Minimization of entropy generation of a closed Brayton cycle based precooling-compression system for advanced hypersonic airbreathing engine

Fuel indirect precooled engines have the potential to radically reform the paradigm of propulsion for next generation in- and trans-atmospheric vehicles. The engine is characterized by a sophisticated thermodynamic cycle with a series of heat exchangers. Reducing irreversibility of the precooling-compression system (PCS) is the key to ensure high engine performance, for which a conjugated optimization coupled with heat exchanger design was performed to evaluate the performance level that can be achieved under the state of technologies. The results indicate that irreversibility of the PCS can be reduced but at the penalty of heavier and larger size of heat exchangers. Moreover, it shows that precooler and regenerator together contributes 75–84% of the total entropy generation rate within the PCS, while hydrogen pump occupies the second largest irreversibility source. Smaller precooling temperature can help to improve the extent of irreversibility of the PCS and increase the maximum achievable air pressure ratio and engine specific thrust, nevertheless the increased fuel consumption and air side pressure drop and the decreased engine specific impulse shouldn't be ignored. Larger regenerator effectiveness is preferred from all aspects of the PCS and engine level figures of merit as long as the total weight and length of the heat exchangers are not increased aggressively.