Lift-off behavior and flame structure of interacting edge flames

Laminar lifted edge flames stabilized above a five-exit slot burner are examined experimentally and numerically. In the present study, partially-premixed methane and air are used in the three-central slots to produce two neighboring edge flames. By controlling the equivalence ratios in the slots, the separation distance between the interacting edge flames is altered. The interaction between the flames is strong enough to prevent the two edges from stabilizing at the same lift-off height, and the separation distance between the edges is found to depend on the total flow rate. In each case studied, multiple stable flame configurations are observed. Particle imaging velocimetry measurements indicate that the divergence around the lower flame edge causes the upper flame to stabilize at an angle and at a velocity larger than the laminar flame speed, presumably due to heat interaction. For very large separation distances, the divergence around the lower flame engulfs the upper flame. Simulations of the same conditions show that the trailing diffusion flame is quenched in the latter case.