Causes of low thermal efficiency of S.I. Engines - Basic Mechanical Engineering
Mechanical Engineering (MCQ) questions and answers
Basic Mechanical Engineering
Q. Thermal efficiency of S.I. engines is low, due to ____
- Published on 02 Sep 15
low compression ratio
high compression ratio
ANSWER: low compression ratio
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-Posted on 08 Jun 17
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-Posted on 12 Nov 15
It is a dimensionless performance measure of thermal devices such as internal combustion engine, boiler, etc.
The ratio of largest volume capacity to smallest volume capacity in the combustion chamber is called as compression ratio.
- S.I engines have low efficiency due to low compression ratio and C.I. engines have high efficiency due to higher compression ratio.
- If an engine has high compression ratio, it extracts more mechanical energy from air-fuel mixture because of its high thermal efficiency.
- The compression ratio for petrol engines lies between 10:1 to 6:1. This compression ratio depends upon the design of cylinder head.
- The brake power, brake thermal efficiency, brake mean effective pressure increases as compression ratio increases and reduces specific consumption.
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