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Artykuły w czasopismach na temat „Flame blowoff”

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Data publikacji: 6 września 2023

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1

Zhang, Qingguo, David R. Noble i Tim Lieuwen. "Characterization of Fuel Composition Effects in H2∕CO∕CH4 Mixtures Upon Lean Blowout". Journal of Engineering for Gas Turbines and Power 129, nr 3 (26.12.2006): 688–94. http://dx.doi.org/10.1115/1.2718566.

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This paper describes measurements of the dependence of lean blowout limits upon fuel composition for H2∕CO∕CH4 mixtures. Blowout limits were obtained at fixed approach flow velocity, reactant temperature, and combustor pressure at several conditions. Consistent with prior studies, these results indicate that the percentage of H2 in the fuel dominates the mixture blowout characteristics. That is, flames can be stabilized at lower equivalence ratios, adiabatic flame temperatures, and laminar flame speeds with increasing H2 percentage. In addition, the blowoff phenomenology qualitatively changes with hydrogen levels in the fuel, being very different for mixtures with H2 levels above and below about 50%. It is shown that standard well stirred reactor based correlations, based upon a Damköhler number with a diffusivity ratio correction, can capture the effects of fuel composition variability on blowoff limits.

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2

SAMESHIMA, Taiki, Mitsuharu TAKAO, Toshiaki YANO i Shuichi TORII. "FLAME BLOWOFF LIMITS EXTENTION BY FLAME HOLDER WITH AIR-SUCTION". Proceedings of Conference of Kyushu Branch 2002.55 (2002): 191–92. http://dx.doi.org/10.1299/jsmekyushu.2002.55.191.

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3

Patel, Vipul, i Rupesh Shah. "Analysis of LPG diffusion flame in tube type burner". Journal of Mechanical Engineering and Sciences 13, nr 3 (26.09.2019): 5278–93. http://dx.doi.org/10.15282/jmes.13.3.2019.05.0431.

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The present research aims to analyse diffusion flame in a tube type burner with Liquefied petroleum gas (LPG) as a fuel. An experimental investigation is performed to study flame appearance, flame stability, Soot free length fraction (SFLF) and CO emission of LPG diffusion flame. Effects of varying air and fuel velocities are analysed to understand the physical process involved in combustion. SFLF is measured to estimate the reduction of soot. Stability limits of the diffusion flame are characterized by the blowoff velocity. Emission characteristic in terms of CO level is measured at different equivalence ratios. Experimental results show that the air and fuel velocity strongly influences the appearance of LPG diffusion flame. At a constant fuel velocity, blue zone increases and the luminous zone decreases with the increase in air velocity. It is observed that the SFLF increases with increasing air velocity at a constant fuel velocity. It is observed that the blowoff velocity of the diffusion flame increases as fuel velocity increases. Comparison of emission for flame with and without swirl indicates that swirl results in low emission of CO and higher flame stability. Swirler with 45° vanes achieved the lowest CO emission of 30 ppm at Φ = 1.3.

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4

Huang, Lung-Weei, i Chiun-Hsun Chen. "FLAME STABILIZATION AND BLOWOFF OVER A SINGLE DROPLET". Numerical Heat Transfer, Part A: Applications 27, nr 1 (styczeń 1995): 53–71. http://dx.doi.org/10.1080/10407789508913688.

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5

CHEN, CHIUN-HSUN, i FANG-BOR WENG. "Flame Stabilization and Blowoff Over a Porous Cylinder". Combustion Science and Technology 73, nr 1-3 (wrzesień 1990): 427–46. http://dx.doi.org/10.1080/00102209008951661.

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6

TORIKAI, Hiroyuki, Akiko MATSUO, Toshihisa UEDA i Masahiko MIZOMOTO. "Blowoff Characteristics and Flame Structure of Edge Flame in the Stagnation Flow." Transactions of the Japan Society of Mechanical Engineers Series B 68, nr 666 (2002): 610–18. http://dx.doi.org/10.1299/kikaib.68.610.

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7

Nair, Suraj, i Tim Lieuwen. "Near-Blowoff Dynamics of a Bluff-Body Stabilized Flame". Journal of Propulsion and Power 23, nr 2 (marzec 2007): 421–27. http://dx.doi.org/10.2514/1.24650.

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8

Santhosh, R., i Saptarshi Basu. "Transitions and blowoff of unconfined non-premixed swirling flame". Combustion and Flame 164 (luty 2016): 35–52. http://dx.doi.org/10.1016/j.combustflame.2015.10.034.

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9

Hindasageri, Vijaykumar, Rajendra Vedula i Siddini Prabhu. "Blowoff Stability of Methane-Air Premixed Flame on Tube Burners". International Journal of Emerging Multidisciplinary Fluid Sciences 3, nr 4 (wrzesień 2011): 209–26. http://dx.doi.org/10.1260/1756-8315.3.4.209.

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10

He, Zhonghao, Hongbo Wang, Fan Li, Yifu Tian, Minggang Wan i Jiajian Zhu. "Effect of Fuel-Injection Distance and Cavity Rear-Wall Height on the Flameholding Characteristics in a Mach 2.52 Supersonic Flow". Aerospace 9, nr 10 (29.09.2022): 566. http://dx.doi.org/10.3390/aerospace9100566.

