Subgrid Modeling of Soot Formation in Non-Premixed Turbulent Flames

2007 ◽  
Author(s):  
H. El-Asrag ◽  
S. Menon
Keyword(s):  
Volume Fraction ◽  
Soot Formation ◽  
Soot Volume Fraction ◽  
Reaction Diffusion ◽  
Mean Free Path ◽  
Current Approach ◽  
Turbulent Flames ◽  
Combustion Model ◽  
Method Of Moment ◽  
Air Jet

A subgrid model for soot dynamics is developed for large-eddy simulation (LES) using the Method of Moment with Interpolative Closure (MOMIC). The soot model is implemented within a subgrid mixing and combustion model so that reaction-diffusion-MOMIC coupling is possible without requiring ad hoc filtering. The combined model includes the entire process, from the initial phase, when the soot nucleus diameter is much smaller than the mean free path, to the final phase, after coagulation and aggregation, where it can be considered in the continuum regime. The soot diffusion and the effect of the thermophoretic forces are included in the model. A relatively detailed but reduced kinetics for ethylene-air is used to simulate an experimentally studied non-premixed ethylene/air jet diffusion flame. In this formulation, acetylene is used as a soot precursor species. The soot volume fraction order of magnitude, the location of its maxima, and the soot particle size distribution are all captured reasonably. Along the centerline, an initial region dominated by nucleation and surface growth is established followed by an oxidation region. A possible initial log-normal distribution followed by a more gaussian distribution downstream the centerline is observed. Limitations of the current approach and possible solution strategies are also discussed.

Numerical Investigation of Soot Formation in Laminar Ethylene-Air Diffusion Flames

2007 ◽  
Author(s):  
Massimiliano Di Domenico ◽  
Peter Gerlinger ◽  
Manfred Aigner
Keyword(s):  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Formation Rate ◽  
Soot Volume Fraction ◽  
Transport Equations ◽  
Combustion Model ◽  
Inlet Temperature ◽  
Elementary Reactions ◽  
Air Diffusion

In this work a new soot formation model is used to predict temperature, species and soot concentrations in laminar ethylene-air diffusion flames. The gas-phase chemistry is described by elementary reactions with transport equations solved for any species. The chemical paths yielding to soot are modeled by a sectional approach for Polycyclic Aromatic Hydrocarbons (PAHs). Soot dynamics is described by a two-equation model for soot mass fraction and particle number density. Phenomena like nucleation, growth and oxidation have been included both for PAHs and soot. Moreover, PAH-PAH and PAH-soot collisions are taken into account. Species, PAH and soot transport equations are implemented in the in-house DLR-THETA CFD code. The laminar, ethylene-air diffusion flame investigated experimentally by McEnally and coworkers (2000) is simulated in order to validate the model. An analysis of the main flame’s features as well as the interaction between them and the soot chemistry will be given. A qualitative correlation between local stoichiometric values and soot formation rate is assessed. In order to study the sensitivity of the combustion model to simulation parameters like the inlet temperature and kinetic mechanism, additional simulations are performed. Results are also compared with experimental data in terms of temperature, species mole fractions and soot volume fraction axial profiles.

scholarly journals 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 ◽  
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.

Analytical Formulation-Based Soot Modelling in Ethylene Laminar Jet Diffusion Flames

2021 ◽  
Author(s):  
Amit Makhija ◽  
Krishna Sesha Giri
Keyword(s):  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Mixture Fraction ◽  
Soot Volume Fraction ◽  
Smoke Point ◽  
Computational Time ◽  
Detailed Model ◽  
Conservation Equations ◽  
Oxidation Rates

Abstract Soot volume fraction predictions through simulations carried out on OpenFOAM® are reported in diffusion flames with ethylene fuel. A single-step global reaction mechanism for gas-phase species with an infinitely fast chemistry assumption is employed. Traditionally soot formation includes inception, nucleation, agglomeration, growth, and oxidation processes, and the individual rates are solved to determine soot levels. However, in the present work, the detailed model is replaced with the soot formation and oxidation rates, defined as analytical functions of mixture fraction and temperature, where the net soot formation rate can be defined as the sum of individual soot formation and oxidation rates. The soot formation/oxidation rates are modelled as surface area-independent processes. The flame is modelled by solving conservation equations for continuity, momentum, total energy, and species mass fractions. Additionally, separate conservation equations are solved to compute the mixture fraction and soot mass fraction consisting of source terms that are identical and account for the mixture fraction consumption/production due to soot. As a consequence, computational time can be reduced drastically. This is a quantitative approach that gives the principal soot formation regions depending on the combination of local mixture fraction and temperature. The implemented model is based on the smoke point height, an empirical method to predict the sooting propensity based on fuel stoichiometry. The model predicts better soot volume fraction in buoyant diffusion flames. It was also observed that the optimal fuel constants to evaluate soot formation rates for different fuels change with fuel stoichiometry. However, soot oxidation strictly occurs in a particular region in the flame; hence, they are independent of fuel. The numerical results are compared with the experimental measurements, showing an excellent agreement for the velocity and temperature. Qualitative agreements are observed for the soot volume fraction predictions. A close agreement was obtained in smoke point prediction for the overventilated flame. An established theory through simulations was also observed, which states that the amount of soot production is proportional to the fuel flow rate. Further validations underscore the predictive capabilities. Model improvements are also reported with better predictions of soot volume fractions through modifications to the model constants based on mixture fraction range.

