, Thus there
is restricted scope for por. positioning as a whole, though the shape, the number and the dimen-
sions of the ports can be varied to quite a large extent, The odd-shaped deflector piston has the
disadvantage of uneven heat stressing, which makes it able o distortion, The success of tis type
largel depends on the design ofthe defector, not oly in ite Function with respect to gas flow, but
also in its mechanical strength and ability to transfer heat
For small engines the ports ae drilled racially to reduce the cos; in large engines the ports
ae made rectangular for beter breathing, The Incoming low charge is directed upwards by the
deflector on the pistons, and then ho cylinder walls and head reverse the direction of flow and
‘push the exhaust gases out through the exhaust port.
‘The cros-flow scavenge engine is the worst ype, in that it is susceptible to shor-circuitng
the charge and is unable to displace the exhaust gases adequately. The altemativeloop-scavenged
system in is various forms is designed to direct the incoming charge by means of inclined and
med ports in such 2 way that both charge loss and mixing are minimized, Three representative
rangements, as shown in Figures 11.20), (c) and (9) will serve as examples, these aro MAN
loop scavenging (Maschinenfabrik Augsburg Nuemberg, a German firm), Sehnvetie-loop seav-
and Curtss-loop scavenging arrangements respectively
5
o > o
Figure 12, tum om tensa) Creo, 2) MAN cop emerging} Schnand-op vom an) Os:
opening,
TwoSeake Einer 347
Fire 114. Sopa ucaırgodtstek enge,
‘expansion stroke, it uncovers the exhaust ports at approximately 65° crank angle before the
bottom dead centre. About 10° ltr, when the cylinder pressure is considerably lowered, the inlet
ports open andthe scavenging proces takes place, The inlet ports are shaped in such a way that
most of he charge flows tote top ofthe cylinder on the ile side and back down onthe exhaust
sie, thus expelling the bumed gases ou through the exhaust por. Tis ensures scavenging ofthe
"per par of the cylinder as wel. Piston deflectors ae not suitable as they are heavy and tend to
become overheated at high output. The scavenging process is more efficient in propery designed
separately scavenged engines than in te usual cranketse compression engines
11,3. SCAVENGING ARRANGEMENTS
Based on te scavenging arrangements te scavenging process can be classified as follows
1. Retum-flow scavenging
2. Uniflow seavenging
‘The retun-flow scavenging is applicable to single-piston engines, while uniflow engines are
of side-by-side cylinder, rin piston type. No uniflow petrl engine with valve gear or opposed
piston has achieved success.
11.3.1. Return-flow Scavenging
In eturnflow scavenging the scavenge ai is direct towards the other end of he cylinder by a
sant of the inet ports or by te shape ofthe piston head or by both and then the ai is retumed to
(be piston head pushing the burned gas out through the exhaust por. In doing so, some of the air
sixes with the bumed gases and escapes with them through the exhaust ports. The scavenging
efficiency is thus lowered, The exhaust and int port are opened and closed by the siding motion
ofthe piston,
A we ee ew
Depending on the shape and relative postion ofthe exhaust and scavenge ports the retum
flow scavengings are divided int:
(a) Cross-fow scavenging, Figure 11.2)
€) Ful-Ioop seavenging (MAN type), Figure 11.209)
(€) Tangential cop scavenging (Schnuerle type), Figure 11.2)
(8) Combination of toop- and cross-scavenging (Curiss type), Figure 1.244)
Most small engines ae cross-scavenged. This ype of engine is the simplest bu it is the least
<lfcient. The cross-flow system requires a piston with shaped crown, and it is necessary forthe
sans and exhaust posto be situated on a diametical line across the cylinder bore, Thus there
is restricted scope for por. positioning as a whole, though the shape, the number and the dimen-
sions of the ports can be varied to quite a large extent, The odd-shaped deflector piston has the
disadvantage of uneven heat stressing, which makes it able o distortion, The success of tis type
largel depends on the design ofthe defector, not oly in ite Function with respect to gas flow, but
also in its mechanical strength and ability to transfer heat
For small engines the ports ae drilled racially to reduce the cos; in large engines the ports
ae made rectangular for beter breathing, The Incoming low charge is directed upwards by the
deflector on the pistons, and then ho cylinder walls and head reverse the direction of flow and
‘push the exhaust gases out through the exhaust port.
