Propagation and extinction of premixed edge-flames in a counterflow slot burner

The propagation rates (Uedge) of single and twin premixed edge-flames in a slot-jet counterflow were measured as a function of global strain rate (σ) for varying mixture strength and reactant Lewis numbers (Le). Electrical heaters at each end of the slot "anchored" the flame edges when needed, enabling both advancing (positive Uedge) and retreating (negative Uedge) edge-flame speeds to be measured. Similar to prior studies of non-premixed edge-flames, for both single and twin premixed flames, high (low) Le mixtures behave like weaker (stronger) mixtures than mixtures with Le ≈ 1. Stability maps in terms of dimensionless strain rate vs. heat loss exhibit regions of propagating and retreating edges, short-length flames, self-induced holes, and total extinction for both single and twin cases. These maps show that low-strain extinction limits are affected by heat loss and are practically independent of Le whereas the high-strain extinction limits are affected primarily by Lewis number and are independent of heat loss. Additionally, the shapes and features of premixed edge flames could be explained based on the combined effects of Lewis number, strain rate, heat losses and thermal expansion.