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.