THE FORMATION OF CO-NO IN A CONFINED CAN COMBUSTOR DUE TO SWIRLING FLOW

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1 THE FORMATION OF CO-NO IN A CONFINED CAN COMBUSTOR DUE TO SWIRLING FLOW M. N. Mohd Jaafar 1 & M. S. A. Ishak 2 1 Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, UTM Johor Bahru, MALAYSIA 2 School of Manufacturing Engineering, Universiti Malaysia Perlis, P.O Box 77, Pejabat Pos Besar, Kangar, Perlis, MALAYSIA Abstract The main purpose of this paper is to study the internal flow effect and the emission production of CO and pollutant NO when varying the swirl number inside the combustor. The flow field inside the combustor is controlled by the liner shape and size, wall side holes shape, size and arrangement (primary, secondary and dilution holes), and primary air swirler configuration. Air swirler adds sufficient swirling to the inlet flow to generate central recirculation region (CRZ) which is necessary for flame stabilization and fuel air mixing enhancement. Therefore designing an appropriate air swirler is a challenge to produce stable, efficient and low emission combustion with low pressure losses. Four radial curved vane swirlers with 30 o, 40 o, 50 o and 60 o vane angles corresponding to swirl number of 0.366, 0.630, and respectively were used in this study to show the vane angles effect on the internal flow field. The flow behavior was investigated numerically using CFD solver Ansys This study has provided the characteristic insight into the flow pattern inside the combustion chamber. Results show that the swirling action is augmented with the increase in the swirl number, which leads to increase in the turbulence strength, recirculation zone size, and amount of recirculated mass. The current study reports that the 50 swirler (swirl number > 0.7), produced enough swirling flow to generate good CRZ in the combustion chamber and stabilize the formation of CO and pollutant NO at early stage. Keywords: Swirler; curved vanes; combustion; emission; turbulence; CFD simulation I. Introduction Swirling jets are used for the stabilisation and control of a flame and to achieve a high intensity of combustion. The common method of generating swirl is by using angled vanes in the passages of air. The characteristic of the swirling jet depends on the swirler vane angle [1]. Various investigation on the effects of swirl on the flame stability for swirl flame in unconfined space have shown increasing fuel/air mixing as the degree of swirl increased [2]. The size and strength of the central recirculation zone (CRZ) also increased with an increase in swirl intensity. At low flow rates or swirl numbers, long yellow and highly luminous flames are produced indicating poor fuel-air mixing [3]. However, when the swirl number is increased, the CRZ increases in size, initially in width until restricted by the diameter of the combustor and then begin to increase in length [3]. Measurements of the flame length and stabilization distance carried out in the series of butane-propane-air flames with swirl have shown that both decrease markedly with increasing degree of swirl [4]. Tian on the other hand, numerically compared the effect of swirling and nonswirling system on combustion [5]. He demonstrated that the existence of swirl helps improve combustion efficiency, decreases all pollutants and increases flame temperature. He also observed that during the presence of a swirl, a shorter blue flame was observed indicating a shorter time for peak temperature resulting in good mixing while non-swirling system showed a longer yellow flame indicating a longer time at peak temperature, and there is still some fuel left unvaporised. Increasing the swirl number improves flame stability due to the presence of the recirculation zone [6]. Increasing the swirl number will increase the angle of the jet thereby increasing the total available surface area per unit volume of the jet. This allows further mixing with the surrounding fluid in the free jet and the central core of the flow [7]. It has also been shown that flames with low swirl have instability problems, because of the absence of the recirculation zone [8]. The main focus of this research is to investigate the effect of varying the swirl angle on formations of carbon monoxide (CO) and pollutant nitric oxide (NO) close to the burner throat inside the combustor. Flow pattern characteristics include velocity components and turbulent stresses, which are the main characteristics of the swirling flows, also have been studied to understand ISBN:

2 the physical process both by numerical modeling CFD software Ansys 14.0 [9]. Computational Fluid Dynamics (CFD) is an attractive design tool, since it has the potential to explain the flow physics inside the combustor. A numerical analysis can be used to reduce the number of design iterations by providing an approach to the changes that a design parameter should undergo regarding the characteristics of the flow. This study focuses on flow aerodynamics inside a gas turbine combustor using CFD. The flow pattern inside the combustor is significantly affected by the air swirler configuration. This paper, therefore, numerically investigates the swirler configuration effects on the flow inside the combustor. Air swirlers are used as a flame holder by adding swirl to the incoming air. The presence of swirl results in setting up of radial and axial pressure gradients, which in turn influence the flow fields. In case of strong swirl the adverse axial pressure gradient is sufficiently large to result in reverse flow along the axis and generating an internal circulation zone [10-13]. In addition swirling flows are used to improve and control the mixing process between fuel and air streams and enhance heat release rate [14-16]. The degree of swirl in the flow is quantified by dimensionless parameter, S known as swirl number which is defines as [14]; Gφ S = G.r o χ where G ø is the axial flux of angular momentum: G G = 2 φ 2π ru x U θ r 0 dr (1) (2) and G x is the axial flux of momentum (axial thurst): χ = 2p 2 ru x rdr + 2p 0 0 prdr (3) In the above equations, r o is the outer radius of the swirler and U x and U θ are the axial and tangential components of velocity at radius r. Since the pressure term in Equation (3) is difficult to calculate due to the fact that pressure varies with position in the swirling jet, the above definition for swirl number can be simplified by omitting this pressure term. Swirl number can be redefined as: S G ' Gφ = ' G x r o where ' x 0 2 = 2π ru xrdr (4) (5) The swirl number should, if possible, be determined from measured values of velocity and static pressure profiles. However, this is frequently not possible due to the lack of detailed experimental results. Therefore, it has been shown Beer and Chigier [14] that the swirl number may be satisfactorily calculated from geometry of most swirl generator. Swirl does not only help to stabilize the flame but also to produce other effect which is beneficial to the combustion system. These effects primarily include promoting fuel and air mixing and assisting the control of combustion temperatures and emissions. This is because of string shear regions, high turbulence and rapid mixing rates produced by the swirling vortices and the resulting toroidal recirculation zone. The various characteristics of swirl combustion are discussed extensively in the literature [15, 17]. The swirling flow spreads as it moves downstream and centrifugal force creates a low pressure zone in the centre of the flow. At a certain point downstream, the low pressure region in the centre of the flow causes the vortex to collapse inwards on itself in a process known as vortex breakdown [18]. This creates a recirculation zone in the centre of the flow. This is essential to provide sufficient time, temperature and turbulence for a complete combustion of the fuel [14, 19]. II. Modeling, Meshing and Boundary Condition The basic geometry of the gas turbine can combustor is shown in Figure 1. The size of the combustor is 1000 mm in the Z direction, 280mm in the X and Y direction. The primary inlet air is guided by radial curved vanes swirler to give the air a swirling velocity component. Four difference vane angles of 30 o, 40 o, 50 o and 60 o were analyzed numerically at different boundary conditions to show the effect of the swirler configuration on the turbulence production, recirculation zone and also pressure loss. The intake condition for the simulations is 50 m/s intake velocity. The technical data of the four swirlers used in this study are listed in Table 1. ISBN:

3 The physical domain of radial swirlers was decomposed to several volumes to facilitate meshing with cooper hexahedral structured grid. The geometry meshing was done to have a variable density distribution by mean of small mesh size which was incorporated in high gradient zone and bigger size in low gradient zone. The combustor model meshing for the present work is shown in Figure 2. Figure 1: Combustor model Table 1: Technical data of the swirlers Swirler Swirl No. (S) Passage width, h (mm) Hub diameter, d (mm) Outer diameter, D (mm) unknown correlation of the fluctuation velocity components, a turbulence model is required for equations closure purposes. In the present simulation, k-epsilon turbulence model was used. Turbulence is represented by the realizable k-epsilon model, which provides an optimal choice and economy for many turbulent flows [20]. Menzies [21], had studied the behavior of five k-epsilon variants in modelling the isothermal flow inside a gas turbine combustor and compared the results with the experimental data of Da Palma [22] for the velocity and turbulence fields. The studied models were the standard, the RNG, the realizable, the Durbin modified, and the nonlinear k- epsilon models. The results showed that the realizable and the Durbin k-epsilon models gave the best agreement with the experimental data. This supported the finding of Durst and Wennerberg [23], where good agreement between k-epsilon model predictions and experimental results were reported. The appropriate choice of boundary conditions is essential and is a critical part in modelling a flow accurately. Typical boundary conditions for FLUENT simulation are the inlet, the wall and the outlet boundaries. At the inlet of the computational region, the inlet boundary condition is defined as velocity inlet while the exit boundary is defined as outflow. Some assumptions for boundary conditions that were not directly measured had to be made as follows: i. Velocity components and turbulence quantities at the inlet were constant, ii. Turbulence at inlet is calculated from the following equations [24]: k = 0.002( u ) inlet e = 1.5 k inlet 0.3 D 2 inlet (6) (7) where u axial inlet flow velocity and D is hydraulic diameter. Figure 2: Combustor model meshing. Due to the complexity of the flow within the gas turbine combustor, CFD is used as a regular tool to enable better understanding of the aerodynamic and process associated with combustion inside the gas turbine combustors. As mentioned above, FLUENT solves the equations for conservation of mass and momentum in their time averaged form for the prediction of isothermal flow fields. For the process of Reynolds decomposition and time averaging results in A collection of physical models was used to simulate the turbulent liquid fuel reacting flows. These models were selected due to their robustness and accuracy for industrial applications. Turbulence Model: The current study uses the realizable k ε turbulence model. This model is in the class of two-equation models in which the solution of two separate transport equations allows the turbulent velocity and length scales to be independently ISBN:

4 determined. The realizable k ε turbulence model is robust, economic and reasonably accurate over a wide range of turbulent flow. The realizable k ε turbulence model solves transport equations for kinetic energy (k) and its dissipation rate (ε). It assumes that the flow is fully turbulent, and the effects of molecular viscosity are negligible. The realizable k ε turbulence model is therefore valid for fully turbulent flows, consistent with the flow characteristics in a typical combustion chamber. Combustion Models: Combustion models are characterized by the type of mixing (e.g. non-premixed, premixed or partially premixed) and the reaction chemistry (e.g. finite-rate chemistry or fast chemistry). Liquid fuel combustion primarily takes place in a diffusion-limited mode (non-premixed) where fuel and oxidant are brought into contact via mixing and then react. In these types of flames, it can generally be assumed that the turbulent mixing rate is much slower than the chemical kinetics rates (fast chemistry), and hence, will be the rate-limiting step. The current study used the eddy-dissipation combustion model, which assumed that the reaction rate is controlled by the turbulent mixing rate. Hence, the turbulent mixing rate in conjunction with a global reaction mechanism is used to predict local temperatures and species profiles. This model solves the conservation equations describing convection, diffusion, and reaction sources for each component species. NOx Formation Models: The NOx formations models used in this study include the primary NO x formation mechanisms, i.e. thermal, prompt, and fuel [9]. For thermal and prompt NO x, only the transport equation of NO is solved. (8) These transport equations are solved based on the given flow field and combustion solution. In other words, NO x is post-processed from the combustion simulation. The formation of thermal NO x is then determined by the extended Zeldovich mechanism and the rate constants for the mechanism are measured from experiments [25]. The current study also applied partial equilibrium model to predict O atom concentrations and assumed lean fuel conditions for OH predictions. The prompt NO x formation depends on local fuel-to-air ratio and carbon numbers. The rate constants in the model are derived empirically for different mixing strength and fuel type [26]. The model inputs are carbon number and equivalence ratio in the combustion zone. The carbon number is 10 (diesel combustion) for volatiles and the equivalence ratio is calculated based on the actual air flow and air demand. III. Results and Discussion All the axial flow characteristics are presented in two parts, first part are Figures 3 to 5 for swirl strength analysis, second part are Figures 6 to 9 for flow variation analysis and third part are Figures 10 to 13 for combustion results. III.1. The Effect of Swirl Strength To validate the first part, CFD model experiments were conducted to measure the axial flow velocity at the axis of the chamber for all swirlers. Figure 3a shows the results of CFD analysis showing the axial flow velocity distribution along the chamber axis. These results were then compared to experimental results as part of the validation of the CFD model, as shown in Figure 3b (results for only 30 and 60 swirlers were presented for clarity). For boundary conditions discussed in article II axial velocity profiles for chambers with different swirler angles are shown in Figures 4a to 4d. For the chamber with the swirler angle of 30 (S=0.366), the axial velocity peak is a lot lower than the chambers with higher swirler angles, and the position where the peak velocity occurs is shifted towards the inlet point. This is due to the fact that there is no recirculation zone for the chamber with 30 swirler angle. The flow in other chambers with higher swirler vane angles resulted in higher negative axial velocities at the core, giving lower overall magnitude of axial velocities. This phenomena can be seen in Figure 4 which shows the axial flow at across sections at distances 10 mm (z/r = 0.036) from the chamber inlet. Axial flow variations across other section further down streams are shown in Figures 4a to 4d. At other sections further away from the inlet, the core reverse flow velocities are significantly reduced. The flow characteristics at the cross sections near the inlet (Figures 4a and 4b) show that there occur significant reverse velocities at the core of the chamber for all chambers except for the one with 30 swirler angle. For the 30 swirler the core flow does not reverse, just that the core reverse axial flow velocity were merely reduced by 50% compared to the chamber with higher swirl angles. As the swirler angles increased, the core flow zone become increasingly negative and the cross section area ISBN:

