Numerical simulations have been carried out for pressurised hydrogen release through a nozzle in a simulated vehicle refilling environment of an experiment carried out in a joint industry project by Shell, bp, Exxon and the UK HSE, Shirvill[1]. The computational domain mimics the experimental set up for a vertical downwards release in a vehicle refuelling environment. Due to lack of detailed data on pressure decay in the storage cylinder following the release, a simple analytical model has also been developed to provide the transient pressure conditions at nozzle exit. The modelling is carried out using the traditional Computational fluid dynamics (CFD) approach based on Reynolds averaged Navier Stokes equations. The Pseudo diameter approach is used to bypass the shock-laden flow structure in the immediate vicinity of the nozzle. For combustion, the Turbulent Flame Closure (TFC) model is used while the shear stress transport (SST) model is used for turbulence.
Comparison between the predictions and measurement has shown that the predictions have captured the trend of the measured pressure waves but varying degrees of discrepancies exist at some monitoring locations. This is thought to be partly due to the differences in the layout of congestion underneath the car in the computational model and the actual experimental set up due to lack of details in the experimental paper.
The average mass fraction of hydrogen was monitored at the location of sparking which represents the rate at which hydrogen was accumulating in the confined environment. Simulations were carried out for varying and constant mass flow rates through nozzle at different spark timings at 0.5 s, 0.6 s, 0.7 s and 0.8 s after the commencement of release. Comparison was made between the overpressures developed at the various monitoring points to gain insight into pressure wave propagation in confined environments.