Cryogenic pumping of liquid hydrogen for aerospace propulsion

Hydrogen fuelled propulsion systems are key to enabling sustainable flight. Efficient conveyance of the hydrogen from the storage tank to the propulsor is critical when realising a successful system. Different propulsion architectures that can be powered with hydrogen include Proton Exchange Membrane Fuel Cells, Hydrogen-Electric hybrid power trains, and Hydrogen combustors. Regardless of the propulsion technology, the hydrogen will likely be stored as a liquid (LH2) and pumped accordingly. The most suitable pump system required to distribute the LH2 will be dependent on the delivery requirements for the propulsor and the aircraft mission.
This review identifies the state-of-the art in pumping cryogenic fluids, specifically LH2. Pumping LH2 presents a significant engineering challenge when considering the low viscosity, small molecule size, and low boiling point of hydrogen. The review is considered regarding three Case Study missions of different aircraft operating with different requirements: urban air mobility, regional propeller aircraft, and long-haul hydrogen combustion. These Case Studies have been modelled under different operational conditions to derive different pump specifications. The three operational ranges required have then been used to develop initial sizes of given pump architectures. This pump sizing was then critiqued using Figures of Merit (FoM) for pump down selection based on initial design calculations. Following a weighted down selection process, pump architectures for the three Case Studies were recommended. Further consideration was given to the electrical motor coupling and drive mechanism for the fluid-mechanical components. Finally, remaining gaps in the literature are identified which must be investigated in order for long-term solutions for LH2 pumping technologies to be developed.