Partially premixed hydrogen-air cellular flames in a tubular burner

Abstract

A combination of chemiluminescence imaging and raster scanned Raman scattering of lean laminar partially premixed tubular flames is presented. Cellular and non-cellular structures are created in a single flame by opposed flows of lean premixed H2-air and CO2 diluted H2. Characterization of partially premixed tubular flame structure at low to moderate stretch rates is performed via chemiluminescence. Significant structural response is shown by varying the premixed equivalence ratio and the stretch rate, producing a range of unique and symmetric flames: axial-symmetric cigar shapes, haloed rings, and flower-like shapes. This study is focused on the flower-like cellular flames with high curvature flame zones and extinction zones due to preferential diffusion. Premixed equivalence ratios near 0.30 create a cellular structure surrounding a diffusion flame ring, resembling a flower. These partially premixed flames are found to exhibit high preferential diffusion by formation of premixed cells and unique star-shaped structures. Flower-like flames are found highly stable with regard to rotation and perturbations. The diffusion flame stabilizes premixed star and cellular structures. Major species and temperature profiles are measured by Raman scattering, showing preferential diffusion in the premixed cells. Peak temperatures across premixed zones are above adiabatic temperatures by nearly 200 K due to preferential diffusion.