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 High-speed, three-dimensional tomographic laser-induced incandescence imaging of soot volume fraction in turbulent flames

2016 ◽  
Vol 24 (26) ◽  
pp. 29547 ◽  
Author(s):  
Terrence R. Meyer ◽  
Benjamin R. Halls ◽  
Naibo Jiang ◽  
Mikhail N. Slipchenko ◽  
Sukesh Roy ◽  
...  
Keyword(s):  
High Speed ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Soot Volume Fraction ◽  
Turbulent Flames ◽  
Laser Induced Incandescence

Prediction of Soot Formation Trends in Turbulent Kerosene-Air Diffusion Jet Flames With Elevated Operating Pressure

2017 ◽  
Author(s):  
Pravin Nakod ◽  
Saurabh Patwardhan ◽  
Ishan Verma ◽  
Stefano Orsino
Keyword(s):  
Environmental Protection Agency ◽  
Volume Fraction ◽  
Soot Formation ◽  
Mixture Fraction ◽  
Soot Volume Fraction ◽  
Operating Pressure ◽  
Jet Flames ◽  
Emission Standard ◽  
Radial Profiles ◽  
Air Diffusion

Emission standard agencies are coming up with more stringent regulations on soot, given its adverse effect on human health. It is expected that Environmental Protection Agency (EPA) will soon place stricter regulations on allowed levels of the size of soot particles from aircraft jet engines. Since, aircraft engines operate at varying operating pressure, temperature and air-fuel ratios, soot fraction changes from condition to condition. Computation Fluid Dynamics (CFD) simulations are playing a key role in understanding the complex mechanism of soot formation and the factors affecting it. In the present work, soot formation prediction from numerical analyses for turbulent kerosene-air diffusion jet flames at five different operating pressures in the range of 1 atm. to 7 atm. is presented. The geometrical and test conditions are obtained from Young’s thesis [1]. Coupled combustion-soot simulations are performed for all the flames using steady diffusion flamelet model for combustion and Mass-Brookes-Hall 2-equation model for soot with a 2D axisymmetric mesh. Combustion-Soot coupling is required to consider the effect of soot-radiation interaction. Simulation results in the form of axial and radial profiles of temperature, mixture fraction and soot volume fraction are compared with the corresponding experimental measured profiles. The results for temperature and mixture fraction compare well with the experimental profiles. Predicted order of magnitude and the profiles of the soot volume fraction also compare well with the experimental results. The correct trend of increasing the peak soot volume fraction with increasing the operating pressure is also captured.

Impact of Soot Radiative Properties, Pressure and Soot Volume Fraction on Radiative Heat Transfer in Turbulent Sooty Flames

2020 ◽  
Author(s):  
Kevin Torres Monclard ◽  
Olivier Gicquel ◽  
Ronan Vicquelin
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Volume Fraction ◽  
Soot Volume Fraction ◽  
Turbulent Flames ◽  
Radiative Properties ◽  
Jet Flame ◽  
Soot Particles

Abstract The effect of soot radiation modeling, pressure, and level of soot volume fraction are investigated in two ethylene-air turbulent flames: a jet flame at atmospheric pressure studied at Sandia, and a confined pressurized flame studied at DLR. Both cases have previously been computed with large-eddy simulations coupled with thermal radiation. The present study aims at determining and analyzing the thermal radiation field for different models from these numerical results. A Monte-Carlo solver based on the Emission Reciprocity Method is used to solve the radiative transfer equation with detailed gas and soot properties in both configurations. The participating gases properties are described by an accurate narrowband ck model. Emission, absorption, and scattering from soot particles are accounted for. Two formulations of the soot refractive index are considered: a constant value and a wavelength formulation dependency. This is combined with different models for soot radiative properties: gray, Rayleigh theory, Rayleigh-Debye-Gans theory for fractal aggregates. The effects of soot radiative scattering is often neglected since their contribution is expected to be small. This contribution is determined quantitatively in different scenarios, showing great sensitivity to the soot particles morphology. For the same soot volume fraction, scattering from larger aggregates is found to modify the radiative heat transfer noticeably. Such a finding outlines the need for detailed information on soot particles. Finally, the role of soot volume fraction and pressure on radiative interactions between both solid and gaseous phases is investigated.

