The physical mechanisms governing flame anchoring have been examined in an effort to extend the range and maneuverability of compact, low-drag, air-breathing engines. Experiments were performed burning premixed methane and air in a planar dump combustor using reacting-flow particle image velocimetry as the primary diagnostic. Instantaneous two-dimensional images and vector fields were studied to determine changes in the fluid-chemical interactions of the shear layer as flame anchorability became more robust Conditional averages of combustion products directed toward incoming reactants were evaluated to establish the connection to self-sustained combustion. A lean mixture of methane-air was used as a baseline, and the equivalence ratio and near-field counterflow were varied to affect anchorability. Dilatation was calculated as a marker for heat release and threedimensionality. Operating points exhibiting a strong flux of products into reactants via a single coherent structure positioned downstream of the step were found to be most stable for flame anchoring. However, a counterflow level equal to 6.2% of the primary stream by mass was found to match the characteristics of a single coherent structure while maintaining multiple structures in the mixing zone, effectively increasing heat release rates at a lower equivalence ratio.
Bibliographical noteFunding Information:
This research would not have been possible without the financial support of the Office of Naval Research, contract N00014-05-1-0253, and the guidance we have received from our technical monitor, Gabriel D. Roy.