5 of these core flows become wider. Although there is a central negative zone, the overall mass flow for the section is still positive. At cross sections further from the inlet point, the core axial velocity continuously become less negative and negative flow cone area become bigger. The axial flow variations from CFD analysis at different cross sections for chambers with 30 to 60 swirler angles are shown in contour form in Figures 5a to 5b respectively. The axial flow velocity distribution shown here confirms the values shown in Figures 4a to 4d. These plots show the reverse flow areas become wider at sections further along the axis of the combustor and hence the peak reverse velocity at these sections reduces significantly. The wider areas indicate more efficient mixing area. The characteristics of the flow point towards good mixing of air and fuel when the core peak reverse velocity is high and these core velocities only cover small cross sectional area. This flow condition occurs for the 40 and 50 swirlers. For more precise maximum mixing phenomenon, more detailed studies should be done for swirl angles from 40 to 50, say at 45. Figure 3a: Axial Flow Velocity results from CFD Analysis for Combustors with different Swirl Angles ISBN:

6 Figure 3b: Axial Flow Velocity comparing CFD and experimental results Figure 4a: Axial Flow Velocity across section z/r = results from CFD Analysis for Combustors with different Swirl Angles Figure 4b: Axial Flow Velocity across section z/r = results from CFD Analysis for Combustors with different Swirl Angles ISBN:

7 Figure 4c: Axial Flow Velocity across section z/r = results from CFD Analysis for Combustors with different Swirl Angles Figure 4d: Axial Flow Velocity acress section z/r = results from CFD Analysis for Combustors with different Swirl Angles Figure 5a: Axial Flow Velocity results from CFD Analysis for Combustors with 30 Swirl Angles at different axial distance from the inlet. ISBN:

8 Figure 5b: Axial Flow Velocity results from CFD Analysis for Combustors with 40 Swirl Angles at different axial distance from the inlet. Figure 5c: Axial Flow Velocity results from CFD Analysis for Combustors with 50 Swirl Angles at different axial distance from the inlet. Figure 5d: Axial Flow Velocity results from CFD Analysis for Combustors with 60 Swirl Angles at different axial distance from the inlet. ISBN:

