Combustion simulation and the effect of the addition of water content on the formation of Nox and soot
Topic
Combustion simulation and the effect of the addition of water content on the formation of Nox and soot.
A project
Submitted in partial fulfillment of the requirement for the award of the certificate
Of
Master Program
(CFD Masters)
By
Nitesh Negi
(Enrolment ID:3081)
Under the supervision of
CFD Team Leader Director of product
Pritam Goel Sarangarajan Iyengar
5th floor, Bristol IT Park
Main Rd, South Phase, Sathya Nagar, Gandhi Nagar, Chennai, Tamil Nadu 600032, +918939850851
CANDIDATE'S UNDERTAKING
I, Nitesh Negi (Enrolment Id:3081) state that the contents and findings of the project entitled “Combustion simulation and the effect of the addition of water content on the formation of Nox and soot using Ansys Fluent”, are original. To the best of my knowledge, the current project does not infringe upon anyone’s copyright nor violate any proprietary rights and that any ideas, techniques, quotations or any other material from the work of other people included in my project, published or otherwise, are fully acknowledged in accordance with the standard referencing practices. Even though later on in case of any complaint pertaining to plagiarism, I am solely responsible for the same and understand that as per norms.
ACKNOWLEDGEMENT
Primarily, I acknowledge this moment of time which has gone just forever but made up my mind to write the word for those who have been with me with their over-whelming gestures throughout this assignment. With deep gratitude, I express my earnest thanks to my respected guides Mr. Pritam Goel, CFD Team Leader, and Mr. Sarangarajan Iyengar, Director of product skill Lync for his constant involvement, energetic efforts, and proficient guidance. Without his wise counsel and encouragement, it would have been impossible to complete the project work in this manner.
I would also thank all the members of Ansys Fluent Skill-Lync what are app group members for support and express my gratitude.
ABSTRACT
Combustion simulation and the effect of the addition of water content on the formation of Nox and soot is the basis of how the reaction model works in the Ansys fluent. Moreover, the mixing characteristics are of considerable interest, and numerous experimental studies and practical application have examined the question of optimal model design. In this project, we discuss computer simulation of mass fraction of component based on the k-epsilon model for turbulent flow. Comparison of the simulation results with different cases and appears to be a useful tool for predicting mixing distances and the effect of water concentration. The Nox and soot are getting formed at the outlet of the combustor. Such formation has harmful effects on the environment and humans. The stringent government norms also demand the least formation of Nox and soot and the effect of adding the water in the fuel marginally reduces the formation of NOx and Soot.
The computational fluid dynamics (CFD) package FLUENT as a fluid flow analysis tool to solve the governing equations, prominently equations of continuity, motion, and energy. Numerical results can be compared with experimental results and which was done by research scholar since due to model setup and lab constraints we will only compare the simulation results of different cases as per our objective. The mesh size is selected to do that the numerical solution is taken considering the computation time and simulation processing time.
Keywords: numerical simulation, Fluent, CFD, k-epsilon,
CONTENTS
Candidate’s undertaking i
Acknowledgment ii
Abstract iii
Contents iv
List of figures v
List of table’s vi
Nomenclature vii
Contents
CHAPTER 1: INTRODUCTION
- What is a combustion?
- Diffrent reaction & combustion model used.
CHAPTER 2: LITERATURE REVIEW
- Introduction
- Review of Literatures
- Objectives
CHAPTER 3: METHODOLOGY
-Flow chart for CFD simulation
-Procedure/Steps for the CFD simulation
CHAPTER 4: RESULT AND DISCUSSIONS
CHAPTER 5: CONCLUSIONS AND FUTURE SCOPE
REFERENCES
LIST OF FIGURES
Figure: Available in the Result and analysis part shows the various counters with graphs plots
LIST OF TABLES
Table (1) Shows a variation of mole fraction at the outlet of the geometry
NOMENCLATURE
CHAPTER 1
INTRODUCTION
What is combustion?
Combustion or burning,[1] is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually, atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion doesn't always result in fire, but when it does, a flame is a characteristic indicator of the reaction. While the activation energy must be overcome to initiate combustion (e.g., using a lit match to light a fire), the heat from a flame may provide enough energy to make the reaction self-sustaining.
