INTRODUCTION

The gas as the working fluid does not undergo any phase change. The engines working on the gas cycles may be either cyclic or non-cyclic. The working fluid is assumed to obey all laws of a perfect gas.

In most of the gas power cycles, the working fluid consists mainly of air. Therefore, it is convenient to analyse the gas power cycles by devising an idealized cycle known as Air Standard Cycle, in which the working fluid is pure air.

The following assumptions are made in the air-standard cycles:

1. The air as the working fluid follows the perfect gas law: pV = mRT.
2. The working fluid is homogeneous throughout and no chemical reaction takes place.
3. The specific heats of air do not vary with temperature.
4. The mass of air in the cycle remains fixed.
5. The combustion process is replaced by an equivalent heat addition process.
6. The exhaust process is replaced by an equivalent heat rejection process.
7. All processes are internally reversible.

The thermal efficiency, η_th, of air standard cycle is given by

The thermal efficiency is also called air-standard efficiency (η_a)

Relative efficiency, (η_r)= Actual thermal efficiency/Air standard efficiency.