This document discusses spark ignition engines and various aspects of their combustion process. It covers topics like air-fuel ratio requirements, the stages of combustion including normal and abnormal combustion. It describes factors that affect knocking, different fuel injection systems, and combustion chamber designs. It also discusses variables that influence knocking in spark ignition engines.

1. UNIT I SPARK IGNITION ENGINES
Air-fuel ratio requirements – stages of combustion – normal
and abnormal combustion – factors affecting knock – fuel
injection systems – mono point, multipoint and direct injection
combustion chambers – effects of compression ratio –
introduction to thermodynamic analysis of combustion process.

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