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The Effect of Swirl Number and Oxidizer Composition on Combustion Characteristics of Non-Premixed Methane Flames Sherif S. Rashwan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00233 • Publication Date (Web): 19 Jan 2018 Downloaded from http://pubs.acs.org on January 20, 2018
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Energy & Fuels
The Effect of Swirl Number and Oxidizer Composition on Combustion Characteristics of Non-Premixed Methane Flames
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By: Sherif S. Rashwan1,2,* 1
2
Mechanical Power Department, Faculty of Engineering, Cairo University, Giza 12613, Egypt Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario, Canada L1H 7K4
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Abstract
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Corresponding author: Sherif S. Rashwan*, E-Mail:
[email protected] [email protected], Tel: +1-289-943-4127, +0020-100-7147-502
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1. Introduction
This paper presents divergent phases of numerical investigations on non-premixed combustion flames. The study has been performed0using the Computational0fluid dynamics0software (CFD). In this study, the effect of swirl number and oxidizer composition on combustion0characteristics of air-methane combustion and comparison will be performed with respect to oxy-fuel0 combustion cases. The0 oxy-fuel0 combustion investigations were performed on three difference oxygen fractions namely 30%, 40% and 50%, to investigate0the effect of the oxidizer flexibility on combustion0characteristics. Both, investigations have been conducted under the non-premixed combustion model and the flame is anchored over a swirl stabilizer. In this work, validation of a previous experimental work was successfully achieved, grid independency study was performed. The axial and radial temperature distribution are analyzed and reported. The velocity stream lines and emissions concentrations are also reported. Furthermore, the effect of swirl number on NOx emissions have been investigated for air-fuel combustion cases only because nitrogen is not allowed in the oxy-combustion cases. The study revealed that, increasing swirl number can reduce the thermal NOx by 95% this can be attributed to the0increase in mixing levels of the combustible mixture. Keywords: Oxy-fuel combustion, Air-fuel combustion, Swirl Number, natural Gas, Emission Analysis, NOx Emissions. and
Gas turbine engines for power generation have used combustors operated with diffusion flames thanks to their reasonable performance and higher stability characteristics 1,2 . However, these kinds of combustors are no longer preferred to be used due to their high combustion pollutant emissions with unacceptable higher concentrations of NOx 3–6 . Power generation industries rely mainly on combined cycle steam power plants and gas turbine engines for energy production from gaseous fuels. Thanks to the new heat recovery technologies which utilize the heat that would be rejected to the atmosphere by recovering and converting it into mechanical energy that can produce electricity through gas turbine engines, thus raising the thermal efficiency of the combined cycles up to 60% 7,8. Carbon dioxide capture technologies0that are being0 developed for CO2 capture from combustion0and gasification technologies include, among others, oxy-fuel technology 9,10 . This0technology is now0 widely used in the glass industry and the steel industry. In oxyfuel0combustion, the combustor is operated with0natural gas and the oxidizer is mainly consisted of a controlled0 mixture of oxygen0and carbon dioxide (O2/CO 2) mixtures. However, this technique brings its own challenges because of the narrow flammability limits that is confined with flashback 1 ACS Paragon Plus Environment
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and blow-off which associated with higher and lower O.F% respectively. Furthermore, the adverse0effects of adding0 carbon dioxide to the oxidizer0 mixture on chemical0kinetics makes the stability is very challengeable issue. In addition to, N 2 is eliminated from air using an air separation unit. The remaining gases which are mainly O 2 and some impurities such as argon are used as oxidizers. This makes the flue gases consist mainly of CO 2 and H2O. In order to0prevent excessively0high temperatures if the fuel is burnt in O 2 alone, some of the CO2 form the flue gases is0recirculated and0 mixed with the oxidizers 11,12. Then, H2O is condensed from the flue0 gas allowing capture and reuse of the condensation heat. Also, the oxy-fuel0 combustion concept can be described as combustion using substitute air in which N 2 is0replaced with CO2. However, the combustion characteristics in oxy-fuel0combustion are totally different from those of airfuel0combustion due to differences in the physical properties of CO 2 and N2 . The replacement of N2 by CO2 in the oxidizer mixture impacts the flame in four issues: changes in mixture0 density, 0volumetric heat0 capacity and adiabatic flame temperature, physical transport properties. Habib et al. 13 reported the effect of replacing N 2 by CO2 on all of the previously mentioned physical transport parameters. Non-premixed combustion enjoys a wider stability range 14,15 . Diffusion flames is defined as; when the fuel and oxidizer combined to form a combustible mixture, then the ignition starts once the mixture is created. In this case, a reaction sheet is created forming the flame border as shown in figure 1, which represents, the co-axial flow jet, the most commonly flow configurations which support diffusion flames. The diffusion flame starts at laminar mode, but it shifts to turbulent diffusion flame when a further increase of flow rate occurs. This could form a flicker at the flame top. The flame length is also increased due to the0increase in0turbulence level 16,17. The diffusion flame structure is also shown below, the fuel concentration is highest on the centerline as the fuel is introduced from the centerline pipe and slightly decreases to reach zero at the flame reaction sheet. The concentration of oxidizer is highest at the wall and tends to zero at the flame reaction sheet.
