Propagating edge flame response to multiple stoichiometric gradients

A five-slot burner with contoured nozzle exit has been used to create multiple lifted partially-premixed flames in close proximity. The burner allows for the creation of a range of stoichiometric gradients below each of the edge flames, while also allowing for the ability to control the distance between stabilization points of the flames. The equivalence ratio gradient and separation distance were varied so that various flame interactions could be studied. For large 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. This bifurcation in edge flame stabilization has been previously reported by our group and is examined here in greater detail. As the gradient was further reduced, the neighboring flames merged and approached the structure of a single premixed flame. In this work, the change in the separation distance between stoichiometric points was varied by controlling the burner slot flow rates, and was found to impact the composition gradients leading to flame interactions. Rayleigh scattering measurements were performed to determine the concentration gradients of fuel below each edge flame studied, characterizing the stabilization scalar dissipation rates while also allowing for the determination of the stoichiometric separation distance.