Opposed-Flow Diffusion Flames

Lutz, A.E., R. J. Kee, J.F. Grcar, and F.M. Rupley. 1997. OPPDIF A Fortran program for computing opposed-flow diffusion flames. Sandia Report SAND96-8243. 

Fig. 1.1 Illustration of a premixed flat-flame burner and an opposed-flow diffusion flame.

The right-hand panel of Fig 1.1 illustrates an opposed-flow diffusion-flame arrangement. Here the fuel and oxidizer flows are separated, only coming together at the flame. Both premixed and nonpremixed flames find use in practical combustion devices. Thus it is important to model and understand the behaviors of both types of flames, as well as combinations. The opposed contraction nozzles illustrated in the figure lead to a desirable flow similarity, which facilitates modeling and data interpretation. 

Fig. 13.12 Opposed-flow diffusion flame between parallel, axisymmetric, burner faces that are fabricated as honeycomb monoliths. As illustrated, the flame is positioned on the oxidizer side of the stagnation plane. However, depending on the flow conditions as well as the fuel and oxidizer composition, the flame may form on the fuel side of the stagnation plane.

Fig. 17.7 Structure of a hydrogen-air, opposed-flow diffusion flame.

As illustrated, here a single variable (the maximum temperature) is chosen as a characteristic function of the solution. For the premixed twin flame, this is a good choice. However, in other circumstances, like an opposed-flow diffusion flame, the choice of a characteristic scalar is less clear. Vlachos avoids the need for a choice by using a norm of the full-solution vector to characterize the solution in the arc length [415,416], The Nish-... 

Fig. 11 Species concentration profiles vs. distance from fuel burner surface for (A) major species and (B) PAHs generated in an ethylene opposed flow diffusion flame. (From Ref.. )...

Experiments under subcritical conditions appear to be most promising in this respect. As an example, we may cite a number of works in which different relationships at the extinction limit were used for the determination of the effective activation energy and preexponential factor of the gas-phase combustion reaction. In particular, Krishnamurthy 87) calculated the kinetic parameters of the gas-phase combustion of PMMA from the relationship between the combustion rate and the oxygen pressure and concentration at the extinction limit (Eg = 88 kJ /mol k0 = 3x 1012 cm3/mol s). Other authors 76,94) did the same by analyzing the relationship between the extinguishing oxidant flow velocity and oxidant concentration, with the help of an opposed flow diffusion flame (OFDF) apparatus. A similar relationship between flow velocity and oxidant temperature was suggested, since preheating of the oxidant was found to immediately affect the flame temperature. For PMMA, PE and polyoxymethylene (POM) Eg = 98.5, 140 and 121 kJ/mol, respectively, were reported. 

A. Dvorjetski, J.B. Greenberg Lewis nurntxa- and droplet slip effects in water spray suppression of opposed flow diffusion flames, 19th Annual Symposium of the Israeli Section of the Combustion Institute, Haifa, December 2003. 

Matthews, R. D. and Sawyer, R. F. Limiting oxygen index measurement and interpretation in an opposed flow diffusion flame apparatus. J. Fire and Flammability, 7, 238 (1976)... 

Sarathy SM, Gail S, Syed SA, Thomson MJ, Dagaut P. A comparison ofsamrated and unsaturated C-4 fatty acid methyl esters in an opposed flow diffusion flame and a jet stirred reactor. Proc Combust Inst. 2007 31 1015-1022. 

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