Figure 1: Reaction zones of Co-Axial Burner schematic for jet diffusion flame. 2 ACS Paragon Plus Environment
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In the industrial combustors, fuel flexibility meaning changing fuel compositions or oxidizer flexibility meaning changing oxidizer compositions can change the combustion characteristics of any combustion process tremendously. For instance, the oxy-fuel combustion which is corresponding to adding oxygen as an oxidizer and carbon dioxide as a dilution. This technique will bring the flame tallest or shortest because the flame will require more or less oxidant to complete combustion, respectively. In the reciprocating engine applications, the fuel is directly injected to the cylinder, the reaction may start at any point where mixing occurring. In these cases, auto ignition is a concern and further investigations should be conducted about auto ignition time scales. Rashwan et al. 18–20 studied the0 effect of oxygen fraction on oxy-fuel combustion. They reported that the O.F. % to obtain a stable flame is from no lower than 29% Vol%. Michitaka et al. 21 reported that NOx emissions in the O2/CO2 mode were 20% lower than those in the air mode. Habib et al. 13 performed an experimental0analysis to obtain the0 stability maps of oxy-methane diffusion flames using a co-axial0gas turbine combustor model. The laminar flame speeds increased with the increase of the0OF% with a quadratic function relationship between the flame0velocities and the O2 concentration 22 . Compared with N2, the high concentration of CO2 decreased the flame speeds and the measured flame speed using CO 2 as a diluent was about onefifth of that using N2 as a diluent 23,24. From the open literature on the statistical analysis side, which merge the combustion technique along with the statistical analysis, Perez and Boehman 25, investigated experimentally the oxygen-enriched0 diesel combustion using0 simulated exhaust gas recirculation. They measured the effect of exhaust gas recirculation on the particulate matter emissions and NOx emissions. The study revealed that, there are a significant reduction in the particulate matter and NOx emissions. In addition to that, the CO 2 addition0reduced the average0combustion temperatures and decreased the rate of increase in0NOx emissions 21 .
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2. Modeling of the combustor
The aim0of this study, is to investigate the effect of swirl number on combustion0 characteristics of air-fuel and oxy-fuel0 combustion. Validation of the present model will be performed with respected to a previous experimental work done by Wilkes et al. 26 on a gas fired boiler. The grid independency study has been performed. Establishing a computational model for a 2-D combustor like the one used in the experimental setup. Run the model to solve the non-premixed air-methane and oxy-fuel flames. Investigations on the effect0 of swirl0 number on combustion0 characteristics will be performed. Four swirl number have been used, namely, Sn=0.0, 0.5, 1.0 and 1.5. As well as, the effect of swirl number on the formation of thermal NOx for air-fuel combustion cases have been also conducted.
