Experimental study on the effects of ignition position and inhomogeneous concentration on vented hydrogen deflagrations in a 7 m3 chamber

Vented inhomogeneous hydrogen deflagrations are conducted in a 7 m3 chamber. The effects of ignition position and inhomogeneous concentration are studied. The results show that a coupling flame structure of jet fire and flame bubble is first observed. In the case of top ignition, a M-shaped flame structure forms for average hydrogen concentration CH2 <= 10.14 vol%. In the cases of center ignition and bottom ignition, the flame bubble rapidly expands towards the walls and the horizontal propagation speed of upper part of flame bubble is obviously higher than that of lower part of flame bubble for CH2 >= 11.27 vol%. Moreover, the speed of horizontal flame front quickly decreases as the flame front moves away from the centerline of hydrogen jet. Three overpressure peaks appear in all scenarios, namely Popen, Phel and Pvib, which results from the vent failure, Helmholtz-type oscillations and thermo-acoustic oscillations respectively. The maximum overpressure dominated by Popen is nearly insensitive to CH2 for top ignition. However, the maximum overpressure induced by center ignition or bottom ignition significantly increases when CH2 >= 10.14 vol%. For a given CH2, Pvib induced by bottom ignition is always the largest.