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Artigos de revistas sobre o tema "Expanding laminar flames"

Autor: Grafiati

Publicado: 29 de março de 2025

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1

Tran, Vu Manh. "USING EXPANDING SPHERICAL FLAMES METHOD TO MEASURE THE UNSTRETCHED LAMINAR BURNING VELOCITIES OF LPG-AIR MIXTURES". Science and Technology Development Journal 12, n.º 8 (28 de abril de 2009): 5–14. http://dx.doi.org/10.32508/stdj.v12i8.2270.

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In the present study, a technique making expanding spherical flames in a constant volume combustion bomb is presented for determining burning velocities of unstretched laminar flames, and applied to liquefy petroleum gas (LPG)-air mixtures. The experimental setup consists of a cylindrical combustion chamber coupled to a classical schlieren system. Flame pictures are recorded by a high speed camera. The laminar burning velocities of LPG-air mixtures are measured over a wide range of preheat temperatures, initial pressures and equivalence ratios. The effects of these initial conditions on the laminar burning velocities are also examined in this paper.

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2

Yousif, Alaeldeen Altag, e Shaharin Anwar Sulaiman. "Experimental Study on Laminar Flame Speeds and Markstein Length of Methane-Air Mixtures at Atmospheric Conditions". Applied Mechanics and Materials 699 (novembro de 2014): 714–19. http://dx.doi.org/10.4028/www.scientific.net/amm.699.714.

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Accurate value of laminar flame speed is an important parameter of combustible mixtures. In this respect, experimental data are very useful for modeling improvement and validating chemical kinetic mechanisms. To achieve this, an experimental characterization on spherically expanding flames propagation of methane-air mixtures were carried out. Tests were conducted in constant volume cylindrical combustion chamber to measure stretched, unstretched laminar flame speed, laminar burning velocity, and flame stretch effect as quantified by the associated Markstein lengths. The mixtures of methane-air were ignited at extensive ranges of lean-to-rich equivalence ratios, under ambient pressure and temperature. This is achieved by high speed schlieren cine-photography for flames observation in the vessel. The results showed that the unstretched laminar burning velocity increased and the peak value of the unstretched laminar burning velocity shifted to the richer mixture side with the increase of equivalence ratio. The flame propagation speed showed different trends at different equivalence ratio for tested mixtures. It was found that the Markstein length was increased with the increase of equivalence ratio.

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3

JOMAAS, G., C. K. LAW e J. K. BECHTOLD. "On transition to cellularity in expanding spherical flames". Journal of Fluid Mechanics 583 (4 de julho de 2007): 1–26. http://dx.doi.org/10.1017/s0022112007005885.

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The instant of transition to cellularity of centrally ignited, outwardly propagating spherical flames in a reactive environment of fuelx–oxidizer mixture, at atmospheric and elevated pressures, was experimentally determined using high-speed schlieren imaging and subsequently interpreted on the basis of hydrodynamic and diffusional–thermal instabilities. Experimental results show that the transition Péclet number, Pec = RcℓL, assumes an almost constant value for the near-equidiffusive acetylene flames with wide ranges in the mixture stoichiometry, oxygen concentration and pressure, where Rc is the flame radius at transition and ℓL the laminar flame thickness. However, for the non-equidiffusive hydrogen and propane flames, Pec respectively increases and decreases somewhat linearly with the mixture equivalence ratio. Evaluation of Pec using previous theory shows complete qualitative agreement and satisfactory quantitative agreement, demonstrating the insensitivity of Pec to all system parameters for equidiffusive mixtures, and the dominance of the Markstein number, Ze(Le – 1), in destabilization for non-equidiffusive mixtures, where Ze is the Zel'dovich number and Le the Lewis number. The importance of using locally evaluated values of ℓL, Ze and Le, extracted from either computationally simulated one-dimensional flame structure with detailed chemistry and transport, or experimentally determined response of stretched flames, in the evaluation of Pec is emphasized.

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4

Zhao, Haoran, Chunmiao Yuan, Gang Li e Fuchao Tian. "The Propagation Characteristics of Turbulent Expanding Flames of Methane/Hydrogen Blending Gas". Energies 17, n.º 23 (28 de novembro de 2024): 5997. http://dx.doi.org/10.3390/en17235997.

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In the present study, the effect of hydrogen addition on turbulent flame propagation characteristics is investigated in a fan-stirred combustion chamber. The turbulent burning velocities of methane/hydrogen mixture are determined over a wide range of hydrogen fractions, and four classical unified scaling models (the Zimont model, Gulder model, Schmidt model, and Peters model) are evaluated by the experimental data. The acceleration onset, cellular structure, and acceleration exponent of turbulent expanding flames are determined, and an empirical model of turbulent flame acceleration is proposed. The results indicate that turbulent burning velocity increases nonlinearly with the hydrogen addition, which is similar to that of laminar burning velocity. Turbulent flame acceleration weakens with the hydrogen addition, which is different from that of laminar flame acceleration. Turbulent flame acceleration is dominated by turbulent stretch, and flame intrinsic instability is negligible. Turbulent stretch reduces with hydrogen addition, because the interaction duration between turbulent vortexes and flamelets is shortened. The relative data and conclusions can provide useful reference for the model optimization and risk assessment of hydrogen-enriched gas explosion.

