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Artykuły w czasopismach na temat "Flame geometrics"
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Sun, Y., N. Liu i W. Gao. "Experimental Study on Geometrical Characteristics of a Square Turbulent Buoyant Jet Flame". Journal of Physics: Conference Series 2442, nr 1 (1.02.2023): 012020. http://dx.doi.org/10.1088/1742-6596/2442/1/012020.
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Abstract This paper gives the experimental results for the buoyant jet diffusion flame in square burners. The flame height and lift-off were measured and discussed. The results show that the normalized flame height and lift-off height of square flames are lower than that of round flames with the same experimental conditions, which indicates enhanced air entrainment in square flames. The model of flame height based on the flame Froude-number, which integrates a correction factor to account for the enhancement of air entrainment, reasonably collapses the square flame data under different experimental cases. The critical Froude number for the transition from buoyancy to momentum controlled regime of a square jet flame is highly dependent on the fuel type and burner size. The lift-off height of the square jet flames increases linearly when the initial velocity increases, but also depends on the fuel type and burner size. A unified correlation using a dimensionless flow number derived from the mixedness-reactedness flamelet model is established, which reasonably predicts the lift-off distances of square jet flames.
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Villani, Manfredi, i Phillip Aquino. "Turbulent Flame Geometry Measurements in a Mass-Production Gasoline Direct Injection Engine". Energies 13, nr 1 (1.01.2020): 189. http://dx.doi.org/10.3390/en13010189.
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Direct optical access to the combustion chamber of a gasoline direct injection (GDI) engine provides extremely valuable information about the combustion process. Experimental measurements of the geometric characteristics of the turbulent flame—such as the flame radius, flame center, flame edges and flame brush thickness—are of fundamental interest in support of the development and validation of any combustion model. To determine the macroscopic properties of sprays and flames, visualization and digital image processing techniques are typically used in controlled experimental setups like single-cylinder optical engines or closed vessels, while optical measurements on mass-production engines are more uncommon. In this paper the optical experimental setup (consisting of a high-speed camera, a laser light source and a data acquisition system) used to characterize the planar turbulent flame propagation in the cylinder of a 3.5 L GDI V6 mass-production engine, is described. The image acquisition process and the image processing that is necessary to evaluate the geometric characteristics of the propagating flame front, which are usually omitted in the referenced literature, are reported in detail to provide a useful guideline to other researchers. The results show that the step-by-step algorithm and the calculation formulae proposed allow to retrieve clear visualizations of the propagating flame front and measurements of its geometrical properties.
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Hicks, E. P. "Rayleigh–Taylor unstable flames at higher Reynolds number". Monthly Notices of the Royal Astronomical Society 489, nr 1 (30.07.2019): 36–51. http://dx.doi.org/10.1093/mnras/stz2080.
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ABSTRACT Rayleigh–Taylor (RT) unstable flames are a key component of Type Ia and Iax supernovae explosions, but their complex hydrodynamics is still not well understood. These flames are affected not only by the RT instability, but also by the turbulence it generates. Both processes can increase the flame speed by stretching and wrinkling the flame. This makes it hard to choose a subgrid model for the flame speed in full star Type Ia or Iax simulations. Commonly used subgrid models get around this difficulty by assuming that either the RT instability or turbulence is dominant and sets the flame speed. In previous work, we evaluated the physical assumptions and predictive abilities of these two types of models by analysing a large parameter study of 3D direct numerical simulations of RT unstable flames. Surprisingly, we found that the flame dynamics is dominated by the RT instability and that RT unstable flames are very different from turbulent flames. In particular, RT unstable flames are thinner rather than thicker when turbulence is strong. In addition, none of the turbulent flame speed models adequately predicted the flame speed. We also showed that the RT flame speed model failed when the RT instability was strong, suggesting that geometrical burning effects also influence the flame speed. However, these results depended on simulations with Re ≲ 720. In this paper, we extend the parameter study to higher Reynolds number and show that the basic conclusions of our previous study still hold when the RT-generated turbulence is stronger.
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Thiesset, F., F. Halter, C. Bariki, C. Lapeyre, C. Chauveau, I. Gökalp, L. Selle i T. Poinsot. "Isolating strain and curvature effects in premixed flame/vortex interactions". Journal of Fluid Mechanics 831 (13.10.2017): 618–54. http://dx.doi.org/10.1017/jfm.2017.641.
