Select the most appropriate sentence applicable to knocking pheno
| Select the most appropriate sentence applicable to knocking phenomena of the S.I. engine
A. In S.I. engine, the detonation occurs near the end of combustion.
B. In S.I. engine, the detonation occurs near the beginning of combustion.
C. In S.I. engine, the detonation is of a heterogenous mixture causing very low rate of pressure rise
D. None of the above
Please scroll down to see the correct answer and solution guide.
Right Answer is: A
SOLUTION
Concept:
- When the spark is advanced, burning gas is compressed by the rising piston and therefore temperature and pressure are increased, thus, the tendency to knock increases.
- In spark ignition (SI) engines, the possibility of knocking can be reduced by decreasing compression ratio as a reduction in compression ratio will result in the generation of lower peak temperature.
- In SI engine, knocking occurs before TDC and because of early combustion of charge/more than one flame propagation.
- Difference in the knocking phenomenon of the SI and CI engine.
- In SI engine, the detonation occurs near the end of combustion whereas in CI engine, detonation occurs near the beginning of combustion.
- The detonation inSI engines of a homogeneous charge causing very high rate of pressure rise and very high maximum pressure. In the CI engine, the fuel and air are imperfectly mixed and hence the rate of pressure rise is normally lower than that in the detonating part of the charge in the SI engine.
- In the CI engine, the fuel is injected into the cylinder only at the end of the compression stroke, there is no question of pre-ignition as in SI engine.