Theoretical engine cycles
Ideal engine cycles such as the Otto cycle, the diesel cycle and others are known as air cycles because the working fluid that drives the engine is assumed to be air. The theoretical constant volume cycle was first proposed by Beau de Rochas in 1862. However, the first working engine that used the Beau de Rochas principles was designed by Otto and the constant volume cycle has been known ever since as the Otto cycle. Some of the factors that are taken into account when comparing practical engine cycles with theoretical ones are as follows. There are: the air and combustion gases in the cylinder are not perfect gases; adiabatic processes are not realised in practice; and instantaneous application and removal of heat energy are practically impossible.