A Numerical Study on the Influence of Hydrogen Addition on Soot Formation in a Laminar Aviation Kerosene (Jet A1) Flame at Elevated Pressure

2021 ◽  
Author(s):  
Mingshan Sun ◽  
Zhiwen Gan
Keyword(s):  
Volume Fraction ◽  
Soot Formation ◽  
Laminar Flame ◽  
Numerical Study ◽  
Soot Volume Fraction ◽  
Elevated Pressure ◽  
Condensation Process ◽  
Hydrogen Addition ◽  
Aviation Kerosene ◽  
Soot Precursor

Abstract The hydrogen addition is a potential way to reduce the soot emission of aviation kerosene. The current study analyzed the effect of hydrogen addition on aviation kerosene (Jet A1) soot formation in a laminar flame at elevated pressure to obtain a fundamental understanding of the reduced soot formation by hydrogen addition. The soot formation of flame was simulated by CoFlame code. The soot formation of kerosene-nitrogen-air, (kerosene + replaced hydrogen addition)-nitrogen-air, (kerosene + direct hydrogen addition)-nitrogen-air and (kerosene + direct nitrogen addition)-nitrogen-air laminar flames were simulated. The calculated pressure includes 1, 2 and 5 atm. The hydrogen addition increases the peak temperature of Jet A1 flame and extends the height of flame. The hydrogen addition suppresses the soot precursor formation of Jet A1 by physical dilution effect and chemical inhibition effect, which weaken the poly-aromatic hydrocarbon (PAH) condensation process and reduce the soot formation. The elevated pressure significantly accelerates the soot precursor formation and increases the soot formation in flame. Meanwhile, the ratio of reduced soot volume fraction to base soot volume fraction by hydrogen addition decreases with the increase of pressure, indicating that the elevated pressure weakens the suppression effect of hydrogen addition on soot formation in Jet A1 flame.

Soot and PAH Formation Characteristics in a Micro Flow Reactor With a Controlled Temperature Profile

2011 ◽  
Author(s):  
Ryu Tanimoto ◽  
Takuya Tezuka ◽  
Susumu Hasegawa ◽  
Hisashi Nakamura ◽  
Kaoru Maruta
Keyword(s):  
Flow Velocity ◽  
Temperature Profile ◽  
Mole Fraction ◽  
Equivalence Ratio ◽  
Flow Reactor ◽  
Volume Fraction ◽  
Soot Formation ◽  
Soot Volume Fraction ◽  
Low Flow ◽  
Micro Flow

To examine soot and PAH formation processes for rich methane/air and acetylene/air mixtures, a micro flow reactor with a controlled temperature profile was employed. In the experiment for a methane/air mixture, four kinds of responses to the variations of flow velocity and equivalence ratio were observed as follows: soot formation without a flame; a flame with soot formation; a flame without soot formation; and neither flame nor soot formation. Soot formations were observed in low flow velocity and high equivalence ratio. Starting point of soot formation shifted to the upstream side, i.e., low-temperature side, of the micro flow reactor with the decrease of flow velocity. One-dimensional steady-state computation was conducted by a flame code. In high flow velocity, low mole fraction of C2H2 and high mole fraction of OH were observed in the whole region of the micro flow reactor. Soot volume fraction did not increase in this case. On the other hand, in low flow velocity, high mole fraction of C2H2 and low mole fraction of OH were observed at the downstream side of the micro flow reactor. Soot volume fraction increased in this case. Since significant soot formation was observed at the low flow velocity and the high equivalence ratio, experiments with gas sampling were conducted for acetylene/air mixture to investigate temperature and equivalence ratio dependence of soot precursor production in such condition. Volume fractions of benzene increased with an increase of temperature. They were larger at higher equivalence ratio at the same temperature. Volume fractions of styrene increased with an increase of temperature. They were larger at higher equivalence ratio when the temperature is less than 1000 K. However the tendency was changed at 1000 K, styrene volume fraction at equivalence ratio of 7.0 was larger than that at equivalence ratio of 8.0.

Fischer-Tropsch Fuel Characterization via Microturbine Testing and Fundamental Combustion Measurements

2008 ◽  
Author(s):  
A. Srinivasan ◽  
B. Ellis ◽  
J. F. Crittenden ◽  
W. E. Lear ◽  
Brandon Rotavera ◽  
...  
Keyword(s):  
Shock Tube ◽  
Volume Fraction ◽  
Soot Formation ◽  
Soot Volume Fraction ◽  
Jet Fuels ◽  
Synthetic Fuels ◽  
Fischer Tropsch ◽  
Ignition Delay Times ◽  
Test Region ◽  
Fuel Characterization

Synthetic fuels such as Fischer-Tropsch (FT) fuels are of interest as a replacement for aviation, diesel, and other petroleum-based fuels, and the present paper outlines a joint program to study the combustion behavior of FT synthetic fuels. To this end, shock-tube spray and high-recirculation combustion rig experiments are being utilized to study the ignition delay times, formation of soot, and emissions of FT jet fuels. Undiluted shock tube spray experiments were conducted using a recently developed heterogeneous technique wherein the fuel is sprayed directly into the test region of a shock tube. The high recirculation combustion rig is a complete gas turbine system where Syntroleum FT jet fuel was combusted, and soot formation and emission characteristics were observed. Reduction of soot volume fraction and unchanged emissions were observed, in agreement with previous investigations. The fundamental shock tube results were found to be consistent with the observations made in the experimental engine.

Sign in / Sign up

Export Citation Format

Share Document