Pore-scale study of complex flame stabilization phenomena in thin-layered radial porous burner

During the last years the thin-layered radial porous burners are of growing interest, primarily due to low pressure loss, advanced flame stability and high radiant output. The aim of this study is to investigate the flame stabilization phenomena in radial flow burner using a pore-scale approach with direct simulation of the realistic three-dimensional porous structure and interstitial flow with thermal interaction between the fluid and solid phases including surface radiation. The stabilization mechanisms are investigated with focus on the detailed inner flame structure and its aerodynamical and thermal interaction with the porous shell. The results demonstrate that three characteristic combustion regimes can be distinguished, namely, the internal, submerged and surface-stabilized flames that form depending on the mixture composition and the flow rate. The general principles governing change of regimes are discussed. A key factor of the internal flame stabilization within the burner cavity is a kinematic balance between flow and burning velocity. When the reaction zone submerges the porous shell, the heat recuperation becomes an important factor of flame stabilization. In the surface-stabilized regime, the large velocity gradients lead to the highly stretched and curved flames that aerodynamically anchor at the external surface of the shell analogously with the perforated plates and bluff bodies but have wrinkled shape due to the nonuniformity of the flow field within irregular porous structure. A characteristic diagram of regime change is proposed. It is discussed that for porous burners with size of structural elements of the same magnitude as shell thickness, application of the quasi-homogeneous assumption is restricted in contrast to the pore-scale simulation approach that considers as a prospective technique for studying combustion phenomena.