COMPARATIVE THERMODYNAMIC STUDY OF AIR STANDARD CYCLES WITH HEAT TRANSFER AND VARIABLE SPECIFIC HEATS OF THE WORKING FLUID

In this paper, finite-time thermodynamics, a powerful thermomechanics method, is applied to analyze the performance of the three standard thermodynamic air cycles, i.e. the Atkinson cycle, Diesel cycle and Otto cycle. Since the large temperature difference exists in the practical cycles, the constant specific heat assumption is not valid in this state. Therefore a polynomial function of the temperature is implemented for the specific heat with constant pressure. Herein, we examine the results of both the constant and variable specific heat cases in the presence of internal irreversibility. We also consider the heat-transfer loss and friction loss between the working fluid and the cylinder wall. The relations between the power output and cycle efficiency versus compression ratio, and also the optimal relation between the power output and the efficiency of the cycles are presented. The effects of the minimum and maximum temperature of the cycle variation on the power output and the cycle efficiencies are checked. The results of this paper may provide guidance for the design of practical internal-combustion engines by selecting the optimal cycle for the desired use.

Otto cycle, Atkinson cycle, Diesel cycle, Finite-time thermodynamics, Internal irreversibility, Variable specific heat, Heat transfer irreversibility, Combustion engines