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Artykuły w czasopismach na temat "Flame flashbacks"
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Krupa, R. J., T. F. Culbreth, B. W. Smith i J. D. Winefordner. "A Flashback-Resistant Burner for Combustion Diagnostics and Analytical Spectrometry". Applied Spectroscopy 40, nr 6 (sierpień 1986): 729–33. http://dx.doi.org/10.1366/0003702864508232.
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A general utility burner for the production of laminar, homogenous diffusion flames, which is immune to flashbacks, is presented. Because the fuel and oxidant mix on the surface of the burner rather than within the spray chamber, the flames cannot flashback. A wide variety of gas mixtures has been investigated, including oxygen, nitrous oxide, and nitric oxide as the oxidants. Any combination of fuel and oxidant can be safely burned to produced a stable, laminar, and audibly quiet flame. Flame temperatures can be varied over a wide range either by changing the fuel-oxidant ratio or by diluting the flame gases with an inert gas. In this manner, the optimum flame temperature and composition can be achieved. These burners are of general use in analytical emission, fluorescence, and photoacoustic spectrometry, as well as combustion diagnostics.
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Carlos E. Arrieta, Mario Luna-DelRisco, Arley Cardona, Jorge Sierra del Río, Alejandro Ruiz Sánchez, Lisandra Rocha-Meneses i Jhojan Stiven Zea Fernández. "Numerical Investigation of Operating Conditions that Lead to Flat Flames, Flashback, and Blowout in A Surface-Stabilized Combustion Burner". CFD Letters 15, nr 4 (16.02.2023): 106–13. http://dx.doi.org/10.37934/cfdl.15.4.106113.
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Surface-stabilized combustion burners or surface-radiant burners use perforated ceramic plates, ceramic foams, or metal fibers to stabilize a premixed flame. These burners are the most straightforward alternative to have both, the benefits of the reactant preheating technique and a great amount of heat transferred by radiation from the burner to the load. However, in its design, one of the greatest difficulties is to predict the flame stability limits; especially under operating conditions that lead to flashbacks and blowouts. This work presents a computational methodology based on the finite volume method with a two-dimensional domain to predict the flame curvature towards the unburned and burned gas that occurs before flashback and blowout, respectively. In the methodology, continuity, momentum, energy, and chemical species equations are solved to obtain the increase in the surface area of the flame. It was observed that this value can be used as a criterion to predict whether an operating condition is stable. When comparing the numerical results with experimental results reported in the literature, good predictions of the operating conditions that lead to flashbacks and blowouts are observed
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Eichler, Christian, Georg Baumgartner i Thomas Sattelmayer. "Experimental Investigation of Turbulent Boundary Layer Flashback Limits for Premixed Hydrogen-Air Flames Confined in Ducts". Mechanical Engineering 134, nr 12 (1.12.2012): 52–53. http://dx.doi.org/10.1115/1.2012-dec-7.
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This article discusses the results of experimental investigation of turbulent boundary layer flashback limits for premixed hydrogen-air flames confined in ducts. A tube burner experiment was set-up to double-check the findings of the channel rig. Unconfined flashback experiments were carried out by stabilizing the flame on top of the pilot burner in free atmosphere. A confined flame configuration was achieved by simply fixing a ceramic ring with a diameter higher by 4 mm on top of the pilot burner. Flashback measurements with unconfined flame holding neatly reproduced literature values for fully premixed, atmospheric H2–air mixtures and turbulent flow. The results of unconfined and confined tube burner experiments were plotted. The results showed that the drastic decrease of wall flashback stability for confined flames was the very same for both, tube and channel.
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Endres, Aaron, i Thomas Sattelmayer. "Numerical Investigation of Pressure Influence on the Confined Turbulent Boundary Layer Flashback Process". Fluids 4, nr 3 (1.08.2019): 146. http://dx.doi.org/10.3390/fluids4030146.
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Boundary layer flashback from the combustion chamber into the premixing section is a threat associated with the premixed combustion of hydrogen-containing fuels in gas turbines. In this study, the effect of pressure on the confined flashback behaviour of hydrogen-air flames was investigated numerically. This was done by means of large eddy simulations with finite rate chemistry as well as detailed chemical kinetics and diffusion models at pressures between 0 . 5 and 3 . It was found that the flashback propensity increases with increasing pressure. The separation zone size and the turbulent flame speed at flashback conditions decrease with increasing pressure, which decreases flashback propensity. At the same time the quenching distance decreases with increasing pressure, which increases flashback propensity. It is not possible to predict the occurrence of boundary layer flashback based on the turbulent flame speed or the ratio of separation zone size to quenching distance alone. Instead the interaction of all effects has to be accounted for when modelling boundary layer flashback. It was further found that the pressure rise ahead of the flame cannot be approximated by one-dimensional analyses and that the assumptions of the boundary layer theory are not satisfied during confined boundary layer flashback.
