Plasma-assisted stabilization of laminar premixed methane/air flames around the lean flammability limit

Studies of nanosecond repetitively pulsed discharge plasma-assisted combustion were carried out on a laminar premixed methane/air flow in the vicinity of the lean flammability limit. Experimental results indicated that complete combustion is achieved when the equivalence ratio is above the known lean flammability limit (ϕ = 0.53) at high discharge repetition rates of 50 kHz. When the ratio is below the limit, the plasma does serve as a flame holder; however, only partial combustion is seen in the downstream flow. Two-dimensional kinetic simulation results were found to be consistent with the experimental results. The simulations revealed that the methane is fully consumed within the discharge region, since the time between discharge pulses is less than that for species diffusion and advection. This creates a source of radicals and high temperature, which diffuse outwards to stabilize the combustion of the surrounding flow.