Observations on the transition from flame liftoff to flame blowout

Abstract

The transition from flame liftoff to flame blowout of a non-premixed turbulent jet flame was observed by comparing a stable lifted flame with a lifted flame near blowout. The near-blowout condition was achieved by changing the coflow speed of a lifted flame in coflow. The velocity field at the flame base and the location of the flame surface were simultaneously obtained using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of CH. Instantaneous images showed the divergence and the deceleration of the flow at the flame base, which is characteristic of a leading edge flame. The width of the flame base was found to be wider when the flame was near blowout. The velocity measurements at the flame base show that the flame base of a flame near blowout is exposed to a higher axial velocity (3.1 S L ) compared to a stable lifted flame (2.3 S L ) These observations are consistent with the numerical study of the laminar triple flame. In addition the axial velocity on the flame surface tends to stay at or near the stoichiometric velocity ( U S ), which is determined by the stoichiometric mixture fraction (Z S ), jet speed, and the coflow speed ( U CF ). Accepting the leading edge flame as the flame stabilization mechanism, we propose a simple blowout mechanism.