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Study Of Liquid Fuel Film Transport And Its Effect On Cold Start Hydrocarbon Emissions In A Carburetted EngineTewari, Sumit 08 1900 (has links) (PDF)
The present work is concerned with fundamental studies on the liquid fuel transport in the intake manifold of small carburetted engines. This work is motivated by the need for development of technologies to meet the stringent cold-start emission norms that are to be prescribed for two-wheelers in particular. More specifically, visualization studies conducted in a transparent manifold made of quartz in a small four-stroke 110-cc two-wheeler engine have shown the presence of gasoline films on the walls of the inlet manifold under cold start conditions. Advanced Laser diagnostic techniques such as Planar Laser Induced Fluorescence (PLIF) have been utilized to measure the thickness of the fuel films. The Sauter Mean Diameter for the fuel droplets at the carburettor exit is measured using Laser Shadowgraphy technique. It is observed that the films are present both at idling conditions and under load. This large amount of liquid fuel entering the engine leads to incomplete combustion and higher emissions of unburned hydrocarbons. A detailed analysis of the effects of heating the inlet manifold has been performed. The potential of this manifold heating strategy in reducing hydrocarbon emissions has been assessed and found to be promising. In addition, a need of proper control of the fuel exiting the carburettor is shown to reduce emissions and increase fuel efficiency.
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[pt] ESTUDO NUMÉRICO E EXPERIMENTAL DA COMBUSTÃO TURBULENTA NÃO PRÉ-MISTURADA DE UM JATO DE HIDROGÊNIO NO AR / [en] NUMERICAL AND EXPERIMENTAL STUDY OF THE TURBULENT NON-PREMIXED COMBUSTION OF A HYDROGEN JET IN AIR08 November 2021 (has links)
[pt] O presente trabalho tem por objetivo a realização de experimentos e simulações numéricas para estudar a interação da turbulência e da combustão em uma chama não pré-misturada de hidrogênio no ar estabilizada a jusante de um corpo rombudo. Para tanto, são utilizadas, simultaneamente,
as técnicas de PIV, para a determinação de dois componentes da velocidade, e a técnica de PLIF para a determinação da intensidade de fluorecência do radical químico OH, que é um bom indicador da localização
da frente de chama. São avaliados os métodos de pós processamento dos resultados do PIV com o intuito de maximizar a resolução espacial da técnica e ao mesmo tempo remover o maior número de vetores espúrios dos campos de velocidade instantâneos. Paralelamente, o queimador é modelado
no software ANSYS/FLUENT e os resultados de simulação validados por comparação com os resultados experimentais. Modelos baseados nas médias de Reynolds são empregados para a caracterização da turbulência e o modelo de elementos de chama é adotado para a descrever a combustão.
Os resultados experimentais indicam que, para as vazões de ar e hidrogênio adotadas, a combustão ocorre no regime de elementos de chama, onde a frente de chama apresenta algumas dobras, mas sem descontinuidades. Os resultados das simulações com combustão não obtiveram boa concordância
com os resultados experimentais, indicando que a malha de cálculo precisa ser aprimorada. / [en] The aim of this work is to carry out experiments and numerical simulations to study the turbulence-combustion interaction in a nonpremixed hydrogen-air ame stabilized in a bluff body wake. For this
purpose, are used a PIV technique for the determination of two velocity components and a PLIF technique to determine the uorescence intensity of the chemical species OH, which is a good indicator of the
flame front location. PIV post-processing methods are evaluated in order to maximize the spatial resolution of the technique and to remove spurious instantaneous velocity vectors. In addition, the burner is modeled in ANSYS / FLUENT and the simulation results are validated by comparisons with
the experimental results. Models based in the Reynolds avareges are used to characterize the turbulence and a flamelet model is adopted to describe combustion. The experimental results indicates that, for the
ow rates of air and hydrogen adopted, combustion occurs in the flamelet regime, where the flame front is wrinkled, but without discontinuities. The reactive cases simulations did not agree with the experimental results, indicating that the computational mesh needs to be improved.
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Nitric Oxide and Other Characterizations of an Atmospheric Pressure Plasma JetPulcini, Annie Rae 14 May 2015 (has links)
No description available.
