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Selective Diffusional Demixing: Occurrence and Size of Cellular Flames.
Prog Energy and Combust Sci 1989 15(3):203-239
The data on cellular flame structures, including those recently reported by several independent investigators, are reviewed and anlayzed in terms of the established mechanisms and concepts of homogeneous flame propagation. A perturbation analysis is used to show how the balance between the processes of selective diffusional demixing and flame stretch readily accounts for the composition domains in which cellular flames occur and also predicts their dimensions. The important, determining properties of the fuel- oxidant moisture are di - dj, the difference in molecular diffusivity between the more diffusive component, I, and the less diffusive component, j; and asu/aci, the slope of the burning velocity curve with respect to the concentration of the more diffusive component. Cellular structures are stable only for stoichiometries in which the more diffusive component, I, is also the deficient component, so that asu/aci > 0. The perturbation analysis also shows that, at the opposing stoichiometry, where the more diffusive component is present in excess, so that asu/aci < 0, selective diffusion tends to erase cellular structures and to stabilize the laminar or one-dimensional ones. A phenomenological theory based on a quantitative balance between selective demixing and flame stretch gives the following result for the cellular flame diameter, d cell:d cell(di - dj)(asu/aci) a2(pu/pb), where a is the effective diffusivity (thermal and mass) across the flame front and pu/pb is the expansion ratio. That equation adequately predicts the absolute magnitude of the cellular f
Issue of Publication
Prog. Energy and Combust. Sci., V. 15, No. 3, 1989, PP. 203-239
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division