Consider the following statements regarding supercharging of CI engines: 1. Supercharging results in a quieter and smoother operation of a CI engine 2. Supercharging of a CI engine requires an increase in valve overlap 3. The limit of supercharging for a CI engine is reached by thermal and mechanical loading Which of the above statements are correct?
Consider the following statements regarding supercharging of CI engines: 1. Supercharging results in a quieter and smoother operation of a CI engine 2. Supercharging of a CI engine requires an increase in valve overlap 3. The limit of supercharging for a CI engine is reached by thermal and mechanical loading Which of the above statements are correct? Correct Answer 1, 2 and 3
Concept:
The purpose of supercharging an engine is to raise the density of the air charge, before it enters the cylinders. Thus, the increased mass of air will be inducted which will then be compressed in each cylinder. This makes more oxygen available for combustion. Consequently, more air and fuel per cylinder will be forced into the cylinder, and this can be effectively burnt during the combustion process to raise the engine power output to a higher value.
Purpose of supercharging:
- Provides better mixing of the air-fuel mixture
- Increase the volumetric efficiency
- Increase the power output of the engine
- It tends to increase the possibility of detonation in an S.I. engine and lessen the possibility of knocking in a C.I. engine
Effects of supercharging on CI engines:
- The increased valve overlap period of 60° to 160° of crank angle
- Smoother operation and reduction in diesel knock tendency
- Improved cold starting
- Reduced exhaust smoke
- Increased mechanical efficiency
- Reduced specific fuel consumption in turbocharging
- Increased heat loss due to increased turbulence.
Limitations of supercharging in CI engines:
The permissible extent of supercharging depends upon the ability of the engine to withstand the increased gas loading and thermal stresses.
