Liquid hydrogen fuel is considered to be the most promising alternative to conventional kerosene based fuels for eliminating CO2 emissions in aviation. However, liquid hydrogen carries many challenges that need to be addressed before proper introduction into the market can be established. One of the main challenges is the extremely low temperature that is associated with the storage method. This requires a complete reconsideration of the design of fuel systems for liquid aircraft, along with their components.
This thesis provides three concepts for aircraft gas turbine LH2 fuel systems, based on existing and proposed fuel systems that have been encountered in literature for LH2 aircraft. Numerical fluid dynamic models have been generated in MATLAB & Simulink for each fuel system concept, using the Simscape Fluids library. Models have been generated for the storage tanks including pressure control systems, lowpressure boost pumps, transfer lines, high pressure fuel pumps, heat exchangers and controlled fuel metering valves. The first model, the basic fuel system, feeds all discharge fuel from the fuel pump directly to the heat exchanger. The second concept, the bypass flow system, includes a bypass flow separation downstream of the fuel pump, splitting into ametered flow stream to the injectors, and a bypass flow stream which is recirculated back to the fuel pump inlet. The third concept, the boost-pump-fed system, feeds the fuel from the boost pumps to the heat exchanger directly, allowing for the omission of the engine pump. This configuration was found to require three scaled boost pumps in series, to generate sufficient pressure gain upstream of the engine fuel system.
The results showed that the basic fuel system and the boost-pump-fed system provided feasible designs in terms of the power requirements of the pumps, the pressure drops in the pipes, and the performance of the heat exchanger. The bypass flow system provided a slight increase in engine pump efficiency at lower power settings, providing a possible longer lifetime of the pump. The basic system configuration benefitted from a lower total power requirement, and a higher net positive suction pressure at the pump inlet. The third configuration revealed very high power requirements due to the inefficiency of the scaling of the pumps. Finally, the metering response and accuracy was found to be highly satisfactory.
Finally, pressure control systems of the tank provided satisfactory control of fluid pressure within its boundaries for all configurations. Furthermore, the heat exchanger provided the desired target fluid temperature rise, required for efficient combustion.
Further in-depth modelling of components within the fuel systems is recommended, along with more in-depth validation when experimental data becomes available. In the future, the model can be used for further exploration for designing innovative concepts for fuel distribution, thermal management and metering systems in the LH2 fuel system.