Combustion of an organic fuel in air is always exothermic because the double bond in O2 is much weaker than other double bonds or pairs of single bonds, and therefore the formation of the stronger bonds in the combustion products CO2 and H2O results in the release of energy.[2] The bond energies in the fuel play only a minor role since they are similar to those in the combustion products; e.g., the sum of the bond energies of CH4 is nearly the same as that of CO2. The heat of combustion is approximately -418 kJ per mole of O2 used up in the combustion reaction and can be estimated from the elemental composition of the fuel.[2]
Uncatalyzed combustion in air requires relatively high temperatures. Complete combustion is stoichiometric concerning the fuel, where there is no remaining fuel, and ideally, no residual oxidant. Thermodynamically, the chemical equilibrium of combustion in air is overwhelmingly on the side of the products. However, complete combustion is almost impossible to achieve, since the chemical equilibrium is not necessarily reached, or may contain unburnt products such as carbon monoxide, hydrogen and even carbon (soot or ash). Thus, the produced smoke is usually toxic and contains unburned or partially oxidized products. Any combustion at high temperatures in atmospheric air, which is 78 percent nitrogen, will also create small amounts of several nitrogen oxides, commonly referred to as NOx, since the combustion of nitrogen is thermodynamically favored at high, but not low temperatures. Since burning is rarely clean, flue gas cleaning or catalytic converters may be required by law.
Incomplete combustion
The reactant burns in oxygen and produces a limited number of products. When a hydrocarbon burns in oxygen, the reaction will primarily yield carbon dioxide and water. When elements are burned, the products are primarily the most common oxides. Carbon will yield carbon dioxide, sulfur will yield sulfur dioxide, and iron will yield iron(III) oxide. Nitrogen is not considered to be a combustible substance when oxygen is the oxidant. Still, small amounts of various nitrogen oxides (commonly designated NOx species) form when the air is the oxidant.
Combustion is not necessarily favorable to the maximum degree of oxidation, and it can be temperature-dependent. For example, sulfur trioxide is not produced quantitatively by the combustion of sulfur. NOx species appear in significant amounts above about 2,800 °F (1,540 °C), and more is produced at higher temperatures. The amount of NOx is also a function of oxygen excess.
Incomplete combustion will occur when there is not enough oxygen to allow the fuel to react completely to produce carbon dioxide and water. It also happens when the combustion is quenched by a heat sink, such as a solid surface or flame trap. As is the case with complete combustion, water is produced by incomplete combustion; however, carbon, carbon monoxide, and hydroxide are produced instead of carbon dioxide.
Carbon monoxide is one of the products from incomplete combustion.[4] Carbon is released in the normal incomplete combustion reaction, forming soot and dust. Since carbon monoxide is considered as a poisonous gas, complete combustion is preferable, as carbon monoxide may also lead to respiratory troubles when breathed since it takes the place of oxygen and combines with hemoglobin.
Problems associated with incomplete combustion
- Environmental problems:[6]
These oxides combine with water and oxygen in the atmosphere, creating nitric acid and sulfuric acids, which return to Earth's surface as acid deposition, or "acid rain." Acid deposition harms aquatic organisms and kills trees. Due to its formation of certain nutrients that are less available to plants such as calcium and phosphorus, it reduces the productivity of the ecosystem and farms. An additional problem associated with nitrogen oxides is that they, along with hydrocarbon pollutants, contribute to the formation of tropospheric ozone, a major component of smog.
- Human health problems:[6]
Breathing carbon monoxide causes headaches, dizziness, vomiting, and nausea. If carbon monoxide levels are high enough, humans become unconscious or die. Exposure to moderate and high levels of carbon monoxide over long periods is positively correlated with the risk of heart disease. People who survive severe carbon monoxide poisoning may suffer long-term health problems.[7] Carbon monoxide from the air is absorbed in the lungs which then binds with hemoglobin in human's red blood cells. This would reduce the capacity of red blood cells to carry oxygen throughout the body.
Reaction models in FLUENT
• Surface reactions:
– Particle surface reactions (e.g. coal combustion).
– Surface reactions at solid (wall) boundaries (e.g. chemical vapor
deposition).
• Combustion or infinitely fast chemistry:
– Pre-mixed combustion models.
– Non-pre-mixed combustion models.
