Willmore, D.J.Lau, T.C.W.Medwell, P.R.Kildare, J.A.C.Evans, M.J.2025-07-092025-07-092024International Journal of Hydrogen Energy, 2024; 110:336-3440360-31991879-3487https://hdl.handle.net/2440/145795The 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.en© 2025 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).hydrogen; autoignition; flame acceleration; bluff-bodyJournal article10.1016/j.ijhydene.2025.02.125729546Lau, T.C.W. [0000-0003-1851-706X]Medwell, P.R. [0000-0002-2216-3033]Kildare, J.A.C. [0000-0002-2380-5755]