Abstract
Hydrogen jet fires from a thermally activated pressure relief device (TPRD) on onboard storage are considered for a vehicle in a naturally ventilated covered car park. Computational Fluid Dynamics was used to predict behaviour of ignited releases from a 70 MPa tank into a naturally ventilated covered car park. Releases through TPRD diameters 3.34, 2 and 0.5 mm were studied to understand effect on hazard distances from the vehicle. A vertical release, and downward releases at 0°, 30° and 45° for TPRD diameters 2 and 0.5 mm were considered, accounting for tank blowdown. direction of a downward release was found to significantly contribute to decrease of temperature in a hot cloud under the ceiling. Whilst the ceiling is reached by a jet exceeding 300 °C for a release through a TPRD of 2 mm for inclinations of either 0°, 30° or 45°, an ignited release through a TPRD of 0.5 mm and angle of 45° did not produce a cloud with a temperature above 300 °C at the ceiling during blowdown. The research findings, specifically regarding the extent of the cloud of hot gasses, have implications for the design of mechanical ventilation systems.
Highlights
Hydrogen is typically stored onboard a vehicle as a compressed gas at 35 MPa for buses and 70 MPa for cars
Numerical experiments with ignited hydrogen releases from thermally activated pressure relief devices (TPRD) of onboard storage of hydrogen-powered vehicles in a naturally ventilated covered car park have been performed for the first time
Hydrogen jet fires from TPRD were investigated in a car park with dimensions L × W × H = 30 × 28.6 × 2.6 m incorporating two vents which provided an opening equivalent in area to 5% of the floor area across two opposing walls following British Standard BS 7346-7:2013
Summary
Hydrogen is typically stored onboard a vehicle as a compressed gas at 35 MPa for buses and 70 MPa for cars. It is recommended by existing standards that the ventilation rate is such that in the case of hydrogen the concentration does not exceed 1% by volume i.e., 25% of the LFL within the car park; this is specified in ISO/DIS 19880-1 [12], NFPA 2 [13] and IEC (60079-10) [14] This was the focus of previous work by the authors where an unignited release was considered within the same covered car park geometry presented here [7]. There are limited published studies, either experimental or numerical investigating safety aspects of an ignited hydrogen release in a large, confined space such as a naturally ventilated covered car park Greater understanding of this topic is critical to underpin the wider introduction of hydrogen vehicles and their safe use in car parks.
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