Causes of low thermal efficiency of S.I. Engines - Basic Mechanical Engineering

Q.  Thermal efficiency of S.I. engines is low, due to ____
- Published on 02 Sep 15

a. low compression ratio
b. high compression ratio

ANSWER: low compression ratio


  • SAMYRAJ   -Posted on 08 Jun 17
    I want to more questions and answers about mechanical engineering new tech
  • Sravanthi    -Posted on 12 Nov 15
    - Thermal efficiency: It is a dimensionless performance measure of thermal devices such as internal combustion engine, boiler, etc.

    - Compression ratio: 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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