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1
Flavel, Benjamin S. [Verfasser]. "Carbon Nanotubes for Electronics and Energy / Benjamin S. Flavel." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/1163728802/34.
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Parker, Nathan Thomas. "Proselytisation and apocalypticism in the British Atlantic world : the theology of John Flavel." Thesis, Durham University, 2013. http://etheses.dur.ac.uk/7276/.
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This thesis examines the theology of the prominent Puritan minister John Flavel (1627-91). In addition to investigating his methods of proselytising and his beliefs about the apocalypse it argues that his evangelistic approach had a significant transatlantic impact in the eighteenth century. Chapter one argues that Flavel’s approach to proselytising can be understood as an interplay between three grids. First, he argued that there were two realisations at which his hearers must arrive in order to be converted. Second, he argued that, from the vantage point of the preacher, there were three faculties within the human soul where he must direct his evangelistic efforts. Third, Flavel maintained that there were (roughly) ten theological events which must transpire within the soul for a person to experience conversion. Whilst the subject was conscious of some of these states, others were imperceptible. Chapter two demonstrates that Flavel posited two distinct levels upon which these theological states operated: common and saving. Chapter three explores the practical ways in which Flavel led people to experience Christian salvation. Chapter four contends that Flavel’s beliefs about the return of Christ changed over time. In the early part of his ministry, he did not speak of the return of Christ as being imminent, but by 1689 he was convinced that it was at hand. This had implications for his evangelism. Chapter five argues that Flavel’s approach to proselytising had a significant impact on individuals in the eighteenth century, especially around the time of the Great Awakening. This case is constructed through the presentation of several pieces of evidence: numerous people who were converted through reading his sermons, an evaluation of Flavel in print, and marginalia located in copies of his books printed between 1664 and 1799.
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Boone, Clifford. "Puritan evangelism : preaching for conversion in late-seventeenth century English puritanism as seen in the works of John Flavel." Thesis, University of Wales Trinity Saint David, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683232.
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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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Takasao, Shinsuke. "Fundamental Magnetohydrodynamic Processes of Solar Flares: Formation of Flare-productive Regions and Evolution of Flare Loops." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215316.
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Lawal, Mohammed Shariff. "Numerical modelling of jet flames in a cross-flow : application to flares." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539693.
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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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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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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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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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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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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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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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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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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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Khanna, Vivek K. "A Study of the Dynamics of Laminar and Turbulent Fully and Partially Premixed Flames." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/28527.
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This present research effort was directed towards developing reduced order models for the dynamics of laminar flat flames, swirl stabilized turbulent flames, and in evaluating the effects of the variation in fuel composition on flame dynamics. The laminar flat flame study was conducted on instrument grade methane, propane, and ethane flames for four total flow rates from 145 cc/sec to 200 cc/sec, and five equivalence ratios from 0.5 to 0.75. The analysis was done by measuring the frequency resolved velocity perturbations, u', and the OH* chemiluminescence, as a measure of unsteady heat release rate, q'. The experimental data showed the corresponding flame dynamics to be fourth order in nature with a pure time delay. One of the resonance was shown to represent the pulsation of the flame location caused by fluctuation in the flame speed and fluctuating heat losses to the flame stabilizer. The other resonance was correlated to the dynamics of the chemical kinetics involved in the combustion process. The time delay was correlated to the chemical time delay. Upon comparing the results of the experiments with the three fuels, it was concluded that for all equivalence ratios studied, propane flame had a higher dynamic gain than methane flames. Ethane flames exhibited a higher dynamic gain than methane flame in the frequency range of 20-100 Hz. Thus, burning of propane instead of methane increased the likelihood of the occurrence of thermo-acoustic instabilities. The experimental techniques developed during the dynamic studies conducted on laminar flat flames were applied to swirl stabilized turbulent flames. Experiments were performed for QAir = 15 scfm and 20 scfm, F = 0.55, 0.6, 0.65, and S = 0.79 and 1.19. The results of fully premixed experiments showed that the flame behaved as a 8th order low pass filter. The results of the partially premixed experiment exhibited a rich spectra, which maintained its bandwidth over the entire range of frequency studied. Comparison of fully and partially premixed flames in the frequency range of 200-400 Hz, indicated that at overall lean conditions the dynamic gain of the totally premixed flames was almost an order of magnitude lower than that of the partially premixed conditions. Thus, it was concluded that combustors with fully premixed flames have a higher probability of being thermo-acoustically stable than those with partially premixed flames.Ph. D.
