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| Fig. 1: Liquid Hydrogen being poured from a dewar. (Source: Wikimedia Commons) - This figure dangles. - RBL |
Hydrogen as an energy source has been widely discussed, but it has a number of practical problems including high flammability, high-pressure storage requirements, manufacturing difficulty, and pollution (when derived from non-green sources). However, if we ignore the practical issues of hydrogen storage and safety concerns, we can theoretically understand how much hydrogen we would need to replace jet fuel.
The energy density in terms of mass is 43 MJ/kg for jet fuel and 120 MJ/kg for hydrogen. [1] Which makes hydrogen three times as dense as jet fuel, a seemingly attractive alternative. However, hydrogen needs to be compressed and cooled into a liquid to utilize properly as a fuel source.
Thus we conclude that the volumetric energy density is 32 MJ/L for jet fuel and 8.5 MJ/L for hydrogen. [1] Which now makes hydrogen four times less dense than jet fuel. Another issue now is that hydrogen needs to be compressed at 700 bar and stored at a temperature of around -240°C, which requires cryogenic tanks. [1] Mid-size planes usually house tanks with around 7000 gallons or 26,500 Liters of fuel. [2]
| 26,500 L × | 32 MJ/L 8.5MJ/L |
= | 99,765 Liters H2 |
We need 99,765 liters of hydrogen fuel to attend to the distances a normal commercial mid-size plane might travel.
Under the current conditions of storage conditions for liquid hydrogen, it does not make sense to replace jet fuel with hydrogen. However, it is interesting to imagine an alternative to a highly pollutive energy source currently being tackled. One possible way to combat this issue is to use hydrogen and a waste resource of carbon (agricultural waste) to create jet fuel, making it a net zero-carbon fuel.
© Layaa Amirthalingam. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] K. T. Møller et al., "Hydrogen - A Sustainable Energy Carrier," Prog. Natural Sci. Mater. Int. 27, 34 (2017).
[2] M. Burns and W. M. Cavage, "Ground and Flight Testing of a Boeing 737 Center Wing Fuel Tank Inerted With Nitrogen-Enriched Air," U.S. Federal Aviation Administration, DOT/FAA-AR-01/63, August 2001.