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KURDYUMOV, VADIM N., i AMABLE LIÑÁN. "STRUCTURE OF A FLAME FRONT PROPAGATING AGAINST THE FLOW NEAR A COLD WALL". International Journal of Bifurcation and Chaos 12, nr 11 (listopad 2002): 2547–55. http://dx.doi.org/10.1142/s0218127402006023.
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The flashback or propagation of premixed flames against the flow of a reacting mixture, along the low velocity region near a cold wall, is investigated numerically. The analysis, carried out using the constant density approximation for an Arrhenius overall reaction, accounts for the effects of the Lewis number of the limiting reactant. Flame front propagation and flashback are only possible for values of the near wall velocity gradient below a critical value. The flame propagation becomes chaotic for small values of the Lewis number.
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Dias, David M., Pedro R. Resende i Alexandre M. Afonso. "A Review on Micro-Combustion Flame Dynamics and Micro-Propulsion Systems". Energies 17, nr 6 (10.03.2024): 1327. http://dx.doi.org/10.3390/en17061327.
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This work presents a state-of-the-art review of micro-combustion flame dynamics and micro propulsion systems. In the initial section, we focus in on the different challenges of micro-combustion, investigating the typical length and time scales involved in micro-combustion and some critical phenomena such as flammability limits and the quenching diameter.We present an extensive collection of studies on the principal types of micro-flame dynamics, including flashback, blow-off, steady versus non-steady flames, mild combustion, stable flames, flames with repetitive extinction, and ignition and pulsatory flame burst. In the final part of this review, we focus on micropropulsion systems, their performance metrics, conventional manufacturing methods, and the advancements in Micro-Electro-Mechanical Systems manufacturing.
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Jiang, Xudong, Yihao Tang, Zhaohui Liu i Venkat Raman. "Computational Modeling of Boundary Layer Flashback in a Swirling Stratified Flame Using a LES-Based Non-Adiabatic Tabulated Chemistry Approach". Entropy 23, nr 5 (2.05.2021): 567. http://dx.doi.org/10.3390/e23050567.
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When operating under lean fuel–air conditions, flame flashback is an operational safety issue in stationary gas turbines. In particular, with the increased use of hydrogen, the propagation of the flame through the boundary layers into the mixing section becomes feasible. Typically, these mixing regions are not designed to hold a high-temperature flame and can lead to catastrophic failure of the gas turbine. Flame flashback along the boundary layers is a competition between chemical reactions in a turbulent flow, where fuel and air are incompletely mixed, and heat loss to the wall that promotes flame quenching. The focus of this work is to develop a comprehensive simulation approach to model boundary layer flashback, accounting for fuel–air stratification and wall heat loss. A large eddy simulation (LES) based framework is used, along with a tabulation-based combustion model. Different approaches to tabulation and the effect of wall heat loss are studied. An experimental flashback configuration is used to understand the predictive accuracy of the models. It is shown that diffusion-flame-based tabulation methods are better suited due to the flashback occurring in relatively low-strain and lean fuel–air mixtures. Further, the flashback is promoted by the formation of features such as flame tongues, which induce negative velocity separated boundary layer flow that promotes upstream flame motion. The wall heat loss alters the strength of these separated flows, which in turn affects the flashback propensity. Comparisons with experimental data for both non-reacting cases that quantify fuel–air mixing and reacting flashback cases are used to demonstrate predictive accuracy.
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Fooladgar, Ehsan, i C. K. Chan. "Large Eddy Simulation of a Swirl-Stabilized Pilot Combustor from Conventional to Flameless Mode". Journal of Combustion 2016 (2016): 1–16. http://dx.doi.org/10.1155/2016/8261560.
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This paper investigates flame and flow structure of a swirl-stabilized pilot combustor in conventional, high temperature, and flameless modes by means of a partially stirred reactor combustion model to provide a better insight into designing lean premixed combustion devices with preheating system. Finite rate chemistry combustion model with one step tuned mechanism and large eddy simulation is used to numerically simulate six cases in these modes. Results show that moving towards high temperature mode by increasing the preheating level, the combustor is prone to formation of thermalNOxwith higher risks of flashback. In addition, the flame becomes shorter and thinner with higher turbulent kinetic energies. On the other hand, towards the flameless mode, leaning the preheated mixture leads to almost thermalNOx-free combustion with lower risk of flashback and thicker and longer flames. Simulations also show qualitative agreements with available experiments, indicating that the current combustion model with one step tuned mechanisms is capable of capturing main features of the turbulent flame in a wide range of mixture temperature and equivalence ratios.
