NUMERICAL ANALYSIS OF NOx REDUCTION FROM BIOGAS COMBUSTION A Thesis
NUMERICAL ANALYSIS OF NOx REDUCTION FROM BIOGAS COMBUSTION
A Thesis
Presented to the faculty of the Department of Mechanical Engineering
California State University, Sacramento
Submitted in partial satisfaction of
the requirements for the degree of
MASTER OF SCIENCE in
Mechanical Engineering by
Jorge Chavero
FALL
2012
NUMERICAL ANALYSIS OF NOx REDUCTION FROM BIOGAS COMBUSTION
A Thesis by
Jorge Chavero
Approved by:
__________________________________, Committee Chair
Timothy Marbach
__________________________________, Second Reader
Dongmei Zhou
____________________________
Date ii
Student: Jorge Chavero
I certify that this student has met the requirements for format contained in the University format manual, and that this thesis is suitable for shelving in the Library and credit is to be awarded for the thesis.
__________________________, Graduate Coordinator ___________________
Akihiko Kumagai Date
Department of Mechanical Engineering iii
Abstract of
NUMERICAL ANALYSIS OF NOx REDUCTION FROM BIOGAS COMBUSTION by
Jorge Chavero
It is estimated that California’s dairies have the potential to produce an estimates 40 million cubic feet of biogas per day, representing a potential capacity of about 140 mW of energy. Due to the distributed nature of these resources, reciprocating engines coupled to generators are a common means of extracting power from the digester gases. One of the most significant challenges facing the combustion digester biogas is high NOx emissions. To address this challenge, an integrated pollution capture and microwave system has been developed to reduce NOx emissions from biogas engines. The feasibility of reburning the captured NOx was assessed and the various operating parameters, including temperature, pressure and reactants composition were determined using chemical equilibration, kinetic modeling and a Computerized Fluid Dynamic simulation using ANSYS FLUENT software.
The NOx removal system is a pair of alternating carbon adsorption vessels installed on the engine exhaust pipe. The carbon will capture cooled exhaust gas NOx and is expected to pass through cleaned exhaust having NOx levels in the range of 1-5 ppm. iv
Each carbon adsorber is equipped with a microwave generator that desorbs the NOx and regenerates the carbon in place when it is isolated from the engine exhaust. Desorbed
NOx is collected in a concentrated small volume sweep gas and reacted in a separate microwave activated reactor with consumable carbon to produce CO2 and N2. This system is currently being demonstrated at a dairy facility in Northern California.
While the amount and cost of the carbon consumed during the microwave activated NOx reduction step is small, it would be desirable to eliminate this step with another means of
NOx destruction. One potential alternative is to use the engine to destroy NOx by dissociation at high temperatures. Traditionally, NOx is formed in the engine by the thermal or prompt mechanisms. However, high concentrations of NOx in the sweep gas would approach equilibrium from the other direction (high concentration to low) and could yield a net NOx reduction. Since the carbon absorber can accept high concentrations of NOx, the absorbers could be used in a potentially sustainable process where NOx is continuously accumulated and destroyed.
The objective of the study is to assess the feasibility of this alternate method of NOx destruction using chemical equilibrium, kinetics and computerized fluid dynamic simulations.
_______________________, Committee Chair
Timothy Marbach
_______________________
Date v
ACKNOWLEDGEMENTS
The author would like to acknowledge professor Marbach for his guidance and teachings,
Professor Zhou for her help and support and Temoc Chavero for the encouragement and patience with his dad. vi
TABLE OF CONTENTS
List of Tables………………………………………………………………………….x
List of Figures...………………………………………………………………………xi
Chapter
CHEMICAL EQUILIBRATION ANALYSIS ......................................................8
Chemical Equilibrium Theory .....................................................................9
Minimization of Gibbs Energy ..................................................................11
Chemical Equilibrium Software (CEA) .....................................................12
Percentage NOx Reduction Calculations ...................................................13
Equilibration Calculation with Temperature Deviations ...........................19
Equilibration Calculations with Pressure Deviations ................................22
Reburning in Engine Modeling ..................................................................35
Reburning in a Steady Flow Burner...........................................................45
COMPUTERIZED FLUID DYNAMICS (CFD) MODEL .................................52
Computational Fluid Dynamic Software ...................................................54
CONCLUSIONS AND RECOMMENDATIONS ..............................................70
Appendix B. Kintecus and GRI Mech 3.0 Data Sheets ..............................................76
viii
ix
LIST OF TABLES
Tables
1.
Mole ratios of fuel and oxide in the fuel-oxide reburned feed into the Internal
Page
Combustion Engine used for the chemical equilibration calculations…………...
16
2.
Chemical equilibration results from flue gases reaction at 700 °K, 45 bar pressure and intake gases taken from table………………………………………………..17
3.
Mass flow rate used during operational parameters used in this study…..............
61 x
LIST OF FIGURES
Figures
1.
Percentage NOX gases reduction as a ratio of the theoretical equilibration
Page ration…………………………………………………………………………..
15
2.
Percentage NOX gases reduction as a function of the Oxygen concentration measured at the exhaust of ICE……………………………………………….
19
3.
Percentage NOX gases reduction as a function of the Conversion factor…….
20
4.
Percentage NOX gases reduction as a function of the % Oxygen concentration at the ICE exhaust…………………………….………...………………………..
22
5.
Percentage NOX gases reduction as a function of the equivalence ratio……..
23
6.
Effects of initial NO concentration on equilibrium NOx reduction at 45 bar and initial temperature of 700 °K………………………………………………….
27
7.
Effects of sweep gas burned in a separate steady-flow reburner with a variable
NO concentrations at 1 bar pressure and initial temperature of 300 K………..
28
8.
Mass fractions of major species for chemical kinetics model at 45 bar and 3.0%
NO……………………………………………………………………………..
36
9.
Mass fractions of selected minor species for chemical kinetics model at 45 bar and 3.0% NO…………………………………………………………………..
37
10.
Effect of equivalence ratio on normalized mass fractions of NOx for 45 bar and initial NO concentration of 3.0 % NO………………………………………… 40
11.
Effect of pressure on normalized NOx mass fraction at an equivalence ratio of
0.95 and initial NO concentration of 3.0 %........................................................
41
12.
Effect of initial temperature on normalized NOx mass fractions at 45 bar, equivalence ratio of 0.95 and initial NO concentration of 3.0%........................
42
13.
Effect of initial NO concentration in the sweep gas at equivalence ratio of 0.95 and 45 bar……………………………………………………………………...
43 xi
14.
Effects of equivalence ratio on normalized NOx mass fraction for fuel-lean operation at 1 bar, initial temperature of 298 K and initial NO concentration of
3.0%....................................................................................................................
46
15.
Effects of equivalence ratio on normalized NOx mass fraction for fuel-rich operation at 1 bar, initial temperature of 298 K and initial NO concentration of
3.0%....................................................................................................................
47
16.
Effects of initial NO concentration on normalized NOx mass fractions for 1 bar, initial temperature of 298 K and equivalence ratio of 1.50…………………… 48
17.
Effects of initial NO concentration on normalized NOx mass fractions for 1 bar, initial temperature of 298 K and equivalence ratio of 1.70…………………… 49
18.
Example of a 40 x 20 Geometry structure mesh created in Gambit for CFD simulation purposes…………………………………………………………… 52
19.
Contours of static temperature effects in CFD combustion simulation using biogas as a feed………………………………………………………………………..
64
20.
Contours of Mole fraction of NO in CFD combustion simulation using biogas as a feed…………………………………………………………………………….
65
21.
Contours of Mole fraction of CH4 in CFD combustion simulation using biogas as a feed…………………………………………………………………………...
66
22.
Velocity vectors of mole fractions of NO in CFD combustion simulation using biogas as a feed………………………………………………………………...
67
23.
Vorticity contours of CFD combustion simulation using biogas as a feed…….
68 xii
1
Chapter 1
1.
NOx TECHNOLOGIES
Introduction
The undeveloped potential generation of landfills, wastewater and food digesters in the United States has been estimated to be in the 3,000 MW and the untapped generation of digester gases extracted from the more that 2000 dairies in the state of
California has been projected to be 700 MWe. [1] In recent years, there is been a concerted effort to extract this potential energy. A number of pilot and demonstration facilities were establish at dairies and other biogas producers. Due to the nature of the resources, one of the most significant challenges facing the combustion of biogas is high NOx emissions. NOx emissions consist mostly of Nitric Oxide (NO) and smaller amounts nitrogen dioxide (N
2
O). NOx emissions are a precursor for photochemical smog, major contributor to acid rain and ozone depletion, and in the U.S., regulated by the Environmental Protection Energy (EPA). To address this issue, reciprocating engines coupled to generators have been used as common means of extracting power from the digester gases.
Dairy digesters typically produce about 50%-60% methane, 40%-50% CO2 and sulfur impurities mostly in the form of Hydrogen Sulfide (H
2
S) in the range of 0.6% to
3.0% [10]. H
2
S has a strong authoritative odor and can be detected at threshold levels of about 0.00047 ppm. One of the main issues with sulfur removal from the biogas is that it poisons the surfaces of expensive catalyst and they quit performing. This in
turn, increases the operating cost of the engine by rendering post combustion control using such catalyst without a reliable Sulfur removal and precluding some of the commercially available systems.
2
H
2
S has an OSHA Immediate Dangerous to Life and Death (IDLH) level of 300 ppm. Assuming emissions of SOx are not an issue; boilers can tolerate H2S, levels up to 1,000 ppm, reciprocating engines about 10 to 100 ppm and some fuel cells up to 10 ppm to 20 ppm.
NOx removal technologies
The following is a list of some of the available technologies for post combustion controls considered for use on reciprocating engines burning biogas:
Non-selective Catalytic Reduction (NSCR)
It is used for control of NOx emissions in a reduce oxygen stream. It is a catalytic based reaction between Nitrogen Oxides and a fuel to give Nitrogen
& water. The gas fuel is introduced into a NOx process upstream where it homogeneously mixes and the following reactions take place:
CH4 + 4NO2 ---> CO2 + 2H2O + 4NO (1.1)
A secondary reaction takes place after all the oxygen has reacted with the fuel gas:
CH4 + 4NO ---> CO2 + 2H2O + 2N2 (1.2)
Where NOx is reducing to harmless nitrogen and water vapor, the catalyst has a long life and provides a very high NOx removal. However, in dealing with biogases, the catalyst is susceptible to Sulfur poisoning and would require reliable and efficient pretreatment of the biogas to remove H2S.
3
Selective Catalytic Reduction (SCR)
Hot Diesel Exhaust Fluid (DEF) from the exhaust, is injected as a fine mist over a catalyst; the DEF is converted into nitrogen, gas and water vapor. SCR is a proven emissions-reduction technology with the ability to deliver near-zero emissions of NOx and been proven in real-world diesel truck engines operations. SCR reduces NOx emissions, while at the same time delivers fuel economy. However, in dealing with biogases, the catalyst is susceptible to
Sulfur poisoning and would require reliable and efficient pretreatment of the biogas to remove H2S.
NOx adsorbants (SCONOX and NOXTECH)
SCONOX is a dry absorbent that removes NOx and must be regenerated, but was developed for turbines and has not been used on Internal Combustion
Engines (ICE). The NOXTECH® system relies on the injection of urea or ammonia into the exhaust of an ICE and reacts with NOx after heating the exhaust to between 1400-1500 degrees Fahrenheit. Additional fuel and
4 chemicals are need and the requirement to heat the exhaust complicates installation of heat recovery equipment on the engine exhaust. [1]
There are also engine modifications functioning in a lean burn and exhaust gas recirculation that can reduce NOx, but some of these modifications do not meet the presumed BACT levels of SCR or the 2007 CARB Standards. [1]
California’s Central Valley Air Quality Management Districts are designating an
SCR catalyst with ammonia or urea injection as the BACT NOx treatment for small biogas engines. Unfortunately, there are no biogas engines, large or small, operating successfully with a SCR system.
