Soot Precursors Analysys Using Detailed Chemical Kinetic Mechanisms in an Ethylene/Air Laminar Diffusion Flame

Abstract

Tens or even hundreds of chemical species are produced in the nascent stages of hydrocarbon-based fuels combustion that eventually lead to the formation of soot particles and aggregates. In such context, the study of sootrelated chemical species formation and its associated physical-chemical phenomena are of great importance to delve into how in combustion processes the formation of this critical pollutant is carried out. In this work thus, accounting for an ethylene/air laminar diffusion flame previously experimentally characterized employing a Gülder burner configuration, both soot precursors and soot formation are analyzed. Computational mesh independence is addressed here by refining grid elements in such a way that element sizes in the reaction zone are of about 30µm, thus capturing species and temperature gradients in such regions. The NBP (Narayanaswamy, Blanquart and Pitsch Stanford University mech) chemical kinetic mechanism featuring 149 chemical species and 1651 reactions is used for describing gas phase chemistry. Radiation effects are addressed using the discrete ordinates method (DOM) and computing the associated absorption coefficient from a WSGG model. Two soot formation models, an acetylene-based semiempirical and a statistical PAH-based method of moments (MOM), are employed in the soot-related numerical simulations carried out. Temperature profiles predicted using the MOM soot formation model are in fair agreement with the experimental results (peak temperature discrepancies of about 3%). Along the flame centerline and near the burner surface, predicted soot volume fractions match as well the corresponding experimental trends. In the radial direction however, both models lack of precision for describing the soot peak values and their physical location. From the species molar fractions results discussed here, it is observed that one and two aromatic ring groups are the most abundant PAH, so these PAH might be sufficient for soot nucleation purposes. The numerical models and methodologies developed in this work will be used in future for predicting soot formation in turbulent diffusion flames.

Parametric Study of Empirical Constants Used in Soot Formation Models Based on Interpolative Closure Methods of Moments

“…The chemical kinetic mechanism, MOMIC and the radiation models used here are also discussed. Further details about the models employed here can be found in Valencia et al (2021b) and Ruiz et al (2021).…”

“…In turn, measurements of temperature fields were performed by means of a two color pyrometry technique. Further details on boundary conditions accounted for in this work are found in Ruiz et al (2021).…”

“…scheme and PISO algorithm were used for pressure interpolation and velocity-pressure coupling, respectively. The mesh utilized here corresponds to a one that was used previously, which was refined through mesh adaptions based on global scaled gradients of specific gaseous chemical species, i.e., C2H6, C3H3 and OH (Da Costa et al, 2022;Ruiz et al, 2021). For these mesh adaptions, normalized threshold values in the range between 0.1 and 0.01 were chosen according to the results obtained progressively.…”