Effect of Impingement Angle on Flame Stability in a Non-Premixed Methane/Oxygen Diffusion Flame Burner

The focus of this research was understanding the effect of varying the secondary flow impingement angle of a single coaxial injector in an experimental non-premixed flame burner on flame stability. The burner was a horizontally mounted, rectangular combustion chamber with retractable spark plug for ignition. Reactants were gaseous oxygen and methane as the primary and secondary flow, respectively. Three injectors were designed and fabricated with exit impingement angles of 15, 30, and 45 degrees with the primary flow. The diffusion flame behavior and flame standoff distance length was observed through optical chamber side windows parallel to the axis of the flame. Stability maps of the diffusion flame behavior based upon equivalence ratio, reactant Reynolds numbers, and injector impingement angle were created. It was observed that the 15 degree impingement angle generated the most stable, anchored diffusion flames for high equivalence ratios and low Reynolds numbers. As impingement angle increased, stable, anchored 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 flow impingement angle can drastically influence the location and range of stable, anchored methane/oxygen diffusion flames.