‘The cros-flow scavenge engine is the worst ype, in that it is susceptible to shor-circuitng
the charge and is unable to displace the exhaust gases adequately. The altemativeloop-scavenged
system in is various forms is designed to direct the incoming charge by means of inclined and
med ports in such 2 way that both charge loss and mixing are minimized, Three representative
rangements, as shown in Figures 11.20), (c) and (9) will serve as examples, these aro MAN
loop scavenging (Maschinenfabrik Augsburg Nuemberg, a German firm), Sehnvetie-loop seav-
and Curtss-loop scavenging arrangements respectively
5
o > o
Figure 12, tum om tensa) Creo, 2) MAN cop emerging} Schnand-op vom an) Os:
opening,
348 Fandamans of nara Combuton Engines
Tuo-troke Engines 349
No piston deflector is required with loop-scavenging, the piston being of norma! shape, fas,
slightly domed, or a combination ofboth. This is o great benefit, as the troubles associated with
an assymimetical shape are eliminated
In the MAN-Ioop scavenge system the entry por ae located immediately above the exhaust
ports onthe same side ofthe cylinder (Figure 11.2). In some designs the exhaust ports placed
above the inlet por on the same side. The incoming flow ofthe charge is directed across the
chamber. Even when using ports of maximum width and minimum height, however ifthe ports
are of adequate cross-sectional arca, a large proportion ofthe sroke length is taken up bythe port
operation. Thus, while acceptable on medium-speed dieses, this arrangement is obviously not
suitable for smaller high-speed peto! engines.
In the Schauere-loop scavenging system (Figure 11.266) two or more transfer ports are
‘often employed, though a similar system can be worked with only one transfer port. The flow is
directed angel and upwards. The location ofthe transfer ports atthe sides instead of diretly
‘opposite the exhaust por, facilitates the use of very short passages having entry from the erankease
Via slots or port in te piston skin, which of course does aot cary much thrust load at these areas,
‘The Curis design (Figure 11.2(6)) makes use of a considerable number of entry port to
make up a large total area The ports are also individually angled in such a manner thatthe con-
verging streams meet some way off the central axis of the cylinder and rise up to the head after
merging. This promotes a displacement of the exhaust gases from the top and their expulsion fom
the exhaust por, Here again, though successful on diesel having sufficient excess ar, multiple
transfer ports have not shown the same advantage on Ih high-speed petrol engines. Apart from
the extra charge volume contained in the multiple transfer passages, which increases the free
space inthe crankcase and lowers the pumping volumetric efficiency, itis found tht the many
transfer streams tend 10 mix excessively withthe exhaust instead of displacing it
11.32. Uniflow Scavenging
Adiiting the fresh charge from one end ofthe eyinder and exhanstng th burned gases fom the
‘ther end gives a aight ow, called wallow scavenging. Tis isthe best rom the viewpoint of
thoroughly purging he cylinder oft exhaust content. The straight low reduces the ubulenee
and hence the mixing of the fresh charge with he bumed gases. Thus the scavenging efficiency
¿s increased, The required degree of turbulence is invariably required, it may have 10 be promoted
‘on the unilow pe by paru attention tothe tangential amangemen ofthe transfer pos.
otherwise the fresh charge inthe intake side cylinder bel may nt get suficiendy agitated. The
passage aerosstheeyinder head assists in promoting wir at this pin, whichis a god condon
5 the spark plug can be placed without esto in the best psion in order to take advantage
ofthis phenomena
Many systems have uniflow scavenging, ot ofthese the two main systems are
1. Port and poppet valve scavenging with one piston, Figure 11 3
2. Port scavenging with opposed piston, Figure 11.4,
Inport and poppet valve scavenging, the exhaust valves are located in the head, I is shown in
Figure 11.3, The admission of fresh charge through the inet pons is contolled by the piston,
while the products of combustion are removed rough the poppet valves provided in the cyliader
head. Provision for adjusting the timing ofthe opening and closing ofthe exhaust valves o suit
gu 1.3 Par ostra
engine speed and scavenge charge pressure are the
rain asset ofthis type of engine.
