Finite-time thermodynamic modeling and analysis for an irreversible Dual cycle

The performance of an air standard Dual cycle is analyzed by using finite-time thermodynamics. An irreversible Dual cycle model which is more close to practice is established. In the model, the nonlinear relation between the specific heats of working fluid and its temperature, the frictional loss computed according to the mean velocity of the piston, the internal irreversibility described by using the compression and expansion efficiencies, and heat transfer loss are considered. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, and the optimal relation between power output and the efficiency of the Dual cycle are derived by detailed numerical examples. Moreover, the effects of internal irreversibility, heat transfer loss, frictional loss and pressure ratio on the cycle performance are analyzed. The power output versus compression ratio and efficiency versus compression ratio curves of the Diesel and Otto cycles are the maximum and minimum envelope lines of the performance of the Dual cycle, respectively. The results obtained herein may provide guidelines for the design of practical internal combustion engines.