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Allred, Joel C. "Observations and radiative hydrodynamic simulations of solar and stellar flares /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9631.
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Calderari, Thaiane Ortolan 1986. "Biodiversidade de fungos aflatoxigênicos e aflatoxinas em castanha do Brasil." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/254596.
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Orientadores: José Luiz Pereira, Marta Hiromi TaniwakiDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: A castanha do Brasil (Bertholletia excelsa) é uma das mais importantes espécies de exploração extrativista da floresta Amazônica, sendo exportada para diversos países devido ao seu alto valor nutritivo. No entanto, os baixos níveis tecnológicos característicos de sua cadeia produtiva, considerada ainda extrativista e as condições inadequadas de manejo da matéria prima, favorecem o aparecimento de contaminação por fungos produtores de aflatoxinas, compostos tóxicos considerados cancerígenos para humanos. Este problema é um entrave para a comercialização do produto, principalmente no mercado externo, dado ao rigoroso controle de países europeus e Estados Unidos em relação aos níveis de toxinas presentes nos alimentos. Nestas condições, o presente trabalho teve por objetivo investigar a incidência de fungos em castanhas do Brasil e avaliar o potencial toxigênico dos isolados Aspergillus section flavi para a produção de aflatoxinas, bem como analisar a presença de aflatoxinas nesta matriz. Um total de 143 amostras provenientes dos Estados do Pará, Amazonas e São Paulo em diferentes etapas da cadeia produtiva da castanha foi analisado. A técnica utilizada para análise da infecção fúngica foi o plaqueamento direto em meio Dicloran 18% Glicerol. Os resultados foram expressos em porcentagem de infecção fúngica. Os isolados suspeitos foram purificados em meio Czapek extrato de levedura ágar e incubados a 25ºC/7 dias em diferentes temperaturas para a identificação das espécies. Para a análise do potencial toxigênico de cada isolado da seção flavi foi utilizada a técnica do ágar plug. Para a análise de aflatoxinas foi utilizada coluna de imunoafinidade para extração e limpeza das amostras e Cromatografia Líquida de Alta Eficiência e detector de fluorescência acoplado ao sistema de derivatização Kobracell para detecção e quantificação das aflatoxinas. Dentre o total de amostras coletadas, aquelas provenientes das florestas foram as que apresentaram maior valor médio de atividade de água, assim como maior porcentagem de infecção fúngica quantificada e biodiversidade de espécies. Considerando todas as amostras avaliadas, foram no total 13.421 isolados de fungos filamentosos, sendo que as espécies mais incidentes foram Aspergillus flavus, Aspergillus nomius, Penicillium citrinum, Aspergillus tamarii, Syncephalastrum racemosum e Penicillium sp. Dentre as espécies encontradas, 450 isolados de Aspergillus nomius e 9 de Aspergillus parasiticus foram identificados e 100% apresentaram capacidade de produção de aflatoxinas AFB1, AFB2, AFG1, AFG2. Dos de 703 isolados de Aspergillus flavus, 63,5% apresentaram a capacidade de produzir aflatoxinas AFB1 e AFB2. A média de contaminação por aflatoxinas totais obtida foi de 7,17 µg/kg (ND-104,2 µg/kg), 1,13µg/kg (ND-7,44µg/kg) e 0,47 µg/kg (ND-0,2 µg/kg) para as amostras dos Estados do Pará, Amazonas e de São Paulo, respectivamente. Das 143 amostras coletadas, apenas 5 amostras excederam o limite máximo de aflatoxinas totais estabelecido pela União Européia e pela ANVISA (10,0ug/kg para castanhas do Brasil sem casca destinadas ao consumo direto para humanos)
Abstract: The Brazil nut (Bertholletia excelsa) is one of the most important species extracted from the Amazon forest, and is exported to several countries due to its high nutritional value. However, the low technological level of its productive chain and inadequate raw material handling favour contamination points for aflatoxin fungi producers aflatoxins. The presence of aflatoxins in Brazil nuts has been a barrier for its marketing, mainly for the export market, due to rigorous control of European countries and the United States. Therefore, the present work had the objective of investigating the incidence of fungi in Brazil nuts and evaluate the toxigenic potential of Aspergillus section flavi isolates to produce aflatoxins, as well as analyzing the presence of aflatoxins in this product. A total of 143 samples from three different states, at different stages of the Brazil nut chain was analyzed. The technique used for fungi infection analized was direct plating in DG18. The results were expressed in percentage of fungal infection. The suspected isolates were purified on Czapek yeast extract agar (CYA) and incubated at different temperature for species identification. For toxin production analysis of each isolatec Aspergillus section flavi the agar plug technique was used. For aflatoxin analysis an immunoafinity