Ammonia energy storage for hybrid electric aircraft

Abstract

This work considers the development of a hybrid electric vertical takeoff and landing aircraft with an NH3 engine. An NH3 cracker with an external heat supply from the engine and a high-temperature catalytic reactor is needed to crack part of the NH3 in H2 and N2. The engine has two turbochargers in cascade, an intercooler, and an SCR catalyst with additional NH3 injection before the catalyst to control emissions. The H2 is used to ignite an NH3 mixture which may also be enriched with hydrogen to address particularly slow-burning points. The proposed learn burn engine which features direct injection and jet ignition of H2 may have power densities above 100 kW per liter and fuel conversion efficiencies approaching 50%. This engine can be further specialized to work on a narrow range of speeds and loads, ideally, one single point, to produce electricity on board the aircraft. The energy storage per unit mass of the complete system is expected to reduce vs. diesel but not dramatically. Importantly, it is much better than the storage of energy in a battery.