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The ethylene-fueled flameholding characteristics of a cavity-based scramjet combustor are experimentally and numerically investigated. The test facility used the air heater, which heats air from room temperature to total temperature 1477 K. A nozzle is installed behind the heater outlet to increase the air speed to Mach 2.52. Two cavity geometries with different rear-wall heights of 8 mm and 10 mm and two injection distances upstream of the cavities of 10 mm and 40 mm are compared to show the effect of these parameters. The CH* spontaneous emission images obtained by dual-camera synchronous shooting and the wall-pressure distribution obtained by a pressure-scan system are used to capture the flame dynamics. The global equivalence ratio range for different combination schemes is controlled from 0.14 to 0.27 in this paper. The results show that the conventional cavity (the rear-wall height is 10 mm) and the shorter injection distance can effectively decrease the lean blowoff limit of the combustor, while the rear-wall-expansion cavity (the rear-wall height is 8 mm) and the longer injection distance can effectively increase the rich blowoff limit. Compared with the injection distance, the rear-wall height of the cavity has little effect on the oscillation distribution of the shear layer-stabilized flame. However, the fuel-injection distance and cavity rear-wall height both have great influence on the spatial distribution of the flame.

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11

Palies, Paul, i Ragini Acharya. "Flame-resolved transient simulation with swirler-induced turbulence applied to lean blowoff premixed flame experiment". Combustion and Flame 226 (kwiecień 2021): 14–30. http://dx.doi.org/10.1016/j.combustflame.2020.11.041.

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12

CHAN, Simon Sze Man, Shuichi TORII i Toshiaki YANO. "Extension of Turbulent Jet Diffusion Flame Blowoff Limits by Doublet Flows." Transactions of the Japan Society of Mechanical Engineers Series B 67, nr 663 (2001): 2841–47. http://dx.doi.org/10.1299/kikaib.67.2841.

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13

Li, Zhen, i Hongbin Gu. "Investigation for Effects of Jet Scale on Flame Stabilization in Scramjet Combustor". Energies 15, nr 10 (21.05.2022): 3790. http://dx.doi.org/10.3390/en15103790.

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Jet scale affects the mixing and combustion of fuel and inflow. With the increase in the scale of scramjet combustors, the study of large-scale jets is particularly significant. The effects of jet scale on flame stability in scramjet combustors were studied by direct-connect combustion experiments. In this paper, the flame distribution characteristics of different jet scales were compared by using similar jet/inflow momentum ratios. The inflow Mach numbers were 2.4 and 3.0, and the total temperature was 1265 K and 1600 K, respectively. The results show that, when the equivalence ratio increases, the combustion intensity increases. Under the condition of same momentum ratio, the increase of jet scale is conducive to fuel injection into the core mainstream, increasing heat release, and the flame stabilization mode will change from cavity stabilization mode to jet-wake stabilization mode. Increasing the distance between jet orifices is not beneficial to combustion, and may even lead to blowoff.

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14

Paterakis, G., K. Souflas, E. Dogkas i P. Koutmos. "A Comparison of the Characteristics of Planar and Axisymmetric Bluff-Body Combustors Operated under Stratified Inlet Mixture Conditions". Journal of Combustion 2013 (2013): 1–15. http://dx.doi.org/10.1155/2013/860508.

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The work presents comparisons of the flame stabilization characteristics of axisymmetric disk and 2D slender bluff-body burner configurations, operating with inlet mixture stratification, under ultralean conditions. A double cavity propane air premixer formed along three concentric disks, supplied with a radial equivalence ratio gradient the afterbody disk recirculation, where the first flame configuration is stabilized. Planar fuel injection along the center plane of theleading faceof a slender square cylinder against the approach cross-flow results in a stratified flame configuration stabilized alongside the wake formation region in the second setup. Measurements of velocities, temperatures,OH∗andCH∗chemiluminescence, local extinction criteria, and large-eddy simulations are employed to examine a range of ultralean and close to extinction flame conditions. The variations of the reacting front disposition within these diverse reacting wake topologies, the effect of the successive suppression of heat release on the near flame region characteristics, and the reemergence of large-scale vortical activity on approach to lean blowoff (LBO) are investigated. The cross-correlation of the performance of these two popular flame holders that are at the opposite ends of current applications might offer helpful insights into more effective control measures for expanding the operational margin of a wider range of stabilization configurations.

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15

Wu, Bifen, Xinyu Zhao, Bikram Roy Chowdhury, Baki M. Cetegen, Chao Xu i Tianfeng Lu. "A numerical investigation of the flame structure and blowoff characteristics of a bluff-body stabilized turbulent premixed flame". Combustion and Flame 202 (kwiecień 2019): 376–93. http://dx.doi.org/10.1016/j.combustflame.2019.01.026.

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16

Noorani, R. I., i R. E. Holmes. "Effects of electric fields on the blowoff limits of a methane-air flame". AIAA Journal 23, nr 9 (wrzesień 1985): 1452–54. http://dx.doi.org/10.2514/3.9108.

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17

Shin, Jaeik, Chanyeong Jeong i Youngbin Yoon. "An Experimental Study of Acoustic Excitation Effect on Blowoff Mechanism for Premixed Flame". Journal of the Korean Society for Aeronautical & Space Sciences 42, nr 12 (1.12.2014): 1004–12. http://dx.doi.org/10.5139/jksas.2014.42.12.1004.

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18

Choe, Jinhoon, i Wenting Sun. "Blowoff hysteresis, flame morphology and the effect of plasma in a swirling flow". Journal of Physics D: Applied Physics 51, nr 36 (7.08.2018): 365201. http://dx.doi.org/10.1088/1361-6463/aad4dc.

