The Effect of a Mini-Scale Flame-Holder on Nano-Particulate Soot Aerosol Formation and CO/CO2 Emissions From a Jet Fuel Combustion Chamber

2015 ◽  
Author(s):  
Masoud Darbandi ◽  
Majid Ghafourizadeh ◽  
Gerry E. Schneider
Keyword(s):  
Combustion Chamber ◽  
Mass Fraction ◽  
Volume Fraction ◽  
Mixture Fraction ◽  
Radiation Heat Transfer ◽  
Soot Volume Fraction ◽  
Transport Equations ◽  
Flame Holder ◽  
Soot Aerosol ◽  
Mass Fractions

A combustion chamber, burning gaseous kerosene, is simulated to investigate the effects of mini-scale flame-holder geometry and its position on the combustion performance and the resulting nano-particulate soot aerosol, carbon monoxide, and carbon dioxide pollutions. To model the complex process of soot nanoparticle formation including the nucleation, coagulation, surface growth, and oxidation, we use a two-equation soot model to solve the soot mass fraction and soot number density transport equations. Considering a detailed chemical kinetic consisting of 121 species and 2613 elementary reactions, we construct the required flamelets library, i.e. the lookup table, and apply the flamelet combustion model, which solves the transport equations of mixture fraction and its variance. We take into account the turbulence-chemistry interaction using the presumed-shape probability density functions PDFs. Applying the two-equation κ-ε turbulence model with round-jet corrections and suitable wall functions, the transport equations of turbulence kinetic energy and its dissipation rate are solved to close the turbulence closure problem. Since it is required to impose the effects of radiation for the most important radiating species, we include the radiation heat transfer of soot and gases assuming the optically-thin flame consideration. In this regard, the radiation heat transfer is determined locally and only affected by the emissions. We evaluate the achieved solutions through our developed method comparing with the data documented in an experimental test, i.e. a gaseous-kerosene/air turbulent nonpremixed flame. The comparisons are provided for the achieved flame structure, i.e., the experimental data reported on the distributions of mixture fraction, temperature, and soot volume fraction. Next, we consider a disk-type mini-scale flame-holder inside the combustion chamber to study its effects on the flow pattern of reacting flow and the distributions of temperature, soot volume fraction, soot particles diameter, CO, and CO2 mass fractions. Our results show that the mounted flame-holder would increase the inside temperature while reduce the temperature, soot volume fraction, CO, and CO2 mass fractions of the exhaust gases. We also study the geometry and position of mini-scale flame-holder numerically in terms of the average values of temperature, soot volume fraction, soot particles diameter, CO mass fraction, and CO2 mass fraction at the outlet of combustion chamber. Our results indicate that increasing the radius of flame holder would lead to a reduction in carbonaceous emissions, i.e. black carbon, CO, and CO2, and the temperature of exhaust gases. Evidently, a maximum temperature increase inside the combustion chamber would augment the combustion performance. We also show that mounting the flame holder at the lower positions above the fuel nozzle exit would lead to the same consequences. The present study provides good informative advices to the researchers who investigate pollution in aero-engine combustion chambers.

The Effect of Inlet Turbulence Intensity on Nano-Particulate Soot Formation in Kerosene-Fueled Combustors

2016 ◽  
Author(s):  
Masoud Darbandi ◽  
Majid Ghafourizadeh
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Soot Formation ◽  
Mixture Fraction ◽  
Radiation Heat Transfer ◽  
Transport Equations ◽  
Maximum Temperature ◽  
Radiation Heat ◽  
Exhaust Gases ◽  
Soot Aerosol

