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Walter, Géza. "Comparison of different flame types /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2006. http://theses.uqac.ca.
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Erard, Valérie. "Etude spatiale et temporelle des champs thermiques et dynamiques de la combustion de prémélange turbulente instationnaire." Rouen, 1996. http://www.theses.fr/1996ROUES073.
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Cette étude a pour but de visualiser et d'analyser la structure spatiale des fronts de flammes turbulentes instationnaires de prémélange méthane-air. Les flammes sont réalisées par étincelle dans une soufflerie verticale et se propagent librement dans un écoulement à turbulence de grille. La technique de mesure adoptée aux phénomènes rapides, est basée sur la tomographie laser couplée à une caméra rapide. Par traitements d'images, il est possible de suivre et de décrire l'évolution temporelle de la combustion. Ainsi, l'application de cette technique de visualisation permet d'accéder à des mesures quantitatives des grandeurs spatiales représentatives de l'interaction entre la chimie et le champ turbulent. Plusieurs de ces grandeurs sont quantifiées : l'évolution des rayons équivalents des flammes en fonction du temps, le taux de plissement, les courbures locales et moyennes, ainsi que les échelles fractales. Par ailleurs, la mesure du champ dynamique instantané est déterminée par l'application de la PIV par intercorrélation sur les mêmes images tomographiques, afin de mettre en évidence l'influence de la propagation de la flamme sur le champ turbulent.
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Nanduri, Jagannath Ramchandra. "A COMPUTATIONAL STUDY OF THE STRUCTURE, STABILITY, DYNAMICS, AND RESPONSE OF LOW STRETCH DIFFUSION FLAME." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1132237973.
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Yamashita, Hiroshi, Naoki Hayashi, Yusuke Isobe, Shinya Kato, and Kazuhiro Yamamoto. "Lifted flame structure of coannular jet flames in a triple port burner." Elsevier, 2011. http://hdl.handle.net/2237/20041.
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Guo, Huimin. "Flame and acoustic waves interactions and flame control." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/flame-and-acoustic-waves-interactions-and-flame-control(d6306221-905e-425f-9144-d40453eabb7f).html.
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In this PhD project, the investigation of the stability of a laminar diffusion flame and the interaction of the flame with acoustic waves inside an acoustically excited cylindrical tube is presented. Interesting phenomena have been observed by studying both the infrasound and sound effect on the flame structure and dynamics.When a cylindrical tube burner is acoustically excited at one end, a standing wave will be produced along the tube burner. By applying a programming controlled signal from a signal generator, the loudspeaker generates acoustic waves with different frequencies and intensities to excite the flame, which can make the flame relatively stable or unstable, even blow out. Different methods in both frequency domain and time domain have been applied to analyze the flame stability affected by acoustic waves. Both infrasound and sound are tested in this research. Infrasound is the acoustic wave with a frequency too low to be heard by human ear covering sounds beneath the lowest limits of human hearing (20Hz) down to 0.001Hz. It is found that infrasound is able to take over buoyancy-driven flame flickering and make the flame flicker at the same frequency as the forcing infrasound. For some infrasound, half excited frequency has been detected clearly in the power spectrum of CH* chemiluminescence signals acquired by a photomultiplier. On the other hand, some higher frequency acoustic wave can have observable effect on flame flickering but the buoyancy-driven flickering is still the dominant oscillating mode; some other higher frequency acoustic wave can make the flame very stable, such as the acoustic wave at 140Hz. Image processing technique has shown that the influence of acoustic waves on the laminar diffusion flame varies spatially. It is also observed that a diffusion flame may oscillate at different frequency spatially. Taking the flame without acoustic excitation as an example, the inner most area of the flame oscillates at the typical flickering frequency, but the most outer areas of the flame oscillate at the second-harmonic of the typical flickering frequency. Finally, some control strategies are developed for the laboratory tube burner based on the gained physical insights in this research.
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Wang, Aijuan. "Experimental and numerical investigation of the confinement effect on the impinging flame in a compartment." Electronic Thesis or Diss., Bourges, INSA Centre Val de Loire, 2021. http://www.theses.fr/2021ISAB0002.
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Le phénomène de flamme de diffusion impactant une paroi est fréquent dans les scénarios d’incendie en milieu clos. Celui-ci peut entraîner à avoir des conséquences désastreuses en termes de vie humaine et de biens matériels. En effet, lorsqu'une flamme incidente se produit dans un compartiment, elle peut augmenter le risque de propagation du feu de celui-ci vers une autre pièce à travers une explosion de fumée représentant une menace pour les personnes pié-gées. Afin d’apporter des éléments de compréhension sur le comportement de ce type de flamme, de nombreuses études ont réalisé. Celles-ci se sont intéressées sur des flammes impac-tant un plafond en milieu ouvert ou semi-confiné. Cependant il y a peu, voire aucuns travaux qui se sont penchés sur l’étude du comportement d’une flamme incidente dans un compartiment confiné sous ventilé. Dans l’objectif d’apporter des éléments de compréhension en lien avec l’effet du confinement sur la dynamique d’une flamme impactant un plafond, une étude expé-rimentale et numérique est réalisée dans le cadre de cette thèse.L’ensemble des données a été obtenu à l’aide d’un dispositif expérimental représentant un appartement d’étudiant à échelle réduite.Le banc d'essai est un compartiment représentant une maquette d’appartement à petite échelle (1 :10). La conception et dimensionnement a été réalisée sur la base des lois de simili-tudes. Les niveaux de confinement ont été définis en fonction des ouvertures de l’enceinte et du débit calorifique potentielle. A partir de ces deux paramètres, le niveau de confinement peut être associé à la richesse de l’enceinte. Pour cela, huit débits caloriques différents ainsi que cinq possibilités d’ouvertures ont été proposés. À partir des expériences réalisées avec les huit débits calorifiques et les cinq configurations d’ouvertures, l'effet de confinement sur la dynamique d’une flamme impactant un plafond a été effectué en se basant sur les paramètres physico-chimiques, tels que l'extension de la flamme, l'oscillation de la flamme, la distribution de la température et l'analyse des gaz.De plus, grâce à la modélisation numérique de la flamme impactant le plafond à l’aide du code CFD : Fire Dynamics Simulator (FDS), il a été possible d’apporter des éléments supplé-mentaires dans l’analyse des écoulements réactifs associée à l’interaction flamme paroi en fonc-tion du niveau de confinement. Le choix des modèles numériques a été effectué à partir d’une étude préliminaire visant à justifier la fiabilité et la précision du modèle numérique à reproduire les données expérimentales ainsi que des évolutions obtenues à partir de corrélations empiriques obtenues dans les littératures.A partir des analyses réalisées dans cette étude, il est possible de fournir des éléments de décisions lors de la conception et la mise en place de détecteurs d'incendie au plafond dans un compartiment et également d’aider à une meilleure estimation de la probabilité de propagation du feu lors d'un incendie de compartiment par le biais d’une explosion de fumée riche en gaz imbrûlésThe phenomenon of diffusion impinging flame is common in industrials, leading to disas-trous consequences in terms of life and property. When impinging flame occurs in a compart-ment, it may enhance the risk of fire propagation and pose a greater threat to trapped people. Lots of studies dealt with flame impinging an unconfined or confined ceiling while little work focused on the impinging flame in a confined compartment. With the objective of providing understanding related to the confinement effect on the impinging flame in a compartment, both experimental and numerical studies carried out to build up the framework of this thesis. A compartment model representing a reduced scale (1:10) student compartment was uti-lized based on the scaling law such that a test bench with suitable instrumentations for carrying out measurements was developed. Configurations of five confinement levels were constructed by the condition of windows and door in the compartment and heat release rate (HRR) was var-ied between 0.5 kW and 18.6 kW. Through series of experiments, the confinement effect on the dynamics of flame impinging a ceiling was addressed with physicochemical parameters, such as flame extension, flame oscillation, temperature distribution and gas analysis. In addition, on account of the numerical modeling of flame impinging a ceiling using the CFD code: Fire Dynamics Simulator (FDS), it was possible to provide additional elements in the analysis of reactive flows associated with the flame-wall interaction as a function of the confinement level. The choice of numerical models was made on the basis of a preliminary study aimed at justifying the reliability and precision of the numerical modelling in reproducing the experimental data as well as the empirical correlations obtained in the literatures. From the analyzes in this study, it is possible to provide guidance for fire safety engineering in the field of fire risk assessment and fire protection design of buildings
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Capil, Tyler George. "Flame Surface Density Measurements and Curvature Statistics for Turbulent Premixed Bunsen Flames." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/75121.
