Simultaneous two-shot CH planar laser-induced fluorescence and particle image velocimetry measurements in lifted CH4/air diffusion flames

Joint two-shot CH planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) measurements near the stabilization region of lifted methane/air diffusion flames stabilized under different flow conditions are presented. The simultaneous technique allows for a determination of the propagation rate of the CH zone relative to the fuel flow. Simultaneous single-shot CH-PLIF and PIV techniques have been used in the past to examine lifted jet flames; however, the double-shot technique of the current study is desirable because it yields information on flame dynamics-as indicated by sequential CH-PLIF-relative to the unburned mixture. Three flow conditions were examined corresponding to three different liftoff heights. While the average velocity at the stabilization point varies between 0.83 m/s for the lowest flow condition (Re-d = 4800) and 1.28 m/s for the highest (Re-d = 8300), the velocity at the stabilization point during instances of zero CH movement (during the time interval of the CH pulses) is constant for all three flow conditions (1.14 +/- 0.4 m/s). Furthermore, the flame is able to stabilize itself against the incoming unburned mixture only when the gas velocity is below a certain limit, above which the flame is convected downstream with the flow.