Port scavenging with opposed pistons (Junker's
design) has a very effective scavenging process. This
‘ype is also called the end-10 end scavenged engine. is
shown in Figure 11.4. The intake pons are covered by
the lower piston and the exhaust ports are covered by Fut. Potscrorging reposado.
the upper piston. All ports are distributed uniformly
‘over the whole circumference. The piston moves inthe opposite direction and a spiral motion of
‘the charge perpendicular tothe cylinder axis is created by the tangential arrangement ofthe inet:
ports. Thus his system produces very good scavenging and charging conditions, The swid helps
10 prevent mixing of fresh charge and combustion products during the scavenging process. In this
{ype the exhaust pons are opened before the inlet ports open and also the exhaust ports are closed
before the inlet pons close. This timing helps this ype of engine in filling its cylinder at fll inet
pressure In this type of engine, the counter-flow within the cylinder is eliminated and there is les
‘opportunity for mixing of fresh charge with the burned gases. I develope high mean effective
pressure. The combustion chamber
disadvantages. I requires a complicated running gear mechanism; there ae difficult in cooling
the pistons; and there are higher costs of manufacture and maintenance.
11.4 SCAVENGING PROCESS
Figure 11,5 shows a 'ighrespring pressure vs crank angle diagram taken of a conventional-loop
scavenged cross-flow type two-stroke engine. After the exhaust ports open (EO), the eylinder
Tuo-troke Engines 349
No piston deflector is required with loop-scavenging, the piston being of norma! shape, fas,
slightly domed, or a combination ofboth. This is o great benefit, as the troubles associated with
an assymimetical shape are eliminated
In the MAN-Ioop scavenge system the entry por ae located immediately above the exhaust
ports onthe same side ofthe cylinder (Figure 11.2). In some designs the exhaust ports placed
above the inlet por on the same side. The incoming flow ofthe charge is directed across the
chamber. Even when using ports of maximum width and minimum height, however ifthe ports
are of adequate cross-sectional arca, a large proportion ofthe sroke length is taken up bythe port
operation. Thus, while acceptable on medium-speed dieses, this arrangement is obviously not
suitable for smaller high-speed peto! engines.
In the Schauere-loop scavenging system (Figure 11.266) two or more transfer ports are
‘often employed, though a similar system can be worked with only one transfer port. The flow is
directed angel and upwards. The location ofthe transfer ports atthe sides instead of diretly
‘opposite the exhaust por, facilitates the use of very short passages having entry from the erankease
Via slots or port in te piston skin, which of course does aot cary much thrust load at these areas,
‘The Curis design (Figure 11.2(6)) makes use of a considerable number of entry port to
make up a large total area The ports are also individually angled in such a manner thatthe con-
verging streams meet some way off the central axis of the cylinder and rise up to the head after
merging. This promotes a displacement of the exhaust gases from the top and their expulsion fom
the exhaust por, Here again, though successful on diesel having sufficient excess ar, multiple
transfer ports have not shown the same advantage on Ih high-speed petrol engines. Apart from
the extra charge volume contained in the multiple transfer passages, which increases the free
space inthe crankcase and lowers the pumping volumetric efficiency, itis found tht the many
transfer streams tend 10 mix excessively withthe exhaust instead of displacing it
11.32. Uniflow Scavenging
Adiiting the fresh charge from one end ofthe eyinder and exhanstng th burned gases fom the
‘ther end gives a aight ow, called wallow scavenging. Tis isthe best rom the viewpoint of
thoroughly purging he cylinder oft exhaust content. The straight low reduces the ubulenee
and hence the mixing of the fresh charge with he bumed gases. Thus the scavenging efficiency
¿s increased, The required degree of turbulence is invariably required, it may have 10 be promoted
‘on the unilow pe by paru attention tothe tangential amangemen ofthe transfer pos.
otherwise the fresh charge inthe intake side cylinder bel may nt get suficiendy agitated. The
passage aerosstheeyinder head assists in promoting wir at this pin, whichis a god condon
5 the spark plug can be placed without esto in the best psion in order to take advantage
ofthis phenomena
Many systems have uniflow scavenging, ot ofthese the two main systems are
1. Port and poppet valve scavenging with one piston, Figure 11 3
2. Port scavenging with opposed piston, Figure 11.4,
Inport and poppet valve scavenging, the exhaust valves are located in the head, I is shown in
Figure 11.3, The admission of fresh charge through the inet pons is contolled by the piston,
while the products of combustion are removed rough the poppet valves provided in the cyliader
head. Provision for adjusting the timing ofthe opening and closing ofthe exhaust valves o suit
gu 1.3 Par ostra
engine speed and scavenge charge pressure are the
rain asset ofthis type of engine.
