Premixed flamelets

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]. 

Lodier, G., Vervisch, L., Moureau, V., Domingo, P. Composition-space premixed flamelet solution with differential diffusion for in situ flamelet-generated manifolds. Combust. Flame 158, 2009-2016 (2011)... 

This recent attempt differs from the previous classification where the wrinkled flamelet regime has been considered up to rj = (5l- Chen and Bilger have proposed to tentatively classify the different turbulent premixed flame structures they observed among four different regimes ... 

Premixed turbulent combustion regime diagram proposed by Chen and Bilger. Two intermediate regimes are delineated between distributed flame front and wrinkled laminar flamelets. (Reprinted from Chen, Y.C. and Bilger, R., Combust. Flame, 131, 400, 2002. With permission. Figure 9, p. 411, copyright Elsevier editions.)... 

A. Mura, F. Galzin, and R. Borghi 2003, A unified PDF-flamelet model for turbulent premixed combustion. Combust. Sci. Technol. 175 (9) 1573-1609. 

Meneveau, C. and T. Roinsot, Stretching and quenching of flamelets in premixed turbulent combustion. Combust. Flame, 1991. 86 311-332. 

A model must be introduced to simulate fast chemical reactions, for example, flamelet, or turbulent mixer model (TMM), presumed mapping. Rodney Eox describes many proposed models in his book [23]. Many of these use a probability density function to describe the concentration variations. One model that gives reasonably good results for a wide range of non-premixed reactions is the TMM model by Baldyga and Bourne [24]. In this model, the variance of the concentration fluctuations is separated into three scales corresponding to large, intermediate, and small turbulent eddies. 

As shown in Fig. 5.20, such regions normally occur only near the inlet zones where micromixing is poor. Further downstream, interaction between flamelets will become significant, and the assumptions on which the flamelet model is based will no longer apply.117 Reactors with recirculation zones are also problematic for flamelet models. For these reactors, partially reacted fluid is brought back to mix with the feed streams so that the simple non-premixed flow model no longer applies. 

An example of such a system is the so-called interacting-flamelet regime for partially premixed combustion. 

Peters, N. (1984). Laminar diffusion flamelet models in non-premixed turbulent combustion. Progress in Energy and Combustion Science 10, 319-339. 

Pitsch, H. and N. Peters (1998). A consistent flamelet formulation for non-premixed combustion considering differential diffusion effects. Combustion and Flame 144,... 

Van Oijen, J. Flamelet-generated manifolds development and application to premixed laminar flames, PhD thesis, Eindhoven University of Technology, Eindhoven, The Netherlands, (2002). 

FlameMaster v3.3 A C+ + Computer Program for OD Combustion and ID Laminar Flame Calculations. FlameMaster was developed by H. Pitsch. The code includes homogeneous reactor or plug flow reactors, steady counter-flow diffusion flames with potential flow or plug flow boundary conditions, freely propagating premixed flames, and the steady and unsteady flamelet equations. More information can be obtained from http //www.stanford.edu/group/pitsch/Downloads.htm. 

Shy, S.S., R. H. Jang, and P. D. Ronney. 1996. Laboratory simulation of flamelet and distributed models for premixed turbulent combustion using aqueous auto-catalytic reactions. Combustion Science Technology 113 329-50. 

Yang, R., Weng, W.G., Fan, W.C., and Wang, Y.S. Subgrid scale laminar flamelet model for partially premixed combustion and its application to backdraft simulation. Fire Safety Journal, 2005. 40(2), 81-98. 

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