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5

Huo, Jialong, Sheng Yang, Zhuyin Ren, Delin Zhu e Chung K. Law. "Uncertainty reduction in laminar flame speed extrapolation for expanding spherical flames". Combustion and Flame 189 (março de 2018): 155–62. http://dx.doi.org/10.1016/j.combustflame.2017.10.032.

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6

Wu, Fujia, Wenkai Liang, Zheng Chen, Yiguang Ju e Chung K. Law. "Uncertainty in stretch extrapolation of laminar flame speed from expanding spherical flames". Proceedings of the Combustion Institute 35, n.º 1 (2015): 663–70. http://dx.doi.org/10.1016/j.proci.2014.05.065.

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7

Володин, В. В., В. В. Голуб e А. Е. Ельянов. "Влияние начальных условий на скорость фронта ламинарного пламени в газовых смесях". Журнал технической физики 91, n.º 2 (2021): 247. http://dx.doi.org/10.21883/jtf.2021.02.50358.215-20.

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The scatter in laminar flame front speed caused by both an error in the composition of the combustible mixture and initial disturbances is reported. It's shown how the configuration of the initially planar front in laminar flame initial disturbances in a gas mixture of the same composition affects the scatter of speeds of expanding spherical flames. The experimental results previously obtained by the authors, demonstrating the scatter in the speed of the laminar flame front in an initially quiescent gas mixture of constant composition under the same conditions, are explained by integrating the Sivashinsky equation with various initial disturbances. The influence of combustible mixture composition errors on the parameters determining the speed of the flame front is analyzed. These parameters were recalculated for a possible scatter in the mixture composition, obtained based on data on the accuracy of the equipment used in previously published experiments.

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8

Shu, Tao, Yuan Xue, Wenkai Liang e Zhuyin Ren. "Extrapolations of laminar flame speeds from expanding spherical flames based on the finite-structure stretched flames". Combustion and Flame 226 (abril de 2021): 445–54. http://dx.doi.org/10.1016/j.combustflame.2020.12.037.

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9

Yang, Sheng, Abhishek Saha, Zirui Liu e Chung K. Law. "Role of Darrieus–Landau instability in propagation of expanding turbulent flames". Journal of Fluid Mechanics 850 (10 de julho de 2018): 784–802. http://dx.doi.org/10.1017/jfm.2018.426.

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In this paper we study the essential role of Darrieus–Landau (DL), hydrodynamic, cellular flame-front instability in the propagation of expanding turbulent flames. First, we analyse and compare the characteristic time scales of flame wrinkling under the simultaneous actions of DL instability and turbulent eddies, based on which three turbulent flame propagation regimes are identified, namely, instability dominated, instability–turbulence interaction and turbulence dominated regimes. We then perform experiments over an extensive range of conditions, including high pressures, to promote and manipulate the DL instability. The results clearly demonstrate the increase in the acceleration exponent of the turbulent flame propagation as these three regimes are traversed from the weakest to the strongest, which are respectively similar to those of the laminar cellularly unstable flame and the turbulent flame without flame-front instability, and thus validating the scaling analysis. Finally, based on the scaling analysis and the experimental results, we propose a modification of the conventional turbulent flame regime diagram to account for the effects of DL instability.

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10

Liao, S. Y., D. L. Zhong, C. Yang, X. B. Pan, C. Yuan e Q. Cheng. "The Temperature and Pressure Dependencies of Propagation Characteris-tics for Premixed Laminar Ethanol-Air Flames". Open Civil Engineering Journal 6, n.º 1 (10 de agosto de 2012): 55–64. http://dx.doi.org/10.2174/1874149501206010055.

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Laminar burning velocity is strongly dependent on mixture characteristics, e.g. initial temperature, pressure and equivalence ratio. In this work, spherically expanding laminar premixed flames, freely propagating from a spark ignition source in initially quiescent ethanol-air mixtures, have been imaged and then the laminar burning velocities were obtained at initial temperatures of 358 K to 500K, pressure of 0.1 to 0.2 MPa and equivalence ratio of 0.7 to 1.4. The measured re-sults and literature data on ethanol laminar burning velocities were accumulated, to analyze the effects of initial tempera-ture and pressure on the propagation characteristics of laminar ethanol-air flames. A correlation in the form of ul=ulo(Tu/Tu0)αT (Pu/Pu0)βP , and validated over much wide temperature, pressure and equivalence ratio ranges. The global activation temperatures were determined in terms of the laminar burning mass flux for ethanol-air flames. And the Zel’dovich numbers were estimated as well. The dependencies of global activation temperature and Zel’dovich number on initial mixture pressure, temperature and equivalence ratio were explored. Additionally, an alterna-tive correlation of laminar burning velocities, from the view of theoretical arguments, was proposed on the basis of the de-termined ethanol-air laminar mass burning flux. Good agreements were obtained in its comparison with the literature data.

