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Liquid hydrogen could become the fuel for some future aircraft, such as the concept pictured. For liquid hydrogen, the tanks would be fuselage-installed and designed to maintain a cryogenic environment. The EnableH2 project received funding from the European Union’s Horizon 2020 research and innovation program.
With ongoing research into liquid hydrogen as a sustainable aviation fuel for a zero-emission future, fuel tank design would have to undergo considerable changes.
“This will be quite a different system that must be integrated into the aircraft to provide the required safety, light weight and the capacity for the sufficient amount of hydrogen for the distance the aircraft is expected to travel,” says Krzysztof Koziol, professor of composites engineering and head of Cranfield University’s Composites and Advanced Materials Center. The differences he cites include tank location in the fuselage—instead of the wings as with fossil fuel systems—along with tank operations at temperatures as low as -253C (-423F).
Koziol stresses there are some design challenges. For one, he explains that hydrogen is a very small molecule that can diffuse even through a metal matrix.
“At Cranfield, we are developing a composite system which will have significantly reduced hydrogen permeability,” he explains. “With the challenges related to cryogenic environment operations, we are looking at a new class of materials which can help us to minimize the heat exchange with the external to the tank environment, to keep the hydrogen at safe pressure levels and to minimize the energy required to maintain the low temperature.”
As for crash resistance, Koziol reports that Cranfield is incorporating a glass fiber composite layer to protect the tank from surface abrasion and impact. However, that will be subject to a series of tests to validate its capability to withstand impact. “Here we are looking for a high-temperature-stability top composite layer,” he says.
Koziol adds that while aircraft-grade liquid hydrogen fuel tanks will use a lighter-weight material than the heavy austenitic steel used to fabricate existing ground liquid hydrogen tanks, he is not sure if the new-generation liquid hydrogen tanks will be lighter than those currently used on aircraft. “The general aim is to reduce their weight as much as we can without compromising safety,” he says.
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