Exhaust Heat Recovery for Cryogenic Hydrogen-Powered Aircraft: From Conceptual Design to Experimental Validation

• Experimentally confirm engine exhaust heat recovery of cryogenic hydrogen aircraft. • The coupling of heat exchange and engine thrust is firstly revealed. • Exhaust heat recovery heats cryogenic hydrogen above 189K. • The heat exchanger causes up to 16.7% engine thrust loss. • Frost prevention and thrust decay mitigation should be focused on the future. Cryogenic hydrogen aircrafts are a critical pathway toward carbon neutrality for the aviation industry; however, the low volumetric energy density of hydrogen hinders their development. Exhaust heat recovery for cryogenic hydrogen heating is considered a promising approach towards higher energy efficiency; however, it lacks experimental validation. Herein, we validate the feasibility of recovering engine exhaust to heat liquid hydrogen through systematic experimentation and provide the first quantitative evaluation of the impact of heat recovery on engine thrust performance. Using thermodynamic analysis of a hydrogen-fueled aircraft engine, it is demonstrated that exhaust heat recovery can heat cryogenic hydrogen from 30 to 250 K while maintaining thrust losses below 0.74%, thereby theoretically validating the concept. Subsequently, a heat exchange test rig was constructed to verify the exhaust heat recovery and experimentally investigate the impact of the technology on engine thrust performance. The experiments were conducted under the idle, takeoff, and cruise conditions of the engine, achieving heat-transfer capacities of 9.89, 25.5, and 29.5 kW, respectively. Exhaust heat recovery can heat hydrogen to temperatures beyond 189 K, exceeding the minimum temperature requirement for a combustor (150 K). Additionally, the flow resistance of the heat exchanger causes exhaust flow deceleration, resulted in a significant 16.7% thrust reduction. Hence, this study experimentally confirms the feasibility of exhaust heat recovery for cryogenic hydrogen aircraft, identifies existing challenges, and provides a clear direction for future development.