Experimental and numerical investigation of the effect of end venting on flame acceleration in an obstructed channel

Hydrogen-air deflagrations with venting at the end of obstructed tubes are studied experimentally and numerically. Mixtures with 13% vol. of hydrogen were ignited from the open end of the tube at the interface between fuel and the ambient air. Three venting ratios were selected, closed, 40% and 100%. In the presence of the venting, the flame initially propagates without acceleration at a velocity close to the laminar flame speed. After an induction period, of the order of1 sec, the flame accelerates more than 100 times, within a period of 3-30 ms, until the steady-state choked regime will be established. The mechanism conducing to such a rapid acceleration was numerically investigated.