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19

Balasubramaniyan, Manikandan, Abhijit Kushwaha, Yu Guan, Jianchang Feng, Peijin Liu, Vikrant Gupta i Larry K. B. Li. "Global hydrodynamic instability and blowoff dynamics of a bluff-body stabilized lean-premixed flame". Physics of Fluids 33, nr 3 (1.03.2021): 034103. http://dx.doi.org/10.1063/5.0029168.

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20

Cha, M. "Boundary-velocity gradient and premixed flame blowoff in U-bend tubes with secondary flow". Combustion and Flame 132, nr 4 (marzec 2003): 601–9. http://dx.doi.org/10.1016/s0010-2180(02)00505-9.

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21

Fernández-Tarrazo, Eduardo, Marcos Vera i Amable Liñán. "Liftoff and blowoff of a diffusion flame between parallel streams of fuel and air". Combustion and Flame 144, nr 1-2 (styczeń 2006): 261–76. http://dx.doi.org/10.1016/j.combustflame.2005.07.012.

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22

TORIKAI, Hiroyuki, Akiko MATSUO, Toshihisa UEDA i Masahiko MIZOMOTO. "512 Blowoff Characteristics of Edge Flames in an Axisymmetric Impinging Jet". Proceedings of Conference of Kanto Branch 2001.7 (2001): 405–6. http://dx.doi.org/10.1299/jsmekanto.2001.7.405.

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23

Olson, Sandra L., Paul V. Ferkul i Jeremy W. Marcum. "High-speed video analysis of flame oscillations along a PMMA rod after stagnation region blowoff". Proceedings of the Combustion Institute 37, nr 2 (2019): 1555–62. http://dx.doi.org/10.1016/j.proci.2018.05.080.

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24

Wu, Bifen, Xinyu Zhao, Bikram Roy Chowdhury, Baki M. Cetegen, Chao Xu i Tianfeng Lu. "Corrigendum to “A numerical investigation of the flame structure and blowoff characteristics of a bluff-body stabilized turbulent premixed flame” [Combustion and Flame (2019) 202, 376-393]". Combustion and Flame 208 (październik 2019): 492. http://dx.doi.org/10.1016/j.combustflame.2019.04.051.

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25

Marcum, Jeremy W., Paul V. Ferkul i Sandra L. Olson. "PMMA rod stagnation region flame blowoff limits at various radii, oxygen concentrations, and mixed stretch rates". Proceedings of the Combustion Institute 37, nr 3 (2019): 4001–8. http://dx.doi.org/10.1016/j.proci.2018.05.081.

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26

Kedia, Kushal S., i Ahmed F. Ghoniem. "Mechanisms of stabilization and blowoff of a premixed flame downstream of a heat-conducting perforated plate". Combustion and Flame 159, nr 3 (marzec 2012): 1055–69. http://dx.doi.org/10.1016/j.combustflame.2011.10.014.

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27

Marcum, J. W., P. Rachow, P. V. Ferkul i S. L. Olson. "Low pressure flame blowoff of the stagnation region of cast PMMA cylinders in axial mixed convective flow". Combustion and Flame 216 (czerwiec 2020): 385–97. http://dx.doi.org/10.1016/j.combustflame.2020.02.031.

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28

CHEN, CHIUN-HSUN. "A Numerical Study of Flame Spread and Blowoff over a Thermally-Thin Solid Fuel in an Opposed Air Flow". Combustion Science and Technology 69, nr 4-6 (luty 1990): 63–83. http://dx.doi.org/10.1080/00102209008951603.

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29

Hashimoto, Nozomu, Harunori Nagata, Tsuyoshi Totani i Isao Kudo. "Determining factor for the blowoff limit of a flame spreading in an opposed turbulent flow, in a narrow solid-fuel duct". Combustion and Flame 147, nr 3 (listopad 2006): 222–32. http://dx.doi.org/10.1016/j.combustflame.2006.07.015.

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30

De, Somnath, Arijit Bhattacharya, Sirshendu Mondal, Achintya Mukhopadhyay i Swarnendu Sen. "Investigation of flame behavior and dynamics prior to lean blowout in a combustor with varying mixedness of reactants for the early detection of lean blowout". International Journal of Spray and Combustion Dynamics 11 (18.11.2018): 175682771881251. http://dx.doi.org/10.1177/1756827718812519.

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Lean blowout is one of the major challenges faced when the gas turbine combustors are operated with lean fuel–air mixture to meet the emission norm. We experimentally study the flame behavior and the dynamics of heat release rate fluctuations during a transition to lean blowout. The study comprising flame visualization and estimating several measures to predict lean blowout for both premixed and partially premixed flames (using fuel ports F1 to F5) in a swirl stabilized dump combustor. To that end, we acquire unsteady heat release rate in terms of CH* chemiluminescence obtained through a photomultiplier tube with a narrow band-pass filter. For evaluating different statistical measures, we use National Instrument Labview software while acquiring the heat release rate oscillations. For premixed and partially premixed flames, such measures and the flame behavior show a different and, in some cases, even opposite trends as lean blowout is approached. However, in both premixed and partially premixed flames, the mean and root mean square values of the heat release rate fluctuation decrease as we decrease the equivalence ratio. Further, we show that the value of mean frequency calculated using Hilbert transform of the heat release rate fluctuations is a good indicator of lean blowout. Apart from the early prediction of lean blowout, different statistics of heat release rate oscillations, such as kurtosis and skewness, are shown to identify only the occurrence of lean blowout for premixed (F1 and F2) and flames with lower level of premixing (F3). They are not useful for the flames with high levels of unmixedness like F4 and F5. On the other side, probability density function is seen useful for both premixed and partially premixed flames. In short, we present the relative importance of different measures stated earlier for the identification and early prediction of lean blowout for both premixed and partially premixed flames.

