A PHENOMENOLOGICAL MODEL FOR SMOKE-POINT AND SOOT FORMATION IN LAMINAR FLAMES

A global soot formation model is proposed, validated and applied based on the postulate that soot formation in laminar diffusion flames is c ontrolled by gaseous reaction processes and not the available soot sur face area. Although this model was not derived from detailed soot form ation mechanisms, it is consistent with such mechanisms if the active sites for soot growth are so many that soot growth depends on the avai lability of gaseous species (e.g., C2H2). Global soot formation models in laminar diffusion models based on a surface growth process can not be reconciled with experiments. For the present model, a soot formati on time in axisymmetric laminar diffusion flames below the smoke-point is shown to be proportional to the smoke-point height. Moreover the p resent model implies that smoke-point heights are proportional to pres sure in agreement with experiments. Predictions of the model for flow, dilution and pressure effects on soot concentrations agree with exper iments, both in laminar jet flow (2-D or axisymmetric) and opposed flo w diffusion flames. The effects of radiant cooling on the flame and th e flow structure are also briefly addressed in this work.