- Email: [email protected]
Numerical Study of a Methane Jet Diffusion Flame in a Longitudinal Tube with a Standing Wave
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 105 (2017) 1539 – 1544
The 8th International Conference on Applied Energy – ICAE2016
Numerical Study of a Methane Jet Diffusion Flame in a Longitudinal Tube with a Standing Wave Song Chena, He Zhaob* , Koong Jye Taya, Ashique Akram Tariquea b
a School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore, 639798 School of Energy and Power Engineering, Jiangsu University of Science and Technology, Zhenjiang, 212003, China
Abstract Flame stability plays an important role in a combustion/propulsion system, which involves the interaction between flow, acoustics, and flame. Although intensive studies have been carried out to investigate the flame-acoustic interactions, the jet flame excited by standing waves formed in a longitudinal tube has not received much attention. In this work, a methane-burnt (CH4) jet diffusion flame in a longitudinal tube with a standing wave produced from a loudspeaker is studied numerically. 2-D unsteady RANS simulations are performed by using ANSYS FLUENT with the standard k H turbulence model and a one-step Eddy-Dissipation combustion model. The acoustic fluctuations are generated by using User Defined Functions. The numerical results show that a longitudinal standing wave can be successfully obtained in the tube by the numerical method, and both the acoustic velocity node and antinode can be observed. It is also found that the jet flame characteristics are highly sensitive to its axial location in the tube when the standing wave is present. The flame is unsteady when it is located at the velocity antinode where large velocity fluctuation exists. When the jet is placed at acoustic velocity nodes, however, the flame is relatively steady. Although the minimum velocity fluctuation at the two velocity nodes is almost at the same level, different flame temperatures are observed, due to the different turbulence kinetic energy. ©©2017 Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 2016The The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review under responsibility of ICAE Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.
Keywords: Flame/acoustic interaction, acoustic standing wave, jet diffusion flame, CFD
1. Introduction It is well-known that flame dynamics can be significantly affected by acoustic waves especially in an enclosed space such as a tube or a cavity, mainly due to the strong coupling between the acoustic waves
* Corresponding author. [email protected] (He Zhao). Tel: +86 156 0528 5679.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.471
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Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
and unsteady heat release rates. Such oscillations are undesirable in gas turbine or aero-engine propulsion systems, because the inherent acoustic-combustion interaction, in some circumstances, can lead to strong engine structure vibrations, flame instability or extinction, enhanced heat flux, and even a complete system failure. In order to better understand the phenomena and to find solutions to solve these problems, extensive research has been performed in the past several decades [1-4] to study premixed or non-premixed flameacoustic interactions. Lieuwen [5], Schadow et al. [6] and Coats [7] provide excellent reviews of flameacoustic wave interactions. Ducruix et al. [8] theoretically and experimentally investigate the dynamic behavior of laminar premixed flames to incident perturbations, which is characterized by a flame transfer function. Palies et al. [9] analyzed the nonlinear combustion instability of turbulent premixed swirling flames based on the flame describing function. Zhang et al. [10] investigated the response of a premixed laminar flame to incoming disturbances and the transfer function with both theoretical and experimental methods. Although many studies have been carried out to investigate the premixed flame-acoustic interactions, the dynamic response of the gaseous diffusion flame in a tube with standing waves has not received much attention. Farhat et al. [11] conducted experiments to investigate jet diffusion flame characteristics in standing waves. They found that the diffusion jet flame is sensitive to the location of the fuel nozzle and the excitation frequencies of the acoustically driven tube. Interestingly, different color and shape jet flames (i.e. yellow flame, mushroom shape flame and blue flame) have been observed respectively at different locations and frequencies. To gain insights on the diffusion flame-acoustics interaction, numerical simulations are needed. However, to the best of the authors’ knowledge, there are few 2D/3D models in the literature to simulate such experiments. Lack of these investigations partially motivated the present work. In this work, a numerical study of methane jet diffusion flames to acoustic perturbations using ANSYS FLUENT v16.1 is performed. Emphasis is placed on the interaction of acoustics-flow-flame and the jet diffusion flame characteristics in standing acoustic wave fields. This study contributes to physical understanding of the diffusion flame characteristics excited by standing waves. It will also help to gain insights on the flame-acoustic interactions [12-21] in a real gas turbine engine. 