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This study focuses on the response of premixed flames to a transient hydrodynamic perturbation in an intermediate situation between laminar stretched flames and turbulent flames: an axisymmetric vortex interacting with a flame. The reasons motivating this choice are discussed in the framework of turbulent combustion models and flame response to the stretch rate. We experimentally quantify the dependence of the flame kinematic properties (displacement and consumption speeds) to geometrical scalars (stretch rate and curvature) in flames characterized by different effective Lewis numbers. Whilst the displacement speed can be readily measured using particle image velocimetry and tomographic diagnostics, providing a reliable estimate of the consumption speed from experiments remains particularly challenging. In the present work, a method based on a budget of fuel on a well chosen domain is proposed and validated both experimentally and numerically using two-dimensional direct numerical simulations of flame/vortex interactions. It is demonstrated that the Lewis number impact neither the geometrical nor the kinematic features of the flames, these quantities being much more influenced by the vortex intensity. While interacting with the vortex, the flame displacement (at an isotherm close to the leading edge) and consumption speeds are found to increase almost independently of the type of fuel. We show that the total stretch rate is not the only scalar quantity impacting the flame displacement and consumption speeds and that curvature has a significant influence. Experimental data are interpreted in the light of asymptotic theories revealing the existence of two distinct Markstein numbers, one characterizing the dependence of flame speed to curvature, the other to the total stretch rate. This theory appears to be well suited for representing the evolution of the displacement speed with respect to either the total stretch rate, curvature or strain rate. It also explains the limited dependence of the flame displacement speed to Lewis number and the strong correlation with curvature observed in the experiments. An explicit relationship between displacement and consumption speeds is also given, indicating that the fuel consumption rate is likely to be altered by both the total stretch rate and curvature.
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Smyth, N. F. "Propagation of flame fronts". Journal of the Australian Mathematical Society. Series B. Applied Mathematics 31, nr 4 (kwiecień 1990): 385–96. http://dx.doi.org/10.1017/s0334270000006743.
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AbstractThe propagation of a flame front in a combusting gas is considered in the limit in which the width of the reaction-zone is small compared with some overall flow dimension. In this approximation, the front propagates along its normals at a speed dependent on the local curvature of the front and is governed by a nonlinear equivalent of the geometric optics equations. Some exact solutions of this equation are found and a numerical scheme is developed to solve the equation for more complicated geometries.
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Adebiyi, Abdulafeez, Olatunde Abidakun i V’yacheslav Akkerman. "Acceleration of Premixed Flames in Obstructed Pipes with Both Extremes Open". Energies 13, nr 16 (7.08.2020): 4094. http://dx.doi.org/10.3390/en13164094.
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Premixed flame propagation in obstructed channels with both extremes open is studied by means of computational simulations of the reacting flow equations with a fully-compressible hydrodynamics, transport properties (heat conduction, diffusion and viscosity) and an Arrhenius chemical kinetics. The aim of this paper is to distinguish and scrutinize various regimes of flame propagation in this configuration depending on the geometrical and thermal-chemical parameters. The parametric study includes various channel widths, blockage ratios, and thermal expansion ratios. It is found that the interplay of these three critical parameters determines a regime of flame propagation. Specifically, either a flame propagates quasi-steady, without acceleration, or it experiences three consecutive distinctive phases (quasi-steady propagation, acceleration and saturation). This study is mainly focused on the flame acceleration regime. The accelerating phase is exponential in nature, which correlates well with the theoretical prediction from the literature. The accelerating trend also qualitatively resembles that from semi-open channels, but acceleration is substantially weaker when both extremes are open. Likewise, the identified regime of quasi-steady propagation fits the regime of flame oscillations, found for the low Reynolds number flames. In addition, the machine learning logistic regression algorithm is employed to characterize and differentiate the parametric domains of accelerating and non-accelerating flames.
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Chien, Yu-Chien, i Derek Dunn-Rankin. "Combustion Characteristics of Methane Hydrate Flames". Energies 12, nr 10 (21.05.2019): 1939. http://dx.doi.org/10.3390/en12101939.
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This research studies the structure of flames that use laboratory-produced methane hydrates as fuel, specifically for the purpose of identifying their key combustion characteristics. Combustion of a methane hydrate involves multiple phase changes, as large quantities of solid clathrate transform into fuel gas, water vapor, and liquid water during burning. With its unique and stable fuel energy storage capability, studies in combustion are focused on the potential usage of hydrates as an alternative fuel source or on their fire safety. Considering methane hydrate as a conventional combustion energy resource and studying hydrate combustion using canonical experimental configurations or methodology are challenges. This paper presents methane hydrate flame geometries from the time they can be ignited through their extinguishment. Ignition and burning behavior depend on the hydrate initial temperature and whether the clathrates are chunks or monolithic shapes. These behaviors are the subject of this research. Physical properties that affect methane hydrate in burning can include packing density, clathrate fraction, and surface area. Each of these modifies the time or the temperature needed to ignite the hydrate flames as well as their subsequent burning rate, thus every effort is made to keep consistent samples. Visualization methods used in combustion help identify flame characteristics, including pure flame images that give reaction zone size and shape and hydrate flame spectra to identify important species. The results help describe links between hydrate fuel characteristics and their resulting flames.
