Temporal and spatial evolution of hydrogen leakage and diffusion from tube fittings on fuel cell vehicles under the effect of ambient wind

Hydrogen has become a competitive energy carrier owing to its high fuel value, cleanliness, and renewability. Fuel cell vehicles (FCVs) are crucial in achieving global carbon neutrality in the transportation sector. This study used Flame Acceleration Simulator (FLACS) software to model hydrogen leaks and diffusion from tube fittings of hydrogen systems with the numerical model validated by experimental data. The effect of wind direction on hydrogen leakage and diffusion in the chassis was investigated. Hydrogen leakage rates from the tube fittings under various pressures, tightening angles, and torques were determined; a release rate of 0.6 NL/min is considered a typical value for hydrogen leakage from the tube fittings of a 1.2-MPa hydrogen supply line. The results demonstrate that in windless conditions, the high concentration region with 1–2% vol. was located around the group of hydrogen storage tanks and that there was no flammable region in the entire chassis area. Wind accelerated hydrogen diffusion and reduced the extension range of the hydrogen envelope by 1–2% vol. Compared with longitudinal wind conditions, a crosswind can more effectively reduce the hydrogen concentration. Cutting off the hydrogen supply resulted in rapid contraction of the hydrogen envelope of 1–2% vol. within 5 s. These results have implications for installation of hydrogen sensors in the chassis of FCVs and the location of the blower for forced ventilation by first responders in the event of hydrogen leakage.