This document discusses spark ignition engines. It covers air-fuel ratio requirements, the stages of combustion including normal and abnormal combustion, factors that affect knocking, and combustion chambers. Knocking occurs when pockets of the air-fuel mixture explode outside of the normal combustion front, disrupting the precise ignition timing. Factors that influence knocking include density, time, and fuel composition. The design of the combustion chamber aims to provide smooth engine operation and high power output through efficient combustion.

1. SPARK IGNITION ENGINES
Air-fuel ratio requirements, Design of carburetor –fuel jet size and
venture size, Stages of combustion-normal and abnormal combustion,
Factors affecting knock, Combustion chambers, Introduction to
thermodynamic analysis of SI Engine combustion process.

2. Air-fuel ratio requirements

3. Air-fuel ratio 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

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

11. 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.

12. 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.

13. Factors affecting knock
1. Density Factors

14. 1. Density Factors

15. 2. Time Factors

16. 2. Time Factors

17. 3. Composition Factors

18. Variables affecting Knocking in Si engine.

19. Combustion Chambers

20. Combustion Chambers
1. Smooth Engine Operation

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

22. Combustion Chambers
Typical Combustion Chamber

23. Combustion Chambers
Typical Combustion Chamber

24. Combustion Chambers
Typical Combustion Chamber