Analysis of energy cascade utilization in the chemically precooled engine cycle from a perspective of indirect combustion

Chemically precooled engine has the potential to raise the flight speed and reduce fuel consumption for next generation hypersonic vehicle. Revealing the mechanism of chemical energy cascade utilization of fuel is the key to guide the design of chemical precooling process and ensure high engine performance, for which the studies about the cascade release of fuel energy level in the indirect combustion process have been performed to evaluate the performance level that can be achieved. The results indicate that there is an optimum relative performance gain of indirect combustion with each fuel, where the ammonia has the highest relative gain of 35%. Further, considering both the heat absorption capacity and calorific value of fuel, a dual fuel solution with ammonia and n-decane is the best precooling method. Besides, increasing the fuel cracking rate is helpful to reduce the energy level loss in the whole energy release process. Moreover, the exergy loss of indirect combustion is 36.13% lower than that of direct combustion. Finally, except for combustors, the exergy losses of nozzle and pre-cooler are larger than other engine components, reaching 8.21% and 5.99% respectively. Overall, the results in this paper are beneficial for developing high performance hypersonic engines.