Numerical study of hydrogen leakage, diffusion, and combustion in an outdoor parking space under different parking configurations

Abstract

As the number of hydrogen fuel cell vehicles (HFCVs) being used is increasing, confirming that their safety level is the same as that of gasoline vehicles is becoming important. HFCVs are commonly parked in outdoor spaces. Thus, the safety of HFCVs in garage scenarios should be ensured and related regulations, codes, and standards for preventing accidents must be developed. In this study, the Flame Acceleration Simulator (FLACS) software was utilized to evaluate the behavior of hydrogen release, dispersion, and flame propagation in the presence of multiple HFCVs in an outdoor parking space through the activation of thermally activated pressure relief devices (TPRDs). The effects of different leak diameters (2, 3, and 4 mm), release directions (upward and downward), and parking configurations (vertical and parallel) on the formation of a flammable gas cloud (FGC) and safety distances were examined, by considering tank blowdown. The results showed that larger TPRD diameters resulted in a larger envelope of the FGC; however, it also dissipated faster in outdoor parking spaces. Compared with the vertical parking configuration, the fire-origin HFCV had less impact on adjacent vehicles in the parallel parking configuration. The direction of an upward release was found to contribute to a decrease in the volume of the FGC in outdoor parking spaces owing to low congestion. This study highlights the significance of the TPRD diameters and parking configurations, providing guidance for the safe introduction of HFCVs in existing outdoor parking spaces and infrastructure.