Propagation and extinction of premixed edge-flames

The propagation rates (U _edge ) of edge-flames in premixed hydrocarbon-oxygen-inert mixtures were measured as a function of global strain rate (?), mixture strength, and (by changing fuel and inert type) Lewis number (Le). Using a counterflow slot-jet burner with electrical heaters at both ends to anchor the flame edges, both advancing (positive U _edge ) and retreating (negative U _edge ) edge-flames were characterized. Results are presented for both twin (premixed gas against premixed gas) and single (premixed gas against cold inert gas) edge-flames in terms of the effects of a non-dimensional strain rate (?) and non-dimensional heat loss (?) on a scaled propagation rate. U _edge showed a strong dependence on Le and flames images show that high (low) Le lead to weaker (stronger) edge-flame burning intensity. U _edge for single edge-flames scaled with the square root of the unburned to burned gas density ratio in a manner similar to nonpremixed flames whereas for premixed flames U _edge scaled linearly with density ratio. Edge-flames exhibited two extinction limits corresponding to a high-? strain induced limit and a low-? heat loss induced limit; a simple description of the low-? limits was proposed and found to correlate well with experiments in twin-premixed, single-premixed, and nonpremixed edge-flames over more than a two-decade range of ?. Results are in good qualitative and reasonable quantitative agreement with simple theories except that retreating twin edge-flames in high-Le mixtures are predicted theoretically but were not observed experimentally.