A laminar premixed flame stabilized inside a honeycomb ceramic was experimentally as well as theoretically investigated here. In previous theoretical studies a stable flame has been predicted in the downstream region of the combustor, but it has never been observed in experiments. In this study, three kinds of combustors were used to stabilize the flame in the downstream of the combustor and in case of combustor type C, a stable downstream flame could be obtained for the lower burning velocity through circumferential heating by a blue flame positioned outside the periphery of the combustor. Also the effects of side heating and acoustic excitation were studied. The existence of the stable downstream flame was confirmed by a direct photography of soot line, and temperature measurements. The measured flame temperature was found to be lower than the adiabatic flame temperature due to its lower heat release. The effect of combustor diameter to flame stability was also considered. As the diameter of the combustor increases, the lean flammability limit was extended.
The one-dimensional flame analysis was also carried out by taking account of the side heating resulting from the blue flame. The downstream as well as upstream solution corresponding to upper and lower solutions could be obtained. While upper flame temperature gets higher, lower flame temperature gets lower as the flame approaches the central part of the combustor. Once the net heat recirculation condition was satisfied for a given flow condition, the numerical procedure was stopped and the solution was thought to be obtained. That is how both upstream and downstream flames could be found for a given mass flow rate. However, in order for the downstream flame to be stabilized, more heat needed to be recirculated towards upstream. As the side heat loss increases, upper and lower flames approaches the central part of the combustor from both ends of the combustor.