Impact of Fuel Conditioning and Combustor Injection Temperature on a Hydrogen Turboprop

Abstract Reducing aviation emissions demands revolutionary propulsive technologies and gaseous hydrogen (H2) combustion offers high potential. However, using this fuel in aero engines requires complex fuel conditioning systems. Cryogenic liquid hydrogen stored in aircraft tanks must be warmed to an adequate temperature for injection in the combustor. Recuperating gas turbine heat via a heat exchanger around the exhaust conditions the fuel without hindering engine performance. This article examines the impact of combustor injection temperature of gaseous hydrogen on the performance of an H2-burn turboprop for a short-range subsonic application. Multipoint design and off-design modelling of the advanced hydrogen cycle enable identification of critical conditions in different phases of flight. Different control strategies were used to evaluate trade-offs between engine specific fuel consumption (SFC), weight and fuel system complexity. To maintain aircraft performance, combustor fuel injection temperatures must be low. Analyses show that at injection temperatures of 400 K, even with a low pressure drop in the engine nozzle, the engine weight increases by 2.5% over a 200 K baseline. Without an integrated heat exchanger, the engine needs to be upsized by 1.8%, 4%, and 9.9% for injection temperatures of 100 K, 200 K, and 400 K, respectively, increasing SFC by 3.7%, 8.6%, and 21%. However, low fuel injection temperatures can cause water around the burner to freeze and reduce fuel injection velocity, leading to flame stability issues. This research emphasises the need to define feasible fuel injection temperatures and velocities, while aiding fuel conditioning optimisation for future H2 aircraft, affecting fuel burn.