Thermodynamic analysis for a novel chemical precooling turbojet engine based on a multi-stage precooling-compression cycle

Precooling technology is an effective way to improve the flight Mach number for turbojet engine. To solve the problem of engine performance degradation caused by excessive fuel consumption, a multi-stage precooling-compression cycle is newly proposed, in which the secondary cooling capacity of fuel is reused by transfer the heat energy from fuel to the mechanical work. To evaluate the engine performance, several new performance parameters are defined and a thermodynamic model is established, in which the optimum distribution of pressure ratio for each stage of turbine/compressor and the performance limit of engine are derived in theory. By calculation, it is found that the heat absorption capacity of fuel and the engine performance could be improved with the increase of stage number. Further, the lower and upper performance boundaries of engine could be obtained when the stage number is set to one and infinity respectively. Moreover, considering the engineering application, the two-stage precooling-compression cycle will be regarded as the best design, and when the engine performance is improved by about 8.15%, the heat transfer area of pre-cooler will be increased by 88.19%, as well as the mass of compressor and turbine will be increased by 30.33% and 11.18% respectively.