The air-standard diesel cycle is shown on p-V and T-s diagrams respectively. This is the ideal cycle for the diesel engine, which is also called the compression ignition engine.
This cycle consists of two reversible adiabatic, one reversible isobar and one reversible isochoric process.
Basic processes in diesel cycle
1-2; Reversible adiabatic compression
2-3: Constant pressure heat addition
3-4: Reversible adiabatic expansion
4-1: Constant volume heat rejection
The normal range of compression ratio for diesel cycle is 16 to 20 whereas for spark-ignition engines it is 6 to 10, due to high compression ratios used in diesel engines the efficiency of a diesel engine is more than that of a gasoline engine.