– Partially premixed combustion models.
– Finite-rate kinetics in turbulent flames (composition PDF transport
model).
• Finite-rate chemistry based on extended Arrhenius equation:
– Laminar finite-rate model.
– Finite-rate/eddy-dissipation.
– Eddy-dissipation.
– Eddy-dissipation concept (EDC).
Based on Phases:
Fluid phase, Volumetric phase/gas phase, Wall surface, Particle surface
CHAPTER 2:
LITERATURE REVIEW
- INTRODUCTION
To begin the proposed work it is required to make a review of research papers in order to discover what work has been done already about the related topic and which procedure or methodology has been adopted to perform the simulation/experiments and conclude the results.
A review of the various published literature on any specific topic is the first important step to be taken to get,
- Knowledge about the state of art.
- Familiarity with the established methods and procedures for conducting work.
- To stop duplication of work.
- LITERATURE REVIEW
There are several numbers of studies conducted by researchers regarding the Combustion simulation and the effect of the addition of water content on the formation of Nox and soot from the turbulence model using Ansys Fluent, some of them are discussed below:-
- Lorenzo Mazzei, Stefano Puggelli, Davide Bertini, Daniele Pampaloni, Antonio Andreini, Modelling soot production and thermal radiation for turbulent diffusion flames, Energy Procedia, Volume 126, 2017,
Pages 826-833, ISSN 1876-6102, https://doi.org/10.1016/j.egypro.2017.08.266. (http://www.sciencedirect.com/science/article/pii/S1876610217337724)
Abstract: This paper presents a systematic investigation on the strategies required for modelling soot when performing CFD simulations of turbulent flames. The first test case consists in a 3D enclosure containing a mixture of N2, CO2, H2O and soot (Coelho, 2003). Results obtained with the gray implementation of the Discrete Ordinate Method in ANSYS Fluent are compared against literature data, assessing different formulations for the absorption coefficient of soot. These considerations are exploited through reactive RANS simulations accounting for radiative heat transfer, with the purpose to test different models for soot formation process on a turbulent non-premixed kerosene-air flame (Young et al., 1994). - Leszek Chybowski, Rafał Laskowski & Katarzyna Gawdzińska An overview of systems supplying water into the combustion chamber of diesel engines to decrease the number of nitrogen oxides in the exhaust gas
- X.S. Bai, M. Balthasar, F. Mauss, L. Fuchs,"Detailed soot modeling in turbulent jet diffusion flames", Symposium (International) on Combustion, Volume 27, Issue 1,1998, Pages 1623-1630, ISSN 0082-0784,
https://doi.org/10.1016/S0082-0784(98)80572-9. (http://www.sciencedirect.com/science/article/pii/S0082078498805729)
Abstract: An approach for modeling the interaction between the formation and oxidation of soot, the radiative heat loss, and the flowfield in turbulent jet diffusion flames is presented. These interactions are modeled by the flamelet library approach in the framework of prescribed probability density functions (PDFs). The formation and oxidation of soot is calculated from a detailed chemical soot model. The laminar flamelet concept is applied to model the rates of soot particle inception, soot volume-dependent surface growth, and oxidation, as well as species and temperature fields, Radiative heat transfer from the soot particles and the gas-phase species, CO2 and H2O, decreases the peak flame temperature, which in turn influences the flamelet structures. Experiments from Young et al. on a turbulent ethylene diffusion flame are used to validate the modeling approach. The calculated fields of mean mixture fraction, temperature, and soot volume fraction are found to be in agreement with the experimental data. The spatially resolved rates of soot inception, surface growth, and oxidation are presented. The maximum rates of the surface independent production occur in the fuel-rich region at a radial position of about 10 mm. In contrast, the maximum rates of surface growth and oxidation are found on the centerline with the oxidation occurring at a higher location in the flame. The total rate has its maximum on the centerline, whereas soot formation and destruction balance on the slightly rich side near the stoichiometric contour. This shows the strong interaction of soot formation and oxidation in the flame. A sensitivity analysis of the calculated soot volume fraction on different model parameters is presented. The rate coefficient of the heterogeneous surface growth reaction is the most sensitive parameter. A 20% increase of this rate leads to a 65% increase of the calculated maximum soot volume fraction.
