Dynamic mechanisms of high-pressure hydrogen self-ignition and flame evolution in obstructed tubes: Experimental insights and implications

Abstract

Experimental investigations on high-pressure hydrogen release into obstructed tubes with varying obstacle positions are conducted to explore the dynamic mechanisms of shock propagation, self-ignition and flame evolution. High-speed photography, pressure sensor and light detector are used in the experiments. The results reveal that obstacle position significantly affects self-ignition by the multi-dimensional interactions and the turbulence-promoted mixing. The reflected shock results in an overpressure rise of twice that behind the leading shock. In addition, the intensity of reflected shock decreases when it propagates upstream. The critical burst pressure for self-ignition first decreases and then increases with a further obstacle position away from the burst disk. The lowest burst pressure for self-ignition is 2.08 MPa arising in the tube with obstacles located at 200 mm axially, half that of the smooth tube. In obstructed tubes, three possible self-ignition regions exist, including inclined obstacle walls, tube centerline and tube sidewalls. The patterns of self-ignition are determined by burst pressure and obstacle position. Besides, flame acceleration is observed in the obstructed, which is related to turbulence promoted by the shock-obstacle interaction. The farther obstacles from the burst disk results in more marked effects on flame acceleration.