Effect of Annular Flow Area on Flame Stability in a Methane/Oxygen Diffusion Flame Burner with a 45 Degree Impingement Angle

This research was performed to determine the influence of secondary annular flow area of a single coaxial injector in an experimental non-premixed flame burner on flame stability. The experimental burner was composed of a horizontally mounted, rectangular chamber that utilized a retractable spark plug for ignition. The primary and secondary gaseous reactants were oxygen and methane, respectively. Three injectors were designed and fabricated with fixed secondary flow exit impingement angles of 45 degrees with the primary flow. Each injector had a different secondary flow area while maintaining a constant primary flow area. The behavior of the resultant diffusion flame and the flame standoff distance length were observed through optical windows parallel to the axis of the flame. Flame stability maps based upon equivalence ratio, reactant Reynolds number, and injector secondary flow area were created. It was observed that the largest secondary flow area generated the most anchored, stable diffusion flames for high equivalence ratios and over the widest range of Reynolds numbers for equivalence ratios <1.8. As secondary flow area decreased, anchored diffusion flames transitioned from existing at fuel-lean highly turbulent primary flows to fuel-rich, highly turbulent flows as well as from fuel-rich, low primary flows to no ignition under the same conditions. Therefore, secondary annular flow area can significantly influence the location and range of stable, anchored methane/oxygen diffusion flames.