Experimental and simulation study on hydrogen diffusion and venting inside a container carrying fuel cell vehicles

Hydrogen safety for fuel cell vehicles (FCVs) should not be limited to their use process and accident scenarios. Their transportation should be a typical scenario, since it is an enclosed space and the carried vehicle has few failures. In this study, the path of hydrogen diffusion and the effect of hydrogen venting during the container transportation have been explored. An experiment of hydrogen leakage from an FCV inside a 40-foot container has been conducted and 8 sensors were used to detect hydrogen concentrations. The leaking hydrogen mainly spreads along the nearest wall to the top, and then diffuses to the distant area. Although the amount of leaking hydrogen is small (5 MPa, 61 L), there still exists large volume of flammable cloud inside. To exhaust the leaking hydrogen, vents must be installed. A computational fluid dynamics (CFD) model for ventilating a 20-foot container was developed and well validated. It was found that under conditions of a fully loaded hydrogen storage tank (70 MPa), high efficiency and complete venting cannot be achieved by a single vent at the same time. The side-wall vents positioned low can exhaust hydrogen quickly, but make hydrogen remain at the top and maximum concentration will be over 40 vol%, while high-positioned vents have the opposite effects. The combined method with both upper and lower vents is considered most effective, particularly when the driving state is considered. Through this configuration, all internal hydrogen can be removed within 120 s, and the maximum concentration can be reduced by 71% compared to conditions without ventilation.