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31

Kibrya, M. G., i G. A. Karim. "Blowout Limits of a Jet Diffusion Flame in the Presence of Small Surrounding Jet Pilot Flames". Journal of Energy Resources Technology 118, nr 2 (1.06.1996): 140–44. http://dx.doi.org/10.1115/1.2792705.

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The blowout limit of a methane jet diffusion flame is examined in the presence of a number of much smaller pilot jet flames of different fuels arranged within an experimental burner assembly in a co-flowing stream of air. It is shown that the blowout limit of the central jet flame can be extended very appreciably by increasing the flow rate through the smaller pilot jets. The basis for this extension to the blowout limit and the role of some changes in the operating parameters are discussed. It is suggested that the extension to the blowout limit observed is due mainly to the thermal contribution of the pilot jet flames.

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32

Papanikolaou, N., i I. Wierzba. "Effect of Burner Geometry on the Blowout Limits of Jet Diffusion Flames in a Co-Flowing Oxidizing Stream". Journal of Energy Resources Technology 118, nr 2 (1.06.1996): 134–39. http://dx.doi.org/10.1115/1.2792704.

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The effects of changes in the jet nozzle geometry, i.e., nozzle shape and lip thickness, on the blowout limits of jet diffusion flames in a co-flowing air stream were experimentally investigated for a range of co-flow air stream velocities. Circular and elongated nozzles of different axes rations were employed. Preliminary results showed that nozzles with low major-to-minor axes ratios improved, while high ratios reduced, the blowout limit of attached flames compared with that for an equivalent circular nozzle. The nozzle shape had no apparent influence on the blowout limits lifted flames and the limiting stream velocity. The experimental blowout limits of lifted flames were found to be a function of the co-flowing stream velocity and jet discharge area. On the other hand, the stability of attached flames was a function of the co-flowing stream velocity, jet discharge area as well as the nozzle shape. The effect of premixing a fuel with the surrounding air was also studied. Generally, the introduction of auxiliary fuel into the surrounding stream either increased or decreased the blowout limit depending on the type of flame stabilization mechanism prior to blowout. The stability mechanism of the flame was found to be a function of the co-flow stream velocity and the auxiliary fuel employed.

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33

Moore, N. J., J. L. McCraw i K. M. Lyons. "Observations on Jet-Flame Blowout". International Journal of Reacting Systems 2008 (2008): 1–7. http://dx.doi.org/10.1155/2008/461059.

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The mechanisms that cause jet-flame blowout, particularly in the presence of air coflow, are not completely understood. This work examines the role of fuel velocity and air coflow in the blowout phenomenon by examining the transient behavior of the reaction zoneat blowout. The results of video imaging of a lifted methane-air diffusion flame at near blowout conditions are presented. Two types of experiments are described. In the first investigation, a flame is established and stabilized at a known, predetermined downstream location with a constant coflow velocity, and then the fuel velocity is subsequently increased to cause blowout. In the other, an ignition source is used to maintain flame burning near blowout and the subsequent transient behavior to blowout upon removal of the ignition source is characterized. Data from both types of experiments are collected at various coflow and jet velocities. Images are used to ascertain the changes in the leading edge of the reaction zone prior to flame extinction that help to develop a physically-based model to describe jet-flame blowout. The data report that a consistent predictor of blowout is the prior disappearance of the axially oriented flame branch. This is witnessed despite a turbulent flames' inherent variable behavior. Interpretations are also made in the light of analytical mixture fraction expressions from the literature that support the notion that flame blowout occurs when the leading edge reaches the vicinity of the lean-limit contour, which coincides approximately with the conditions for loss of the axially oriented flame structure.

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Papanikolaou, N., i I. Wierzba. "The Effects of Burner Geometry and Fuel Composition on the Stability of a Jet Diffusion Flame". Journal of Energy Resources Technology 119, nr 4 (1.12.1997): 265–70. http://dx.doi.org/10.1115/1.2795000.

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The effect of the burner configuration and fuel composition on the stability limits of jet diffusion flames issuing into a co-flowing air stream is presented. Circular and elliptic nozzles of various lip thicknesses and aspect ratios were employed with methane as the primary fuel and hydrogen, carbon dioxide, and nitrogen as additives. It was found that the effects of nozzle geometry, fuel composition, and co-flowing stream velocity on the blowout limits were highly dependent on the type of flame stabilization mechanism, i.e., whether lifted or rim-attached, just prior to blowout. The blowout behavior of lifted flames did not appear to be significantly affected by a change in the nozzle shape as long as the discharge area remained constant, but it was greatly affected by the fuel composition. In contrast, attached flame stability was influenced by both the fuel composition and the nozzle geometry which had the potential to extend the maximum co-flowing stream velocity without causing the flame to blow out. The parameters affecting the limiting stream velocity were studied.

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35

Griebel, P., E. Boschek i P. Jansohn. "Lean Blowout Limits and NOx Emissions of Turbulent, Lean Premixed, Hydrogen-Enriched Methane/Air Flames at High Pressure". Journal of Engineering for Gas Turbines and Power 129, nr 2 (15.08.2006): 404–10. http://dx.doi.org/10.1115/1.2436568.