In this work, we numerically study the effects of turbulence intensity at the fuel and oxidizer stream inlets on the soot aerosol nano-particles formation in a kerosene fuel-based combustor. In this regard, we study the turbulence intensity effects specifically on the thermal performance and nano-particulate soot aerosol emissions. To construct our computer model, we simulate the soot formation and oxidation using the Polycyclic Aromatic Hydrocarbons PAHs-inception and the hydroxyl concept, respectively. Additionally, the soot nucleation process is described using the phenyl route, in which the soot inception is described based on the formations of two-ringed and three-ringed aromatics from acetylene, benzene, and phenyl radical. We use the two-equation soot model in which the soot mass fraction and the soot number density transport equations are solved considering the evolutionary process of soot nanoparticles, where all the nucleation, coagulation, surface growth, and oxidation phenomena are suitable considered in calculations. For the combustion modeling part, we benefit from the flamelets library, i.e., a lookup table, considering a detailed chemical kinetic mechanism consisting of 121 species and 2613 elementary reactions and solve the transport equations for the mean mixture fraction and its variance. We take into account the turbulence-chemistry interaction using the presumed-shape probability density functions PDFs. We apply the two-equation high-Reynolds-number k-ε turbulence model with round-jet corrections and suitable wall functions in performing our turbulence modeling. Solving the transport equations of turbulence kinetic energy and its dissipation rate, the turbulence closure problem can be resolved suitably. Furthermore, we take into account the radiation heat transfer of soot and gases assuming optically-thin flame, in which the radiation heat transfer of the most important radiating species is determined locally through the emissions. To evaluate our numerical solutions, we first solve an available well-documented experimental test, which provides the details of a kerosene-fueled turbulent nonpremixed flame. Then, we compare the achieved flame structure, i.e., the distributions of mean mixture fraction, temperature, and soot volume fraction, with those measured in the experiment. Next, we change the turbulence intensities of the incoming fuel and oxidizer streams gradually. So, we become able to evaluate the effects of different turbulence intensities on the achieved temperature and soot aerosol concentrations. Our results show that using moderate turbulence intensities at both fuel and oxidizer stream inlets would effectively increase the maximum temperature inside the combustor and this would reduce the exhaust gases temperature. It also reduces the concentrations of soot in the combustor and its emission to the exhaust gases effectively.

scholarly journals Soot Volume Fraction Profiles in Forced-Combusting Boundary Layers

1983 ◽  
Vol 105 (1) ◽  
pp. 159-165 ◽  
Author(s):  
R. A. Beier ◽  
P. J. Pagni
Keyword(s):  
Boundary Layer ◽  
Mass Fraction ◽  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Volume Fraction ◽  
Liquid Hydrocarbon ◽  
Forced Flow ◽  
Volume Fractions ◽  
Ambient Oxygen ◽  
Mass Fractions

A multiwavelength laser transmission technique is used to determine soot volume fraction fields and aproximate particle size distributions in a forced flow combusting boundary layer. Measurements are made in diffusion flames of polymethylmethacrylate (PMMA) and five liquid hydrocarbon fuels (n-heptane, iso-octane, cyclohexane, cyclohexene, and toluene) with ambient oxygen mass fractions in the range of 0.23 ≲ Y0∞ ≲ 0.50. Soot is observed in a region between the pyrolyzing fuel surface and the flame zone. Soot volume fraction increases monotonically with Y0∞, e.g., n-heptane and PMMA are similar with soot volume fractions, fν, ranging from fν ∼ 5 × 10−7 at Y0∞ = 0.23 to fν ∼ 5 × 10−6 at Y0∞ = 0.50. For an oxygen mass fraction the same as air, Y0∞ = 0.23, soot volume fractions are approximately the same as values previously reported in pool fires and a free combusting boundary layer. However, the shape of the fν profile changes with more soot near the flame in forced flow than in free flow due to the different y-velocity fields in these two systems. For all fuels tested, a most probable particle radius is between 20 nm and 80 nm, and does not appear to change substantially with location, fuel, or oxygen mass fraction.

scholarly journals Numerical Investigation of Soot Formation in Turbulent Diffusion Flame With Strong Turbulence–Chemistry Interaction

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
B. Manedhar Reddy ◽  
Ashoke De ◽  
Rakesh Yadav
Keyword(s):  
Mass Fraction ◽  
Volume Fraction ◽  
Soot Formation ◽  
Mixture Fraction ◽  
Soot Volume Fraction ◽  
Turbulent Diffusion Flame ◽  
Flamelet Model ◽  
Soot Mass ◽  
One Step ◽  
Gas Flame

The present work is aimed at examining the ability of different models in predicting soot formation in “Delft flame III,” which is a nonpremixed pilot stabilized natural gas flame. The turbulence–chemistry interactions are modeled using a steady laminar flamelet model (SLFM). One-step and two-step models are used to describe the formation, growth, and oxidation of soot particles. One-step is an empirical model which solves the soot mass fraction equation. The two-step models are semi-empirical models, where the soot formation is modeled by solving the governing transport equations for the soot mass fraction and normalized radical nuclei concentration. The effect of radiative heat transfer due to gas and soot particulates is included using P1 approximation. The absorption coefficient of the mixture is modeled using the weighted sum of gray gases model (WSGGM). The turbulence–chemistry interaction effects on soot formation are studied using a single-variable probability density function (PDF) in terms of a normalized temperature or mixture fraction. The results shown in this work clearly elucidate the effect of radiation and turbulence–chemistry interaction on soot formation. The soot volume fraction decreases with the introduction of radiation interactions, which is consistence with the theoretical predictions. It has also been observed in the current work that the soot volume fraction is sensitive to the variable used in the PDF to incorporate the turbulence interactions.