NOx reduction by biogas combustion
The biogas contains significant concentrations of sulfur. This sulfur (primarily
H2S in the reactants and SOx in the products) poisons post-combustion catalysts, rendering them ineffective. To address this challenge, an integrated catalytic capture and microwave system has been developed to reduce NOx and SOx emissions from biogas engines [1].
The NOx removal system is a pair of alternating carbon adsorption vessels installed on the engine exhaust pipe. The carbon adsorption vessels capture exhaust gas NOx. The exhaust gases were expected to have cleaner NOx levels in the range of 1-5 ppm.
Each carbon adsorber is equipped with a microwave generator that desorbs the
NOx and regenerates the carbon in place when it is isolated from the engine exhaust.
Desorbed NOx is collected in a concentrated small volume sweep gas and reacted in a separate microwave activated reactor with consumable carbon to produce CO2 and
N2.
5
The potential of the NOx removal system is highly attractive and can be used on engines operating on gas from landfills, municipal digesters, food digesters and waste gas engines because the carbon will also capture VOC's (volatile organic compounds) in the engine exhaust and the microwave regeneration system will remove or destroy these contaminants.
While the amount and cost of the carbon consumed during the microwave activated NOx reduction step is small, it would be desirable to eliminate this step with another means of NOx destruction. One potential alternative is to reburn the NOx, causing dissociation into the N2 and O2. Practically, the simplest and most cost effective method of NOx reduction, would be to reburn the sweep gas by feeding it back into the compression ignition engine. This can be achieved by using a supplemental digester gas-fired burner or by feeding the sweep gas coming from the adsorber into the Internal Combustion Engine (ICE) air intake. Traditionally, NOx is formed in the engine, however, high concentrations of NOx in the sweep gas would approach equilibrium from the high to the low concentration and could yield a net
NOx reduction. Since the carbon absorber can accept high concentrations of NOx, the absorbers could be used in a potentially sustainable process where NOx is continuously accumulated and destroyed by alternating between the two adsorbers.
6
The biogas available at a demonstration facility located in a California Dairy farm, was composed primarily of CH4 (70%) and CO2 (28%) with lower concentrations of other gases, such as H2S. For the three areas of study, the fuel was assumed an ideal gas mixture of 71.4% CH4 and 28.6% CO2. The sweep gas created by regeneration of the absorber was composed of NO and air. The NO concentration coming from the demonstration unit was measure to be approximately 30,000 ppm or 3% by volume.
The remainder of the sweep gas was assumed to have a composition of 79% N2 and
21% O2. For example, a sweep gas with 3% NO was assumed to be an ideal gas mixture composed of 76.6% N2, 20.4% O2, and 3.0% NO by volume.
The mass fractions of oxides were varied accordingly to the initial amount of measured oxygen in the exhaust, which in turn varied the conversion factor and the amount of oxides in the feed composition.
Reburning, in general, involves mixing NOx with unburned hydrocarbon, typically injected immediately downstream of the primary combustion zone, creating a local fuel rich reburn zone. Smoot, Hill and Xu report that under fuel rich conditions NOx reburn proceeds via the following pathway [2],
CH i
HCN
NO
HCN
O
NCO
H products
NCO
H
NH
CO
NH
N
H
NO
N
N
2
H
2
O
2 (1.3)
Objective
The purpose of this study was to determine the overall NOx reduction feasibility by reburning and its effects. The scope of the project is focused around three (3) major study sections: Chemical Equilibration Calculations, Kinetic analysis and a 2d
Computerized Fluid Dynamic (CFD) simulation. Each area of study considers the compositions and amounts of fuel and oxidizer gases feed into the ICE.
7
Chapter 2
2.
CHEMICAL EQUILIBRATION ANALYSIS
Methodology
The calculations for the chemical equilibration were considered to be in a fixed volume and the reaction to be adiabatic. The combustion byproducts were considered as simple mixtures of ideal gases.
The stoichiometry quantity of fuel and oxidizer supplied into the chamber were determine by a mass balance and assumed that the fuel reacts to form an ideal set of products. On other words, the major species dissociate producing a number of minor species. The Nitrogen Oxide (NO) concentration in the oxide corresponds to the released NOx gases restrained by the carbon column and re-released with the aid of microwave rays. The effects of reactant temperature, pressure, equivalence ratio (fuel lean and fuel rich) and NOx concentration in the sweep gas on equilibrium concentration were determined.
Conversion Factor
The calculation for the conversion factor (φ) was obtained according to an initial percentage of oxygen measured at the exhaust of the ICE. The composition of biogas entering the engine was considered to be 70% Methane (CH
4
), 28% CO
2
and an
8
9 approximation of 20,000 parts per million (ppm) H
2
S. The following was the balancing equation used for the calculation of the equivalence ratio:
0.7 CH
4
+ 0.28 CO
2
+ 0.002 H
2
S + (A/φ)(0.2 O
2
+ 0.77 N
2
+ 0.03 NO)
(2.1)
Where, A is constant of proportionality. The ratio of proportionality of the oxide feed components is determined by writing atom balances. For the particularity of calculating the Constant of proportionality, it is assumed that the fuel reacts to form an ideal set of products that completely dissociate into H
2
O and CO
2
, which in turn, forms the perfect equilibration reaction and hence the equivalence ratio to be one (1).
The value of the constant of proportionality can then be calculated when the properties of the equivalence equilibration reaction is the perfect reaction and all of the components are completely decomposed to be H
2
O and CO
2
.
The equivalence ratio was varied and calculated for various amounts of percentages concentrations of oxygen at the exhaust of the ICE.
Chemical Equilibrium Theory
The concept of chemical equilibrium has its bases on the second law of thermodynamics that states that in an isolated system, the natural processes are spontaneous when they lead to an increase in disorder, or entropy. Considering a fixed volume, adiabatic reaction in which a fixed mass of reactants form product, as the reactions proceed, both the temperature and pressure rise until an equilibrium condition is reached. Per the first law of thermodynamics, energy is conserved and it
can be neither created nor destroyed, the entropy of the products in a mixture can be calculated by summing the product species entropies.
10
Since the reaction conditions for the system implied no heat or work added to the system and the reaction conditions assumed absolute internal energy of the mixture, fixed volume and mass, the second law requires that the entropy change internal to the system is greater than zero.
(dS)≥ 0 (2.2)
Therefore, the composition of the system shifts towards the point of maximum entropy. Once maximum entropy is reached, no further change in composition is allowed.
In Summary, by fixing the internal energy, volume and mass of an isolated system, the application of the first two laws of thermodynamics define the equilibrium temperature, pressure and chemical composition.
In order to calculate the composition the mixture at a given temperature, pressure and stoichiometry, the Gibbs free energy replaces the entropy as the important thermodynamic property. By minimizing and independently treating the free energy of each species, the Gibbs function attains equilibrium. Such minimization of free energy formulation is used in the CEA program.
11
Minimization of Gibbs Energy by
For a number of species (NS) per kilogram in a mixture, the Gibbs energy is given
(2.3) where the chemical potential per kilogram-mole of species j is defined to be
(2.4)
The condition for chemical equilibrium is the minimization of free energy. This minimization is usually subject to certain constraints, such as the following mass balance constraints:
(2.5) or
(2.6) where the stoichiometry coefficients a ij
are the number of kilogram-atoms of element I per kilogram-mole of species j, the index l is the number of chemical elements, is the assigned number of kilogram-atoms of element i per kilogram of total reactants and is the number of kilogram-atoms of element i per kilogram of mixure. Such terms permit the determination of equilibrium compositions for thermodynamics states
12 specified by an assigned initial temperature and pressure where equation 2.6 also gives the mass-balance equation.
In principle, the equilibrium compositions are obtained by the means of the
Newton-Raphson iteration procedure, which solves corrections to initial estimates of compositions of moles of gaseous species and temperature where an arbitrary initial estimate of T=3800 K is used by the program. After that, it uses a set of iterations where the number of kilogram-moles of each species per kilogram mixture is set to
0.1/NG where NG is the number of gaseous species being consider as the first iteration.
Chemical Equilibrium Software (CEA)
Once the mass fractions were calculated for the amounts of feed compositions, the
NASA’s Chemical Equilibration with Applications (CEA) software program, was used to determine the chemical equilibrium compositions and properties of the products at the exhaust. The CEA program calculates chemical equilibrium product concentrations from a set of reactants and determines thermodynamic properties of the product mixture. Such program used the minimization of free Gibbs free energy to calculate the mole fractions of the products. The CEA program characterized the thermodynamic state and functions of each of the species at their assigned temperature and pressure. The program assumes constant pressures in an adiabatic system [3]. A total of 1340 possible products were calculated and species with mole fractions less than 10 -6 were neglected.
13
Percentage NOx Reduction Calculations
The percentage reduction of NOx was calculated based on the mole fraction results obtained from CEA software and the composition of gases feed into the ICE. The feed fractions were composed of biogas feed from digester as well as the reburn gases from the absorbers.
For the chemical equilibration calculations, the system was assumed to be adiabatic and isobaric. No work effects were consider and the products of the combustion were simple mixtures of ideal gases with no interaction among its phases
The mole fractions of oxides varied according to theoretical amounts of oxygen as a product, which in turn varied the conversion factor and the amounts of oxides in the feed composition. As per the mole fractions calculations, the theoretical composition of products, were obtain by the CEA program. The mass fractions calculations were, according to the completion of the following chemical reaction and its concentrations
CH
4
CO
2
H
2
S
2 2
CO
2
H
2
O
2 2
SO
2
(2.7)
The % NOx reduction was calculated using the following equation
% NO x
X
NO , reactants
X
NO x
, products
X
NO , reactants
(2.8)
Where concentration of reactants include NO mass fraction in the reactants and products and is assumed to be the sum of the NO and NO2 mass fractions.
14
The percentage reduction of NO gases was a result based on the mole fractions of the feed gases obtained from the CEA program. The feed fractions were composed of biogas feed from digester as well as the sweep gases regenerated by the absorbers.
Results and Discussion
Fig. 2.1 presents the ratio of the theoretical percentage reduction of NOx gases to its equivalence ratio. The theoretical equilibrium equation calculations were carried according to base line temperature and pressure parameters for the loop feedback flue gases into the ICE and the percentage of oxygen concentration of the exhaust was from a 0 – 8% range. Base conditions of 45.0 bar pressure and 700 °K were chosen as comparison to typical working conditions for an ICE. The modeling equilibration equation was predicted by a steady flow of reactants under such temperature and pressure considerations.
Table 1: shows the stoichiometry fuel-oxide ratio chosen for the equilibration calculations used for the combustion. Such calculations yield a stoichiometry dissociation of species and the results are depicted on table 2. All calculations were subjected to temperature, pressure and constraints of the conservation of number of moles of each element present in the initial concentration of flue gases within the initial mixture. The equivalence ratio determining the system performance was calculated using the percent of the stoichiometry air and its relation to the composition of the mixture and its product.
15
The enthalpy of vaporization for the inlet fuel was not taking into consideration for the chemical equilibration calculation. Variations of temperature and Pressure parameters were modify for comparisons and study purposes.
16
Figure 1: Percentage NOX gases reduction as a ratio of the theoretical equilibration ration. The theoretical equilibration ratio was calculated according to the Oxygen concentration of exhaust gas. Temperature and pressures chosen were typical working conditions for an Internal Combustion Engine for Biogas.
