Soot topography in a planar diffusion flame wrapped by a line vortex

Abstract

An experimental study of the interaction of a planar diffusion flame with a line vortex is presented. A planar diffusion flame is established between two coflowing, equal velocity streams of acetylene diluted with nitrogen and air. A line vortex is generated on demand by momentarily pulsing one of the flow streams by way of electromagnetic actuation of a piston in the flow apparatus. The flame–vortex interactions are diagnosed by planar laser-induced incandescence for soot yield and by particle image velocimetry for vortex flow characterization. The results show that soot formation and distribution are influenced by the reactant streams from which vortices are initiated. The vortices interacting with the flame from the air side produce more soot and soot is distributed in and around the vortex core in diffuse layers. In contrast, topography of soot in vortices interacting from the fuel side is such that soot is confined to thinner layers around the vortex core which does not contain any soot. The flame curvature is found to influence the local soot production with the flame regions convex to the fuel side containing more soot locally. It is also found that the overall soot yield is less sensitive to the vortex strength and is of lower magnitude when vortex is spun from the fuel side. The knowledge of this type of asymmetry in soot yield in flame–vortex interactions is useful for combustion engineering and design of practical devices.