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.

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.

Fast Running Pool Fire Computer Code for Risk Assessment Calculations

2003 ◽  
Author(s):  
Miles Greiner ◽  
Ahti Suo-Anttila
Keyword(s):  
Heat Transfer ◽  
Reaction Rate ◽  
Volume Fraction ◽  
Radiation Heat Transfer ◽  
Soot Volume Fraction ◽  
Computer Code ◽  
Pool Fire ◽  
Temperature Measurements ◽  
Radiation Heat ◽  
Transportation Risk

The Isis-3D computational fluid dynamics/radiation heat transfer computer code was developed to simulate heat transfer from large fires to engulfed packages for transportation risk studies. These studies require accurate estimates of the total heat transfer to an object and the general characteris tics of the object temperature distribution for a variety of fire environments. Since risk studies require multiple simulations, analysis tools must be rapid as well as accurate. In order to meet these needs Isis-3d employs reaction rate and radiation heat transfer models that allow it to accurately model large-fire heat transfer even when relatively coarse computational grids are employed. In the current work, parameters for the reaction rate model were selected based on comparison with soot volume fraction and temperature measurements acquired in a recent 6 m square pool fire under light wind conditions. The soot volume fraction Isis-3D uses to define the edge of the optically thick fire was determined using temperature measurements of a pipe engulfed 20-m-diameter pool fire with a steady 9.5 m/s crosswind. Accelerated simulations, in which the specific heat of the engulfed pipe was reduced by a factor of twelve below the measured values, reproduce the temperature data in the 11-minute crosswind fire using only 3.5 hours on a standard desktop workstation.

CAFE-3D: A Fast Running Computational Tool for Analysis of Radioactive Material Packages in Fire Environments

2004 ◽  
Author(s):  
Narendra Are ◽  
Miles Greiner ◽  
Ahti Suo-Anttila
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Volume Fraction ◽  
Radiation Heat Transfer ◽  
Fire Behavior ◽  
Soot Volume Fraction ◽  
Radioactive Material ◽  
Computational Time ◽  
Fe Model ◽  
Transportation Risk

The Container Analysis Fire Environment (CAFE-3D) is a computer code developed at Sandia National Laboratories to simulate heat transfer from large fires to engulfed packages for transportation risk studies. These studies require accurate estimates of the total heat transfer to an object and the general characteristics of the object temperature distribution for a variety of fire environments. Since risk studies require multiple simulations, analysis tools must be rapid as well as accurate. In order to meet these needs, CAFE-3D links Isis-3D (a general purpose computational fluid dynamics/radiation heat transfer code that calculates fire behavior) to commercial finite element (FE) codes that calculates package response. In this scheme, CAFE-3D runs Isis-3D only periodically during the calculation to update local fire boundary conditions to the FE model. The frequency and duration of the fire update calculations are user controlled based on the fire time and/or package temperature rise. In this paper we outline various models employed by Isis-3D and the method for finding the soot volume fraction used to define the edge of the diffusively radiating fire zone. Then, the linkage between Isis-3D and the MSC P\Thermal finite element code is explained. Finally a benchmarking simulation, which reproduced the temperature data from the 30-minute light-crosswind fire using only 10 hrs of computational time on a standard workstation, is described.

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.

Recent Advances in Measurement of Turbulent Reacting Flows in Which Heat Transfer is Dominated by Radiation

2010 ◽  
Author(s):  
G. J. Nathan ◽  
P. A. M. Kalt ◽  
Z. T. Alwahabi ◽  
B. B. Dally ◽  
P. R. Medwell ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Volume Fraction ◽  
Mixture Fraction ◽  
Soot Volume Fraction ◽  
Reacting Flows ◽  
Diagnostic Methods ◽  
Practical Significance ◽  
Turbulent Reacting Flows ◽  
Detailed Measurement ◽  
Recent Advances

Recent advances in diagnostic methods are providing new capacity for detailed measurement of turbulent, reacting flows in which heat transfer is dominant. Radiation typically becomes dominant in flames containing soot and/or with sufficient physical size, so is important in many flames of practical significance. The presence of particles, including soot, increases the coupling between the turbulence, chemistry and radiative heat transfer processes. Particles also increase the difficulties of laser-based measurements by increasing the interferences to the signal and the attenuation of the beam. The paper reviews recent advances in techniques to measure temperature, mixture fraction, soot volume fraction, velocity, particle number density and the scattered, absorbed and transmitted components of radiation propagation through particle laden systems.

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