Analysis of back-gas behaviour of an automotive liquid hydrogen storage system during refilling at the filling station

While refuelling liquid hydrogen storage systems using current technology a certain amount of gas evaporates and is transferred back to the filling station. This so-called back-gas contributes significantly to a deterioration of the overall energy balance of liquid hydrogen as a fuel for automobiles. Based on data gained from dedicated measurements of a current prototype tank system the thermodynamic state of the filled hydrogen was varied. It could be confirmed that a minimum amount of back-gas can be reached if the temperature of the transferred liquid is more than 2 K below the boiling temperature. Moreover, the data prove that the reason for the production of back-gas is not so much flashing but evaporation due to heat in-leak into the filling line. Based on these data an optimised filling procedure for automotive liquid hydrogen storage systems shall be defined. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.