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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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Huang, Kai, Louis Benteux, Wenhu Han i Damir M. Valiev. "Combined Impact of the Lewis Number and Thermal Expansion on Laminar Flame Flashback in Tubes". Fluids 9, nr 1 (19.01.2024): 28. http://dx.doi.org/10.3390/fluids9010028.
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The understanding of the boundary layer flame flashback (BLF) has considerably improved in recent decades, driven by the increasing focus on clean energy and the need to address the operational issues associated with flashback. This study investigates the influence of the Lewis number (Le) on symmetric flame shapes under the critical conditions for a laminar boundary layer flashback in cylindrical tubes. It has been found that the transformation of the flame shape from a mushroom to a tulip happens in a tube of a given radius, as the thermal expansion coefficient and Le are modified. A smaller Lewis number results in a local increase in the burning rate at the flame tip, with the flame being able to propagate closer to the wall, which significantly increases the flashback propensity, in line with previous findings. In cases with a Lewis number smaller than unity, a higher thermal expansion results in a flame propagation happening closer to the wall, thus facing a weaker oncoming flow and, consequently, becoming more prone to flashback. For Le > 1, the effect of the increase in the thermal expansion coefficient on the flashback tendency is much less pronounced.
Rozprawy doktorskie na temat "Flame flashbacks"
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Klein, Jean-Michel. "Étude des instabilités de combustion, mouvements de flamme et flashbacks dans un foyer comprenant un élargissement brusque". Electronic Thesis or Diss., Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2024. http://www.theses.fr/2024ESMA0012.
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La conception des futurs statoréacteurs bénéficierait d'une meilleure compréhension des instabilités de combustion apparaissant dans les écoulements rapides présentant des recirculations : une problématique étudiée à l'ONERA avec le banc MICAEDI au LAboratoire des Ecoulements Réactifs et de leurs Techniques d'Etude (LAERTE) de l'ONERA. Dans ce dispositif, une flamme de prémélange méthane-air s’établit au voisinage d’une marche descendante, dans un environnement présentant des similitudes avec les foyers de statoréacteurs. Pour certains points de fonctionnement, d’importantes oscillations de pression accompagnées de remontées de flammes (flashbacks) périodiques y apparaissent sous l'effet de l'excitation de modes acoustiques longitudinaux. Dans le cadre cette thèse, le code de calcul CEDRE est utilisé afin de restituer ces instabilités, les analyser et en améliorer la compréhension. Pour cela, une méthodologie de post-traitement basée sur les bilans d’énergie des perturbations (BEP) a été appliquée tout d'abord dans le cas d'une flamme de prémélange unidimensionnelle forcée acoustiquement. Grâce à ce formalisme, la dynamique de cette flamme peut alors être décrite au travers d'une loi d'échelle au moyen de deux nombres adimensionnels : (i) un nombre de Strouhal associé aux mouvements de la flamme qui compare son amplitude de battement à l’épaisseur de flamme laminaire et (ii) l’amplitude de la perturbation en vitesse adimensionnée par la vitesse de propagation de flamme laminaire. Sont ensuite réalisées des simulations numériques aux grandes échelles de flammes s'établissant au voisinage d'une marche descendante. En deux dimensions (2D), une telle approche permet de restituer, à moindre coût de calcul, une dynamique de combustion similaire à celle observée sur le banc MICAEDI. Une étude de sensibilité conduite sur les principaux paramètres opératoires met en évidence les processus associés au développement d'instabilités de combustion et à l'apparition de flashbacks. Il apparaît que la rétroactions entre des modes acoustiques longitudinaux et les oscillations du front de flamme sont favorisées si la symétrie des plissements de la flamme est rompue par l’action de la bulle de recirculation s'établissant au pied de la marche descendante. Ce mécanisme est favorisé si le mode acoustique présente un nœud de vitesse au niveau de la marche descendante et si sa fréquence est basse et/ou proche de la fréquence caractéristique de l'instabilité de Kelvin-Helmholtz. Des oscillations peuvent également apparaître à de plus basses fréquences lors du battement du point de raccordement de la flamme à la paroi supérieure. Ces oscillations peuvent provoquer des flashbacks suivant deux mécanismes : (i) synchronisation entre les oscillations des modes acoustiques et les détachements périodiques de la bulle de recirculation s'élevant au-dessus de la marche, bloquant la flamme et la faisant temporairement remonter en amont, avant d'être convectée plus en aval et (ii) action de la flamme qui, lors de sa propagation dans la couche limite à de basses fréquences, y cause son décollement et favorise ainsi l'apparition de nouveaux flashbacks à de