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In this work, turbulent premixed combustion was analyzed through CH (methylidyne) planar laser induced fluorescence (PLIF). Flame topography measurements in terms of flame surface density and curvature were calculated based on the flame front detected by the CH PLIF signal. The goal of this work was to investigate turbulent flames with extremely high turbulence intensity using a recently developed HiPilot burner (a Bunsen-type burner). The studies were first conducted on a series of piloted jet flames to validate the methodology, and then conducted on the highly turbulent flames generated by the HiPilot burner. All flames were controlled by combusting methane and air under a fuel to air equivalence ratio of Φ=1.05, and the Reynolds number varied from 7,385 to 28,360. Flame surface density fields and profiles for the HiPilot burner are presented. These flame surface density measurements showed an overall decrease with height above the burner. In addition, curvature statistics for the HiPilot flames were calculated and probability density functions of the curvature samples were determined. The probability density functions of curvature for the flames showed Gaussian-shaped distributions centered near zero curvature. To conclude, flame topography measurements were verified on jet flames and were demonstrated on the new HiPilot flames.Master of Science
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Zeltner, Darrel Patrick. "NO, Burnout, Flame Temperature, Emissivity, and Radiation Intensity from Oxycombustion Flames." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3221.
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This work produced the retrofit of an air-fired, 150 kW reactor for oxy-combustion which was then used in three oxy-combustion studies: strategic oxy-combustion design, oxy-combustion of petroleum coke, and air versus oxy-combustion radiative heat flux measurements. The oxy-combustion retrofit was accomplished using a system of mass flow controllers and automated pressure switches which allowed safe and convenient operation. The system was used successfully in the three studies reported here and was also used in an unrelated study. A study was completed where a novel high oxygen participation burner was investigated for performance while burning coal related to flame stability, NO, and burnout using a burner supplied by Air Liquide. Parameters investigated included oxygen (O2) injection location, burner swirl number and secondary carbon dioxide (CO2) flow rate. The data showed swirl can be used to stabilize the flame while reducing NO and improving burnout. Center O2 injection helped to stabilize the flame but increased NO formation and decreased burnout by reducing particle residence time. Additional CO2 flow lifted the flame and increased NO but was beneficial for burnout. High O2 concentrations up to 100% in the secondary were accomplished without damage to the burner. Petroleum coke was successfully burned using the Air Liquide burner. Swirl of the secondary air and O2 injection into the center tube of the burner were needed to stabilize the flame. Trends in the data similar to those reported for the coal study are apparent. Axial total radiant intensity profiles were obtained for air combustion and three oxy-combustion operating conditions that used hot recycled flue gas in the secondary stream. The oxygen concentration of the oxidizer stream was increased from 25 to 35% O2 by decreasing the flow rate of recycled flue gas. The decrease in secondary flow rate decreased the secondary velocity, overall swirl, and mixing which elongated the flame. Changing from air to neat CO2 as the coal carrier gas also decreased premixing which elongated the flame. Flame elongation caused increased total heat transfer from the flame. The air flame was short and had a higher intensity near the burner, while high O2 concentration conditions produced lower intensities near the burner but higher intensities and temperatures farther downstream. It was shown that oxycombustion can change flame shape, temperature and soot concentration all influencing heat transfer. Differences in gas emission appear negligible in comparison to changes in particle emission.
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Duchaine, Patrick. "Experimental analysis of the dynamics of gaseous and two-phase counterflow flames submitted to upstream modulations." Phd thesis, Ecole Centrale Paris, 2010. http://tel.archives-ouvertes.fr/tel-00545418.
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Modern combustion systems benefit from constant technological advanceswhich aim at reducing the emissions of chemical pollutants and at wideningregimes of stable operation. Further progress in the combustion field requiresa better understanding and modelling of the combustion dynamics. In thesesystems, the combustible is often injected as a liquid polydisperse spray. Experimentaldata are thus required to validate simulation tools in configurationswith flames interacting with controlled structures in multi-phase flows.This thesis aims at studying some of these fundamental interactions in wellcontrolledlaminar flows submitted to upstream modulations. Two experimentalconfigurations are investigated comprising counterflow flames and free inertjets, fed with gaseous or liquid combustibles. The flows may be submittedto upstream velocity modulations to reproduce effects of unsteadiness. Dependingon the pulsation frequency, vortices of controlled sizes are shed fromthe burner lips and convected with the flow, while interacting with the sprayand the flame.In the first part of this thesis, the dynamics of a premixed stretched flameis analysed in a stagnation flow. The study focuses on determining the flowand flame structures under upstream modulations, and principally on studyingthe dynamics of flame/vortex interactions. Different responses of the flameare identified and analysed relative to the size of the vortex ring generated atthe burner outlet. Two propagation modes for the velocity perturbations areidentified, corresponding to a bulk oscillation of the entire reaction zone orto a flame perturbed only at its periphery. This leads to a discussion on thechoice of velocity boundary conditions to conduct 1D simulations of theseconfigurations. Comparisons between simulations and measurements of thevelocity field illustrate these conclusions. Flame transfer functions betweenheat release rate and velocity perturbations imposed at the burner outlet areestablished for different flow conditions. These measurements relying on localand global chemiluminescence of the flame show again a distinct behaviourof the emission originating from the flame region close to the burner axis andthe whole flame. Mechanisms of sound production by partially and perfectlypremixed flames are also identified and analysed relative to flame/vortex interactions.In the second part, the dynamics of a spray convected by a free inert jet or impinginga diffusion flame submitted to velocity modulations is analysed. Theoriginality of this work consists in characterizing the flow and spray dynamicsusing a set of advanced diagnostics. Phase-conditioned images at different instantsin the modulation cycle are used to analyse the interactions between thegaseous phase and the spray. The spatial distribution of combustible vapourand liquid phases is determined using Laser Induced Exciplex Fluorescence(LIEF). Velocities and sizes distribution of droplets from the spray are determinedlocally by Phase Doppler Anemometry (PDA) and in a plane by InterferometricParticle Imaging (IPI). Laser Doppler Velocimetry (LDV) andParticle Image Velocimetry (PIV) are also used to determine the response ofgaseous phase. These phase-conditioned analysis highlight some interactionsbetween the gaseous and liquid phases and constitute an interesting databasefor detailed simulation of these two-phase flows.
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Jaafar, Nisrine. "The blue flame and the red flame : love and eroticism." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ64032.pdf.
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Maugendre, Mathieu. "Etude des particules de suie dans les flammes de kérosène et de diester." Thesis, Rouen, INSA, 2009. http://www.theses.fr/2009ISAM0016/document.
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Les suies se présentent sous la forme de fines particules carbonées de diamètres compris entre quelques dizaines de nanomètres à quelques micromètres. Dans l’atmosphère, elles entraînent des enjeux climatiques, de par leurs propriétés radiatives, mais aussi des enjeux sanitaires, du fait de leur faible taille : elles pénètrent facilement dans le système respiratoire et même, pour les plus fines, dans le système sanguin. L’objectif est de parfaire les connaissances sur les propriétés physiques des suies produites par différents systèmes de combustion. C’est dans le but de mieux comprendre l’influence des systèmes de combustion, faisant intervenir des temps de séjours différents, des propriétés de turbulence, d’oxydation et de pression distinctes que nous avons choisi d’étudier trois types de combustion spécifiques : d’une part, des flammes de diffusion laminaires à pression atmosphérique, initiées dans un brûleur développé au cours de ces travaux ; d’autre part, une flamme de diffusion laminaire sous atmosphère pressurisée (3 à 5 bars) ; enfin, une flamme turbulente produite par une chambre tubulaire, elle aussi sous atmosphère pressurisée (1.2 à 3 bar). Un autre enjeu de ce travail était d’approfondir les informations relatives à la combustion de carburants liquides, à savoir le kérosène et le diester. Les travaux effectués visent à déterminer les caractéristiques morphologiques (dimension fractale, diamètre des monomères...) et l’indice complexe m* des suies issues des différents systèmes de combustion. La technique employée pour la mesure de l’indice complexe de réfraction des suies, repose sur l’analyse d’une partie des fumées produites par les flammes. Ces fumées sont acheminées dans un banc d’analyse permettant la mesure de signaux d’extinction et de diffusion, ainsi que de distributions de taille des suies. Par ailleurs, des analyses de clichés obtenus par microscope en transmission d’électrons (TEM) permettent l’obtention d’informations sur la morphologie des agrégats de suies. L’utilisation de la théorie de la diffusion de la lumière pour des agrégats fractals dans la limite de Rayleigh (RDG-FA) permet d’estimer à partir de ces données deux fonctions de l’indice complexe E(m) et F(m), et ainsi de retrouver m*Soot are carbonaceous fine particles, which diameters are ranged from a few nanometres to a few micrometers. They have an impact on climate, due to their radiative properties, as well as on health, due to their small size. That’s why particulate matter is an important concern. In order to gain a better understanding of the influence of the combustion devices, which implies specific residence time and also specific turbulence, oxidation and pressure properties, we studied three specific kinds of combustion : first, laminar diffusion flames at atmospheric pressure ; then, a laminar diffusion flame a high pressures (3 to 5 bar) ; finally, a turbulent flame produced in a combustor at high pressures (1,2 to 3 bar). Another objective of this work was to improve the knowledge about soot produced by the combustion of liquid fuels, namely kerosene and biofuel. We studied morphological properties (fractal dimension, primary particle size…) and the refractive index m* of soot produced by these combustion systems. The technique employed to characterize the soot refractive index is based on the analysis of a part of smokes produced by flames. These are transported towards two optical cells, so that extinction and scattering coefficients can be measured, in addition to soot size distributions. Furthermore, a morphological characterization of the aggregates is conducted, using transmission electron microscopy (TEM) photographs. Rayleigh-Debye-Gans theory for fractal aggregates is used to determine two functions of the refractive index E(m) and F(m), so that m* can be deduced
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Williams, R. "Submerged flame combustion." Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636655.