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Flame stability is a crucial issue in low NOx combustion systems operating at extremely lean conditions. Hydrogen enrichment seems to be a promising option to extend lean blowout limits (LBO) of natural gas combustion. This experimental study addresses flame stability enhancement and NOx reduction in turbulent, high-pressure, lean premixed methane/air flames in a generic combustor capable of a wide range of operating conditions. Lean blowout limits and NOx emissions are presented for pressures up to 14bar, bulk velocities in the range of 32–80m∕s, two different preheating temperatures (673K, 773K), and a range of fuel mixtures from pure methane to 20% H2∕80%CH4 by volume. The influence of turbulence on LBO limits is also discussed. In addition to the investigation of perfectly premixed H2-enriched flames, LBO and NOx are also discussed for hydrogen piloting. Experiments have revealed that a mixture of 20% hydrogen and 80% methane, by volume, can typically extend the lean blowout limit by ∼10% compared to pure methane. The flame temperature at LBO is ∼60K lower resulting in the reduction of NOx concentration by ≈35%(0.5→0.3ppm∕15%O2).

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Abdul, Gani. "Experimental investigation on lift off, blowout and drop back in partially premixed LPG open flames in tubular burner". Thermal Science, nr 00 (2022): 31. http://dx.doi.org/10.2298/tsci211126031a.

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The higher pollutant level in non premixed combustion and safety issues pertaining to premixed combustion can be counteracted by partially-premixed mode of combustion. The partially premixed flames (PPF) exhibit the benefits of both premixed and non premixed flames. PPF enhances complete combustion leading to reduced soot formation and hence lower emission. However, the equivalence ratio plays an important role in the stability of such flames. This paper reports the experimental investigation on the flame characteristics and stability of partially premixed LPG-air flames in tubular burner. The stability curve obtained for the base case without any secondary flow shows that the velocity at lift-off, drop-back and blowout increases with increasing equivalence ratio. In the presence of secondary co-flow air, the lift-off and blow off velocity decreases compared to base case indicating poor stability due to extensive flame stretch leading to aerodynamic quenching. The experimental results show that the velocity of flow at lift off, blow out and drop back are higher in the presence of secondary swirl air than the base case. Co-swirl air increases the stability due to better mixing at the flame base with increased residence time. Flame stability deteriorates with co-flow air as co-flow strains the flame boundary due to flame stretch.

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Smith, Tracy, Chendhil Periasamy, Benjamin Baird i S. R. Gollahalli. "Trajectory and Characteristics of Buoyancy and Momentum Dominated Horizontal Jet Flames From Circular and Elliptic Burners". Journal of Energy Resources Technology 128, nr 4 (21.10.2005): 300–310. http://dx.doi.org/10.1115/1.2358145.

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Relative effects of buoyancy and momentum on the characteristics of horizontally oriented circular (Circ) and elliptic (E) burner flames in a quiescent environment over a wide range of jet exit velocities are presented. The major axis of the elliptic burner was oriented horizontally and vertically (referred to as Emaj and Emin flames, respectively). Propane was used as fuel and a small amount of hydrogen was piloted to attach flames to the burner. Global flame characteristics such as flame dimensions, centerline trajectory, emission indices (EI) and radiative fraction, and in-flame transverse concentration and temperature profiles were measured. At a jet exit Reynolds number (Rej) of 2000, based on the area-equivalent diameter of the burner, the flame characteristics were affected by the burner geometry and its orientation. Also, the vertical dimension of the burner exit dictated buoyancy effects. At Rej=12,500, the influence of burner geometry or its orientation was negligible. Elliptic burner flames exhibited lower liftoff and blowout velocities than circular burner flames. Furthermore, the flame stability and nitric oxide emissions were not much affected by the orientation of elliptic burner. Although the elliptic burners produced higher EINO at lower jet exit velocities, the variation in EINO among three burners (Circ, Emaj, and Emin) was insignificant at higher velocities. Some effects of buoyancy on EICO were observed at lower jet exit velocities and the EICO was the lowest for the burners with largest buoyancy flux. Elliptic burner flames produced greater peak flame temperature than the corresponding circular burner flames under most conditions.

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38

Gomes, Jonathan N., James D. Kribs i Kevin M. Lyons. "Stability and Blowout Behavior of Jet Flames in Oblique Air Flows". Journal of Combustion 2012 (2012): 1–9. http://dx.doi.org/10.1155/2012/218916.

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The stability limits of a jet flame can play an important role in the design of burners and combustors. This study details an experiment conducted to determine the liftoff and blowout velocities of oblique-angle methane jet flames under various air coflow velocities. A nozzle was mounted on a telescoping boom to allow for an adjustable burner angle relative to a vertical coflow. Twenty-four flow configurations were established using six burner nozzle angles and four coflow velocities. Measurements of the fuel supply velocity during liftoff and blowout were compared against two parameters: nozzle angle and coflow velocity. The resulting correlations indicated that flames at more oblique angles have a greater upper stability limit and were more resistant to changes in coflow velocity. This behavior occurs due to a lower effective coflow velocity at angles more oblique to the coflow direction. Additionally, stability limits were determined for flames in crossflow and mild counterflow configurations, and a relationship between the liftoff and blowout velocities was observed. For flames in crossflow and counterflow, the stability limits are higher. Further studies may include more angle and coflow combinations, as well as the effect of diluents or different fuel types.

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39

Karbasi, M., i I. Wierzba. "Prediction and Validation of Blowout Limits of Co-Flowing Jet Diffusion Flames—Effect of Dilution". Journal of Energy Resources Technology 120, nr 2 (1.06.1998): 167–71. http://dx.doi.org/10.1115/1.2795029.

