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To solve the problem of engine performance degradation caused by excessive fuel consumption in the precooled engine cycle, a new optimization method based on the cascade utilization of cold source is proposed, in which the cold sources with different temperature ranges and different working fluids are reasonably matched and adequately utilized. Based on this method, two new optimization cycles are put forward, i.e., the air reheat precooling cycle (ARPC) and the hydrogen reheat precooling cycle (HRPC). To evaluate the performances of these two cycles, a unified model is established. According to the simulation results, the fuel consumption of the HRPC could be reduced by 0–21.04% compared with the traditional precooled engine. Besides, the specific impulse of the HRPC, which can be raised by 16.78% when the heat transfer effectiveness is set to 0.9, is higher than that of the ARPC, which can be increased by 12.64% at most. Moreover, considering the operating constraints, the reduction of the minimum temperature difference of the regenerator and the increase of the pressure recovery coefficient of intake are effective ways to expand the performance boundaries. The results in this paper are beneficial for the performance optimization of the precooled engine cycle. • Cascade using of cold source is proposed to improve performance of precooled cycle. • Two new cycles are put forward based on the proposed optimization method. • The optimized cycles can dramatically improve specific impulse of precooled engine. • The optimized cycles can greatly reduce synthesis difficulty of precooled engine. • Future research directions and potential applications are summarized. [ABSTRACT FROM AUTHOR]

• Fuel indirect precooled engine is promising for greener and faster air propulsion. • Closed Brayton cycle based precooling-compression system is the core of the engine. • Entropy minimization of the system coupled with heat exchanger design is performed. • Trade-off feature observed between heat exchanger mass/size and entropy generation. • Criteria suggested for parameter selection and design of heat exchangers and cycle. 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. [ABSTRACT FROM AUTHOR]

Indirect precooled engine (IPE) is a promising power for single-stage-to-orbit (SSTO) and the booster stage of a two-stage-to-orbit (TSTO) vehicles. Thrust of IPE is realized the most decisive factor that affects vehicle mission performance; therefore it is particularly critical to ensure that the engine can fully exert its thrust performance through active control since the flight parameters will change substantially alongside the trajectory. On account of this, control law of maximizing thrust for a single branch IPE is developed in current study. To this end, a high-fidelity off-design model of IPE is constructed to evaluate how engine performance is regulated by the various changeable parameters. The results indicate that engine thrust and specific impulse are functions of total fuel mass flow, nozzle throat area and the temperatures of preburner and main combustor, which can be conveniently controlled in real engines by actuators or changing the related fuel mass flow through fuel valves. Based on the influence characteristics revealed, the maximum thrust control law of the engine is synthetized, with the range of engine thrust can be regulated along a representative flying trajectory is evaluated. The results may provide some useful guidance about performance control of IPE with complex multi-branch intermediate cycles. • High-fidelity off-design model for single branch IPC engine developed for analysis. • Main characteristics of IPC engine under off-design conditions are revealed. • Control strategy of maximum thrust state of the engine is designed. • Thrust adjustment boundary and performance in typical mission trajectory evaluated. [ABSTRACT FROM AUTHOR]