CoFlame: A refined and validated numerical algorithm for modeling sooting laminar coflow diffusion flames

Mitigation of soot emissions from combustion devices is a global concern. For example, recent EURO 6 regulations for vehicles have placed stringent limits on soot emissions. In order to allow design engineers to achieve the goal of reduced soot emissions, they must have the tools to so. Due to the complex nature of soot formation, which includes growth and oxidation, detailed numerical models are required to gain fundamental insights into the mechanisms of soot formation. A detailed description of the CoFlame FORTRAN code which models sooting laminar coflow diffusion flames is given. The code solves axial and radial velocity, temperature, species conservation, and soot aggregate and primary particle number density equations. The sectional particle dynamics model includes nucleation, PAH condensation and HACA surface growth, surface oxidation, coagulation, fragmentation, particle diffusion, and thermophoresis. The code utilizes a distributed memory parallelization scheme with strip-domain decomposition. The public release of the CoFlame code, which has been refined in terms of coding structure, to the research community accompanies this paper. CoFlame is validated against experimental data for reattachment length in an axi-symmetric pipe with a sudden expansion, and ethylene–air and methane–air diffusion flames for multiple soot morphological parameters and gas-phase species. Finally, the parallel performance and computational costs of the code is investigated.

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The influence of aliphatics on soot inception modelling

10.32920/ryerson.14655627 ◽

2021 ◽

Author(s):

Nemanja Ceranic

Keyword(s):

Volume Fraction ◽

Diffusion Flames ◽

Soot Formation ◽

Fluid Dynamic ◽

Soot Volume Fraction ◽

Surface Reactivity ◽

Complex Nature ◽

Laminar Diffusion Flames ◽

Laminar Diffusion ◽

Polycyclic Aromatic

Soot models have been investigated for several decades and many fundamental models exist that prescribe soot formation in agreement with experiments and theories. However, due to the complex nature of soot formation, not all pathways have been fully characterized. This work has numerically studied the influence that aliphatic based inception models have on soot formation for coflow laminar diffusion flames. CoFlame is the in-house parallelized FORTRAN code that was used to conduct this research. It solves the combustion fluid dynamic conservation equations for a variety of coflow laminar diffusion flames. New soot inception models have been developed for specific aliphatics in conjunction with polycyclic aromatic hydrocarbon based inception. The purpose of these models was not to be completely fundamental in nature, but more so a proof-of-concept in that an aliphatic based mechanism could account for soot formation deficiencies that exist with just PAH based inception. The aliphatic based inception models show potential to enhance predicative capability by increasing the prediction of the soot volume fraction along the centerline without degrading the prediction along the pathline of maximum soot. Additionally, the surface reactivity that was used to achieve these results lied closer in the range of numerically derived optimal values as compared to the surface reactivity that was needed to match peak soot concentrations without the aliphatic based inception models.

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PAHs and Soot Emissions in Oxygenated Ethylene Diffusion Flames at Elevated Pressures

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2018-77180 ◽

2018 ◽

Cited By ~ 1

Author(s):

Krishna C. Kalvakala ◽

Suresh K. Aggarwal

Keyword(s):

Diffusion Flames ◽

Soot Formation ◽

Computational Study ◽

Mixture Fraction ◽

Flame Temperature ◽

Primary Objective ◽

Soot Emission ◽

Elevated Pressures ◽

Polycyclic Aromatic ◽

Soot Emissions

Operating combustion systems at elevated pressures has the advantage of improved thermal efficiency and system compactness. However, it also leads to increased soot emission. We report herein a computational study to characterize the effect of oxygenation on PAHs (Polycyclic Aromatic Hydrocarbons) and soot emissions in ethylene diffusion flames at pressures 1–8atm. Laminar oxygenated flames are established in a counterflow configuration by using N2 diluted fuel stream along with O2 enriched oxidizer stream such that the stoichiometric mixture fraction (ζst) is varied, but the adiabatic flame temperature is not materially changed. Simulations are performed using a validated fuel chemistry model and a detailed soot model. The primary objective of the study was to expand the fundamental understanding of PAH and soot formation in oxygenated flames at elevated pressures. At a given pressure, as the level of oxygenation (ζst) is increased, we observe a significant reduction in PAHs (benzene and pyrene) and consequently in soot formation. Further, at a fixed ζst, as pressure is increased, it leads to increased benzene and pyrene formation, and thus increased soot emission. The reaction path analysis indicates that this can be attributed to the fact that at higher pressures, the C2/C4 path becomes more significant for benzene formation compared to the propargyl recombination path.