plus hautes fréquences. Si les détachements de la bulle provoquent des flashbacks pour des niveaux importants d'oscillations de vitesse (la direction de l'écoulement est proche de s'inverser, voire s'inverse périodiquement), les remontées de flamme par la couche limite sont susceptibles d'apparaître pour des niveaux d'oscillation plus modérés. Pour les simulations en trois dimensions (3D), l'utilisation d'une géométrie représentative du foyer MICAEDI permet une restitution fine des instabilités observées. En effet, le cycle limite obtenu numériquement présente de nombreuses similitudes avec les données expérimentales. Les principaux mécanismes analysés sur les simulations 2D sont également retrouvés sur ce cas 3D assurant une modélisation plus fidèle de la turbulence et de l'acoustique, validant ainsi l'ensembleThe design of future ramjets would benefit from a better understanding of the combustion instabilities that occur in flows featuring recirculation zones : a problem studied at ONERA by the means of the MICAEDI combustor from the LAERTE test facility. In this experimental setup, a methane-air premixed flame stabilizes at the vicinity of a backward-facing step, in an environment comparable to ramjet combustors. At certain operating points, significant pressure oscillations accompanied by periodic flame flashbacks appear due to the triggering of longitudinal acoustic modes. In this thesis work, the CEDRE CFD solver is used in order to restitute those instabilities, to study them and to improve their understanding. A post-processing methodology based on disturbance energy budgets (DEB) is elaborated. Its first application to the case of a one-dimensional acousticallyforced premixed flame puts into evidence two dimensionless numbers that can be used to describe its dynamicsby means of scaling laws : (i) a Strouhal number associated with the the flames motions that compares its flapping magnitude to the laminar flame thickness, and (ii) the magnitude of the velocity perturbation normalized using the laminar flame propagation speed. Large-eddy simulations of flames stablized in the vicinity of a backward-facing step are then carried out. In two dimensions (2D), this approach makes it possible to reproduce combustion dynamics similar to that observed in the MICAEDI experiment at a moderate computational cost. A sensitivity study is conducted on the operating parameters to clarify the phenomenology associated with the development of combustion instabilities and the occurence of flame flashbacks. It appears that the feedback loop between longitudinal acoustic modes and flame front oscillations is favoured if the symmetry of the flame wrinkles is broken by the action of the recirculation bubble establishing itself at the foot of the step. This mechanism is favoured if the acoustic mode displays a velocity node at the vicinity of the step and if its frequency is low and/or close to the characteristic frequency of the Kelvin-Helmholtz instability. Oscillations may also occur at lower frequencies as a result of flapping of the point where the flame re-attaches to the combustor upper wall.These oscillations can cause flashbacks by the mean of two mechanisms : (i) synchronization between the oscillations of the acoustic modes and the periodic detachments of the recirculation bubble which then rises above the step before being convected downstream, a process during which the flame is transported upstream and (ii)action of the flame which, during its propagation in the boundary layer at low frequencies, causes its detachment and thus favours the birth of new flashbacks at higher frequencies. While bubble detachment causes flashbacks at high levels of velocity oscillation (the direction of the flow is close to reversing, or even reverses periodically), boundary layer flashbacks are likely to occur at more moderate levels. In three dimensions (3D), the use of a geometry representative of the MICAEDI combustor allows a detailed reproduction of the observed instabilities. Indeed, the limit cycle obtained numerically shows many similarities with the experimental data. The main mechanisms analysed on the 2D simulations are also observed on this 3D case, ensuring a more accurate modelling of the turbulence and acoustics, thus validating the whole approach followed in this manuscript
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Baumgartner, Georg [Verfasser]. "Flame Flashback in Premixed Hydrogen-Air Combustion Systems / Georg Baumgartner". München : Verlag Dr. Hut, 2015. http://d-nb.info/107080018X/34.
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Dam, Bidhan Kumar. "Flashback propensity of gas mixtures". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Eichler, Christian Thomas [Verfasser]. "Flame Flashback in Wall Boundary Layers of Premixed Combustion Systems / Christian Eichler". München : Verlag Dr. Hut, 2011. http://d-nb.info/1018982884/34.
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Lapeyre, Corentin. "Numerical study of flame stability, stabilization and noise in a swirl-stabilized combustor under choked conditions". Phd thesis, Toulouse, INPT, 2015. http://oatao.univ-toulouse.fr/14493/1/Lapeyre.pdf.
