Characteristics of the velocity field near the instantaneous base of lifted non-premixed turbulent jet flames

Abstract

The fluid velocity, the flame velocity (in the lab frame of reference), and the strain rates just upstream of the instantaneous location of the flame base are measured in methane and ethylene lifted coflowing jet flames. These measurements are motivated by the supposition that partially premixed laminar flame dynamics and heat release may play important roles in turbulent jet flame stabilization. Although the measurements have significant uncertainty in the flame velocity, a positive correlation exists between fluid and flame velocity, and most of the relative speeds of the flame and the fluid are observed to be in the range 0–3 S L , where S L is the maximum laminar flame speed. It is also found that the measured strain rates experienced by the leading edge of the stabilization flame are approximately one order of magnitude smaller than the extinction strain rates for typical stoichiometric flames. This result casts some doubt on the notion that the flame is a stoichiometric premixed flame extinguished by strain rates induced by large-scale vortical structures in the jet.