Experimental Study of the Explosion Severity of Vented Methane/Hydrogen Deflagrations

Adding hydrogen to mains natural gas has been identified as one of the main strategies to reduce CO2 emissions in the United Kingdom. This work aims to characterise the explosion severity of 80:20 v./v. methane/hydrogen blends (‘a blend’) and methane vented deflagrations. The explosion severity of homogenous mixtures was measured in a 15 m3 cubic, steel chamber, in which the relief area was provided by four windows and a door covered with polypropylene sheet. The pressure increase over time was characterised using piezo-resistive pressure transducers and the flame speed was estimated using ionisation probes installed in the walls of the enclosure. The explosion severity of both mixtures was determined for different equivalence ratios, from lean to rich mixtures. The pressure over time presented very similar behaviour for both mixtures, comprising multiple peaks divided into three main stages: a first stage related to a spherical confined explosion until the opening of the vent, a second stage generated by increased combustion during venting, and an oscillatory peak generated by acoustic disturbances with the enclosure. A slight increase in the first stage overpressure was observed for the blend in comparison with methane regardless of the equivalence ratio, but no general trend in pressure was observed for other stages of the propagation. The effect of the blockage ratio on explosion severity was studied by adding metallic elements representing furniture in a room.