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Air transportation is an essential part of modern business and leisure needs, and the number of passengers carried per year is rapidly increasing worldwide. The International Civil Aviation Organization estimates that this number went from 2.2 billion in 2009 to 3.0 billion in 2013, due in part to rapid growth in emerging countries such as China. Many challenges for aircraft designers arise from this increase in air traffic, such as meeting pollutant and noise emission regulations. The engines play a major part in these emissions, and combustor technology has evolved towards high-pressure Lean Prevaporized Premixed (LPP) combustion to increase efficiency and decrease pollutant emissions. Unfortunately, this technology tends to reduce engine robustness, with a decrease in flame stability and stabilization margins. Recent studies suggest that combustion noise could also be increased in these systems. New methods are needed to describe and understand the mechanisms at hand for future design and optimization in order to operate these engines safely while still achieving emission targets. Large Eddy Simulation (LES) is a numerical approach to these problems which has shown excellent results in the past and is very promising for future design. The description of unsteady phenomena in these power-dense, confined and unsteady systems is essential to describe flame-turbulence interactions, acoustics and multiphysic couplings. As computing power grows, so does the amount of physics which can be modeled. Computational domains can be increased, and have gone from including only the reacting zone, to adding the fuel-air mixing areas, the heat liners and secondary flows, and the upstream and downstream elements. In this Ph.D., a compressible LES solver named AVBP is used to describe an academic test rig operated at the EM2C laboratory named CESAM-HP, a pressurized combustion chamber containing a swirl-stabilized partially-premixed flame and ended by a choked nozzle with high-speed flow. This leads to an accurate description of the chamber outlet acoustic behavior, and offers the possibility to investigate the dynamic behavior of the full system, and the occurrence of flame-acoustic coupling leading to combustion instabilities. It also gives insight into the combustion noise mechanisms, which are known to occur both in the reacting zone and in the nozzle. As shown in this study, this behavior also has an impact on flame stabilization in this system. This manuscript is organized as follows. In a first part, the context for chemistry, motion and acoustics of reacting multi-species flow is given. State of the art theories on reacting multi-species flow thermodynamics, thermoacoustics, combustion noise and flame stabilization in swirled burners are presented. Basic toy models and test cases are derived to validate the understanding of direct and indirect combustion noise, and numerical validations are performed. In a second part, the practical details about numerical investigation of such systems are reported. Finally, the third part describes the application of these tools and methods to the CESAM-HP4 test rig. The inclusion of the compressible nozzle in the LES computation yields results concerning three major issues for the burner: (1) flame stability, related to thermoacoustic instabilities; (2) flame stabilization, and the occurrence of flame flashback into the system’s injection duct; (3) combustion noise produced by the system, and identification of its separate contributions.
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Hassanaly, Malik. "Large eddy simulations (LES) of boundary layer flashback in wall-bounded flows". Thesis, 2014. http://hdl.handle.net/2152/28248.
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In the design of high-hydrogen content gas turbines for power generation, flashback of the turbulent flame by propagation through the low velocity boundary layers in the premixing region is an operationally dangerous event. The high reactivity of hydrogen combined with enhanced flammability lim- its (compared to natural gas) promotes flame propagation along low-speed boundary layers adjoining the combustion walls. This work focuses on the simulation of boundary layer flashback using large-eddy simulations (LES). A canonical channel configuration is studied to assess the capabilities of LES and determine the modeling requirements for boundary layer flashback simulations. To extend this work to complex geometries, a new reactive low-Mach number solver has been written in an unstructured code.text
Części książek na temat "Flame flashbacks"
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Sun, Mingbo, Hongbo Wang, Zun Cai i Jiajian Zhu. "Flame Flashback in Supersonic Flows". W Unsteady Supersonic Combustion, 241–305. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-3595-6_5.
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"Flame Stabilization, Flashback, Flameholding, and Blowoff". W Unsteady Combustor Physics, 379–405. Wyd. 2. Cambridge University Press, 2021. http://dx.doi.org/10.1017/9781108889001.011.
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"Flame Flashback for Low Reynolds Number Flows". W Dynamics of Reactive Systems Part I: Flames; Part II: Heterogeneous Combustion and Applications, 367–83. Washington DC: American Institute of Aeronautics and Astronautics, 1988. http://dx.doi.org/10.2514/5.9781600865879.0367.0383.
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Benim, Ali Cemal, i Khawar J. Syed. "Flashback Due to Flame Propagation in Boundary Layers". W Flashback Mechanisms in Lean Premixed Gas Turbine Combustion, 59–71. Elsevier, 2015. http://dx.doi.org/10.1016/b978-0-12-800755-6.00008-8.
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Benim, Ali Cemal, i Khawar J. Syed. "Flashback Due to Turbulent Flame Propagation in the Core Flow". W Flashback Mechanisms in Lean Premixed Gas Turbine Combustion, 45–57. Elsevier, 2015. http://dx.doi.org/10.1016/b978-0-12-800755-6.00007-6.
Pełny tekst źródłaStreszczenia konferencji na temat "Flame flashbacks"
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Eichler, Christian, i Thomas Sattelmayer. "Experiments on Flame Flashback in a Quasi-2D Turbulent Wall Boundary Layer for Premixed Methane-Hydrogen-Air Mixtures". W ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-23401.
