Assessment of Soot Formation Models in Lifted Ethylene/Air Turbulent Diffusion Flame

TL;DR

This study numerically compares different soot formation models in a turbulent ethylene-air lifted diffusion flame, assessing their accuracy against experimental data and analyzing the effects of radiation heat transfer.

Contribution

It introduces a comprehensive comparison of semi-empirical and quadrature-based soot models within a detailed turbulent flame simulation framework.

Findings

Discrepancies due to under-predicted OH radicals and poor mixing.

Radiation effects do not significantly alter soot trend predictions.

Models show varying accuracy in predicting soot formation stages.

Abstract

In the present study, soot formation in the turbulent lifted diffusion flame, consisting of ethylene-air is numerically investigated using three different soot modeling approaches and is comprehensively reported. For turbulence-chemistry interaction, Flamelet generated manifold (FGM) model is used. A detailed kinetics is used which is represented through POLIMI mechanism (Ranzi et al. 2012). Soot formation is modeled using two different approaches, semi-empirical two-equation approach and Quadrature methods of moments approach, where both the approaches consider various sub-processes such as nucleation, coagulation, surface growth and oxidation. The radiation heat transfer is taken into account considering four fictitious gasses in conjunction with the weighted-sum-of-gray gas (WSSGM) approach for modeling absorption coefficient. The experimental and earlier published numerical data from K\"ohler et al. (2012) and Blacha et al. (2011) are used for assessment of different soot modeling approaches. The discrepancies between numerical and experimental data are observed due to under-prediction of OH radicals concentration and poor fuel-air mixing ratios in the vicinity of the fuel jet region leading to early soot formation and the trends are unaffected after invoking radiation.