column was used for extraction and cleaning of the sample, high performance liquid for aflatoxin detection and quantification in Brazil nuts, chromatography (HPLC) with a fluorescence detector was used, coupled with the Kobracell derivatization system. Among the analyzed samples, the ones collected directly from the forests had the highest water activity, the highest fungal infection and greatest biodiversity of species. A total of 13,421 filamentous fungi were quantificated from all the samples with the most common isolated species were: Aspergillus flavus, Aspergillus nomius, Penicillium citrinum, Aspergillus tamarii, Syncephalastrum racemosum e Penicillium spp. All the 450 strains of Aspergillus nomius and 9 strains of Aspergillus parasiticus, showed 100% capacity of aflatoxin B1, B2, G1, G2 production. Out of 703 species of Aspergillus flavus isolated, 63.5% showed capacity of aflatoxin B1 e B2 production. The average of total aflatoxin contamination was: 7.17µg/kg (ND-104.2 µg/kg), 1.13µg/kg (ND-7.44µg/kg) and 0.47 µg/kg (ND-0.2 µg/kg) for samples from Pará, Amazon and São Paulo, respectively. Out of 143 analyzed samples, only 5 samples exceded the maximum level for total aflatoxins established by the European Union and ANVISA of 10 µg/kg for shelled Brazil nuts intended for direct human consumption
Mestrado
Ciência de Alimentos
Mestre em Ciência de Alimentos
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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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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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Fecteau, Andre. "The Effects of Compressibility on the Propagation of Premixed Deflagration." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39402.
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The thesis addresses the influence of compressible effects on the stability of deflagration waves. Due to the quasi-isobaric nature of slow flames, compressible effects in laminar flames are usually neglected. Nevertheless, turbulent deflagrations may propagate at substantially higher speeds, suggesting that compressible effects may play a role in their dynamics. In the present thesis, the stability of diffusion-dominated high-speed deflagrations is addressed. The deflagration is studied in the thickened regime, hence addressing the long wavelength limit of these deflagrations. The deflagrations are modelled by the compressible reactive Navier-Stokes equations with a single-step Arrhenius reaction model. The 2D stability of the steady traveling-wave solution is studied by direct simulation. It is found that, as the flame compressibility becomes significant, not only does the growth rates of the cellular profile of the deflagration waves increase, but the traditional correlation of the burning velocity and the flame surface area become far less strong. Significant compression regions form in front of the nonlinear flames. These compression regions have been found to increase the growth rates by increasing the temperature of the unburned gas in front of the flames, as well as convecting the flame forward. The results show that the flame propagation velocity in references to the unburned gas was significantly faster than the burning velocity. The vorticity was given consideration, as the compressibility of flame increase one can expect the baroclinic source to be of greater significance. The vorticity was show to, in effect, increase as compressibility increases while unexpectedly having a stabilizing direction of rotation on the cellular structure of the flames.
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Park, Doyoub. "EFFECTS OF TRANSPORT PROPERTIES AND FLAME UNSTEADINESS ON NITROGEN OXIDES EMISSIONS FROM LAMINAR HYDROGEN JET DIFFUSION FLAMES." Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2968.
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Experimental studies on the coupled effects of transport properties and unsteady fluid dynamics have been conducted on laminar, acoustically forced, hydrogen jet diffusion flames diluted by argon and helium. The primary purpose of this research is to determine how the fuel Lewis number and the flow unsteadiness play a combined role in maximum flame temperature and affect NOx emission from jet diffusion flame. The fuel Lewis number is varied by increasing/decreasing the mole fraction of diluents in the fuel stream. Therefore, maximum flame temperatures and then NOx emission levels were expected to differ for Ar- and He-diluted flames. In an investigation of unsteady flames, two different frequencies (10 and 100 Hz) were applied to observe a behavior of NOx emission levels and flame lengths by changes of unsteady fluid dynamics and transport properties.M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
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Amato, Alberto. "Leading points concepts in turbulent premixed combustion modeling." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52247.
