Flame structure

Fristrom, R. M. and Westenberg, A. A., Flame Structure, McGraw-Hill Book Co., New York, 1965. 

The chronology of the most remarkable contributions to combustion in the early stages of its development is as follows. In 1815, Sir Humphry Davy developed the miner s safety lamp. In 1826, Michael Faraday gave a series of lectures and wrote The Chemical History of Candle. In 1855, Robert Bunsen developed his premixed gas burner and measured flame temperatures and flame speed. Francois-Ernest Mallard and Emile Le Chatelier studied flame propagation and proposed the first flame structure theory in 1883. At the same time, the first evidence of detonation was discovered in 1879-1881 by Marcellin Berthelot and Paul Vieille this was immediately confirmed in 1881 by Mallard and Le Chatelier. In 1899-1905, David Chapman and Emile Jouguet developed the theory of deflagration and detonation and calculated the speed of detonation. In 1900, Paul Vieille provided the physical explanation of detonation... 

Kasper, T.S. et al., Ethanol flame structure investigated by molecular beam mass spectrometry. Combust. Flame, 150,220,2007. 

This thermal flame structure indicates local heat flow from the flame tip to the adjacent combustion gases in... 

D. Veynante, L. Vervisch, T. Poinsot, A. Linan, and G. R. Ruetsch, Triple flame structure and diffusion flame stabilization, Proceedings of the Summer Program, Center for Turbulent Research 55-73,1994. 

Y. Huang and V. Yang. Bifurcation of flame structure in a lean-premixed swirl-stabilized combustor Transition from stable to unstable flame. Combust. Flame, 136(3) 383-389, 2004. 

To scrutinize the sensitivity of the flame structure to the description of the outer-flow field, we compared the flame structure obtained from the two limiting boundary conditions at the extinction state, which can be considered to be the most aerodynamically and kinetically sensitive state of the flame for a given mixture concentration, and demonstrated that they were basically indistinguishable from each other. This result thus suggests that the reported discrepancies in the extinction stretch rates as mentioned in the work by Kee et al. [19] are simply the consequences of the "errors" associated with the evaluation of the velocity gradients. 

In this simplified situation, can we really consider that the mean flame structure and thickness are steady, after certain delay and distance from initiation, and then the "turbulent flame speed" is a well-defined intrinsic quantity Indeed, with the present state of knowledge, there is no certainty in any answer to this question. Of course, it is hardly possible to build an experiment with nondecaying turbulence without external stirring. In deca)dng turbulence, the independence of the turbulent flame speed on the choice of reference values of progress variable has been verified in neither experiment nor theory. 

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 ... 

Wrinkled laminar flamelet regime. The well-known ideal regime where the laminar flame structure is only wrinkled by turbulence without any modification of ifs internal structure. 

B. Renou, M. Boukhalfa, D. Puechberty, and M. Trinite 2000, Local flame structure of freely propagating premixed turbulent flames at various Lewis number. Combust. Flame 123 107-115. 

B. Renou, A. Mura, E. Samson, and M. Boukhalfa 2002, Characterization of the local flame structure and the flame surface density for freely propagating premixed flames at various Lewis number. Combust. Sci. Technol. 174 143-179. 

Y.C. Chen, N. Peters, G.A. Schneemarm, N. Wruck, U. Renz, and M.S. Mansour 1996, The detailed flame structure of highly stretched turbulent premixed methane-air flames. Combust. Flame 107 223-244. 

J. Abraham, RA. Williams, and RV. Bracco 1985, A discussion of turbulent flame structure in premixed charge, SAE Paper 850343, in Engine Combustion Analysis New Approaches, p. 156. 

Chemiluminescence images of a turbulent CH4/H2/N2 jet flame (Re = 15,200) measured with two different exposure times. The long-exposure image (far left) indicates the mean flame structure, and the six shorter exposures to the right illustrate the instantaneous turbulent structure. 

Transient computations of methane, ethane, and propane gas-jet diffusion flames in Ig and Oy have been performed using the numerical code developed by Katta [30,46], with a detailed reaction mechanism [47,48] (33 species and 112 elementary steps) for these fuels and a simple radiation heat-loss model [49], for the high fuel-flow condition. The results for methane and ethane can be obtained from earlier studies [44,45]. For propane. Figure 8.1.5 shows the calculated flame structure in Ig and Og. The variables on the right half include, velocity vectors (v), isotherms (T), total heat-release rate ( j), and the local equivalence ratio (( locai) while on the left half the total molar flux vectors of atomic hydrogen (M ), oxygen mole fraction oxygen consumption rate... 

Fristrom, R.M., Flame Structure and Processes, Oxford University Press, New York, 1995, Chapter 1. 

Abraham, J., FA. Williams, and F.V. Bracco, A Discussion of Turbulent Flame Structures in Premixed Charges. SAE, 850345, 1985. 

Smith, J.R., The influence of turbulence on flame structure in and engine, in Flows in Internal Combustion Engines, T. Uzkan, Editor, ASME New York, 1982, pp. 67-72. 

Comprehensive Theory and Laminar Flame Structure Analysis... 

To determine the laminar flame speed and flame structure, it is now possible to solve by computational techniques the steady-state comprehensive mass, species, and energy conservation equations with a complete reaction mechanism for the fuel-oxidizer system which specifies the heat release. The numerical... 

To examine the effect of turbulence on flames, and hence the mass consumption rate of the fuel mixture, it is best to first recall the tacit assumption that in laminar flames the flow conditions alter neither the chemical mechanism nor the associated chemical energy release rate. Now one must acknowledge that, in many flow configurations, there can be an interaction between the character of the flow and the reaction chemistry. When a flow becomes turbulent, there are fluctuating components of velocity, temperature, density, pressure, and concentration. The degree to which such components affect the chemical reactions, heat release rate, and flame structure in a combustion system depends upon the relative characteristic times associated with each of these individual parameters. In a general sense, if the characteristic time (r0) of the chemical reaction is much shorter than a characteristic time (rm) associated with the fluid-mechanical fluctuations, the chemistry is essentially unaffected by the flow field. But if the contra condition (rc > rm) is true, the fluid mechanics could influence the chemical reaction rate, energy release rates, and flame structure. 

The interaction of turbulence and chemistry, which constitutes the field of turbulent reacting flows, is of importance whether flame structures exist or not. 

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