17
5.54959
5.55718
5.56480
5.57245
5.58013
5.58785
5.59559
5.13275
5.19354
5.25661
5.32210
5.39014
5.46089
5.53451
5.54203
1.44145
1.44342
1.44540
1.44739
1.44939
1.45139
1.45340
1.33318
1.34897
1.36535
1.38236
1.40004
1.41841
1.43753
1.43949
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.280
0.280
0.280
0.280
0.280
0.280
0.280
0.280
0.280
0.280
0.280
0.280
0.280
0.280
0.280
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.9041
0.9029
0.9017
0.9004
0.8992
0.8979
0.8967
0.9776
0.9661
0.9545
0.9428
0.9309
0.9188
0.9066
0.9054
Table 1: Mole ratios of fuel and oxide in the fuel-oxide reburned feed into the Internal
Combustion Engine used for the chemical equilibration calculations. The temperature and pressure parameters were chosen to be 700 °K and 45.0 bar, which would represent typical working conditions for an ICE .
Conversio
Fuel Oxide n Factor
φ
CH4 CO2 H2S O2 N2 NO
1.0000 0.700 0.280 0.002 1.30326 5.01753 0.19549
0.9888 0.700 0.280 0.002 1.31795 5.07412 0.19769
0.21622
0.21651
0.21681
0.21711
0.21741
0.21771
0.21801
0.19998
0.20235
0.20480
0.20735
0.21001
0.21276
0.21563
0.21592
18
Table 2: Chemical equilibration results from flue gases reaction at 700 °K, 45 bar pressure and intake gases taken from table 1
Φ
CO CO2 H HO2 H2 H2O NO NO2 N2 O OH O2 SO2
0.930
9
0.918
8
0.954
5
0.942
8
0.977
6
0.966
1
1.000
0
0.0108
0
0.988
8
0.00944
0.0082
4
0.0071
9
0.0062
7
0.0054
6
0.0047
5
0.0041
3
0.899
2
0.897
9
0.896
7
0.901
7
0.900
4
0.904
1
0.902
9
0.906
6
0.905
4
0.0035
9
0.0035
4
0.0033
0
0.0032
5
0.0032
1
0.0034
9
0.0034
4
0.0033
9
0.0033
4
0.1189
0
0.1191
1
0.1191
2
0.1189
6
0.1186
3
0.1181
5
0.1175
5
0.1168
2
0.1159
9
0.1159
0
0.1154
5
0.1153
5
0.1152
6
0.1158
1
0.1157
2
0.1156
3
0.1155
4
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0002
0
0.0001
8
0.0001
7
0.0001
5
0.0001
4
0.0001
2
0.0001
1
0.0000
9
0.0000
8
0.0000
8
0.0000
8
0.0000
8
0.0000
8
0.0000
8
0.0000
8
0.0000
8
0.0000
8
0.1812
0
0.1798
5
0.1784
2
0.1769
1
0.1753
3
0.1736
9
0.1719
9
0.1702
4
0.1684
3
0.1682
5
0.1673
3
0.1671
4
0.1669
5
0.1680
7
0.1678
8
0.1677
0
0.1675
1
0.0026
4
0.0022
9
0.0019
9
0.0017
3
0.0015
1
0.0013
1
0.0011
4
0.0009
9
0.0008
7
0.0008
5
0.0008
0
0.0007
9
0.0007
8
0.0008
4
0.0008
3
0.0008
2
0.0008
1
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0000
1
0.0030
4
0.0033
7
0.0036
9
0.0040
1
0.0043
0
0.0045
9
0.0048
4
0.0050
8
0.0052
9
0.0053
1
0.0054
1
0.0054
3
0.0054
5
0.0053
3
0.0053
5
0.0053
7
0.0053
9
0.0041
1
0.0051
2
0.0062
9
0.0075
9
0.0090
3
0.0106
0
0.0122
9
0.0140
9
0.0159
9
0.0161
9
0.0171
8
0.0173
9
0.0175
9
0.0163
9
0.0165
8
0.0167
8
0.0169
8
0.0032
1
0.0033
3
0.0034
3
0.0034
9
0.0035
3
0.0035
4
0.0035
4
0.0035
0
0.0034
5
0.0034
5
0.0034
2
0.0034
1
0.0034
0
0.0034
4
0.0034
4
0.0034
3
0.0034
2
0.0002
6
0.0002
6
0.0002
6
0.0002
5
0.0002
5
0.0002
5
0.0002
5
0.0002
5
0.0002
4
0.0002
4
0.0002
4
0.0002
4
0.0002
4
0.0002
4
0.0002
4
0.0002
4
0.0002
4
0.0001
5
0.0001
6
0.0001
7
0.0001
8
0.0001
9
0.0001
9
0.0002
0
0.0002
0
0.0002
0
0.0002
0
0.0002
0
0.0002
0
0.0002
0
0.0002
0
0.0002
0
0.0002
0
0.0002
0
0.6754
8
0.6768
7
0.6782
2
0.6795
3
0.6808
1
0.6820
7
0.6833
3
0.6845
8
0.6858
3
0.6859
6
0.6865
8
0.6867
1
0.6868
4
0.6860
8
0.6862
1
0.6863
3
0.6864
6
19
Equilibration Calculation with Temperature Deviations
Figure 2: shows the effect of reactant temperature on % NOx reduction at a pressure of 45 bar and a total composition of 20k ppm of NO gases in the oxide feed.
The percentage O2 was based on a theoretical amount of product composition in the exhaust. Previous measurements were established to be at 8 % of O
2
product measured at the exhaust.
Figure 3: indicates the percentage reduction of the NOx Concentration based on the decreasing values of the equivalence ratio; such ratio was calculated based on the amount of theoretical oxygen as a bypass product of the system.
The results also indicate that NOx reduction increase as the reactant temperature decreased. This is most likely due to due to the effect of the lower flame temperature.
This topic is further study in the kinetics conditions of the reaction.
20
Figure 2: Percentage NOX gases reduction as a function of the Oxygen concentration measured at the exhaust of ICE. For comparison and calculation purposes, the Pressure was held constant at 45 bar and the temperature was varied.
21
Figure 3: Percentage NOX gases reduction as a function of the Conversion factor.
The Conversion factor was calculated according to the theoretical amount of oxygen measured at the ICE exhaust and ranges varies from 0-8 % Oxygen concentration. For comparison and calculation purposes, the Pressure was held constant at 45 bar and the temperature was varied .
22
Equilibration Calculations with Pressure Deviations
Figure 4: represents a pressure variation from the base line parameters of 45 bar.
Such results are an illustration of constant reaction temperature of 700 °K in the ICE, with a total composition of 20k ppm of NO gases in the oxide feed. The percentage of
NOx reduction is based on the chemical equilibration calculations by holding a temperature constant and varying the pressures inside the ICE. The percentage O
2
is based on a theoretical amount of product composition in the exhaust. Previous measurements were established to be at 8%. For comparison purposes, a chosen range of 0-8% oxygen theoretical concentration was chosen for contrasting purposes. The percentage of NOx reduction was compared with the initial amount of NO gases initially located within the feed of the ICE and the results from the combustion reaction product calculation from the CEA software program. Results show that pressure had an insignificant to no effect on the reaction. Figure 5: indicates the percentage reduction of the NOx Concentration based on the decreasing values of the equivalence ratio, such ratio was calculated based on the amount of theoretical oxygen produced as a bypass product of the reaction.
23
Figure 4: Percentage NOX gases reduction as a function of the % Oxygen concentration at the ICE exhaust. For comparison purposes, the temperature was held constant and the pressure parameter was varied.
24
Figure 5: Percentage NOX gases reduction as a function of the equivalence ratio. For comparison purposes, the temperature was held constant while pressure parameter were varied.
25
Conclusions
Since the chemical equilibration calculations equilibrium represent the theoretical maximum amount of NOx reduction inside a combustion engine, a kinetic analysis was necessary to determine the reburning reaction rate and its results are discuss later on. The Chemical equilibrium calculations along with reburning in a steady flow burner were taken into consideration along with the effects of operating conditions, such as temperature, pressure, equivalence ratio and NOx concentration in the sweep gas were considered.
Figure 3 represents the theoretical NOx reduction inside an internal combustion engine at a constant pressure of 45 bar and initial NO concentration of 3.0% by volume in the sweep gas. The equilibrium NOx concentration was at least 75% smaller than the initial concentrations for all reactant inlet temperatures. The equilibrium NOx reduction at the equivalence ratio of 0.91 was between 76 and 82%, depending on the temperature of the reactants at the end of the compression stroke.
The NOx equilibrium concentrations decreased as the equivalence ratio approached unity as a direct result of the O
2
concentration in the products approached zero.
Further reduction could be achieved by operating the engine in fuel-rich mode.
However, high unburned hydrocarbon and carbon monoxide emissions associated with fuel rich operation may make reburning within the engine under fuel-rich operation to be impractical.
26
It is observed that as the reactant temperature decreases, the % NOx reduction at equilibrium increases. This is most likely due to the strong temperature dependence of the NOx formation reactions. Increasing the reactant temperature raises the equilibrium NOx concentration in the products and reduces the potential NOx reduction.
Figure 5 represents the effects of modifying the pressure on NOx reduction at equilibrium. The reactant temperature was 700 K and the initial NO concentration was
3.0% by volume. Pressure had very little impact on NOx equilibrium concentrations within the range of pressures expected inside a compression ignition engine. However, the compression ratio would also affect the temperature at the end of compression, which would affect equilibrium concentrations, as seen in Figure 3.
Figure 6 represents the effects of initial NO concentration in the sweep gas on
NOx reduction at an initial temperature of 700 K and a constant pressure of 45 bar.
Increasing the NO concentration in the reactants had little impact on the actual equilibrium NOx concentrations. Thus, the percent NOx reduction increased significantly as the NO concentration in the reactants increases.
As previously described, the sweep gas could be burned in a separate steady-flow reburner instead of inside the compression ignition engine. To analyze the effectiveness of this scenario, the initial temperature and pressure parameters were chosen to be a 300 ° K and 1 bar pressure. Figure 7 represents the NOx reduction at equilibrium for these conditions. Again, the NOx reduction at a given equivalence
27 ratio increased as the initial NO concentration increased. Compared to reburning in the compression ignition engine, the percent NOx reduction was greater at atmospheric pressure and an initial temperature of 300 ° K, most likely because of the lower flame temperature at a given equivalence ratio.
28
Figure 6: Effects of initial NO concentration on equilibrium NOx reduction at 45 bar and initial temperature of 700 °K.
29
Figure 7: Effects of sweep gas burned in a separate steady-flow reburner with a variable NO concentrations at 1 bar pressure and initial temperature of 300 K
30
Chapter 3
3.
CHEMICAL KINETICS
Introduction
Chemical kinetics is the study of the rates at which chemical reactions occur and found at the heart of almost all industrial chemical reactions. As in any chemical reaction, its reactivity and safety are most important to successful endeavors. For the purpose of this study, the feasibility of the reaction rate were considered. Since the results from the chemical equilibration yielded a favorable result, the kinetics of the reaction were studied in order to understand the viability of the combustion of the
NOx flue gases into a combustion engine.
Methodology
For the kinetics study, the reaction conditions considered were similar to the operating condition parameters found inside an ICE and its influences. The conditions, reaction yield information, composition of the reactants and composition of byproducts were assessed.
Rate of Reaction
The term chemical reaction refers to the notion that a detectable number of molecules have lost their identity and assumed a new form. The changes in the molecules can be observed in the in the number of atoms and/or changes in their
structure or configuration. This is the classical approach in which it is assumed that the total mass is neither created nor destroyed when a chemical reaction occurred.
31
To understand the conditions affecting chemical reactions rates, an accounting of all chemical species entering and leaving the reaction system was required. A mole balance of the chemical reactants involved in the reaction was achieved. When considering the reactants involved in this reaction, a reference to the rate of disappearance of mass was quantified as the number of molecules that lost their chemical identity through breaking and subsequent re-forming chemical bonds and the appearance of by-products.
