Performance comparison between closed-Brayton-cycle power generation systems using supercritical carbon dioxide and helium–xenon mixture at ultra-high turbine inlet temperatures on hypersonic vehicles

Closed-Brayton-cycle (CBC) has considerable potential for power generation on hypersonic vehicles, but its power level is limited by the cold source onboard, commonly the hydrocarbon fuel. To achieve power enhancement of CBC with finite cold source, this study assessed and compared the power output and thermal efficiency of supercritical carbon dioxide (S–CO₂) and helium-xenon mixture (He–Xe) CBCs at ultra-high turbine inlet temperature (TIT), taking into account the thermal cracking of hydrocarbon fuel. Results indicate that raising TIT can significantly increase the electric power output for both CBC working fluids. The electric power under per unit mass flowrate of fuel is as high as 1600 kJ/kg at the TIT of 2000 K, making it easy to achieve megawatt-level power generation. The power enhancement of He–Xe CBC is more significant than S–CO₂ CBC when the TIT exceeds 2000 K. Moreover, the compressor inlet temperatures and cycle pressure of S–CO₂ CBCs are much higher than those of He–Xe CBC, causing additional challenges in the aerodynamic design and component manufacture. Therefore, He–Xe CBC operating at ultra-high TITs may be more suitable than S–CO₂ CBCs for high-power electricity generation mission on hypersonic vehicles.