A simplified model for soot formation and oxidation in CFD simulation of non-premixed hydrocarbon flames

Abstract

A new approach to modeling soot formation and oxidation in non-premixed hydrocarbon flames has been developed and subjected to an initial calibration. The model considers only the phenomena essential for obtaining sufficiently accurate predictions of soot concentrations to make CFD calculations of fire radiation feasible in an engineering context. It is generalized to multiple fuels by relating the peak soot formation rate to a fuel's laminar smoke point height, an empirical measure of relative sooting propensity, and applying simple scaling relationships to account for differences in fuel stoichiometry. Soot oxidation is modeled as a surface area independent process because it is controlled by the diffusion of molecular oxygen into the zone of active soot oxidation rather than being limited by reaction of OH· radicals with the available soot surface area. The soot model is embedded within a modified version of NIST's Fire Dynamics Simulator and used for a comparison of predicted and measured temperatures, soot volume fractions, and velocities in laminar ethylene, propylene, and propane flames. The basic approach, though promising, is not yet mature and several suggestions for future work are presented.