For the sake of investigating the effect of different operating parameters on combustion characteristics and0NOx emission behavior, an axis of symmetric combustor fueled with natural gas have been established. The combustor have been established based on the experimental data that have been reported by0Wilkes et al. 26 to validate our model0and to compare the numerical0results. The experimental work done by Wilkes were performed on a gas fired combustor. This combustor is consisted of two inlet sections, the fuel is introduced at the center and air is introduced through the annulus tube. The combustor length is 0.9 m and has a radius of 0.15 m as shown in Figure 2 below. Therefore, a 2-D axis-symmetric swirl combustor model have been created with the same dimensions of the gas-fired boiler by Gambit and grid meshing was performed. Noting that the swirl stabilizer will only affect the air stream axial and tangential velocities. 3 ACS Paragon Plus Environment
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0.9 m
0.106 m 0.150 m Air Stream
Flue Gas 11 mm
Fuel Jet
6 mm
Axis of Symmetry
Figure 2: Gas fired boiler Combustor schematic 2 3 4 5 6 7 8 9 10 11 12 13
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The combustor is generated, and boundary conditions have been set including, air and fuel inlet sections, pressure outlet, combustor walls and an axis of symmetry. Then the computational domain will be numerically solved by FLUENT. It solves the governing equations for fluid and species using the FVM (finite volume method). A HPC (high performance PC) have been used to solve the non-premixed combustion cases. The K-epsilon viscous model will be used for this analysis. The most important input parameters used in setting up the combustion/species model is reported in detail in Table 1 below, including axial and tangential velocity, the turbulent kinetic energy and dissipation of rate of turbulence. These parameters have been evaluated by trial and error to give the most accurate agreement with the experimental work. Table 1: CFD Input Parameters for air-methane non-premixed combustion Boundary0 Conditions Fuel Air Axial0 Velocity m/s 15.0 12.8 Tangential Velocity (Sn=0) 0 0 Turbulent0kinetic0Energy m2 /s2 2.26 1.63 2 2 Turbulence Dissipation0rate m /s 1132 695 Temperature K 300 300 After setting all the previous parameters, then the combustion model is set to non-premixed under the species model because the fuel and the oxidizer are0 not mixed before0 the combustion0chamber, consequently the flame is0 diffusion. Rausch et al. 27,28 reported that the species equations0are Reynolds-averaged, which leads to0unknown terms for the turbulent0scalar flux and the mean reaction rate. The turbulent scalar flux is modeled by gradient diffusion, treating turbulent0convection as enhanced0diffusion. The mean reaction rate0is modeled by the finite-rate, eddy-dissipation, or EDC models. Since the reaction0rate is invariably0highly non-linear, modeling the mean reaction rate in a turbulent flow is difficult and prone to error. An alternative to Reynolds-averaging the species and energy equations is to derive a transport equation for their single-point, joint probability density function (PDF). This PDF, denoted by P, can be considered to be proportional to the fraction of the time that the fluid spends at each species and temperature state. The species concentrations should be prepared to generate the Probability-Density Function (PDF). From the0PDF, any thermochemical0moment can0be calculated. The species concentrations are presented in Table 2 and 4 ACS Paragon Plus Environment
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Energy & Fuels
Table 3 for the air-fuel0combustion and oxy-fuel0combustion cases that are used to generate the PDF file, respectively. All numerical simulations were performed at the stoichiometric condition. Table 2: Air-methane combustion reactant compositions Species Fuel O2 0 N2 0 CH4 1.0
Air 0.21 0.79 0
Table 3: Oxy-methane combustion reactant compositions, OF = 40% Species Fuel O2 0 CO2 0 CH4 1.0
Oxidizer 0.4 0.6 0
The swirl is implemented in the air side or the annulus side of the combustor. The swirl number Sn is defined as the ratio0 of the tangential momentum0 flux over the axial momentum0 flux, and it is calculated from the following equation 29 : 𝐑
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𝑺=
∫𝟎 𝛒𝐮𝐰𝐫𝟐 𝐝𝐫
1
𝐑
∫𝟎 𝛒𝐮𝟐 𝐫 𝐝𝐫
Chemical reactions at the stoichiometric conditions for the air-fuel0and oxy-fuel0combustion at are presented in equations 2 and 3 respectively 19,30: Air-methane combustion (Stoichiometric):
𝐂𝐇𝟒 + 𝟐 (𝐎𝟐 + 𝟑. 𝟕𝟔 𝐍𝟐) → 𝐂𝐎𝟐 + 𝟐𝐇𝟐𝐎 + 𝟕. 𝟓𝟐 𝐍𝟐
2
Oxy-fuel combustion, general combustion equation: 𝛂 𝟐
𝛂
𝐂𝐇𝟒 + [𝛂 𝐎𝟐 + (𝟏 − 𝛂)𝐂𝐎𝟐] → (𝟏 − ) 𝐂𝐎𝟐 + 𝛂 𝐇𝟐𝐎 𝟐
3
21 22 23
Where α is the oxygen fraction. It can be defined0as the mole fraction of oxygen0 in the oxidizer
