Otto Cycle

Several engines may be approximated by an Otto cycle, such as petrol engine and gas engine. The otto cycle is an ideal air standard cycle which consists of four processes:

1 to 2: Isentropic compression
2 to 3: Reversible constant volume heating
3 to 4: Isentropic expansion
4 to 1: Reversible constant volume cooling
The thermal efficiency of an Otto cycle with a perfect gas as working fluid is:

It can be shown that:

where,
r= V1/V2= Compression ratio
n=1 - = a constant depending on specific heat capacity