2. Computational Domain and Numerical Method A 2-D jet diffusion flame-acoustic interaction model is developed according to the experimental setup proposed by Farhat et al. [11], as shown in Fig. 1. It consists of a cylindrical tube with a diameter of D1 and a length of L1, a cone tube with a diameter of D2 and a length of L2 and a fuel injector. One end of the cone tube is attached below the cylindrical tube. The fuel injector is located inside the cylindrical tube at a height of h measuring from the bottom of the cylindrical tube. The methane fuel, CH4, is injected out through a small hole with a diameter of D4 from a cylinder with a diameter of D3 and length of L3. The fuel injector is always placed at the axis of the cylindrical tube, and its axial location can be varied. All the dimensions of the burner system are summarized in Table 1. The top end of the burner system is open to the ambient air, and a loudspeaker is placed at the bottom of the cone tube. The connection between the loudspeaker and the cone tube is not airtight, so fresh air is still able to flow in from the bottom of the tube. When the loudspeaker is turned on, tone sound with certain frequency is produced and propagates through the tube. Thus an unsteady velocity field and pressure field is induced in the tube by the loudspeaker. If the wave length of the sound is much larger than the diameter of the tube, one-dimensional plane wave propagation can be justified. For certain frequencies, standing waves can be induced in the longitudinal tube. Gaseous methane fuel is used in this system, with a fixed injecting velocity 0.52 m/s. A jet diffusion flame will be obtained when sufficient amount of energy is provided to ignite the fuel. In the current numerical model, an unsteady velocity boundary condition is used to replace the loudspeaker to generate
Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
the oscillating velocity field and standing waves present in the tube. The unsteady velocity boundary condition with a frequency of 375 Hz is expressed as: A ª º u z t U «1.0 sin 2S 375 t » (1) U ¬ ¼ where u z is the axial velocity, A is the amplitude of the fluctuating velocity (A = 2.0), and t is time. A mean axial flow U with a velocity of 0.1 m/s has also been added to mimic the air co-flow driven by the jet flame in the experiment. The reason of selecting 375 Hz is that a longitude standing wave with one velocity antinode and two velocity nodes can be established with the current tube dimensions as shown in Table 1. Three locations for the variable h (0.12 m, 0.33 m, and 0.55 m) will be studied. The flow field of this 2-D combustion system is assumed to be unsteady and turbulent. The standard k H model is employed for the turbulence closure, and the one-step Eddy-Dissipation model is used for the combustion modeling.
Fig. 1. Schematic of the burner system Table 1. Dimensions of the burner system
3. Results and Discussion
Parameter
Value (unit: mm)
D1
125
L1
755
D2
210
L2
378
D3
5
L3
15
D4
1.8
h
variable
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1542
Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
3.1. Mode shapes The pressure and velocity mode shapes along the tube, which can show whether the standing wave is established, are plotted and compared with the experimental data in Fig. 2. Both the pressure and velocity are root-mean-averaged, and they are normalized by their maximum values. It can be seen that the typical mode shapes with the node and antinode has been obtained in the current numerical simulations. For example, the mode shape of pressure as shown in Fig. 2(a) has two antinodes (one at z = 0.1 m and the other at z = 0.5 m) and one node at z = 0.3 m, while the mode shape of velocity has two nodes (one at z = 0.1 m and the other at z = 0.5 m) and one antinode at z = 0.3 m as shown in Fig. 2(b). Due to the existence a small mean flow going through the tube, the mode shape of velocity has been shifted slightly. Furthermore, three different locations where the fuel injector will be put are also indicated in the mode shapes. The three different locations correspond to the three special points (the node and antinode). From the mode shapes, it can be confirmed that a standing wave has been successfully obtained in the tube at 375 Hz in our simulations.
(a)
(b)
Fig. 2. The mode shapes in the cylindrical tube with 375 Hz: (a) normalized Prms, and (b) normalized Urms.