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The propagation of premixed flames in turbulent flows is a problem of wide physical and technological interest, with a significant literature on their propagation speed and front topology. While certain scalings and parametric dependencies are well understood, a variety of problems remain. One major challenge, and focus of this thesis, is to model the influence of fuel/oxidizer composition on turbulent burning rates.
Classical explanations for augmentation of turbulent burning rates by turbulent velocity fluctuations rely on global arguments - i.e., the turbulent burning velocity increase is directly proportional to the increase in flame surface area and mean local burning rate along the flame. However, the development of such global approaches is complicated by the abundance of phenomena influencing the propagation of turbulent premixed flames. Emphasizing key governing processes and cutting-off interesting but marginal phenomena appears to be necessary to make further progress in understanding the subject.
An alternative approach to understand turbulent augmentation of burning rates is based upon so-called "leading points", which are intrinsically local properties of the turbulent flame. Leading points concepts suggest that the key physical mechanism controlling turbulent burning velocities of premixed flames is the velocity of the points on the flame that propagate farthest out into the reactants. It is postulated that modifications in the overall turbulent combustion speed depend solely on modifications of the burning rate at the leading points since an increase (decrease) in the average propagation speed of these points causes more (less) flame area to be produced behind them. In this framework, modeling of turbulent burning rates can be thought as consisting of two sub-problems: the modeling of (1) burning rates at the leading points and of (2) the dynamics/statistics of the leading points in the turbulent flame. The main objective of this thesis is to critically address both aspects, providing validation and development of the physical description put forward by leading point concepts.
To address the first sub-problem, a comparison between numerical simulations of one-dimensional laminar flames in different geometrical configurations and statistics from a database of direct numerical simulations (DNS) is detailed. In this thesis, it is shown that the leading portions of the turbulent flame front display a structure that on average can be reproduced reasonably well by results obtained from model geometries with the same curvature. However, the comparison between model laminar flame computations and highly curved flamelets is complicated by the presence of negative (i.e., compressive) strain rates, due to gas expansion. For the highest turbulent intensity investigated, local consumption speeds, curvatures, strain rates and flame thicknesses approach the maximum values obtained by the laminar model geometries, while other cases display substantially lower values.
To address the second sub-problem, the dynamics of flame propagation in simplified flow geometries is studied theoretically. Utilizing results for Hamilton-Jacobi equations from the Aubry-Mather theory, it is shown how the overall flame front progation under certain conditions is controlled only by discrete points on the flame. Based on these results, definitions of leading points are proposed and their dynamics is studied. These results validate some basic ideas from leading points arguments, but also modify them appreciably. For the simple case of a front propagating in a one-dimensional shear flow, these results clearly show that the front displacement speed is controlled by velocity field characteristics at discrete points on the flame only when the amplitude of the shear flow is sufficiently large and does not vary too rapidly in time. However, these points do not generally lie on the farthest forward point of the front. On the contrary, for sufficiently weak or unsteady flow perturbations, the front displacement speed is not controlled by discrete points, but rather by the entire spatial distribution of the velocity field. For these conditions, the leading points do not have any dynamical significance in controlling the front displacement speed. Finally, these results clearly show that the effects of flame curvature sensitivity in modifying the front displacement speed can be successfully interpreted in term of leading point concepts.
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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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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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Anderson, Anne Lee. "Assessment of thermal radiation arithmetic's for jet flames : A study involving generic calculation methods concerning radiation from jet flames with the purpose to determine the safety distance for flame effects." Thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-67173.
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Jet flames are commonly used as flame effects in pyrotechnical shows, and are also a possible risk in industries that uses pressurised flammable gas. For these users it is important to make fire safety engineering calculations to minimise the risks. This project focus on jet flames that are used in pyrotechnic shows where, e.g. it is important to determine the safety distance to the audience. Up to now most studies made concerning jet flames regards jet flames in subsonic regiments, whilst there is a lack of studies concerning sonic jet flames and mathematical formulations for radiation from these cases are limited. This makes pre-determination of temperatures, safety distances, flame heights etc. a challenge. Based on information found, and assumptions when needed, calculations of the safety distance were made.
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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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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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Hinton, Nathan Ian David. "Measuring laminar burning velocities using constant volume combustion vessel techniques." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:5b641b04-8040-4d49-a7e8-aae0b0ffc8b5.
