Flame Behaviors Near Extinction Limit in Laminar Lifted Coflow-Jet Flames

Characteristics of laminar lifted flames in coflow-jet of propane with helium-diluted coflowing air have been studied experimentally and numerically. Two distinct self-excitations existed: a buoyancy-driven self-excitation and a self-excitation with capsized flame near flame extinction. In particular, the flame dynamics for the latter flame were related to buoyancy effects caused by the difference in the densities between the fuel and coflow streams. To identify the mechanism of capsized flame, Mie-scattering technique, OH radical and numerical simulation of cold and reacting flow were performed.