Experimental investigation on dynamic characteristics of methane/air combustion in double-layer pellets porous media

Abstract

The double-layer porous media burner is considered as an effective way to realize stable lean-burn. In order to quickly achieve a stable combustion state in a double-layer porous media burner, this work investigated the dynamic characteristics of methane/air premixed combustion in a bench-scale double-layer porous media burnspanning from ignition to stable combustion and ultimately flameout. The experimental results indicate that regulating the equivalence ratio and the inlet velocity enables the establishment of a stable flame front and the φ = 0.75 and the V_in = 0.20 m/s are the appropriate start-up conditions. The average propagation velocity of the combustion wave variation along the axial direction and ranged approximately from −0.022 to −0.078 mm/s. Moreover, the transition time to a stable combustion state is reduced by nearly 47.14% as the equivalence ratio increases from 0.60 to 0.70. During start-up stage, there are significant fluctuations in CO and NOx concentrations, but both emissions remain low during steady combustion state, with the maximum concentrations of 37.5 and 40.2 mg/m³, respectively. Furthermore, the porous media combustion exhibits a pronounced re-ignition capacity. At higher equivalence ratios, longer interruptions of premixed gas are allowed.