To summarized, the rate at which the reaction proceeds was simplified as the number of moles of reactants disappearing per unit time per unit volume and would be known as the rate of the reaction of the system. The reactants were considered mix at a zero time and the concentration of NOx was measured at various times. The rate of the reaction was then determined as a function of time as represented by equation 3.1
r
NO x
f
T , P
dNO x dt
(3.1)
This chemical reaction rate is an intensive quantity that depends on several combustion condition parameters such as temperature, pressure and reactant concentrations.
32
Rate Law
In chemical kinetics, the rate of reaction is directly related to the limiting reactant, such reactant is chosen as the basis for the calculation and its rate of disappearance is dependent on parameters such as temperature, pressure and composition. This in turn is expressed as the product of a reaction rate constant ( k ) and it gives the relationship between the reaction rate and its concentration. The algebraic equation that relates the rate of disappearance of the species is called the kinetic expression or rate law. See equation 3.2
r a
[ k
NO x
( T , P )][ fn ( NO x
) (3.2)
In the prediction of hydrocarbon reburn systems, the rate of reactions have been poorly understood, however there has been mechanisms that reasonably predict their behaviors. [4][5] In many of the reactions, the rate of reaction changes as the reaction progresses. Initially, the reaction is relative large, while at relative long times the rate of reaction significantly decreases (at which point the reaction is complete). In order to characterize the kinetic behavior of the reaction, it was desirable to determine how the rate of reaction varies as the reaction progresses. On other words, the rate of the reaction, mathematically described the progress of the reaction.
In general, rate laws are determined experimentally, however for this project, the differential rate law was taking into consideration. The differential rate law relates the rate of reaction to the concentrations of the various species in the system. The
33 differential rate law describes how the rate of reaction varies with the concentrations of various species, usually reactants, in the system. The rate of reaction is proportional to the rates of change in concentrations of the reactants and products; that is, the rate is proportional to a derivative of a concentration. While this approach might work for simple systems with numerically exact data, this method for determining a rate law does not work well in practice. The experimental data suffers from random error and frequently one only collects points infrequently, consequently it is difficult or impossible to determine the slope accurately.
Arrhenius Equation
In calculating the reaction rate constant for reburn reactions, it is assumed that the reaction rate constant is not truly a constant but temperature dependent and merely independent of the concentrations of the species involved in the reaction. This was the premise first correlated by the following equation known as the Arrhenius equation . k
NO x
( T )
Ae
E a
/ RT
(3.3)
Where: A = frequency factor
E a
= activation energy
R = gas constant
T = absolute temperature
34
The activation energy refers to the minimum amount of energy required by the reaction to occur and it is temperature independent. This explanation is deducted from the kinetic theory of gases, where the factor e^(E/RT) gives the afored mentioned minimum energy to generate the collisions between molecules. [4]
Some reactions have temperature dependent activation energies, and have rate constants that behave like, k
aT m e
(
E
RT
'
)
(3.4)
Where a, m and E’ are temperature independent constants and related by by the following equations:
A
aT m e m
E a
E
' mRT
(3.5)
(3.6)
Numerical Modeling
To model the reburning of NOx, the GRI-Mech 3.0 and Kintecus were used. Such programs used further modifications of the mentioned equations [5]. In this manner, the system was assumed to be under constant pressure and several models were demonstrated including a steady flow model where the pressure was assumed to be 1 atm. The temperature was assumed to be equal to the adiabatic flame temperature for each reaction mixture using the chemical equilibrium model described previously.
35
Kintecus© is a software program that has the ability to model reactions by using input from thermodynamics database spreadsheets over a wide temperature range. In such program, Adiabadic and isothermal reactions can be model, under constant volume or constant pressure descriptions from a set of defined species and parameter.
Within Kintecus©, there are many kinetic models. The GRI (Gas Research
Institute)_Mech 3.0 has been model to optimized mechanism designed to model natural gas combustion, including NO formation and reburn chemistry. The
GRI_Mech 3.0 uses the Lindeman Reactions in the modeling of the natural gas and
NOx reburning and widely used by research for various combustion models. Such mechanism, is a set of 325 integrated rate equations solved simultaneously by using the ratio of mass fraction at time t to mass fraction at t = 0. Its optimization process has been design to provide basic kinetics modeling and the predictability of basic combustion properties.
Results and Discussion
Two separate chemical Kinetic analyses were studied in order to assess rates of
NOx reburning at conditions similar to those experienced in the compression ignition engine and in a separate reburner. These results are discussed below.
Reburning in Engine Modeling
Figures 8 and figure 9 present mass fractions of various species during the first
0.01 ms of the chemical kinetics simulation at a constant pressure of 45 bar and an equivalence ratio of 0.95. Figure 8 shows that the reactions involving the major
36 species occur relatively quickly. For example, the CO2 mass fraction increases from approximately 0.05 (bound in the fuel) to approximately 0.19 within the first 0.005 ms of the simulation. Similarly, the CH4 and O2 were consumed quickly and the N2 concentration remained relatively constant. The mass fractions of all major species approached their equilibrium concentrations within the first 0.010 ms of the simulation.
Furthermore, Figure 8 shows that OH radicals were created and began to decrease within the first 0.001 ms. The NO concentration decreased slightly and the NO2 mass fraction was small during the first 0.01 ms of the simulation. However, the NOx (NO
+ NO2) mass fraction had not approached its equilibrium concentration at 0.010 ms because the reactions involving NO and NO2 are relatively slow.
37
Figure 8: Mass fractions of major species for chemical kinetics model at 45 bar and
3.0% NO.
38
Figure 9: Mass fractions of selected minor species for chemical kinetics model at 45 bar and 3.0% NO.
39
Figure 10 shows the effect of equivalence ratio on the NOx mass fraction for a constant pressure of 45 bar and an initial NO concentration of 3.0%. Raising the equivalence ratio was beneficial for NOx destruction kinetics for several reasons. As the mixture approaches an equivalence ratio of unity, the flame temperature increased, speeding up the reverse Zeldovich reactions. Additionally, higher equivalence ratios had lower oxygen concentrations, making more likely that the oxygen would be used for oxidation (forming CO2 or H2O) than in the formation of NO or NO2.
Figure 11 presents the effect of pressure on normalized NOx mass fractions at equivalence ratio of 0.95 and initial NO concentration of 3.0%. As seen with the equilibrium calculations, pressure has very little effect on the chemical kinetics associated with reburning NOx.
Figure 12 presents the effect of reactant temperature on normalized NOx concentrations at an equivalence ratio of 0.95, pressure of 45 bar and initial NO concentration of 3.0%. Early in the simulation, raising the reactant temperature accelerated the NOx reduction kinetics. However, as time progressed and the NOx approached its equilibrium mass fraction, the higher initial temperature resulted in higher NOx concentrations. In a practical reburning situation, the temperature likely would have dropped before 5 ms and the more rapid kinetics would outweigh the slight difference in equilibrium concentration.
40
Figure 13 presents the effect of reactant NO concentration on the normalized NOx product concentrations. Raising the NOx concentration in the sweep gas promotes faster NOx reduction and lower NOx concentrations
41
Figure 10: Effect of equivalence ratio on normalized mass fractions of NOx for 45 bar and initial NO concentration of 3.0 % NO.
42
Figure 11: Effect of pressure on normalized NOx mass fraction at an equivalence ratio of 0.95 and initial NO concentration of 3.0 %.
43
Figure 12: Effect of initial temperature on normalized NOx mass fractions at 45 bar, equivalence ratio of 0.95 and initial NO concentration of 3.0%
44
Figure 13: Effect of initial NO concentration in the sweep gas at equivalence ratio of
0.95 and 45 bar
Reburning in a Steady Flow Burner
The kinetics analysis of the reburning in a steady flow was considered due to the premise of being a simple and cost effective method to reduce NOx emissions by simply feeding the sweep gases back into the compression engine.
45
Figure 14 presents the effect of reburning the sweep gas under fuel-lean operation at 1 bar with an initial temperature of 298 K. Even with a residence time of 5 ms at the adiabatic flame temperature of the reactant mixture, the NOx reduction was relatively small. This indicates that there was not sufficient time to approach the equilibrium concentrations because the flame temperatures were low. For the steady flow case, the reactant mixture was assumed to be 298 K, compared to 700 K when reburning in the engine. Thus, reburning the sweep gas under fuel-lean operation with the reactants at room temperature would not be a viable alternative for reducing NOx from the system.
Figure 15 presents the effect of reburning the sweep gas under fuel-rich conditions at 1 bar with a reactant temperature of 298 K. At equivalence ratio of 1.0, little reduction was observed. However, as the equivalence ratio increased to 1.5, NOx reburning became more effective. Comparing the case for
= 1.6 to the case for
= 1.5, the
NOx reduction for the higher equivalence ratio was slightly lower (most likely due to the lower flame temperature), but the NOx concentrations reached a lower value by the end of the simulation (at 5 ms). This trend continued through
= 1.8. As the
equivalence ratio increased to 2.0, the flame temperature was so low that the NOx reducing reactions did not take place within the 5 ms timeframe. The optimal equivalence ratio for reburning would depend on the type of burner used and its associated temperatures and residence times. Increasing the residence time at higher temperatures and increasing the (fuel-rich) equivalence ratio yields greater NOx reduction.
46
Figures 16 and 17 present the effect of initial NO concentration on normalized NOx mass fraction at
= 1.5 and
= 1.7, respectively. Unlike the analyses run for reburning within the engine (Fig. 3.6), the NO concentration in the sweep gas did not have a large impact on NOx reduction for fuel-rich operation. This result was somewhat unexpected, but desirable, since increasing the concentration in the sweep gas would require a redesign of the absorber and microwave system
47
Figure 14: Effects of equivalence ratio on normalized NOx mass fraction for fuel-lean operation at 1 bar, initial temperature of 298 K and initial NO concentration of 3.0%.
48
Figure 15: Effects of equivalence ratio on normalized NOx mass fraction for fuel-rich operation at 1 bar, initial temperature of 298 K and initial NO concentration of 3.0%.
49
Figure 16: Effects of initial NO concentration on normalized NOx mass fractions for
1 bar, initial temperature of 298 K and equivalence ratio of 1.50.
50
Figure 17: Effects of initial NO concentration on normalized NOx mass fractions for
1 bar, initial temperature of 298 K and equivalence ratio of 1.70
51
Conclusions
As a result of the Chemical Equilibrations and the Kinetic studies, a set of observations were deduced from such studies.
By increasing the equivalence ratio to near 1.0 and increasing the reactant temperature by using a high compression ratio, the reduction of the NOx gases in a compression engine could be maximized.
It was perceived that the increment of NO concentration in the sweep gases had the potential to reduce the overall NOx concentrations and to increase the reaction rate at which the NO was reduced. Pressure had little or no effect on the chemical equilibration and reburn reaction rates.
At this point, it would be desire to obtained a more detailed kinetic modeling that could correlate time dependency as a function of the cylinder temperature and perhaps more practical experiments of the NOx reburning in a compression ignition engine and/or some physical testing to optimized a two-stage reburn system.
52
Chapter 4
4.
COMPUTERIZED FLUID DYNAMICS (CFD) MODEL
To have a better understanding of reaction conditions inside a compression engine, a Computational Fluid Dynamic (CFD) approach was taken. CFD software packages are widely used in engineering industries by modeling and solving problems in various disciplines. ANSYS FLUENT software was used to predict the conditions inside the combustion chamber and to predict temperature, pressure and flow patterns. Its simulation capabilities are very important in the analysis of a wide variety of chemical processes and its simulation results can be used for large-scale problems can result in savings in product developing costs.
For our purpose, a 2dd configuration in ANSYS FLUENT software was chosen.
Such design required a detailed knowledge of the working parameters of species compositions involved in the reaction, equivalence ratios, intermediate chemical compounds and percentage fraction of reactants and oxides.
Methodology
The 2d geometric figure employed in the CFD model was from a drawing created in Gambit software. The geometry was designed such that the mass flow rate enters thought a small opening of 2 mm on one end of the 4 x 1 cm chamber and the flow
53 outlet is on the opposite side where atmospheric pressure was imposed as a boundary condition.
