Analysis of NH3 Powered Turbofan Engine With sCO2 Waste Heat Recovery System

This is the authors' abstract. We don't add key points for this paper.

In the search for alternative aviation fuels, ammonia shows much promise. The higher density and boiling point of ammonia compared to hydrogen could mean ammonia could be used without a dramatic rethinking of aircraft architecture. Instead, the possibility exists that current aircraft and engines could be retrofitted to use ammonia instead of traditional jet fuel. This paper aims to address the engine aspect of such a retrofit. The open-source Toolbox for Modeling and Analysis of Thermodynamic Systems (T-MATS) is modified to allow for the modeling of ammonia fueled engines and the addition of heat exchangers and other technologies. A thermodynamic cycle model of a baseline ammonia engine is created retaining the turbomachinery maps, duct sizes, nozzle areas, and bleed flow rates from a kerosene engine. This engine is then modified by adding heat exchangers and a supercritical CO2 waste heat recovery (WHR) cycle to produce power for the engine and aid in the preheating of the ammonia. Preliminary analysis is performed to determine the ideal location of heat exchangers to benefit cycle efficiency. This analysis suggests that using the ammonia as a heat sink to intercool and recuperate the engine allows for significant improvements over baseline performance. From there, optimization of the geometry of the added heat exchangers is performed to limit heat exchanger size and minimize engine fuel consumption at cruise. The addition of these heat exchangers allows for a reduction in fuel burn of 3%–9% over the baseline engine. Additionally, the WHR cycle can produce the required 250 horsepower (186 kW) of electrical power for the aircraft and the ammonia temperature is increased from 420°R to over 1400°R (233K to 778K). Investigating the results of the optimization shows that making more substantial changes to engines could allow for further improvements to engine performance past that of a retrofit.