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Polycyclic Aromatic Hydrocarbons and Soot Emissions in Oxygenated Ethylene Diffusion Flames at Elevated Pressures

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4043394 ◽

2019 ◽

Vol 141 (7) ◽

Cited By ~ 1

Author(s):

Krishna C. Kalvakala ◽

Suresh K. Aggarwal

Keyword(s):

Polycyclic Aromatic Hydrocarbons ◽

Aromatic Hydrocarbons ◽

Volume Fraction ◽

Diffusion Flames ◽

Soot Formation ◽

Computational Study ◽

Flame Temperature ◽

Elevated Pressures ◽

Polycyclic Aromatic ◽

Soot Emissions

We report herein a computational study to characterize the effect of oxygenation on polycyclic aromatic hydrocarbons (PAHs) and soot emissions in ethylene diffusion flames at pressures 1–8 atm. Laminar oxygenated flames are established in a counterflow configuration by using N2 diluted fuel stream along with O2-enriched oxidizer stream such that the stoichiometric mixture fraction (ζst) is varied, but the adiabatic flame temperature is not materially changed. Simulations are performed using a validated fuel chemistry model and a detailed soot model. The primary objective is to enhance the fundamental understanding of PAHs and soot formation in oxygenated flames at elevated pressures. At a given pressure, as the level of oxygenation (ζst) is increased, we observe a significant reduction in PAHs (benzene and pyrene) and consequently in soot formation. On the other hand, at a fixed ζst, as pressure is increased, it leads to increased PAHs formation and thus higher soot emission. Both soot number density and soot volume fraction increase with pressure. The reaction path analysis indicates that at higher pressures, the C2/C4 path becomes more significant for benzene formation compared to the propargyl recombination path. Results further indicate that the effectiveness of oxygenation in reducing the formation of pyrene and soot becomes less pronounced at higher pressures. In contrast, the effect of pressure on pyrene and soot formation becomes more pronounced at higher oxygenation levels. The behavior can be explained by examining the flame structure and hydrodynamics effects at different pressure and oxygenation levels.

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The influence of aliphatics on soot inception modelling

10.32920/ryerson.14655627.v1 ◽

2021 ◽

Author(s):

Nemanja Ceranic

Keyword(s):

Volume Fraction ◽

Diffusion Flames ◽

Soot Formation ◽

Fluid Dynamic ◽

Soot Volume Fraction ◽

Surface Reactivity ◽

Complex Nature ◽

Laminar Diffusion Flames ◽

Laminar Diffusion ◽

Polycyclic Aromatic

Soot models have been investigated for several decades and many fundamental models exist that prescribe soot formation in agreement with experiments and theories. However, due to the complex nature of soot formation, not all pathways have been fully characterized. This work has numerically studied the influence that aliphatic based inception models have on soot formation for coflow laminar diffusion flames. CoFlame is the in-house parallelized FORTRAN code that was used to conduct this research. It solves the combustion fluid dynamic conservation equations for a variety of coflow laminar diffusion flames. New soot inception models have been developed for specific aliphatics in conjunction with polycyclic aromatic hydrocarbon based inception. The purpose of these models was not to be completely fundamental in nature, but more so a proof-of-concept in that an aliphatic based mechanism could account for soot formation deficiencies that exist with just PAH based inception. The aliphatic based inception models show potential to enhance predicative capability by increasing the prediction of the soot volume fraction along the centerline without degrading the prediction along the pathline of maximum soot. Additionally, the surface reactivity that was used to achieve these results lied closer in the range of numerically derived optimal values as compared to the surface reactivity that was needed to match peak soot concentrations without the aliphatic based inception models.

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Effect of the Preheated Oxidizer Temperature on Soot Formation and Flame Structure in Turbulent Methane-Air Diffusion Flames at 1 and 3 atm: A CFD Investigation

Energies ◽

10.3390/en14123671 ◽

2021 ◽

Vol 14 (12) ◽

pp. 3671

Author(s):

Subrat Garnayak ◽

Subhankar Mohapatra ◽

Sukanta K. Dash ◽

Bok Jik Lee ◽

V. Mahendra Reddy

Keyword(s):

Mole Fraction ◽

Air Temperature ◽

Reaction Rate ◽

Volume Fraction ◽

Diffusion Flames ◽

Soot Formation ◽

Flame Structure ◽

Soot Volume Fraction ◽

Computational Domain ◽

Pressure Elevation

This article presents the results of computations on pilot-based turbulent methane/air co-flow diffusion flames under the influence of the preheated oxidizer temperature ranging from 293 to 723 K at two operating pressures of 1 and 3 atm. The focus is on investigating the soot formation and flame structure under the influence of both the preheated air and combustor pressure. The computations were conducted in a 2D axisymmetric computational domain by solving the Favre averaged governing equation using the finite volume-based CFD code Ansys Fluent 19.2. A steady laminar flamelet model in combination with GRI Mech 3.0 was considered for combustion modeling. A semi-empirical acetylene-based soot model proposed by Brookes and Moss was adopted to predict soot. A careful validation was initially carried out with the measurements by Brookes and Moss at 1 and 3 atm with the temperature of both fuel and air at 290 K before carrying out further simulation using preheated air. The results by the present computation demonstrated that the flame peak temperature increased with air temperature for both 1 and 3 atm, while it reduced with pressure elevation. The OH mole fraction, signifying reaction rate, increased with a rise in the oxidizer temperature at the two operating pressures of 1 and 3 atm. However, a reduced value of OH mole fraction was observed at 3 atm when compared with 1 atm. The soot volume fraction increased with air temperature as well as pressure. The reaction rate by soot surface growth, soot mass-nucleation, and soot-oxidation rate increased with an increase in both air temperature and pressure. Finally, the fuel consumption rate showed a decreasing trend with air temperature and an increasing trend with pressure elevation.

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