Gambit
Geometry and grid generation was done using Gambit, which is a pre-processor for
CFD analysis that can be used as computer-aided design package. For this project a
2d mesh was created using the “bottom up” approach (in contrast with the “top down”). For the “bottom up” ” approach method, a creation of vertices was build first.
The vertices were connected to create edges and faces (in 3-D, you would stitch the faces together to create volumes). The geometry created was used to generate the structure map mesh intended for use with the ANSYS FLUENT software. The mesh has a unique identifiable set of 40 x 20 grid points. A set of boundary types were assigned to all edges in order to be able to export the structure into the ANSYS
FLUENT software and the no slip boundary condition was imposed on the outer walls of the structure.
Figure 18: Example of a 40 x 20 Geometry structure mesh created in Gambit for CFD simulation purposes. The mesh structure used for the CFD simulation process was created using the Gambit software.
54
Computational Fluid Dynamic Software
ANSYS FLUENT is a computational fluid dynamics (CFD) solver that provides a wide array of advanced physical models for gas, liquid flows and heat transfer applications. The ANSYS FLUENT software can simulate two and three dimensional, steady/unsteady, compressible/incompressible flows in structured and unstructured grids. It uses finite-volume methods to solve governing equations and provides capabilities to use physical parameter such as incompressible or compressible, inviscid or viscous, laminar or turbulent. Its parametric trends can cut on the number of practical experimentations, this in turn, allows study variations for short periods of time and ultimately save money on developmental costs and experimentation. One of the particular strength of ANSYS FLUENT is its ability to model combustion phenomena using a variety of models that include eddy dissipation, probability density functions, and other reacting models such as formation of pollutants like NOx.
ANSYS FLUENT models are capable to solve the conservation equations and mass momentum for all flows. A set of additional equations are used within ANSYS
FLUENT if the flows include species reactions and species conservation.
For our case of study, ANSYS FLUENT solves the mass transport equation for the
NO species by taking into account the convection, diffusion and consumption of NO and its related species. The approach is derived from the principle of mass conservation:
55
(4.1)
Where: Y
NO
is a mass fraction
D is the effective diffusion coefficient and
S
NO
is determined using equation 4.2
(4.2)
Where: M w, NO
Is the Molecular weight of NO (kg/mol) and d[NO]/dt is calculated according to the rate of formation of NO.
ANSYS FLUENT capabilities for the modeling of thermal, prompt, fuel and
NOx formation from intermediates are part of the basis for this computational model.
A recap of such modules and capabilities of the software are described.
Thermal NOx Formation: The formation of thermal NO is determined by a set of high temperature dependent chemical reactions known as the extended Zeldovich mechanism. Such reactions governed the formation of thermal NOx from molecular nitrogen:
(4.3)
(4.4)
At near stoichiometric equilibrium and in a rich fuel environment conditions, the following equation demonstrats the formation of thermal NOx.
(4.5)
The net rate of formation of NO by such reactions is given by equation 4.6:
56
(4.6) where the rate constants for the reactions were experimentally measured and evaluated by Baulch et al [14] and Hanson and Salimian [15]. The expression coefficient numbers used for the formation of thermal NOx are as follows:
(4.7)
The rate models used for the calculations were developed at the department of Fuel and Energy at the University of Leeds in England and from open literature as well.
Prompt NOx Formation: During combustion of hydrocarbon fuels, the NOx formation rate can exceed that produced by thermal NOx formation, such mechanism is called prompt NOx. Prompt NOx gases, are more prevalent in rich flames
environments with low temperature, fuel rich conditions and short residence times.
For the prediction of prompt NOx emissions, ANSYS FLUENT uses transport equations for nitric Oxide (NO) concentrations and its possible intermediates species represented by equation 4.8. Such equations are solved on a given flow fields and combustion solutions.
57
CH + N
2
↔ HCN + N
N + O
2
↔ NO + O
HCN + OH ↔ CN + H
2
O
CN + O
2
↔ NO + CO
CH
2
+ O
2
↔ NO + CO
CH
2
+ N
2
↔ HCN + NH
(4.8)
The products of these reactions can then form amines and cyano compounds that subsequently react to form NO by oxidation of the nitrogen in the fuel. i.e. HCN + N ↔ N
2
+……. (4.9)
The formation of prompt NOx is directly proportional to the number of carbon atoms present in the unit volume. The quantity of HCN formed increases with the concentration of hydrocarbon radicals, which in turn increases with equivalence ratio.
As the equivalent ratio increases, prompt NOx production increases at first, then it passes peak, and finally decreases due to oxygen deficiency in the feed.
58
The primary reaction that describes the prompt NOx formation rate is given by equation 4.10
(4.10)
According to such, the majority of prompt NOx formation is obtained when CH reaches its peak at the flame base of the combustion. In ANSYS FLUENT, a global kinetic parameter is used to derive the experimental values of total NOx formation rate and the rate of formation is calculated by numerical integrations of empirical reaction rates of NOx and N2 formation. The overall formation rate is predicted by equation
4.11.
……..(4.11)
In the stages where the prompt NOx is formed by fuel-rich conditions near the flame, the oxygen concentration is high and the N radical almost exclusively forms
NOx rather than nitrogen, therefore the prompt NOx formation is roughly equal to the overall prompt NOx formation rate:
(4.12)
Where:
(4.13)
59 and E a
= 251151 j/mol, a= Oxygen reaction rate
R = Universal gas constant
P = Pressure
Equation 4.13 was tested against experimental data for a numerous of mixture strengths and fuel types and it was demonstrated that the model performance declined significantly under fuel rich conditions and for higher hydrocarbon fuels. [16]. To reduce error and properly predict prompt NOx formation under such conditions, a modified correction factor was established. Such factor incorporates the effect of the type of fuel used to the air-to-fuel ratio and it turns into the modified equation 4.14.
(4.14) and
(4.14)
(4.14) where: E a
= 303474 j/mol, n = number of carbon atoms per molecule of hydrocarbon fuel
60
φ = equivalence ratio a= Oxygen reaction rate
R = Universal gas constant
P = Pressure
This correction factor was experimentally fit and valid for alkane hydrocarbons fuels (C n
H
2n+2
) and equivalence ratios between 0.6 and 1.6. The values of and were developed at the Department of Fuel and Energy at the University of Leeds in
England
Fuel NOx Formation: Nitrogen containing organic compounds used as liquid or solid fuels, can contribute to the total NOx formation during a combustion process.
This particular fuel nitrogen is a source of NOx emissions for fuel oil and coal. Fuel oil and coal typically contain 0.3-2% nitrogen by weight.
The conversion of such fuel nitrogen compounds to NOx is dependent on the local combustion characteristics and their initial concentrations of nitrogen bound compounds. After this type of fuels are heated and devolatized by the combustion, they form radicals like HCN, NH
3
, N, CN and NH. In turn, the radicals react and form
NOx. ANSYS FLUENT NOx module models such emissions as it considers them as fluids, coal or a combination of both fuels. For the computational purposes, the fuel source was methane and mass fractions of Carbon Dioxide, Nitrogen, oxygen
61 concentrations and the reburning feed stream with an average of 2 % NO. No other
Nitrogen compounds were included in the stream.
NOx Formation from Intermediate N2O: The N2O intermediate mechanism is of importance in systems operated in flameless mode such as diluted combustion, flameless combustion, flameless oxidations and Oxygen flux measuring (FLOX) systems. In a flameless mode, fuel and oxygen are highly diluted in inert gases so that the combustion reactions and resulting heat release are carried out into a diffuse zone.
Consequently, elevated temperatures are avoided and preventing thermal NOx. In this sort of environment, the N2O intermediate mechanism contributes about 90% of the
NOx emissions and the rest is attributed to the formation of prompt NOx.
Setup Procedure
The physical CFD modeling was implemented using FLUENT Version: 2d, pbns, lam (2d, pressure-based, laminar). Revision 13.0.0 for the ANSYS Release Version
13.0 with Graphics version: 17.15-1. A simulated control volume of 4 x 1 cm with a pipe like structure containing 800 computational cells in a 40 x 20 array was chosen as model for the computational analysis. The method used had some simplification assumptions such as isothermal and incompressible flow. The stream feed was chosen to be at 300 ° K under constant, uniform and ambient conditions. For simplicity, no drag forces per unit volume of flow mixture were taking into consideration.
The gas feed source material entered through a 2mm opening located at the center of the structure with an initial velocity flow of 0.5 m/s. Atmospheric conditions were
62 imposed as a boundary condition at the flow outlet and no slip conditions at the walls.
The location of the gas reaction interface was determined by the CFD computation.
Stoichiometry parameters were taking into consideration and depicted in Table 3.
The standard k-epsilon viscous model was used along with Standard Wall Functions.
The energy equation was enabled. The simulation included the species transport model with volumetric reactions, Inlet Diffusion, Diffusion Energy Source, Thermal
Diffusion and Relax to Chemical Equilibrium as options. Eddy-Dissipation was preferred as the Turbulent-Chemistry Interaction. The Four NOx model pathways,
Thermal NOx, Prompt NOx, Fuel NOx and N2O Intermediate, were also facilitated for the computational purposes. Details of the ANSYS FLUENT set up and reports are summarized in Appendix C.
Table 3. Mass flow rate used during operational parameters used in this study.
Compound Chemical Formula Mole Fraction
Methane CH 4 0.068
Oxigen
Nitrogen
Carbon Dioxide
Nitrogen Oxide
O 2
N 2
CO 2
NO
0.186
0.700
0.027
0.018
63
Results and Discussion
Figure 19 demonstrated the temperature contours of the reaction simulation carried in ANSYS FLUENT. In such, the simulated biogas feedstream enters the chamber with a uniform velocity profile normal to the surface of the structure at a velocity of
0.5 m/s. The entrance temperature of the biogas was set at 300 K and an initial
Laminar flow rate with a calculated Reynolds number of 261. From the contours of temperature, it can be observed the increased in temperature as the exothermic reaction takes place and it propagates throughout the chamber.
Figure 20 shows the contours of mole fraction composition inside the reaction chamber. The biogas feed had an initial composition of 2% Nitrogen Oxide. From this figure, it can be observed that the rate of disappearance of NO as the reaction takes place. From such contours, one can quantified the percentage reduction of NO.
An enter value of 0.0409 mole fraction entered while a 0.00259 was calculated at the exit and rending a reduction percentage of 93.7. The observed percentage reduction of
NO aligns with values obtained by the CEA chemical equilibrium software.
From figures 19 and 20 it is observed that the rate of creation and reduction of formation of NO is significant and directly correlated to a change in temperature inside the chamber. This is likely due to the required energy needed to break the strong N2 triple bond (dissociation energy of 941 kj/mol). This assumption can be supported by the effects of the activation energy of the reaction, therefore making the rate of formation as the limiting reaction step and the extended Zeldovich mechanism as the
64 limiting step under perfect reaction conditions. The before mentioned assumption could be corroborated by the velocity vector profile with respect to the mole fraction on NO which is shown in figure 22. In this manner, if there is sufficient oxygen as in a fuel-lean flame, the rate of comsumption of nitrogen and methane becomes equal to the rate of formation of bypass products in this quasy-steady state. This assumption is valid for most combustion cases and should be evaluated under fuel-rich combustion conditions.
Figure 23, incorporates the effects of vorticity transport associated with the boundary conditions of the biogas feed flow into the chamber. The reaction simulation shows instability of the vorticity. The amplitude of oscillation is observed to directly correlate with the increasing heat release due to the reaction driving mechanism and ultimately leads to the flow and propagation of the temperature and pressure throughout the chamber. By idealizing the combustion, the reaction occurs over a short distance leading to the increase of NO reduction from the biogas flow.
