Effect of impingement angle on flame stability in a non-premixed methane/oxygen diffusion flame burner

The focus of this research work was understanding the effect of varying the impingement angle of a single coaxial injector in an experimental non-premixed flame burner on flame stability. The reactants were methane and oxygen, mixed and ignited in a horizontally-mounted, rectangular combustion chamber using a retractable spark plug. Gaseous oxygen was the primary flow and gaseous methane was the secondary flow. Three injectors were fabricated with exit impingement angles of 15^o, 30^o, and 45^o with the primary flow. Using optical windows on both sides of the chamber parallel to the axis of the flame, the product flame behavior and flame standoff distance was observed. Stability maps of the non-premixed flame behavior based upon equivalence ratio, reactant Reynolds numbers, and injector impingement angle were created. It was observed that the 15^o impingement angle injector 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 GCH4/GO2 diffusion flames.