Abstract
It is significant to assess the hydrogen safety of fuel cell vehicles (FCVs) in parking garages with a rapidly increased number of FCVs. In the present work, a Flame Acceleration Simulator (FLACS), a computational fluid dynamics (CFD) module using finite element calculation, was utilized to predict the dispersion process of flammable hydrogen clouds, which was performed by hydrogen leakage from a fuel cell vehicle in an outdoor parking garage. The effect of leakage diameter (2 mm, 3 mm, and 4 mm) and parking configurations (vertical and parallel parking) on the formation of flammable clouds with a range of 4–75% by volume was considered. The emission was assumed to be directed downwards from a Thermally Activated Pressure Relief Device (TPRD) of a 70 MPa storage tank. The results show that the 0.7 m parking space stipulated by the current regulations is less than the safety space of fuel cell vehicles. Compared with a vertical parking configuration, it is safer to park FCVs in parallel. It was also shown that release through a large TPRD orifice should be avoided, as the proportion of the larger hydrogen concentration in the whole flammable domain is prone to more accidental severe consequences, such as overpressure.
Highlights
Hydrogen safety in diverse situations is the most critical aspect of fuel cell vehicles (FCVs) as hydrogen has high flammability (4–75% by volume) [1] and low ignition energy and is prone to leakage
The results reveal that the entire domain under the fuel cell vehicle has already become explosion hazard areas; hydrogen sensors need to be installed under the chassis close to the Thermally Activated Pressure Relief Device (TPRD) vent pipe to detect any hydrogen leakage and raising an alarm in advance to help personals take appropriate emergency measures
Unignited hydrogen release through a Thermally Activated Pressure Relief Device (TPRD) from onboard hydrogen storage tanks in an outdoor parking garage has been studied in the present numerical work
Summary
Hydrogen safety in diverse situations is the most critical aspect of FCVs as hydrogen has high flammability (4–75% by volume) [1] and low ignition energy and is prone to leakage. One of the most hazardous scenarios is hydrogen leakage from a high-pressure storage tank placed on the chassis underneath the vehicle in an outside parking garage since the semi-closed space formed by adjacent automobiles contributes to hydrogen accumulation. Experimentally studied the effects of residential-garage geometry, shape, and number of vents on hydrogen concentration and delamination. CFD methods have been performed to numerically evaluate the behavior of hydrogen dispersion so that emergency measures can be taken immediately to reduce the hydrogen concentration under a lower flammable limit (LFL) [22,23,24]. The permeated hydrogen dispersion with the permeation rate of 1 Nml/h/L and 45 Nml/h/L from a high-pressure storage tank in a typical garage was studied analytically by Saffers, J.-B. et al [26]. Hydrogen diffused and accumulated uniformly upward toward the ceiling after the leakage, and the concentration reached quasi-steady at 60 s and 12 s for 1 Nml/h/L and 45 Nml/h/L permeation rate, respectively
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