Effects of ignition location, obstacles, and vent location on the vented hydrogen-air deflagrations with low vent burst pressure in a 20-foot container

A series of experiments on vented lean hydrogen-air deflagrations with low vent burst pressure was performed in a 20-foot container. The effects of hydrogen concentration, ignition position, vent location, and obstacles were studied, and all tests were performed at about 290 K and 101 kPa. For the cases with end vent, three over-pressure peaks of P1, P2, and P3 were recorded, resulting from the vent rupture, flame propagation to the vent, and the Helmholtz oscillation, respectively. Moreover, at the middle and later stages of the vented explosion, the acoustic oscillations with high-frequency were observed due to the thermo-acoustic-vibration coupling caused by the instability of lean hydrogen combustion. The peak overpressure for the case with the obstacle is lower than that without the obstacle. Vent rupture occurs quickly for front ignition and low hydrogen concentrations. For the tests with high hydrogen concentration such as 24 vol% and 28 vol%, since the polyethylene film can reach its static activation pressure and rupture, the peak overpressure is much larger. For the cases with the ceiling vents, only one overpressure peak P1, corresponding to the rupture of the vent cover, was recorded and its value increases with the hydrogen concentration. The obstacle causes the propagation direction of the flame to change, and resultantly the flame spreads upward and burns the polyethylene film, which decreases the internal overpressure rise time. This phenomenon is particularly evident for the tests with high hydrogen concentrations. Except for 16 vol%, the obstacle reduces the peak overpressure.