Combustion in a hybrid porous burner packed with alumina pellets and silicon carbide foams with a gap

Combustion of premixed methane/air in a hybrid porous burner is experimentally studied. The burner is filled with alumina pellets in the preheating zone and silicon carbide foams with a gap in the combustion region. Different lengths and locations of gap are evaluated to identify how the geometric parameters affect flame stability, flame temperature, and pollutant emission (CO, HC, and NOx). The maximum stable flame range is obtained when the gap length is 15 mm and located between the packed alumina pellets and silicon carbide foams. When the gap is inside the foam region, the flame always stabilizes in the porous region regardless of the foam before or after the gap. The flame temperature decreases with the increase of gap length or with the decrease of foam region after the gap. The CO emission and the flame temperature exhibit opposite tendencies with the variation of flame speed. The HC emission increases with the increase of gap length δ or when the gap moves to the downstream. It implies that the preheating effect caused by the gap location is dominant to the formation of HC emission. The NO_x emission is 4 ppm, which is relatively low attributable to the lower flame temperature.