Simultaneous PIV and OH-PLIF measurements in an unsteady counterflow propane-air diffusion flame

The transient response of a diffusion flame to an unsteady flow-field was studied via simultaneous Particle Image Velocimetry and OH measurements in an oscillating counterflow diffusion flame using Planar Laser Induced Fluorescence. For the forcing frequencies considered, the strain rate fluctuations lagged the velocity fluctuations, but the phase difference decreased with increasing forcing frequency. The width of the OH field responded quasi-steadily at lower forcing frequencies, and showed transient effects as forcing frequency increased. The dilatation velocity, defined as the difference between the minimum velocity in the preheat zone and maximum velocity in the reaction zone, was used as flame temperature indicator. The dilatation velocity showed that the phase difference between the velocity and temperature increased with increasing forcing frequency, confirming the existence of a ″diffusion limited″ response. Original is an abstract.