Unit 1 automotive engine auxiliary systems

OAT551 Automotive Systems Unit - 1 1-AUTOMOTIVE ENGINE AUXILIARY SYSTEMS

1. OAT551 AUTOMOTIVE SYSTEMS UNIT - 1 P.HARIPRASAD ASSISTANT PROFESSOR, DEPARTMENT OF MECHANICAL ENGINEERING, KIT-KALAIGNAR KARUNANIDHI INSTITUTE OF TECHNOLOGY, COIMABATORE - 641402

2. UNIT - 1-AUTOMOTIVE ENGINE AUXILIARY SYSTEMS Automotive engines External combustion engines Internal combustion engines Classification of engines SI Engines CI Engines

3. UNIT - 1-AUTOMOTIVE ENGINE AUXILIARY SYSTEMS Two stroke engines construction and working principles Four stroke engines construction and working principles IC engine components‐ functions and materials Valve timing –port timing diagram Injection system ‐Unit injector system‐ Rotary distributor type ‐ Electronically controlled injection system for SI engines‐CI engines‐Ignition system ‐ Electronic ignition system ‐Transistorized ignition system, capacitive discharge ignition system.

4. What is an engine ? An engine is an device which is use to convert chemical energy into mechanical energy or work. Chemical energy -> mechanical energy

5. EXTERNAL COMBUSTION ENGINE

6. EXTERNAL COMBUSTION ENGINE An external combustion engine (EC engine) is a heat engine where a working fluid, contained internally, is heated by combustion in an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine, produces motion and usable work.

7. EXTERNAL COMBUSTION ENGINE The fluid is then cooled, compressed and reused (closed cycle), or dumped (open cycle). In these types of engines, the combustion is primarily used as a heat source, and the engine can work equally well with other types of heat sources.

8. INTERNAL COMBUSTION ENGINE

9. INTERNAL COMBUSTION ENGINE An internal combustion engine (ICE) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine.

10. INTERNAL COMBUSTION ENGINE The force is applied typically to pistons, turbine blades, rotor or a nozzle. This force moves the component over a distance, transforming chemical energy into useful work.

11. CLASSIFICATIONS OF ENGINES

12. Spark Ignition Engine An SI engine starts the combustion process in each cycle by use of a spark plug. The spark plug gives a high-voltage electrical discharge between two electrodes which ignites the air-fuel mixture in the combustion chamber surrounding the plug.

13. Combustion Ignition Engine The combustion process in a CI engine starts when the air-fuel mixtures self-ignites due to high temperature in the combustion chamber caused by high compression.

14. FOUR STROKE ENGINE A 4 stroke petrol engine shown in figure. The valve operating the inlet is called inlet valve and the valve operating the exhaust is called exhaust valve. The spark plug fitted at the top of cylinder head initiates the ignition of the air fuel mixture. The piston performs four stroke to complete one working cycle. The four different strokes are;

15. FOUR STROKE ENGINE Suction stroke Compression stroke Power stroke Exhaust stroke

16. SUCTION STROKE During this stroke, inlet valve opens and exhaust valve closed, the pressure in the cylinder will be atmosphere . As the piston moves from the TDC To BDC , the volume in the cylinder increase , while simultaneously pressure decreases. This create a pressure difference between the atmosphere and inside of the cylinder. Due to this pressure difference the petrol and air mixture will enter into the cylinder through carburettor.

17. The crankshaft has now made half rotation i.e. 180 degree of crank angle. At the end of this stroke, the cylinder will filled completely with petrol and air mixture called charge and inlet valve is closed.

18. COMPRESSION STROKE During this stroke both the inlet valve and exhaust valve are closed, the piston moves from BDC to TDC . As this stroke being performed ,the petrol and air mixture contained in the cylinder will be compressed , so pressure and temperature of mixture increases. The process of compression is shown in fig.

19. Near the end of this stroke , the petrol and air mixture is ignited by the electric spark given out by the spark plug. The combustion of petrol releases the hot gases which will increases the pressure at the constant volume.

20. POWER STROKE During this stroke both the inlet valve and exhaust valve are closed, the piston moves from TDC to BDC. The high pressure and high temperature burnt gases force the piston to perform this stroke, called power stroke. This stroke is also known as expansion or working stroke. The engine produces mechanical work or power during this stroke. As the piston moves from TDC to BDC , the pressure of hot gases gradually decreases and volume increases.

21. Near the end of this stroke, the exhaust valve opens which will release the burnt gases to the atmosphere. This will suddenly bring the cylinder pressure to the atmospheric pressure.

