Figure shows the Otto cycle plotted on p – V diagram. The Otto cycle has following main processes:
Adiabatic compression process (1 – 2)
Constant volume heat addition (2 – 3)
- Heat is added at constant volume from an external heat source, both pressure and temperature are increases.
- Heat supplied to the gas during constant volume process (2 – 3),
Adiabatic expansion process (3 – 4)
Constant volume heat addition (4 – 1)
- Heat is rejected to the external sink at constant volume. This process is so controlled that ultimately the working fluid comes to its initial state 1 and the cycle is repeated
- Heat rejected from the gas during constant volume process (4 – 1),
The expression of efficiency of Otto cycle:
Substitute the value of and
Above equation proved that the efficiency of Otto cycle is a function of compression ratio.