Diesel Cycle

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.

Pressure-volume and Temperature-entropy diagram for the air-standard Diesel cycle

Pressure-volume and Temperature-entropy diagram for the air-standard Diesel cycle

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

Thermal efficiency:

Diesel cycle Thermal efficiency
Thermal efficiency equation for diesel cycle

Where, Compression ratio = rk = v1/v2 ,
Expansion ratio = re = v4/v3 ,
Cut off ratio = rcv3/v2 .
 

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.

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