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11

Kelley, A. P., e C. K. Law. "Nonlinear effects in the extraction of laminar flame speeds from expanding spherical flames". Combustion and Flame 156, n.º 9 (setembro de 2009): 1844–51. http://dx.doi.org/10.1016/j.combustflame.2009.04.004.

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12

Yang, Sheng, Abhishek Saha, Fujia Wu e Chung K. Law. "Morphology and self-acceleration of expanding laminar flames with flame-front cellular instabilities". Combustion and Flame 171 (setembro de 2016): 112–18. http://dx.doi.org/10.1016/j.combustflame.2016.05.017.

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13

Shu, Tao, Yuan Xue, Zijun Zhou e Zhuyin Ren. "An experimental study of laminar ammonia/methane/air premixed flames using expanding spherical flames". Fuel 290 (abril de 2021): 120003. http://dx.doi.org/10.1016/j.fuel.2020.120003.

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14

Zhang, Yakun, Stephanie A. Coronel e Rémy Mével. "Numerical study of synthetic spherically expanding flames for optimization of laminar flame speed experiments". Fuel 310 (fevereiro de 2022): 122367. http://dx.doi.org/10.1016/j.fuel.2021.122367.

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15

Huo, Jialong, Abhishek Saha, Zhuyin Ren e Chung K. Law. "Self-acceleration and global pulsation in hydrodynamically unstable expanding laminar flames". Combustion and Flame 194 (agosto de 2018): 419–25. http://dx.doi.org/10.1016/j.combustflame.2018.05.025.

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16

Anggono, Willyanto, I. N. G. Wardana, M. Lawes, K. J. Hughes, Slamet Wahyudi e Nurkholis Hamidi. "Laminar Burning Velocity and Flammability Characteristics of Biogas in Spark Ignited Premix Combustion at Reduced Pressure". Applied Mechanics and Materials 376 (agosto de 2013): 79–85. http://dx.doi.org/10.4028/www.scientific.net/amm.376.79.

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Biogas as a “Powergas” is an alternative fuel produced in digestion facilities, that is sustainable and renewable. Based on chemical analysis, the composition of the biogas produced in East Java is 66.4% methane, 30.6% carbon dioxide and 3% nitrogen. Methane is a flammable gas, whereas, nitrogen and carbon dioxide are inhibitors. Given it has a different composition to traditional fuels, a fundamental study of biogas flame propagation characteristics is desirable to quantify this important fuel property. Spherically expanding flames propagating at constant pressure are employed to measure the laminar burning velocity and flammability characteristics as mixture function of the mixture composition. These important parameters were measured using a photographic technique in a high pressure fan-stirred bomb. The characteristics of biogas-air flames were initially studied at reduced pressure and at various equivalence ratios from the lower flammable limit to the upper flammable limit. The results were compared with those from biogas-air flames at atmospheric pressure. Based on this experimental investigation, the laminar burning velocities of biogas-air mixtures at reduced pressure were 0.218 m/s for ϕ=0.75, 0.246 m/s for ϕ=0.80 and 0.269 m/s for ϕ=0.85 respectively and only for these biogas mixtures propagated at reduced pressure. At the same equivalence ratio (ϕ), the laminar burning velocities of the biogas-air mixtures at reduced pressure are higher than those at atmospheric pressure. The flammable region of biogas became narrower by reducing initial pressure. The dilution effect is stronger at reduced pressure. Therefore, the flammable composition mixture areas of biogas-air mixtures are more limited at reduced pressure than those at atmospheric pressure.

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17

Karpov, Vladimir P., Andrei N. Lipatnikov e Piotr Wolanski. "Finding the markstein number using the measurements of expanding spherical laminar flames". Combustion and Flame 109, n.º 3 (maio de 1997): 436–48. http://dx.doi.org/10.1016/s0010-2180(96)00166-6.

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18

Zhao, Haoran, Jinhua Wang, Xiao Cai, Hongchao Dai, Xiao Liu, Gang Li e Zuohua Huang. "On accelerative propagation of premixed hydrogen/air laminar and turbulent expanding flames". Energy 283 (novembro de 2023): 129106. http://dx.doi.org/10.1016/j.energy.2023.129106.

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19

Duva, Berk Can, Lauren Elizabeth Chance e Elisa Toulson. "The critical lower radius limit approach for laminar flame speed measurement from spherically expanding stretched flames". Experimental Thermal and Fluid Science 121 (fevereiro de 2021): 110284. http://dx.doi.org/10.1016/j.expthermflusci.2020.110284.

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20

Jayachandran, Jagannath, Runhua Zhao e Fokion N. Egolfopoulos. "Determination of laminar flame speeds using stagnation and spherically expanding flames: Molecular transport and radiation effects". Combustion and Flame 161, n.º 9 (setembro de 2014): 2305–16. http://dx.doi.org/10.1016/j.combustflame.2014.03.009.

