Computational Fluid Dynamics simulations are performed to investigate the effect of relevant parameters on the temperature field during the filling process of hydrogen tanks. The injector direction, the injector diameter, and the initial/ambient temperature affect the dynamics of the temperature distribution in the gas and in the tank material during the process. The development of potentially detrimental phenomena like thermal stratification and temperature inhomogeneity could occur, depending on the interactions of the effects of the 3 parameters. One of the most relevant findings is that, depending also on the other conditions, the injector direction can have a significant impact on the thermal stratification and on the critical parameters which provide an indication on the occurrence of stratification like the flow velocity at the injector exit and the Richardson number. The upward direction of the injector contributes to completely avert or at least reduce/delay the thermal gas stratification compared to injectors with a straight or downward direction. (C) 2019 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.