Port scavenging with opposed pistons (Junker's
design) has a very effective scavenging process. This
‘ype is also called the end-10 end scavenged engine. is
shown in Figure 11.4. The intake pons are covered by
the lower piston and the exhaust ports are covered by Fut. Potscrorging reposado.
the upper piston. All ports are distributed uniformly
‘over the whole circumference. The piston moves inthe opposite direction and a spiral motion of
‘the charge perpendicular tothe cylinder axis is created by the tangential arrangement ofthe inet:
ports. Thus his system produces very good scavenging and charging conditions, The swid helps
10 prevent mixing of fresh charge and combustion products during the scavenging process. In this
{ype the exhaust pons are opened before the inlet ports open and also the exhaust ports are closed
before the inlet pons close. This timing helps this ype of engine in filling its cylinder at fll inet
pressure In this type of engine, the counter-flow within the cylinder is eliminated and there is les
‘opportunity for mixing of fresh charge with the burned gases. I develope high mean effective
pressure. The combustion chamber
disadvantages. I requires a complicated running gear mechanism; there ae difficult in cooling
the pistons; and there are higher costs of manufacture and maintenance.
11.4 SCAVENGING PROCESS
Figure 11,5 shows a 'ighrespring pressure vs crank angle diagram taken of a conventional-loop
scavenged cross-flow type two-stroke engine. After the exhaust ports open (EO), the eylinder
vw PRAGA INA neuen www
350 Funtumenal of item Combien Engines
Twosvoke Engines 351
8l
Prose — 59
Poets
pen 103 tar
Wot o TT aa
Er
Pure 115. Lgspbgdagen era teen o ar ans ta comenonleepscaenged cessor ype
area sows Po adabaeconpesson ton pato escort,
pressure falls rapidly in the Blowdown process. The blowdown angle is defined as the craie
angle from the exhaust port opening to he point at which the cylinder pressure equals the exhaust
pressure.
‘Ate he blowdown process he cylinder pressure usualy falls below the exhaust pressure
fora few degrees because ofthe inertia ofthe gases. Soon afer the exhaust ports begin to open,
‘he inlet ports open (0); and as soon a the eylinder pressure fall below the scavenging pressure.
fresh mixture Flows ito the cylinder. This flow continues as the inlet ports are open and the inlet
total pressure exceeds the pressure in the cylinder.
‘While the gases flow into he inlet pos, the exhaust ease continue to low out ofthe exhaust,
ports. Flow inthis direction takes place because during the blowdown period the gases flow at
high velocity inthis direction and alo the rest mixture lowing in through the inlet ports eventu-
ally builds up a pressure inthe cylinder which exceeds the exhaust system pressure,
‘The crank angle during which both the inlet and exhaust pots are open is called the scaveng-
ing angle, and the corresponding time is called the scavenging perio.
‘Whether the inlet ports close (IC) first or the exhaust ports close (EC) first, depende onthe
‘ylinder design. Afterall the ports are close, the eyele proceeds through compression, combus-
ton and expansion
“The exhaust ports must open well before BDC in oder tha the cylinder pressure be substan-
tially equal to the exhaust system pressure before the piston reaches BDC and so thatthe excessive
blow-back of unbumed gases into the inlet system can be avoided.
11.5. SCAVENGING PARAMETERS
In order to discuss the gas exchange performance ofthe two-stroke engines, it i essential to
define several scavenging parameters
Delivery ratio
Ik compares the actual scavenging air mass or mixture mass (air mass is used in Cl engines and
air-foel mixture mass is used in ST engines) o that required in an ideal charging process.
mass of fresh charge delivered per cyele(
reference mas (Mag)
‘The delivery mai, Ry= ay
+ The reference mass is defined as the product of swept volume and the ambient fresh charge
density
Seavenging ratio.
eis te ratio ofthe “mass flow rate ofthe fresh charge supplied tothe engine” to the “mass flow
rate ofthe fresh charge supplied during ihe seavenging process’ which would jus fill the cylinder
at BDC at inlet temperature and pressure.