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21

Haq, M. Z. "Correlations for the Onset of Instabilities of Spherical Laminar Premixed Flames". Journal of Heat Transfer 127, n.º 12 (25 de janeiro de 2005): 1410–15. http://dx.doi.org/10.1115/1.2098867.

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A spherically expanding flame in a quiescent premixture is a bifurcation phenomenon, in which the flame becomes unstable at a radius, greater than some critical value, while remaining stable below that critical radius. Beyond this critical radius, developing instabilities are initiated by propagating cracks to form a coherent structure covering the entire flame surface and the flame accelerates. The present paper reports a Schlieren photographic study of spherical flame propagation in methane—air, iso-octane—air and n-heptane—air premixtures at different initial conditions where the onset of instability and the flame acceleration are clearly perceived. Critical size and corresponding elapsed time for the development of such instability are measured and these values are correlated with the appropriate flame parameter.

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22

Movaghar, Ashkan, Robert Lawson e Fokion N. Egolfopoulos. "Confined spherically expanding flame method for measuring laminar flame speeds: Revisiting the assumptions and application to C1C4 hydrocarbon flames". Combustion and Flame 212 (fevereiro de 2020): 79–92. http://dx.doi.org/10.1016/j.combustflame.2019.10.023.

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23

Berger, Lukas, Raik Hesse, Konstantin Kleinheinz, Michael J. Hegetschweiler, Antonio Attili, Joachim Beeckmann, Gregory T. Linteris e Heinz Pitsch. "A DNS study of the impact of gravity on spherically expanding laminar premixed flames". Combustion and Flame 216 (junho de 2020): 412–25. http://dx.doi.org/10.1016/j.combustflame.2020.01.036.

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24

Moccia, V., J. D’Alessio e N. Rispoli. "Inferring laminar burning properties from spherical expanding flames: the pitfalls of an established approach". Journal of Physics: Conference Series 1589 (julho de 2020): 012015. http://dx.doi.org/10.1088/1742-6596/1589/1/012015.

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25

Turner, Mattias A., Tyler T. Paschal, Pradeep Parajuli, Waruna D. Kulatilaka e Eric L. Petersen. "Application of high-speed, species-specific chemiluminescence imaging for laminar flame speed and Markstein length measurements in spherically expanding flames". Experimental Thermal and Fluid Science 129 (novembro de 2021): 110477. http://dx.doi.org/10.1016/j.expthermflusci.2021.110477.

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26

Zhang, Yakun, Marine Jeanson, Rémy Mével, Zheng Chen e Nabiha Chaumeix. "Tailored mixture properties for accurate laminar flame speed measurement from spherically expanding flames: Application to H2/O2/N2/He mixtures". Combustion and Flame 231 (setembro de 2021): 111487. http://dx.doi.org/10.1016/j.combustflame.2021.111487.

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27

Lipatnikov, Andrei N., Shenqyang S. Shy e Wun-yi Li. "Experimental assessment of various methods of determination of laminar flame speed in experiments with expanding spherical flames with positive Markstein lengths". Combustion and Flame 162, n.º 7 (julho de 2015): 2840–54. http://dx.doi.org/10.1016/j.combustflame.2015.04.003.

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28

Jayachandran, Jagannath, Alexandre Lefebvre, Runhua Zhao, Fabien Halter, Emilien Varea, Bruno Renou e Fokion N. Egolfopoulos. "A study of propagation of spherically expanding and counterflow laminar flames using direct measurements and numerical simulations". Proceedings of the Combustion Institute 35, n.º 1 (2015): 695–702. http://dx.doi.org/10.1016/j.proci.2014.05.031.

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29

Moghaddas, Ali, Kian Eisazadeh-Far e Hameed Metghalchi. "Laminar burning speed measurement of premixed n-decane/air mixtures using spherically expanding flames at high temperatures and pressures". Combustion and Flame 159, n.º 4 (abril de 2012): 1437–43. http://dx.doi.org/10.1016/j.combustflame.2011.12.005.

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30

Nawaz, Behlol, Md Nayer Nasim, Shubhra Kanti Das, Joshua Landis, Amina SubLaban, Juan Pablo Trelles, Dimitris Assanis, Noah Van Dam e J. Hunter Mack. "Combustion characteristics and emissions of nitrogen oxides (NO, NO2, N2O) from spherically expanding laminar flames of ammonia–hydrogen blends". International Journal of Hydrogen Energy 65 (maio de 2024): 164–76. http://dx.doi.org/10.1016/j.ijhydene.2024.03.366.

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31

Concetti, Riccardo, Josef Hasslberger e Markus Klein. "Direct numerical simulations with multi-step chemistry of liquid water interaction with laminar spherically expanding premixed hydrogen/air flames". International Journal of Hydrogen Energy 115 (abril de 2025): 10–23. https://doi.org/10.1016/j.ijhydene.2025.02.286.