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Premixed combustion of hydrogen-rich mixtures involves the risk of flame flashback through wall boundary layers. For laminar flow conditions, the flashback mechanism is well understood and is usually correlated by a critical velocity gradient at the wall. Turbulent transport inside the boundary layer considerably increases the flashback propensity. Only tube burner setups have been investigated in the past and thus turbulent flashback limits were only derived for a fully-developed Blasius wall friction profile. For turbulent flows, details of the flame propagation in proximity to the wall remain unclear. This paper presents results from a new experimental combustion rig, apt for detailed optical investigations of flame flashbacks in a turbulent wall boundary layer developing on a flat plate and being subject to an adjustable pressure gradient. Turbulent flashback limits are derived from the observed flame position inside the measurement section. The fuels investigated cover mixtures of methane, hydrogen and air at various mixing ratios. The associated wall friction distributions are determined by RANS computations of the flow inside the measurement section with fully resolved boundary layers. Consequently, the interaction between flame back pressure and incoming flow is not taken into account explicitly, in accordance with the evaluation procedure used for tube burner experiments. The results are compared to literature values and the critical gradient concept is reviewed in light of the new data.
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Verma, Ishan, Rakesh Yadav, Naseem Ansari, Stefano Orsino, Shaoping Li i Pravin Nakod. "Modeling of Flashback With Different Blends of CH4 and H2 by Using Finite Rate Chemistry With Large Eddy Simulation". W ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/gt2022-82601.
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Abstract Due to its clean combustion characteristics, hydrogen fuel is gaining attention in power generation. New designs of engine systems and components are being explored to allow blending with the increasing amount of hydrogen in natural gas. Adding H2 increases the probability of flashback and often is one of the main constraints in using high H2 blends in premixed combustors. There are several mechanisms of flashback like boundary layer flashback, combustion induced vortex break down, turbulence in the flow, fluctuations in equivalence ratio, etc. Semi-empirical models, based on non-dimensional numbers and flame speed, have successfully predicted flashback propensity for a given operating condition. The semi-empirical models are computationally very efficient; however, they lack generality. A typical combustor can have multiple flashback mechanisms. The relative importance of each mechanism can change with a change in the combustor design or even with a difference in the operating conditions for the same combustor. Since prediction of flashback requires accurate modeling of highly transient chemistry phenomena and the impact of heat loss on chemistry, a viable detailed chemistry solution is preferred to model flashback. This paper describes the use of a finite rate chemistry model to predict flashbacks in a turbulent premixed combustor in this work. The configuration used is a swirl stabilized combustor (SimVal) from National Energy Technology Laboratory. The current computations are done with Finite Rate Chemistry (FRC) and Large Eddy Simulations (LES). Simulations are carried out for a varied percentage of CH4/H2 blends, ranging from 0% H2 to 100% H2 at a fixed equivalence ratio and inlet mass flow. As the percentage of H2 is increased in the fuel, flame speed also increases. With this, the propensity for flashbacks also increases. A 28-species reduced mechanism for CH4/H2 blend flames is used to keep the simulations computationally tractable. The simulations with the reduced mechanism are performed by considering non-adiabatic effects from heat loss near the walls and multi-component property considerations. This improves the accuracy of the FRC-LES simulations to capture the onset of boundary layer flashback towards the inlet. The simulations from FRC-LES suggest a fine mesh in the boundary layer for an accurate prediction that makes the simulations expensive. Therefore, an Adaptive Mesh Refinement (AMR) approach has been used for different CH4/H2 blends to accurately model the flashback without any loss in generality as the AMR criteria used here are applicable for a wide range of conditions. The FRC-based solution strategy proposed in this work provides a framework to model flashback for different blends without any case-specific tuning.
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Sattelmayer, Thomas, Christoph Mayer i Janine Sangl. "Interaction of Flame Flashback Mechanisms in Premixed Hydrogen-Air Swirl Flames". W ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-25553.
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An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen-air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed PIV/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approx. 1/3 of the typical flow velocities in gas turbine burners. In that range the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approx. 0.45 and delivers NOx-emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.
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Ebi, Dominik, i Noel T. Clemens. "Flow-flame interaction in turbulent boundary layer flashback of swirl flames". W Ninth International Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2015. http://dx.doi.org/10.1615/tsfp9.360.
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Hoferichter, Vera, Christoph Hirsch i Thomas Sattelmayer. "Prediction of Boundary Layer Flashback Limits of Laminar Premixed Jet Flames". W ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-75546.
