COMBUSTION AND FLAME 79: 287-298 (1990) 287 A Soot Formation Rate Map for a Laminar Ethylene Diffusion Flame J. H. KENT and D. R. HONNERY Department of Mechanical Engineering, University of Sydney, N.S.W. 2006, Australia Measured soot volume fraction profiles are combined with the modeled temperatures, velocities, and mixture fractions in an axisymmetric laminar diffusion flame to derive local soot formation rates. The flame is modeled by solving transport equations for momentum, mixture fraction, and enthalpy together with a radiation model. The measured soot concentration profiles are differentiated along the computed particle trajectories. The soot formation rates are correlated with local mixture fraction and temperature. Although the range of mixture fraction-temperature combinations available in this flame is not complete, the map provides quantitative information in the principal soot- producing region. NOMENCLATURE ag gravitational acceleration D diffusivity Eox monochromatic blackbody emissive power fv soot volume fraction I radiation intensity K soot absorption coefficient L mean beam length ths soot mass formation rate per unit gas vol- ume r radial coordinate S, source/sink term for ~b variable T temperature u axial component of velocity V t thermophoretic velocity x axial coordinate Greek Symbols accommodation coefficient Fo transport coefficient for scalar emissivity 0 azimuthal angle X wavelength /~ dynamic viscosity v kinematic viscosity Copyright © 1990 by The Combustion Institute Published by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 O density o Stefan-Boltzmann constant ~k scalar variable, mixture fraction or enthalpy ~b stream function Subscripts c~ in surrounding air S soot ~, monochromatic INTRODUCTION The determination of soot concentrations in prac- tical flames for radiation or pollution emission predictions remains one of the unsolved problems in combustion engineering. A popular approach with modeling major and some minor species in diffusion flames is to relate the species concentra- tions to a conserved scalar, the mixture fraction [1, 2]. Solution of the transport equation for mixture fraction then yields species concentration profiles. This approach is valid when the chemical kinetic rates governing the species are fast compared with the molecular mixing rates in the flow. Soot for- mation rates, however, are not necessarily faster than mixing rates [3] and soot concentrations do 001~21~/~/~3.50