Md. Smooke et al., Computational and experimental study of soot formation in a coflow, laminar diffusion flame, COMB FLAME, 117(1-2), 1999, pp. 117-139
A detailed soot growth model in which the equations for particle production
have been coupled to the flow and gaseous species conservation equations h
as been developed for an axisymmetric, laminar, coflow diffusion flame. Res
ults from the model have been compared to experimental data for a confined
methane-air flame. The two-dimensional system couples detailed transport an
d finite rate chemistry in the gas phase with the aerosol equations in the
sectional representation. The formulation includes detailed treatment of th
e transport, inception, surface growth, oxidation, and coalescence of soot
particulates. Effects of thermal radiation and particle scrubbing of gas-ph
ase growth and oxidation species are also included. Predictions and measure
ments of temperature, soot volume fractions, and selected species are compa
red over a range of heights and as a function of radius. Flame heights are
somewhat overpredicted and local temperatures and volume fractions are unde
rpredicted. We believe the inability to reproduce accurately bulk flame par
ameters directly inhibits the ability to predict soot volume fractions and
these differences are likely a result of uncertainties in the experimental
inlet conditions. Predictions of the distributions of particle sizes indica
te the existence of (relatively) low-molecular-weight species along the cen
terline of the burner and trace amounts of the particles that escape from t
he flame, unoxidized. Oxidation of particulates is dominated by reactions w
ith hydroxyl radicals which attain levels approximately 10 times higher tha
n calculated equilibrium levels. Gas cooling effects due to radiative loss
are shown to have a very significant effect on predicted soot concentration
s. (C) 1999 by The Combustion Institute.