Experimental Investigation of Flame Extinction Limit in Planar Microchannel
The flammability limits of stretched flames stabilized in a planar microchannel with heat conducting walls were experimentally investigated in present work. Lean 0.6<ϕ<0.8 methane-air premixture was used. Original construction of the burning device consisting of two opposite directed slot-jet burners and two 50x50 mm and ~1.4 mm thickness quartz plates forming the planar microchannel allowed to reduce the influence of buoyancy effect and investigate the lean mixtures combustion at low values of stretched rate in conditions of normal gravity. Besides that, such system allows to investigate the effects related with heat recirculation from combustion products to unburned gas through the heat conducting channel walls.
The various regimes of combustion, such as flat flame, pulsating flame and also stable tubular flame at moderate values of stretched rate which was not observed previously were revealed during the investigation. The diagram of existence of various combustion regimes in dependence of stretched rate and equivalence ratio was plotted. The possibility of stable combustion of gas mixtures in such system at stretched rate values much smaller than limit value for ordinary stretched flames in conditions of normal gravity. Experimental results were verified by numerical simulations within the framework of one dimensional thermal-diffusive model taking into account the heat exchange between gas and channel walls and also the heat transfer through the channel walls.