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Abam, D. P. S. "Methane Combustion in Laminar Diffusion Flames". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power Engineering 203, nr 1 (luty 1989): 65–72. http://dx.doi.org/10.1243/pime_proc_1989_203_008_02.
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This paper is concerned with methane combustion in laminar diffusion flames. Data on methane concentration distributions in different diffusion flame geometries are correlated against a conserved scalar called mixture fraction. The correlation is used to determine a global methane combustion rate applicable in the rich to stoichiometric regions of laminar diffusion flames. The global rate is consistent with methane disappearance through the forward kinetic step: CH4 + H → CH3 + H2 with [H] equilibrated according to [Formula: see text] on the rich side. This equilibration results from the three-body reaction [Formula: see text] which is equilibrated in the region 1.1 ≤ φ ≤ 2.74, 1300 K ≤ T ≤ 2000 K. These results indicate that initial radical attack on the fuel molecule provides the rate-controlling step for methane combustion.
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Sattelmayer, T., W. Polifke, D. Winkler i K. Do¨bbeling. "NOx-Abatement Potential of Lean-Premixed GT Combustors". Journal of Engineering for Gas Turbines and Power 120, nr 1 (1.01.1998): 48–59. http://dx.doi.org/10.1115/1.2818087.
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The influence of the structure of perfectly premixed flames on NOx formation is investigated theoretically. Since a network of reaction kinetics modules and model flames is used for this purpose, the results obtained are independent of specific burner geometries. Calculations are presented for a mixture temperature of 630 K, an adiabatic flame temperature of 1840 K, and 1 and 15 bars combustor pressure. In particular, the following effects are studied separately from each other: • molecular diffusion of temperature and species; • flame strain; • local quench in highly strained flames and subsequent reignition; • turbulent diffusion (no preferential diffusion); • small scale mixing (stirring) in the flame front. Either no relevant influence or an increase in NOx production over that of the one-dimensional laminar flame is found. As a consequence, besides the improvement of mixing quality, a future target for the development of low-NOx burners is to avoid excessive turbulent stirring in the flame front. Turbulent flames that exhibit locally and instantaneously near laminar structures (“flamelets”) appear to be optimal. Using the same methodology, the scope of the investigation is extended to lean-lean staging, since a higher NOx-abatement potential can be expected in principle. As long as the chemical reactions of the second stage take place in the boundary between the fresh mixture of the second stage and the combustion products from upstream, no advantage can be expected from lean-lean staging. Only if the primary burner exhibits much poorer mixing than the second stage can lean-lean staging be beneficial. In contrast, if full mixing between the two stages prior to afterburning can be achieved (lean-mix-lean technique), the combustor outlet temperature can in principle be increased somewhat without NO penalty. However, the complexity of such a system with a larger flame tube area to be cooled will increase the reaction zone temperatures, so that the full advantage cannot be realized in an engine. Of greater technical relevance is the potential of a lean-mixlean combustion system within an improved thermodynamic cycle. A reheat process with sequential combustion is perfectly suited for this purpose, since, first, the required low inlet temperature of the second stage is automatically generated after partial expansion in the high pressure turbine, second, the efficiency of the thermodynamic cycle has its maximum and, third, high exhaust temperatures are generated, which can drive a powerful Rankine cycle. The higher thermodynamic efficiency of this technique leads to an additional drop in NOx emissions per power produced.
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Winkler, Dieter, Weiqun Geng, Geoffrey Engelbrecht, Peter Stuber, Klaus Knapp i Timothy Griffin. "Staged combustion concept for gas turbines". Journal of the Global Power and Propulsion Society 1 (27.09.2017): CVLCX0. http://dx.doi.org/10.22261/cvlcx0.
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AbstractGas turbine power plants with high load flexibility are particularly suitable to compensate power fluctuations of wind and solar plants. Conventional gas turbines suffer from higher emissions at low load operation. With the objective of improving this situation a staged combustion system has been investigated. At low gas turbine load an upstream stage (first stage) provides stable combustion at low emissions while at higher loads the downstream stage (second stage) is started to supplement the power. Three injection geometries have been studied by means of computational fluid dynamics (CFD) simulations and atmospheric tests. The investigated geometries were a simple annular gap, a jet-in-cross-flow configuration and a lobe mixer. With CFD simulations the quality of mixing of second stage fresh gas with first stage exhaust gas was assessed. The lobe mixer showed the best mixing quality and hence was expected to also be the best variant in terms of combustion. However atmospheric combustion tests showed lower emissions for the jet-in-cross-flow configuration. Comparing flame photos in the visible and ultraviolet (UV) range suggest that the flame might be lifted off for the lobe mixer, leading to insufficient time for carbon monoxide (CO) burnout. CFD analysis of turbulent flame speed, turbulence and strain rates support the hypotheses of lifted off flame. Overall the staged concept was found to show very promising results not only with natural gas but also with natural gas enriched with propane or hydrogen. The investigations showed that apart from having an efficient and compact mixing of the two stages it is also very important to design the flow field such that the second flame can be anchored properly in order to achieve compact flames with sufficient time for CO burnout.