65
Figure 19: Contours of static temperature effects in CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x 20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS
FLUENT software program.
66
Figure 20: Contours of Mole fraction of NO in CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x 20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS
FLUENT software program
67
Figure 21: Contours of Mole fraction of CH4 in CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x 20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS
FLUENT software program
68
Figure 22: Velocity vectors of mole fractions of NO in CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x
20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS
FLUENT software program
69
Figure 23: Vorticity contours of CFD combustion simulation using biogas as a feed.
Combustion chamber consists of 800 grids arranged in a 40 x 20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS FLUENT software program
70
Chapter 5
5.
CONCLUSIONS AND RECOMMENDATIONS
Substantial information was obtained in the efforts to numerically calculate the reduction of NOx from biogas by reburnig percentages of NO as part of the feed composition for an internal combustion engine. From the initial chemical equilibration and kinetics of the reaction, we can deduce that the reduction on NOx is feasible under optimal initial conditions. The reburn efficiency under lean conditions was questionable; however, positive results were obtained when there was an optimal equivalence ratio for a given initial concentration of NO. The kinetics of the reaction results aligned with chemical equilibrium conditions and NOx reduction is feasible under previous conditions and within times of 5 ms.
In Summary, in order to maximize NOx reduction in a compression Ignition
Engine, The Equivalence ration should be increase to near 1.0, Increase the reactant temperature to an average temperature of 700 ºK, this can be done by a high compression ratio and Increase the concentration in the sweep gas to a ratio of 5 to 10 percent. Under those parameters, pressure was found to have no significant effect.
The CFD simulation results agree with predictions made by kinetic theory and the chemical equilibrium with respects to the reduction of NOx by reburning of NO inside an ICE. The CFD however, suggest a more in-depth study of the reaction with respect
71 to changes in geometrical figures under different biogas feed compositions. CFD work may lead to improved methods of prediction in more complicated geometries.
The present study could serve as a starting point of various numerical interpretations and simulations of a more realistic complex flows and take fully advantage of the computational simulations. A farther refinement in the studies with the CFD could help us understand spurred behaviors that can be difficult to detect without a more extensive refinement of the studies. Using knowledge based on this dynamic study, it could be possible to do a more extensive studies with nonequilibration feed inputs. These efforts can make the simulations more practical by allowing initial inputs that could determine a more implicit dynamic approach and more comprehensive refinement of the real physics of the problem at hand before the construction of a real model.
72
APPENDICES
Appendix A. CEA Data Tables.
Chemical equilibration data input into CEA program simulation. Mole ratio calculations of fuel and ratios of fuel and oxide in the fuel-oxide were feed into model.
Temperature and pressure parameters were chosen to be 600 °K and 45.0 bar, which would represent typical working conditions for an ICE.
Parameters
Pressure = 45.0 bar,
Temperature
600 K
Conversion factor
φ
1.0000
0.9888
0.9776
0.9661
0.9545
0.9428
0.9309
0.9188
0.9066
0.9054
0.9041
0.9029
0.9017
0.9004
0.8992
0.8979
0.8967
CH4
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
0.700
Fuel Oxide
CO2 O2 N2 NO
0.280 1.30326 5.01753 0.19549
0.280 1.31795 5.07412 0.19769
0.280 1.33318 5.13275 0.19998
0.280 1.34897 5.19354 0.20235
0.280 1.36535 5.25661 0.20480
0.280 1.38236 5.32210 0.20735
0.280 1.40004 5.39014 0.21001
0.280 1.41841 5.46089 0.21276
0.280 1.43753 5.53451 0.21563
0.280 1.43949 5.54203 0.21592
0.280 1.44145 5.54959 0.21622
0.280 1.44342 5.55718 0.21651
0.280 1.44540 5.56480 0.21681
0.280 1.44739 5.57245 0.21711
0.280 1.44939 5.58013 0.21741
0.280 1.45139 5.58785 0.21771
0.280 1.45340 5.59559 0.21801
73
Chemical equilibration results obtained by CEA program simulation using data input from Table A1. Mole ratios of fuel and oxides were feed into model with a temperature and pressure parameters were chosen to be 600 °K and 45.0 bar, which would represent typical working conditions for an ICE.
CO2
0.1181
5
0.1171
9
0.1170
9
0.1169
9
0.1168
8
0.1167
8
0.1166
7
0.1165
7
0.1164
6
0.1163
6
0.1210
4
0.1212
0
0.1211
3
0.1208
5
0.1203
9
0.1197
7
0.1190
2
CO
0.0029
2
0.0025
0
0.0024
6
0.0024
2
0.0023
8
0.0023
5
0.0023
1
0.0022
8
0.0022
4
0.0022
1
0.0088
5
0.0075
3
0.0064
1
0.0054
6
0.0046
6
0.0039
8
0.0034
1
Results from Chemical equilibration software program
H
0.0000
6
0.0000
5
0.0000
5
0.0000
5
0.0000
5
0.0000
5
0.0000
5
0.0000
5
0.0000
5
0.0000
5
0.0001
4
0.0001
3
0.0001
1
0.0001
0
0.0000
9
0.0000
8
0.0000
7
NO
0.0044
7
0.0046
5
0.0046
7
0.0046
9
0.0047
1
0.0047
2
0.0047
4
0.0047
6
0.0047
7
0.0047
9
0.0024
8
0.0028
1
0.0031
4
0.0034
5
0.0037
4
0.0040
1
0.0042
5
H2O
0.1710
4
0.1691
9
0.1690
0
0.1688
2
0.1686
3
0.1684
4
0.1682
5
0.1680
6
0.1678
7
0.1676
8
0.1822
7
0.1809
0
0.1794
4
0.1778
9
0.1762
7
0.1745
8
0.1728
4
H2
0.0007
2
0.0006
2
0.0006
1
0.0006
0
0.0005
9
0.0005
8
0.0005
7
0.0005
7
0.0005
6
0.0005
5
0.0022
0
0.0018
6
0.0015
8
0.0013
4
0.0011
4
0.0009
8
0.0008
4
O
0.0001
4
0.0001
4
0.0001
4
0.0001
4
0.0001
4
0.0001
4
0.0001
4
0.0001
4
0.0001
4
0.0001
4
0.0001
0
0.0001
1
0.0001
2
0.0001
3
0.0001
3
0.0001
4
0.0001
4
N2
0.6855
6
0.6867
7
0.6868
9
0.6870
1
0.6871
3
0.6872
5
0.6873
8
0.6875
0
0.6876
2
0.6877
4
0.6767
3
0.6781
1
0.6794
2
0.6806
9
0.6819
2
0.6831
4
0.6843
5
OH
0.0028
3
0.0027
7
0.0027
7
0.0027
6
0.0027
6
0.0027
5
0.0027
4
0.0027
4
0.0027
3
0.0027
2
0.0025
5
0.0026
7
0.0027
7
0.0028
3
0.0028
6
0.0028
7
0.0028
6
O2
0.01
647
0.01
668
0.01
688
0.01
709
0.01
386
0.01
585
0.01
606
0.01
626
0.01
730
0.01
751
0.00
700
0.00
852
0.01
018
0.01
197
0.00
337
0.00
441
0.00
562
74
Chemical equilibration data input into CEA program simulation. Mole ratio calculations of fuel and ratios of fuel and oxide in the fuel-oxide were feed into model.
Temperature and pressure parameters were chosen to be 298°K and 1 bar, which would represent conditions as if the the sweep gas could be burned in a separate steady-flow reburner instead of inside the compression ignition engine. This particular data input includes a percentage conversion factor error between the conversion factor stoichiometry calculated vs calculated by CEA program As well as a percentage of the
Sulfur dioxide which is regularly found in biogas feestreams.
Paramet ers
Pressure
= 1.0 bar,
Tempera ture 298
K
φ
Conversion factor
1.0000
0.9891
0.9781
0.9669
0.9556
0.9441
0.9325
0.9208
0.9089
0.9077
0.9065
0.9053
0.9041
0.9029
0.9017
0.9004
0.8992
φ
Calculat ed from
CEA
1.0014
0.9905
0.9795
0.9683
0.9570
0.9455
0.9339
0.9221
0.9102
0.9090
0.9078
0.9066
0.9054
0.9042
0.9029
0.9017
0.9005
φ % error
CH4
Fuel
CO2 H2S
0.1424 0.700 0.280 0.002
0.1424 0.700 0.280 0.002
0.1424 0.700 0.280 0.002
0.1430 0.700 0.280 0.002
0.1424 0.700 0.280 0.002
0.1426 0.700 0.280 0.002
0.1430 0.700 0.280 0.002
0.1427 0.700 0.280 0.002
0.1426 0.700 0.280 0.002
0.1427 0.700 0.280 0.002
0.1427 0.700 0.280 0.002
0.1430 0.700 0.280 0.002
0.1424 0.700 0.280 0.002
0.1427 0.700 0.280 0.002
0.1426 0.700 0.280 0.002
0.1431 0.700 0.280 0.002
0.1427 0.700 0.280 0.002
O2
1.4739
0
1.4758
7
1.4778
4
1.4798
2
1.4818
0
1.4308
0
1.4490
7
1.4680
6
1.4700
0
1.4719
5
1.4838
0
1.3342
9
1.3489
8
1.3641
9
1.3799
4
1.3962
8
1.4132
2
Oxide
N2
5.20371
5.26101
5.32033
5.38178
5.44547
5.51155
5.58013
5.65138
5.72543
5.73300
5.74060
5.74822
5.75588
5.76357
5.77129
5.77904
5.78682
NO
0.14
739
0.14
759
0.14
778
0.14
798
0.14
818
0.14
308
0.14
491
0.14
681
0.14
700
0.14
719
0.14
838
0.13
343
0.13
490
0.13
642
0.13
799
0.13
963
0.14
132
75
Chemical equilibration results obtained from data input into CEA program simulation.
Mole ratio calculations of fuel and ratios of fuel and oxide in the fuel-oxide were feed into model. Temperature and pressure parameters were chosen to be 298°K and 1 bar, which would represent conditions if the sweep gas could be burned in a steady-flow reburner instead of inside the compression ignition engine. This particular set of results includes a percentage Sulfur dioxide found in biogas feeds.
