Premixed flame strained

COSILAB Combustion Simulation Software is a set of commercial software tools for simulating a variety of laminar flames including unstrained, premixed freely propagating flames, unstrained, premixed burner-stabilized flames, strained premixed flames, strained diffusion flames, strained partially premixed flames cylindrical and spherical symmetrical flames. The code can simulate transient spherically expanding and converging flames, droplets and streams of droplets in flames, sprays, tubular flames, combustion and/or evaporation of single spherical drops of liquid fuel, reactions in plug flow and perfectly stirred reactors, and problems of reactive boundary layers, such as open or enclosed jet flames, or flames in a wall boundary layer. The codes were developed from RUN-1DL, described below, and are now maintained and distributed by SoftPredict. Refer to the website http //www.softpredict.com/cms/ softpredict-home.html for more information. 

Egolfopoulos, F.N., Zhang, H., and Zhang, Z., Wall effects on the propagation and extinction of steady, strained, laminar premixed flames. Combust. Flame, 109,237,1997. 

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]. 

Marzouk,Y.M., Ghoniem, A.F., and Najm, H.N., Dynamic response of strained premixed flames to equivalence ratio gradients, Proc. Combust. Inst., 28,1859, 2000. 

Turbulent mass burning rate versus the turbulent root-mean-square velocity by Karpov and Severin [18]. Here, nis the air excess coefficient that is the inverse of the equivalence ratio. (Reprinted from Abdel-Gayed, R., Bradley, D., and Lung, F.K.-K., Combustion regimes and the straining of turbulent premixed flames. Combust. Flame, 76, 213, 1989. With permission. Figure 2, p. 215, copyright Elsevier editions.)... 

R. Abdel-Gayed, D. Bradley, and F.K.-K. Lung 1989, Combustion regimes and the straining of turbulent premixed flames. Combust. Flame 76 213-218. 

In flame extinction studies the maximum temperature is used often as the ordinate in bifurcation curves. In the counterflowing premixed flames we consider here, the maximum temperature is attained at the symmetry plane y = 0. Hence, it is natural to introduce the temperature at the first grid point along with the reciprocal of the strain rate or the equivalence ratio as the dependent variables in the normalization condition. In this way the block tridiagonal structure of the Jacobian can be maintained. The flnal form of the governing equations we solve is given by (2.8)-(2.18), (4.6) and the normalization condition... 

A number of theoretical (5), (19-23). experimental (24-28) and computational (2), (23), (29-32). studies of premixed flames in a stagnation point flow have appeared recently in the literature. In many of these papers it was found that the Lewis number of the deficient reactant played an important role in the behavior of the flames near extinction. In particular, in the absence of downstream heat loss, it was shown that extinction of strained premixed laminar flames can be accomplished via one of the following two mechanisms. If the Lewis number (the ratio of the thermal diffusivity to the mass diffusivity) of the deficient reactant is greater than a critical value, Lee > 1 then extinction can be achieved by flame stretch alone. In such flames (e.g., rich methane-air and lean propane-air flames) extinction occurs at a finite distance from the plane of symmetry. However, if the Lewis number of the deficient reactant is less than this value (e.g., lean hydrogen-air and lean methane-air flames), then extinction occurs from a combination of flame stretch and incomplete chemical reaction. Based upon these results we anticipate that the Lewis number of hydrogen will play an important role in the extinction process. 

Figure 18.6 Time-averaged strain Ur and velocity field (a) and instantaneous strain and velocity field (6) of the premixed flame for —U jU 1 = 0.0. The scale of the velocity vector length is 3.6 m/s per 1 mm...

Li, S. C., and N. llincic. 1995. Influences of sprays on strained partially premixed flames. AIAA Paper No. 95-2555. 

DuPont, V., M. Pourkashanian, A. P. Richardson, A. Williams, and M. J. Scott. 1996. The importance of prompt-NO formation and of NO reconversion in strained laminar binary rich partially premixed flames. In Transport phenomena in combustion. Washington, DC Taylor Francis 1 263-74. 

Opposed-flow configurations can be used to establish strained premixed flames. Like the diffusion-flame situation, there are several ways to create the opposed flow, including opposed porous plates [197] or opposed contraction nozzles [349]. As illustrated in Fig. 17.8, two opposed contraction nozzles form a symmetric flow. When the mixture stoichiometry, temperature, and flow rates are equal in both nozzles, twin flames are stabilized near the center. 

Fig. 17.8 Schematic of an opposed-nozzle configuration, leading to twin, strained, premixed flames.

Fig. 17.10 Velocity profiles for opposed-flow premixed flames, using both the finite-separation and semi-infinite formulation. Both profiles have the same apparent strain rate of 1200 s 1.

R.G. Abdel-Gayed, D. Bradley and F.K-K. Lung, Combustion Regimes and the Straining of Turbulent Premixed Flames, Comb, and Flame 76 (1989) 213. 

Fig. 42.13 Extinction mass concentration with respect to strain rate for different powder particle sizes in a propane/air, counterflow, non-premixed flame [1]...

Egolfopoulos FN Dynamics and structure of unsteady, strained, laminar premixed flames, Proc Combust Inst 25 1365—1373, 1994. 

J. -B. Liu and R D. Rormey, Premixed edge-flames in spatially-varying straining flows. Combust. Sci. Tech. 144 21-45,1999. 

Yang, S.l. and Shy, S.S., Global quenching of premixed CH4/air flames Effects of turbulent straining, equivalence ratio, and radiative heat loss, Proc. Combust. Inst., 29,1841,2002. 

Libby, R, Lihan, A., and Williams, R, Strained premixed laminar flames with nonunity Lewis numbers. Combust. Set. Technol, 34, 257, 1983. 

Darabiha, N., Candel, S., and Marble, R, The effect of strain rate on a premixed laminar flame. Combust. Flame, 64, 203, 1986. 

Giovangigli, V. and Smooke, M., Extinction of strained premixed laminar flames with complex chemistry. Combust. Sci. Technol., 53,23, 1987. 

Kee, R.J., Miller, J.A., Evans, G.H., and Dixon-Lewis, G., A computational model of the structure and extinction of strained, opposed flow, premixed methane-air flames, Proc. Combust. Inst., 22, 1479, 1988. 

Chapter 6.2, contributed by S.S. Shy, is devoted to the problem of flame quenching by turbulence, which is important from the point of view of combustion fundamentals as well as for practical reasons. Effecfs of turbulence straining, equivalence ratio, and heat loss on global quenching of premixed furbulenf flames are discussed. 

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