Rozprawy doktorskie na temat "Flame geometrics"
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Bjorkhaug, M. "Flame acceleration in obstructed radial geometries". Thesis, City University London, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374279.
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Gabriel, Silva Vitor [Verfasser], i Ulrich [Gutachter] Krause. "Flame propagation in complex geometries / Vitor Gabriel Silva ; Gutachter: Ulrich Krause". Magdeburg : Universitätsbibliothek Otto-von-Guericke-Universität, 2020. http://d-nb.info/1219966495/34.
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Gabriel, Silva Vitor Verfasser], i Ulrich [Gutachter] [Krause. "Flame propagation in complex geometries / Vitor Gabriel Silva ; Gutachter: Ulrich Krause". Magdeburg : Universitätsbibliothek Otto-von-Guericke-Universität, 2020. http://d-nb.info/1219966495/34.
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Kučiš, Michal. "Simulace vlastností objektivu". Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2012. http://www.nusl.cz/ntk/nusl-236575.
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Computer vision algorithms typically process real world image data acquired by cameras or video cameras. Such image data suffer from imperfections cause by the acquisition process. This paper focuses on simulation of the acquisition process on simulation of the acquisition process in order to enable rendering of images based on a 3D generated model. Imperfections, such as geometry distorion, chromatic aberration, depth of field effect, motion blur, vignetting and lens flare are considered.
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Harshavardhana, A. U. "Flame Particle Tracking Analysis of Turbulence-Premixed Flame Interaction". Thesis, 2018. http://etd.iisc.ac.in/handle/2005/4187.
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This work describes the computational and theoretical developments made in the understanding of turbulence-premixed flame interaction, using both lean and rich H2-air mixtures, in a flow field of near-isotropic turbulence. Two classical flame geometries are considered for the present study viz., 1) statistically planar flame in an in flow-out flow channel (type-I) and 2) premixed igniting flame kernel in a box (type-II). These simple geometries, which could be considered as building blocks of turbulent flames in practical combustors, elucidate the intricate physics of turbulence-premixed ame interaction. In the present work, using direct numerical simulations (DNS) and flame particle tracking (FPT) framework, we investigate two cases of turbulent premixed flames: 1) an intensely burning flame, and 2) extinguishing ignition kernels.
The interaction between turbulence, molecular transport, and energy transport coupled with chemistry determine the characteristics of intensely turbulent premixed flames such as the evolution of flame surface geometry, propagation, annihilation, and local extinction/re-ignition. In the first part of the thesis, we describe the turbulence-premixed flame interactions for intensely burning turbulent premixed flames using the type-I configuration. The objective is to 1) understand the behavior of ame displacement speed (Sd) in the negatively curved regions and/or flame islands, corresponding to two different isotherms (665 K and 1321 K), which eventually dissolve in the product gases, and 2) decipher the role of transport in this behavior. This is carried out by considering lean H2-air mixtures ( = 0:81 and 0:7; Le < 1). DNS computations are performed with different initial conditions and turbulence intensity levels and FPT is used to analyze these Eulerian datasets. An increase in Sd with time for the annihilating regions of isotherms is a common trend observed across four simulation conditions considered. Further investigation reveals that the sharp increase in Sd is due to:
1) heat conduction, 2) increased negative curvature of the flame surface, and 3) eventual
homogenization of temperature gradients (jrT j ! 0). The curves of normalized flame displacement speed (hSd=SL;T i) vs. stretch rate (hKaSi) in the normalized time for four different cases of turbulence intensity levels collapse on a narrow band for < 1, suggesting a
unified behavior in the Lagrangian description. Principal curvature evolution statistics show an ellipsoidal geometry for the annihilating ame islands/pockets.
The second part of the thesis addresses the extinction dynamics of igniting kernels in a rich H2-air ( = 4; Le > 1) premixture in near-isotropic turbulence. This is accomplished using the configuration of type-II. Here, the analysis procedures, DNS and FPT remain the same as mentioned earlier. Turbulence is found to extinguish a freshly ignited, initially spherical premixed ame kernel, which otherwise sustains in a quiescent flow field by propagating beyond the minimum radius. The mechanism of kernel extinction is investigated by tracking lifetime trajectories of ame particles on an O2 mass-fraction iso-surface in the ame displacement speed-curvature (Sd ) space using the well-known concept of minimum radius from laminar flames. The classical S -curve in the temperature-Damkohler number (T Da) space was also analyzed. Ensemble-averaged Sd and S -curves display corresponding turning points which help to elucidate the intricate mechanisms involved in turbulent ignition kernel extinction dynamics. Turbulence locally wrinkles the YO2 iso-surface to positively curved structures
2 which lead to turning points in Sd space, such that the minimum radius is never reached either locally or as an ensemble. A budget analysis of the principal curvature evolution equation highlights the role of turbulence in bending the surface to form positively curved pointed structures where heat loss is enhanced, further lowering Da towards extinction.