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32

Khan, A. R., S. Anbusaravanan, Lokesh Kalathi, Ratnakishore Velamati e C. Prathap. "Investigation of dilution effect with N2/CO2 on laminar burning velocity of premixed methane/oxygen mixtures using freely expanding spherical flames". Fuel 196 (maio de 2017): 225–32. http://dx.doi.org/10.1016/j.fuel.2017.01.086.

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33

Xiouris, Christodoulos, Tailai Ye, Jagannath Jayachandran e Fokion N. Egolfopoulos. "Laminar flame speeds under engine-relevant conditions: Uncertainty quantification and minimization in spherically expanding flame experiments". Combustion and Flame 163 (janeiro de 2016): 270–83. http://dx.doi.org/10.1016/j.combustflame.2015.10.003.

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34

Eisazadeh-Far, Kian, Ali Moghaddas, Faranak Rahim e Hameed Metghalchi. "Burning Speed and Entropy Production Calculation of a Transient Expanding Spherical Laminar Flame Using a Thermodynamic Model". Entropy 12, n.º 12 (21 de dezembro de 2010): 2485–96. http://dx.doi.org/10.3390/e12122485.

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35

Helling, Tobias, Florian Reischl, Andreas Rosin, Thorsten Gerdes e Walter Krenkel. "Atomization of Borosilicate Glass Melts for the Fabrication of Hollow Glass Microspheres". Processes 11, n.º 9 (26 de agosto de 2023): 2559. http://dx.doi.org/10.3390/pr11092559.

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Direct atomization of a free-flowing glass melt was carried out using a high-speed flame with the aim of producing tiny, self-expanding glass melt droplets to form hollow glass microspheres. Atomization experiments were carried out using a specially adapted free-fall atomizer in combination with a high-power gas burner to achieve sufficient temperatures to atomize the melt droplets and to directly expand them into hollow glass spheres. In addition, numerical simulations were carried out to investigate non-measurable parameters such as hot gas velocities and temperatures in the flame region by the finite volume-based software Star CCM+® (v. 2022.1.1), using the Reynolds-Averaged Navier–Stokes (RANS) turbulence and the segregated flow model. To calculate the combustion process, the laminar flamelet method was used. The experiments and simulations indicated that a maximum gas velocity of about 170 m/s was achieved at the point of atomization in the flame. The particle size distribution of the atomized glass droplets, either solid or hollow, ranged from 2 µm to 4 mm. Mean particle sizes in the range of 370 µm to 650 µm were highly dependent on process parameters such as gas velocity. They were in good agreement with theoretically calculated median diameters. The formation of hollow glass microspheres with the proposed concept could be demonstrated. However, only a small fraction of hollow glass spheres was found to be formed. These hollow spheres had diameters up to 50 µm and, as expected, a thin wall thickness.

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36

Sawant, N., B. Dorschner e I. V. Karlin. "A lattice Boltzmann model for reactive mixtures". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 379, n.º 2208 (30 de agosto de 2021): 20200402. http://dx.doi.org/10.1098/rsta.2020.0402.

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A new lattice Boltzmann model for reactive ideal gas mixtures is presented. The model is an extension to reactive flows of the recently proposed multi-component lattice Boltzmann model for compressible ideal gas mixtures with Stefan–Maxwell diffusion for species interaction. First, the kinetic model for the Stefan–Maxwell diffusion is enhanced to accommodate a source term accounting for the change in the mixture composition due to chemical reaction. Second, by including the heat of formation in the energy equation, the thermodynamic consistency of the underlying compressible lattice Boltzmann model for momentum and energy allows a realization of the energy and temperature change due to chemical reactions. This obviates the need for ad-hoc modelling with source terms for temperature or heat. Both parts remain consistently coupled through mixture composition, momentum, pressure, energy and enthalpy. The proposed model uses the standard three-dimensional lattices and is validated with a set of benchmarks including laminar burning speed in the hydrogen–air mixture and circular expanding premixed flame. This article is part of the theme issue ‘Progress in mesoscale methods for fluid dynamics simulation’.

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37

Tindemans, Irma, Maria E. Joosse e Janneke N. Samsom. "Dissecting the Heterogeneity in T-Cell Mediated Inflammation in IBD". Cells 9, n.º 1 (2 de janeiro de 2020): 110. http://dx.doi.org/10.3390/cells9010110.