-OBJECTIVE
Combustion simulation and the effect of the addition of water content on the formation of Nox and soot using Ansys Fluent.
PART-I
Perform a combustion simulation on the combustor model and plot the variation of the mass fraction of the different species’ in the simulation using line probes at different locations of the combustor as shown in Fig. You need to plot for CO2, H2O, CH4, N2, O2, NOx emissions & Soot formation.
Part II
As you must have observed from the above simulation, the Nox and soot are getting formed at the outlet of the combustor. Such formation has harmful effects on the environment and humans. The stringent government norms also demand the least formation of Nox and soot and to satisfy those requirements, you need to check the effect of adding the water in the fuel.
In this part, you need to add the water content in the fuel from 5% to 30% by mole and observe the effect of it on the results. It is necessary to provide line plots and contours to prove your claim.
You can use the parametric study approach if required.
Note:-
1. Use methane-air-2step as a mixture of material than methane-air. [It allows to add water in the fuel or air]
2. Use a one-step soot model to calculate the soot formation.
CHAPTER 3
-METHODOLOGY
The complete methodology that has been adopted to conduct the present project work is shown in the form of the flow chart in figure 3.1
Figure 3.1: Flow Chart for Methodology
-Procedure for CFD simulation of Mixing Tee
Selection of material
The material property is not necessary for this simulation since we are not considering the heat transfer through the wall i.e. is approximate an adiabatic process.
Further, we will know that in this type of simulation we consider the selection of material for the fluid which are methane-air-2step as a mixture material
Cad Model Preparation
-Procedure for CFD simulation of Mixing Tee
Cad Model Preparation
Step1: Open the workbench & double click open Flow Fluent
Step2: Double click on geometry to open space claim> open the file from saved location.
Step4: Preparation of the geometry by extracting from the 3D model; here prepared as per the dimension mentioned below.
Step5: Close space claim workbench and save files if required.
Preprocessing
Step6: Double click on Mesh from workbench>Generate Mesh by right-clicking the mesh icon and click generate mesh option and mesh will be generated; here you can change mesh size from element size option in the mesh tree.
Step7: Give a name to required parts by face section/edge selection>click update by right-clicking on the mesh>check the mesh metric matrix by select element quality should be not less than 5%.
The Name selection of model are:-
Fuel inlet
Air inlet
Axis
Wall
Outlet
As shown in image
Meshing element size = 5mm
Total number of elements =38034
Total number of nodes =38034
Step8: The mesh method used is quard type and inflation at the fuel and air interface for refinement.
Setup/Processing
Step9: Double click on setup to open the workbench
Step10: select for Time -steady-state solution, Solver Type -pressure-based solvers, Velocity Formulation - Absolute and Physics-energy from the model.>select the Viscous Model -k-epsilon for turbulent flow based upon the condition as shown in the setup
Step11: setup the boundary condition as per the given data.
Solver: steady-state, pressure-based, absolute, and axisymmetry.
Viscous model: K-epsilon, standard, standard wall treatment.
Zones: air-inlet-velocity inlet-0.5m/s
species-O2-0.23
fuel-inlet-velocity inlet- 80m/s
species-CH4-1
NOx model -on
soot model>one step -on
Step12: The velocity of air at inlet 0.5m/s> Temperature of air 300k > Velocity of fuel at the inlet is 80m/s> Temperature of fuel 300k> Working fluid is air>Pressure at the outlet of the geometry 0 gauge.
Step13: In solution select the report for standard deviation temperature & average temperature.>initialize the solution>run for the calculation by entering the no.of iteration
Post-processing/Results
Step14: Open results workbench by double-clicking on the result option>Open the geometry by unchecking the named parameters>create XY plane to plot the contour of velocity and temperature>plot for temperature & velocity by drawn the line along & across the pipe
Step15: Open the workbench & double click open Flow Fluent
Step16: Double clicks on geometry to open space claim> open the file from saved location.
Step17: Draw all plots/graphics. by the creation of the of line parallel. to outlet/inlet in the combustion place
CHAPTER 4:
RESULT AND DISCUSSIONS
The results of various Simulation tests conducted for combustion are calculated and explained with the help of different graphs and charts which are plotted by using Ansys Fluent & MS-Excel software. Comparisons of results are also done Case I and Case II. The compared results are summarized as the following:-
-
PART-I
Perform a combustion simulation on the combustor model and plot the variation of the mass fraction of the different species’ in the simulation using line probes at different locations of the combustor as shown in Fig. You need to plot for CO2, H2O, CH4, N2, O2, NOx emissions & Soot formation.