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Preventing flame flashback into the premixing section is one of the major challenges in premixed combustion systems. For jet flames, the flame typically propagates upstream inside the low velocity region close to the burner wall, referred to as boundary layer flashback. The physical mechanism of boundary layer flashback of laminar flames is mainly influenced by flame-wall interaction and flame quenching. Flashback is initiated if the burning velocity at some wall distance is higher than the local flow velocity. Since the burning velocity drops towards the wall due to heat losses, the wall distance of flashback can be defined at the location closest to the wall where the burning velocity still is sufficiently high. The well-established critical gradient concept of Lewis and von Elbe to predict flashback limits of laminar flames represents these assumptions but neglects the important influence of flame stretch on the burning velocity close to the wall. For that reason, a modified prediction model is developed in this work based on similar assumptions as in the critical gradient concept, but including the effect of flame stretch. A validation for hydrogen-air and methane-air flames highlights its advantages compared to the critical gradient concept and shows good prediction accuracy.
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Hoferichter, Vera, i Thomas Sattelmayer. "Boundary Layer Flashback in Premixed Hydrogen-Air Flames With Acoustic Excitation". W ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-63080.
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Lean premixed combustion is prevailing in gas turbines to minimize nitrogen oxide emissions. However, this technology bears the risk of flame flashback and thermoacoustic instabilities. Thermoacoustic instabilities induce velocity oscillations at the burner exit which, in turn, can trigger flame flashback. This article presents an experimental study at ambient conditions on the effect of longitudinal acoustic excitation on flashback in the boundary layer of a channel burner. The acoustic excitation simulates the effect of thermoacoustic instabilities. Flashback limits are determined for different excitation frequencies characterizing intermediate frequency dynamics in typical gas turbine combustors (100–350 Hz). The excitation amplitude is varied from 0 to 36 % of the burner bulk flow velocity. For increasing excitation amplitude, the risk of flame flashback increases. This effect is strongest at low frequencies. For increasing excitation frequency the influence of the velocity oscillations decreases as the flame has less time to follow the changes in bulk flow velocity. Two different flashback regimes can be distinguished based on excitation amplitude. For low excitation amplitudes flashback conditions are reached if the minimum flow velocity in the excitation cycle falls below the flashback limit of unexcited unconfined flames. For higher excitation amplitudes, where the flame starts to periodically enter the burner duct, flashback is initiated if the maximum flow velocity in the excitation cycle is lower than the flashback limit of confined flames. Consequently, flashback limits of confined flames should also be considered in the design of gas turbine burners as a worst case scenario.
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Eichler, Christian, Georg Baumgartner i Thomas Sattelmayer. "Experimental Investigation of Turbulent Boundary Layer Flashback Limits for Premixed Hydrogen-Air Flames Confined in Ducts". W ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45362.
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The design of flashback-resistant premixed burners for hydrogen-rich fuels is strongly dependent on reliable turbulent boundary layer flashback limits, since this process can be the dominant failure type for mixtures with high burning velocities. So far, the flashback data published in literature is based on tube burner experiments with unconfined flames. However, this flame configuration may not be representative for the most critical design case, which is a flame being already present inside the duct geometry. In order to shed light on this potential misconception, boundary layer flashback limits have been measured for unconfined and confined flames in fully premixed hydrogen-air mixtures at atmospheric conditions. Two duct geometries were considered, a tube burner and a quasi-2D turbulent channel flow. Furthermore, two confined flame holding configurations were realized, a small backward-facing step inside the duct and a ceramic tile at high temperature, which was mounted flush with the duct wall. While the measured flashback limits for unconfined tube burner flames compare well with literature results, a confinement of the stable flame leads to a shift of the flashback limits towards higher critical velocity gradients, which are in good agreement between the tube burner and the quasi-2D channel setup. The underestimation of flashback propensity resulting from unconfined tube burner experiments emerges from the physical situation at the burner rim. Heat loss from the flame to the wall results in a quenching gap, which causes a radial leakage flow of fresh gases. This flow in turn tends to increase the quenching distance, since it constitutes an additional convective heat loss. On the one hand, the quenching gap reduces the local adverse pressure gradient on the boundary layer. On the other hand, the flame base is pushed outward, which deters the flame from entering the boundary layer region inside the duct. The flashback limits of confined flames stabilized at backward-facing steps followed this interpretation, and experiments with a flush ceramic flame holder constituted the upper limit of flashback propensity. It is concluded that the distribution of the flame backpressure and the flame position itself are key parameters for the determination of meaningful turbulent boundary layer flashback limits. For a conservative design path, the present results obtained from confined flames should be considered instead of unconfined tube burner values.
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Hoferichter, Vera, Christoph Hirsch i Thomas Sattelmayer. "Prediction of Confined Flame Flashback Limits Using Boundary Layer Separation Theory". W ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56155.