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Infiltration of the lamina propria by inflammatory CD4+ T-cell populations is a key characteristic of chronic intestinal inflammation. Memory-phenotype CD4+ T-cell frequencies are increased in inflamed intestinal tissue of IBD patients compared to tissue of healthy controls and are associated with disease flares and a more complicated disease course. Therefore, a tightly controlled balance between regulatory and inflammatory CD4+ T-cell populations is crucial to prevent uncontrolled CD4+ T-cell responses and subsequent intestinal tissue damage. While at steady state, T-cells display mainly a regulatory phenotype, increased in Th1, Th2, Th9, Th17, and Th17.1 responses, and reduced Treg and Tr1 responses have all been suggested to play a role in IBD pathophysiology. However, it is highly unlikely that all these responses are altered in each individual patient. With the rapidly expanding plethora of therapeutic options to inhibit inflammatory T-cell responses and stimulate regulatory T-cell responses, a crucial need is emerging for a robust set of immunological assays to predict and monitor therapeutic success at an individual level. Consequently, it is crucial to differentiate dominant inflammatory and regulatory CD4+ T helper responses in patients and relate these to disease course and therapy response. In this review, we provide an overview of how intestinal CD4+ T-cell responses arise, discuss the main phenotypes of CD4+ T helper responses, and review how they are implicated in IBD.

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38

Adamski, Robert, Dorota Siuta, Bożena Kukfisz, Michał Frydrysiak e Mirosława Prochoń. "Integration of Safety Aspects in Modeling of Superheated Steam Flash Drying of Tobacco". Energies 14, n.º 18 (18 de setembro de 2021): 5927. http://dx.doi.org/10.3390/en14185927.

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Knowledge of the drying properties of tobacco in high temperatures above 100 °C and its dust are crucial in the design of dryers, both in the optimization of the superheated-steam-drying process and in the correct selection of innovative explosion protection and mitigation systems. In this study, tobacco properties were determined and incorporated into the proposed model of an expanding superheated steam flash dryer. The results obtained from the proposed model were validated by using experimental data yielded during test runs of an industrial scale of a closed-loop expansion dryer on lamina cut tobacco. Moreover, the explosion and fire properties of tobacco dust before and after the superheated steam-drying process at 160, 170, 180, and 190 °C were experimentally investigated, using a 20 L spherical explosion chamber, a hot plate apparatus, a Hartmann tube apparatus, and a Godbert–Greenwald furnace apparatus. The results indicate that the higher the drying temperature, the more likely the ignition of the dust tobacco cloud, the faster the explosion flame propagation, and the greater the explosion severity. Tobacco dust is of weak explosion class. Dust obtained by drying with superheated steam at 190 °C is characterized by the highest value of explosion index amounting to 109 ± 14 m·bar·s−1, the highest explosion pressure rate (405 ± 32 bar/s), and the maximum explosion pressure (6.7 ± 0.3 bar). The prevention of tobacco-dust accumulation and its removal from the outer surfaces of machinery and equipment used in the superheated steam-drying process are highly desirable.

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39

Rokni, Emad, Ali Moghaddas, Omid Askari e Hameed Metghalchi. "Measurement of Laminar Burning Speeds and Investigation of Flame Stability of Acetylene (C2H2)/Air Mixtures". Journal of Energy Resources Technology 137, n.º 1 (3 de setembro de 2014). http://dx.doi.org/10.1115/1.4028363.

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Laminar burning speeds and flame structures of spherically expanding flames of mixtures of acetylene (C2H2) with air have been investigated over a wide range of equivalence ratios, temperatures, and pressures. Experiments have been conducted in a constant volume cylindrical vessel with two large end windows. The vessel was installed in a shadowgraph system equipped with a high speed CMOS camera, capable of taking pictures up to 40,000 frames per second. Shadowgraphy was used to study flame structures and transition from smooth to cellular flames during flame propagation. Pressure measurements have been done using a pressure transducer during the combustion process. Laminar burning speeds were measured using a thermodynamic model employing the dynamic pressure rise during the flame propagation. Burning speeds were measured for temperature range of 300–590 K and pressure range of 0.5–3.3 atm, and the range of equivalence ratios covered from 0.6 to 2. The measured values of burning speeds compared well with existing data and extended for a wider range of temperatures. Burning speed measurements have only been reported for smooth and laminar flames.

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40

Li, Hong-Meng, Guo-Xiu Li, Zuo-Yu Sun, Zi-Hang Zhou, Yuan Li e Ye Yuan. "Fundamental Combustion Characteristics of Lean and Stoichiometric Hydrogen Laminar Premixed Flames Diluted With Nitrogen or Carbon Dioxide". Journal of Engineering for Gas Turbines and Power 138, n.º 11 (24 de maio de 2016). http://dx.doi.org/10.1115/1.4032315.

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In this work, the laminar combustion characteristics of H2/N2/air (H2/CO2/air) were systematically investigated under different hydrogen ratios (40–100%) and equivalence ratios (0.4–1.0) in a closed combustion vessel using the spherical expanding flame method associated with Schlieren technology. The unstretched laminar burning velocities were compared with data from previous study, and the result indicates that excellent agreements are obtained. Numerical simulations were also conducted using GRI3.0 and USC II mechanisms to compare with the present experimental results. The Markstein length for H2/inert gas can be decreased by decreasing the equivalence ratio and hydrogen ratio. The results indicate that the H2/inert gas premixed flames tend to be more unstable with the decrease of equivalence ratio and hydrogen ratio. For H2/N2 mixture, the suppression effect on laminar burning velocity is caused by modified specific heat of mixtures and decreased heat release, which result in a decreased flame temperature. For H2/CO2 mixture, the carbon dioxide has stronger dilution effect than nitrogen in reducing laminar burning velocity owing to both thermal effect and chemical effect.

