in order to compare thermal efficiency of actual runing engine its performance is compared with theoretical thermal efficiency of ideal cycle ysing air as a fluid .the theoratical thermal efficiency of ideal cycle is known as air standard efficiency.
Actual engine can have maximum possible efficiency equal to air standard efficiency in ideal condition but practically efficiency of engine is always less than air standard eaciency and every attempt made to improve engine design so that efficiency of engine will be close to air standard efficiency.
Assumptions of Air Standard Cycle “
Following are the assumptions made for derivation of air standard cycle :
1 • The working fluid is throughout the cycle and followss-operfect gas law.
- The working fluid is homogeneous throughout the cycle and no chemical reaction should take place.
- specsc heat Cp and Cv do not vary with temperature.
The mass of air in cycle should remai fixed i.e. the cycle should be closed cycle.