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The blowout limits of a co-flowing turbulent methane jet diffusion flame with addition of diluent in either jet fuel or surrounding air stream is studied both analytically and experimentally. Helium, nitrogen, and carbon dioxide were employed as the diluents. Experiments indicated that an addition of diluents to the jet fuel or surrounding air stream decreased the stability limit of the jet diffusion flames. The strongest effect was observed with carbon dioxide as the diluent followed by nitrogen and then by helium. A model of extinction based on recognized criterion of the mixing time scale to characteristic combustion time scale ratio using experimentally derived correlations is proposed. It is capable of predicting the large reduction of the jet blowout velocity due to a relatively small increase in the co-flow stream velocity along with an increase in the concentration of diluent in either the jet fuel or surrounding air stream. Experiments were carried out to validate the model. The predicted blowout velocities of turbulent jet diffusion flames obtained using this model are in good agreement with the corresponding experimental data.

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40

Sloan, D. G., i G. J. Sturgess. "Modeling of Local Extinction in Turbulent Flames". Journal of Engineering for Gas Turbines and Power 118, nr 2 (1.04.1996): 292–307. http://dx.doi.org/10.1115/1.2816591.

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The Eddy Dissipation Concept (EDC), proposed by Magnussen (1985), advances the concept that the reactants are homogeneously mixed within the fine eddy structures of turbulence and that the fine structures may therefore be regarded as perfectly stirred reactors (PSRs). To understand more fully the extent to which such a subgrid scale stirred reactor concept could be applied within the context of a computational fluid dynamics (CFD) calculation to model local or global extinction phenomena: (1) Various kinetic mechanisms are investigated with respect to CPU penalty and predictive accuracy in comparisons with stirred reactor lean blowout (LBO) data and (2) a simplified time-scale comparison, extracted from the EDC model and applied locally in a fast-chemistry CFD computation, is evaluated with respect to its capabilities to predict attached and lifted flames. Comparisons of kinetic mechanisms with PSR lean blowout data indicate severe discrepancies in the predictions with the data and with each other. Possible explanations are delineated and discussed. Comparisons of the attached and lifted flame predictions with experimental data are presented for some benchscale burner cases. The model is only moderately successful in predicting lifted flames and fails completely in the attached flame case. Possible explanations and research avenues are reviewed and discussed.

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41

Mohammad Nurizat Rahman, Mohd Fairus Mohd Yasin i Mohd Shiraz Aris. "Reacting Flow Characteristics and Multifuel Capabilities of a Multi-Nozzle Dry Low NOx Combustor: A Numerical Analysis". CFD Letters 13, nr 11 (11.11.2021): 21–34. http://dx.doi.org/10.37934/cfdl.13.11.2134.

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The fluctuating quality of natural gas (NG) in Peninsular Malaysia (PM) makes it challenging for the gas turbine (GT) combustor to meet the combustion performance requirements from the Original Equipment Manufacturer (OEM). Moreover, the gas quality sensitivity is more apparent in modern dry low NOx (DLN) combustors. Many of the prior combustion investigations were conducted on a modest scale in the laboratory. In actuality, combustion characterizations in complicated DLN combustors are more valuable to the power generation sector. Hence, the current numerical analysis utilized the RANS formulation and a detailed chemistry to examine the impact of ethane (C2H6), carbon dioxide (CO2), and nitrogen (N2) proportions in NG on combustion characteristics in a multi-nozzle DLN (MN-DLN) combustor, with the support of Modified Wobbe Index (MWI) calculations. Validations were performed using the combustor outlet temperature (COT) from the power plant where the actual MN-DLN combustor is operated, which revealed less than 10 % discrepancy. Qualitative validations were carried out by comparing the burn trace from the actual combustor wall to the predicted results, revealing an adequate Structural Similarity Index (SSIM) of 0.43. From numerical results of flame fronts and COTs, the addition of 20 % diluents (CO2 and N2) to NG demonstrated the blowoff risk. When MWIs of Kerteh and the JDA (major NG resources) were used as baselines, MWI ranges of all NG compositions under study surpassed the OEM’s ± 5 % limit. The increase in CO2 proportion results in a wide MWI range, especially when Kerteh is used as the baseline. Therefore, any GTs in PM that have previously been calibrated to use Kerteh's NG are more likely to have combustion instabilities if CO2 levels in NG suddenly increase. The higher MWI range backs up the current numerical results that showed the deleterious effects of a high CO2 composition throughout the combustor firing process. However, increasing the amount of C2H6 by up to 20 % is predicted to have minor effects on combustion characteristics. Overall, the validated numerical model of the MN-DLN combustor provided critical information about combustion characteristics and multifuel capabilities in respect to the NG quality in PM.

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Hamed, AM, AE Hussin, MM Kamal i AR Elbaz. "Combustion of a hydrogen jet normal to multiple pairs of opposing methane–air mixtures". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 231, nr 2 (6.01.2017): 145–58. http://dx.doi.org/10.1177/0957650916685944.

