Simulation Study of a Waste Heat Recovery Cycle With Integrated Ammonia Cracking for Zero Carbon Emissions Aircraft

Decarbonizing aviation requires propulsion systems capable of eliminating onboard carbon emissions while maintaining the performance of modern turbofan engines. This work proposes and evaluates an integrated supercritical CO₂ (sCO₂) waste-heat recovery cycle coupled with an ammonia catalytic cracking system as a viable pathway for enabling ammonia–hydrogen combustion in a LEAP-1B-class turbofan engine. Ammonia is used as a carbon-free hydrogen carrier and thermally decomposed to produce a 50/50 NH₃–H₂ blend with improved flame stability, reduced NOₓ formation, and favorable ignition characteristics. The sCO₂ cycle is designed to extract thermal energy from the turbine exhaust and deliver it to the ammonia preheater, superheater, and cracker, eliminating the need for external heating. A detailed thermodynamic model is developed in Aspen Plus, incorporating experimentally validated Temkin–Pyzhev kinetics for a 3% Ru/2D-boron catalyst. Results show that the integrated cycle supplies sufficient heat to achieve approximately 40–50% ammonia conversion while maintaining realistic pressure and temperature limits. The cracker exhibits strong agreement with experimental data, and sensitivity analyses demonstrate feasible heat-transfer performance within compact exchanger geometries. This integrated system provides a promising route toward zero-carbon aviation, efficiently utilizing onboard waste heat while avoiding the challenges of storing molecular hydrogen.To summarize, this design helps us achieve the zero-carbon emissions goal in aviation while optimizing heat within the engine and helping us avoid the expensive hydrogen storage.