24
𝜶=
25 26 27 28 29 30 31 32
° ° Where 𝑉𝑂2 and 𝑉C𝑂2 denoted the volumetric flow rate of and carbon dioxide in the oxidizer mixture. The composition of air is 21% O 2 and 79% N2. Comparisons with oxy-fuel combustion will be quantified, analyzed and reported. An0eddy-dissipation model 32 that relates0the rate of reaction to the rate0of dissipation of the reactant- and0product-containing eddies is used to calculate0the reaction rate. This model is widely used in the predictions of many industrial and research flames 33. The chemical source of any species0i due to reaction, Ri; is well computed as the summation of the total reaction0sources over0the N R reactions and given by equation 5 34 :
blends can be identified by the following formula of equation 4 31: 𝑽°𝑶𝟐
4
𝑽°𝑪𝑶𝟐 +𝑽°𝑶𝟐
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𝑵
𝑹 𝑹𝒊 = 𝑴𝒊 ∑𝒌=𝟏 𝑹𝒊,𝒌
5
Where Mi is representing the molecular weight of species i and Ri,k is rate of creation in a molar basis of any species i in reaction k. The reaction rate, Ri,k is also controlled by the so called Arrhenius kinetic rate. Equations 6 and 7 give expression for the rate of reaction for any species i. Ri,k is evaluated by selecting the minimum value of the following expressions 34:
𝑹𝒊,𝒌 = 𝝂𝒊,𝒌 𝑴𝒊 𝑨𝝆
𝜺
𝒎𝑹
6
𝑲 𝝂𝑹,𝒌 𝑴𝑹
9
𝜺
∑𝒑 𝒎𝒑
10
𝑹𝒊,𝒌 = 𝝂𝒊,𝒌 𝑴𝒊 𝑨𝑩𝝆
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Where mR and mp is the mass fraction of any reactant (R) and the product (P), respectively. A and B are empirical constants equal to 4.0 and 0.50 respectively. While, 𝜈𝑖,𝑘 is the stoichiometric coefficient0 for any reactant i in0reaction k. Radiation0 from gas to the0combustor walls are extremely important due to a significant amount of heat will be transferred from the combustion chamber through the walls. Thus, the P-I0radiation model is applied to take into considerations the huge amount of radiated heat and to have a reasonable agreement0 with the experimental data. The P-1 radiation model is the0simplest case of the more general0P-N model, which is based on the expansion of the0radiation intensity I into an orthogonal series of spherical0harmonics 35,36.
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7
𝑲 ∑𝑵 𝒋 𝝂𝒊,𝒌 𝑴𝒋
3. Model Validation In order to validate this numerical work, a 2-D axis-symmetric combustor model have been created with the same dimensions of the gas-fired boiler at the same experimental conditions and a comparison is0 made between the predicted axial and radial temperatures with an experimental work by Wilkes et al. 26. The comparisons are presented in Figure 3 and Figure 4. As shown in the corresponding figures below, the present model gives a good0agreement with the0 experimental data done by Wilkes et al. [3] for both the axial and radial temperature distribution.
Figure 3: Validation on the axial temperature distribution
Figure 4: Validation on the radial temperature distribution
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Figure 5: Validation on the temperature distribution using different models. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
In Figure 3 model validation on the axial temperature distribution, while Figure 4 is the model validation with respect to the radial temperature distribution. Both validations for axial and radial temperatures of the combustor have been successfully achieved. It can be seen that the present numerical study has a good agreement with the experimental work. A further validation has been made on the K-Є model for more accurate results 37,38 . The Standard k-Є model has much better agreement with the experimental data. Therefore, the K-Є standard model have been used for all simulations.
4. Grid Independency Study Grid independency study has been performed to make sure that the results are no longer changes while changing the grid size. For the sake of examining the mesh and solution convergence, a grid independency study has been conducted for five different mesh sizes including 5600, 16100; 32000; 64000; and 136900 before numerical solution conducted. The comparisons between the different five mesh sizes have been reported based on the values of the axial and radial temperatures and presented in Figure 6 and Figure 7, respectively. The predicted temperature of 16,200 and 32,000 nodes/cells show the same profile. The temperature distribution of 64,000 and 136,952 nodes illustrate same trends with respect to the experimental data. Furthermore, the grid independency study revealed that increasing the nodes/cells or refining the mesh size more than 64,000, does not have any changes, except it makes the calculation more time consuming. Consequently, the grid nodes of 64,000 is chosen for all calculation in the present study for both air and0oxy fuel combustion cases for the sake of saving time.
