Enabling Cryogenic Hydrogen-Based CO2-Free Air Transport: Meeting the demands of zero carbon aviation

Flightpath 2050 from the European Union (EU) sets ambitious targets for reducing the emissions from civil aviation that contribute to climate change. Relative to aircraft in service in year 2000, new aircraft in 2050 are to reduce CO
₂
emissions by 75% and nitrogen oxide (NOx) emissions by 90% per passenger kilometer flown. While significant improvements in asset management and aircraft and propulsion-system efficiency and are foreseen, it is recognized that the Flightpath 2050 targets will not be met with conventional jet fuel. Furthermore, demands are growing for civil aviation to target zero carbon emissions in line with other transportation sectors rather than relying on offsetting to achieve “net zero.” A more thorough and rapid greening of the industry is seen to be needed to avoid the potential economic and social damage that would follow from constraining air travel. This requires a paradigm shift in propulsion technologies. Two technologies with potential for radical decarbonization are hydrogen and electrification. Hydrogen in some form seems an inevitable solution for a fully sustainable aviation future. It may be used directly as a fuel or combined with carbon from direct air capture of CO
₂
or other renewable carbon sources, to synthesize drop-in replacement jet fuels for existing aircraft and engines. As a fuel, pure hydrogen can be provided as a compressed gas, but the weight of the storage bottles limits the practical aircraft ranges to just a few times that is achievable with battery power. For longer ranges, the fuel needs to be stored at lower pressures in much lighter tanks in the form of cryogenic liquid hydrogen (LH
₂
).