Nonpremixed edge flames

Relevance of Nonpremixed Edge Flames to Turbulent Flames.62... 

Nonpremixed edge flames (a) 2D mixing layer (From Kioni, P.N., Rogg, B., Bray, K.N.C., and Linan, A., Combust. Flame, 95, 276, 1993. With permission.), (b) laminar jet (From Chung, S.H. and Lee, B.J., Combust. Flame, 86, 62,1991.), (c) flame spread (From Miller, F.J., Easton, J.W., Marchese, A.J., and Ross, H.D., Proc. Combust. Inst., 29, 2561, 2002. With permission.), (d) autoignition front (From Vervisch, L. and Poinsot, T., Annu. Rev. Fluid Mech., 30, 655, 1998. With permission.), and (e) spiral flame in von Karman swirling flow (From Nayagam, V. and Williams, F.A., Combust. Sci. Tech., 176, 2125, 2004. With permission.). (LPF lean premixed flame, RPF rich premixed flame, DF diffusion flame). 

Propagation speed of nonpremixed edge flames of propane with concentration gradient. (From Kim, M.K., Won, S.H., and Chung, S.H., Pwc. Combust. Inst., 31, 901, 2007.)... 

The relevance of nonpremixed edge flames to turbulent nonpremixed flames can be described in two aspects. One is the mechanism of turbulent nonpremixed lifted flames and the other, the flame-hole dynamics. For turbulent lifted flames in nonpremixed jets, the liftoff height is linearly dependent on jet velocity. There have... 

Furthermore, analytical solutions of premixed edges were studied and the dependence of edge speed with the Damkohler number was reported [61], in which the edge speed ranged from positive to negative values, in a similar fashion as nonpremixed edge flames. 

M. L. Shay and P. D. Ronney, Nonpremixed edge flames in spatially varying straining flows. Combust. Flame 112 171-180, 1998. 

Various factors affecting the nonpremixed edge speed, such as flame stretch, preferential diffusion, and heat loss, have also been investigated, including cellular and oscillatory instabilities of edge flames [1,39 3]. 

The relevance of premixed edge flames to turbulent premixed flames can also be understood in parallel to the nonpremixed cases. In the laminar flamelet regime, turbulent premixed flames can be viewed as an ensemble of premixed flamelets, in which the premixed edge flames can have quenching holes by local high strain-rate or preferential diffusion, corresponding to the broken sheet regime [58]. 

A flame edge can be defined as the boundary between the burning and the nonbuming states along the tangential direction on a flame surface, which could exist in both premixed and nonpremixed flames [1,2]. The base of a nozzle-attached flame, either premixed or nonpremixed systems, is a typical example. 

When a premixed or a nonpremixed flame has an edge, fhe neighborhood of edge exhibifs premixed or... 

---