A hydrogen leak from a facility, which uses highly compressed hydrogen gas (714 bar, 800 K) during operation was studied. The investigated scenario involves supersonic hydrogen release from a 10 cm2 leak of the pressurized reservoir, turbulent hydrogen dispersion in the facility room, followed by an accidental ignition and burn-out of the resulting H2-air cloud. The objective is to investigate the maximum possible flame velocity and overpressure in the facility room in case of a worst-case ignition. The pressure loads are needed for the structural analysis of the building wall response. The first two phases, namely unsteady supersonic release and subsequent turbulent hydrogen dispersion are simulated with GASFLOW-MPI. This is a well validated parallel, all-speed CFD code which solves the compressible Navier-Stokes equations and can model a broad range of flow Mach numbers. Details of the shock structures are resolved for the under-expanded supersonic jet and the sonic-subsonic transition in the release. The turbulent dispersion phase is simulated by LES. The evolution of the highly transient burnable H2-air mixture in the room in terms of burnable mass, volume, and average H2-concentration is evaluated with special sub-routines. For five different points in time the maximum turbulent flame speed and resulting overpressures are computed, using four published turbulent burning velocity correlations. The largest turbulent flame speed and overpressure is predicted for an early ignition event resulting in 35 -71 m/s, and 0.13 – 0.27 bar, respectively.

The main objective of this study is an insight into physical phenomena underlying spontaneous ignition of hydrogen at sudden release from high pressure storage and its transition into the sustained jet fire. This paper describes modelling and large eddy simulation (LES) of spontaneous ignition dynamics in a tube with a rupture disk separating high pressure hydrogen storage and the atmosphere. Numerical experiments carried out by a LES model have provided an insight into the physics of the spontaneous ignition phenomenon. It is demonstrated that a chemical reaction commences in a boundary layer within the tube, and propagates throughout the tube cross-section after that. Simulated by the LES model dynamics of flame formation outside the tube has reproduced experimental observation of combustion by high-speed photography, including vortex induced "flame separation". It is concluded that the model developed can be applied for hydrogen safety engineering, in particular for development of innovative pressure relief devices.

This study addresses one of knowledge gapsin hydrogen safety science and engineering, i.e. apredictive model for calculation of deterministic separation distancesdefined bythe parameters ofa blast wave generated by a high-pressure gasstorage tank rupture in a fire. An overview of existing methods to calculate stored in a tank internal(mechanical) energy anda blast wave decayis presented. Predictions by the existing techniqueand anoriginal modeldeveloped in this study, whichaccountsforthe real gas effects and combustion of the flammable gasreleasedintotheair(chemical energy),arecompared againstexperimental dataon high-pressurehydrogen tank rupture in thebonfiretest. The main reasonfor a poor predictive capability of the existing models isthe absenceof combustion contribution to the blast wave strength. The developed methodologyis able to reproduce experimental data on a blast wave decay after rupture of a stand-alone hydrogen tank and atank under avehicle.In this study, the chemical energy isdynamically added to the mechanical energy and is accounted for in the energy-scaled non-dimensional distance. The fractionof the total chemical energy of combustion released to feed the blast wave is 5%2and9%2 howeverit is 1.4 and 30 times larger than the mechanical energy in the stand-alone tank test and the under-vehicle tank test respectively.The model isappliedas a safetyengineering tool to fourtypical hydrogen storage applications,includingon-board vehicle storage tanksand a stand-alone refuelling station storage tank. Harm criteria topeople and damage criteria for buildings froma blast wave are selected by the authorsfrom literature to demonstratethe calculation of deterministicseparation distances.Safety strategiesshouldexclude effectsoffire on stationary storage vessels, and requirethermal protection of on-board storage to prevent dangerous consequences ofhigh-pressure tank rupture in a fire.