Abstract
The use of hydrogen storage tanks at 100% of nominal working pressure (NWP) is expected only after refuelling. Driving between refuellings is characterised by the state of charge SoC <100%. There is experimental evidence that Type IV tanks tested in a fire at initial pressures below 1/3 NWP, leaked without rupture. This paper aims at understanding this phenomenon. The numerical research has demonstrated that the heat transfer from fire through the composite overwrap at storage pressures below NWP/3 is sufficient to melt the polymer liner. This melting initiates hydrogen microleaks through the composite before it loses the load-bearing ability. The fire-resistance rating (FRR) is defined as the time to rupture in a fire of a tank without or with blocked thermally activated pressure relief device. The dependence of a FRR on the SoC is demonstrated for the tanks with defined material properties and volumes in the range of 36–244 L. A composite wall thickness variation is shown to cause a safety issue by reducing the tank’s FRR and is suggested to be addressed by tank manufacturers and OEMs. The effect of a tank’s burst pressure ratio on the FRR is investigated. Thermal parameters of the composite wall, i.e., decomposition heat and temperatures, are shown in simulations of a tank failure in a fire to play an important role in its FRR.
Highlights
The assessment was performed for scenarios when onboard hydrogen storage was tank filled to 100% of the nominal working pressure (NWP)
The pressure of the compressed hydrogen storage system (CHSS) is not always the NWP, i.e., the state of charge (SoC) is below 100%
This study aims to investigate the effect of the state of charge (SoC), burst pressure ratio (BPR) and thermal properties of a resin in a composite tank overwrap, i.e., Hd and
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The authors state that hydrogen “was leaking across its entire surface with slightly more leakages at the ends” and that during the test “epoxy resin seems to have disappeared but the carbon fibres did not burn” [4] There is another experimental study on fire testing of NWP = 70 MPa 36 L Type IV tanks at different initial pressures [6]. It will allow for more heat transfer through the tank wall and for a longer time, with subsequent liner melting This is the mechanism behind the “no rupture but a leak” of tanks in fire tests with lower pressure compared to the NWP initial hydrogen pressure in a tank observed experimentally in [4,6]. The study will be performed using the validated non-adiabatic blowdown in a fire model [5,12]
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