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The objective of this work is to better understand the operation of Submerged Flame Burners, commonly known as Submerged Combustion Burners. Two main aspects require consideration, namely: practical applications of the technology in industry; secondly, theoretical modelling of the flame behaviour within the Submerged Combustion Burner in order to ensure flame stability in the burner and hence heat transfer efficiency and reliable operation. The current status of the Submerged Combustion Technology has been reviewed, detailing the separation equipment items that, overall, make up an industrial Submerged Combustion package. The functionality of the different items has been considered in the context of the primary objective of the equipment, i.e. the establishment of a stable flame within the Submerged Burner. Cases detailing specific instances of the application of Submerged Combustion technology in industry are presented in order that practical aspects of the operation of such units can be better appreciated. The flame system within the Submerged Burner has been modelled using a commercially available Computational Fluid Dynamic Package. A simplified model was used in order to represent the processes occurring within the burner for the combustion of methane with air as the oxidant. The K- turbulence model was used for the prediction of turbulence behaviour within the system. The results of the Computational Fluid Dynamic modelling cover a range of operating parameter values that might be expected to be encountered in industrial applications of Submerged Combustion. The results of the theoretical analysis have been considered in terms of the significance to the design and operation of industrial Submerged Combustion units. The discussions of the practical application of the technology have also led to recommendations being made in respect of the design of the ancillary equipment associated with the Submerged Combustion Burners. The observations made and conclusions drawn in this work provide a better understanding of the processes involved with the production of a stable flame within a Submerged Combustion Burner. Recommendations have been made for future work building on the work reported here.
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Piffaretti, Stefano Giuseppe. "Flame age model : a transient laminar flamelet approach for turbulent diffusion flames /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16961.
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Hartl, Sandra. "Flamelet/progress variable modelling and flame structure analysis of partially premixed flames." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2017. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-227684.
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This dissertation addresses the analysis of partially premixed flame configurations and the detection and characterization of their local flame regimes.
First, the identification of flame regimes in experimental data is intensively discussed. Current methods for combustion regime characterization, such as the flame index, rely on 3D gradient information that is not accessible with available experimental techniques. Here, a method is proposed for reaction zone detection and characterization, which can be applied to instantaneous 1D Raman/Rayleigh line measurements of major species and temperature as well as to the results of laminar and turbulent flame simulations, without the need for 3D gradient information. Several derived flame markers, namely the mixture fraction, the heat release rate and the chemical explosive mode, are combined to detect and characterize premixed versus non-premixed reaction zones. The methodology is developed and evaluated using fully resolved simulation data from laminar flames. The fully resolved 1D simulation data are spatially filtered to account for the difference in spatial resolution between the experiment and the simulation, and experimental uncertainty is superimposed onto the filtered numerical results to produce Raman/Rayleigh equivalent data. Then, starting from just the temperature and major species, a constrained homogeneous batch reactor calculation gives an approximation of the full thermochemical state at each sample location. Finally, the chemical explosive mode and the heat release rate are calculated from this approximated state and compared to those calculated directly from the simulation data. After successful validation, the approach is applied to Raman/Rayleigh line measurements from laminar counterflow flames, a mildly turbulent lifted flame and turbulent benchmark cases. The results confirm that the reaction zones can be reliably detected and characterized using experimental data. In contrast to other approaches, the presented methodology circumvents uncertainties arising from the use of limited gradient information and offers an alternative to known reaction zone identification methods.
Second, this work focuses on the flame structure of partially premixed dimethyl ether (DME) flames. DME flames form significant intermediate hydrocarbons in the reaction zone and are classified as the next more complex fuel candidate in research after methane. To simulate DME combustion processes, accurate predictions by computational combustion models are required. To evaluate such models and to identify appropriate flame regimes, numerical simulations are necessary. Therefore, fully resolved simulations of laminar dimethyl ether flames, defined by different levels of premixing, are performed. Further, the qualitative two-dimensional structures of the partially premixed DME flames are discussed and analyses are carried out at selected slices and compared to each other as well as to experimental data. Further, the flamelet/progress variable (FPV) approach is investigated to predict the partially premixed flame structures of the DME flames. In the context of the FPV approach, a rigorous analysis of the underlying manifold is carried out based on the newly developed regime identification approach and an a priori analysis. The most promising flamelet look-up table is chosen for the fully coupled tabulated chemistry simulations and the results are further compared to the fully resolved simulation data.
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Moore, Nancy Jennings. "Effects of Leading-Edge Flame Behavior on Flame Stabilization and Blowout." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-10012009-135737/.
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The goal of this work was to identify the mechanisms that effect stabilization of hydrocarbon jet flames. Methane, nitrogen, and co-flowing air were regulated and directed through a burner that created fully-developed fuel flow with concurrent air. The behavior of the reaction zone at the leading-edge was analyzed from digital images obtained from a camera optimally positioned to capture the movements of the entire flame front. Low Reynolds number flows allowed for the investigation of hysteretic behavior. The hysteresis regime refers to the situation where the jet flame has dual positions favorable to flame stabilization: attached and lifted. Results indicate that flame height in hysteresis is significantly impacted by high velocities of co-flow and that past a critical value a local minimum will be created. Fully turbulent lifted flames were also studied to determine the fluctuations in the height of lifted methane flames in the presence of air co-flow. The partially-premixed flame front of the lifted flame fluctuates in the axial direction, with the fluctuations becoming greater in flames stabilized further downstream. These fluctuations are also observed in flames where blowout is imminent. The height and rate of these fluctuations are studied with respect to average height, flow velocities, and Reynolds number. Additionally, the mechanisms that cause jet-flame blowout, particularly in the presence of air co-flow, are not completely understood. Two types of experiments are described, and the data report that a predictor of blowout is the prior disappearance of the axially-oriented flame branch which is consistently witnessed despite a turbulent flameâs inherent variable behavior. The conclusions are supported by experiments with nitrogen-diluted flames. A blowout parameter is also calculated for methane flames in co-flow and diluted methane flames that can be used to predict at what flow velocities blowout will occur. This work analyzes flames near the burner, in the far field, and approaching blowout. The comprehensive study allows for the realization that the mechanisms of flame stabilization differ throughout the combustible field.
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Owen, Steven Andrew. "Burnout, NO, and Flame Characterization from an Oxygen-Enriched Biomass Flame." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5263.
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Concern for the environment and a need for more efficient energy generation have sparked a growing interest throughout the world in renewable fuels. In order to reduce emissions that negatively contribute to global warming, especially CO2, enormous efforts are being invested in technologies to reduce our impact on the environment. Biomass is an option that is considered CO2 friendly due to the consumption of CO2 upon growth. Co-firing biomass with coal offers economic advantages because of reduced capital costs as well as other positive impacts, such as NOx and SOx emission reductions. However, due to the large average particle size of biomass, issues arise such as poor flame stability and poor carbon burnout. Larger particles can also result in longer flames and different heat transfer characteristics. Oxygen enrichment is being investigated as a possible solution to mitigate these issues and enable co-firing in existing facilities. An Air Liquide designed burner was used in this work to explore the impact of oxygen enrichment on biomass flame characteristics, emissions, and burnout. Multiple biomass fuels were used (medium hardwood, fine hardwood, and straw) in conjunction with multiple burner configurations and operating conditions. Exhaust ash samples and exhaust NO were collected for various operating conditions and burner configurations. All operating parameters including O2 addition, swirl, and O2 location could be used to reduce LOI but whenever LOI was reduced, NO increased producing an NO-LOI trade-off. Starting with high LOI, various parameters such as O2 addition and increased swirl could be used to reduce LOI with only small increases of NO. As O2 or swirl increased further, small decreases in LOI were obtained only with large increases in NO. This behavior was captured through NO-LOI trade-off curves where a given configuration or operating condition was deemed better when the curve was shifted toward the origin. Global enrichment or O2 addition to the secondary stream and O2 addition to the primary stream produced better trade-off results than center O¬2 injection. Straw produced NO-LOI trade-off curves just as the wood particles but the curve was shifted further from the origin, likely due to the higher nitrogen content of the straw. Flame characterization results showed that small amounts of O2 in the center improved flame attachment and stability while increasing flame temperature and pyrolysis rates.
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Proust, Christophe. "Contribution à l'étude des mécanismes de propagation des flammes dans les mélanges hétérogènes gaz-particules solides." Poitiers, 1988. http://www.theses.fr/1988POIT2268.
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Etude de la propagation d'une flamme laminaire air-particules d'amidon dans un tube. Determination des grandeurs caracteristiques de la flamme. Un des processus possibles de propagation des flammes dans les melanges air-particules d'amidon est celui des ondes de combustion dans les premelanges gazeux
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Delamare, Ludovic. "Modélisation numérique de la propagation d'une flamme turbulente en milieu confiné." Rouen, 1992. http://www.theses.fr/1992ROUES057.
