Counterflow flames

Yamaoka, 1. and Tsuji, H., Determination of burning velocity using counterflow flames, Proc. Combust. Inst.,... 

Observed premixed edge flames (a) Bunsen flame-tip opening, (b) propagating premixed flame in tube (From Jarosinski, J., Strehlow, R.A., and Azarbarzin, A., Proc. Combust. Inst., 19, 1549, 1982. With permission.), (c) slanted counterflow flame (From Liu, J.-B. and Ronney, P.D., Combust. Sci. Tech., 144,21,1999. With permission.), and (d) spinning premixed flames in sudden expansion tube [7]. 

One significant result from the studies of stretched premixed flames is that the flame temperature and the consequent burning intensity are critically affected by the combined effects of nonequidiffusion and aerodynamic stretch of the mixture (e.g.. Refs. [1-7]). These influences can be collectively quantified by a lumped parameter S (Le i-l)x, where Le is the mixture Lewis number and K the stretch rate experienced by the flame. Specifically, the flame temperature is increased if S > 0, and decreased otherwise. Since Le can be greater or smaller than unity, while K can be positive or negative, the flame response can reverse its trend when either Le or v crosses its respective critical value. For instance, in the case of the positively stretched, counterflow flame, with k>0, the burning intensity is increased over the corresponding unstretched, planar, one-dimensional flame for Le < 1 mixtures, but is decreased for Le > 1 mixtures. 

Experimentally, two modes of extinction, based on the separation between the twin flames are observed. Specifically, the extinction of lean counterflow flames of n-decane/02/N2 mixtures occurs with a finite separation distance, while that of rich flames exhibits a merging of two luminous flamelets. The two distinct extinction modes can be clearly seen in Figure 6.3.2. As discussed earlier, the reactivity of a positively stretched flame with Le smaller (greater) than unity increases (decreases) with the increasing stretch rate. Therefore, the experimental observation is in agreement with the... 

First, for nonequidiffusive, positively stretched counterflow flames, results showed that the flame response exhibited opposite behavior when the mixture s effective Lewis number was greater or less... 

Second, the sensitivity of the flame structure and extinction limit to the description of the outer-flow field was examined. Comparison of the flame structure obtained from different boundary conditions at the extinction state suggested that the reported discrepancies in the computed extinction stretch rates were simply the consequences of how the velocity gradient was evaluated. Further investigation is required to identify an unambiguous parameter characterizing the counterflow-flame extinction limit. 

Kaiser, C., Liu, J.B., and Ronney, P.D., Diffusive-thermal instability of counterflow flames at low lewis number, 38th Aerospace Sciences Meeting and Exhibit, AIAA Paper 2000-0576, 2000. 

Scatter plots of temperature atx/d = 15 in turbulent Cl-14/air jet flames with Reynolds numbers of 13,400 (Flame C) and 44,800 (Flame F). The stoichiometric mixture fraction is = 0.351. The line shows the results of a laminar counterflow-flame calculation with a strain parameter of a = 100 s and is included as a visual guide. (From Barlow, R.S. and Frank, J.H., Proc. Combust. Inst, 27,1087,1998. With permission.)... 

Sardi, E., A. M. K.P. Taylor, and J.H. Whitelaw. 1999. Extinction of turbulent counterflow flames under periodic strain. Combustion Flame 120(3) 265-84. 

Tanoff, M. A., M. D. Smooke, R. J. Osborne, T. M. Brown, and R. W. Pitz. 1996. The sensitive structure of partially premixed methane-air vs. air counterflow flames. 26th Symposium (International) on Combustion Proceedings. Pittsburgh, PA The Combustion Institute. 1121-28. 

Since the possible simultaneous presence of three phenomena— convection, diffusion, and reaction—complicate analyses, it can be helpful to eliminate one of the three formally by means of a transformation. This is achieved in the analysis of the counterflow flame [184] by writing the equations in a convection-free form that is, by finding a transformation to a new spatial variable such that the convective and diffusive terms coalesce into a... 

I 1.1.7. Magnetic Gliding Arc Discharge Ignition of Counterflow Flame... 

H. K. Chelliah, P. C. Wanigarathne, A. M. Lentati, R. H. Krauss, G. S. Fallrai Effect of sodium bicarbonate particle size on the extinction condition of non-premixed counterflow flames. Combust. Flame 134(3), 261-272 (2003). 

E. J. P. Zegers, B. A. Williams, R. S. Sheinson, J. W. Fleming Dynamics and suppression effectiveness of monodisperse water droplets in non-premixed counterflow flames. Proceedings of the Combustion Institute, Vol. 28, pp. 2931-2937, Combustion Institute, Pittsburgh (2000). 

Knyazkov, D. Shmakov, A. Korobeinichev, O. (2007). Application of molecular beam mass spectrometry in studying the structure of a diffusive counterflow flame of CH4/N2 and O2/N2 doped with trimethylphosphate. Combustion and Flame, Vol. 151, No.1-2 pp. 37-45, ISSN 0010-2180... 

Bongers, H., van Oijen, J.A., de Goey, L.P.H. The Flamelet generated manifold method applied to steady planar partially premixed counterflow flames. Combust. Sci. Technol. 177, 2373-2393 (2005)... 

Fiorina, B., Gicquel, O., Vervisch, L., Carpentier, S., Darabiha, N. Approximating the chemical structure of partially premixed and diffusion counterflow flames using FPI flamelet tabulation. Combust Flame 140, 147-160 (2005)... 

Counterflow flame geometries. Stretched one-dimensional flames... 

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