scholarly journals Impact of pressure-based HACA rates on soot formation in varying-pressure coflow laminar diffusion flames

2021 ◽  
Author(s):  
Amin Mansouri ◽  
Leonardo Zimmer ◽  
Seth B. Dworkin ◽  
Nickolas A. Eaves
Keyword(s):  
Growth Mechanism ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Reaction Rates ◽  
Surface Reactivity ◽  
Scaling Factor ◽  
Laminar Flames ◽  
Temperature History ◽  
Laminar Diffusion Flames ◽  
History Of

There are several processes to occur in soot formation and destruction for which some in the growth regime require a better understanding. In this work, a consistent surface reactivity model, developed in recent years, has been implemented across various sooting laminar flames at varying pressures. The surface reactivity function proposed by Khosousi and Dworkin [1] is employed in the present study. It is based on the temperature history of soot particles. As the functionally dependent model has been derived and validated for atmospheric pressure flames, there are discrepancies between simulation and experiment that can be observed as pressures vary. One reason for these discrepancies could be explained by the fact that chemical reaction rates for the soot growth mechanism at atmospheric combustion do not adequately characterize the kinetics at higher pressures. Based on a recently published study [2], the elementary reaction rates that compose the Hydogen-Addition-Carbon-Abstraction soot surface growth mechanism depend on pressure and an empirical pressure scaling factor to account for this pressure dependence has been introduced. It has been determined that after applying the new empirical pressure scaling factor for the soot growth mechanism, the performance of the functionally dependent surface reactivity model improves in the wing regions of the flame for pure-ethylene flames; however, there is minimal change on the wings for the nitrogen-diluted flames. Additionally, the quantity for soot concentration along the centerline of all flames is nearly independent of the surface reactivity model chosen and needs further investigation. For the flames investigated, it is concluded that pressure dependent HACA rates do not alleviate all discrepancies between the numerical and experimental results and that further work is required.

scholarly journals Impact of pressure-based HACA rates on soot formation in varying-pressure coflow laminar diffusion flames

2021 ◽  
Author(s):  
Amin Mansouri ◽  
Leonardo Zimmer ◽  
Seth B. Dworkin ◽  
Nickolas A. Eaves
Keyword(s):  
Growth Mechanism ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Reaction Rates ◽  
Surface Reactivity ◽  
Scaling Factor ◽  
Laminar Flames ◽  
Temperature History ◽  
Laminar Diffusion Flames ◽  
History Of

There are several processes to occur in soot formation and destruction for which some in the growth regime require a better understanding. In this work, a consistent surface reactivity model, developed in recent years, has been implemented across various sooting laminar flames at varying pressures. The surface reactivity function proposed by Khosousi and Dworkin [1] is employed in the present study. It is based on the temperature history of soot particles. As the functionally dependent model has been derived and validated for atmospheric pressure flames, there are discrepancies between simulation and experiment that can be observed as pressures vary. One reason for these discrepancies could be explained by the fact that chemical reaction rates for the soot growth mechanism at atmospheric combustion do not adequately characterize the kinetics at higher pressures. Based on a recently published study [2], the elementary reaction rates that compose the Hydogen-Addition-Carbon-Abstraction soot surface growth mechanism depend on pressure and an empirical pressure scaling factor to account for this pressure dependence has been introduced. It has been determined that after applying the new empirical pressure scaling factor for the soot growth mechanism, the performance of the functionally dependent surface reactivity model improves in the wing regions of the flame for pure-ethylene flames; however, there is minimal change on the wings for the nitrogen-diluted flames. Additionally, the quantity for soot concentration along the centerline of all flames is nearly independent of the surface reactivity model chosen and needs further investigation. For the flames investigated, it is concluded that pressure dependent HACA rates do not alleviate all discrepancies between the numerical and experimental results and that further work is required.

scholarly journals The influence of aliphatics on soot inception modelling

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.

scholarly journals The influence of aliphatics on soot inception modelling

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.

scholarly journals Detailed numerical study of soot surface growth and oxidation in laminar diffusion flames

2021 ◽  
Author(s):  
Ali Khosousi
Keyword(s):  
Diffusion Flames ◽  
Soot Formation ◽  
Surface Reactivity ◽  
Surface Growth ◽  
New Model ◽  
Laminar Diffusion Flames ◽  
Surface Character ◽  
Laminar Diffusion ◽  
Soot Loading ◽  
Ethanol Blends

he focus of the present study is to obtain detailed knowledge of the soot formation and oxidation processes in laminar diffusion flames. The present work studies the effects of various flame properties on soot growth and oxidation, and how they affect a flame’s sooting behaviour. Numerically modelling of soot formation in laminar coflow diffusion flames of vaporized gasoline/ethanol blends at atmospheric pressure is performed. The numerical results are compared with experimental data to gain improved understanding of ethanol addition to gasoline on soot formation. Four gasoline/ethanol blends are investigated to quantify how soot loading varies with the amount of ethanol blending in the fuel. The results of experimental and numerical modelling agree relatively well in terms of the levels of soot volume fraction. Both results show a decrease in soot loading as more ethanol is added in the fuel stream. The work continues by numerically studying the oxidation of soot in laminar ethylene/air coflow diffusion flames. A new model for soot oxidation, a complex process in numerical soot modelling, is developed based on the observation that soot ageing reduces surface reactivity. Using this new model, it is possible to capture the correct behaviour of both smoking and non- smoking flames in various flame configurations. Along with a detailed soot sectional model, the new model predicts the correct soot volume fractions, smoke emission characteristics, and primary particle diameters for different flames without any variation in model parameters. The work extends to study soot surface reactivity in the growth and oxidation regions. Laminar ethylene/air and methane/air coflow diffusion flames are numerically studied to develop a unique soot surface reactivity model. A newly developed surface character model simultaneously accounts for soot surface reactivity in surface growth and oxidation by considering soot ageing and its effects on the particle surface. The new model, which eliminates tuning of one modelling parameter, reconciles the quantification of the evolving soot surface character for both growth and oxidation. The model is shown to be uniquely capable of predicting soot concentrations and smoke emissions within experimental uncertainty in a wide range of laminar diffusion sooting flames.