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Cette thèse a pour but d'étudier les interactions turbulence-combustion, combustion-écoulement moyen, et écoulement moyen-turbulence dans le cas d'une flamme turbulente se propageant dans un volume fermé. Ces études résultent en des formes modélisées pour le taux de réaction chimique moyen et pour les différents flux de diffusion turbulente. Le comportement de ces modèles a été testé sur des cas simples et sur un cas réel de combustion turbulente en milieu confiné. Nous avons montré que la modélisation du taux de réaction moyen devait tenir compte de l'influence du mouvement des flammelettes laminaires. D'autre part, la forte anisotropie de la turbulence, générée par la propagation de la flamme, rend nécessaire la prise en compte de corrections au 2ème ordre dans les modèles de turbulence
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Nivarti, Girish Venkata. "The bending effect in turbulent flame propagation." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270335.
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In the present thesis, the sensitivity of flame propagation to the turbulent motion of burning gases is investigated. The long-standing issue of the 'bending effect' is focused upon, which refers to the experimentally-observed inhibition of flame propagation velocity at high intensities of turbulence. Plausible mechanisms for the bending effect are investigated by isolating systematically the effects of turbulence intensity. By providing a novel perspective on this topic, the thesis addresses the fundamental limits of turbulent burning. The investigation employs Direct Numerical Simulation (DNS), which enables the basic conditions of burning to be controlled directly. A parametric DNS dataset is designed and generated by increasing turbulence intensity over five separate simulations. Effects of turbulent motion are isolated in this manner, such that the bending effect is reproduced in the variation of flame propagation velocity recorded. Subsequently, the validity of Damköhler's hypotheses is investigated to ascertain the mechanism of bending. Analysis of the DNS dataset highlights the significance of kinematic flame response in determining turbulent flame propagation. Damköhler's first hypothesis is found to be valid throughout the dataset, suggesting that the bending effect may be a consequence of self-regulation of the flame surface. This contradicts the dominant belief that bending occurs as a result of flame surface disruption by the action of turbulence. Damköhler's second hypothesis is found to be valid in a relatively limited regime within the dataset, its validity governed by flame-induced effects on the prescribed turbulent flow field. Therefore, this thesis presents turbulent flame propagation and the bending effect as emergent from the dynamics of a flame surface that retains its internal thermo-chemical structure. Finally, experimental validation is sought for the proposed mechanisms of bending. Comparisons have been initiated with measurements in the Leeds explosion vessel, based on which the widely accepted mechanism of bending was hypothesized twenty-five years ago. Modifications to the DNS framework warranted by this comparison have aided the development of novel computationally-efficient algorithms. The ongoing work may yield insights into the key mechanism of the bending effect in turbulent flame propagation.
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Aldawsari, Saeed Mubarak N. "Simulations of Turbulent Flames with Varying Inhomogeneity and Pressure Using MMC-LES." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/29619.
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This thesis presents an improved version of the Lagrangian multiple mapping conditioning model coupled with large eddy simulation (MMC-LES). The model is used to compute the structure of a range of turbulent mixed-mode flames on the Sydney piloted burner with compositionally inhomogeneous inlet. In addition, sparse MMC-LES is applied to compute the structure of turbulent non-premixed flames with different values of pressures up to 20 bars to study the pressure effects.
The most commonly deployed version and code for MMC-LES uses a mixture-fraction-based approach and a sparse-Lagrangian notional particle method that is most suitable for non-premixed combustion. The improvements reported here are achieved by leveraging (i) a more rigorous density coupling approach, (ii) a more refined mixing time scale, and (iii) selective particle intensification to improve localness in physical space as well as mixture fraction space. The computed results show good agreement with experimental data hence confirming the feasibility of the improved MMC-LES approach in being able to account for mixed-mode combustion as well as for finite-rate chemistry effects.
The effects of increasing pressure, up to 20 bars, are explored for cases that have constant velocity or the Reynolds numbers. Finite-rate chemistry effects are computed for flames approaching blow-off at pressures of one, five and ten bars. Calculations for cases that have the same Reynolds number indicate that the local extinction decreases as pressure increases. However, for flames with fixed bulk jet velocity, the local extinction increases as pressure increases. The results for atmospheric and high pressure cases show similar behaviour towards blow-off point.
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Hadjiconstantinou, Nicolas G. (Nicholas George). "A model for conversting SI engine flame arrival signals into flame contours." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/35444.
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Usowicz, James E. "An Experimental Study of Flame Lengths and Emissions of fully-Modulated Diffusion Flames." Digital WPI, 2001. https://digitalcommons.wpi.edu/etd-theses/640.
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A pulsed fuel injector system was used to study flame structure, flame length, and emissions of ethylene jet diffusion flames over a range of injection times and duty-cycles with a variable air co-flow. In all cases the jet was completely shut off between pulses (fully-modulated) for varying intervals, giving both widely-spaced, non-interacting puffs and interacting puffs. Imaging of the luminosity from the flame revealed distinct types of flame structure and length, depending on the duration of the fuel injection interval. Flame lengths for isolated puffs (small injection times) were up to 83% less than steady state flames with the same injection velocities. With the addition of co-flow flame lengths grew to a maximum of 30% longer than flames without any co-flow. A scaling argument is also developed to predict the amount of co-flow that gives a 15% increase in mean flame length. Interacting flames with a small co-flow and small injection times (injection time = 5.475 ms) experienced flame length increases of up to 212% for a change in injection duty-cycle from 0.1 to 0.5. For interacting flames with long injection times (on time = 119 ms), essentially no change in flame length was noticeable over the same range of duty-cycles. Emission measurements suggest partial quenching of the reaction in isolated puffs with low duty-cycles and injection times (injection times less than 5.475 ms) resulting in high CO and UHC concentrations and low NO and NOx concentrations. With an increase in duty-cycle, the puffs began to interact and CO and UHC concentrations decreased while NO and NOx concentrations increased. For flames with injection times greater than 5.475 ms emission concentrations seem to be reasonably constant, with a slight increase in NO and NOx concentrations as the duty-cycle increased. Also the duty-cycle experienced in the vicinity of the probe is estimated and used as a scaling factor for the emission measurements.
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Ma, Terence Kwai Kin. "Flame surface density modelling for the large eddy simulation of turbulent premixed flames." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/14645.
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Large Eddy Simulation (LES) has become an increasingly useful tool for the prediction of turbulent reactive flows with the increasing availability of cheaper and faster computing power. In the context of premixed combustion, LES encounters the challenge of resolving the flame thickness, which is normally smaller than the filter width used in typical engineering applications. This thesis considers the Flame Surface Density (FSD) approach to provide closure to the filtered LES reaction rate. The FSD can either be modelled algebraically (FSDA) or determined through a transport equation (FSDT) and both approaches are investigated in the LES of three different test cases. The first case explores the response of different FSDA models towards changes in turbulence levels, and compares the instantaneous flame structures and reaction rates predicted by FSDA and FSDT methods. The remaining cases examine the LES of two turbulent premixed burners. A relatively large range of FSDA models are tested under the same operating conditions for the first time, and the LES-FSDT equation is applied to premixed flames that involve a higher level of geometric complexity than earlier work. Generally, the results show that the performance of some FSDA models are inconsistent between the two premixed burners, suggesting that the models may operate optimally under different turbulent conditions. By contrast, the consistently good agreement of the FSDT results with experiments suggests that the method has much potential in the LES modelling of turbulent premixed flames. However, the improved FSDT predictions were dependent on the value of the model constant within the sub-grid curvature model, and the value yielded an additional dependency on filter width. For these reasons as well as for the higher computational expense, the effective use of FSDT requires further development, while the application of the FSDA models remains a viable alternative to the FSDT approach.
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Diao, Zhaojin. "CHARACTERIZATION OF METHANE-AIR DIFFUSION FLAMES FOR FLAME SYNTHESIS APPLICATION THROUGH OPTICAL DIAGNOSTICS." UKnowledge, 2018. https://uknowledge.uky.edu/me_etds/121.
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Flame synthesis is a growing field of research aiming at forming new materials and coatings through injection of seed materials into a flame. Accurate prediction of the thermal structure of these flames requires detailed information on the radiative properties and a thorough understanding of the governing combustion processes. The objective of this work is to establish a basic optical diagnostic characterization of different methane-air diffusion flames of different complexity. The basic principles are developed and demonstrated at a rotational symmetric co-flow burner and finally applied to a burner consisting of six clustered microflames which is designed for future flame synthesis work. This work focuses on the demonstration of the optical techniques for characterizing the optical emissions from diffusion flames and of the proposed method for the determination of radiating species properties from these optical measurements.
In the co-flow diffusion flame setup, the fuel of methane diluted with nitrogen is provided through an inner tube while the air is applied through an outer duct surrounding the fuel nozzle. Filtered imaging and spectrally resolved measurements of the chemiluminescence of CH* and C2* and of water emission were conducted. A procedure for using the HITRAN database to support the spectroscopic analysis of the water emission was developed.
