Performance of an Ammonia Turbofan With the Inclusion of an Optimized Bleed Air Heat Exchanger

Abstract

Abstract. With the push for decarbonization in aviation, Ammonia has emerged as a promising fuel source due to its well-established production methods, defined transportation infrastructure, and higher volumetric energy density compared to pure liquid hydrogen. However, the slow kinetics and low flame speeds of ammonia combustion require the introduction of a hydrogen promoter. Hydrogen is attained through in-flight ammonia cracking. Toward this, heat is extracted from the cooling air (CA) taken from the high-pressure compressor using an entropy-optimized tube bank heat exchanger. The impact of the tube bank on the ammonia-powered turbofan is analyzed through tmats together with cantera in simulink. This study specifically investigates the impact of the cooled cooling air (CCA) on turbine cooling requirements, and consequently, the overall turbofan performance. Key performance metrics, such as thrust specific fuel consumption and thermal efficiency, are compared across three scenarios: a typical kerosene engine, an ammonia engine, and a “split-flow,” ammonia engine all with impact from the CCA. It is shown that CA lacks sufficient heat for ammonia cracking. To reduce the cracking heat, catalyst-dependent optimization is performed. The aim is to adjust the required cracking efficiency to achieve the desired fuel blend while minimizing additional cracking heat requirements. This involves splitting ammonia into two streams—one to be cracked and the other to bypass the heat exchanger. Ru-K/CaO is considered for high-pressure ammonia cracking and the Leap 1b as a reference turbofan.