Investigation of Ammonia Fed SOFCC-GT Hybrid System for Commercial Aviation

Griffin Layhew, September 17, 2024

Carbon emissions can be reduced in the aviation industry with the introduction of electric aircraft and hybridization of existing architecture. A hybrid electric mixed turbofan using ammonia fueled SOFCC-GT could eliminate all carbon emissions while still being able to meet the thrust and power demanded by commercial aircraft for domestic applications. Ammonia was chosen as a carbonless fuel due to its higher volumetric energy density than hydrogen (~1.5x higher), though it lacks in specific energy density compared to hydrogen (~6x less). This higher volumetric energy density, as well as its less restrictive storage solutions, makes ammonia a reasonable candidate for carbonless electric aviation. Though ammonia is considered a candidate fuel, it also has its own operational and safety risks. Ammonia decomposition, called cracking, is an endothermic process requiring external heat to break down into nitrogen and hydrogen that the fuel cells use to generate electrical power. Though the fuel cell’s environment is hospitable for ammonia to crack due to the high operational temperature (750 ºC), as well as catalysts in the ceramic structure, this endothermic reaction could cause a sizable temperature gradient to form along the ceramic tubes, which in turn could result in structural damage to the cell. To mitigate this issue, the ammonia in this system is cracked using the turbine’s exhaust. This recuperation also has the added benefit of increasing system efficiency. Size, weight, and power (SWaP) analysis was integrated with aerodynamics and electrical disciplines to aid in choosing the ideal design from a design space that meets the criteria and requirements for a commercial aircraft. Dynamic models have shown that this hybrid system is able to dynamically react to a given thrust profile, while being able to reduce emissions with increased system efficiencies.