The document discusses spark ignition engines. It covers mixture requirements, fuel injection systems including monopoint, multipoint, and direct injection. It describes the stages of normal and abnormal combustion as well as factors that affect knocking. It also discusses combustion chambers and their role in smooth engine operation and high power output.

2. UNIT-I SPARK IGNITION ENGINES
Mixture requirements – Fuel injection systems – Monopoint, Multipoint
& Direct injection - Stages of combustion – Normal and Abnormal
combustion – Knock - Factors affecting knock – Combustion
chambers.

3. Air-fuel ratio or Mixture requirements

4. Air-fuel ratio or Mixture requirements

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

6. Automotive A/F ratio requirements

7. Carburetor

8. Monopoint Injection
Fuel injection is a system for mixing fuel with air in an internal combustion
engine. The functional objectives for fuel injection systems vary but all of
them share the central task of supplying fuel to the combustion process.

9. Multipoint Injection
In the Multipoint Injection System, we have one injector per cylinder, the
injector injects the fuel into the admission valve which admits the fuel and air into
the cylinder. This gives an individual control on this cylinder, improving the fuel
consumption in relation of the Single point injection.

10. Direct Injection

11. Stages of combustion

12. Stages of combustion

13. Stages of combustion

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

15. 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.

16. 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.

17. Factors affecting knock
1. Density Factors

18. 1. Density Factors

19. 2. Time Factors

20. 2. Time Factors

21. 3. Composition Factors

22. Variables affecting Knocking in Si engine.

23. Combustion Chambers

24. Combustion Chambers
1. Smooth Engine Operation

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

26. Combustion Chambers
Typical Combustion Chamber

27. Combustion Chambers
Typical Combustion Chamber

28. Combustion Chambers
Typical Combustion Chamber