The plots and the graphs are shown below are as follows:-
-
Residual:
Temperature Contour:
Mass fraction of CO2Contour/plot
Mass fraction of H20 Contour/plot
Mass fraction of CH4 Contour/plot
Mass fraction of O2 Contour/plot
Mass fraction of NO Contour/plot
Mass fraction of soot formation Contour/plot
The geometry of the combustion part is available in 2D
Line probes at different locations of the combustor:
Case 1: @ 0% H2O
Residual:
Temperature Contour:
<iframe frameborder="0" src="//www.youtube.com/embed/dCgQIHzsgzw"></iframe>
Mass fraction of CO2:
Mass fraction of H20:
Mass fraction of CH4:
Mass fraction of N2:
Mass fraction of O2:
Mass fraction of NOx:
Mass fraction of soot formation:
Part II
As you must have observed from the above simulation, the Nox and soot is getting formed at the outlet of the combustor. Such formation has harmful effects on the environment and humans. The stringent government norms also demand the least formation of Nox and soot and to satisfy those requirements, you need to check the effect of adding the water in the fuel.
In this part, you need to add the water content in the fuel from 5% to 30% by mole and observe the effect of it on the results. It is necessary to provide line plots and contours to prove your claim.
You can use the parametric study approach if required.
Note:-
1. Use methane-air-2step as a mixture material than methane-air. [It allows to add water in the fuel or air]
2. Use a one-step soot model to calculate the soot formation.
Case 1: @5%H2O
Residual:
Temperature Contour:
<iframe frameborder="0" src="//www.youtube.com/embed/niL9-TyEVDI"></iframe>
Mass fraction of CO2:
Mass fraction of H20:
Mass fraction of CH4:
Mass fraction of O2:
Mass fraction of NOx:
Mass fraction of soot formation:
Case 2: @10%H2O
Residual:
Temperature Contour:
<iframe frameborder="0" src="//www.youtube.com/embed/mVtaeO2PZ7Y"></iframe>
Mass fraction of CO2:
Mass fraction of H20:
Mass fraction of CH4:
Mass fraction of O2:
Mass fraction of NOx:
Mass fraction of soot formation:
Case 3: @20%H2O
Residual:
Temperature Contour:
Mass fraction of CO2:
Mass fraction of H20:
Mass fraction of CH4:
Mass fraction of O2:
Mass fraction of NOx:
Mass fraction of soot formation:
Case 4: @30%H2O
Residual:
Temperature Contour:
<iframe frameborder="0" src="//www.youtube.com/embed/jn6rq6VK8xg"></iframe>
Mass fraction of CO2:
Mass fraction of H20:
Mass fraction of CH4:
Mass fraction of O2:
Mass fraction of NOx:
Mass fraction of soot formation:
CHAPTER 5
CONCLUSIONS AND FUTURE SCOPE
In this chapter, we will discuss the outcome from a different Simulation performed i.e. Case I, Case II, and the graphs, plots. There are some results that support the previous outcome of research work and finds that increasing the water ratio will reduce the NOx and soot formation to some extent. The influence of temperature on the combustion shows more the moles of water increase the temperature. Based on observation, and analysis made in the study of Mixing Tee following conclusions are drawn:-
Various other substances begin to appear in significant amounts in combustion products when the flame temperature is above about 1600 K. When excess water is used, nitrogen may oxidize to NO and, to a much lesser extent, to NO2. CO forms by disproportionation of CO2, and H2 and OH form by disproportionation of H2O.
Table(1) shows the variation/emission of the by-product at the outlet as an average value.
