Propagation and extinction of premixed H2[sbnd]O2[sbnd]N2 edge-flames

Abstract

The effects of equivalence ratio (ϕ), global strain rate (σ) and mixture strength on the shapes and propagation rates (Uedge) of premixed edge-flames in H2O2N2 mixtures were investigated experimentally using a counterflow slot-jet apparatus. Results are presented for both single (premixed gas against cold inert gas) and twin (premixed gas against premixed gas) configurations. Both advancing (Uedge > 0) and retreating edge-flames (Uedge < 0) were characterized. Flame images show that for lean mixtures where H2 is the deficient species and thus the effective Lewis number (Leeff) is less than unity, the leading edge-flame has a stronger burning intensity than the trailing strained premixed flame. For mixtures with low ϕ (thus low Leeff) at near-extinction conditions corresponding to sufficiently high or low σ, transitions from continuous to broken structures were observed due to diffusive-thermal instabilities. Such transitions enable flames to survive under conditions where extinction would have occurred without transition. The combined effects of ϕ, adiabatic flame temperature and σ were found to correlate well in terms of the effect of a non-dimensional strain rate (ε) on a scaled propagation rate Ũ.