Insulation Design for Liquid Cryogenic Hydrogen Fuel Tanks for Hydrogen Powered Aircraft

The use of liquid hydrogen as a fuel for aircraft requires containment within liquid cryogenic fuel tanks. Proper insulation needs to be designed to decrease boil-off of liquid hydrogen due to heat transfer into the tank. A one-dimensional steady-state heat transfer model with an electric circuit analogy is developed to calculate insulation thickness and weight based on boil-off rate for spherical and hemisphere capped cylindrical tank geometries located in the fuselage of Boeing 737 and 767 aircraft. Three insulation types - MLI, EPS, and Glass Bubbles - are compared. Comparison with existing literature shows that the boil-off rate of the liquid hydrogen in internal aircraft tanks is lower than in tanks mounted externally. For tanks located inside the fuselage of the aircraft, the on-ground idle conditions of the liquid hydrogen fuel tank represents the limiting case. Based on the results at 50% of idle fuel usage rate, it is shown that the spherical and cylindrical tanks should be designed with EPS insulation thicknesses of 1.19 in and 5.55 inches, respectively. Additionally, a new model based on the insulation techniques developed at NASA was created which accurately predicted the required insulation thickness for large on-ground spherical liquid cryogenic hydrogen tanks.