Characteristics of edge flame in the wall jet region in an axisymmetric impinging jet

Transition processes from the edge flame without premixed flame to the edge flame with premixed flame, the triple flame, of methane-air edge flame are experimentally investigated by using the novel burner system. The burner system forms a diffusion flame in an axisymmetric wall jet. The measurements of the stability limits and the flame locations, and the observation of the flame shapes have been performed. The burner can make three types of the stable edge flame. First one is the edge flame without premixed flame, whose location is determined by the wall interaction with the edge flame, that is, the thermal factor. Second one is the edge flame with premixed flame, whose location is still determined by the thermal factor. Third one is the edge flame with premixed flame, and the location is determined by a balance between the propagation rate of the edge flame and the local velocity of unburnt mixture, that is, the fluid dynamical factor. The change of the dominant factor for flame location is due to the increase in the partially premixing region ahead of the edge flame. The increase in the partially premixing region makes it possible to form premixed flame and the first edge flame changes into the second one. Further increase in the partially premixing region lead to an increase in a total amount of the heat release around the edge flame region and the flow field ahead of the edge flame diverges. Finally, the edge flame is lifted up by the flow divergence and the dominant factor to determine the edge flame location changes from the thermal factor to the fluid dynamical factor.