UNIT-I -------SPARK IGNITION ENGINES.ppt

Introduction of SI Engines

1. UNIT I
SPARK IGNITION ENGINES

2. Air-fuel ratio or Mixture requirements

3. Air-fuel ratio or Mixture requirements

4. Variation of Power output , BSFC with A/F ratio.

5. Automotive A/F ratio requirements

6. Carburetor

7. Stages of combustion

8. Stages of combustion

9. Stages of combustion

11. Normal Combustion
Under ideal conditions the common internal combustion engine burns the
fuel/air mixture in the cylinder in an orderly and controlled fashion.

12. Abnormal Combustion
When unburned fuel/air mixture beyond the boundary of the flame front is
subjected to a combination of heat and pressure for a certain duration (beyond
the delay period of the fuel used),
 detonation may occur. Detonation is
characterized by an instantaneous, explosive ignition of at least one pocket of
fuel/air mixture outside of the flame front. A local shockwave is created
around each pocket and the cylinder pressure may rise sharply beyond its
design limits.

13. Knocking
Knocking
 (also called knock, detonation, spark knock, pinging or pinking) in spark-
ignition
 IC engine occurs when combustion of the air/fuel mixture in the cylinder
starts off correctly in response to ignition by the
 spark plug, but one or more
pockets of air/fuel mixture explode outside the envelope of the normal combustion
front.
The fuel-air charge is meant to be ignited by the spark plug only, and at a precise
point in the piston's stroke. Knock occurs when the peak of the combustion process
no longer occurs at the optimum moment for the 4 stroke cycle. The shock wave
creates the characteristic metallic "pinging" sound, and cylinder pressure increases
dramatically. Effects of engine knocking range from inconsequential to completely
destructive.

14. Factors affecting knock

15. Factors affecting knock
1. Density Factors

16. 1. Density Factors

17. 2. Time Factors

18. 2. Time Factors

19. 3. Composition Factors

20. Variables affecting Knocking in Si engine.

21. Combustion Chambers

22. Combustion Chamber design
for SI Engine

26. Combustion Chambers
1. Smooth Engine Operation

27. Combustion Chambers
2. High Power Output and thermal Efficiency

28. Combustion Chambers
Typical Combustion Chamber

29. Combustion Chambers
Typical Combustion Chamber

30. Combustion Chambers
Typical Combustion Chamber

31. TYPES OF INJECTION SYSTEMS
The fuel injection system can be classified as:
1. Gasoline direct injection into the cylinder
(GDI)
2. Port injection
(a) Timed
(b) Continuous
3. Manifold injection

32. i) Continuous injection systems
This system usually has a rotary pump. The pump
maintains a fuel line gauge pressure of about 0.75 to 1.5
bar. The system injects the fuel through a nozzle located
in the manifold immediately downstream of the throttle
plate
ii) Timed fuel injection system:
This system has a fuel supply pump which sends fuel at
a low pressure of about 2 bar when the engine is
running at maximum speed. A fuel metering or injection
pump and a nozzle are the other parts of the system

34. Different methods of fuel injection

36. Single Point Injection

37. Multi Point Fuel Injection

38. Single Point and Multi point
Injection Systems

39. Mechanical Injection

40. Electronic Injection