The stabilization mechanism of the lifted jet diffusion flame in the hysteresis region

Recent experimental efforts focused on near-field coherent vortex dynamics, and their impact on stabilization of a lifted jet diffusion flame in the hysteresis region are reported. Simultaneous jet flow and flame visualizations are conducted first to obtain a global feature of flow/flame interaction. The statistical liftoff heights are calculated by a DIP (digital image processing) method. The gas concentration and velocity distributions induced by the vortex evolution as well as the corresponding flame front motion are deduced from phase-averaged measurements of planar Mie-scattering gas concentration images, LDV and ion-signals, respectively. The planar gas concentration technique employed here extends our previous work (Chao et al. 1990, 1991 a) to include phase-averaging. Results of the experiments show that the most probable flame base locations in the hysteresis region are at the coherent vortex roll-up and pairing locations. The deeply entrained air lump caused by large-scale vortices during roll-up and pairing is the main obstruction to flame propagation back to the nozzle exit and causes the hysteresis phenomenon.