Soot formation with C1 and C2 fuels using an improved chemical mechanism for PAH growth

Abstract

Recently, an improved chemical mechanism of PAH growth was developed and tested in soot computations for a laminar co-flow non-premixed ethylene-air diffusion flame. In the present work, the chemical mechanism was enhanced further to accommodate the PAH gas phase growth in methane, ethylene and ethane co-flow flames. The changes in the mechanism were tested on a methane/oxygen and two ethane/oxygen premixed flames to ensure no degradation in its application to C 2 fuels. The major soot precursors were predicted in a satisfactory matter.The robustness of the soot solution methodology was tested for different fuels by solving methane/air, ethane/air and ethylene/air co-flow laminar diffusion flames using a single solution algorithm for all three cases. The peak soot volume fractions, which varied by two orders of magnitude between fuels, were predicted within a factor of two for all flames. The computations were also able to reproduce the spatial distributions of soot and to explain the variation in soot formation pathways among the fuels. Despite a similarity in bulk properties of the flame, the soot particles in different flames exhibit significantly different growth modes.Ethylene/air flames tend to form soot earlier than methane/air flames and inception plays a bigger role in the latter.

Experimental and numerical study of soot formation in laminar coflow diffusion flames of gasoline/ethanol blends

“…O 2 oxidation is based on the oxidation of Phenyl proposed by Frenklach and Wang [33]. In previous numerical studies based on the CoFlame code [17,[20][21][22][23][24][25], the steric factor α, which represents the fraction of soot surface sites for HACA surface reactions (except oxidation by OH) [31,33], was considered as a model parameter, whose value was tuned to provide good agreement with available experimental data. Although various efforts have been made to correlate α as a function of temperature, particle size, and in a recent study as a function of thermal age [41], it is unlikely to establish a generic expression for α that can be applied for flames of different fuels.…”

“…An in-house algorithm, known as the CoFlame code, was used to perform the computations in the present study. The CoFlame code has been validated for a variety of fuels [13,[17][18][19][20][21][22][23][24][25]. However, it has not been applied to laminar coflow gasoline/ethanol diffusion flames.…”

Soot modeling of counterflow diffusion flames of ethylene-based binary mixture fuels

“…Earlier models were empirical in nature and soot formation was directly linked to the fuel [22], C 2 H 2 [23] or the benzene concentration [24]. More recent models considered gaseous PAH molecules as soot precursors and treat the inception of soot particles through PAH (typically pyrene) dimerization [7,25,26]. Soot surface growth is mainly through surface HACA mechanism and the particle dynamics has been modeled by the method of moments [27,28].…”

A computational study of ethylene–air sooting flames: Effects of large polycyclic aromatic hydrocarbons

“…As compared with the earlier but widely used ABF PAH mechanism [10], the predictions of pyrene concentrations showed improved agreement with the experimental data. In most recent developments of detailed soot models [23][24][25][26], the primary particle is formed through the dimerization of pyrene (C 16 H 10 or A4). As an attempt to enhance the soot nucleation rates, some of these studies made an unrealistic assumption that every collision leads to a successful creation of a soot nucleus.…”