scholarly journals Detailed numerical study of soot surface growth and oxidation in laminar diffusion flames

2021 ◽  
Author(s):  
Ali Khosousi
Keyword(s):  
Diffusion Flames ◽  
Soot Formation ◽  
Surface Reactivity ◽  
Surface Growth ◽  
New Model ◽  
Laminar Diffusion Flames ◽  
Surface Character ◽  
Laminar Diffusion ◽  
Soot Loading ◽  
Ethanol Blends

he focus of the present study is to obtain detailed knowledge of the soot formation and oxidation processes in laminar diffusion flames. The present work studies the effects of various flame properties on soot growth and oxidation, and how they affect a flame’s sooting behaviour. Numerically modelling of soot formation in laminar coflow diffusion flames of vaporized gasoline/ethanol blends at atmospheric pressure is performed. The numerical results are compared with experimental data to gain improved understanding of ethanol addition to gasoline on soot formation. Four gasoline/ethanol blends are investigated to quantify how soot loading varies with the amount of ethanol blending in the fuel. The results of experimental and numerical modelling agree relatively well in terms of the levels of soot volume fraction. Both results show a decrease in soot loading as more ethanol is added in the fuel stream. The work continues by numerically studying the oxidation of soot in laminar ethylene/air coflow diffusion flames. A new model for soot oxidation, a complex process in numerical soot modelling, is developed based on the observation that soot ageing reduces surface reactivity. Using this new model, it is possible to capture the correct behaviour of both smoking and non- smoking flames in various flame configurations. Along with a detailed soot sectional model, the new model predicts the correct soot volume fractions, smoke emission characteristics, and primary particle diameters for different flames without any variation in model parameters. The work extends to study soot surface reactivity in the growth and oxidation regions. Laminar ethylene/air and methane/air coflow diffusion flames are numerically studied to develop a unique soot surface reactivity model. A newly developed surface character model simultaneously accounts for soot surface reactivity in surface growth and oxidation by considering soot ageing and its effects on the particle surface. The new model, which eliminates tuning of one modelling parameter, reconciles the quantification of the evolving soot surface character for both growth and oxidation. The model is shown to be uniquely capable of predicting soot concentrations and smoke emissions within experimental uncertainty in a wide range of laminar diffusion sooting flames.

Influence of Pressure on Soot Formation in Laminar Diffusion Flames of Methane

2005 ◽  
Author(s):  
Omer Gulder ◽  
Kevin Thomson ◽  
Elizabeth Weckman ◽  
Roydon Fraser ◽  
Greg Smallwood ◽  
...  
Keyword(s):  
Diffusion Flames ◽  
Soot Formation ◽  
Laminar Diffusion Flames ◽  
Laminar Diffusion

scholarly journals A Numerical Investigation on Soot Formation From Laminar Diffusion Flames of Ethylene/Methane Mixture

2008 ◽  
Author(s):  
Hongsheng Guo ◽  
Stephanie Trottier ◽  
Matthew R. Johnson ◽  
Gregory J. Smallwood
Keyword(s):  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Soot Volume Fraction ◽  
Fuel Mixture ◽  
Methyl Radical ◽  
Laminar Diffusion Flames ◽  
Laminar Diffusion ◽  
Methane Mixture ◽  
Phase Chemistry

The sooting propensity of laminar diffusion flames employing ethylene/methane mixture fuel is investigated by numerical simulation. Detailed gas phase chemistry and moments method are used to describe the chemical reaction process and soot particle dynamics, respectively. The numerical model captures the primary features experimentally observed previously. At constant temperatures of air and fuel mixture, both maximum soot volume fraction and soot yield monotonically decrease with increasing the fraction of carbon from methane in the fuel mixture. However, when the temperatures of air and fuel mixture are preheated so that the adiabatic temperatures of all flames are same, the variation of the maximum soot yield becomes higher than what would be expected from a linear combination of the flames of pure ethylene and pure methane, showing a synergistic phenomenon in soot formation. Further analysis of the details of the numerical results suggests that the synergistic phenomenon is caused by the combined effects of the variations in the concentrations of acetylene (C2H2) and methyl radical (CH3). When the fraction of carbon from methane in fuel mixture increases, the concentration of C2H2 monotonically decreases, whereas that of methyl radical increases, resulting in a synergistic phenomenon in the variation of propargyl (C3H3) radical concentration due to the reactions C2H2 + CH3 = PC3H4 + H and PC3H4 + H = C3H3 + H2. This synergistic phenomenon causes a qualitatively similar variation trend in the concentration of pyrene (A4) owing to the reaction paths C3H3 → A1 (benzene) → A2 (naphthalene) → A3 (phenanthrene) → A4. Consequently, the synergistic effect occurs for soot inception and PAH condensation rates, leading to the synergistic phenomenon in soot yield. The similar synergistic phenomenon is not observed in the variation of peak soot volume fraction, since the maximum surface growth rate monotonically decreases, as the fraction of carbon from methane in fuel mixture increases.

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