Interactive transient flamelet modeling for soot formation and oxidation processes in laminar non-premixed jet flames

Abstract

The Interactive Transient Flame let (IF) model has been devised to realistically simulate slow processes such as soot formation and radiation in a laminar non-premixed flame with a relatively long residence time. In context with the ITF model, soot formation in the laminar non-premixed jet flame is modeled by the two-equation soot model to simulate physical processes such as nucleation, surface growth, oxidation and agglomeration. In the present ITF approach, gaseous chemistry is effectively coupled with soot chemistry. The present ITF model accounts for radiative cooling induced by gaseous species and soot particles in the same mixture fraction space simultaneously while it treats the unphysical diffusion of soot to be practically zero. Moreover, the present ITF procedure can maintain consistency to extend the present transient flamelet model to the simulation of turbulent non-premixed sooting flames. To validate the present ITF approach together with the two-equation soot model, in terms of soot volume fraction, number density, temperature, OH and C2H2 mass fractions, as well as reaction rates for nucleation, surface growth, and oxidation, numerical results are compared with those obtained by the full transport equation approach. Furthermore, to assess the applicability of the present ITF approach and to evaluate the effects of gaseous differential diffusion on the soot formation processes, numerical results obtained by the present ITF model with equal and differential diffusion are also compared with experimental data in terms of temperature; CH4, OH, H2O, CO2 and C2H2 mole fractions; and soot volume fraction. Based on these numerical results, the detailed discussion has been made for the capability and limitations of the present ITF approach to predict the precise flame structure and soot formation characteristics in the laminar non-premixed methane/air jet flames. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.