The novel Lagrangian viewpoint of flame particle tracking applied on solutions of DNS thus emerges as a powerful tool where turbulence, flame, and their interaction dynamics can be systematically analyzed. These eventually provide unified viewpoints of local flame propagation and flame extinction in turbulence.
Książki na temat "Flame geometrics"
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1947-, Evans James W., Setiabudi Dody i Forest Products Laboratory (U.S.), red. Flake furnish characterization: Modeling board properties with geometric descriptors. Madison, WI (One Gifford Pinchot Dr., Madison, 53705-2398): U.S. Dept. of Agriculture, Forest Service, Forest Products Laboratory, 1999.
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Flake Furnish Characterization, Modeling Board Properties With Geometric Descriptors... Research Paper FPL-RP-577... U.S. Department Of Agriculture. [S.l: s.n., 1999.
Znajdź pełny tekst źródłaCzęści książek na temat "Flame geometrics"
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Xing, V., i C. J. Lapeyre. "Deep Convolutional Neural Networks for Subgrid-Scale Flame Wrinkling Modeling". W Lecture Notes in Energy, 149–74. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-16248-0_6.
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AbstractSubgrid-scale flame wrinkling is a key unclosed quantity for premixed turbulent combustion models in large eddy simulations. Due to the geometrical and multi-scale nature of flame wrinkling, convolutional neural networks are good candidates for data-driven modeling of flame wrinkling. This chapter presents how a deep convolutional neural network called a U-Net is trained to predict the total flame surface density from the resolved progress variable. Supervised training is performed on a database of filtered and downsampled direct numerical simulation fields. In an a priori evaluation on a slot burner configuration, the network outperforms classical dynamic models. In closing, challenges regarding the ability of deep convolutional networks to generalize to unseen configurations and their practical deployment with fluid solvers are discussed.
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Kupervasser, Oleg. "Dynamics and Wrinkling of Radially Propagating Fronts Inferred from Scaling Laws in Channel Geometries". W Pole Solutions for Flame Front Propagation, 67–83. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-18845-4_4.
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Conceição, Eusébio, João Gomes, Maria Manuela Lúcio, Domingos Xavier Viegas i Maria Teresa Viegas. "Two-dimensional model of heat transfer in a pine trunk under the influence of a forest fire environment". W Advances in Forest Fire Research 2022, 1789–95. Imprensa da Universidade de Coimbra, 2022. http://dx.doi.org/10.14195/978-989-26-2298-9_277.
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This paper presents a study on two-dimensional model of heat transfers in a pine tree trunk under the influence of a forest fire environment. In this study, a thermal response model of the tree trunk was developed, starting from a geometric model of complex topology of the trunk obtained using mesh generation. The thermal response model of the tree trunk is founded on energy and mass equations. In energy equations, heat exchanges are considered by conduction inside the tree trunk, by convection between the outside surface of the tree trunk and the surrounding environment and by radiation between the outside surface of the tree trunk and the surrounding area including the fire front. The heat exchanges by radiation between the tree trunk and the fire front are calculated using view factors obtained taking into account the geometric model of the tree trunk. In the numerical simulation, the forest fire environment is represented by a fire front, 10 m wide and 1 m high, which moves, with an inclination of 45º, at a constant speed. The numerical results of the temperature distribution tree trunk were obtained for a wind speed of 5 m/s and an average flame temperature of 500ºC. These results allow us to locate the tissues of the tree trunk that will reach lethal conditions.
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"Simple Models of Constant Flames in Three Partially Confined Geometries". W Dynamics of Reactive Systems Part I: Flames and Configurations; Part II: Modeling and Heterogeneous Combustion, 180–91. New York: American Institute of Aeronautics and Astronautics, 1986. http://dx.doi.org/10.2514/5.9781600865794.0180.0191.
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Paquet, A. F., i B. M. Paquet. "Estimating an Enclosure Temperature During Solid Propellant Fires". W Future Developments in Explosives and Energetics, 176–88. Royal Society of Chemistry, 2023. http://dx.doi.org/10.1039/9781788017855-00176.
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In any industrial energetic facility, it is useful to predict the effect of an accidental fire. Solid propellants are designed to quickly transform into high temperature gases. It is therefore necessary to predict the pressure evolution during a confined fire. Some methods are semi-empirical and thus do not depend on many thermodynamic variables. Other methods are numerical and require that many variables be defined. In any safety application, choosing the right method will depend on the risks involved, possible consequences and means available. Lack of precise knowledge of these variables is often what discourages facilities and equipment designers from modelling the behaviour of their systems. One such variable is the temperature in an enclosure during a fire for which the pressure generation is the main concern. For events involving low charge densities, using the flame temperature is an over-approximation. Assuming instantaneous perfect mixing of the enclosure air and combustion gases results in an under-approximation. In this paper, these approximations will first be considered compared to an event sequence. Three temperature models will be reviewed. Firstly, a simple model will consider the geometric mean of the previously described extreme values. Secondly, the radiative heating of the enclosure air due to a localized fire source will be studied. Finally, a finite volume multidimensional numerical model which includes turbulence effects will be presented. These three methods are seen to be of increasing complexity and will be compared to the event timescale. This timescale will help indicate if the level of complexity is warranted.