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The laminar burning velocity is an important fundamental property of a fuel-air mixture at given conditions of temperature and pressure. Knowledge of burning velocities is required as an input for combustion models, including engine simulations, and the validation of chemical kinetic mechanisms. It is also important to understand the effect of stretch upon laminar flames, to correct for stretch and determine true (unstretched) laminar burning velocities, but also for modelling combustion where stretch rates are high, such as turbulent combustion models. A constant volume combustion vessel has been used in this work to determine burning velocities using two methods: a) flame speed measurements during the constant pressure period, and b) analysis of the pressure rise data. Consistency between these two techniques has been demonstrated for the first time. Flame front imaging and linear extrapolation of flame speed has been used to determine unstretched flame speeds at constant pressure and burned gas Markstein lengths. Measurement of the pressure rise during constant volume combustion has been used along with a numerical multi-zone combustion model to determine burning velocities for elevated temperatures and pressures as the unburned gas ahead of the spherically expanding flame front is compressed isentropically. This burning velocity data is correlated using a 14 term correlation to account for the effects of equivalence ratio, temperature, pressure and fraction of diluents. This correlation has been modified from an existing 12 term correlation to more accurately represent the dependence of burning velocity upon temperature and pressure. A number of fuels have been tested in the combustion vessel. Biogas (mixtures of CH4 and CO2) has been tested for a range of equivalence ratios (0.7–1.4), with initial temperatures of 298, 380 and 450 K, initial pressures of 1, 2 and 4 bar and CO2 fractions of up to 40% by mole. Hydrous ethanol has been tested at the same conditions (apart from 298 K due to the need to vaporise the ethanol), and for fractions of water up to 40% by volume. Binary, ternary and quaternary blends of toluene, n-heptane, ethanol and iso-octane (THEO) have been tested for stoichiometric mixtures only, at 380 and 450 K, and 1, 2 and 4 bar, to represent surrogate gasoline blended with ethanol. For all fuels, correlation coefficients have been obtained to represent the burning velocities over wide ranging conditions. Common trends are seen, such as the reduction in burning velocity with pressure and increase with temperature. In the case of biogas, increasing CO2 results in a decrease in burning velocity, a shift in peak burning velocity towards stoichiometric, a decrease in burned gas Markstein length and a delayed onset of cellularity. For hydrous ethanol the reduction in burning velocity as H2O content is increased is more noticeably non-linear, and whilst the onset of cellularity is delayed, the effect on Markstein length is minor. Chemical kinetic simulations are performed to replicate the conditions for biogas mixtures using the GRI 3.0 mechanism and the FlameMaster package. For hydrous ethanol, simulations were performed by Carsten Olm at Eötvös Loránd University, using the OpenSMOKE 1D premixed flame solver. In both cases, good agreement with experimental results is seen. Tests have also been performed using a single cylinder optical engine to compare the results of the hydrous ethanol tests with early burn combustion, and a good comparison is seen. Results from tests on THEO fuels are compared with mixing rules developed in the literature to enable burning velocities of blends to be determined from knowledge of that of the pure components alone. A variety of rules are compared, and it is found that in most cases, the best approximation is found by using the rule in which the burning velocity of the blend is represented by weighting by the energy fraction of the individual components.
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Katragadda, Mohit. "Development of flame surface density closure for turbulent premixed flames based on a priori analysis of direct numerical simulation data." Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/2195.
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In turbulent premixed flames the modelling of mean or filtered reac tion rate translates to the closure of flame surface to volume ratio, which is commonly referred to as the Flame Surface Density(FSD). The FSD based reaction rate closure is well established in the context of Reynolds Averaged Navier-Stokes (RANS) simulations for unity Lewis numbers. However, models for FSD in context of Large Eddy Simulations (LES) are relatively rare. In this study three-dimensional Direct Numerical Simulations (DNS) of freely propagating statistically planar premixed flames encompassing a range of different turbulent Reynolds numbers and global Lewis numbers was used. The variation of turbulent Reynolds number has been brought about by modifying the Karlovitz and the Damkohler numbers independently of each other. The DNS data has been explicitly Reynolds averaged and LES filtered for a prior assessment of existing FSD models and for the purpose of proposing new models where necessary.
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Glaser, Michael. "Snow Flakes." Bowling Green State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1174418689.
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Paul, Barbara. "Flavor-Nutrient Learning in Novel and Familiar Flavor Conditions." Marietta College / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=marietta1525882069126835.
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Hartl, Sandra [Verfasser], Christian [Akademischer Betreuer] Hasse, Christian [Gutachter] Hasse, and Dirk [Gutachter] Geyer. "Flamelet/progress variable modelling and flame structure analysis of partially premixed flames / Sandra Hartl ; Gutachter: Christian Hasse, Dirk Geyer ; Betreuer: Christian Hasse." Freiberg : Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2017. http://d-nb.info/1221069020/34.