In the six clustered microflames burner setup, the burner consisted of six micro-nozzles arranged in a circle surrounding a central nozzle through which air and TaN seed particles with sizes between 0.3 and 3 μm were injected. Spectrally resolved measurements of the chemiluminescence of CH* and C2* were conducted for temperature measurements. Imaging results obtained from a spectral integration of the molecular emission were compared to results from Japanese collaborators who applied a tomographic analysis method to filtered emission measurements of CH* emission which can yield spatially resolved three dimensional mapping of the flame front. The analysis of the spatial distribution of the integrated band emission of CH* and C2* showed that the emission of both species is generated at the same locations in the flame which are the thin flame sheets shown in the tomography results of CH*. The ratio of the C2* and the CH* emission from the emission spectroscopy measurements was used to determine a local equivalence ratio through empirically derived correlations for premixed flames reported in literature. Rotational and vibrational temperature distributions of CH* and C2* radicals throughout the entire flame were determined from the spectrally resolved emission from CH* and C2*. The temperatures of TaN seed particles were characterized using VIS-NIR emission spectra while varying fuel-air flow rates. The temperature profiles of the particles at various heights above the base of the central nozzle, obtained by their VIS-NIR continuum emission, showed a well-defined constant temperature region that extended well beyond the actual flame front and changed as fuel and oxidizer flow rates were varied. The results demonstrate the ability to control the duration to which seed particles are subjected to high temperature reactions by adjusting fuel and oxidizer flow rates in the clustered microflames burner.
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Thumuluru, Sai Kumar. "Effect of harmonic forcing on turbulent flame properties." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37099.
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Lean premixed combustors are highly susceptible to combustion instabilities, caused by the coupling between heat release fluctuations and combustor acoustics. In order to predict the conditions under which these instabilities occur and their limit cycle amplitudes, understanding of the amplitude dependent response of the flame to acoustic excitation is required. Extensive maps of the flame response were obtained as a function of perturbation amplitude, frequency, and flow velocity. These maps illustrated substantial nonlinearity in the perturbation velocity - heat release relationship, with complex topological dependencies that illustrate folds and kinks when plotted in frequency-amplitude-heat release space. A detailed analysis of phase locked OH PLIF images of acoustically excited swirl flames was used to identify the key controlling physical processes and qualitatively discuss their characteristics. The results illustrate that the flame response is not controlled by any single physical process but rather by several simultaneously occurring processes which are potentially competing, and whose relative significance depends upon forcing frequency, amplitude of excitation, and flame stabilization dynamics. An in-depth study on the effect of acoustic forcing on the turbulent flame properties was conducted in a turbulent Bunsen flame using PIV measurements. The results showed that the flame brush thickness and the local consumption speed were modulated in the presence of acoustic forcing. These results will not only be a useful input to help improve combustion dynamics predictions but will also help serve as validation data for models.
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Saeed, Muhammad Azam. "Pulverised biomass flame propagation." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/15264/.
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A resource analysis for Pakistan has demonstrated that abundant crop residues offer a viable, and environmental-friendly alternative to currently inadequate, oil-based power generation. Similarly, in many countries there is legislative pressure and incentives to replace coal with biomass, in electricity production. Efficient and safe exploitation of such biofuels requires data on flame propagation rates and explosibility characteristics. Crop residues (bagasse, rice husk, wheat-straw, corn-cob and peanut-shell) and different raw and thermally treated woods were tested using the modified Hartmann tube and the modified 1 m3 explosion vessel. The modified Hartmann tube was operated for varying ignition delays using a digital timer. A hemispherical disperser with drilled pipe was calibrated for the testing of fibrous and coarse size biomass mixtures. Thermogravimetric analysis data from these materials enabled the application of two different models for the determination of volatile release kinetics. Biomass samples were found to have lower activation energies with higher volatile release rates at low temperatures, compared to coals. Despite their higher ash content, pulverised crop-residues showed leaner minimum explosible concentrations (0.2-0.5 equivalence-ratio) than woods (0.3-0.7) - depending on particle size. Biomass samples were more sensitive to explosion than coal, resulting in flame propagation in coarse-size-range fractions (300-500-μm) that was not experienced with coals. Maximum explosion pressures of near 9 barg were measured for the fine size fraction (less than 63-μm) samples, with no less than 7 barg for coarse size fraction (less than 1 mm). Milling of thermally treated biomass samples resulted in higher fines fraction than untreated biomass, for the same sieve size and this was considered as one of the reasons of the higher reactivity (higher flame speed and higher deflagration index of these samples). The detailed data from this work are usable in the design of safe and efficient combustion systems for power generation from crop residues and other biomass fuels.
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Roussos, Ioannis. "Image based flame lighting." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399940.
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Preetham, Preetham. "Modeling the Response of Premixed Flames to Flow Disturbances." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19817.
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Modeling the Response of Premixed Flames to Flow Disturbances
Preetham
178 pages
Directed by Dr. Tim Lieuwen
Low emissions combustion systems for land based gas turbines rely on a premixed or partially premixed combustion process. These systems are exceptionally prone to combustion instabilities which are destructive to hardware and adversely affect performance and emissions. The success of dynamics prediction codes is critically dependent on the heat release model which couples the flame dynamics to the system acoustics. So the principal objective of the current research work is to predict the heat release response of premixed flames and to isolate the key non-dimensional parameters which characterize its linear and nonlinear dynamics.
Explicit analytical solutions of the G- equation are derived in the linear and weakly nonlinear regime using the Small Perturbation Method (SPM). For the fully nonlinear case, the flame-flow interaction effects are captured by developing an unsteady, compressible, coupled Euler-G-equation solver with a Ghost Fluid Method (GFM) module for applying the jump conditions across the flame.
The flame s nonlinear response is shown to exhibit two qualitatively different behaviors. Depending on the operating conditions and the disturbance field characteristics, it is shown that a combustor may exhibit supercritical bifurcations leading to a single stable limit cycle amplitude or exhibit sub-critical bifurcations wherein multiple stable solutions for the instability amplitude are possible. In addition, this study presents the first analytical model which captures the effects of unsteady flame stretch on the heat release response and thus extends the applicability of current models to high frequency instabilities, such as occurring during screech. It is shown that unsteady stretch effects, negligible at low frequencies (100 s of Hz) become significant at screeching frequencies (1000 s of Hz). Furthermore, the analysis also yields insight into the significant spatial dependence of the mean and perturbation velocity field induced by the coupling between the flame and the flow field. In order to meaningfully compare the heat release response across different flame configurations, this study has identified that the reference velocity (for defining the transfer function) should be based on the effective normal velocity perturbing the flame and the Strouhal number should be based on the effective residence time of the flame wrinkles.
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Dumont, Jean-Paul. "Etude de la structure spatiale de flammes turbulentes par laser." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37604738z.
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Lamige, Sylvain. "Analyse de l'influence des conditions aux limites thermiques sur la stabilisation des flammes non-prémélangées." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0099/document.
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La problématique de la stabilisation des flammes non-prémélangées reste primordiale. Il faut pour la résoudre déterminer l’importance relative des phénomènes aérodynamiques, thermiques et chimiques intervenant dans les mécanismes de stabilisation. La démarche expérimentale utilisée pour cela au cours de cette thèse porte une attention particulière sur l’influence des conditions aux limites thermiques, et comporte deux volets à travers lesquels le rôle des transferts thermiques est mis en exergue. D’abord, la zone d’attachement d’une flamme stabilisée derrière la lèvre du brûleur est examinée, en considérant les couplages entre le positionnement du bout de flamme à proximité du brûleur et la température de la lèvre. Différentes régions ont ainsi pu être identifiées selon le comportement du bout de flamme, qui évolue depuis une nature diffusive vers une nature propagative à l’approche des limites aérodynamiques de stabilité. Par ailleurs, une modification des propriétés thermiques du brûleur a permis de mettre en évidence une évolution, avec la température de la lèvre, du rôle relatif des modes de coincement thermique et chimique de la flamme par la paroi du brûleur. Ensuite, l’étude concerne non plus un état stabilisé de la flamme, mais les transitions entre les différents régimes de combustion, et plus particulièrement le décrochage d’une flamme attachée. L’examen des conditions conduisant à la déstabilisation de la flamme est un moyen d’apporter des éléments-clefs de compréhension quant aux couplages et aux équilibres aérothermochimiques prévalant préalablement au décrochage. Une évolution du processus de décrochage a ainsi été mise en avant avec l’augmentation de la température initiale des réactants, en lien avec l’évolution de phénomènes transitoires d’extinction locale de la zone de réactionNon-premixed flame stabilization is still an important issue in combustion. Addressing this issue requires to evaluate the relative importance of aerodynamic, thermal and chemical phenomena involved in the stabilization mechanisms. This thesis develops to this end an experimental approach, with a particular focus on the influence of thermal boundary conditions, examining the role of heat transfer in a twofold analysis. At first, the attachment zone of a rim-stabilized jet-flame is investigated, by careful consideration of the coupling existing between the burner lip temperature and the flame attachment location relative to the burner. Several regions have been identified according to the flame leading edge behavior, which evolves from diffusive to propagative closer to the aerodynamic stability limits. Besides, by modifying the burner thermal properties, a change has been shown in the relative roles of thermal and chemical quenching of the flame by the burner wall, depending on the burner lip temperature. Secondly, the attention is directed to transitions between different combustion regimes, namely attached and lifted flames. In particular, beyond the stable state of an attached flame, its lifting process is investigated. Examining in which conditions destabilization of the flame occurs indeed appears to be an ideal opportunity to gain insight into the aerothermochemical coupling and equilibriums existing prior to lift-off. Thus, the lifting process has been shown to be modified by the reactant initial temperature, in close relationship with the change in occurrence of localized transitory extinction events of the reaction zone
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Lacas, François. "Modélisation et simulation numérique de la combustion turbulente dans les moteurs fusée cryotechniques." Châtenay-Malabry, Ecole centrale de Paris, 1989. http://www.theses.fr/1989ECAP0095.
