Supercritical CO2 Waste Heat Recovery for Enhanced Efficiency in Ammonia Cracked Hydrogen Turbofan Engines

Abstract This study aims to reduce CO2 emissions by replacing conventional Jet A fuel with ammonia-cracked hydrogen in a modified turbofan engine. The thermodynamic processes involved in ammonia cracking are analyzed, with liquid ammonia onboard being cracked into hydrogen before entering the combustion chamber. The sCO2 cycle is introduced as a secondary power generation method, where heat extracted from the engine exhaust is transferred to a sCO2 loop, providing additional power while minimizing the heat lost to the environment. The simulation of the sCO2 cycle is carried out using Simcenter Amesim, a robust system simulation tool capable of evaluating both steady-state and transient behavior. In addition to steady-state analysis, transient simulations will provide deeper insights into the performance and capabilities of the sCO2 cycle under varying conditions. The heat exchangers in the sCO2 system capture waste heat from the exhaust stream, lowering the required fuel input to a given thrust level and thus reducing fuel consumption. A 4% total pressure drop is assumed due to the heat exchange process in the flow path. The energy extraction after the LPT impacts the cycle performance due to the associated pressure and temperature losses. However, by heating the fuel more, more energy needs to be taken out of the exhaust flow. Still, on the other hand, less fuel will be required to achieve a certain combustor outlet temperature, thereby providing performance benefits. Overall, the study evaluates the impact of energy extraction on engine performance and identifies the optimal thermal conditions for ammonia cracking and sCO2 cycle integration. This hybrid system proposes a sustainable alternative to conventional Jet A fuel, contributing to aviation’s decarbonization goals.