Percentage of water increases per cases at the outlet | ||||||
Elements | Sr.no. | 1 | 2 | 3 | 4 | 5 |
Case 1(0% H2O) | Case 2(5% H2O) | Case 3(10% H2O) | Case 5(20% H2O) | Case 6(30% H2O) | ||
CO2 emissions | 0.132562 | 0.132204 | 0.13242 | 0.131497 | 0.132315 | |
1 | 4 | 2 | 5 | 3 | ||
H2O emissions | 0.111509 | 0.120143 | 0.127637 | 0.145131 | 0.158447 | |
5 | 4 | 3 | 2 | 1 | ||
CH4 emissions | 0.0945994 | 0.0870782 | 0.0802369 | 0.0647713 | 0.049838 | |
1 | 2 | 3 | 4 | 5 | ||
N2 emissions | 0.658819 | 0.65798 | 0.657127 | 0.656105 | 0.657134 | |
1 | 1 | 4 | 5 | 3 | ||
O2 emissions | 4.72403e-013 | 2.79457e-012 | 7.4303e-011 | 2.09473e-011 | 0 | |
NOx emissions | 7.35253e-005 | 6.76179e-005 | 5.47372e-005 | 0.0093277 | 0.000274651 | |
5 | 2 | 3 | 1 | 4 | ||
Soot emissions | 3.15709e-038 | 2.95155e-038 | 2.80373e-038 | 2.25257e-026 | 5.16259e-031 | |
3 | 4 | 5 | 1 | 2 | ||
N2O emissions | 3.77493e-012 | 3.78187e-012 | 6.9051e-012 | 5.60128e-008 | 4.89655e-011 | |
3 | 4 | 5 | 1 | 2 | ||
Temperature (max.) | 2266.22K | 2268.16K | 2234.74K | 2506.79K | 2885.80K | |
5 | 4 | 3 | 2 | 1 | ||
Temperature outlet | 1833.63 [K] | 1845.84 [K] | 1861.3 [K] | 1884.33 [K] | 1917.48 [K] | |
5 | 4 | 3 | 2 | 1 | ||
It does not need an ignition source to initiate the combustion. The eddy dissipation model, fuels are fast burning and the overall rate of reaction is controlled by turbulence mixing. In this model, the chemical reaction is governed by a large eddy mixing time scale. Combustion initiates whenever there is turbulence present in the flow.
-From the overall NOX emission plot & one step soot model, we can say that efficient combustion has happened. and more the addition of water performed the uniform temperature variation found in the temperature contour
FUTURE SCOPE
The same parameters can be taken as the BC and used in the different model to check the feasibility and accuracy of other models whereas can also perform the heat transfer and energy generation analysis to know how much the variation is effective, and of course, comparing the simulated value with the experimental values.
REFERENCES
[1] source form Wikipedia and google search
[2] Lorenzo Mazzei, Stefano Puggelli, Davide Bertini, Daniele Pampaloni, Antonio Andreini, Modelling soot production and thermal radiation for turbulent diffusion flames, Energy Procedia, Volume 126, 2017,
Pages 826-833, ISSN 1876-6102, https://doi.org/10.1016/j.egypro.2017.08.266. (http://www.sciencedirect.com/science/article/pii/S1876610217337724)
[3]Leszek Chybowski, Rafał Laskowski & Katarzyna Gawdzińska An overview of systems supplying water into the combustion chamber of diesel engines to decrease the number of nitrogen oxides in the exhaust gas
[4]X.S. Bai, M. Balthasar, F. Mauss, L. Fuchs,"Detailed soot modeling in turbulent jet diffusion flames", Symposium (International) on Combustion, Volume 27, Issue 1,1998, Pages 1623-1630, ISSN 0082-0784
[5] Felske J, Tien C. The use of the Milne-Eddington absorption coefficient for radiative heat transfer in combustion systems. ASME J Heat Transf 1977;99:458–65.
[6] Modest MF. Radiative Heat Transfer. Academic Press; 2013.
[7]Kennedy I. Models of soot formation and oxidation. Prog Energy Combust 1997;23:95–132.
[8] Khan I, Greeves G, Probert D. Prediction of soot and nitric oxide concentrations in diesel engine exhaust. Air Pollut Control Transp Engines C 1971;142:205–17.
[9] Lindest R. Simplified soot nucleation and surface growth steps for non-premixed flames. Soot Form. Combust., Berlin: Springer-Verlag; 1994, p. 417–39.
[10] Fairweather M, Jones W, Lindstedt R. Predictions of radiative transfer from a turbulent reacting jet in a cross-wind. Combust Flame
1992;89:45–63.