22. EXHAUST STROKE During this stroke, the exhaust valve opens and the inlet valve is closed . The piston moves from BDC to TDC and during this motion piston pushes the exhaust gases (combustion product) out of the cylinder at constant pressure. Again the inlet valve open and the new cycle starts

23. TWO STROKE ENGINE As the name itself implies, all the processes in the two stroke cycle engine are completed in two strokes. These engine have 1 power stroke per revolution of the crankshaft. In the two stroke engine there is a two opening called ports are provided in place of valve of four stroke engines. These ports are opened and closed by reciprocating motion of the piston in the cylinder.

24. One port known as a inlet port and another port is known as a exhaust port. Two stroke engine consist of a cylinder with one end fitted with a cylinder head and other end fitted with a hermitically sealed crankcase which enables it to function as a pump in conjuction with the piston.

25. FIRST STROKE

26. At the beginning of the first stroke piston Is at the TDC as shown in fig. A. Piston moves from TDC to BDC. The electric spark ignites the compressed charge . The combustion of the charge will release the hot gases which increase the temperature and pressure in cylinder. The high pressure combustion engine to force piston downward . The piston perform power stroke till it uncovers the exhaust port As shown in fig. B. The combustion gases which are at the pressure slightly higher than atmosphere pressure escape through exhaust port.

27. The piston uncovers the transfer port the fresh charge flow from the crankcase into cylinder through transfer port as shown in fig. B. Which enters the cylinder pushes the burnt gases , so more amount of exhaust gases come out through exhaust port as shown in fog. B. This swiping out of exhaust gases by incoming fresh charge is called scavenging. This will continue till the piston covers both the transfer and exhaust port during next upward stroke.

28. SECOND STROKE

29. In this stroke piston moves from BDC to TDC. When it covers the transfer port in fig. C. , the supply of charge is stopped and then when it moves further up it covers the exhaust port completely in fig. D stop the scavenging. Further upward motion of the piston will compressed the charge in the cylinder. After the piston reaches TDC the first stroke repeats again.

30. IC Engine components

31. Internal combustion Engine Components:- 1. Engine Block : Body of the engine containing cylinders, made of cast iron or aluminium.

32. C 2. Cylinder : A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels .

33. 3. Head : The piece which closes the end of the cylinders, usually containing part of the clearance volume of the combustion chamber.

34. 4. Connecting Rod : In a reciprocating piston engine , the connecting rod or conrod connects the piston to the crank or crankshaft.

35. P i s t on 5. Piston: The piston of an internal combustion engine is acted upon by the pressure of the expanding combustion gases in the combustion chamber space at the top of the cylinder .

36. 6. Piston rings : A piston ring is a metal rings that fit into circumferential grooves around the piston and form a sliding surface against the cylinder walls.

37. 7. Crankshaft: Rotating shaft through which engine work output is supplied to external systems .

38. 8. Camshaft : Rotating shaft used to pu s h ope n v alve s a t t h e pr o pe r t im e in the engine cycle, either directly or t hroug h me c h a n i c a l or hydraulic linkage (push rods, rocker arms, tappets) .

39. 9. Intake manifold: Piping system which deliver incoming air to the cylinders, usually made of cast metal, plastic, or composite material . In most SI engines, fuel is added to the air in the intake manifold system either by fuel injectors or with a carburetor.

40. 10. Exhaust manifold : Piping system which carries exhaust gases away from the engine cylinders, usually made of cast iron

41. 11. Spark plug : Electrical device used to initiate combustion in an SI engine by creating high voltage discharge across an electrode gap

42. 12. Flywheel : Rotating mass with a large moment of inertia connected to the crank shaft of the engine. The purpose of the flywheel is to store energy .

43. 13. Fuel injector : A p r e ssuriz e d nozzle that sprays fuel into the incoming air (SI engines )or into the cylinder (CI engines).

44. 14. Combustion chamber: The end of the cylinder between the head and the piston face where combustion occurs . The size of combustion chamber continuously changes from minimum volume when the piston is at TDC to a maximum volume when the piston at BDC.

45. Valve Timing Diagram A valve timing diagram is a graphical representation of the opening and closing of the intake and exhaust valve of the engine, The opening and closing of the valves of the engine depend upon the movement of piston from TDC to BDC. This relation between piston and valves is controlled by setting a graphical representation between these two, which is known as valve timing diagram.

46. Valve Timing Diagram The valve timing diagram comprises of a  360 degree figure which represents the movement of the piston from TDC to BDC in all the strokes of the engine cycle, Which is measured in degrees and the opening and closing of the valves is controlled according to these degrees.

47. Why do We Need Valve Timing diagram? Synchronization between the steps of a cycle of the engine from the intake of air-fuel ratio to the exhaust of the combustion residual. Complete seizure of the combustion chamber at the instant at which the combustion of air-fuel mixture takes place as the leakage can cause damage to the engine and can be hazardous. Provide engine with a mixed air and fuel or air in case of diesel engine when required ( at the time of suction) which is the necessity of the engine.

48. Provide the exit for the combustion residual so that the next cycle of the engine can take place. Ideal timing for the opening and closing of the inlet and outlet valve which in turn protect the engine from defects like knocking or detonation. A high compression ratio required to combust the fuel especially in case of diesel engine by overlapping the closing of the valve. The cleaning of engine cylinder which in turn maintain the quality of combustion and decreases wear and tear inside the cylinder. The study of the details of the combustion that is required for the modification of the power of the engine.

49. Valve Timing Diagram for 4-Stroke Engine Suction Stroke-  The engine cycle starts with this stroke, Inlet valve opens as the piston which is at TDC  starts moving towards BDC and the air-fuel mixture in case of petrol and fresh air in case of diesel engine starts entering the cylinder,till the piston moves to BDC. Compression Stroke-  After the suction stroke the piston again starts moving from BDC to TDC in order to compress the air-fuel (petrol engine) and fresh air (diesel engine) which in turn raises the pressure inside the cylinder which is essential for the combustion of the fuel. The inlet valve closes during this operation to provide seizure of the chamber for the compression of the fuel.

50. Valve Timing Diagram for 4-Stroke Engine Expansion Stroke-  After compressing the fuel, The combustion of the fuel takes place which in turn pushes the piston which is at TDC towards BDC in order to release the pressure developed by the combustion and output is obtained . Exhaust Stroke-  After expansion stroke the piston which is at BDC starts moving towards TDC  followed by the opening of exhaust valve for the removal of the combustion residual. Exhaust valve closes after the piston reaches TDC.

51. THEORETICAL

52. ACTUAL OR PRACTICAL PROCESS

53. ACTUAL OR PRACTICAL PROCESS

54. Port Timing Diagram for 2-Stroke Engine Expansion stroke- At the beginning of the expansion stroke the piston which is at TDC starts moving towards BDC due to the combustion of compressed air-fuel (petrol engine) and (diesel sprayed charge in diesel engine) during compression stroke and the power output is obtained. The air-fuel(petrol engine) and air (diesel diesel ) enters through the inlet port during the expansion strokes as the piston moves from TDC to BDC during this stroke. The expansion stroke continuous till the piston reaches BDC.

55. Compression Stroke- At the end of the expansion stroke, the piston which is at BDC starts moving towards TDC and the compression of air-fuel (petrol engine) and diesel sprayed charge (diesel engine) starts along with the exhaust of combustion residual through exhaust port due to the movement of the piston from BDC to TDC. The piston closes both inlet port and exhaust port due to its movement from BDC to TDC which in turn raises the pressure inside the combustion chamber. At the end of the compression stroke i.e. when the piston reaches TDC combustion of the air-fuel (petrol engine) due to spark and diesel sprayed charge (diesel engine) due to the high pressure takes place, And the cycle repeats again.

56. THEORETICAL PROCESS

57. ACTUAL OR PRACTICAL PROCESS

58. ACTUAL OR PRACTICAL PROCESS

59. Fuel Injection Systems The Functions of Fuel Injection System, To enhance the engine Performance Fuel economy Initiating and controlling the combustion process. Preparation of the combustible charge (Just like carburettor).

60. Carburettor Carburettor : Fuel is atomized by processes relying on the air speed greater than fuel speed at the fuel nozzle, The amount of fuel drawn into the engine depends upon the air velocity in the venturi .

61. Types of Carburettor Simple Carburettor S.U Carburettor – Constant Vacuum type Zenith Carburettor – Compound jet with inner main jet. Solex Carburettor – Down Draught type Carter Carburettor - Down Draught type

62. Fuel Injection System Fuel Injection System The fuel speed at the point of delivery is greater than the air speed to atomize the fuel. The amount of fuel delivered into the air stream going to the engine is controlled by a pump which forces the fuel under pressure.

63. Functional Requirements of An Injection System Accurate metering of the fuel injected per cycle. Timing the injection of the fuel correctly in the cycle. Proper control of rate of injection Proper atomization of fuel into very fine droplets. Proper spray pattern to ensure rapid mixing of fuel and air

64. Functional Requirements of An Injection System Uniform distribution of fuel droplets throughout the combustion chamber. To supply equal quantities of metered fuel to all cylinders case of multi cylinder Engines. No lag during beginning and end of Injection.

65. Classification of Injection Systems A fuel-injection system is required to inject and atomize fuel in to the cylinder of CI engines. For producing the required pressure for atomizing the fuel either air or a mechanical means is used. Thus the injection systems can be classified as: Air injection system Solid injection systems

66. Air injection system Fuel is forced into the cylinder by means of compressed air. It has good mixing of fuel with the air with resultant higher mean effective pressure. It has the ability to utilize high viscosity (less expensive) fuels. The system is obsolete due to the requirement of multistage air compressors.

67. Solid Injection System In this system the liquid fuel is injected directly into the combustion chamber without the aid of compressed air. Solid injection systems can be classified into four types. Individual pump and nozzle system Unit injector system Common rail system Distributor system

68. Components of Fuel Injection System

69. Fuel tank : To Store the fuel, Fuel filters: to prevent dust and abrasive particles from entering the pump and injectors thereby minimizing the wear and tear of the components Fuel feed pump: to supply fuel from the main fuel tank to the injection system. Injection pump: to meter and pressurize the fuel for injection, Governor: to ensure that the amount of fuel injected is in accordance with variation in load, Injector: to take the fuel from the pump and distribute it in the combustion chamber by atomizing it into fine droplets,

70. Individual Pump and Nozzle System In this system, each cylinder is provided with one pump and one injector. The pump may be placed close to the cylinder or they be arranged in cluster The high pressure pump plunger is actuated by a cam, and produces the fuel pressure necessary to open the injector valve at the correct time.

71. UNIT INJECTOR SYSTEM Unit Injector System is one in which the pump and the Injector nozzle are combined with one housing. Each cylinder is provided with one of these unit injectors Fuel is brought up to the injector by low pressure pump, where at the proper time, a rocker arm actuates the plunger and thus injects the fuel into the cylinder

72. Common Rail System A HP pump supplies fuel, under high pressure, to a fuel header. High pressure in the header forces the fuel to each of the nozzles located in the cylinders At the proper time mechanically operated valve allows the fuel to enter the cylinder through the nozzle. The amount of fuel entering the cylinder is regulated by varying the length of the push rod stroke

73. Distributor System In this system the pump which pressurizes the fuel also meters and times it. Fuel pump after metering the required amount of fuel supplies it to a rotating distributor at the correct time for supply to each cylinder. The number of injection strokes per cycle for the pump is equal to the number of cylinders Since there is one metering element in each pump, a uniform distribution is automatically ensured.

74. Types of Injection system Single or Multi-point injection Indirect or Direct injection

75. Single point injection Injector located inside throttle body. Injector sprays fuel from above throttle valve. ECU control injector openings.

76. Multi-point injection Multi point fuel injection (MPFI) is a newer technology than the single point type. Basically, this type is the same as the first type but the number of injectors is adjusted to the number of cylinders. This means that for a 4 cylinder engine using 4 injectors. Injector located below Throttle valve. Injector sprays fuel Directly to ports. ECU controls opening.

77. 1 – Fuel supply, 2 – Air intake, 3 – Throttle, 4 – Intake manifold, 5 – Fuel injector (or injectors), 6 – Engine

78. Direct Injection Injector is fixed to the top of combustion chamber. Fuel is injected above Piston head. Smaller combustion space, better thermal efficiency.

79. Indirect Injection Indirect Injection System has a small swirl chamber above the cylinder. Fuel is injected in swirl chamber. Higher compression ratio needed to aid starting.

80. Electronic Fuel Injection System System Components Fuel tank Electric fuel pump Fuel filter Electronic control unit Common rail and Pressure sensor Electronic Injectors Fuel line

81. ELECTRONIC CONTROL UNIT In automotive electronics, electronic control unit (ECU) is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle. An engine control unit (ECU), also known as power-train control module (PCM), or engine control module (ECM) It is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running. It does this by reading values from multidimensional maps which contain values calculated by sensor devices monitoring the engine.

82. WORKING OF ECU Control of fuel injection : If the throttle pedal is pressed further down, the ECU will inject more fuel according to how much air is passing into the engine. If the engine has not warmed up yet, more fuel will be injected Control of ignition timing: An ECU can adjust the exact timing of the spark (called ignition timing) to provide better power and economy.

83. Control of idle speed : The engine RPM is monitored by the crankshaft position sensor which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor.

84. COMMON RAIL AND PRESSURE SENSOR The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high pressure. This accumulator supplies multiple fuel injectors with high pressure fuel.

85. ELECTRONIC FUEL INJECTORS The injectors can survive the excessive temperature and pressure of combustion by using the fuel that passes through it as a coolant. The electronic fuel injector is normally closed, and opens to inject pressurized fuel as long as electricity is applied to the injector's solenoid coil. When the injector is turned on. it opens. spraying atomized fuel at the combustion chamber. Depending on engine operating conditions injection quantity will vary.

86. FUEL LINE Fuel line hose carry gasoline from the tank to the fuel pump, to the fuel filter, and to the fuel injection system. While much of the fuel lines are rigid tube, sections of it are made of rubber hose, which absorb engine and road vibrations There are two basic types of fuel hose: Fuel and oil hoses that meet the SAE 30R7 standard, and fuel injection hose that meets the requirements of SAE 30R9.

87. What is Ignition System ? The system in an internal-combustion engine that produces the spark to ignite the mixture of fuel and air: includes the battery, ignition coil, distributor, spark plugs, and associated switches and wiring.

88. IGNITION FUNCTION Produces 30,000 volt spark across spark plug. Distributes high voltage spark to each spark plug in correct sequence. Times the spark so it occurs as piston is nearing top dead centre. Varies spark timing with load, speed, and other conditions.

89. BASIC IGNITION SYSTEM COMPONENTS BATTERY IGNITION SWITCH IGNITION COIL SWITCHING DEVICE SPARK PLUG IGNITION SYSTEM WIRES

90. BASIC IGNITION SYSTEM Battery supplies power to entire system Ignition Switch turns engine on or off Coil transforms volts Switching device triggers ignition coil Spark Plug and wires distribute spark

91. IGNITION COIL Transformer 2 sets of windings Primary windings Secondary windings Iron core Produces magnetic field

92. IGNITION SYSTEM TYPES Basically Convectional Ignition systems are of 2 types : (a) Battery or Coil Ignition System, and (b) Magneto Ignition System. Both these conventional, ignition systems work on mutual electromagnetic induction principle.

93. Battery ignition system was generally used in 4 -wheelers , but now-a-days it is more commonly used in 2-wheelers also (i.e. Button start, 2-wheelers like Pulsar, Kinetic Honda; Honda- Activa , Scooty , Fiero , etc.). In this case 6 V or 12 V batteries will supply necessary current in the primary winding. Magneto ignition system is mainly used in 2-wheelers, kick start engines . (Example, Bajaj Scooters, Boxer, Victor, Splendor , Passion, etc.). In this case magneto will produce and supply current to the primary winding. So in magneto ignition system magneto replaces the battery.

94. Battery or Coil Ignition System

95. Primary Circuit : It consists of 6 or 12 V battery, ammeter, ignition switch, primary winding it has 200-300 turns of 20 SWG (Sharps Wire Gauge) gauge wire, contact breaker, capacitor. Secondary Circuit : It consists of secondary winding. Secondary Ignition Systems winding consists of about 21000 turns of 40 (S WG) gauge wire. Bottom end of which is connected to bottom end of primary and top end of secondary winding is connected to centre of distributor rotor. Distributor rotors rotate and make contacts with contact points and are connected to spark plugs which are fitted in cylinder heads (engine earth).

96. Working : When the ignition switch is closed and engine in cranked, as soon as the contact breaker closes, a low voltage current will flow through the primary winding. It is also to be noted that the contact breaker cam opens and closes the circuit 4-times (for 4 cylinders) in one revolution. When the contact breaker opens the contact, the magnetic field begins to collapse. Because of this collapsing magnetic field, current will be induced in the secondary winding. And because of more turns (@ 21000 turns) of secondary, voltage goes into 28000-30000 volts.

97. Working : This high voltage current is brought to centre of the distributor rotor. Distributor rotor rotates and supplies this high voltage current to proper stark plug depending upon the engine firing order. When the high voltage current jumps the spark plug gap, it produces the spark and the charge is ignited - combustion starts - products of combustion expand and produce power.

98. Magneto Ignition System

99. Magneto Ignition System In this case magneto will produce and supply the required current to the primary winding. In this case as shown, we can have rotating magneto with fixed coil or rotating coil with fixed magneto for producing and supplying current to primary, remaining arrangement is same as that of a battery ignition system.

100. Battery Ignition Magneto Ignition Battery is a must. No battery needed. Battery supplies current in primary circuit. Magneto produces the required current for primary circuit. A good spark is available at low speed also. During starting the quality of spark is poor due to slow speed. Occupies more space. Very much compact. Recharging is a must in case battery gets discharged. No such arrangement required. Mostly employed in car and bus for which it is required to crank the engine. Used on motorcycles, scooters, etc. Battery maintenance is required. No battery maintenance problems.

101. TYPES OF ELECTRONIC IGNITION SYSTEM Electronic Ignition System is as follow : (a) Capacitance Discharge Ignition system (b) Transistorized system (c) Piezo -electric Ignition system (d) The Texaco Ignition system

102. DRAWBACKS OF CONVENTIONAL IGNITION SYSTEMS Because of arcing, pitting of contact breaker point and which will lead to regular maintenance problems. Poor starting : After few thousands of kilometers of running, the timing becomes inaccurate, which results into poor starting (Starting trouble). At very high engine speed, performance is poor because of inertia effects of the moving parts in the system. Some times it is not possible to produce spark properly in fouled spark plugs.

103. ADVANTAGES OF ELECTRONIC IGNITION SYSTEM Moving parts are absent-so no maintenance. Contact breaker points are absent-so no arcing. Spark plug life increases by 50% and they can be used for about 60000 km without any problem. Better combustion in combustion chamber, about 90-95% of air fuel mixture is burnt compared with 70-75% with conventional ignition system. More power output. More fuel efficiency.

104. Capacitance Discharge Ignition System

105. Capacitance Discharge Ignition System It mainly consists of 6-12 V battery, ignition switch, DC to DC convertor, charging resistance, tank capacitor, Silicon Controlled Rectifier (SCR),SCR-triggering device, step up transformer, spark plugs. A 6-12 volt battery is connected to DC to DC converter i.e. power circuit through the ignition switch, which is designed to give or increase the voltage to 250-350 volts. This high voltage is used to charge the tank capacitor (or condenser) to this voltage through the charging resistance. The charging resistance is also so designed that it controls the required current in the SCR.

106. Capacitance Discharge Ignition System Depending upon the engine firing order, whenever the SCR triggering device, sends a pulse, then the current flowing through the primary winding is stopped. And the magnetic field begins to collapse. This collapsing magnetic field will induce or step up high voltage current in the secondary, which while jumping the spark plug gap produces the spark, and the charge of air fuel mixture is ignited.

107. Transistorized Assisted Contact (TAC) Ignition System

108. Transistorized Assisted Contact (TAC) Ignition System When the engine is started, the crankshaft will rotate the pick up coil so that the pick up coil generates a low voltage current. This will cause the transistor base to be active so that the collector is connected to the emitter. In the ignition coil, the current from the battery will flow in both coil in the ignition coil. As explained above, the pickup coil will generate zig-zag electric current.

109. Transistorized Assisted Contact (TAC) Ignition System Current from the pick up coil is then transmitted to the base leg of the transistor. Induction in the ignition coil occurs when the base foot does not get an electric current, but it lasts for an instant, therefore in one cycle of the 4 cylinder engine can occur four times the induction process. The induction produces high voltage which is distributed to the distributor to be distributed to each spark plug according to the firing order.

110. Piezo -electric Ignition System The development of synthetic piezo -electric materials producing about 22 kV by mechanical loading of a small crystal resulted in some ignition systems for single cylinder engines. But due to difficulties of high mechanical loading need of the order of 500 kg timely control and ability to produce sufficient voltage, these systems have not been able to come up.

111. Texaco Ignition System Due to the increased emphasis on exhaust emission control, there has been a sudden interest in exhaust gas recirculation systems and lean fuel-air mixtures. To avoid the problems of burning of lean mixtures, the Texaco Ignition system has been developed. It provides a spark of controlled duration which means that the spark duration in crank angle degrees can be made constant at all engine speeds. It is a AC system. This system consists of three basic units, a power unit, a control unit and a distributor sensor. This system can give stable ignition up to A/F ratios as high as 24 : 1.

112. FIRING ORDER The order or sequence in which the firing takes place, in different cylinders of a multicylinder engine is called Firing Order. In case of SI engines the distributor connects the spark plugs of different cylinders according to Engine Firing Order.