Burke-Schumann diffusion flames convective-diffusive zones

In the present analysis, the outer convective-diffusive zones flanking the reaction zone are treated in the Burke-Schumann limit with Lewis numbers unity. Lewis numbers different from unity are taken into account where reactions occur. These Lewis-number approximations are especially accurate for methane-air flames and would be appreciably poorer if hydrogen or higher hydrocarbons are the fuels. To achieve a formulation that is independent of the flame configuration, the mixture fraction is employed as the independent variable. The connection to physical coordinates is made through the so-called scalar dissipation rate. 

For steady-state diffusion flames with thin reaction sheets, it is evident that outside the reaction zone there must be a balance between diffusion and convection, since no other terms occur in the equation for species conservation. Thus these flames consist of convective-diffusive zones separated by thin reaction zones. Since the stretching needed to describe the reaction zone by activation-energy asymptotics increases the magnitude of the diffusion terms with respect to the (less highly differentiated) convection terms, in the first approximation these reaction zones maintain a balance between diffusion and reaction and may be more descriptively termed reactive-diffusive zones. Thus the Burke-Schumann flame consists of two convective-diffusive zones separated by a reactive-diffusive zone. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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