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Paquet, A. F., i B. M. Paquet. "Estimating an Enclosure Temperature During Solid Propellant Fires". W Future Developments in Explosives and Energetics, 176–88. Royal Society of Chemistry, 2023. http://dx.doi.org/10.1039/9781839162350-00176.
Pełny tekst źródłaStreszczenie:
In any industrial energetic facility, it is useful to predict the effect of an accidental fire. Solid propellants are designed to quickly transform into high temperature gases. It is therefore necessary to predict the pressure evolution during a confined fire. Some methods are semi-empirical and thus do not depend on many thermodynamic variables. Other methods are numerical and require that many variables be defined. In any safety application, choosing the right method will depend on the risks involved, possible consequences and means available. Lack of precise knowledge of these variables is often what discourages facilities and equipment designers from modelling the behaviour of their systems. One such variable is the temperature in an enclosure during a fire for which the pressure generation is the main concern. For events involving low charge densities, using the flame temperature is an over-approximation. Assuming instantaneous perfect mixing of the enclosure air and combustion gases results in an under-approximation. In this paper, these approximations will first be considered compared to an event sequence. Three temperature models will be reviewed. Firstly, a simple model will consider the geometric mean of the previously described extreme values. Secondly, the radiative heating of the enclosure air due to a localized fire source will be studied. Finally, a finite volume multidimensional numerical model which includes turbulence effects will be presented. These three methods are seen to be of increasing complexity and will be compared to the event timescale. This timescale will help indicate if the level of complexity is warranted.
Streszczenia konferencji na temat "Flame geometrics"
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Knapton, Jonathan N., Simon Blakey i Frank Nicolleau. "Understanding the Effects of Fractal Blockage Geometries on Flame Acceleration in Propane-Air Flames". W 51st AIAA/SAE/ASEE Joint Propulsion Conference. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2015. http://dx.doi.org/10.2514/6.2015-4147.
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Hariharan, P., C. Periasamy i S. R. Gollahalli. "Aspect Ratio Effects on Partially Premixed Flames From Elliptic Burners in Coflow". W ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-13109.
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In this paper, partially premixed flames of propane-hydrogen blends from elliptic burner geometries in coflow environment have been experimentally studied. Two different elliptic burner geometries with aspect ratios (AR) of 3:1 and 4:1 were used. A circular burner with the same discharge area as that of the elliptic burner was employed for comparison. Measurements were taken at stoichiometric and three other equivalence ratios. Global flame characteristics such as visible height, emission indices, and flame radiation were measured. Flame structure data such as transverse profiles of inflame concentrations of combustion products and local flame temperature were also measured at three axial locations in the flame. Results indicate that elliptic burner flames were shorter, more radiating, and produced lower NO and CO emissions than the corresponding circular burner flames. Results from the inflame measurements of NO and CO were in good agreement with the corresponding global data. Further, the 4:1 AR elliptic burners exhibited a twin-jet flame structure at fuel-rich conditions. The twin-flame structure was evident from the inflame measurements of temperature and combustion species. This study suggests that the combination of elliptic burner geometry and coflow reduces NO and CO emissions from combustion systems, which could potentially lead to cleaner environment.
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Yalcinkaya, Yagiz, Ogeday E. Bozkurt i Ayse G. Gungor. "Influence of Pressure Gradient on Flame-Vortex Interaction and Flame Stability". W ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/gt2022-82517.
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Abstract This study presents numerical investigations of turbulent premixed bluff-body stabilized flame by emphasizing the influence of pressure gradient on flame-vortex interaction and flame stability for lean combustion applications. Large eddy simulations of four different geometrical configurations, diffuser 3°, diffuser 1.5°, nominal, and nozzle that resulted in mild to strong pressure gradients are presented. Numerical investigations allowed determining the effects of geometry-induced pressure gradient on the flame structure, development of the flame-front vorticity and turbulent structures and flame stabilization. It is shown that the pressure gradient plays a key role for the spatial and temporal development of the flame front vorticity and baroclinic torque. The flow deceleration in diffuser geometries suppresses the flame-induced vorticity mechanisms, which in turn lead to large wrinkle forms of the flame and may lead to local extinctions along the flame front. The favorable pressure gradient in the nozzle geometry, on the contrary, increases the baroclinic torque that restrains the development of the shear layer vorticity and hence prevents local extinctions.
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Zhu, Shengrong, i Sumanta Acharya. "Effects of Hydrogen Addition on Swirl-Stabilized Flame Properties". W ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-23686.
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The role of hydrogen addition to swirl-stabilized methane flames is studied experimentally. Of specific interest are flame properties including flame surface density and curvature. The measurements are based on Particle Image Velocimetry (PIV), Mie-scattering and CH-chemiluminescence imaging. Identification of the flame front and its geometric characterization provides an understanding of the flame properties. Compared to the non-reacting flow, the methane flame broadens the central recirculation zone. Hydrogen enriched flames reduce the central recirculation zone and scales down the characteristic length of the flow. With hydrogen addition, the distribution of the flame front curvature is broadened and flame surface density is increased. This indicates that hydrogen addition increases the reaction front thermo-diffusive instability, causing the flame front to be more wrinkled, and increasing the flame surface area leading to an increase in the burning velocity.
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Noda, Susumu, Yuzuru Nada, I. Gede Parwatha i Shingo Fukushige. "Effects of Flow Field on Combustion Characteristics of Confined Jet Nonpremixed Flames". W ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32638.
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Confined flames are widely used in the industrial field. The flame characteristics can be strongly dominated by the combination of a burner and furnace geometries, which were not paid much attention before. In the present study, flow fields in confined flames are discussed in terms of the flame characteristics. The flow characteristics of confined flames have been investigated for propane nonpremixed flames in cylindrical furnaces. The effects of the inner diameter of the cylindrical furnace D1, the turbulence at the flame boundary, and the global equivalence ratio φ are examined in terms of the relation between the emission of NOx and the flow fields. The emission index of NOx, EINOx, decreases roughly with these parameters. The decrease in EINOx is thought to be related to the dilution of mixtures by the burned gas and the flame stretch. The dilution is attributable to vortices formed at the bottom of the furnace, and the flame stretch is attributable to the air velocity difference ΔUa created by two air nozzles. In the present study, it was found that the increases in D1, ΔUa, and φ enlarge and strengthen recirculation vortices to dilute the flame.
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Ahmed, K. A., i D. J. Forliti. "Flame Holding and Combustion Characteristics of a Geometrical Flame Holder". W ASME 2008 Heat Transfer Summer Conference collocated with the Fluids Engineering, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/ht2008-56304.
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Flame Stabilization in a high-speed premixed environment requires the presence of a mechanism to stabilize the flame. Bluff bodies or geometrical flame holders introduce a recirculation zone that anchor the flame. The current study considers the influence of equivalence ratio and the boundary layer state at the trailing edge of the flame holder on the flowfield and combustion characteristics. It was found that the recirculation zone is shortened as the equivalence ratio increases towards unity. A secondary shear region emerges downstream of the recirculation zone and is caused by the accelerated low-density combustion products. The emergence of the secondary shear region moves upstream with increasing equivalence ratio. Tripping the boundary layer causes a dramatic reduction in the length of the recirculation zone, and the secondary shear region is greatly augmented. Visualizations show that tripping the boundary layer resulted in a greatly disturbed flame near the trailing edge and large flame scales. Flowfield measurements suggest that the heat release is increased by approximately 50% when the boundary layer tripped.
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Baird, Benjamin D., i S. R. Gollahalli. "Effects of Temperature and Hydroxyl Radical Concentration Distributions on Emissions of Partially Premixed Flames From Elliptical Burners". W ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90065.
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Non-circular burner geometries have shown some promise of reducing pollutant emissions form combustion systems. The use of non-axisymmetric geometries has the potential to alter the behavior of a flame through modification of the flow field. To investigate these flow field effects on combustion performance, a study of the partially premixed flames emitted from a circular burner and a 3:1 aspect ratio (major axis / minor axis) elliptical burner of equal exit area was performed. For laminar conditions, the elliptical and circular burner produced similar global emissions of carbon monoxide and nitric oxide. In turbulent flames, the elliptical burner produced a larger amount of carbon monoxide, but reduced nitric oxide production. In turbulent flames, the enhanced mixing facilitated by elliptical burners froze the CO oxidation reaction and thus increased its emission. In laminar flames, the elasticity did not significantly affect mixing rates, and thus resulted in similar CO emissions between the burners. The hypothesis on CO reaction freezing was confirmed with inflame structure measurements of CO, OH, and temperature. The decreased NO production in turbulent flame was attributed to a reduction of the flame length of the 3:1 aspect ratio elliptical burner and thus a decrease of residence time compared to the circular burner.
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Bade, Stefanie, Michael Wagner, Christoph Hirsch, Thomas Sattelmayer i Bruno Schuermans. "Design for Thermo-Acoustic Stability: Modeling of Burner and Flame Dynamics". W ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-95058.
