ANALYSIS OF PERFORMANCE OF AMMONIA AIR-BREATHING VARIABLE CYCLE ENGINE

In response to the demand of air-breathing power for wide-range aircraft with flight Mach number 0 ~ 10, a wide-range air-breathing variable cycle engine using ammonia as the fuel and coolant is proposed in the research. There are three working modes: turbine mode, pre-cooling mode and ramjet mode. Firstly, the feasibility of the engine at Mach 0 ~ 10 was preliminarily verified by modeling the thermodynamic cycle process of each mode and calculating the performance parameters such as specific thrust, specific impulse and total efficiency. Then, methane and decane were selected as the typical representatives of low temperature and low density and kerosene hydrocarbon fuels, and the performance of the engines fueled by ammonia and hydrocarbon fuels in turbine mode, pre-cooling mode and ramjet mode were comprehensively compared. The results show that due to the outstanding equivalent total heat sink and equivalent heat value of ammonia, the performance of it in the pre-cooling mode at Mach 3 ~ 5 is better than that of hydrocarbon fuels. In turbine mode and ramjet mode, the specific impulse of the engine using ammonia as the fuel is lower, but the specific thrust and total efficiency are better than that of hydrocarbon fuels. In the end, the operating characteristics of various fuels at Mach 0 ~ 10 were compared and analyzed, it shows that ammonia precooling can significantly improve engine performance in terms of wide-range operating characteristics, especially in the high Mach number, when ammonia is thermally decomposed into hydrogen and nitrogen in the regenerative cooling channel on the combustion chamber wall, the specific thrust and specific impulse of the engine will be further improved. And using ammonia as the coolant will not block the cooling channel, so it can meet the wide-range flight requirements of Mach 0 ~ 10. Kerosene hydrocarbon fuel is limited by low specific thrust and pyrolysis coking problems, and generally the maximum working Mach number does not exceed 8. In conclusion, the air-breathing variable cycle engine using ammonia as the fuel proposed in this paper has excellent equivalent cooling capacity and specific thrust index, and is suitable for applications such as the primary power of the two-stage orbiting vehicle, high Mach number air-breathing flight and future hypersonic civil aviation.