Lifted Diffusion Flame Stabilisation: Conditional Analysis of Multi-Parameter High-Repetition Rate Diagnostics at the Flame Base

Data from simultaneous 5 kHz OH-PLIF and Stereo-PIV at the stabilisation region of a propane/ argon lifted diffusion jet flame are presented for jet-exit Reynolds numbers of 10,000 and 15,000. The time history leading to the upstream appearance of flame islands is investigated for both flames. These flame islands are found to be preceded, on average, by a increased out-of-plane fluid velocity. Conditioning local flame statistics on the instantaneous flame base, as indicated by the OH image, permits analysis of upstream and downstream flame motions (in laboratory co-ordinates). The relative velocity is investigated by conditioning out the data with significant out-of-plane fluid velocity. This has introduced greater accuracy over previous attempts at estimating this quantity. No evidence is found for a correlation between increased turbulence intensity or the passage of large scale eddies with increased flame propagation speeds. Furthermore, divergence at the flame base is not found to correlate with upstream flame motion (as a combination of propagation and convection). The volume of the data investigated has led to the development of robust statistics for all quantities presented here.