Results from Chemical equilibration software program
CO CO2 H HO2 H2 H2O NO NO2 N2 O OH O2 SO2
0.1147
5
0.1146
7
0.1145
8
0.1144
8
0.1143
9
0.1143
0
0.1142
1
0.1141
1
0.1140
2
0.1179
7
0.1181
0
0.1180
5
0.1178
3
0.1174
6
0.1169
6
0.1163
3
0.1155
9
0.0027
2
0.0026
7
0.0026
3
0.0025
9
0.0025
4
0.0025
0
0.0024
6
0.0024
2
0.0023
8
0.0092
2
0.0079
8
0.0068
9
0.0059
4
0.0051
0
0.0043
8
0.0037
4
0.0031
9
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
9
0.0000
9
0.0000
9
0.0000
9
0.0000
8
0.0000
8
0.0000
8
0.0000
8
0.0000
8
0.0002
5
0.0002
3
0.0002
1
0.0001
8
0.0001
6
0.0001
4
0.0001
2
0.0001
1
0.1659
4
0.1657
7
0.1656
0
0.1654
2
0.1652
5
0.1650
7
0.1648
9
0.1647
2
0.1645
4
0.1778
8
0.1766
4
0.1753
1
0.1739
0
0.1724
3
0.1708
9
0.1693
0
0.1676
5
0.0007
9
0.0007
8
0.0007
7
0.0007
6
0.0007
4
0.0007
3
0.0007
2
0.0007
1
0.0007
0
0.0026
7
0.0023
0
0.0019
8
0.0017
1
0.0014
7
0.0012
6
0.0010
8
0.0009
3
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0000
0
0.0026
3
0.0026
4
0.0026
5
0.0026
6
0.0026
6
0.0026
7
0.0026
8
0.0026
8
0.0026
9
0.0015
8
0.0017
5
0.0019
2
0.0020
7
0.0022
1
0.0023
4
0.0024
5
0.0025
5
0.000
18
0.000
18
0.000
18
0.000
18
0.000
18
0.000
18
0.000
18
0.000
18
0.000
18
0.000
19
0.000
19
0.000
19
0.000
19
0.000
15
0.000
16
0.000
17
0.000
18
0.6937
7
0.6939
0
0.6940
3
0.6941
5
0.6942
8
0.6944
0
0.6945
3
0.6946
6
0.6947
8
0.6832
2
0.6846
4
0.6860
1
0.6873
5
0.6886
7
0.6899
6
0.6912
4
0.6925
1
0.002
51
0.002
50
0.002
50
0.002
49
0.002
48
0.002
55
0.002
54
0.002
53
0.002
52
0.002
73
0.002
71
0.002
67
0.002
62
0.002
55
0.002
63
0.002
69
0.002
72
0.000
24
0.000
24
0.000
24
0.000
24
0.000
24
0.000
24
0.000
24
0.000
24
0.000
24
0.000
25
0.000
25
0.000
24
0.000
24
0.000
26
0.000
26
0.000
25
0.000
25
0.017
11
0.017
31
0.017
51
0.017
71
0.017
91
0.016
33
0.016
52
0.016
72
0.016
91
0.009
33
0.010
92
0.012
62
0.014
43
0.004
25
0.005
31
0.006
52
0.007
86
76
Appendix B. Kintecus and GRI Mech 3.0 Data Sheets
Example of data calculations used as input for GRI30 Mechanism. Kinetic information was obtained from the GRI30 mechanism in order to evaluate rate of reaction of combustion for a reburned NO mixed with biogas feed into an ICE chamber where initial temperature, pressure and pollutant NO were taken into consideration.
CH4
CO2
O2
N2
NO
Ptotal (kPa)
Eq Ratio
Temp (K)
NO mole faction in
100
0.7
300
0.02
N moles Mole Fraction Partial Pressure Moles/cm3
0.714 0.06830446 6.830445962 2.73853E-06
0.286 0.02736005 2.736004965 1.09695E-06
1.945468026 0.186112244 18.6112244 7.4618E-06
7.318665431 0.700136537 70.01365369 2.80706E-05
0.189063948 0.01808671 1.808670981 7.25151E-07
Appendix C. CFD Report, Contours and Graphs
CFD ANSY FLUENT Report
FLUENT
Version: 2d, pbns, spe, ske (2d, pressure-based, species, standard k-epsilon)
Release: 13.0.0
Model Settings
Space 2D
Time Steady
Viscous Standard k-epsilon turbulence model
Wall Treatment Standard Wall Functions
Heat Transfer Enabled
Solidification and Melting Disabled
Radiation None
Species Reacting (10 species)
Coupled Dispersed Phase Disabled
NOx Pollutants Enabled
SOx Pollutants Disabled
Soot Disabled
Mercury Pollutants Disabled
Material Properties
77
78
Material: nitrogen-oxide; mixture-template, (fluid)
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 935.60007 0.34720925
-0.00091515347 1.4457943e-06 -6.7783063e-10) (1000-5000: 899.27216 0.35166341
-0.00013898446 2.5407012e-08 -1.7388453e-12)
Molecular Weight kg/kgmol constant 30.0061
Standard State Enthalpy j/kgmol constant 90288480
Standard State Entropy j/kgmol-k constant 210640
Reference Temperature k constant 298
L-J Characteristic Length angstrom constant 4
L-J Energy Parameter k constant 100
Speed of Sound m/s none #f
Material: carbon-dioxide, mixture-template. (fluid)
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 429.92889 1.8744735 -
0.001966485 1.2972514e-06 -3.9999562e-10) (1000-5000: 841.37645 0.59323928 -
0.00024151675 4.5227279e-08 -3.1531301e-12)
Molecular Weight kg/kgmol constant 44.00995
Standard State Enthalpy j/kgmol constant -3.9353235e+08
Standard State Entropy j/kgmol-k constant 213720.2
Reference Temperature k constant 298.15
L-J Characteristic Length angstrom constant 3.941
79
L-J Energy Parameter k constant 195.2
Speed of Sound m/s none #f
Material: carbon, mixture-template (fluid)
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 1729.566 0.055971235
-0.00018673958 2.1048488e-07 -7.660448e-11) (1000-5000: 1801.2127 -0.12370504
6.2902174e-05 -7.9600504e-09 2.2918273e-13)
Molecular Weight kg/kgmol constant 12.01115
Standard State Enthalpy j/kgmol constant 7.1670938e+08
Standard State Entropy j/kgmol-k constant 157994.97
Reference Temperature k constant 298
L-J Characteristic Length angstrom constant 4
L-J Energy Parameter k constant 100
Speed of Sound m/s none #f
Material: carbon-monoxide, mixture-template (fluid)
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 968.38986 0.44878771
-0.0011522171 1.6568822e-06 -7.34637e-10) (1000-5000: 897.93053 0.42823161 -
0.00016713923 3.0234435e-08 -2.05137e-12)
Molecular Weight kg/kgmol constant 28.01055
Standard State Enthalpy j/kgmol constant -1.1053956e+08
Standard State Entropy j/kgmol-k constant 197531.64
80
Reference Temperature k constant 298.15
L-J Characteristic Length angstrom constant 4
L-J Energy Parameter k constant 100
Speed of Sound m/s none #f
Material: methane, mixture-template (fluid)
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 403.58469 9.0573349 -
0.014425086 1.5805188e-05 -6.343051e-09) (1000-5000: 872.4671 5.3054729 -
0.0020082949 3.5166462e-07 -2.3339101e-11)
Molecular Weight kg/kgmol constant 16.04303
Standard State Enthalpy j/kgmol constant -74895176
Standard State Entropy j/kgmol-k constant 186040.09
Reference Temperature k constant 298.15
L-J Characteristic Length angstrom constant 3.758
L-J Energy Parameter k constant 148.6
Speed of Sound m/s none #f
Material: cyanid-radical, mixture-template (fluid)
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 1170.6242 -
0.36958378 0.00069134528 5.9253615e-08 -2.625112e-10) (1000-5000: 1188.8121
0.048520857 6.3509331e-05 -1.2138186e-08 4.2445294e-13)
Molecular Weight kg/kgmol constant 26.01785
81
Standard State Enthalpy j/kgmol constant 4.3515917e+08
Standard State Entropy j/kgmol-k constant 202542
Reference Temperature k constant 298
L-J Characteristic Length angstrom constant 4
L-J Energy Parameter k constant 100
Speed of Sound m/s none #f
Material: hydroxyl, mixture-template (fluid)
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 1778.1389
0.090484863 -0.00081942138 1.167024e-06 -4.1218527e-10) (1000-5000: 1409.2712
0.49569846 -0.00011130898 1.0631305e-08 -2.5060807e-13)
Molecular Weight kg/kgmol constant 17.00737
Standard State Enthalpy j/kgmol constant 38979600
Standard State Entropy j/kgmol-k constant 183587.55
Reference Temperature k constant 298.15
L-J Characteristic Length angstrom constant 2.75
L-J Energy Parameter k constant 80
Speed of Sound m/s none #f
Material: mixture-template, (mixture)
Mixture Species (h2o o2 n2 oh cn ch4 co c co2 no)
Reaction: eddy-dissipation (stoichiometry) (arrhenius 1e+15 100 0) (mixing-rate 4
0.5) (specified-rate-exponents? . #t)
82
Mechanism: reaction-mechs
((mechanism-1 (reaction-type . volumetric) (reaction-list reaction-1) (site-info)))
Density kg/m3 incompressible-ideal-gas #f
Cp (Specific Heat) j/kg-k mixing-law #f
Thermal Conductivity w/m-k constant 0.045400001
Viscosity kg/m-s constant 1.72e-05
Mass Diffusivity m2/s constant-dilute-appx (2.8799999e-05)
Thermal Diffusion Coefficient kg/m-s kinetic-theory #f
Speed of Sound m/s none #f
Material: nitrogen, mixture-template (fluid)
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 979.04298 0.4179639 -
0.0011762792 1.6743943e-06 -7.2562971e-10) (1000-5000: 868.62291 0.44162954 -
0.00016872295 2.9967875e-08 -2.0043858e-12)
Molecular Weight kg/kgmol constant 28.0134
Standard State Enthalpy j/kgmol constant 0
Standard State Entropy j/kgmol-k constant 191494.78
Reference Temperature k constant 298.15
L-J Characteristic Length angstrom constant 3.621
L-J Energy Parameter k constant 97.53
Speed of Sound m/s none #f
Material: water-vapor, mixture-template (fluid)
83
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 1563.0767 1.6037546 -
0.0029327841 3.2161009e-06 -1.1568268e-09) (1000-5000: 1233.2338 1.4105233 -
0.00040291411 5.5427718e-08 -2.949824e-12)
Molecular Weight kg/kgmol constant 18.01534
Standard State Enthalpy j/kgmol constant -2.418379e+08
Standard State Entropy j/kgmol-k constant 188696.44
Reference Temperature k constant 298.15
L-J Characteristic Length angstrom constant 2.605
L-J Energy Parameter k constant 572.4
Speed of Sound m/s none #f
Material: oxygen, mixture-template (fluid)
Property Units Method Value(s)
Cp (Specific Heat) j/kg-k polynomial (300-1000: 834.82647 0.29295801
-0.00014956371 3.4138849e-07 -2.2783585e-10) (1000-5000: 960.75234 0.15941258
-3.2708852e-05 4.6127648e-09 -2.9528324e-13)
Molecular Weight kg/kgmol constant 31.9988
Standard State Enthalpy j/kgmol constant 0
Standard State Entropy j/kgmol-k constant 205026.86
Reference Temperature k constant 298.15
L-J Characteristic Length angstrom constant 3.458
L-J Energy Parameter k constant 107.4
84
Speed of Sound m/s none #f
Material: aluminum (solid)
Property Units Method Value(s)
Density kg/m3 constant 2719
Cp (Specific Heat) j/kg-k constant 871
Thermal Conductivity w/m-k constant 202.4
Cell Zone Conditions
Setup Conditions: fluid
Condition Value
Specify source terms? no
Source Terms ((mass) (x-momentum) (ymomentum) (k) (epsilon) (species-0) (species-1) (species-2) (species-3) (species-4)
(species-5) (species-6) (species-7) (species-8) (energy))
Specify fixed values? no
Fixed Values ((x-velocity (inactive . #f) (constant .
0) (profile )) (y-velocity (inactive . #f) (constant . 0) (profile )) (k (inactive . #f)
(constant . 0) (profile )) (epsilon (inactive . #f) (constant . 0) (profile )) (species-0
(inactive . #f) (constant . 0) (profile )) (species-1 (inactive . #f) (constant . 0) (profile
)) (species-2 (inactive . #f) (constant . 0) (profile )) (species-3 (inactive . #f) (constant
. 0) (profile )) (species-4 (inactive . #f) (constant . 0) (profile )) (species-5 (inactive .
