Study on feasible boundary of heat and work for turbojet engine thermal management system in high-speed aircraft

The thermal load and electrical demand in a turbojet engine accessory compartment increase with flight Mach number, requiring the Thermal Management System (TMS) to address waste heat and electricity generation. This paper proposes a method to determine the feasible boundary of removed waste heat and electricity generation for turbojet engine TMS in high-speed aircraft. The method is demonstrated on two architectures: TMS1 is the baseline architecture without the AARHX, while TMS2 is the enhanced architecture with the AARHX. System models are established for flight environment, engine fuel consumption, and TMS components. At an altitude of 20 km and Mach 0 to 5, feasible boundaries are obtained by NSGA-II under temperature, fuel penalty, and installation space constraints. The results show that TMS1 achieves the maximum feasible Mach number of 3.5 with a peak heat removal capacity of 275 kW at Mach 2.5. Beyond Mach 2.5 aerodynamic heating increases the ram air temperature, reducing the heat transfer temperature difference and decreasing the waste heat removal capacity. TMS2 extends the feasible range to Mach 5 and increases the peak heat removal capacity to 425 kW at Mach 2.5 because the AARHX recovers exhaust cooling to lower inlet air temperature. At Mach 3.5, TMS2 removes 250 kW of waste heat, five times that of TMS1, and generates 214.8 kW of electricity, compared to 81.3 kW for TMS1. The proposed method shifts conventional single-point optimization to system level feasible boundary analysis, enabling quantitative evaluation and comparison of TMS architectures across the flight envelope.