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Premixed combustion is a common technology applied in modern gas turbine combustors to minimize nitrogen oxide emissions. However, early mixing of fuel and oxidizer opens up the possibility of flame flashback into the premixing section upstream of the combustion chamber. Especially for highly reactive fuels boundary layer flashback is a serious challenge. For high preheating and burner surface temperatures, boundary layer flashback limits for burner stabilized flames converge to those of so-called confined flames, where the flame is stabilized inside the burner duct. Hence, the prediction of confined flashback limits is a highly technically relevant task. In this study, a predictive model for flashback limits of confined flames is developed for premixed hydrogen-air mixtures. As shown in earlier studies, confined flashback is initiated by boundary layer separation upstream of the flame tip. Hence, the flashback limit can be predicted identifying the minimum pressure rise upstream of a confined flame causing boundary layer separation. For this purpose, the criterion of Stratford is chosen which was originally developed for boundary layer separation in mere aerodynamic phenomena. It is shown in this paper that it can also be applied to near wall combustion processes if the pressure rise upstream of the flame tip is modeled correctly. In order to determine the pressure rise, an expression for the turbulent burning velocity is derived including the effects of flame stretch and turbulence. A comparison of the predicted flashback limits and experimental data shows high prediction accuracy and wide applicability of the developed model.
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Choi, Minjun, Inyeong Gu, Youngjun Shin, Eun-Seong Cho, Jeongjae Hwang, Min Kuk Kim i Dong-Hyuk Shin. "Development of Near-Wall Treatment to Improve Flame Flashback Prediction for Hydrogen Flames". W ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-101199.
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Abstract Numerical investigations on prediction of flashback of a lean premixed hydrogen flame in an industrial gas turbine combustor were conducted. Three combustion models were tested for prediction capabilities: (i) the flamelet-generated manifold-finite rate (FGM-FR) model, (ii) the flamelet-generated manifold-turbulent flame speed (FGM-ST) model, and (iii) the eddy dissipation concept (EDC) model. Without an additional wall damping model, the three models are unable to predict the flame flashback limit correctly. A wall damping model was applied to modify the reaction rate near the wall. With certain values of the wall damping coefficient, the FGM-FR and FGM-ST models successfully predict the flame flashback limit.
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Noble, David R., Qingguo Zhang, Akbar Shareef, Jeremiah Tootle, Andrew Meyers i Tim Lieuwen. "Syngas Mixture Composition Effects Upon Flashback and Blowout". W ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90470.
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This paper reports experimental data on flashback and lean blowout characteristics of H2/CO/CH4 mixtures. Data were obtained over a range of fuel compositions at fixed approach or burned flow velocity, reactant temperature, and combustor pressure at several conditions up to 4.4 atm and 470 K inlet reactants temperature. Consistent with prior studies, these results indicate that the percentage of H2 in the fuel dominates the mixture blowout characteristics. These blowout characteristics can be captured with classical Damko¨hler number scalings to predict blowoff equivalence ratios to within 10%. Counter-intuitively, the percentage of hydrogen had far less effect on flashback characteristics, at least for fuels with hydrogen mole fractions less than 60%. This is due to the fact that two mechanisms of “flashback” were noted: rapid flashback into the premixer, presumably through the boundary layer, and movement of the static flame position upstream along the centerbody. The former and latter mechanisms were observed at high and low hydrogen concentrations. In the latter mechanism, flame temperature, not flame speed, appears to be the key parameter describing flashback tendencies. We suggest that this is due to an alteration of the vortex breakdown location by the adverse pressure gradient upstream of the flame, similar to the mechanism proposed by Sattelmayer and co-workers [1]. As such, a key conclusion here is that classical flashback scalings derived from, e.g., Bunsen flames, may not be relevant for many parameter regimes found in swirling flames.
Raporty organizacyjne na temat "Flame flashbacks"
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Clemens, Noel. Large Eddy Simulation Modeling of Flashback and Flame Stabilization in Hydrogen-Rich Gas Turbines Using a Hierarchical Validation Approach. Office of Scientific and Technical Information (OSTI), wrzesień 2015. http://dx.doi.org/10.2172/1253136.
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Clemens, Noel, i Venkat Raman. Predictive LES Modeling and Validation of High-Pressure Turbulent Flames and Flashback in Hydrogen-enriched Gas Turbines. Office of Scientific and Technical Information (OSTI), kwiecień 2019. http://dx.doi.org/10.2172/1506058.
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Kalantari, Alireza, Elliot Sullivan-Lewis i Vincent McDonell. Development of Criteria for Flashback Propensity in Jet Flames for High Hydrogen Content and Natural Gas Type Fuels. Office of Scientific and Technical Information (OSTI), październik 2016. http://dx.doi.org/10.2172/1357931.
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Ihme, Matthias, i James Driscoll. Development and Experimental Validation of Large Eddy Simulation Techniques for the Prediction of Combustion-Dynamic Process in Syngas Combustion: Characterization of Autoignition, Flashback, and Flame-Liftoff at Gas-Turbine Relevant Operating Conditions. Office of Scientific and Technical Information (OSTI), sierpień 2015. http://dx.doi.org/10.2172/1337558.
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