The influence of a bluff-body obstruction on the autoignition and flame acceleration of high-pressure hydrogen jets

The release of high-pressure hydrogen is studied to develop the understanding of the potential for ignition and flame acceleration. Numerical simulations of the sudden release of 12.5 MPa hydrogen through a 7.5 mm orifice into a semi-enclosed concave domain are reported and analysed. An obstructing cylindrical bluff-body is positioned downstream of the hydrogen jet. Ignition was observed to be initiated through shock-shock intersection, regardless of obstruction. In addition to this, ignition due to bluff-body stagnation was observed. Intersection between the hydrogen jet, the shock-wave and the cylindrical bluff-body resulted in a localised heating at the stagnation point, forming a hot-spot which transitioned into a deflagration. The presence of an introduced bluff-body impingement promotes mixing, resulting in the deflagration undergoing significant flame acceleration and exceeding the local speed of sound. The absence of the impinging cylindrical bluff-body results in the shock-wave reaching the concave reflecting wall unobstructed, and the subsequent shock reflections from this surface self-intersect, providing the energy required for autoignition and consequent deflagration.