Maximum thermal efficiency of a Diesel cycle

Description

The Diesel cycle is a combustion process of a reciprocating internal combustion engine. In it, fuel is ignited by heat generated by compressing air in the combustion chamber, into which fuel is injected. This is in contrast to igniting it with a spark plug as in the Otto cycle (four-stroke/petrol) engine. Diesel engines (heat engines using the Diesel cycle) are used in automobiles, power generation, diesel-electric locomotives, and submarines. The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber of the diesel engine. The constant pressure adiabatic flame temperature is the temperature that results from a complete combustion process that occurs without any heat transfer or changes in kinetic or potential energy. For the constant pressure adiabatic process, while combustion is occurring the piston is moving in order to keep the pressure constant. The maximum thermal efficiency of a Diesel cycle is dependent on the compression ratio and the cut-off ratio (ratio between the end and start volume for the combustion phase).

Related formulas

Variables

nthThermal efficiency (dimensionless)
CRThe compression ratio V1/V2 (dimensionless)
γThe ratio of specific heats Cp/Cv (dimensionless)
aThe cut-off ratio V3/V2 (ratio between the end and start volume for the combustion phase) (dimensionless)