An experimental investigation of extinction of curved laminar hydrogen diffusion flames

The extinction limits of steady curved, diluted H-2 (and D-2) counterflow diffusion flames have been measured as a function of curvature. Steady curved flames are established in the wake of a bluff-body, which is installed ill one of the nozzles of a counterflow burner. The curvature is essentially varied by changing the gas throughput. The radius of flame curvature has been measured by planar laser-induced fluorescence (LIF) from OH, or OD, respectively In addition, two-dimensional laser-based velocity measurements have been performed, in particular to determine the strain rate of the curved flames. A new flow tagging scheme, which is based on photodissociation and LIF detection of acetone, is proposed and applied for particle-free velocity measurements in the counterflow burner Flame extinction turns out to be strongly influenced by the orientation of the curvature with regard to the H-2 (or O-2) streams and the radius of curvature. This can be explained by curvature and preferential diffusion effects. Furthermore, we investigated the influence of curvature and preferential diffusion separately by comparing the extinction limits of H-2/N-2-O-2/N-2 flames with those from D-2/N-2-O-2/N-2 and H-2/He-O-2/He flames as a function of curvature. The results can basically be explained by the corresponding binary diffusion coefficients.