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Mise au point de modèles représentatifs des phénomènes fondamentaux de la combustion turbulente, monophasique d'hydrogène et d'oxygène dans les moteurs fusée cryotechniques. Application du modèle de la flamme cohérente au cas d'allumage de flamme de diffusion.
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Bouamoul, Amal. "Modélisation mathématique d'une flamme de diffusion méthane-air avec viciation et en configuration contre courant /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1999. http://theses.uqac.ca.
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Yamashita, Hiroshi, Yoshinori Ogata, and Kazuhiro Yamamoto. "Flame structure and flame spread rate over a solid fuel in partially premixed atmospheres." Elsevier, 2011. http://hdl.handle.net/2237/20040.
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Kao, Shiung-po. "Modified source-type flame model and vorticity generated by the flame and bluff bodies." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/37751.
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A numerical model is developed to simulate the wrinkled laminar flame sheet flapping in weakly turbulent premixed combustion. The wrinkled laminar flame sheet is represented by a discrete distribution of volume sources called source disks. These source disks are utilized to produce the acceleration of combustion products behind the flame sheet. The laminar flame speed is allowed to vary according to flame stretch. A modified source model is proposed against the background of the existing source model's physically unrealistic symmetric expansion in both the upstream and the downstream directions. This flame model also includes flame-generated vorticity which is associated with the increasing entropy intrinsic to any system going through an irreversible process. The flame-generated vorticity is treated as discrete vortex disks. Vorticity created on the surface of the flame holder is computed with the vortex sheet method and diffuses into the surrounding flow in the form of vortex disks. The freestream turbulence is simulated by injecting vortex disks into an initially uniform freestream.
Flame-flow interactions are studied when a thin circular cylinder, a large circular cylinder, and a flat plate normal to freestream are used as flame holders. Results sho\v that the modified source model gives more accurate prediction of flame angle than the existing source model does, the relative errors can be reduced by as much as four times. The modified source model also produces velocity profiles closer to those found in experiment, the deviations are cut by half at most sampling points in the flow. The vorticity shed from a thin circular cylinder flame stabilizer is found to only influence downstream regions very close to the cylinder. The eddy shedding behind a bluff body flame holder is suppressed in reacting flow simulations and the computed recirculating zone in a reacting flow is nearly half as long as that in a cold flow. When the relative size of the flame holder is one order of magnitude larger than the thickness of flame sheet, the vorticity shed by the flame holder can no longer be neglected. Flame wrinkling and flame extinction caused by vortical fluid motion behind the flame holder are found through numerical simulation.Ph. D.
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Bush, Scott M. "Characterization of flame stabilization technologies." Cincinnati, Ohio : University of Cincinnati, 2006. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1163730308.
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Uddholm, Per. "Numerical Simulation of Flame Propagation." Thesis, Uppsala University, Department of Information Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-98325.
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The effects of the temperature and length, of the preheat zone, on the deflagration to detonation transition are investigated through numerical simulation. The Navier-Stokes equations, with a reaction term, are solved in one dimension. The time integration is a one-dimensional adaptation of an existing two-dimensional finite volume method code. An iterative scheme, based on an overlap integral, is developed for the determination of the deflagration to detonation transition. The code is tested in a number of cases, where the analytical solution (to the Euler equations) is known. The location of the deflagration to detonation transition is displayed graphically through the preheat zone temperature as a function of the fuel mixture temperature, for fixed exhaust gas temperature and with the preheat zone length as a parameter. The evolution of the deflagration to detonation transition is investigated for an initial state well within the regime where the deflagration to detonation transition occurs. Graphs displaying the temporal evolution of pressure, temperature, reaction rate, and fuel mass fraction are presented. Finally, a method for estimating the flame velocity during the deflagration and detonation phases, as well as the flame acceleration during the intermediate phase, is developed.
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Isitman, Nihat Ali. "Flame Retardancy Of Polymer Nanocomposites." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614258/index.pdf.
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This thesis is aimed to understand the role of nanofiller type, nanofiller dispersion, nanofiller geometry, and, presence of reinforcing fibers in flame retardancy of polymer nanocomposites. For this purpose, montmorillonite nanoclays, multi-walled carbon nanotubes, halloysite clay nanotubes and silica nanoparticles were used as nanofillers in polymeric matrices of poly (methyl methacrylate) (PMMA), high-impact polystyrene (HIPS), polylactide (PLA) and polyamide-6 (PA6) containing certain conventional flame retardant additives. Furthermore, the influence of nanofiller and flame retardant additives on fiber/matrix interfacial interactions was studied.
Materials were prepared by twin-screw extrusion melt-mixing and ultrasound-assisted solution-mixing techniques. Characterization of nanocomposite morphology was done by X-ray diffraction and transmission electron microscopy. Flame retardancy was investigated by mass loss cone calorimetry, limiting oxygen index measurements and UL94 standard tests. Flame retardancy mechanisms were revealed by characterization of solid fire residues by scanning electron microscopy, transmission electron microscopy, infrared spectroscopy and X-ray diffraction. Thermal degradation and stability was studied using thermogravimetric analysis. Mechanical properties were determined by tension tests and fracture surfaces were observed under scanning electron microscope.
Influence of nanofiller type was investigated comparing the behavior of montmorillonite nanoclay and multi-walled carbon nanotube reinforced PMMA nanocomposites containing phosphorous/nitrogenous intumescent flame retardant. Carbon nanotubes hindered the formation of intumescent inorganic phosphate barrier which caused the samples to be exposed to larger effective heat fluxes during combustion. Contrarily, nanoclays physically reinforced the protective barrier without disrupting the intumescent character, thereby allowing for lower heat release and mass loss rates, and increased amounts of residue upon combustion.
Influence of nanofiller dispersion was studied comparing nanocomposite and microcomposite morphologies in montmorillonite nanoclay reinforced HIPS containing aluminum hydroxide flame retardant. Relative to microcomposite morphology, reductions in peak heat release rates were doubled along with higher limiting oxygen index and lower burning rates with nanocomposite formation. Improved flame retardancy was attributed to increased amounts of char residue and lower mass loss rates. Nanocomposite formation allowed for the recovery of tensile strength reductions caused by high loading level of the conventional flame retardant additive in polymer matrix.
Influence of nanofiller geometry was investigated for phosphorus based intumescent flame-retarded PLA nanocomposites. Fire performance was increased in the order of rod-like (1-D) <spherical (0-D) <
<
plate-like (2-D) geometries which matched qualitatively with the effective surface area of nanoparticles in the nanocomposite. Well-dispersed plate-like nanoparticles rapidly migrated and accumulated on exposed sample surface resulting in the formation of strong aluminum phosphate/montmorillonite nanocomposite residue. Mechanical properties were increased in the order of 0-D <
1-D <
2-D nanofillers corresponding to the order of their effective aspect ratios in the nanocomposite. Influence of fiber reinforcement was studied for montmorillonite nanoclay containing short-glass fiber-reinforced, phosphorus/nitrogen based flame-retarded PA6 composites. Substitution of a certain fraction of conventional additive with nanofiller significantly reduced peak heat release rate, delayed ignition and improved limiting oxygen index along with maintained UL94 ratings. Improved flame retardancy was ascribed to the formation of a nanostructured carbonaceous boron/aluminum phosphate barrier reinforced by well-dispersed montmorillonite nanolayers. Fiber/matrix interfacial interactions in flame-retarded PA6 and HIPS containing nanoclays were investigated using a micromechanical approach, and it was found that the influence of nanoclay on the interface depends on crystallinity of polymer matrix. While the fiber/matrix interfacial strength is reduced with nanoclay incorporation into amorphous matrix composites, significant interfacial strengthening was imparted by large surface area, well-dispersed clay nanolayers acting as heterogeneous nucleation sites for the semi-crystalline matrix.
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de, Rooy S. C. "Improved efficiencies in flame weeding." Lincoln University, 1992. http://hdl.handle.net/10182/18.
