Damage-mutation mode of premixed methane-air explosions in a small-L/D vented vessel

Limited experimental data has led to significant gaps in understanding gas-explosion damage modes in small L/D vessels or constructions. To address this, we developed a novel two-dimensional gas explosion system. In a typical L-shaped vessel, we investigated 10 vol% methane-air explosions under varying vent-ignition conditions and low failure pressures. Influenced by the L-shaped space and vent-ignition relationship, combustion and pressure exhibit strong coupling and mutual reinforcement. Two newly identified flame mutation modes enhance the burning damage of gas explosions. Flame return driven by a pressure gradient, which depends on the volume of unburnt premixed gas, intensifies local combustion and amplifies overpressure, particularly at short vent-ignition distances. Flame collision between two flame fronts, under conditions of abundant unburnt premixed gas and short vent-ignition distances, generates intense turbulence and produces violent combustion. The long vent-ignition distance and L-shaped space mitigate the Helmholtz oscillation while amplifying the overpressure peak P₃^′. The violent combustion caused by the flame collision dramatically increases P₄^′. These atypical peaks, P₃^′ and P₄^′, further exacerbate the overpressure damage. These findings demonstrate that under specific vent-ignition conditions, flame mutation modes can increase the overpressure peak by up to 141 %, underscoring their crucial role in the investigation and prevention of gas explosion incidents.