Effect of the leakage mass flow rate and ignition time on the explosion characteristics of hydrogen leaked from hydrogen-powered train in tunnel

Hydrogen energy is one of the indispensable power sources and rail transit is one of main applications. The safety in tunnel is one of the major concerning issues related to the development of hydrogen powered rail transit, however, most previous studies are focused on open space and pipe scenarios. The effect of ignition time (10, 15 and 20 s) and mass flow rate (0.267, 0.324, 0.375 and 0.426 kg/s) on the inhomogeneous hydrogen distribution, the overpressure and propagation of the pressure wave and temperature distribution are studied numerically. The hydrogen diffusion distance and volume fraction increase with the increase of the leakage mass flow rate and leakage time. The pressure wave propagates to the tunnel exits horizontally and oscillates vertically. The high-temperature region touches and then spreads along the tunnel roof. Then it moves down to the floor and finally fills the entire space. The hydrogen volume fraction increases with the increase of leakage time and mass flow rate. Overpressure and temperature show a decreasing trend when ignition time and mass flow rate increases. Due to increase of hydrogen concentration participating in the chemical reaction, the explosion intensity is inhibited and shows a decreasing trend of explosion overpressure and temperature with increase of ignition time and mass flow rate.