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41

Cai, Xiao, Jinhua Wang, Zhijian Bian, Haoran Zhao, Zhongshan Li e Zuohua Huang. "Propagation of Darrieus–Landau unstable laminar and turbulent expanding flames". Proceedings of the Combustion Institute, setembro de 2020. http://dx.doi.org/10.1016/j.proci.2020.06.247.

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Bechtold, John K., Gautham Krishnan e Moshe Matalon. "Hydrodynamic theory of premixed flames propagating in closed vessels: flame speed and Markstein lengths". Journal of Fluid Mechanics 998 (4 de novembro de 2024). http://dx.doi.org/10.1017/jfm.2024.919.

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A hydrodynamic theory of premixed flame propagation within closed vessels is developed assuming the flame is much thinner than all other fluid dynamic lengths. In this limit, the flame is confined to a surface separating the unburned mixture from burned combustion products, and propagates at a speed determined from the analysis of its internal structure. Unlike freely propagating flames that propagate under nearly isobaric conditions, combustion in a closed vessel results in continuous increases in pressure, burning rate and flame temperature, and a progressive decrease in flame thickness. The flame speed is shown to depend on the voluminal stretch rate, which measures the deformation of a volume element of the flame zone, and on the rate of pressure rise. Both effects are modulated by pressure-dependent Markstein numbers that depend on heat release and mixture properties while capturing the effects of temperature-dependent transport and stoichiometry. The model applies to flames of arbitrary shape propagating in general flows, laminar or turbulent, within vessels of general configurations. The main limitation of hydrodynamic flame theories is the assumption that variations inside the flame zone due to chemistry or turbulence, which could potentially alter its internal structure, are physically unresolved. Nonetheless, the theory, deduced from physical first principles, identifies the various mechanisms involved in the combustion process as demonstrated in detailed discussions of planar flames propagating in rectangular channels and spherically expanding flames in spherical vessels. It also enables the construction of instructive models to numerically simulate the evolution of multi-dimensional and corrugated flames under confinement.

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43

Liu, Zirui, Vishnu R. Unni, Swetaprovo Chaudhuri, Chung K. Law e Abhishek Saha. "Local statistics of laminar expanding flames subjected to Darrieus–Landau instability". Proceedings of the Combustion Institute, agosto de 2020. http://dx.doi.org/10.1016/j.proci.2020.06.118.

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Yin, Geyuan, Erjiang Hu, Xiaotian Li, Xin Lv e Zuohua Huang. "Laminar Flame Instability of n-Hexane, n-Octane, and n-Decane in Spherical Expanding Flames". Journal of Thermal Science, 11 de janeiro de 2024. http://dx.doi.org/10.1007/s11630-024-1844-0.

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45

Zhao, Haoran, Jinhua Wang, Xiao Cai, Hongchao Dai, Xiao Liu e Zuohua Huang. "On Accelerative Propagation of Premixed Hydrogen/Air Laminar and Turbulent Expanding Flames". SSRN Electronic Journal, 2022. http://dx.doi.org/10.2139/ssrn.4183159.

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46

Huo, Jialong, Abhishek Saha, Tao Shu, Zhuyin Ren e Chung K. Law. "Self-acceleration and global pulsation in expanding laminar H2−O2−N2 flames". Physical Review Fluids 4, n.º 4 (16 de abril de 2019). http://dx.doi.org/10.1103/physrevfluids.4.043201.

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47

Duva, Berk, Yen-Cheng Wang, Lauren Chance e Elisa Toulson. "Laminar Flame Characteristics of Sequential Two-Stage Combustion of Premixed Methane/Air Flames". Journal of Engineering for Gas Turbines and Power, 15 de setembro de 2020. http://dx.doi.org/10.1115/1.4048450.

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Abstract The present study investigates laminar flame characteristics of the combustion within the second stage of a sequential combustor. The method of constant pressure for spherically expanding flames was employed to obtain laminar burning velocities (LBV) and burned gas Markstein lengths (Lb) of premixed methane/air mixtures diluted using flue gas at 3 bar and 423 K. Combustion residuals were imitated using a 19.01% H2O + 9.50% CO2 +71.49% N2 mixture by volume, while tested dilution ratios were 0%, 5%, 10%, and 15%. Experimental results showed that the LBV was decreased by 18-23%, 36-42%, and 50-52% with additions of 5%, 10%, and 15% combustion products, respectively. As the dilution and equivalence ratios increased, the Lb values increased slightly, suggesting that the stability and stretch of the CH4/air flames increased at these conditions. Numerical results were obtained from CHEMKIN using the GRI-Mech 3.0, USC Mech II, San Diego, HP-Mech, NUI Galway, and AramcoMech 1.3 mechanisms. The GRI-Mech 3.0 and HP-Mech performed best, with an average of 2% and 3% difference between numerical and experimental LBVs, respectively. The thermal-diffusion (TD), dilution (D), and the chemical (C) effects of inert post-combustion gases on the LBV were found using numerical results. The dilution effect was primarily responsible, accounting for 79-84% of the LBV reduction.