3.2. Flame at the velocity antinode (z = 0.33 m) and velocity nodes (z = 0.12 m and 0.55 m) When the fuel injector is located at the velocity antinode (z = 0.33 m) where the maximum fluctuation of velocity exists, the flame shapes are presented in Fig. 3. It is found that interesting flame shapes that are apparently different from normal jet flames have been formed. The flame is unsteady, as the flame front changes with time. Considering the fuel injector is located at the velocity antinode of the longitudinal standing wave, the unsteadiness of the flame front is thus caused by the velocity fluctuations at this region. When the fuel injector is located at the velocity nodes (z = 0.12 m and z = 0.55 m) where the minimum velocity fluctuation exists as shown in Fig. 2(b), the flame shapes are also provided in Fig. 4. Different from the previous case in which the flame is unsteady at the velocity node, flames at the current two locations are quite steady, as the flame shapes almost do not change with time. However, the temperatures of the two flames are rather different, although the large scale velocity fluctuation level for the two cases is almost same. As shown in Fig. 4(a), the maximum flame temperature is around 1100 K, while the other in Fig. 4(b) is around 1500 K. It was learnt that this phenomenon is caused by the different turbulence kinetic energy at the two locations, although their mean flow velocities are almost
Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
same. As the turbulence kinetic energy at z = 0.55 m is about 30% larger than that at z = 0.12 m, the flame thus has a higher temperature as mixing is significantly improved by the higher turbulence levels.
Fig. 3. Temperature contours within a period at z = 0.33 m: (a) T/8, (b) 3T/8, (c) 5T/8, and (d) 7T/8
(a)
(b)
Fig. 4. Temperature contours at: (a) z = 0.12 m, and (d) 0.55 m
4. Conclusions A methane-burnt (CH4) jet diffusion flame to a standing wave in a longitudinal tube are numerically studied in this work. It is shown that the jet and flame characteristics are highly sensitive to its axial location, when standing waves are present. The jet experiences large velocity fluctuations, and flow unsteadiness is observed when the jet is placed at acoustic velocity antinodes. However, the jet and flame
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Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
are much stable in the velocity node region. But different flame temperatures are observed due to the different mixing performance caused by the turbulence kinetic energy levels. References [1] Keller JJ. Thermoacoustic oscillations in combustion chamber of gas turbines. AIAA Journal. 1995;33(12):2280-7. [2] Yang V, and Anderson W. (ed). Liquid rocket engine combustion instability. Progress in Astronautics and Aeronautics: AIAA Publications; 1995. [3] Cammarata L, Fichera A, and Pagano A. Neural prediction of combustion instability. Applied Energy. 2002;72:513-28. [4] Singh AV, Yu M, Gupta AK, and Bryden KM. Thermo-acoustic behavior of a swirl stabilized diffusion flame with heterogeneous sensors. Applied Energy. 2013;106:1-16. [5] Lieuwen T. Modeling premixed combustion-acoustic wave interactions: a review. Journal of Propulsion and Power. 2003;19(5):765-81. [6] Schadow K, and Gutmark E. Combustion instability related to vortex shedding in dump combustors and their passive control. Progress in Energy and Combustion Science. 1992;18:117-32. [7] Coats C. Coherent structures in combustion. Progress in Energy and Combustion Science. 1996;22:427-509. [8] Ducruix S, Durox D, and Candel S. Theoretical and experimental determinations of the transfer function of a laminar premixed flame. Proceeding of the Combustion Institute. 2000;28:765-73. [9] Palies P, Durox D, Schuller T, and Candel S. Nolinear combustion instability analysis based on the flame describing function applied to turbulent premixed swirling flames. Combustion and Flame. 2011;158(10):1980-91. [10] Zhang Z, Zhao D, Dobriyal R, Zheng Y, and Yang W. Theoretical and experimental investigation of thermoacoustics transfer function. Applied Energy. 2015;154:131-42. [11] Farhat S, Kleiner D, Zhang Y. Jet diffusion flame characteristics in a loudspeaker-induced standing wave. Combustion and Flame. 2005;142:317-23. [12] Zhao D, Li X. Minimizing transient energy growth of nonlinear thermoacoustic oscillations, Intenational Journal of Heat and Mass Transfer, 2015;81:188-197. [13] Ji C, Zhao D, Li X, Li S, Li J. Nonorthogonality analysis of a thermoacoustic system with a premixed V-shaped flame, Energy Conversion and Management. 2014;85:102-111. [14] Li S, Zhao D, Ji C, Li J. Combustion instabilities in a bifurcating tube: open- and closed-loop measurements, AIAA Journal. 2014;52(11):2513-2523. [15] Zhao D, Ega E. Energy harvesting from self-sustained aeroelastic limit cycle oscillations of rectangular wings, Applied Physics Letter. 2014;105(10):103903. [16] Zhao D, Ji C, Teo C, Li S. Performance of small-scale bladeless electromagnetic energy harvesters driven by water and air, Energy. 2014;74:99-108. [17] Han N, Schluter J, Zhao D, Goh E, Zhao H, Jin X. Performance evaluation of 3D printed miniature electromagnetic energy harvesters driven by air flow, Applied Energy, 2016;178:672-680. [18] Zhao D, Li S, Zhao H. Entropy-involved energy measure study of intrinsic thermoacoustic oscillations, Applied Energy, 2016;177:570-578. [19] Zhao D, Chow Z. Thermoacoustic instability of a laminar premixed flame in Rijke tube with a hydrodynamic region, Journal of. Sound and Vibration, 2013;332(14):3419-3437. [20] Li L, Zhao D, Yang X. Effect of entropy waves on transient energy growth of flow disturbances in triggering thermoacoustic instability, Intenational Journal of Heat and Mass Transfer, 2016;99:219-233. [21] Li X, Zhao D, Yang X, Wang S. Unity maximum transient energy growth of heat-driven acoustic oscillations, Energy Conversion and Management, 2016;116:1-10.
Biography Mr. He Zhao is currently a Master student in School of Energy and Power Engineering, Jiangsu University of Science and Technology. His research interests focus on combustion, CFD, and propulsion.
ScienceDirect Energy Procedia 105 (2017) 1539 – 1544
The 8th International Conference on Applied Energy – ICAE2016
Numerical Study of a Methane Jet Diffusion Flame in a Longitudinal Tube with a Standing Wave Song Chena, He Zhaob* , Koong Jye Taya, Ashique Akram Tariquea b
a School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore, 639798 School of Energy and Power Engineering, Jiangsu University of Science and Technology, Zhenjiang, 212003, China
Abstract Flame stability plays an important role in a combustion/propulsion system, which involves the interaction between flow, acoustics, and flame. Although intensive studies have been carried out to investigate the flame-acoustic interactions, the jet flame excited by standing waves formed in a longitudinal tube has not received much attention. In this work, a methane-burnt (CH4) jet diffusion flame in a longitudinal tube with a standing wave produced from a loudspeaker is studied numerically. 2-D unsteady RANS simulations are performed by using ANSYS FLUENT with the standard k H turbulence model and a one-step Eddy-Dissipation combustion model. The acoustic fluctuations are generated by using User Defined Functions. The numerical results show that a longitudinal standing wave can be successfully obtained in the tube by the numerical method, and both the acoustic velocity node and antinode can be observed. It is also found that the jet flame characteristics are highly sensitive to its axial location in the tube when the standing wave is present. The flame is unsteady when it is located at the velocity antinode where large velocity fluctuation exists. When the jet is placed at acoustic velocity nodes, however, the flame is relatively steady. Although the minimum velocity fluctuation at the two velocity nodes is almost at the same level, different flame temperatures are observed, due to the different turbulence kinetic energy. ©©2017 Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 2016The The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review under responsibility of ICAE Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.
Keywords: Flame/acoustic interaction, acoustic standing wave, jet diffusion flame, CFD
1. Introduction It is well-known that flame dynamics can be significantly affected by acoustic waves especially in an enclosed space such as a tube or a cavity, mainly due to the strong coupling between the acoustic waves
* Corresponding author. [email protected] (He Zhao). Tel: +86 156 0528 5679.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.471
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Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
and unsteady heat release rates. Such oscillations are undesirable in gas turbine or aero-engine propulsion systems, because the inherent acoustic-combustion interaction, in some circumstances, can lead to strong engine structure vibrations, flame instability or extinction, enhanced heat flux, and even a complete system failure. In order to better understand the phenomena and to find solutions to solve these problems, extensive research has been performed in the past several decades [1-4] to study premixed or non-premixed flameacoustic interactions. Lieuwen [5], Schadow et al. [6] and Coats [7] provide excellent reviews of flameacoustic wave interactions. Ducruix et al. [8] theoretically and experimentally investigate the dynamic behavior of laminar premixed flames to incident perturbations, which is characterized by a flame transfer function. Palies et al. [9] analyzed the nonlinear combustion instability of turbulent premixed swirling flames based on the flame describing function. Zhang et al. [10] investigated the response of a premixed laminar flame to incoming disturbances and the transfer function with both theoretical and experimental methods. Although many studies have been carried out to investigate the premixed flame-acoustic interactions, the dynamic response of the gaseous diffusion flame in a tube with standing waves has not received much attention. Farhat et al. [11] conducted experiments to investigate jet diffusion flame characteristics in standing waves. They found that the diffusion jet flame is sensitive to the location of the fuel nozzle and the excitation frequencies of the acoustically driven tube. Interestingly, different color and shape jet flames (i.e. yellow flame, mushroom shape flame and blue flame) have been observed respectively at different locations and frequencies. To gain insights on the diffusion flame-acoustics interaction, numerical simulations are needed. However, to the best of the authors’ knowledge, there are few 2D/3D models in the literature to simulate such experiments. Lack of these investigations partially motivated the present work. In this work, a numerical study of methane jet diffusion flames to acoustic perturbations using ANSYS FLUENT v16.1 is performed. Emphasis is placed on the interaction of acoustics-flow-flame and the jet diffusion flame characteristics in standing acoustic wave fields. This study contributes to physical understanding of the diffusion flame characteristics excited by standing waves. It will also help to gain insights on the flame-acoustic interactions [12-21] in a real gas turbine engine. 2. Computational Domain and Numerical Method A 2-D jet diffusion flame-acoustic interaction model is developed according to the experimental setup proposed by Farhat et al. [11], as shown in Fig. 1. It consists of a cylindrical tube with a diameter of D1 and a length of L1, a cone tube with a diameter of D2 and a length of L2 and a fuel injector. One end of the cone tube is attached below the cylindrical tube. The fuel injector is located inside the cylindrical tube at a height of h measuring from the bottom of the cylindrical tube. The methane fuel, CH4, is injected out through a small hole with a diameter of D4 from a cylinder with a diameter of D3 and length of L3. The fuel injector is always placed at the axis of the cylindrical tube, and its axial location can be varied. All the dimensions of the burner system are summarized in Table 1. The top end of the burner system is open to the ambient air, and a loudspeaker is placed at the bottom of the cone tube. The connection between the loudspeaker and the cone tube is not airtight, so fresh air is still able to flow in from the bottom of the tube. When the loudspeaker is turned on, tone sound with certain frequency is produced and propagates through the tube. Thus an unsteady velocity field and pressure field is induced in the tube by the loudspeaker. If the wave length of the sound is much larger than the diameter of the tube, one-dimensional plane wave propagation can be justified. For certain frequencies, standing waves can be induced in the longitudinal tube. Gaseous methane fuel is used in this system, with a fixed injecting velocity 0.52 m/s. A jet diffusion flame will be obtained when sufficient amount of energy is provided to ignite the fuel. In the current numerical model, an unsteady velocity boundary condition is used to replace the loudspeaker to generate
Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
the oscillating velocity field and standing waves present in the tube. The unsteady velocity boundary condition with a frequency of 375 Hz is expressed as: A ª º u z t U «1.0 sin 2S 375 t » (1) U ¬ ¼ where u z is the axial velocity, A is the amplitude of the fluctuating velocity (A = 2.0), and t is time. A mean axial flow U with a velocity of 0.1 m/s has also been added to mimic the air co-flow driven by the jet flame in the experiment. The reason of selecting 375 Hz is that a longitude standing wave with one velocity antinode and two velocity nodes can be established with the current tube dimensions as shown in Table 1. Three locations for the variable h (0.12 m, 0.33 m, and 0.55 m) will be studied. The flow field of this 2-D combustion system is assumed to be unsteady and turbulent. The standard k H model is employed for the turbulence closure, and the one-step Eddy-Dissipation model is used for the combustion modeling.
Fig. 1. Schematic of the burner system Table 1. Dimensions of the burner system
3. Results and Discussion
Parameter
Value (unit: mm)
D1
125
L1
755
D2
210
L2
378
D3
5
L3
15
D4
1.8
h
variable
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1542
Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
3.1. Mode shapes The pressure and velocity mode shapes along the tube, which can show whether the standing wave is established, are plotted and compared with the experimental data in Fig. 2. Both the pressure and velocity are root-mean-averaged, and they are normalized by their maximum values. It can be seen that the typical mode shapes with the node and antinode has been obtained in the current numerical simulations. For example, the mode shape of pressure as shown in Fig. 2(a) has two antinodes (one at z = 0.1 m and the other at z = 0.5 m) and one node at z = 0.3 m, while the mode shape of velocity has two nodes (one at z = 0.1 m and the other at z = 0.5 m) and one antinode at z = 0.3 m as shown in Fig. 2(b). Due to the existence a small mean flow going through the tube, the mode shape of velocity has been shifted slightly. Furthermore, three different locations where the fuel injector will be put are also indicated in the mode shapes. The three different locations correspond to the three special points (the node and antinode). From the mode shapes, it can be confirmed that a standing wave has been successfully obtained in the tube at 375 Hz in our simulations.
(a)
(b)
Fig. 2. The mode shapes in the cylindrical tube with 375 Hz: (a) normalized Prms, and (b) normalized Urms.
3.2. Flame at the velocity antinode (z = 0.33 m) and velocity nodes (z = 0.12 m and 0.55 m) When the fuel injector is located at the velocity antinode (z = 0.33 m) where the maximum fluctuation of velocity exists, the flame shapes are presented in Fig. 3. It is found that interesting flame shapes that are apparently different from normal jet flames have been formed. The flame is unsteady, as the flame front changes with time. Considering the fuel injector is located at the velocity antinode of the longitudinal standing wave, the unsteadiness of the flame front is thus caused by the velocity fluctuations at this region. When the fuel injector is located at the velocity nodes (z = 0.12 m and z = 0.55 m) where the minimum velocity fluctuation exists as shown in Fig. 2(b), the flame shapes are also provided in Fig. 4. Different from the previous case in which the flame is unsteady at the velocity node, flames at the current two locations are quite steady, as the flame shapes almost do not change with time. However, the temperatures of the two flames are rather different, although the large scale velocity fluctuation level for the two cases is almost same. As shown in Fig. 4(a), the maximum flame temperature is around 1100 K, while the other in Fig. 4(b) is around 1500 K. It was learnt that this phenomenon is caused by the different turbulence kinetic energy at the two locations, although their mean flow velocities are almost
Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
same. As the turbulence kinetic energy at z = 0.55 m is about 30% larger than that at z = 0.12 m, the flame thus has a higher temperature as mixing is significantly improved by the higher turbulence levels.