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The combustion performance of a cylindrical burner accommodating up to six multiple pairs of opposing methane–air mixtures with a cross-flow of hydrogen was addressed. The cross-flow initially duplicated the stagnation impact and enriched the vortical structures. Aided by the resulting flow strain, the transport of heat and active species from the hydrogen oxidation zone to the methane reaction zones accelerated the combustion across the opposing premixed flames and reduced the peak temperature across the outer diffusion flame. Increasing the cross-flow/opposing jets’ velocity ratio to 0.89 merged the two stagnation centers and maximized the shearing stress. By the slight increase in the velocity ratio to 1.07, the H and OH pools provided for methane combustion became closer to the ports such that a hydrogen/methane mass percent of 10.3% extended the stoichiometric blowout velocity from 28.3 to 35.7 m/s. Since the turbulent kinetic energy thus increased to 8.4 m2/s2, the firing intensity reached values as high as 48.2 MW/m3. Not only was there a reduction in the residence time for NOx formation, but also the blowout velocity relative gain overrode the relative increase in the NOx formation rates such that the NOx emission index decreased to 17 g/MWhr. By the excessive increase in velocity ratio, the vortical structures shrank such that the NOx exponential increase became dominant above 21 ppm. With fuel-lean mixtures, the hydrogen was partially combusted by the excess air from the opposing flames but the blowout velocity decreased to 13.1 m/s at Φ = 0.50. The hydrogen flame NOx emissions decreased by providing the excess air at larger jets’ diameter/separation ratios, thus reducing the residence times for thermal NOx formation and simultaneously interrupting the prompt NOx formation. At the lean operational limit, tripling the number of opposing jets decreased the hydrogen flame length by 54% such that the NOx emissions decreased by 38.4%.

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Chang, Liuyong, Boxuan Cui, Chenglin Zhang, Zheng Xu, Guangze Li i Longfei Chen. "Monitoring and Characterizing the Flame State of a Bluff-Body Stabilized Burner by Electrical Capacitance Tomography". Processes 11, nr 8 (10.08.2023): 2403. http://dx.doi.org/10.3390/pr11082403.

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Unstable combustion phenomena such as flame flashback, flame liftoff, extinction and blowout frequently take place during the operation of the bluff-body stabilized burner. Therefore, flame state monitoring is necessary for the safe operation of the bluff-body stabilized burner. In the present study, an electrical capacitance tomography (ECT) system was deployed to detect the permittivity distribution in the premixing channel and further characterize the flame states of stabilization, flashback, liftoff, extinction and blowout. A calderon-based reconstruction method was modified to reconstruct the permittivity distribution in the annular premixing channel. The detection results indicate that the permittivity in the premixing channel increases steeply when the flame flashback takes place and decreases obviously when the flame lifts off from the combustor rim. Based on the varied permittivity distribution at different flame states, a flame state index was proposed to characterize the flame state in quantification. The flame state index is 0, positive, in the range of −0.64–0, and lower than −0.64 when the flame is at the state of stable, flashback, liftoff and blowout, respectively. The flame state index at the flame state of extinction is the same as that at the flame state of liftoff. The extinction state and the blowout state can be distinguished by judging whether the flame flashback takes place before the flame is extinguished. These results reveal that the ECT system is capable of monitoring the flame state, and that the proposed flame state index can be used to characterize the flame state.

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Durbin, M. D., M. D. Vangsness, D. R. Ballal i V. R. Katta. "Study of Flame Stability in a Step Swirl Combustor". Journal of Engineering for Gas Turbines and Power 118, nr 2 (1.04.1996): 308–15. http://dx.doi.org/10.1115/1.2816592.

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A prime requirement in the design of a modern gas turbine combustor is good combustion stability, especially near lean blowout (LBO), to ensure an adequate stability margin. For an aeroengine, combustor blow-off limits are encountered during low engine speeds at high altitudes over a range of flight Mach numbers. For an industrial combustor, requirements of ultralow NOx emissions coupled with high combustion efficiency demand operation at or close to LBO. In this investigation, a step swirl combustor (SSC) was designed to reproduce the swirling flow pattern present in the vicinity of the fuel injector located in the primary zone of a gas turbine combustor. Different flame shapes, structure, and location were observed and detailed experimental measurements and numerical computations were performed. It was found that certain combinations of outer and inner swirling air flows produce multiple attached flames, aflame with a single attached structure just above the fuel injection tube, and finally for higher inner swirl velocity, the flame lifts from the fuel tube and is stabilized by the inner recirculation zone. The observed difference in LBO between co- and counterswirl configurations is primarily a function of how the flame stabilizes, i.e., attached versus lifted. A turbulent combustion model correctly predicts the attached flame location(s), development of inner recirculation zone, a dimple-shaped flame structure, the flame lift-off height, and radial profiles of mean temperature, axial velocity, and tangential velocity at different axial locations. Finally, the significance and applications of anchored and lifted flames to combustor stability and LBO in practical gas turbine combustors are discussed.

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45

JÃ³zsa, Viktor, i Gergely Novotni. "Wavelet analysis of flame blowout of a liquid-fueled swirl burner with quarls". Noise Control Engineering Journal 67, nr 5 (1.09.2019): 394–403. http://dx.doi.org/10.3397/1/376734.

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Lean swirl combustion is the leading burner concept today, used in several steadyoperating applications to ensure awide operating range and low pollutant emissions. Approaching lean blowout is highly desired by design to achieve the lowest possible NOX emission. It was shown earlier that quarls could significantly extend the operating regime of liquid-fueled swirl burners. In the present study, the accompanying acoustic noise is evaluated by continuous wavelet transformation to show the effect of various quarl geometries on lean flame blowout. However, the desired flame shape of swirl burners is V, first, and a straight flame, and then a transitory regime can be observed before the developed V-shaped flame through increasing the swirl number. If the axial thrust is excessive, blowout might occur in earlier stages. Presently, the characteristic bands before blowout were analyzed and evaluated at various quarl geometries, swirl numbers, and atomizing pressures. The latter parameter also acts as an axial thrust control to adjust the swirl number. firstly, a straight flame, then a transitory regime can be observed before the developed V-shaped flame through increasing the swirl number. If the axial thrust is excessive, blowout might occur in earlier stages. Presently, the characteristic bands before blowout were analyzed and evaluated at various quarl geometries, swirl numbers, and atomizing pressures. The latter parameter also acts as an axial thrust control to adjust the swirl number.