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Figure 6: Comparison of the grid independency solutions of axial temperature
Figure 7: Comparison of the grid independency solutions of radial temperature at x=0.04. 1 2 3 4 5 6 7 8 9 10
5. Results and discussion 5.1 Results of Air-fuel combustion In the0 following section, the results of the non-premixed air-fuel combustion are going to be presented. A comparison of the radial temperature distribution is made at different radial distances from the burner tip. The study shows that at the beginning of the combustion chamber the temperature were fluctuating until reaching 200 mm after which the fluctuations disappears. The maximum temperature where allocated at x= 200 mm, which is can be seen in Figure 9 and Figure 8 that the highest temperature highlighted by the red-hot spot.
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Energy & Fuels
Figure 8: The radial temperature distribution at different axial distances of air fuel combustion
Figure 9: Temperature Contours of Air fuel combustion 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
5.2Results of oxy-fuel combustion and a comparison with air In this section, the results of oxy-fuel combustion will be presented. The effect of oxidizer flexibility or changing oxidizer composition on combustion characteristics, including axial and radial temperature distribution, axial velocity and flue gas emissions distribution, by using oxyfuel combustion technique. While investigating three different oxygen fractions including 30%, 40% and 50%. In order to examine the effect of using different oxidizers. The oxy-fuel combustion cases have been compared with its correspondents of air-fuel combustion. 5.2.1 The effect of oxidizer flexibility on temperature distribution The flame centerline temperature for different oxygen fraction along the combustor axis are presented in Figure 10 as compared with air. While the oxygen fraction increases, maximum temperature location moves toward the tip of the burner. The maximum temperature level is around 2000, 1800, 1700 and 1600 for the oxygen fraction of 50%, 40% 30% and air, respectively. At different axial distances, namely, 0.04, 0.20 and 0.40 m are plotted in Figure 10. Increasing the oxygen fraction increases temperature levels this can be attributed to the increase in the rate of reaction. 9 ACS Paragon Plus Environment
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(a)
(b)
(c)
(d)
Figure 10: Comparison of Axial Temperature distribution (a) and Radial temperature distribution at different axial distances x=0.04 (b), x=0.2 (c) and x=0.4 (d) 2 3 4 5 6 7 8 9
Axial velocity distribution along the centerline of the combustor at various swirl numbers are plotted in Figure 11. The oxygen fraction affects the axial0velocity and the flow0 field structure. It seems that all cases for oxy-fuel combustion and air-fuel0 combustion have the same profile. The peak of the0axial velocity is recorded for the highest oxygen fraction, they can be attributed to adding more oxygen will increase the burning velocity and consequently the axial velocity profile will increase.
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Figure 11:Axial Velocity Distribution along the centerline of the combustor 1 2 3 4 5 6 7 8 9 10 11 12
5.2.2 The Effect of oxygen fraction on Gas Concentration distribution Gas concentration gradients including CO 2 , O2, and H2O for different oxygen fractions along the combustor’s axis are plotted in The0 distributions of CO2, O2 and H2O along centerline of the0combustor are given for different oxygen fraction as well as the air in Figure 12. Both CO 2 and0H2O are the product of0 chemical combustion the0chemical0reaction, so the distribution of CO2 and H2O are directly related to the oxygen fraction. As oxygen concentration increases, the concentration of CO2, H2O and O2 will be increased. It can be0 concluded that, as the oxygen fraction increases the flame temperature increase this can be0attributed to the increase in the adiabatic flame temperature while increasing the oxygen concentration as compared to air-fuel combustion.
(a)
(b)
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(c)
Figure 12: Gas concentrations gradient along the centerline of air-fuel combustion and oxy-fuel combustion for different species namely, CO2 (a), O2 (b) and H2O (c). 1 2 3 4 5 6 7 8 9 10 11
5.2.3 The Effect of oxygen fraction on Streamlines distribution Stream lines contours shown in figures below. As shown there is a recirculation zone have been created beside the inlet section of air and fuel, this recirculation zone enhances the flame stability as this recirculates the hot flue gases again with the incoming reactant which can make the flame is robust. The outer recirculation zone (ORZ) size slightly decreases while0increasing the oxygen concentration, this can be0attributed to the increase in the turbulence levels associated with increasing the oxygen fraction and it will reduce the axial velocity shown in Figure 13, the size of the recirculation0 zone and the strength of the vortex doesn’t change a lot in the four studied cases as shown in the figure below.
