Performance analysis of a scramjet engine thermoelectric conversion system using the SCO₂ closed Brayton cycle

This study presents a thermoelectric conversion system (TCS) for a scramjet engine, based on the supercritical carbon dioxide (SCO₂) closed Brayton cycle (CBC). A coupled model is developed, integrating the scramjet engine's combustion chamber, wall cooling channels, and the SCO₂ CBC. The system's performance is analyzed under a free-stream Mach number of 7.7, with compressor outlet pressure (p_C,out) varying from 17.5 MPa to 30 MPa, while considering the impact of working fluid mass flow rate (m) and recompression split ratio (x_RC). The results indicate that there are crossover points in the performance between the regenerative CBC (Reg.CBC) and recompression CBC (Rec.CBC) as p_C,out varies. Specifically, when p_C,out is below a certain threshold, the Reg.CBC performs better, while the Rec.CBC achieves superior performance when p_C,out exceeds this value. Within the parameter range studied, the optimal performance for the Reg.CBC corresponds to a thermal efficiency (η_th) of 32.33 %, net power (P_net) of 492.01 kW, and cooling fuel mass flow rate (m_fc) of 0.490 kg/s. The optimal performance for the Rec.CBC corresponds to a η_th of 35.65 %, P_net of 541.12 kW, and m_fc of 0.471 kg/s.