#f) (constant . 0) (profile )) (species-6 (inactive . #f) (constant . 0) (profile )) (species-
85
7 (inactive . #f) (constant . 0) (profile )) (species-8 (inactive . #f) (constant . 0) (profile
)) (temperature (inactive . #f) (constant . 0) (profile )))
Frame Motion? no
Relative To Cell Zone -1
Reference Frame Rotation Speed (rad/s) 0
Reference Frame X-Velocity Of Zone (m/s) 0
Reference Frame Y-Velocity Of Zone (m/s) 0
Reference Frame X-Origin of Rotation-Axis (cm) 0
Reference Frame Y-Origin of Rotation-Axis (cm) 0
Reference Frame User Defined Zone Motion Function none
Mesh Motion? no
Relative To Cell Zone -1
Moving Mesh Rotation Speed (rad/s) 0
Moving Mesh X-Velocity Of Zone (m/s) 0
Moving Mesh Y-Velocity Of Zone (m/s) 0
Moving Mesh X-Origin of Rotation-Axis (cm) 0
Moving Mesh Y-Origin of Rotation-Axis (cm) 0
Moving Mesh User Defined Zone Motion Function none
Deactivated Thread no
Laminar zone? no
Set Turbulent Viscosity to zero within laminar zone? yes
Embedded Subgrid-Scale Model 0
Momentum Spatial Discretization 0
Cwale 0.325
Cs 0.1
Porous zone? no
X-Component of Direction-1 Vector 1
Y-Component of Direction-1 Vector 0
Relative Velocity Resistance Formulation? yes
Direction-1 Viscous Resistance (1/m2) 0
Direction-2 Viscous Resistance (1/m2) 0
Choose alternative formulation for inertial resistance? no
Direction-1 Inertial Resistance (1/m) 0
Direction-2 Inertial Resistance (1/m) 0
C0 Coefficient for Power-Law 0
C1 Coefficient for Power-Law 0
Porosity 1
Solid Material Name aluminum
Reaction Mechanism 0
Activate reaction mechanisms? yes
Surface-Volume-Ratio (1/m) 0
Boundary Conditions
name id type
outlet 3 pressure-outlet
86
entrance 4 velocity-inlet
entrance/top 5 wall
entrance/bottom 6 wall
bottom 7 wall
top 8 wall
Setup Conditions outlet
Condition Value
Gauge Pressure (pascal) 0
Backflow Total Temperature (k) 300
Backflow Direction Specification Method 1
X-Component of Flow Direction 1
Y-Component of Flow Direction 0
X-Component of Axis Direction 1
Y-Component of Axis Direction 0
Z-Component of Axis Direction 0
X-Coordinate of Axis Origin (cm) 0
Y-Coordinate of Axis Origin (cm) 0
Z-Coordinate of Axis Origin (cm) 0
Turbulent Specification Method 3
Backflow Turbulent Kinetic Energy (m2/s2) 1
Backflow Turbulent Dissipation Rate (m2/s3) 1
87
88
Backflow Turbulent Intensity (%) 9.9999998
Backflow Turbulent Length Scale (cm) 100
Backflow Hydraulic Diameter (cm) 99.999998
Backflow Turbulent Viscosity Ratio 10
Specify Species in Mole Fractions? No Backflow
(((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile ))
((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )) ((constant
. 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )))
Backflow Pollutant NO Mass Fraction 0
Backflow Pollutant HCN Mass Fraction 0
Backflow Pollutant NH3 Mass Fraction 0
Backflow Pollutant N2O Mass Fraction 0
is zone used in mixing-plane model? no
Specify Average Pressure Specification no
Specify targeted mass flow rate no
Targeted mass flow (kg/s) 1
Upper Limit of Absolute Pressure Value (pascal) 5000000
Lower Limit of Absolute Pressure Value (pascal) 1 entrance
Condition Value
Velocity Specification Method 2
Reference Frame 0
Velocity Magnitude (m/s) 0.2
Supersonic/Initial Gauge Pressure (pascal) 0
X-Velocity (m/s) 0
Y-Velocity (m/s) 0
X-Component of Flow Direction 1
Y-Component of Flow Direction 0
X-Component of Axis Direction 1
Y-Component of Axis Direction 0
Z-Component of Axis Direction 0
X-Coordinate of Axis Origin (cm) 0
Y-Coordinate of Axis Origin (cm) 0
Z-Coordinate of Axis Origin (cm) 0
Angular velocity (rad/s) 0
Temperature (k) 300
Turbulent Specification Method 0
Turbulent Kinetic Energy (m2/s2) 0
Turbulent Dissipation Rate (m2/s3) 0
Turbulent Intensity (%) 9.9999998
Turbulent Length Scale (cm) 100
Hydraulic Diameter (cm) 99.999998
Turbulent Viscosity Ratio 10
Specify Species in Mole Fractions? yes
89
90
(((constant . 0) (profile )) ((constant . 0.17878233) (profile )) ((constant .
0.67256211) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )) ((constant .
0.093734761) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )) ((constant
. 0) (profile )))
Pollutant NO Mass Fraction 0.02
Pollutant HCN Mass Fraction 0
Pollutant NH3 Mass Fraction 0
Pollutant N2O Mass Fraction 0
is zone used in mixing-plane model? no entrance/top
Condition Value
Wall Thickness (cm) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 1
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 0
Free Stream Temperature (k) 300
Wall Motion 0
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
91
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
External Emissivity 1
External Radiation Temperature (k) 300
Wall Roughness Height (cm) 0
Wall Roughness Constant 0.5 (0)
(((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile ))
((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )) ((constant
. 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )))
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (cm) 0
Y-Position of Rotation-Axis Origin (cm) 0
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0 entrance/bottom
Condition Value
Wall Thickness (cm) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 1
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 0
Free Stream Temperature (k) 300
Wall Motion 0
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
External Emissivity 1
External Radiation Temperature (k) 300
Wall Roughness Height (cm) 0
92
93
Wall Roughness Constant 0.5 (0)
(((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile ))
((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )) ((constant
. 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )))
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (cm) 0
Y-Position of Rotation-Axis Origin (cm) 0
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0 bottom
Condition Value
Wall Thickness (cm) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 1
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 0
Free Stream Temperature (k) 300
Wall Motion 0
94
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
External Emissivity 1
External Radiation Temperature (k) 300
Wall Roughness Height (cm) 0
Wall Roughness Constant 0.5 (0)
(((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile ))
((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )) ((constant
. 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )))
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (cm) 0
Y-Position of Rotation-Axis Origin (cm) 0
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0 top
Condition Value
Wall Thickness (cm) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 1
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 0
Free Stream Temperature (k) 300
Wall Motion 0
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
External Emissivity 1
95
96
External Radiation Temperature (k) 300
Wall Roughness Height (cm) 0
Wall Roughness Constant 0.5
(((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile ))
((constant . 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )) ((constant
. 0) (profile )) ((constant . 0) (profile )) ((constant . 0) (profile )))
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (cm) 0
Y-Position of Rotation-Axis Origin (cm) 0
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0
Solver Settings
Equation Solved
Flow yes
Turbulence yes
h2o yes
o2 yes
n2 yes
oh no
cn no
ch4 yes
co no
c no
co2 yes
Pollutant no yes
Pollutant hcn yes
Pollutant nh3 yes
Pollutant n2o yes
Energy yes
Numerics
Numeric Enabled
Absolute Velocity Formulation yes
Relaxation
Variable Relaxation Factor
Pressure 0.3
Density 1
Body Forces 1
Momentum 0.7
Turbulent Kinetic Energy 0.8
Turbulent Dissipation Rate 0.8
Turbulent Viscosity 1
h2o 0.89999998
97
o2 0.89999998
n2 0.89999998
oh 0.89999998
cn 0.89999998
ch4 0.89999998
co 0.89999998
c 0.89999998
co2 0.89999998
Pollutant no 0.5
Pollutant hcn 0.5
Pollutant nh3 0.5
Pollutant n2o 0.9
Energy 1
Linear Solver
Solver Termination Residual Reduction
Variable Type Criterion Tolerance
Pressure V-Cycle 0.1
X-Momentum Flexible 0.1 0.7
Y-Momentum Flexible 0.1 0.7
Turbulent Kinetic Energy Flexible 0.1 0.7
Turbulent Dissipation Rate Flexible 0.1 0.7
h2o Flexible 0.1 0.7
98
o2 Flexible 0.1 0.7
n2 Flexible 0.1 0.7
oh Flexible 0.1 0.7
cn Flexible 0.1 0.7
ch4 Flexible 0.1 0.7
co Flexible 0.1 0.7
c Flexible 0.1 0.7
co2 Flexible 0.1 0.7
Pollutant no Flexible 0.1 0.7
Pollutant hcn Flexible 0.1 0.7
Pollutant nh3 Flexible 0.1 0.7
Pollutant n2o Flexible 0.1 0.7
Energy Flexible 0.1 0.7
Pressure-Velocity Coupling
Parameter Value
Type SIMPLE
Discretization Scheme
Variable Scheme
Pressure Standard
Momentum First Order Upwind
Turbulent Kinetic Energy First Order Upwind
Turbulent Dissipation Rate First Order Upwind
99
h2o First Order Upwind
o2 First Order Upwind
n2 First Order Upwind
oh First Order Upwind
cn First Order Upwind
ch4 First Order Upwind
co First Order Upwind
c First Order Upwind
co2 First Order Upwind
Pollutant no First Order Upwind
Pollutant hcn First Order Upwind
Pollutant nh3 First Order Upwind
Pollutant n2o First Order Upwind
Energy First Order Upwind
Solution Limits
Quantity Limit
Minimum Absolute Pressure 1
Maximum Absolute Pressure 5e+10
Minimum Temperature 1
Maximum Temperature 5000
Minimum Turb. Kinetic Energy 1e-14
Minimum Turb. Dissipation Rate 1e-20
100
Maximum Turb. Viscosity Ratio 100000
101
CFD Contours
102
Contours of mole fractions of CO2 in CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x 20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS FLUENT software program
103
Contours of dynamic pressure inside CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x 20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS FLUENT software program.
104
Contours of mass fraction of NO created by reaction in CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x
20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS
FLUENT software program.
105
Contours of mole fraction of O2 reaction in CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x 20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS FLUENT software program.
106
Contours of rate of NO created by the Prompt reaction in CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x
20 array and simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS
FLUENT software program.
107
Contours of rate of NO reduction by the thermal in CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x 20 array, simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS
FLUENT software program.
108
Contours of rate of mole fraction of H2O created during CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x
20 array, simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS
FLUENT software program.
109
Velocity vectors of mole fraction of CH4 during CFD combustion simulation using biogas as a feed. Combustion chamber consists of 800 grids arranged in a 40 x 20 array, simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS
FLUENT software program.
110
Velocity vectors of Static temperature during CFD combustion simulation using biogas with a 2 % of NO as a feed. Combustion chamber consists of 800 grids arranged in a 40 x 20 array, simulating a 4 x 1 cm ICE. CFD simulation was executed using ANSYS FLUENT software program.
111
Bibliography
[1] Mark Rawson, Senior Project Manager . Removal of H
2
S from Biogas and NOx from Engine Exhaust at a Dairy Digester Using Microwave Technology. A proposal to the Innovative Clean Air Technology Program California Air and Resources Board.
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[2] Smoot, L.D., Hill, S.C. and Xu, H., NOx control through reburning. Progress
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Lewis Research Center and Sanford Gordon, Sanford Gordon and Associates,
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Arrhenius Parameters. Carbon 44 (2006): 307-324.
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[7] Ianni, James C., " A Comparison of the Bader-Deuflhard and the Cash-Karp
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[9] Turns, Stephen R. An Introduction to Combustion: Concepts and Applications.
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[10] Smith, J. M., Van Ness, H. C., Abbott, M. M., Introduction to Chemical
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[11] Cengel, Yanus. Boles, Michael. Thermodynamics: An Engineering Approach.
7th ed. New York: McGraw-Hill, 2011.
[12] ANSYS FLUENT 6.0 Users Guide: Modeling Turbulence. 30 November
2009. <http://www.ent.ohiou.edu/~juwt/HTMLS/ANSYS FLUENT/ANSYS
FLUENT6/ug/chp10.pdf>.
[13] GAMBIT/ANSYS FLUENT, Flow Modeling Software. Software package, ver12.0. Canonsburg, PA, 2009.
[14]
D.L Baulch et al..”
Evaluated Kinetic Data for Combustion Modelling” J.
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”Survey of Rate Constants in H/N/O Systems”
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