Flamelet modeling of soot formation in laminar ethyne/air-diffusion flames

Abstract

Formation, surface growth, and oxidation of soot in an axisymmetric laminar diffusion flame have been calculated using a detailed chemical model for soot formation and oxidation. The laminar flamelet concept has been employed to couple chemical reactions in the gas phase with the flow field. The flow field of the flame is calculated by solving the Navier-Stokes equations in axisymmetric formulation using the SIMPLER algorithm for pressure correction. In addition to the momentum conservation equations, a conservation equation for the mixture fraction and a transport equation for the soot volume fraction are solved in the CFD code. The required source terms for the transport equation for the soot volume fraction are calculated in the mixture fraction/scalar dissipation rate space for laminar flamelets and tabulated in a library. Surface growth and oxidation rates are weighted with the locally calculated soot volume fractions, whereas the source term for particle inception is taken directly from the flamelet calculations. Radiative heat losses from the gas-phase products have been taken into account in the limit of optically thin gases. The soot formation rates are influenced by the heat losses at low scalar dissipation rates. The calculated soot volume fractions agree well with the experimental data from Gomez et al. The sensitivity of the calculated soot volume fractions with respect to the different contributions to the appearance rates has been analyzed.