Numerical modeling of soot formation in a turbulent C₂H₄/air diffusion flame

Abstract

Soot formation in a lifted C 2 H 4 -Air turbulent diffusion flame is studied using two different paths for soot nucleation and oxidation; by a 2D axisymmetric RANS simulation using ANSYS FLUENT 15.0. The turbulence-chemistry interactions are modeled using two different approaches: steady laminar flamelet approach and flamelet-generated manifold. Chemical mechanism is represented by POLIMI to study the effect of species concentration on soot formation. P1 approximation is employed to approximate the radiative transfer equation into truncated series expansion in spherical harmonics while the weighted sum of gray gases is invoked to model the absorption coefficient while the soot model accounts for nucleation, coagulation, surface growth, and oxidation. The first route for nucleation considers acetylene concentration as a linear function of soot nucleation rate, whereas the second route considers two and three ring aromatic species as function of nucleation rate. Equilibrium-based and instantaneous approach has been used to estimate the OH concentration for soot oxidation. Lee and Fenimore-Jones soot oxidation models are studied to shed light on the effect of OH on soot oxidation. Moreover, the soot-radiation interactions are also included in terms of absorption coefficient of soot. Furthermore, the soot-turbulence interactions have been invoked using a temperature/mixture fraction-based single variable PDF. Both the turbulence-chemistry interaction models are able to accurately predict the flame liftoff height, and for accurate prediction of flame length, radiative heat loss should be accounted in an accurate way. The soot-turbulence interactions are found sensitive to the PDF used in present study.

Soot modeling in turbulent diffusion flames: review and prospects

“…Using semi-empirical models frequently involves the adjustment of the empirical model constants for a wider fuel application and to correctly fit the experimental data [106]. In recent years, the implementation of semi-empirical models has been related to the numerical modeling of methane/air flames [99], [107], ethylene/air diffusion flames [108], methane and heptane turbulent diffusion flames [109], and sooty kerosene/air diffusion flames [86]. Most of these research efforts accounted for radiation effects and their influence on flame temperature and chemical species formation.…”

Large-Eddy Simulation and analysis of a sooting lifted turbulent jet flame

“…In steady-state simulations of the SLTJF, a high sensitivity of soot formation to the correct prediction of fuel and air mixing is observed [15,[20][21][22]. This holds for other sooting jet flames, too.…”

Assessment of soot formation models in lifted ethylene/air turbulent diffusion flame

“…Primarily to include soot formation in the higher hydrocarbons, Hall et al [13] extended the soot inception rate in the previous model, which is based on the formation of two-ringed and three-ringed aromatics from acetylene, benzene and phenyl radicals. Recently, Reddy et al [14][15][16] explored empirical as well as semi-empirical soot models in Delft Flame III [17] and turbulent lifted ethylene-air flame [18] and achieved agreeable predictions as compared to experimental measurements and the published data as well. Lignell et al [19] performed two-dimensional DNS simulations combined with semi-empirical soot modeling in non-premixed turbulent counter-flowing ethylene-air flame using acetylene as a soot precursor; later on Bisetti et al [20] performed DNS in heptane/air turbulent counter-flow non-premixed flame using HMOM as soot model with soot inception rate, based on PAH molecules and their study has provided a brief insights in the soot particle dynamics and particle size distributions.…”

“…Fig 16. Contours of the soot volume fraction field where (a) experimental measurement[18]; (b) Moss-Brookes (MB) approach; (c) Moss-Brookes-Hall (MBH) approach; and (d) Method of Moment (MOM) approach using non-gray radiation and equilibrium approach.…”