Finite-Time Thermodynamic Analysis of An Irreversible Diesel-Cycle With a Variable Specific Heat Ratio of Working Fluids

An irreversible Diesel-cycle model using finite-time thermodynamic analysis is presented. Multiple irreversibilities were considered including finite rate heat transfer, heat leakage between working fluids, friction loss between the piston and cylinder wall, and the specific heats of working fluids are a function of temperature. Also, the work fluid is referred to as the fuel-air mixture gas making the presented results more compatible with practical situations. The results show that the power out first increases with an increased compression ratio, and then begins decreasing when the compression ratio exceeds a certain value. A higher air-fuel ratio indicates a lower power output and reduced thermal efficiency. Furthermore, the power output is optimized with respect to the cycle temperatures for a typical set of operating conditions using a genetic algorithm approach. The results can be helpful in the designing and evaluating the performance of practical Diesel engines.