Explosion Characteristics of a Premixed Methane-Air Vapor Cloud Induced by a Jet Flame

Explosion characteristics of premixed methane/air vapor cloud ignited by a jet flame are estimated numerically using CFD software FLACS to comprehensively understand the explosion propagation mechanism of mixed gas at quiescent ambient air condition. Simulation scenarios were constructed to investigate the effect of methane concentration on the explosive properties of the freely dispersed vapor cloud. The premixed jet flame was ejected from a cuboid tube filled with varying concentrations of methane, and the mushroom shaped flame front was mainly attributed to the combustion of the ejected unburnt gas. The numerical simulations match the empirical and analytical formulas well, indicating the numerical model provides acceptable accuracy in assessing the explosion behaviors. The research results show that the methane concentration plays an important role in determining the jet flame length and temperature which reach respectively a peak value, 3.3 m, and a minimum value, 779.12K, at 11 % methane concentration. The dependence of the critical ignition distance Dc on the methane concentration is similar to that of the flame length, but the ignition temperature exhibits an opposite tendency. Additionally, the critical ignition distance is found much smaller than the jet flame length. The flame geometry is significantly enlarged due to the ignited vapor cloud, which may cause severe secondary disaster in practical scenarios.