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Kutkan, Halit, Alberto Amato, Giovanni Campa, Giulio Ghirardo, Luis Tay Wo Chong Hilares e Eirik Æs⊘y. "Modelling of Turbulent Premixed CH4/H2/Air Flames Including the Influence of Stretch and Heat Losses". Journal of Engineering for Gas Turbines and Power, 3 de agosto de 2021. http://dx.doi.org/10.1115/1.4051989.

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Abstract This paper presents a RANS turbulent combustion model for CH4/H2/air mixtures which includes the effect of heat losses and flame stretch. This approach extends a previous model concept designed for methane/air mixtures and improves the prediction of flame stabilization when hydrogen is added to the fuel. Heat loss and stretch effects are modelled by tabulating the consumption speed of laminar counter flow flames in a fresh-to burnt configuration with detailed chemistry at various heat loss and flame stretch values. These computed values are then introduced in the turbulent combustion model by means of a turbulent flame speed expression which is derived as a function of flame stretch, heat loss and H2 addition. The model proposed in this paper is compared to existing models on experimental data of spherical expanding turbulent flame speeds. The performance of the model is further validated by comparing CFD predictions to experimental data of an atmospheric turbulent premixed bluff-body stabilized flame fed with CH4/H2/air mixtures ranging from pure methane to pure hydrogen.

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Turner, Mattias, e Eric Petersen. "High-Pressure Laminar Flame Speeds and Markstein Lengths of Syngas Flames Diluted in Carbon Dioxide and Helium". Journal of Engineering for Gas Turbines and Power, 27 de setembro de 2022. http://dx.doi.org/10.1115/1.4055796.

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Abstract New laminar flame speed and burned-gas Markstein length data for H2-CO-O2-CO2-He mixtures have been measured from spherically expanding flames. Experiments were conducted at 10 atm and room temperature for H2:CO ratios ranging from 2:1 to 1:4 and for overall CO2 mole fractions from 0 to 30%. CO2 dilution had little effect on Markstein length, but CO2 dilutions of 10%, 20%, and 30% caused average reductions in flame speed of 47%, 73%, and 89% respectively, regardless of H2:CO ratio. The study was designed to isolate the dilution effect of CO2 on flame speed, and a detailed analysis using the FCO2 method was used to show that the chemical-kinetic participation of CO2 was responsible for up to 20% of the reduction in flame speed. Hence, the majority (80% or more) of the reduction in flame speed due to CO2 is from the thermal effect. Accurate flame speed predictions were produced by five different chemical kinetics mechanisms for most conditions, with the slight exception of high-CO, high-CO2 mixtures. A thorough sensitivity analysis highlighted the larger effect of CO2 dilution on the important kinetics reactions than the effect of changing H2:CO. Sensitivity analysis also showed that the chain branching reaction H2O+O?OH+OH could be modified (albeit beyond its uncertainty) to achieve more accurate flame speed predictions, but also indicated that further improvement of flame speed modeling would require changes to many lesser reactions.

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Amerighi, Matteo, Giada Senatori, Antonio Andreini, Thierry Schuller, Tarik Yahou e James Dawson. "Complete Dynamics from Ignition to Stabilization of a Lean Hydrogen Flame with Thickened Flame Model". Journal of Engineering for Gas Turbines and Power, 19 de setembro de 2024, 1–13. http://dx.doi.org/10.1115/1.4066590.

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Abstract In recent years, attention has been paid to hydrogen thanks to its carbon-free nature and its interesting characteristics as an energy vector. Despite the large number of numerical analyses regarding hydrocarbon combustion in all the steady and unsteady processes, few papers that cover all those aspects are available in the literature for hydrogen flames. Therefore, a numerical methodology to explore the complete ignition sequence from the spark release to the flame stabilization is validated on a single-sector hydrogen burner. In this context, a preliminary DNS investigation of laminar spherical expanding flames is performed using different diffusive transport models to isolate their impact. The present work, carried out within the European project HESTIA, investigates the atmospheric test rig installed at the Norwegian University of Science and Technology operating with a lean, perfectly premixed, hydrogen-air flame stabilized on a conical bluff body. Four simulations are performed adopting the Thickened Flame Model with an energy deposition strategy to assess the impact of preferential and thermal diffusion, as well as grid resolution, on flame dynamics. 3D flame structure visualization coupled with detailed PIV/OH-PLIF measurements allows the investigation of the key mechanisms involved during the ignition. The dynamic response of the flame through axial fluctuations once the ignition transient is concluded, is reconstructed by the numerical strategy employed. Although the overall behavior is almost unchanged by including or not thermal diffusion effects, their local impact on the flame is evident leading to a better agreement with experimental data.

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