Diffusion-flame dynamics in Von Kármán boundary layers

Experimental and theoretical results are reported for flat diffusion flames adjacent to a spinning fuel disk in an oxidizing atmosphere. Disk-shaped flames are observed, the radii of which increase or decrease with time, depending on whether an appropriate Damköhler number is large or small. Experimentally, initially large flame disks expand at sufficiently high Damköhler numbers, while at sufficiently small Damköhler numbers, initially small flame disks contract, as predicted by theory. A stability map is derived theoretically in a plane of the Damköhler number and the flame-disk radius normalized by a diffusion length scale, showing regimes of disk growth and shrinkage.