Otto cycle is also known as constant volume cycle, as the heat is received and rejected at a constant volume. Otto cycle is used in gas, petrol and many of the oil engines. The petrol engine works on Otto cycle.
The ideal Otto cycle consists of two constant volume and two reversible adiabatic or isentropic processes.
Otto cycle is taken as a standard of comparison for internal combustion engines. For the purpose of comparison with other cycles, the air is assumed to be the working substance.