9 III.2. The Effect of Velocity variation on Swirl Strength To validate the second part of CFD model analysis, experiments were conducted to measure the axial flow velocity at the axis of the chamber for 50 m/s inlet velocity. Figure 6 shows the results of CFD analysis compared to experimental results as part of the validation of the CFD model. A past researcher shows that, 50 swirl gives the best result in terms of swirl zone and size of recirculation areas [27, 28]. From the results, further work was conducted to see the effects of variations in axial velocity on the centre core flow in the combustion chamber. The flow was varied from 30 m/s to 60 m/s (equivalent to Reynolds Number from 0.6 to 1.2 x 106). The results showing the variations in the transient core flow at 25s after the air was injected into the chamber are depicted in Figure 7. The figure shows the reverse axial velocities in the central axial section of the chamber. The white portion of the figure means the axial flow is positive. The results show similar flow pattern for all injection velocities, or at all Reynolds numbers, but as the injection velocities increased the reverse flow velocities in the core increases from 15 m/s for the 30 m/s injection (Figure 8a) to 30m/s for 60 m/s injection (Figure 8d). But the core size does not change. Taking the cross section at L/D= 0.1, the core size is r/r=0.05 for all injections velocities. The differences are mainly due to higher injection velocities, where the core reverse flow velocities also increases. These can be seen in the reverse axial velocities at different cross sections as shown in Figures 8a to 8d. Another significant result is that the core axial flow velocities at cross sections nearer to the injection point increases with injection velocities. But after the distance of L/D=0.4 the central core axial velocity do not change significantly. This can be seen clearly in the Figures 8a to 8d. The axial flow velocities along the central chamber axis were then plotted until 200 mm (L/D=0.71) from the injection point. Figure 9 shows that near the injection point, the reverse flow velocities are directly related to the injection velocities. The higher the injection velocities, the faster are the reverse flow velocities. This is accompanied by the reduction in size of the core reverse flow volume. This is understandable since the swirl angle is constant (so is the swirl number), such that the higher injection velocities would produce higher reverse core flow, thus enhancing mixing of fuel in the chamber. Figure 6: Axial Flow Velocity results from CFD Analysis for Combustors with 50 Swirl Angles, experiment with 50 m/s air inlet velocity. ISBN:

10 Figure 7: Transient flow at 25 s with the injection of various velocities Figure 8a: Axial flow across chamber diameter for injection velocity 30 m/s, at different cross section distances from the injection point. ISBN:

11 Figure 8b: Axial flow across chamber diameter for injection velocity 40 m/s, at different cross section distances from the injection point. Figure 8c: Axial flow across chamber diameter for injection velocity 50 m/s, at different cross section distances from the injection point. Figure 8d: Axial flow across chamber diameter for injection velocity 60 m/s, at different cross section distances from the injection point. ISBN:

12 Figure 9: Axial flow along the velocities for different III.3. Swirl Strength on the Formation of CO-NO X Transversal profiles of total carbon monoxide (CO) population in the liquid fuel combustor were obtained similar from the temperature analysis. The CO population was found to be high for low swirl combustion compared to high swirl combustion as seen in Figure 10 and Figure 11. For high swirl flow, the CO population stabilized at short distance from the swirler throat (for SN=1.427 stabilizes at z/d=0.4). For low swirl combustion, the CO population continues to increase from the swirler throat at an average rate of 20% for every z/d of 0.2. It had not stabilized even at z/d=0.8. This was calculated from the area below the graphs at each station in Figures 10a to 10d. These phenomena could be explained by the presence of the swirl immediately after the swirler throat and the central internal recirculation zone at the core of the chamber. These two physical phenomena helped to quicken the completion of combustion because the mixing of fuel is more thorough, and the reintroduction of hot species from the initial combustion zone into the combustion core due to recirculation. Transversal profiles of total pollutant nitrogen oxide (NO) population in the liquid fuel combustor were obtained from the temperature analysis (Figure 12). The NO population was found to be well distributed across the combustor for high swirl flow but for low swirl flow this pollutants are more concentrated at the core (SN= after z/d=0.6 and for SN=0.366 after z/d=0.8). This correlates with the flame intensity positions, where that intense heat would produce more NO [14]. In addition, for SN=0.366 the NO concentration at the combustor core near the swirler throat is very low, which can be explained by the fact that there is no flame at that point. Due to buoyancy, the flame really started at z/d=0.4, after which point the concentration pollutant NO at the core starts to increase. ISBN:

13 (a) z/d=0.2 (a) z/d=0.2 (b) z/d=0.4 (c) z/d=0.6 (d) z/d=0.8 Figure 10 Transversal profiles of total carbon monoxide at different axial station Figure 11 Total Carbon Monoxide (CO) Contour in Axial Section of the Combustor (Scale is in ppm) From Figures 12 and 13, the rate of increase in concentration of NO for high swirl flows (SN=0.978 and 1.427) starts at 50% from z/d=0.2 to 0.4, and continued at the same rate to z/d=0.6. There after the ISBN:

14 concentration stabilizes, which means there was no more production of NO after z/d=0.6. For the low swirl flow, the NO concentration was very low at positions near the swirler throat and did not increase until z/d=0.6. From this point to z/d=0.8 the concentration increased by 40% and continued increase by 80% up to z/d=1.0. It should be noted here that the high swirl flows produce wider flames covering the whole of the can cross section, resulting in flames without intense temperature point. This prevents the formation of NO due to high temperatures. For low swirl flows, the flame is more concentrated at the core of the can, away from the swirler throat. This resulted in high temperature intensity zone, which encouraged the formation of thermal NO. These results point to the importance of elimination of flame peak temperatures from combustors using high swirl flows would reduce the production of NO. (a) z/d=0.2 (b) z/d=0.4 (c) z/d=0.6 (d) z/d=0.8 (e) z/d=1.0 Figure 12 Transversal profiles of total NO Pollutant at different axial station ISBN:

15 Figure 13 Total Pollutant Nitrogen Oxide (NO) Contour in Axial Section of the Combustor (Scale is in ppm) IV. Conclusion This paper presented the results of CFD study on the axial flow in a circular chamber with different swirl numbers affected by different swirlers of different angles. The initial results were compared with actual measurements to validate the CFD model. The validated model was then used to study further variations of the flow in the chamber. The study indicated that the central core of the flow has low recirculation zone at low swirl numbers, but recirculation behavior became significant when the swirl number is more than 0.63 (swirler angle more than 40 ). The central recirculation zone length is also very short but it occurs over a wide cross section. As the swirl number increases, the central recirculation zone lengthens but narrows such that the central axial flow is faster. If the chamber is used for combustion, the long and narrow recirculation zone would be able to return unburnt fuel towards the injection point and it will also bring back the hot species, thus helping in the combustion. The velocity variation analysis shows results of CFD study on the axial flow in a circular chamber with different inlet velocity varying from 30 m/s to 60 m/s (equivalent to Reynolds Number from 0.6 to 1.2 x 10 6 ) of 50 degree radial vane angle swirler. The initial results were compared with actual measurements to validate the CFD model. The validated model was then used to study further variations of the flow in the chamber. The study indicated that at all injection velocity, similar flow pattern was found, but as the injection velocities increased the reverse flow velocities in the core increases but the core size does not change. The differences are mainly due to higher injection velocities, where the core reverse flow velocities also increases. Another significant result is that the core axial flow velocities at cross sections nearer to the injection point increases with injection speeds. But after the distance of L/D=0.4 the central core axial velocity do not change significantly. From the results of various injection velocities, it shows that the differences are mainly due to higher injection velocities, where the core reverse flow velocities also increases. The combustion simulation proves that the formation of CO-NO near burner throat in swirling flow combustion system is related to the swirler number/swirler angle. High swirler number produces short but wide flame, and this reduces the time and distance for burning. Besides, it also reduces the peak temperature of the flame, which prevented the formation of pollutant NO. Moreover, high swirler number also leads to the well distributed temperature distribution in the combustor cross section. Because of all these factors, the formation of CO-NO near burner throat is reduced. Therefore, for the future works in the development of an efficient combustion system, the relationship between the swirler number/swirler angle and the formation of CO-NO must be taken into consideration. Acknowledgements The authors would like to thank the Ministry of Higher Education of Malaysia & Research Management Center, Universiti Teknologi Malaysia (project number: 01G60) for the research grant to undertake this project. The authors would also like to thank the Faculty of ISBN:

16 Mechanical Engineering, Universiti Teknologi Malaysia for providing the research facilities and space to undertake this work. References 1) Mathur, D.L A New Design of Vanes for Swirl Generation IE (I) Journal Me, Vol.55 pp ) Fricker, N. and Leuckel, W The Characteristic of Swirl Stabilized Natural Gas Flame Part 3: The Effect of Swirl and Burner Mouth Geometry on Flame Stability, J. Inst. Furl, 49, pp ) Mestre, A and Benoit, A Combustion in Swirling Flow, 14th Symposium (International) on Combustion, The Combustion Institute, Pittersburg, pp ) Chervinskey, A. and Manheimertiment, Y Effect of Swirl on Flame Stabilization, Israel Journal of Technology, Vol. 6, No. 2, pp ) Tian, Z. F., Witt, P. J., Schwarz, M. P., & Yang, W Numerical modeling of Victorian brown coal combustion in a tangentially fired furnace.energy & Fuels, 24(9), ) Khalil, K. H., El-Mehallawy, F. M. and Moneib, H. A Effect of Combustion Air Swirl on the Flow Pattern in a Cylindrical Oil Fired Furnace, 16th Symposium (International) on Combustion, The Combustion Institute, Pittersburg, pp ) Apack, G Interaction of Gaseous Multiple Swirling Flames, Phd thesis, Department of Chemical Engineering and Fuel Technology, University of Sheffield. 8) Gupta, A. K., Lilley, D. G. and Syred, N Swirl Flows, Abacus Press, Tunbridge Wells, England. 9) FLUENT 14.0 User's Guide, Fluent Inc. (2012) 10) Lefebvre, A.: Gas Turbine Combustion. McGraw-Hill, USA (1983) 11) Mellor, A.M.: Design of Modern Gas Turbine Combustors. Academic Press. (1990) 12) Mattingly, J.D.: Elements of Gas Turbine Propulsion. McGraw-Hill International Edition, Singapore (1996) 13) Ganesan, V.: Gas Turbines. Tata McGraw- Hill, New Delhi (2003) 14) Beer, J.M.; Chigier, N.A.: Combustion Aerodynamics. Applied Science Publisher, London (1972) 15) Gupta, A.K.; Lilley, D.G.; Syred, N.: Swirl Flows. Abacus Press, Tunbridge Wells, England (1984) 16) Ishak, M.S.A.; Mohd Jaafar, M.N., The Effect of Radial Swirl Generator on Reducing Emissions from Bio-Fuel Burner System, Modern Appl. Sci., Vol. 3, no. 6, pp ) Sloan, D.G.; Smith, P.J.; Smoot, L.D.,1986. Modeling of Swirl in Turbulent Flow System. Prog. Energy Combust. Sci, Vol 12, pp ) Wang, Y.; Yang, V.; Yetter, R.A.: Numerical Study on Swirling Flow in an Cylindrical Chamber, 42nd AIAA Aerospace Sciences Meeting, Reno, Nevada (2004) 19) Syred, N.; Beer, J.M., Combustion in Swirling Flows: A Review. Combustion and Flame, Vol. 23, pp ) Kim, Y. M.; Chung, T. J., Finite- Element Analysis of Turbulent Diffusion Flames. AIAA J., Vol. 27, no. 3, pp ) Menzies, K.R.: An Evolution of Turbulence Models for the Isothermal Flow in a Gas Turbine Combustion System. 6th International Symposium on Engineering Turbulence Modelling and Experiments, Sardinia, Italy (2005) 22) Da Palma, J.L.: Mixing in Non-Reacting Gas Turbine Combustor Flows. PhD Thesis, University of London, UK (1988) 23) Durst, F.; Wennerberg, D., Numerical Aspects of Calculation of Confined Swirling Flows with Internal Recirculation. Int. J. Numerical methods Fluids, Vol. 12, pp ) Versteeg, H.K.; Malalasakera, W.: An Introduction to Computational Fluid Dynamics, the Finite Volume Method. Longman Group Ltd (1995). 25) King, P. T., Andrews, G. E., Pourkashanian, M. M., & McIntosh, A. C Nitric Oxide ISBN:

17 Predictions for Low NOx Radial Swirlers With Central Fuel Injection Using CFD. In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition (pp ). American Society of Mechanical Engineers. 26) Zhou, W., Moyeda, D., Payne, R., & Berg, M Application of numerical simulation and full scale testing for modeling low NOX burner emissions. Combustion Theory and Modelling, 13(6), ) Mohd Jaafar M.N., Eldrainy Y.A., Ahmad M.F.,2009. Investigation of Radial Swirler Effect on Flow Pattern inside Gas Turbine Combustor. Modern Appl. Sci., 3(5): ) Yehia A.E., Hossam S.A., Khalid M.S., Mohd Jaafar M.N., A Multiple. Inlet Swirler for Gas Turbine Combustors, Int. J. Mechanical Syst. Sci. Eng., 2(2): ISBN: