| 1. |
- Li, Mao, et al.
(författare)
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Experimental study of hydrogen addition effects on a swirl-stabilized methane-air flame
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- The effects of H2 addition on a premixed methane-air flame was studied experimentally with a swirl-stabilized gas turbine model combustor. Experiments with 0%, 25%, and 50% H2 molar fraction in the fuel mixture were conducted under atmospheric pressure. The primary objectives are to study the impacts of H2 addition on flame lean blowout (LBO) limits, flame shapes and anchored locations, flow field characteristics, precessing vortex core (PVC) instability, as well as the CO emission performance. The flame LBO limits were identified by gradually reducing the equivalence ratio until the condition where the flame physically disappeared. The time-averaged CH chemiluminescence was used to reveal the characteristics of flame stabilization, e.g., flame structure and stabilized locations. In addition, the inverse Abel transform was applied to the time-averaged CH results so that the distribution of CH signal on the symmetric plane of the flame was obtained. The particle image velocimetry (PIV) was used to detect the characteristics of the flow field with a frequency of 2 kHz. The snapshot method of POD (proper orthogonal decomposition) and fast Fourier transform (FFT) were adopted to capture the most prominent coherent structures in the turbulent flow field. CO emission was monitored with an exhaust probe that was installed close to the combustor exit. The experimental results indicated that the H2 addition extended the flame LBO limits and the operation range of low CO emission. The influence of H2 addition on the flame shape, location, and flow field was observed. With the assistance of POD and FFT, the combustion suppression impacts on PVC was found.
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| 2. |
- Li, Mao, et al.
(författare)
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Impact of vitiation on a swirl-stabilized and premixed methane flame
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:10
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Tidskriftsartikel (refereegranskat)abstract
- Vitiation refers to the condition where the oxygen concentration in the air is reduced due to the mix of dilution gas. The vitiation effects on a premixed methane flame were investigated on a swirl-stabilized gas turbine model combustor under atmospheric pressure. The main purpose is to analyze the combustion stability and CO emission performance in vitiated air and compare the results with the flame without vitiation. The N2, CO2, and H2O (steam) were used as the dilution gas. Measurements were conducted in a combustor inlet temperature of 384 K and 484 K. The equivalence ratio was varied from stoichiometric conditions to the LBO (Lean Blowout) limits where the flame was physically blown out from the combustor. The chemical kinetics calculation was performed with Chemkin software to analyze the vitiation effects on the flame reaction zone. Based on the calculation results, the changes in the temperature gradient, CO concentration, and active radicals across the flame reaction zone were identified. The time-Averaged CH chemiluminescence images were recorded and the results indicated the features of the flame shape and location. The CH signal intensity provided the information about the heat-release zone in the combustor. The combustion LBO limits were measured and the vitiation of CO2 and H2O were found to have a stronger impact to elevate the LBO limits than N2. Near the LBO limits, the instability of the flame reaction was revealed by the high-speed chemiluminescence imaging and the results were analyzed by FFT (Fast Fourier Transfer). CO emission was measured with a water-cooled probe which is located at the exit of the combustor. The combustion vitiation has been found to have the compression effect on the operation range for low CO emission. However, this compression effect could be compensated by improving the combustor inlet temperature.
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| 3. |
- Li, Mao, et al.
(författare)
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Influence of the steam addition on premixed methane air combustion at atmospheric pressure
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- Steam-diluted combustion in gas turbine systems is an effective approach to control pollutant emissions and improve the gas turbine efficiency. The primary purpose of the present research is to analyze the influence of steam dilution on the combustion stability, flame structures, and CO emissions of a swirl-stabilized gas turbine model combustor under atmospheric pressure conditions. The premixed methane/air/steam flame was investigated with three preheating temperatures (384 K/434 K/484 K) and the equivalence ratio was varied from stoichiometric conditions to the flammability limits where the flame was physically blown out from the combustor. In order to represent the steam dilution intensity, the steam fraction Ω defined as the steam to air mass flow rate ratio was used in this work. Exhaust gases were sampled with a water-cooled emission probe which was mounted at the combustor exit. A 120 mm length quartz liner was used which enabled the flame visualization and optical measurement. Time-averaged CH chemiluminescence imaging was conducted to characterize the flame location and it was further analyzed with the inverse Abel transform method. Chemical kinetics calculation was conducted to support and analyze the experimental results. It was found that the LBO (lean blowout) limits were increased with steam fraction. CH chemiluminescence imaging showed that with a high steam fraction, the flame length was elongated, but the flame structure was not altered. CO emissions were mapped as a function of the steam fraction, inlet air temperature, and equivalence ratios. Stable combustion with low CO emission can be achieved with an appropriate steam fraction operation range.
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| 4. |
- Li, Mao, et al.
(författare)
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Investigation of methane oxy-fuel combustion in a swirl-stabilised gas turbine model combustor
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- CO2 has a strong impact on both operability and emission behaviours in gas turbine combustors. In the present study, an atmospheric, preheated, swirl-stabilised optical gas turbine model combustor rig was employed. The primary objectives were to analyse the influence of CO2 on the fundamental characteristics of combustion, lean blowout (LBO) limits, CO emission and flame structures. CO2 dilution effects were examined with three preheating temperatures (396.15, 431.15, and 466.15 K). The fundamental combustion characteristics were studied utilising chemical kinetic simulations. To study the influence of CO2 on the operational range of the combustor, equivalence ratio (Φ) was varied from stoichiometric conditions to the LBO limits. CO emissions were measured at the exit of the combustor using a water-cooled probe over the entire operational range. The flame structures and locations were characterised by performing CH chemiluminescence imaging. The inverse Abel transformation was used to analyse the CH distribution on the axisymmetric plane of the combustor. Chemical kinetic modelling indicated that the CO2 resulted in a lower reaction rate compared with the CH4/air flame. Fundamental combustion properties such as laminar flame speed, ignition delay time and blowout residence time were found to be affected by CO2. The experimental results revealed that CO2 dilution resulted in a narrower operational range for the equivalence ratio. It was also found that CO2 had a strong inhibiting effect on CO burnout, which led to a higher concentration of CO in the combustion exhaust. CH chemiluminescence showed that the CO2 dilution did not have a significant impact on the flame structure.
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| 5. |
- Liu, Xiao, et al.
(författare)
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Investigation of transient ignition process in a cavity based scramjet combustor using combined ethylene injectors
- 2017
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Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765. ; 137, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Large Eddy Simulation (LES) and experiment were employed to investigate the transient ignition and flame propagation process in a rearwall-expansion cavity scramjet combustor using combined fuel injection schemes. The compressible supersonic solver and three ethylene combustion mechanisms were first validated against experimental data and results show in reasonably good agreement. Fuel injection scheme combining transverse and direct injectors in the cavity provides a benefit mixture distribution and could achieve a successful ignition. Four stages are illustrated in detail from both experiment and LES. After forced ignition in the cavity, initial flame kernel propagates upstream towards the cavity front edge and ignites the mixture, which acts as a continuous pilot flame, and then propagates downstream along the cavity shear layer rapidly to the combustor exit. Cavity shear layer flame stabilization mode can be concluded from the heat release rate and local high temperature distribution during the combustion process.
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| 6. |
- Tong, Yiheng, et al.
(författare)
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An experimental study of effects of confinement ratio on swirl stabilized flame macrostructures
- 2017
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Ingår i: Boilers and Heat Recovery Steam Generator; Combustion Turbines; Energy Water Sustainability; Fuels, Combustion and Material Handling; Heat Exchangers, Condensers, Cooling Systems, and Balance-of-Plant. - 9780791857601 ; 1
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Konferensbidrag (refereegranskat)abstract
- Swirl stabilized premixed flames are common in industrial gas turbines. The flame shape in the combustor is highly related to the combustion stability and the performance of the gas turbine. In the current paper, the effects of confinement on the time averaged flame structures or flame macrostructures are studied experimentally. Experiments are carried out with swirl number S = 0.66 in two cylindrical confinements with diameters of d1 = 39 mm and d2 = 64 mm and confinement ratio c1 = 0.148 and c2 = 0.0567. All the experiments were carried out in atmospheric. CH∗ chemiluminescence from the flame was recorded to visualize the flame behavior. An inverse Abel image reconstruction method was employed to better distinguish the flame macrostructures. Different mechanisms forming the time averaged M shape flames are proposed and analyzed. It is found that the confinement wall plays an important role in determining the flame macrostructures. The flow structures including the inner and outer recirculation zones formed in the confinement are revealed to be the main reasons that affects different flame macrostructures. Meanwhile, the alternation of flame shapes determines the flame stability characteristics. A smaller confinement diameter forced the flame front to bend upstream into the outer recirculation zone hence forming a M shape flame. A strong noise caused by the interaction of the flame front in the outer recirculation zone with the combustor wall was observed. Another unsteady behavior of the flame in the bigger combustor, which was caused by the alternation of the flame root position inside and outside the premixing tube, is also presented. The V shape flame in the two combustors radiated weaker chemiluminescence but the main heat release zone was elongated than the M shape flame. Other operating conditions, i.e. total mass flow rate of the air flow and the equivalence ratio also affect the flame macrostructures. The flame blowout limits were also altered under different test conditions. The bigger confinement has better performance in stabilizing the flame by having lower lean blowout limits.
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| 7. |
- Tong, Yiheng, et al.
(författare)
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Effects of the position of a bluff-body on the diffusion flames : A combined experimental and numerical study
- 2018
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 131, s. 507-521
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Tidskriftsartikel (refereegranskat)abstract
- The effects of the position of a bluff-body on diffusion flame structures and flame instability characteristics were investigated both experimentally and numerically. The flame pattern diagram and the stability limits of the methane-air diffusion flame were investigated to evaluate the effects caused by the alternation of the position of a bluff-body. A disk-shape bluff-body was mounted 10 mm above or at the same height with the annular channel exit. The bulk velocity of the annular air flow varied between Ua = 0 to 8 m/s; while the fuel jet velocity being ranged from Uj = 0 to 30 m/s. Various flame patterns, including the recirculation zone flame, the stable diffusion flame, the split flame and the lifted flame till flame blowoff, were observed and recorded by the high-speed camera. High-speed Particle Image Velocimetry (PIV) was also adopted to give deeper insight into the characteristics of the flow fields and the flame patterns. The hybrid RANS/LES model was utilized to simulate the mixing characters of the reactants, the scalar dissipation rates, the flow fields and their interactions with the flame structures. The size and strength of the recirculation zones downstream of the bluff-body altered with the change in the position of the bluff-body. It is found that flames in burners with two different bluff-body positions behave similarly with each other, except those under conditions with high annular air velocities (Ua > 6.8 m/s). Mounting the bluff-body 10 mm above the annular channel exit could better stabilize the flame. A recirculation vortex was found adjacent to the outer wall of the bluff-body. It played an important role in the flame stabilization. Combustion affected the flow fields significantly by accelerating the central jet and enlarging the outer recirculation zone.
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| 8. |
- Tong, Yiheng
(författare)
-
Experimental and Numerical Investigations of Flames Stabilized by Swirl Flow and Bluff-body:Flame Structures and Flame Instabilities
- 2017. - Media-Tryck
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Combustion and its control are essential to our existence on this planet since we knew it. Nowadays, the largest share of the world’s electricity and most of our transportation systems are powered by combustion. In addition, industrial processes also rely heavily upon combustion. In most industrial combustion systems, combustion occurs under turbulent flow conditions that can produce combustion instabilities. These are problematical since they can result in oscillations in thrust, low- or high-cycle fatigue of system components, flame blowoff or flashback, and oscillations in combustion efficiency together with high emission levels or even damage to the combustion systems. Thus, flame stabilization is of fundamental importance in the design, the efficient performance and the reliable operation of the combustion systems.Experimental and numerical investigations of swirl and bluff-body stabilized flames are presented in the thesis. Both premixed and diffusion flames are investigated in detail. Different parameters including the operating conditions, the burner geometries, fuel injection strategies are examined. High-speed PIV, high-speed PLIF and intensified CH* chemiluminescence, together with thermography and corresponding image analysis methods are adopted in the experimental work. In addition, DES and LES turbulence models on the basis of ANSYS Fluent and OpenFOAM, respectively, are employed in the numerical studies. The doctoral work is concerned above all with flame structures and flame instabilities.For swirl stabilized lean premixed flames, the operating conditions, including the total mass flow rate and the equivalence ratio of the reactants all play an important role in determining flame structures and lean blowout limits of swirl stabilized lean premixed flames. The geometries of the confinement, including the cross-sectional shape and the cylindrical confinement diameter, strongly affect the swirl stabilized flame structures and flame dynamics. Proposals are made regarding the mechanisms behind the forming of swirl stabilized lifted M-shape flames and corresponding flame dynamics. Fuel injection strategy employed also affects the characteristics of low-swirl stabilized flames, such as the time-averaged flame structures and the flame oscillations that occur. An axial fuel injection strategy leads to a more compact flame and a leaner blowout limit than a tangential fuel injection method does. The flame oscillation frequency near lean blowout is affected when fuel injection strategy is altered. When the global equivalence ratio decreases, flame dynamics frequency is reduced until the occurrence of flame lean blowout.A central fuel or air jet through the bluff-body axis makes the bluff-body stabilized premixed flame less stable. When a central fuel injection takes place, the flame is found to be lifted off from the bluff-body, with a circular motion of the flame tip along the outer edge of the bluff-body. The injection of a central fuel or air jet results in a higher lean blowout limit. At the same time, the temperature on the upper surface of the bluff-body becomes lower.Different patterns of bluff-body stabilized diffusion flames are presented: the recirculation zone flame, the stable jet diffusion flame, the lifted flame, the split-flashing flame being included here. The position of a bluff-body in relation to the annular channel exit affects the instabilities of the diffusion flame, particularly when the annular air flow velocity is high. Mounting the bluff-body downstream of the annular channel exit makes it able to better stabilize the flame. The flame stabilization is achieved by the recirculation bubble that was adjacent to the outer wall of the bluff-body. A diffusion flame stabilized by a combination of swirl and bluff-body is studied both experimentally and numerically. The effects both of a bluff-body on a swirl-stabilized diffusion flame and of swirl on a bluff-body stabilized diffusion flame are investigated. Diffusion flame ‘flashback’ is studied, the mechanisms behind it being proposed. When a larger bluff-body is employed, air driven recirculation zone is found to be located further upstream near the burner exit. The flame is found to be better stabilized by use of a larger bluff-body and/or a stronger swirling flow.
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| 9. |
- Tong, Yiheng, et al.
(författare)
-
Experimental and numerical study on bluff-body and swirl stabilized diffusion flames
- 2018
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 217, s. 352-364
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Tidskriftsartikel (refereegranskat)abstract
- Bluff-body and swirl flow are commonly utilized to stabilize diffusion flames in industrial applications, such as gas turbines, ramjets and furnaces. Flame stabilization mechanisms of these two kinds of burners are similar with each other: the interaction between the recirculation zone and the fuel jet. In the present paper, flow fields within flames stabilized by combinations of swirl flow and bluff-body were captured using high-speed PIV; while the flame structures were visualized by high-speed CH2O PLIF, CH∗ chemiluminescence and broadband chemiluminescence. The global CO emissions from the flames were captured as well. In addition, based on the CFD software OpenFOAM, simulations were adopted to better understand the interactions between flames and flow structures. Flames stabilized by bluff-bodies with different diameters (db = 14 mm and 20 mm), or only by swirl flow without a bluff-body, were studied. All reacting experiments were carried out with a constant mass flow rate of the central fuel jet (with thermal power 2.01 kW) and a constant mass flow rate of the total air flow (m = mt + ma = 200 ln/min). The swirl strength was controlled by the mass flow rate ratio of the tangential to the axial air flow. The geometrical swirl number was altered between Sg = 0 and Sg = 4.08. Simulation results matched well with experimental data, especially in predicting the spatial distribution of CH2O. The position of the outer recirculation zone would be affected by the size of the bluff-body and the swirl strength. In addition, the recirculation zone determined the flame structures and the global CO emission levels. With a larger bluff-body, the air driven recirculation zone located more upstream near the burner exit. Flame prone to be more stable with a larger bluff-body and/or a stronger swirl flow. Flame was observed propagating into the upstream region in cases without a bluff-body or in cases with the small bluff-body (db = 14 mm), when the swirl strength was sufficiently strong. The mechanism for the diffusion flame ‘flashback’ was proposed. Flames in cases with a larger swirl number were shorter while its CO emission levels were higher.
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| 10. |
- Tong, Yiheng, et al.
(författare)
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Experimental Investigation on Effects of Central Air Jet on the Bluff-body Stabilized Premixed Methane-air Flame
- 2017
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 107, s. 23-32
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Tidskriftsartikel (refereegranskat)abstract
- Flame stabilized by a bluff-body is a common scene in many engineering applications due to the enhanced mixing characteristics, improved flame stability, and ease of combustion control. We recently designed a burner which has a conical bluff body with a central air injector. In the current work, effects of the central air jet on the heat load of the bluff body, the flame structures and the flame blowoff limits were investigated. It was found that the central air jet can significantly reduce the heat load to the bluff body. It is a considerable solution to the problem caused by the high heat load in practical applications. The flame structures and blowout limits were altered with the addition of central air jet as well. Different blowout behaviors caused by the air jet were observed and reported. The bluff-body could be cooled down by the center air injection but then it seems not to stabilize the flame any more.
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| 11. |
- Tong, Yiheng, et al.
(författare)
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Experimental investigation on the influences of bluff-body's position on diffusion flame structures
- 2017
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Ingår i: Boilers and Heat Recovery Steam Generator; Combustion Turbines; Energy Water Sustainability; Fuels, Combustion and Material Handling; Heat Exchangers, Condensers, Cooling Systems, and Balance-of-Plant. - 9780791857601 ; 1
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Konferensbidrag (refereegranskat)abstract
- Effects of the bluff-body's position on diffusion flame structures and flame instability characteristics were investigated experimentally. A flame regime diagram together with the corresponding flow fields were proposed to evaluate the influences caused by the alternation of bluff-body's position. The disk shape bluff-body was placed 10 mm downstream or at the same height with the annular channel exit. The bulk velocity of the annular air flow varied from 0 to 8.6m/s while the central jet fuel velocity ranged from 0 to 30m/s. Various flame patterns including the recirculation zone flame, the stable diffusion jet flame, split-flashing flame and lifted flame were observed and recorded with a high speed camera. It is found that the flame has approximately the same patterns with different bluff-body's positions, except for cases with high air flow rate (Ua > 6.8m/s) and low fuel flow rate (Uj < 5m/s). Under that operating conditions, placing the disk bluff-body 10 mm above the annular channel could better stabilize the flame. High speed Particle Image Velocimetry (PIV) was also used to get deeper insight into the characteristics of the flow fields and flame stabilization. The size and strength of the recirculation zone downstream of the bluff-body altered with the changing of bluff-body's position and other operating conditions. The recirculation zone, in the burner with the bluff-body placed 10 mm above the air channel exit, was found larger and stronger than that in the other burner geometry. In the reacting case, a recirculation bubble was formed besides the bluff-body's outer wall which enhanced the flame stabilization. It is also found that the combustion changed the flow fields by enlarging the recirculation bubbles downstream of the bluff-body.
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| 12. |
- Tong, Yiheng, et al.
(författare)
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Experimental study on bluff-body stabilized premixed flame with a central air/fuel jet
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:12
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Tidskriftsartikel (refereegranskat)abstract
- Bluff-body flame holders are commonly employed in many industrial applications. A bluff-body is usually adopted to enhance the downstream mixing of the combustion products and the fresh fuel-air mixtures, thus to improve the flame stability and to control the combustion process. In the present paper, flames stabilized by a conical-shape bluff-body flame holder with a central air/fuel jet were studied. Effects of both a central air jet and a central fuel jet on the structures and lean blowout limits of the premixed annular flames, and on the temperature on the upper surface of the bluff-body were investigated and presented. It was revealed that a central jet led to a considerable reduction of the temperature on the upper surface of the bluff-body. It was proposed to be caused by the alternation of flow structures (in the case with a central air jet) altogether with the flame lifting from the burner (in the case with a central fuel jet). Thus, it might be used to solve the problem of the bluff-body with high heat loads in practical applications. The flame stability characteristics, for example the unstable flame dynamics and the lean blowout limits, varied with the injection of an air or fuel jet through the central pipe. Different blowout behaviors, being with or without the occurrence of flame split and flashing, caused by a central air jet were presented in the paper. In addition, when a small amount of central fuel jet (i.e., Uf/Ua = 0.045) was injected into the flow fields, an unsteady circular motion of the flame tip along the outer edge of the bluff-body was observed as well. Whereas, with an increase in the amount of the central fuel jet, the flame detached from the outer edge of the bluff-body and then became much more unstable. With a central air or fuel jet injecting into the flow field, premixed flames stabilized by the bluff-body became more unstable and easier to blowout.
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| 13. |
- Tong, Yiheng, et al.
(författare)
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Experimental study on dynamics of a confined low swirl partially premixed methane-hydrogen-air flame
- 2017
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 42:44, s. 27400-27415
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Tidskriftsartikel (refereegranskat)abstract
- The addition of hydrogen to swirl stabilized methane-air flame in gas turbine has gained more and more attentions in recent years. In the current study, flame structures, flame dynamics and lean blowout limits of partially premixed hydrogen-methane-air flames were investigated. The swirling flow, which was generated from the tangential flow injection, was utilized to stabilize the flame. The flow swirl number was kept low varying from S ≈ 0.28 to S ≈ 0.34 while the thermal power of the burner ranged from 10.8 kW to 13.8 kW. Two different fuel injection strategies were investigated and compared with each other. Long exposure CH* chemiluminescence from the flame was captured to visualize the time averaged flame shapes. In addition, an intensified high speed camera was adopted to study the flame dynamics. A high speed PIV system was utilized to investigate the interaction of flame dynamics and flow fields oscillations. Based on the experimental results, it can be concluded that: in the current experimental cases, fuel injection strategy plays an important role in determining the flame macro-structures and thus strongly affects the flame dynamics and lean blowout limits. Flame with fuel injected through the axial flow has lower lean blowout limits. The flashback and vortex breakdown were observed when fuel was injected in the tangential flow near lean blowout. High frequency flame oscillations (f ≈ 170 Hz) were observed when the global equivalence ratio Φ g > 0.72 while lower frequency oscillations (f ≈ 50 Hz and f ≈ 20 Hz) were found near lean blowout limits, Φ g < 0.55. Combustion dynamic and its interaction with the pressure oscillation, flow fields alternation and mass flow rate oscillation are proposed. The differences on fuel concentration at the burner exit are proposed as the main reason for different flame instabilities and flame structures.
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| 14. |
- Tong, Yiheng, et al.
(författare)
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Influence of combustor geometry on swirl stabilized premixed methane-air flame
- 2016
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Ingår i: Proceedings of ASME 2016 Turbo Expo: Turbomachinery Technical Conference and Exposition. - 9780791849767 ; 4B-2016
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Konferensbidrag (refereegranskat)abstract
- Flame structures, blowout limits and emissions of swirlstabilized premixed methane-air flames were studied experimentally in a small atmospheric combustor rig. Combustion sections with rectangular cross section (30mm by 40mm) and circular cross section (inner diameter = 39mm) were used to investigate effects of combustor geometry on the flame's performance. Flame structures and instabilities were obtained from CH∗ chemiluminescence captured by a high speed intensified CMOS camera. Maps of flame blowout limits (ΦBO) versus total mass flow rates (m = 70∼130 standard liter per minute, SLPM) were obtained with the combustor inlet flow temperature (Tin) kept at Tin = 397 ± 5K and a flow swirl number of S = 0.6. Emission data of mole fraction of CO in the exhaust gas versus equivalence ratio was obtained under the conditions of Tin= 293 ± 5K and S = 0.66. It is found that the flame became longer and more unstable with decreasing equivalence ratio or increasing total mass flow rates. A strong high-amplitude and low-frequency oscillation was found to be the reason for the flame blowout. A possible reason for flame instability and blowout is presented in the paper. Within the parameters investigated in this study, the equivalence ratio had the strongest impact on flame stabilities and CO emission. Both in the rectangular and circular combustors, when the flame length increased to a critical value (LIBO, which was approximately the same for these two combustors), flame could not be stabilized anymore and blowout occurred. Compared with the rectangular combustor, the circular one had lower blowout limits and was better in stabilizing the flame. Combustor geometry did not significantly affect CO emission in the current study.
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