Instantaneous flame-stabilization velocities in lifted-jet diffusion flames

Liftoff height and velocity measurements are presented for turbulent, lifted methane and ethylene flames. A range of Reynolds numbers from 3800 to 22,000 is investigated, and the effect of coflow velocity is examined. The mean liftoff height is shown to increase with jet-exit and coflow velocity, while the rms fluctuation about the mean increases with distance from the jet exit. Particle image velocimetry (PIV) is used to provide instantaneous, two-dimensional velocity fields in the region of the lifted flame base. The results show that the instantaneous flame base is anchored primarily in the low-velocity regions of the jet, with axial and radial movement of the flame to meet this criterion. The fluid velocity conditioned on the instantaneous flame base location is less than three times the laminar flame speed, and the velocity profiles through the flame base are similar in nature to those predicted by recent simulations of triple flames. (C) 1997 by The Combustion Institute.