An experimental study on vortex–flame interaction of a spark-ignited flame with coherent structure in a plane premixed shear flow

In order to elucidate the enhancement mechanisms of turbulent flame propagation, it is indispensable to examine and clarify the process of vortex–flame interaction in detail. This is because it constitutes one of the key processes in the promotion of flame propagation velocity. In this investigation, a series of large-scale organized eddies formed in the plane propane–air premixed shear flow are selected as an objective eddy field. Two devised techniques are introduced and combined with each other; one is the acoustic excitation of the shear flow, the other is the simultaneous two-directional high-speed schlieren photography. The former makes the organized eddy formation extremely regular and enables synchronized ignition with a high-speed video camera. The latter provides the opportunity to analyze two different directional views of a single propagating flame. In this study a spark-ignited flame, which is initiated at the center of a premixed organized eddy and is propagating along the axis, is optically observed and analyzed by using the proposed technique. It is shown that the propagation velocity along the axis of the eddy is promoted by the vortex bursting and is about 80% greater than that in the radial direction. It is also shown that after completing combustion in the radial direction within an organized eddy, the flame travels to the boundary regions between two adjacent eddies on the upstream and downstream sides, mainly promoted by the rolling-up motion in the coherent structure. These results suggest that there exist two kinds of vortex–flame interactions of a spark-ignited flame with coherent structure in the plane shear flow.