The effects of variable specific heats of working fluid on the performance of an irreversible Otto cycle

The performance of an air-standard Otto cycle with variable specific heats of working fluid and heat resistance and friction irreversible losses is analysed by using finite-time thermodynamics. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of variable specific heats of working fluid on the irreversible cycle performance are analysed. The results show that the effects of variable specific heats of working fluid on the cycle performance are obvious, and it should be considered in practice cycle analysis. The results obtained in this paper may provide guidance for the design of practice internal combustion engines.