Propagating edge flame response to multiple stoichiometry gradients

A five-slot burner has been used to create two lifted partially-premixed flames in close proximity. The burner allows for the control of the stoichiometric profile upstream of each flame, allowing for studies of flame interactions. For large concentration gradients the edge flames showed very little interaction as both flames stabilized at similar liftoff heights and with similar flame shapes. As the composition gradient below the flames was decreased, the edge flames broadened leading to an aerodynamic interaction where a lift-off height difference between the two flames was observed. As the gradient was further reduced, the neighboring flames merged and approached the structure of a single premixed flame. This bifurcation in edge flame stabilization has been previously reported by our group and is examined here in greater detail. In this work, Rayleigh scattering measurements were performed to determine the concentration gradients of fuel below each edge flame studied and for the extraction of flame curvature. Planar laser induced fluorescence measurements of hydroxyl and formaldehyde were performed to measure species concentrations and estimate reaction rates for flame comparisons. All measurements were studied to characterize effects of neighboring flames on one another, ultimately showing that interactions are driven mainly by aerodynamic affects.