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Simultaneous and two-directional highspeed schlieren observation of effects of ignition points on vortex-flame interaction

To observe and analyze detailed processes of the vortex-flame interaction in the two-dimensional coherent structure, a premixed flame is generated by a spark ignition either at the center of an organized eddy or at the midpoint between two adjacent eddies, and the initial propagation stage of the spark-ignited flame is optically observed using the simultaneous and two-directional high speed schlieren photography. The tangential velocity of organized eddy and the equivalence ratio of the shear flow are varied as two main parameters. The results obtained and analyzed show that there exists another type of vortex-flame interaction in addition to the vortex bursting, and that it is due to the eddying motion peculiar to the coherent structure in the plane shear flow. The vortex-flame interaction is named here the vortex boosting. It is concluded therefore that in the ordinary turbulent premixed flames these two fundamental vortex-flame interactions get tangled with each other in complicated manners to augment the propagation velocity. An empirical expression which takes into account of effects of both vortex and chemical properties is finally proposed.