Finite-time thermodynamic modelling and analysis of an irreversible diesel cycle

The performance of an air-standard diesel cycle is analysed using finite-time thermodynamics. An irreversible cycle model which is closer to practice is established. In the model, the non-linear relation between the specific heats of the working fluid and its temperature, the friction loss computed according to the mean velocity of the piston, the internal irreversibility described by using the compression and expansion efficiencies, and the heat transfer loss are considered. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimum relation between the power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of internal irreversibility, heat transfer loss, and friction loss on the cycle performance are analysed. The results obtained herein may provide guidance for the design of practical internal combustion diesel engine.