Pr
Senna to = ze CE)
wert
y = mas ow rt ofthe fe charge sopplied othe engine
Ma = mass flow ate ofthe fresh charge supplied in the dal scavenging process which
ould us il he cylinder at BDC at inlet temperatur and exhaust pressure
‘The sui is sed for the inlet condi andthe sfc eis wed for tr exh condo.
Now.
aus VO ary
where
1 = engine speed in ros
V2 total eylinder volume = V+,
Ve = clearance volume
Vi = swept volume
1 = density of fresh mixture,
ME, E.
Compression rato, ee
and an
where
Ay = area of cross-section of the piston
Densi ay)
where
‘= Universal gas constan
350 Funtumenal of item Combien Engines
Twosvoke Engines 351
8l
Prose — 59
Poets
pen 103 tar
Wot o TT aa
Er
Pure 115. Lgspbgdagen era teen o ar ans ta comenonleepscaenged cessor ype
area sows Po adabaeconpesson ton pato escort,
pressure falls rapidly in the Blowdown process. The blowdown angle is defined as the craie
angle from the exhaust port opening to he point at which the cylinder pressure equals the exhaust
pressure.
‘Ate he blowdown process he cylinder pressure usualy falls below the exhaust pressure
fora few degrees because ofthe inertia ofthe gases. Soon afer the exhaust ports begin to open,
‘he inlet ports open (0); and as soon a the eylinder pressure fall below the scavenging pressure.
fresh mixture Flows ito the cylinder. This flow continues as the inlet ports are open and the inlet
total pressure exceeds the pressure in the cylinder.
‘While the gases flow into he inlet pos, the exhaust ease continue to low out ofthe exhaust,
ports. Flow inthis direction takes place because during the blowdown period the gases flow at
high velocity inthis direction and alo the rest mixture lowing in through the inlet ports eventu-
ally builds up a pressure inthe cylinder which exceeds the exhaust system pressure,
‘The crank angle during which both the inlet and exhaust pots are open is called the scaveng-
ing angle, and the corresponding time is called the scavenging perio.
‘Whether the inlet ports close (IC) first or the exhaust ports close (EC) first, depende onthe
‘ylinder design. Afterall the ports are close, the eyele proceeds through compression, combus-
ton and expansion
“The exhaust ports must open well before BDC in oder tha the cylinder pressure be substan-
tially equal to the exhaust system pressure before the piston reaches BDC and so thatthe excessive
blow-back of unbumed gases into the inlet system can be avoided.
11.5. SCAVENGING PARAMETERS
In order to discuss the gas exchange performance ofthe two-stroke engines, it i essential to
define several scavenging parameters
Delivery ratio
Ik compares the actual scavenging air mass or mixture mass (air mass is used in Cl engines and
air-foel mixture mass is used in ST engines) o that required in an ideal charging process.
mass of fresh charge delivered per cyele(
reference mas (Mag)
‘The delivery mai, Ry= ay
+ The reference mass is defined as the product of swept volume and the ambient fresh charge
density
Seavenging ratio.
eis te ratio ofthe “mass flow rate ofthe fresh charge supplied tothe engine” to the “mass flow
rate ofthe fresh charge supplied during ihe seavenging process’ which would jus fill the cylinder
at BDC at inlet temperature and pressure.
Pr
Senna to = ze CE)
wert
y = mas ow rt ofthe fe charge sopplied othe engine
Ma = mass flow ate ofthe fresh charge supplied in the dal scavenging process which
ould us il he cylinder at BDC at inlet temperatur and exhaust pressure
‘The sui is sed for the inlet condi andthe sfc eis wed for tr exh condo.
Now.
aus VO ary
where
1 = engine speed in ros
V2 total eylinder volume = V+,
Ve = clearance volume
Vi = swept volume
1 = density of fresh mixture,
ME, E.
Compression rato, ee
and an
where
Ay = area of cross-section of the piston
Densi ay)
where
‘= Universal gas constan
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