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Grib, Stephen William. "LAMINAR AND TURBULENT STUDY OF COMBUSTION IN STRATIFIED ENVIRONMENTS USING LASER BASED MEASUREMENTS." UKnowledge, 2018. https://uknowledge.uky.edu/me_etds/117.
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Practical gas turbine engine combustors create extremely non-uniform flowfields, which are highly stratified making it imperative that similar environments are well understood. Laser diagnostics were utilized in a variety of stratified environments, which led to temperature or chemical composition gradients, to better understand autoignition, extinction, and flame stability behavior. This work ranged from laminar and steady flames to turbulent flame studies in which time resolved measurements were used.
Edge flames, formed in the presence of species stratification, were studied by first developing a simple measurement technique which is capable of estimating an important quantity for edge flames, the advective heat flux, using only velocity measurements. Both hydroxyl planar laser induced fluorescence (OH PLIF) and particle image velocimetry (PIV) were used along with numerical simulations in the development of this technique. Interacting triple flames were also created in a laboratory scale burner producing a laminar and steady flowfield with symmetric equivalence ratio gradients. Studies were conducted in order to characterize and model the propagation speed as a function of the flame base curvature and separation distance between the neighboring flames. OH PLIF, PIV and Rayleigh scattering measurements were used in order to characterize the propagation speed. A model was developed which is capable of accurately representing the propagation speed for three different fuels. Negative edge flames were first studied by developing a one-dimensional model capable of reproducing the energy equation along the stoichiometric line, which was dependent on different boundary conditions. Unsteady and laminar negative edge flames were also simulated with periodic boundary conditions in order to assess the difference between the steady and unsteady cases. The diffusive heat loss was unbalanced with the chemical heat release and advective heat flux energy gain terms which led to the flame proceeding and receding. The temporal derivative balanced the energy equation, but also aided in the understanding of negative edge flame speeds. Turbulent negative edge flame velocities were measured for extinguishing flames in a separate experiment as a function of the bulk advective heat flux through the edge and turbulence level. A burner was designed and built for this study which created statistically stationary negative edge flames. The edge velocity was dependent on both the bulk advective heat flux and turbulence levels. The negative edge flame velocities were obtained with high speed stereo-view chemiluminescence and two dimensional PIV measurements.
Autoignition stabilization was studied in the presence of both temperature and species stratification, using a simple laminar flowfield. OH and CH2O PLIF measurements showed autoignition characteristics ahead of the flame base. Numerical chemical and flow simulations also revealed lower temperature chemistry characteristics ahead of the flame base leading to the conclusion of lower temperature chemistry dominating the stabilization behavior. An energy budget analysis was conducted which described the stabilization behavior.
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Powell, Jodi. "Evaluation of Initial Flavor Fade in Fresh Roasted Peanuts using Gas Chromatography-Flame Ionization Detection, Gas Chromatography-Olfactometry, Sensory Analysis, and Chemosensory Techniques." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29127.
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Preventing flavor fade requires an understanding of the relationship between carbonyl amine and lipid oxidation reactions. The polyunsaturated fatty acid content of lipids in peanuts makes them more susceptible to lipid oxidation. The major by-products of the oxidation reaction are nonanal, hexanal, octanal, and decanal. These chemicals are associated with cardboardy, painty, and oxidized flavors associated with flavor fade. The carbonyl-amine reaction yields a variety of pyrazines with positive flavor attributes.
Initial flavor notes were explored through sensory work, Gas Chromatography-Olfactometry, and chemical analysis. The fresh roasted volatiles produced from roasted peanuts and the aldehydes resulting from oxidation were also evaluated using GC-FID to quantify and identify the pyrazines and hexanal over a 21 day storage period. Electronic Nose was used to determine differences between storage periods.
Gas chromatography-Olfactometry identified potent pyrazines contributing to fresh roasted peanutty aroma in fresh peanuts. Using GC-FID a significant decrease (p<.05) in 2-ethylpyrazine and 2,3-diethylpyrazine concentration was found over a 21-day period. No significant difference (p>0.05) was noted in the other pyrazines evaluated. A significant increase (p<0.05) was noted in the hexanal concentration over a 21-day period. The peroxide values and sensory analysis correlated directly with the GC-FID results with a significant increase (p<0.05) in peroxide value at Day 14 and Day 21, and a significant decrease (p<0.05) in fresh roasted peanuty flavor from days 0-21 and a significant increase (p<.05) in painty, cardboardy and bitter from days 7-21. The electronic nose successfully separated Day 0 and Day 21 samples from Day 7 and 14, which were also separated, but with minimal overlap.Ph. D.