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46

Boopathi, S., P. Maran, V. Caleb Eugene i S. Prabhu. "Analysis of Lift off Height and Blow-Off Mechanism of Turbulent Flame by V-Gutter Bluff Body". Applied Mechanics and Materials 787 (sierpień 2015): 727–31. http://dx.doi.org/10.4028/www.scientific.net/amm.787.727.

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The experimental investigation has been carried out to study the stabilization and blowout mechanisms of turbulent flame stabilized by V-gutter bluff body in a square duct at reactive and non-reactive conditions. V-shaped bluff bodies made of stainless steel having 1.6 mm thicknessare used for stabilization of the flame.Experiments have been conducted at selective velocities of commercially available methane and oxygen with 60 degree V-gutter as flame holder. It is observed that at stoichiometric conditions, the V-gutter is dominated by shear layer stabilized flames. The flame stability is influenced by bluff body dimensions and mass flow rate which play a major role in combustion instabilities mixing of air fuel ratio and blow off. The lift off decreases at higher blockage ratios.A strong recirculation zone is found in this test rig immediately downstream of the V-Gutter which gradually subsides and disappears far downstream.The lift off height is not much affected by the velocity of the fuel-air mixture.

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47

Zhang, Bin, Haoyang Liu, Xunchen Liu i Hong Liu. "Prediction Method of Swirling Flame Lean Blowout Based on Flame Image Morphological Features". Applied Sciences 13, nr 5 (1.03.2023): 3173. http://dx.doi.org/10.3390/app13053173.

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Swirling flame oscillation, with a local extinguishment-and-reignition phenomenon in advanced low-pollution lean premixed combustion technology, remains a challenge in understanding the underlying physics and predict in technical combustors. Here, a prediction method on swirling flame lean blowout (LBO) is proposed from flame image morphological features. In this method, flame features are first extracted by performing morphological algorithms on flame images. Then, the information of the time series of images is included. By designing the blowout state judgment criterion and the blowout state description method, the typical binary judgment is transformed into a numerical prediction. Finally, a random forest regression model is applied to build a predictive model for the swirling flame LBO. The results show that, with the data set from nine operating conditions, the model can achieve a determination coefficient of 0.9766 and a root mean square error of 3.78 on the 10% test set, which shows a strong generalization ability. This method exhibits potential for practical application in LBO control due to its simplicity and efficiency.

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Morales, Anthony J., Ian M. Lasky, Marissa K. Geikie, Christian A. Engelmann i Kareem A. Ahmed. "Mechanisms of flame extinction and lean blowout of bluff body stabilized flames". Combustion and Flame 203 (maj 2019): 31–45. http://dx.doi.org/10.1016/j.combustflame.2019.02.002.

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Al-Tayyar, Mohammed A., Dhirgham Alkhafaji i Haroun A. K. Shahad. "An Investigation into Burner Configuration Effects on Premixed Flame Characteristics for LPG Diluted with CO<sub>2</sub>". Applied Mechanics and Materials 914 (15.05.2023): 53–66. http://dx.doi.org/10.4028/p-gu777j.

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Meeting stringent emission regulations, the demand for environmentally friendly fuels is increasing by the day. Alternative fuel must be burned alongside conventional fuel to increase the availability of such clean energy sources. The current experimental study investigates the characteristics of the premixed LPG flames with CO2 dilution in tube swirling and non-swirling burners. The study including testing the effects of equivalence ratios, φ, (0.8, 1, 1.2, & 1.4), CO2 dilution ratios (0%, 5%, 7.5%, & 10%), and aspect ratio of the non-swirling burner (2, 4, 6, 8, & 10). Two swirling burners with swirl number was tested, namely 0.78 & 0.48. The dilution of CO2 has been observed lengthens the flame, particularly at higher equivalence ratios and/or flow rates since there is more than one influence, they all agree on a similar influence on flame height. The flame shortens clearly when using a swirling burner. Besides, when increasing the swirl number, the flame height increases slightly. Also, the swirling burner divided the flame's inner core into segments equal to the number of swirl vanes, and a flower-shaped flame was generated at low flow rates. The burner’s aspect ratio affects flame height insignificantly. Flame stability limits increase for a higher equivalence ratio and it enhances due to CO2 addition. The LPG-CO2/air mixture has an improved reply to beat flame flashback. The addition of CO2 expands the flow rate of stable flame by about 40% and 25% for φ = 1 and 1.2 respectively. Utilizing a swirling burner improves flame stability greatly. The limit between flashback and blowout increased by about three times as a result of using a swirling burner.

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Wu, Y., Y. Lu, I. S. Al-Rahbi i G. T. Kalghatgi. "Prediction of the liftoff, blowout and blowoff stability limits of pure hydrogen and hydrogen/hydrocarbon mixture jet flames". International Journal of Hydrogen Energy 34, nr 14 (lipiec 2009): 5940–45. http://dx.doi.org/10.1016/j.ijhydene.2009.01.084.

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