The Performance Characteristics Analysis Of Irreversible Braysson, Diesel And Otto Heat Engine Cycle

In 1997, Frost et al proposed and analyzed the Braysson cycle using the first law of thermodynamics and derived the analytical expressions of the output power, the output power density and efficiency with the isobaric temperature ratio. The numerical example is given to show the influences of thermal conductivity distribution of the heat exchanger at the high-, low-temperature sides and the ratio of the temperature of the working fluid on the optimal performance of output power, the output power density and efficiency. The Braysson cycle is a hybrid gas turbine cycle composed of a conventional Brayton cycle for the high temperature heat addition and an Ericsson cycle for the low temperature heat rejection. Since Braysson heat engine is seldom researched, it is worthy to further analyze its performance of the Braysson heat engine. Diesel engine and Otto engine were the application of a very wide range of heat engine. Some factors of the irreversibilities are considered in the most heat engine model, thus it is also very necessary to establish an more general heat engine model. Based on the above cases in this thesis, the generalized irreversible Braysson heat engine cycle, generalized irreversible Diesel heat engine cycle and generalized irreversible Otto heat engine cycle performance characteristics are studied. By theoretical analysis and numerical calculation, the following works are made.In Chapterâ…¡, on the basis of previous research, the generalized irreversible model of the Braysson heat engine with heat resistance, heat leak and internal irreversibility is established. The performance parameters at the maximum output power, efficiency and ecological function are optimized. The analytical expressions of the optimal output power, efficiency and ecological function are derived. We have calculated the maximum output power, maximum efficiency, maximum ecological function and the corresponding parameter values. Their changes are reflected by the chart. Moreover, the influences of heat leak and internal irreversibility on the performance parameters of the heat engine are discussed and the optimal operating regions of the important parameters are determined. We have obtained that the dimensionless power output at the maximum dimensionless ecological function is smaller than the maximum dimensionless power output, but the efficiency at the maximum dimensionless ecological function is much greater than the efficiency at the maximum dimensionless power output. Taking into account the theme of energy saving and environmental protection, based on the ecological optimization criterion was a more reasonable state of optimal performance about the heat engine optimization.In Chapterâ…¢, based on previous studies of various Diesel heat engine models, the generalized irreversible heat engine cycle model of the air-standard Diesel heat engine with temperature-variable heat capacities, heat leak through the cylinder wall, finite-rate heat transfer, friction loss and the internal irreversibility of non-isentropic adiabatic compression process and non-isentropic adiabatic expansion process is established. The analytic expressions of power output and efficiency of generalized Diesel heat engine are derived. By numerical calculation, we have obtained the maximum output power, maximum efficiency and the corresponding parameter values. We make the graph to reflect their changes. Moreover, the influences of the heat leak, internal irreversibility, temperature-variable heat capacities and friction loss on the performance parameters of the Diesel heat engine are discussed and the optimal operating regions of the important parameters are determined.In Chapterâ…£, we set up the generalized irreversible heat engine cycle model of the air-standard Otto heat engine, which contains finite-rate heat transfer, heat leak loss through the cylinder wall, temperature-variable heat capacities, friction loss and the internal irreversibility. The analytic expressions of the power output and efficiency of generalized Otto heat engine are derived. By comparing the graph of the output power with volume ratio and the efficiency with volume ratio, we have found their optimal operating regions. Moreover, the influences of the heat leak, temperature-variable heat capacities, internal irreversibility and friction loss on the performance parameters of the Otto heat engine are discussed.