Ignitability and Mixing of Under Expanded Hydrogen Jets

Reliable methods are needed to predict ignition boundaries that result from compressed hydrogen bulk storage leaks without complex modelling or experimentation. To support the development of these methods, a new high-pressure stagnation chamber has been integrated into Sandia National Laboratories Turbulent Combustion Laboratory so that relevant compressed gas release scenarios can be replicated. For the present study, a jet with a 10:1 pressure ratio issuing from a small 0.75 mm radius nozzle has been examined. Jet exit shock structure was imaged by schlieren photography, while quantitative Planar Laser Rayleigh Scatter imaging was used to measure instantaneous hydrogen mole fractions downstream of the Mach disk. Measured concentration statistics and ignitable boundary predictions compared favourably to analytic reconstructions of downstream jet dispersion behaviour. Model results were produced from subsonic jet dispersion models and by invoking self similarity jet scaling arguments with length scaling by experimentally measured effective source radii. Similar far field reconstructions that relied on various notional nozzle models to account for complex jet exit shock phenomena failed to satisfactorily predict the experimental findings. These results indicate further notional nozzle refinement is needed to improve the prediction fidelity. Moreover, further investigation is required to understand the effect of different pressure ratios on measured virtual origins used in the jet dispersion model.