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Pederson, Steven Patrick. "Flawed nature cosmology." University of Southern Queensland, Faculty of Sciences, 2008. http://eprints.usq.edu.au/archive/00004433/.
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[Abstract]: This thesis presents a new cosmological model based on a blank-slate reconsideration of the issue of the first cause in cosmology. It is proposed that a pre-Big Bang evolution of nature occurred that removes the need for postulating the existence of matter, energy and time. This new approach leads to an underlyingconceptualisation of nature consistent with quantum mechanics.The problems of first cause and initial conditions in cosmology are reconsidered. It is proposed that the initial conditions were flawed and evolved toproduce the Big Bang as a natural response to these flaws. This contrasts with the traditional approach of postulating a homogeneous initial state requiring perturbation by an additional first cause.In flawed nature cosmology the origin of time occurs as a natural response to the flawed set of initial conditions, and removes the need to postulate time. The development of causality remains an ongoing process rather than being fully determined by the first cause. Ongoing development of causality provides a conceptual understanding of the probabilistic nature of quantum mechanics and itsrelationship with classical physics.Flawed nature cosmology is used to examine pre-Big Bang evolution, in order to justify rather than postulate a set of conditions leading to the Big Bang. Thisexamination of pre-Big Bang evolution also introduces a structured method to start addressing the question of the origin of matter and the forces of nature.Flawed nature cosmology reconsiders the issues that introduced the manyuniverses concept into physics such as spontaneous first causes, the many-worlds interpretation of quantum mechanics, brane cosmology’s use of the extra dimensions in string theory, and parallel universes to solve the fine tuning problem. The manyuniversesconcept has found favour, as much of the puzzling behaviour of the universe can be avoided by simply stating that if there are many universes, one couldmatch our experience. In contrast, flawed nature cosmology demonstrates that the universe we experience is the unique product of its evolutionary history.
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Svoboda, Jiří. "Flavin-based photocatalysts." kostenfrei, 2007. http://www.opus-bayern.de/uni-regensburg/volltexte/2008/859/.
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Azuah, Unoma Nguemo. "Sky High Flames." VCU Scholars Compass, 2003. http://scholarscompass.vcu.edu/etd_retro/123.
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Sky-high Flames is about Ofunne Ofili, an intelligent and ambitious young woman in a Nigerian oppressive patriarchal society who, nevertheless, dreams of becoming a teacher. Once in school, her high spiritedness leads her to constant trouble. After her mother falls ill, Ofunne's father demands that she withdraw from school. But she completes her education with the help of Reverend Sister Dolan, who was her school principal, and who was drawn to Ofunne's personality. After graduation, Ofunne's father insists that she marry a man she barely knows. She consents only because the man is both Catholic and educated. After three years of marriage, her in-laws threaten her with divorce because she has not yet produced a child. While suffering from the guilt of childlessness, Ofunne discovers that her husband has infected her with syphilis. Sky High Flames is about how our hopes and dreams can turn out to become the very tools that destroy us.
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Mossa, Fouzi. "Flames in tubes." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/7142/.
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Bouvet, Nicolas. "Etude des vitesses fondamentales des flammes laminaires prémélangées : application aux mélanges méthane/air et syngas (H2/CO)/air." Thesis, Orléans, 2009. http://www.theses.fr/2009ORLE2078.