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A Design for Thermo-Acoustic Stability (DeTAS) procedure is presented, that aims at selecting a most stable burner geometry for a given combustor. It is based on the premise that a thermo-acoustic stability model of the combustor can be formulated and that a burner design exists, which has geometric design parameters that sufficiently influence the dynamics of the flame. Describing the flame dynamics in dependence of the geometrical parameters an optimization procedure involving a linear stability model of the target combustor maximizes the damping and thereby yields the optimal geometrical parameters. To demonstrate the procedure on an existing annular combustor a generic burner design was developed that features a significant variability of dynamical flame response in dependence of two geometrical parameters. In this paper the experimentally determined complex burner acoustics and complex flame responses are described in terms of physics based parametric models with excellent agreement between experimental and model data. It is shown that these model parameters correlate uniquely with the variation of the burner geometrical parameters, allowing to interpolate the model with respect to the geometrical parameters. The interpolation is validated with experimental data.
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Hariharan, P., i S. R. Gollahalli. "Effect of Equivalence Ratio and Burner Geometry on the Characteristics of Laminar Premixed Flames at Moderate Coflow". W ASME 2004 Power Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/power2004-52015.
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The importance of studying laminar premixed flames lies in applications such as gas ranges and ovens, heating appliances and Bunsen burners. With the current demand for large amounts of economical, clean power, there is a need for research in increasing the combustion efficiency. Laminar premixed Propane/Hydrogen/Air flames with 3 m/s coflow and without coflow, with a variation of jet equivalence ratio (JEQ) from 0.5 to 4 for 20 m/s jet velocity, have been studied experimentally to determine the interactions of burner geometry of premixed flames and coflow. Two different burner geometries (circular burner, and 3:1 aspect ratio (AR) burners) were used in the experiments. The stability tests indicated that for 20 m/s jet velocity both at quiescent and coflow conditions the circular burner was more stable than the 3:1AR elliptical burner. Flame height studies indicated that circular burner flames were taller than the 3:1AR elliptical burner flames. However, there was a reduction in flame height when coflow air velocity of 3 m/s was introduced. Temperature profile indicated a higher peak temperature for circular burners followed by elliptical burner, both at quiescent and coflow conditions. The introduction of moderate coflow showed a decrease in NO production rate. In order to explain the structure of the flame in detail and various mechanisms that lead to the explanation of global flame characteristics, inflame concentration measurements were taken in near burner (25% of flame height), mid burner (50% of flame height) and far burner (75% of flame height) regions of the flame.
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Hariharan, P., i S. R. Gollahalli. "Characteristics of Partially Premixed Elliptic Burner Flames in Coflow-Velocity Air Streams". W ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-60336.
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This paper presents the results of an extension of the previous study where the effects of jet equivalence ratio and burner geometry on the characteristics of partially premixed propane/hydrogen/air flames at a coflow air velocity of 3 m/s were presented. The results here pertain to the experiments where the coflow velocity was doubled to understand the effects of coflow. Two different burner geometries (Circular, and 3:1 aspect ratio-AR elliptical burners) were used in the experiments with circular burner flames as baseline condition. During the study, the exit velocity was held constant at 20 m/s for all conditions. Stability tests indicated that circular burner flames were more stable than the 3:1AR elliptical burner flames at quiescent conditions. At 6 m/s coflow air velocity, stability of both the circular and the 3:1AR elliptic flames was enhanced. Circular burner flames were longer than 3:1AR elliptical burner flames. Introduction of 6 m/s coflow air velocity reduced the flame height. Global NO and CO emission indices decreased considerably after the introduction of coflow air in both burners. Peak temperature of circular burner flames was higher than that of 3:1AR elliptic burner at all conditions. Inflame concentration measurements were also taken in near-burner (25% flame height), midflame (50% flame height) and far-burner (75% flame height) regions.
Raporty organizacyjne na temat "Flame geometrics"
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Beshouri. PR-309-04200-R01 Modeling Methodology for Parametric Emissions Monitoring System for Combustion Turbines. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), marzec 2005. http://dx.doi.org/10.55274/r0010731.
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Prior attempts to develop a generic Parametric Emissions Monitoring methodology for combustion turbines, particularly low emissions units, have failed due either to the reduction of a complex problem to too few degrees of freedom or the brute force reliance on regression analysis. Field test data collected by the research team clearly illustrated that a successful PEMS model will need to incorporate multiple zones to account for pilot fuel versus pre-mixed combustion, and changes in air/fuel ratio at the flame front. The information reported herein shows that, ideally, the PEMS model should rely on speed, fuel flow, compressor discharge pressure and temperature, and ambient conditions as the inputs. The model can utilize (combustion turbine) turbine discharge temperatures as cross checks and/or for tuning. Make and model specific geometric characteristics should include compressor air flow versus speed, air splits between the combustor and the cooling air, and the fuel splits between diffusion and premixed. Finally, the model should be able to accommodate fuel that varies in composition based on provided gas speciation.