Air
Oxy-OF30% Oxy-OF40% Oxy-OF50% Figure 13: Velocity Streamlines of the four cases, air and oxy with O.F. % of (30%, 40% and 50%). 12 ACS Paragon Plus Environment
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5.3The effect of the swirl number on combustion characteristics The effect of swirl number has been investigated for the air-fuel combustion cases to investigate different combustion parameters such as axial and radial temperatures, axial velocity, and flue gas concentrations. Four different swirl numbers have been included in our study, namely, 0 (no swirl) 0.5, 1.0, 1.5. The swirl number will affect input axial velocity and tangential velocity components. Figure 14 presents the effect of swirl number on the axial and radial temperature distribution and axial velocity distribution as well. This study revealed that increase the swirl number will shift the peak0temperature location0toward the burner tip. The average temperature levels are around 1800 K. Temperature profiles for 0 and 0.5 swirl number show similar0trend. However, temperature profile for 1.0 and 1.5 value of the swirl number is different. The impact of swirl0 number on radial0temperature distribution an axial distance namely, 0.04 is plotted in Figure 14. Increasing swirl number increases temperature level, this result is to be expected because a higher swirl numbers leads to increased mixing between air and0 fuel streams 39–41. The impact of changing swirl number on velocity field have been also investigated. Axial velocity distribution along the centerline of the combustor at different0 swirling numbers are presented in Figure 14. It is clear that increasing swirl number affect the axial velocity field structure this is because of additional recirculation zone have been established due to the axial velocity have been reduced with increasing swirl number. While the swirl number is zero, there is no central recirculation zone (CTRZ). While at Sn =1.0 and 1.5, the central recirculation zone has been created and the axial velocity recorded negative values as an indication of the CTRZ.
Figure 14: The effect of swirl number on Axial and radial temperature distribution and axial velocity distribution 13 ACS Paragon Plus Environment
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Additional zone has been generated in the flow field called external recirculation zone (ETRZ) as shown in Figure 15 at the largest swirl number with the increasing0 swirl number due to the increase of the swirl velocity and the reduction of the axial velocity at the meanwhile. The size and strength of the0recirculation zone are strongly influenced by0the swirl level.
Sn=0
Sn=0.5
Sn=1.0
Sn=1.5 Figure 15: Streamlines at different Sn=0.0, 0.5, 1.0, 1.5. 7 8 9 10 11 12 13 14 15
5.4The effect of Swirl number on thermal NOx In this section, the effect of swirl0 number on the exhaust and centerline thermal NOx are going to be presented. As per the open literature, it is well known that the thermal NOx is reduced by increasing the swirl number, this is can be attributed0to the increase in the turbulence levels 42–44 and hence, the increase on the mixing between the air and fuel. Consequently, the thermal NOx is going to be reduced 21,45. The thermal NOx mole fraction concentration has been significantly dropped by 95% as shown in Figure 16.
Figure 16: NO concentration at the centerline (left) and at the exit section (right) 16
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Acknowledgment
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References
Numerical study has been performed to investigate the effect of the non-premixed combustion type on flame characteristics in terms of axial and radial temperature distribution, temperature contours, velocity contours, streamlines contours and species concentrations. The numerical model is validated and compared to one numerical model and one experimental data. While increasing the swirl number, the inner/central recirculation zone (CRZ) has been established which enhances the flame stabilization. Increasing swirl number increases temperature level, this result is to be expected because a higher swirl numbers leads to increased mixing between air and fuel streams. Furthermore, It is clear that increasing swirl number affect the axial velocity field structure this is because of additional recirculation zone have been established due to the axial velocity have been reduced with increasing swirl number. While increasing the swirl number, the thermal NOx dropped by a percentage of 95%, this can attributed to the increasing of the premixing levels between the air and fuel which will bring the combustion temperature down, hence thermal NOx decreased. The present study provides new0ideas to designer and engineers0for combustion devices0such as gas turbines, gas fired boilers and burners.
The author would like to thank the Government of Ontario, Canada, for providing the funding for this work in the form of the Ontario Trillium Scholarship (OTS).
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