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Cette étude est consacrée à l'élaboration d'une méthodologie de détermination des vitessesfondamentales des flammes laminaires, en utilisant un diagnostic de Vélocimétrie par Imagerie deParticules (PIV). Ce dernier est appliqué aux écoulements réactifs avec point de stagnation, permettant lastabilisation de flammes planes, stationnaires et en conditions quasi adiabatiques. Les effets d’étirementssubits par la flamme sont également quantifiables et parfaitement maîtrisés. L’approche ici développée atout d’abord été appliquée aux mélanges méthane/air pour validation. Une comparaison exhaustive desrésultats obtenus avec les données de la littérature est effectuée. Les codes de combustion 1D (PREMIX,OPPDIF) et 2D (Fluent©) ont été utilisés afin de confirmer la fiabilité et la précision de l’approche proposée.Une attention particulière a été accordée à la caractérisation du mouvement des particules ensemencéesdans les écoulements réactifs divergents, avec notamment la prise en considération de la force dethermophorèse. La méthode développée a ensuite été appliquée à la détermination des vitesses deflammes laminaires de divers mélanges de syngas (H2+CO). Une étude comparative sur ces mélanges aété conduite en utilisant des approches expérimentales multiples comprenant : les flammes à contrecourant,les flammes à propagation sphérique ainsi que les flammes stabilisées coniques. Les résultatsobtenus pour chaque approche ont été confrontés et la sensibilité à l’étirement des flammes de syngas aété caractérisée pour une large gamme de richesses (E.R.=0.4 to 5.0) et de compositions de mélanges(5/95 to 50/50 % H2/CO)In the context of CO2 emission reduction, the present study is devoted to the development of alaminar flame speed measurement methodology, using the Digital Particle Image Velocimetry (DPIV)diagnostic. The latter is applied to stagnation flow flames, seen to have considerable assets for suchstudies. Indeed, flames stabilized in these diverging flows are planar, steady and in near-adiabaticconditions, while subtraction of strain effects on flame is intrinsically allowed. The methodology developedherein has been applied to the well-characterized methane/air mixtures for validation. An extensivecomparison with the literature datasets has been provided. Both 1D (PREMIX, OPPDIF) as well as 2D(Fluent©) numerical tools have been used to confirm the reliability and accuracy of the developed approach.A particular attention has been given to the characterization of the seeding particle motion within thediverging flow, with consideration of the often-neglected thermophoretic force. Fundamental flame velocitiesof various syngas (H2+CO) mixtures have been investigated using multiple experimental approachesincluding the aforementioned counterflow methodology as well as spherical and conical flameconfigurations. Performed measurements from the different approaches have been confronted and flamesensitivities to stretch have been characterized for a wide range of equivalence ratios (E.R.=0.4 to 5.0) andmixture compositions (5/95 to 50/50 % H2/CO)
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Nambully, Suresh Kumar. "A Filtered-Laminar-Flame PDF subgrid scale closure for LES of Premixed Turbulent Flames : Application to a Stratified Bluff-body burner with Differential Diffusion." Phd thesis, INSA de Rouen, 2013. http://tel.archives-ouvertes.fr/tel-00845904.
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A sub-grid scale closure for Large Eddy Simulation (LES) of turbulent combustion, based on physical space filtering of laminar flames is presented. The proposed formalism relies on a presumed probability density function (PDF) derived from the filtered laminar flames and flamelet tabulated chemistry. The combustion LES filter size is not fixed in this novel approach when sub-grid scale wrinkling occurs, but calibrated depending on the local level of unresolved scalar fluctuations. The model was validated by simulating 1D filtered laminar flames and 2D Bunsen flames. Subsequently, the model was tested on a 3D turbulent scenario by performing LES of the premixed and stratified configurations of the Cambridge swirl burner, experimentally studied by Sweeney and co-workers. Comparison of simulation and experiments for both the premixed and stratified configurations showed good agreement emphasizing the model characteristiscs. Instantaneous and time averaged LES data were analyzed to extract
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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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Lautenberger, Christopher W. "CFD simulation of soot formation and flame radiation." Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-0115102-002543.
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Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: soot formation; FDS; flame radiation; soot oxidation; field modeling; diffusion flames; soot. Includes bibliographical references (p. 14-15).
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Pacitti, Antony Gerard. "Droplet motion in flames." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421855.
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Asgyer, Abulkasem A. "Turbulent premixed impinging flames." Thesis, University of Manchester, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488202.
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Abdullatif, Tawfik A. "Turbulent diffusion impinging flames." Thesis, University of Manchester, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488402.
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Çakır, Muammer Altan Demir Durmuş Ali. "Flavor violation in supersymmetry/." [s.l.]: [s.n.], 2006. http://library.iyte.edu.tr/tezler/master/fizik/T000535.pdf.
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Thesis (Master)--İzmir Institute of Technology, İzmir, 2006.Keywords: Flavor violation, flavor violation in supersymmetry, fcnc currents, threshold correction in supersymmetry. Includes bibliographical references (leaves 83-88).
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Lepeintre, François. "Supersymmetric models of flavor /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9699.
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Kaplan, David Elazzar. "Flavor mediated supersymmetry breaking /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/9729.
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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.