Fig. 3. Temperature contours within a period at z = 0.33 m: (a) T/8, (b) 3T/8, (c) 5T/8, and (d) 7T/8
(a)
(b)
Fig. 4. Temperature contours at: (a) z = 0.12 m, and (d) 0.55 m
4. Conclusions A methane-burnt (CH4) jet diffusion flame to a standing wave in a longitudinal tube are numerically studied in this work. It is shown that the jet and flame characteristics are highly sensitive to its axial location, when standing waves are present. The jet experiences large velocity fluctuations, and flow unsteadiness is observed when the jet is placed at acoustic velocity antinodes. However, the jet and flame
1543
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Song Chen et al. / Energy Procedia 105 (2017) 1539 – 1544
are much stable in the velocity node region. But different flame temperatures are observed due to the different mixing performance caused by the turbulence kinetic energy levels. References [1] Keller JJ. Thermoacoustic oscillations in combustion chamber of gas turbines. AIAA Journal. 1995;33(12):2280-7. [2] Yang V, and Anderson W. (ed). Liquid rocket engine combustion instability. Progress in Astronautics and Aeronautics: AIAA Publications; 1995. [3] Cammarata L, Fichera A, and Pagano A. Neural prediction of combustion instability. Applied Energy. 2002;72:513-28. [4] Singh AV, Yu M, Gupta AK, and Bryden KM. Thermo-acoustic behavior of a swirl stabilized diffusion flame with heterogeneous sensors. Applied Energy. 2013;106:1-16. [5] Lieuwen T. Modeling premixed combustion-acoustic wave interactions: a review. Journal of Propulsion and Power. 2003;19(5):765-81. [6] Schadow K, and Gutmark E. Combustion instability related to vortex shedding in dump combustors and their passive control. Progress in Energy and Combustion Science. 1992;18:117-32. [7] Coats C. Coherent structures in combustion. Progress in Energy and Combustion Science. 1996;22:427-509. [8] Ducruix S, Durox D, and Candel S. Theoretical and experimental determinations of the transfer function of a laminar premixed flame. Proceeding of the Combustion Institute. 2000;28:765-73. [9] Palies P, Durox D, Schuller T, and Candel S. Nolinear combustion instability analysis based on the flame describing function applied to turbulent premixed swirling flames. Combustion and Flame. 2011;158(10):1980-91. [10] Zhang Z, Zhao D, Dobriyal R, Zheng Y, and Yang W. Theoretical and experimental investigation of thermoacoustics transfer function. Applied Energy. 2015;154:131-42. [11] Farhat S, Kleiner D, Zhang Y. Jet diffusion flame characteristics in a loudspeaker-induced standing wave. Combustion and Flame. 2005;142:317-23. [12] Zhao D, Li X. Minimizing transient energy growth of nonlinear thermoacoustic oscillations, Intenational Journal of Heat and Mass Transfer, 2015;81:188-197. [13] Ji C, Zhao D, Li X, Li S, Li J. Nonorthogonality analysis of a thermoacoustic system with a premixed V-shaped flame, Energy Conversion and Management. 2014;85:102-111. [14] Li S, Zhao D, Ji C, Li J. Combustion instabilities in a bifurcating tube: open- and closed-loop measurements, AIAA Journal. 2014;52(11):2513-2523. [15] Zhao D, Ega E. Energy harvesting from self-sustained aeroelastic limit cycle oscillations of rectangular wings, Applied Physics Letter. 2014;105(10):103903. [16] Zhao D, Ji C, Teo C, Li S. Performance of small-scale bladeless electromagnetic energy harvesters driven by water and air, Energy. 2014;74:99-108. [17] Han N, Schluter J, Zhao D, Goh E, Zhao H, Jin X. Performance evaluation of 3D printed miniature electromagnetic energy harvesters driven by air flow, Applied Energy, 2016;178:672-680. [18] Zhao D, Li S, Zhao H. Entropy-involved energy measure study of intrinsic thermoacoustic oscillations, Applied Energy, 2016;177:570-578. [19] Zhao D, Chow Z. Thermoacoustic instability of a laminar premixed flame in Rijke tube with a hydrodynamic region, Journal of. Sound and Vibration, 2013;332(14):3419-3437. [20] Li L, Zhao D, Yang X. Effect of entropy waves on transient energy growth of flow disturbances in triggering thermoacoustic instability, Intenational Journal of Heat and Mass Transfer, 2016;99:219-233. [21] Li X, Zhao D, Yang X, Wang S. Unity maximum transient energy growth of heat-driven acoustic oscillations, Energy Conversion and Management, 2016;116:1-10.
Biography Mr. He Zhao is currently a Master student in School of Energy and Power Engineering, Jiangsu University of Science and Technology. His research interests focus on combustion, CFD, and propulsion.