IC engine Emissions and related parameters

ic engine & emission

1. Advances in IC Engines AEZG516 Lecture

2. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 2 Preliminaries

3. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 3 Demands on IC Engine

4. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 4 Gasoline Vs Diesel

5. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 5 Gasoline Vs Diesel https://www.youtube.com/watch?v=Zph5usgWkN0

6. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 6 Air Properties

7. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 7 Combustion stoichiometry (Propane) The relationship between the relative quantities of substances taking part in a reaction

8. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 8 Chemical Equation Petrol Diesel

9. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 9 Ratios

10. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 10 Ratios The fuel/air equivalence ratio ϕ , Relative air/fuel ratio λ ,

11. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 11 Engine Emissions

12. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 12 Spark Ignition Engine (Gasoline) Runs stoichiometric AFR or slightly rich Leaner mixture (Less fuel compared to air) give lower emissions and beyond certain level of leanness , the combustion quality is reduced, misfire happens and HC emission happen In cold engines, richer mixtures are used which produce CO and HC emission Richer mixture reduces NOx as there is no enough oxygen in the system

13. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 13 Diesel Engine(Compression Ignition Engine) Engine runs Lean (More air than Fuel) Always Oxygen is available (So, NO is higher)

14. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 14 Diesel Engine(Compression Ignition Engine) NO X : NO emissions will steadily increase as ϕ increases due to increasing fraction of the cylinder contents being burned gases close to stoichiometric during combustion, and due to higher peak temperatures and pressures CO : CO emissions will be low at all equivalence ratios since excess air is always available. HC : Will decrease slightly with increasing ϕ due to higher cylinder temperatures making it easier to burn up any overmixed (very lean) or undermixed (rich) fuel-air mixture. At high loads, however, HC may increase again if the amount of fuel in regions too rich to burn during the primary combustion process increases rapidly.

15. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 15 Diesel Engine(Compression Ignition Engine)

16. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 16 NOx

17. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 17 NO formation N 2 + O 2 = 2NO Also Oxygen disassociates at around 1000°C, the monoatomic oxygen occurs Highly endothermic(Heat absorbing reactions)

18. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 18 NO 2 Formation If NO 2 producing flame is quenched (In diesel, mixing with fresh fluid is done) 2 nd reaction does not take place , thereby NO 2 percentage is higher in Diesel engine than in Petrol engine

19. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 19 NO 2 / NO Ratio

20. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 20 Kinetics of NO formation The strong dependence of d [NO]/ dt on temperature in the exponential term is evident. High temperatures and high oxygen concentrations result in high NO formation rates

21. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 21 SI Engine NO formation The most important engine variables that affect NO emissions are the Relative air/fuel ratio (or fuel/air equivalence ratio) Burned gas fraction of the in-cylinder unburned mixture Spark timing

22. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 22 SI Engine Relative Air fuel Ratio Maximum burned gas temperatures occur at λ ≈ 0.9; however, at this relative air/fuel ratio oxygen concentrations are low As the mixture is further enriched ( oxygen is less ), burned gas temperatures fall As the mixture is leaned out, increasing oxygen concentration initially offsets the falling gas temperatures and NO emissions peak at λ ≈ 1.1.

23. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 23 SI Engine- Burnt gas residuals The burned gases act as a diluent in the unburned mixture; the absolute temperature reached after combustion varies inversely with the burned gas mass fraction. Increasing the burned gas fraction reduces NO emissions levels. However, it also reduces the combustion rate and, therefore, makes stable combustion more difficult to achieve The primary effect of the burned gas diluent in the unburned mixture on the NO formation process is that it reduces flame temperatures by increasing the heat capacity of the cylinder charge . The burned gases are residual gas from the previous cycle

24. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 24 SI Engine- Burnt gas residuals η v Substantial reductions in NO concentrations are achieved with 10 to 15% EGR, which is about the maximum amount of EGR the engine will tolerate under normal part-throttle conditions.

25. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 25 SI Engine- Burnt gas residuals X b – Burnt gas fraction in the cylinder m r – Residual Gas left in cylinder m c – Total charge in the cylinder

26. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 26 SI Engine- Burnt gas residuals Note that increasing mixture dilution (through higher residual or EGR) at the stoichiometric A/F decreases NO emissions faster than does leaner operation (increasing A/F above the stoichiometric value of about 14.6) at constant residual plus EGR. This is largely due to the fact that when lean, a portion of the residual and EGR can be thought of as “air” since the burned gases contain oxygen. ( Oxygen aids in formation of NO ) Excessive dilution (More Gas/ Fuel Ratio) results in poor combustion quality, partial burning, and, eventually, misfire

27. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 27 SI Engine- Spark Timing Advancing the timing so that combustion occurs earlier in the cycle increases the peak cylinder pressure Retarding the timing decreases the peak cylinder pressure Higher peak cylinder pressures result in higher peak burned gas temperatures, and hence higher NO formation rates. For lower peak cylinder pressures, lower NO formation rates result Advance Retard

28. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 28 Compression Ignition engine Nox formation UHC- Unburned hydrocarbon

29. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 29 Compression Ignition engine Nox formation

30. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 30 Compression Ignition engine NOx formation

31. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 31 Flame production

32. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 32 NO formation mechanism NO formation in high-temperature high-pressure burned gases is close to stoichiometric NO formation rates are high, and within a factor of 2 of the maximum value for 0.85 ≲ ϕ ≲ 1.1. Thus, little NO will form during the fuel rich premixed burning phase; almost all the NO will form in the mixing-controlled diffusion-flame burning process

33. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 33 NO formation After the time of peak pressure, burned gas temperatures will decrease as the cylinder gases expand. The decreasing temperature due to expansion and due to mixing of the high-temperature gases with air slows down and then freezes the NO chemistry. This second effect ( which occurs only in the diesel ) means that freezing occurs more rapidly than in the spark-ignition engine, and less decomposition of the NO occurs. 2NO = N 2 + O 2

34. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 34 NO formation – Cylinder / Exhaust NO concentrations reach a maximum shortly after time of peak pressure. There is a modest amount of NO decomposition. Variations in engine speed have little effect on the shape of this curve

35. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 35 NOx – Equivalence ratio Though NO levels decrease with a decreasing overall equivalence ratio, they do so much less rapidly than do spark-ignition engine NO emissions In the diesel, the zones where NO formation rates are highest are stoichiometric. Though the amount of fuel injected decreases , almost all fuel still burns close to stoichiometric

36. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 36 Compression Ignition engine Effect of increasing EGR at higher, mid-, and lower-loads. The engine can tolerate high EGR levels (50%) at low load since at very lean operating condition ( ϕ ∼ 0.2), a major fraction of this EGR is effectively “air.”

37. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 37 CO

38. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 38 Compression Ignition engine Diesels, always operate well on the lean side of stoichiometric hence complete burning of CO is ensured; CO emissions from diesels are low enough

39. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 39 Spark Ignition Engine CO results from incomplete oxidation of fuel carbon when insufficient oxygen is available to completely oxidize the fuel. CO rises steeply as the air-fuel (A/F) ratio is decreased below the stoichiometric A/F ratio. During the Cold running of the engine, AFR is low, leading to CO During acceleration and deceleration again CO Peaks Poor mixing, Local rich regions, incomplete combustion will lead to CO Different Fuels 1-11

40. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 40 HC

41. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 41 HC formation in SI Engine

42. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 42 HC formation in SI Engine

43. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 43 HC formation in SI Engine • Gasoline vapor-air mixture compressed into the combustion chamber crevice volumes. • Gasoline compounds absorbed in oil layers on the cylinder liner. • Gasoline absorbed by and/or contained within deposits on the cylinder head and piston crown. • Quench layers on the combustion chamber wall left as the flame extinguishes close to the wall • Gasoline vapor-air mixture left unburned when the flame extinguishes prior to reaching the walls • Liquid gasoline within the cylinder that does not evaporate and mix with sufficient air to burn prior to the end of combustion • Leakage of unburned mixture through the (nominally) closed exhaust valve

44. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 44 HC formation in SI Engine

45. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 45 HC formation in SI Engine - Crevices The overall piston crevice region consists of a series of volumes, connected by flow restrictions such as the ring side clearance and ring gap, whose geometry changes as the ring moves up and down in the ring groove sealing either the top or (mostly) bottom ring surface. The important result is that a fraction of the total fuel mass in the cylinder (5 to 10 % ) is trapped in these regions at the time of peak cylinder pressure and escapes the primary combustion process. Most of this trapped gas flows back into the cylinder during the expansion process without undergoing combustion

46. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 46 HC formation in SI Engine - Crevices

47. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 47 HC formation in SI Engine - Crevices

48. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 48 HC formation in SI Engine – Lubricating oil absorption and desorption During intake oil absobs fuel air rich mixture due to concentration differences. During the expansion and exhaust strokes, the oil layer on the liner, , has higher concentrations of gasoline compounds in the oil than correspond to equilibrium with the close to or zero levels of gasoline in the burned gases which fill the cylinder. This is desorption Thus hydrocarbons are desorbed out of the oil film and diffuse into the cylinder gases. If they do not then oxidize, they can exit the cylinder and contribute to the engine-out unburned hydrocarbon emissions. ( 1 0 to 25 percent)

49. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 49 HC formation in SI Engine - Deposits Over extended mileage, deposits build up on the intake valves The deposits on the outside of the intake valve, which are porous, absorb some of the liquid fuel injected onto the back (intake side) of the valve. Delays fuel entry into the cylinder during engine transients The in-cylinder mixture is therefore leaner than intended during accelerations (throttle openings) richer than intended during decelerations (throttle closings). Intake valve deposits primarily affect HC emissions during changes in engine load and, during starting and warm-up . They do not significantly affect steady-state HC emissions

50. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 50 HC formation in SI Engine – Flame quenching Flame extinguishes a short distance from the cooled combustion chamber walls Quench layers diffuses into the hot combustion products outside the layer and burns up during expansion, under most engine operating conditions Hence, flame quenching walls is not a serious HC problem (0.5%) Flame extinguishment prematurely , before the above-described flame quenching at the chamber walls occurs, is potentially a more significant contributor to engine-out HC emissions When an engine is operated close to its dilute operating limit (e.g., with high EGR), or its lean operating limit. Then flame Extinguishment will occur

51. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 51 HC formation in SI Engine – Liquid fuel on the Cylinder Walls In Port injection, if fuel is injected during the closed intake valves, it lands on backside of the intake valve When inlet valve opens, the exhaust gases enter and assists fuel vaporization and cylinder charge is without liquid fuel. If fuel is injected during the open intake valves, most of it enters in liquid form as droplets or ligaments along with the air flow. Many of the liquid mixes well with the air and participates in combustion but left out liquid will be deposited on walls or enters crevices which does not get oxidized thus leading to HC Emission. During starting of the engine, rich mixture is supplied and chances of HC production is high.

52. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 52 HC formation in SI Engine -Direct Injection (DI Engines) In port-injected systems, due to the buildup of liquid fuel films within the intake port, there are fuel transport delays and, during engine start up, significantly more fuel must be injected than enters the cylinder during the first several cycles. DI fuel injection has the potential for reducing the cold-engine fuel enrichment required, since fuel is directly injected into cylinders. For homogeneous-charge DI spark-ignition engines under quasi-steady operating conditions with gasoline, the HC emissions mechanisms are essentially the same as with port-fuel-injection engines DI gasoline engines that are operated stratified at light- and mid-load generally, have higher HC emissions than homogeneous stoichiometric operating DI engines. Flame quenching near the outer boundary of the close to- stoichiometric fuel-containing cloud occurs due to the very lean mixtures, then usual HC Emissions will occur.

53. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 53 HC Overall Chart – SI Engine

54. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 54 HC- Compression Ignition Engine As soon as fuel injection into the cylinder commences, a distribution in fuel/air equivalence ratio across each fuel spray develops. The amount of fuel that is mixed leaner than the lean combustion limit ( ϕ ≈ 0.3) increases rapidly with time and will not auto ignite. This is known as “Over leaning” condition φ – Fuel / Air Equivalence Ratio

55. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 55 HC- Compression Ignition Engine

56. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 56 HC- Compression Ignition Engine Injector SAC volumes) At the end of the fuel-injection process, the injector sac volume (the small volume left in the tip of the injector after the needle seats) is left filled with fuel. As the combustion and expansion processes proceed, this fuel is heated and vaporizes, and enters the cylinder at low velocity through the nozzle holes. This fuel vapor (and perhaps drops of fuel also ) will mix relatively slowly (undermixing) with air and may escape the primary combustion process.

57. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 57 HC- Compression Ignition Engine Engine-out hydrocarbon emissions from diesel engines are low (of order 0.1% of the fuel) over much of the engine’s operating range. However, at very light loads (especially engine idle), HC emissions as a fraction of the fuel can be several times higher. Hydrocarbon emissions have been shown to be sensitive to oil and coolant Temperature. When these temperatures were increased from 40 to 90°C in a DI diesel, HC emissions decreased by 30%. Engine-out hydrocarbon emissions from diesel engines are low (of order 0.1% of the fuel) over much of the engine’s operating range. HC is a reducing agent, therefore helps reducing NOx emissions , it may be even a good strategy to deliberately introduce HC to reduce NOx (See Heywood Page 1073)

58. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 58 Particulate Emission (PM)

59. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 59 Particulate Emission Definition : Particulate is any substance other than water that can be collected by filtering diluted exhaust at or below 325 K.

60. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 60 Particulate Emission- SI Engine Depending on the sulfur content in the fuel, significant sulfate emissions can occur with oxidation-catalyst equipped engines. Gasolines can contain from 10 up to some 500 ppm by weight sulfur (depending on the extent of sulfur removal in the refinery), which is oxidized within the engine cylinder to sulfur dioxide. This SO 2 can be oxidized by the exhaust catalyst to SO 3 which combines with water at ambient temperatures to form a sulfuric acid aerosol. Other particulates, such as Lead etc are less as fuel contains 0.005 g/ Liter (BS VI norms) Stratified charge direct-injection engines have much higher particulates (more nucleation particles) than do homogeneous stoichiometric DI engines.

61. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 61 Particulate Emission- CI Engine Diesel combustion is heterogeneous in nature Max PM emissions occurs at Wide open throttle conditions

62. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 62 Particulate Emission- CI Engine Diesel combustion is heterogeneous in nature According to this model, combustion takes place in two stages. If in the first stage , 𝑐 < 𝑎 ∕2 , there is not enough oxygen present to convert all the carbon in the fuel to carbon monoxide, the carbon--oxygen ratio > 1 , resulting in the production of soot or solid carbon C(s). The second stage burns the CO, soot, and other first stage products to completion in a diffusion flame. If there is enough oxygen present, that is, 𝑐 ≥ 𝑎 ∕2 , then the flame is clean since no solid carbon is formed. Incomplete oxidation will result in a sooting flame.

63. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 63 Soluble Organic Fraction(SOF) 90% of Carbon will burn and never get exhausted Out of 10% exhausted out of cylinder - 25% of carbon comes from lubricating oil components - Rest comes from fuel itself Because cylinder cooling by expansion stroke, high boiling point components ( Hydrocarbons ) found in the fuel and the lubricating oil condenses on the surface of carbon soot particles. This absorbed portion of the soot particles is SOF . Under low engine load conditions( Temp is less) and therefore SOF can be as high as 50%

64. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 64 Particulate Emission- CI Engine AS EGR Increases , the charge in the cylinder contains less oxygen, therefore, increases soot. EGR increase will decrease NOx As start of injection is delayed , NOx will decrease, where as Soot will increase due to incomplete time for combustion!

65. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 65 PM – NOx trade off

66. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 66 Particulate matter

67. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 67 Summary

68. 25-Jul-24 Advances in IC Engines AEZG516 BITS Pilani 68 Thank you