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Possible areas of improving the efficiencies of the Lincoln University flame weeder are identified and investigated. The Hoffmann burner initially used in the Lincoln University flame weeder was found not to entrain sufficient air to allow complete combustion of the LPG used. A new burner, the Modified Lincoln University burner, was designed to improve the entrainment of air. Results show that the new design entrained sufficient air to theoretically allow complete combustion of the LPG, and this resulted in a 22.7% increase in heat output per Kg of LPG used over the Hoffmann burner. Temperature x time exposure constants required to kill weeds 0 - 15, 15 - 30, and 30 - 45 mm in size, were found to be respectively 750, 882, and 989 degrees Celsius.Seconds. These constants can be used to calculate the maximum speed of travel an operator can use a flame weeder at, once the temperature profile underneath its shields are established at various travel speeds, and therefore ensure that the flame weeder is used at its maximum efficiency. The constants can also be used to establish the cost efficiency of any flame weeder (in $/Ha), depending on the size of the weeds to be treated. The materials and methods used in establishing the temperature x time exposure constants can be used to establish the temperature x time exposure constant of any weed species at any size.
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Petchenko, Arkady. "Numerical study of flame dynamics." Doctoral thesis, Umeå : Institute of Physics, Umeå Univ, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1313.
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Elbasuney, Sherif. "Enhanced flame retardant polymer nanocomposites." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/14587/.
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Fire is a continuous threat to life and property. The total annual UK fire loss is estimated to be 0.25% of its gross domestic product (GDP) (Goddard, 1995). According to fire statistics, more than 12 million fires break out every year in the United States, Europe, Russia, and China killing about 166,000 people and injuring several hundreds of thousands (Morgan and Wilkie, 2007). Polymers which take up 80% of the organic chemical industry, are known for their high flammability with the production of heat, corrosive toxic gases, and smoke (Bent, 2010). Improving the fire retardancy of polymeric materials is a major concern and also a major challenge. Nanotechnology could have a significant impact on polymeric materials through the achievement of polymer nanocomposites (PNs) with enhanced functional properties (Giannelis, 1996, Schartel and Batholmai, 2006). If this can be achieved, there will be an enormous increase in the use of improved flame retardant (FR) PNs in mass transportation, aerospace, and military applications where fire safety will be of utmost importance (Horrocks and Price, 2008). In this research project nanoparticles that could have a synergistic effect with traditional FR systems, or that could have a FR action (nano-fire extinguishers), were formulated and surface modified during continuous hydrothermal synthesis (CHS). The bespoke nanoparticles were developed in a structure that could be easily integrated and effectively dispersed into a polymeric matrix. A solvent blending approach for integrating and dispersing colloidal organic modified nanoparticles into polymeric matrices was developed. The impact of nanoparticles of different morphologies including nanospheres, nanoplates, and nanorods on epoxy mechanical, thermal, and flammability properties was evaluated. A laboratory based technique using a Bunsen, video footage, and image analysis was developed to quantify the nanocomposite's direct flame resistance in a repeatable fashion. A new self extinguishing epoxy nanocomposite was developed which showed an enhanced performance in extreme conditions and with good mechanical properties.
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Wu, Z. Y. "Studies in unsteady flame propagation." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38197.
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BUSH, SCOTT M. "CHARACTERIZATION OF FLAME STABILIZATION TECHNOLOGIES." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163730308.
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Lemon, Brian R. "Characteristics and applications of micro-scale flames." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/15931.
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Marshall, Andrew. "Turbulent flame propagation characteristics of high hydrogen content fuels." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53859.
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Increasingly stringent pollution and emission controls have caused a rise in the use of combustors operating under lean, premixed conditions. Operating lean (excess air) lowers the level of nitrous oxides (NOx) emitted to the environment. In addition, concerns over climate change due to increased carbon dioxide (CO2) emissions and the need for energy independence in the United States have spurred interest in developing combustors capable of operating with a wide range of fuel compositions. One method to decrease the carbon footprint of modern combustors is the use of high hydrogen content (HHC) fuels. The objective of this research is to develop tools to better understand the physics of turbulent flame propagation in highly stretch sensitive premixed flames in order to predict their behavior at conditions realistic to the environment of gas turbine combustors.
This thesis presents the results of an experimental study into the flame propagation characteristics of highly stretch-sensitive, turbulent premixed flames generated in a low swirl burner (LSB). This study uses a scaling law, developed in an earlier thesis from leading point concepts for turbulent premixed flames, to collapse turbulent flame speed data over a wide range of conditions. The flow and flame structure are characterized using high speed particle image velocimetry (PIV) over a wide range of fuel compositions, mean flow velocities, and turbulence levels. The first part of this study looks at turbulent flame speeds for these mixtures and applies the previously developed leading points scaling model in order to test its validity in an alternate geometry. The model was found to collapse the turbulent flame speed data over a wide range of fuel compositions and turbulence levels, giving merit to the leading points model as a method that can produce meaningful results with different geometries and turbulent flame speed definitions. The second part of this thesis examines flame front topologies and stretch statistics of these highly stretch sensitive, turbulent premixed flames. Instantaneous flame front locations and local flow velocities are used to calculate flame curvatures and tangential strain rates. Statistics of these two quantities are calculated both over the entire flame surface and also conditioned at the leading points of the flames. Results presented do not support the arguments made in the development of the leading points model. Only minor effects of fuel composition are noted on curvature statistics, which are mostly dominated by the turbulence. There is a stronger sensitivity for tangential strain rate statistics, however, time-averaged values are still well below the values hypothesized from the leading points model. The results of this study emphasize the importance of local flame topology measurements towards the development of predictive models of the turbulent flame speed.
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Haynes, Joel M. "Aerodynamic design of no NOx oil diffusion flames using the radially stratified flame core burner." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/11224.
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Kruger, Hermanus Joachim. "Characterisation of expandable graphite and its flame retardant abilities in flame retardant systems for polyethylene." Thesis, University of Pretoria, 2017. http://hdl.handle.net/2263/61304.
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In the pursuit of lower cost intumescent flame retardant (IFR) systems, the compound expandable graphite (EG) was identified. This compound delivers high flame retardant performance but provides non-uniform thermal shielding when exposed to open flame from below due to negative gravitational effects. It was theorised that this may be remedied either through ion exchange of the interstratified ions with low glass transition ions or through use in binary systems with other compounds. Two classes of commercial EG were identified, namely a low and a high expansion onset temperature EG compound. Extensive characterisation of each EG compound was undertaken to assess its composition, expansion mechanisms and onset temperatures in order to identify compatible compounds for binary use. The susceptibility of each compound to ion exchange was also assessed. An industrial IFR ethylenediamine phosphate (EDAP) and a novel flame retardant were synthesised for assessment in binary use with EG. Coupled with the above study, this project developed two novel fire testing techniques as low cost alternatives to well-established fire testing methods such as cone calorimetry.
The first technique involved an open flame fire testing method which allowed vertical or horizontal testing. Digital and infrared (IR) video recording during operation facilitated comparison of multiple performance indicators further strengthening this method. The second technique allowed assessment of the mass loss resistance of each compound during laser pyrolysis. Characterisation of the EG compounds allowed development of structural models to describe each compound and explain the mechanisms of their expansion and gaseous release. Exhaustive ion exchange testing did not deliver favourable results, necessitating the pursuit of compounds for binary use with EG. A novel IFR was synthesised by neutralising 3,5-diaminobenzoic acid hydrochloride salt with ammonium dihydrogen phosphate. This compound, which melts at 257 °C, decomposes concurrently to release carbon dioxide gas which promotes intumescent charring. The flame retardant performance of this compound and EDAP as primary flame retardants and in combination with expandable graphite was evaluated. As a proof of concept, the novel compound was tested as a primary flame retardant using cone calorimetry after which its utility in binary systems with low temperature expandable graphite was tested. Substantial decreases in peak heat release rate (pHRR) and flame out time were achieved for all binary systems. This success led to testing of a number of combinations of low and high expansion onset EG and the other IFRs to identify the highest performing combination, which proved to be the 10-10 EDAP-EG system. Combinations of EG and the novel compound also showed excellent results. The novel fire testing techniques proved effective in identifying high performance combinations and showed comparable trends to those measured in cone calorimetry, at a greatly reduced cost and material requirement. IR analysis of open flame fire testing indicated increases in the temperatures required for ignition and burn through of the substrate. Observations, corroborated by optical video, showed that cohesive and uniform thermal shielding was achieved in all binary systems tested.
This study illustrates that systems of 10% EG combined with either 10% DABAP or 10% EDAP are both the most economical binary systems tested but are extremely high performance systems as well. Both of these systems delivered excellent results while being more economic than the widely used industrial system with a 25-30% EDAP loading. It is recommended that these compounds be considered for industrial use. Furthermore, the effective fire testing techniques developed in this study may be utilised in future fire testing to identify high performance compounds at a lower cost prior to further assessment through methods such as cone calorimetry.Thesis (PhD)--University of Pretoria, 2017.
Chemical Engineering
PhD
Unrestricted
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Jiang, Ching-Biau. "A model of flame spread over a thin solid in concurrent flow with flame radiation." Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1062696685.
