Hydrogen has often been studied as a possible fuel of the future due to its capabilities to support zero emissions and sustainable energy conversion. Hydrogen can be used in a fuel cell to generate electricity at high efficiencies and with zero emissions. In addition, hydrogen can be renewably produced via electrolysis reactions that are powered from otherwise curtailed renewable energy. One possible means of storing and delivering renewable hydrogen is to inject it into the existing natural gas (NG) system and thus decarbonize gas end-uses. The NG system has potential to serve as a storage, transmission and distribution system for renewably produced hydrogen. Despite the potential of hydrogen to reduce the carbon intensity of the NG system, the unique characteristics of hydrogen (low molecular weight, high diffusivity, lower volumetric heating value, propensity to embrittle pipeline materials) has led to justified concerns over the safety of introducing hydrogen blends into the NG system. While many studies have attempted to quantitatively predict leakage rates of hydrogen using classical fluid mechanics theories, such as Hagen-Poiseuille flow, there have been limited studies which quantitatively assess gaseous fuel leakage to support the predictions made from theoretical analyses and computations. In this paper we present a summary of the literature related to gaseous fuel leakage and results from preliminary experiments which support the idea that entrance effects may significantly affect gaseous fuel leakage from practical leak scenarios such as NG fittings, resulting in similar leakage rates between hydrogen and NG.

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