Numerical Simulation and Experiments of Hydrogen Diffusion Behaviour for Fuel Cell Electric Vehicle

Research was conducted on hydrogen diffusion behaviour to construct a simulation method for hydrogen leaks into complexly shaped spaces such as around the hydrogen tank of a fuel cell electric vehicle (FCEV). To accurately calculate the hydrogen concentration distribution in the vehicle underfloor space, it is necessary to take into account the effects of hydrogen mixing and diffusion due to turbulence. The turbulence phenomena that occur in the event that hydrogen leaks into the vehicle underfloor space were classified into the three elements of jet flow, wake flow, and wall turbulence. Experiments were conducted for each turbulence element to visualize the flows, and the hydrogen concentration distributions were measured. These experimental values were then compared with calculated values to determine the calculation method for each turbulence phenomenon. Accurate calculations could be performed by using the k-ω Shear Stress Transport (SST) model for the turbulence model in the jet flow calculations, and the Reynolds Stress Model (RSM) in the wall turbulence calculations. In addition, it was found that the large fluctuations produced by wake flow can be expressed by unsteady state calculations with the steady state calculation solutions as the initial values. Based on the above information, simulations of hydrogen spouting were conducted for the space around the hydrogen tank of an FCEV. The hydrogen concentration calculation results matched closely with the experimental values, which verified that accurate calculations can be performed even for the complex shapes of an FCEV.