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Kypraiou, Anna-Maria. "Experimental investigation of the response of flames with different degrees of premixedness to acoustic oscillations." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275743.
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This thesis describes an experimental investigation of the response of lean turbulent swirling flames with different degrees of premixedness (i.e. different mixture patterns) to acoustic forcing using the same burner configuration and varying only the fuel injection strategy. Special emphasis was placed on the amplitude dependence of their response. Also, the behaviour of self-excited fully premixed flames was examined. kHz OH* chemiluminescence was used to study qualitatively the heat release response of the flames, while kHz OH Planar Laser Induced Fluorescence (PLIF) was employed to understand the response of the flame structure and the behaviour of the various parts of the flame. The Proper Orthogonal Decomposition (POD) method was used to extract the dominant structures of the flame and their periodicity. In the first part of the thesis, self-excited oscillations were induced by extending the length of the duct downstream of the bluff body. It was found that the longer the duct length and the higher the equivalence ratio, the stronger the self-excited oscillations were, with the effect of duct length being much stronger. The dominant frequencies of the system were found to increase with equivalence ratio and bulk velocity and decrease with duct length. For some conditions, three simultaneous periodic motions were observed, where the third motion oscillated at a frequency equal to the difference of the other two frequencies. A novel application of the POD method was proposed to estimate the convection velocity from the most dominant reaction zone structures detected by OH* chemiluminescence imaging. For a range of conditions, the convection velocity was found to be in the range of 1.4-1.7 bulk flow velocities at the inlet of the combustor. In the second part, the response of fully premixed, non-premixed with radial fuel injection (NPR) and axial fuel injection (NPA) flames was investigated and compared. All systems exhibited a nonlinear response to acoustic forcing. The highest response was observed by the NPR flame, followed by the fully premixed and the non-premixed with axial fuel injection flame. The proximity of forced flames to blow-off was found to be critical in their heat release response, as close to blow-off the flame response was significantly lower than that farther from blow-off. In the NPR and NPA systems, it was shown that the acoustic forcing reduced the stability of the flame and the stability decreased with the increase in forcing amplitude. In the fully premixed system, the flame area modulations constituted an important mechanism of the system, while in the NPR system both flame area and equivalence ratio modulations were important mechanisms of the heat release modulations. The quantification of the local response of the various parts of the flame at the forcing frequency showed that the ratio RL (OH fluctuation at 160 Hz to the total variance of OH) was greater in the inner shear layer region than in the other parts in the case of NPR and NPA flames. In fully premixed flames, greater RL values were observed in large regions on the downstream side of the flame than those in the ISL region close to the bluff body. The ratio of the convection velocity to the bulk velocity was estimated to be 0.54 for the NPR flame, while it was found to be unity for the respective fully premixed flame. In the last part of the thesis, the response of ethanol spray flames to acoustic oscillations was investigated. The nonlinear response was very low, which was reduced closer to blow-off. The ratio RL was the highest in the spray outer cone region, downstream of the annular air passage, while RL values were very low in the inner cone region, downstream of the bluff body. Unlike NPR and fully premixed flames, in case of spray and NPA systems, it was found that forcing did not affect greatly the flame structure. The understanding of the nonlinear response of flames with different degrees of premixedness in a configuration relevant to industrial systems contributes to the development of reliable flame response models and lean-burn devices, because the degree of premixedness affects greatly the flame response. Also, the understanding of the behaviour of forced spray flames is of great interest for industrial applications, contributing to the development of thermoacoustic models for liquid fuelled combustors. Finally, the estimation of the convection velocity is of importance in the modelling of self-excited flames and flame response models, since the convection velocity affects the flame response significantly.
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Palacios, Rosas Adriana. "Study of Jet Fires Geometry and Radiative Features." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/6487.
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Entre els accidents greus que poden ocórrer a les instal·lacions industrials o durant el transport de substàncies perilloses, els dolls de foc presenten un especial interès. Tot i que tenen una distància relativament més curta d'afectació que altres accidents greus, es caracteritzen per originar grans fluxos de calor i, en cas de contacte de la flama amb un equip, originen sovint un efecte domino, desencadenant una subseqüent explosió, incendi o altres esdeveniments amb greus conseqüències.Diversos estudis experimentals i teòrics han estat efectuats; no obstant això, la majoria d'aquests han estat enfocats a dolls de foc a escala de laboratori, flames subsòniques o torxes, les condicions de les quals difereixen significativament d'aquelles trobades en dolls de foc accidentals reals, que normalment assoleixen majors longituds de flama i velocitats de sortida sònica. Aquesta manca d'investigació és la raó per explicar perquè els dolls de foc eren encara molt mal coneguts i la predicció dels seus efectes i conseqüències era encara un problema. Aquesta tesi ha estat elaborada per a obtenir informació nova i útil sobre els dolls de foc, millorant la comprensió de la seva geometría i de les característiques tèrmiques, mitjançant l'anàlisi, l'experimentació i el modelatge matemàtic.
Aquest estudi s'ha centrat alhora en dades existents i en noves dades experimentals, implicant Aixa dolls de foc verticals i horitzontals alliberats en absència de vent, implicant diversos combustibles (hidrogen, metà i propà). L'estudi comprèn una àmplia gamma de variables d'operació (velocitats de sortida del combustible, pressions en la canonada i diàmetres d'orifici de sortida). L'estudi experimental ha implicat dolls de foc amb flames de fins a 10.3 m de longitud i 1.5 m d'amplada. El combustible utilitzat ha estat propà, amb velocitats de sortida sònica i subsònica, utilitzant diversos diàmetres d'orifici de sortida. Els dolls de foc han estat filmats amb dues càmeres de vídeo (VHS) i una càmera termográfica d'alta velocitat (IR). Les principals característiques geomètriques de les flames (dimensions i forma) han estat analitzades en funció de la velocitat de sortida del combustible,
del flux màssic i del diàmetre d'orifici de sortida. L'anàlisi i tractament d'imatges infraroges i de les mesures obtingudes amb tres sensors de flux de calor situats a diferents distàncies de la sortida del doll de foc han permès l'obtenció de les seves principals característiques de radiació: flux de calor irradiat als voltants (persones i instal·lacions) en funció de la distancia, poder emissiu i emisivitat de les flames. Diverses expressions han estat proposades per estimar les dimensions de la flama en funció de diverses variables (flux màssic, diàmetre d'orifici de sortida i nombres de Froude i Reynolds). Els resultats i expressions obtinguts en aquest estudi contribueixen a una millor comprensió dels dolls de foc, representant un avanç en les metodologies i l'establiment de noves mesures, normes i polítiques de planificació per a la prevenció i/o el control d'aquest tipus d'accident greu amb foc, tant en establiments industrials com en el transport de materials perillosos.
Among the major accidents that can occur in processing plants or in the transportation of hazardous materials, jet fires are of particular interest. Although they have a relatively shorter distance of influence than other major accidents, they are characterized by high heat fluxes and if there is flame impingement they can originate a domino effect, leading to a subsequent explosion, large fire, or other events with severe effects. Several experimental and theoretical studies have been carried out; however, most of those works have been focused on small-scale jet fires, subsonic flames or flares, the conditions of which significantly differ from those found in real accidental jet fires, usually reaching larger flame lengths and sonic exit velocities. This lack of research is the reason to explain why the current knowledge of jet fires was still rather poor and the accurate prediction of their effects and consequences was still a problem. The present thesis has been addressed to produce a significant amount of novel and useful information on jet fires, by improving understanding of jet fire structure, reach and radiative features, through analyses, experiment and mathematical modelling. This study has been focused on both existing and also new experimental jet flame data, comprising all together, turbulent non-premixed jet flames vertically and horizontally released into still air, involving several fuels (hydrogen, methane and propane), over a wide range of operational conditions (jet exit velocities, release pressures and pipe diameters). The experimental study developed in this thesis has concerned relatively large jet fires with flames of up to 10.3 m in length and 1.5 m in width. The fuel was propane, and both sonic and subsonic jet exit velocities were obtained from different outlet diameters. The jet fires were filmed with two videocameras registering visible light (VHS) and a thermographic camera (IR). The main geometrical features of the flames were analyzed as a function of the fuel velocity, mass flow rate and jet outlet diameter: jet flame size and flame shape. The treatment of infrared images and measurements obtained from three heat flow sensors located at different distances from the jet fire outlet also led the main radiative features of jet fires to be obtained: incident thermal radiation heat over a target, surface emissive power and emissivity of the flames.
Expressions for estimating jet flame reach as a function of several variables (mass flow rate, orifice exit diameter, Froude and Reynolds numbers) have also been proposed. The results and the expressions obtained in this study contribute to a better understanding of jet fires for accurate risk assessment, allowing the obtention of important advances in risk assessment methodologies and the establishment of new measures, regulations, and risk planning policies for the prevention and/or control of this type of major fire, occurred world-wide in industrial establishments and in the transportation of hazardous materials.
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Kariuki, James Mwangi. "Turbulent premixed flame stabilization and blow-off." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607695.
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