A new criterion is proposed for predicting the length of gaseous turbulent diffusion flames at high Reynolds numbers. The flame tip is identified with the point on the axis of maximum fuel concentrations where the fuel has been diluted to the lean flammability limit. A direct test using data in the literature shows good agreement. Flame-length equations are derived using the new criterion, together with data from the literature on entrainment of air into flames, transverse concentration profiles in turbulent jets, and flammability limits. With no arbitrary constants, these equations are in reasonable agreement with data and published equations for a turbulent diffusion flame in still air. With presently available data, the new criterion appears to be useful for predicting flame shapes and lengths in flows for which cold-flow concentration data are available from model studies. New experiments on turbulent diffusion flames at high Reynolds numbers are required for a definitive assessment of the proposed concepts.
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