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Application de la LIF de molécules aromatiques au dosage de carburants fossiles et biocarburants / Application of the aromatic-based laser-induced fluorescence diagnostic to the quantitative chemical probe of Fossil fuels and BiofuelsLedier, Constantin 13 December 2011 (has links)
Les industries automobile et aéronautique sont confrontées dans le futur proche à une raréfaction des carburants fossiles, ainsi qu’au problème de pollution de l’environnement émis par les systèmes propulsifs. Pour s’affranchir de ces problèmes, l’utilisation de carburants alternatifs censés apporter rendement et préservation de l’environnement, s’est considérablement développée ces derniers temps. Cependant, leurs impacts sur la pollution, consommation et rendement de combustion ne sont toujours pas clairement établis. En particulier, il est nécessaire de quantifier leurs effets sur les phénomènes physiques clés à la base des processus que sont l’évaporation du carburant liquide et le mélange carburant vapeur/air. L’analyse expérimentale de ces processus physiques nécessite alors l’emploi de diagnostics lasers non-intrusifs et quantitatifs, permettant de mesurer des grandeurs physiques comme les distributions spatiales instantanées de température et de concentration du carburant en phase vapeur. Parmi les techniques optiques les plus attrayantes, l’imagerie de fluorescence induite par laser (PLIF) offre de nombreux avantages. L’objectif de la thèse a été, dans un premier temps, de caractériser les propriétés spectroscopiques de quatre carburants multi-composants, le kérosène (Jet A1), le Biomass-to-Liquid (BtL), le Diesel et l’Ester Méthylique Huile Végétale (EMHV) qui, mis à part le premier, possèdent des propriétés spectroscopiques encore peu connues. L’exploitation de leurs propriétés de fluorescence a ensuite permis d’évaluer leurs capacités à fournir des signaux autorisant la mesure de la température et de la concentration du carburant en phase vapeur. Dans un second temps, un étude exhaustive des propriétés de fluorescence de plusieurs cétones (3-pentanone, benzophénone) et aromatiques (fluoranthène, acénaphtène, naphtalène, 1,2,4-triméthylbenzène…) en fonction de la température et du quenching de l’oxygène moléculaire, a été réalisée à pression atmosphérique pour identifier les traceurs fluorescents potentiellement adaptés au dosage optique des quatre carburants. Les données photophysiques collectées ont ensuite été utilisées pour parfaire l’établissement des couples carburants/traceurs fluorescents ainsi que les stratégies de mesures de température et de concentration de carburant associées. L’exploitation des données acquises lors de différentes campagnes de mesures a ainsi mis en évidence la possibilité de détecter simultanément la fluorescence de plusieurs molécules aromatiques (mono-, di- et/ou tri-aromatique) naturellement présentes ou ajoutées artificiellement dans les carburants. Le cas du Diesel a nécessité le développement d’un carburant modèle pour permettre une étude de son évaporation. L’application de cette nouvelle approche PLIF a été validée sur un injecteur hélicoptère LPP de nouvelle génération fonctionnant avec trois carburants spécifiques que sont le Jet A1, le BtL et un mélange Jet A1/BtL / The automotive and aviation industries are presently confronted with the twin crises of fossil fuel depletion and environmental degradation. Research for alternative fuels, which promise a harmonious correlation with sustainable development, energy conservation, efficiency and environmental preservation, has become highly pronounced in the present context. However, their influence on pollution, consumption and combustion yield are not clearly defined yet. In particular, their effects on key physical processes that initiate these phenomena like fuel evaporation and mixing processes between fuel vapour and air have to be quantified. Experimental analysis of these processes requires the use of non-intrusive and quantitative laser diagnostics, allowing the measurement of key physical parameters like instantaneous spatial distribution of temperature and fuel vapour concentration. Among the optical techniques available thus far, planar laser-induced fluorescence (PLIF) offers many advantages for the study such processes in combustors. The objective of this thesis is then to propose and to develop innovative PLIF strategies to measure fuel distribution and mixture formation when fossil fuels and biofuels are used in aeronautical and automotive combustion chambers. In particular, the fluorescence of various fossil fuels like kerosene (Jet A1) and Diesel, the biodiesel fuel containing Esters (FAME) and the Biomass-To-Liquid fuel (BtL) are investigated. The exploitation of their fluorescence was then used to analyse their capacity to generate signals providing from fluorescent tracers (either present naturally in the fuel or chemically added) that could be used as probe molecules for the measurement of temperature and fuel vapour concentration. To select theses tracers, an exhaustive study of the fluorescence properties of various ketones (3-pentanone, benzophenone) and aromatic molecules (fluoranthene, acenapthene, naphthalene, 1,2,4-trimethylbenzene) with temperature and quenching with molecular oxygen was performed at atmospheric pressure. The photophysical data collected during these experiments have been then used to associate the various fuels with specific fluorescent tracers and to elaborate the strategies of measurement of temperature and fuel concentration associated. Exploitation of the data collected during this thesis thus highlighted the possibility to detect simultaneously the fluorescence of various aromatic molecules (mono-, di-, tri-aromatics) naturally present or artificially seeded in fuels. The specific case of Diesel required the development of a surrogate fuel which allows the study of its evaporation process. An application of these innovative strategies of PLIF measurements has been finally performed on a new generation LPP helicopter injection system running at atmospheric pressure with the following fuels: Jet A1, BtL and a mixture of Jet A1 and BtL. Results obtained allowed the validation of the PLIF strategies defined in this thesis.
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Experimental investigation of multi-component jets issuing from model pipeline geometries with application to hydrogen safetySoleimani nia, Majid 21 December 2018 (has links)
Development of modern safety standards for hydrogen storage infrastructure requires fundamental insight into the physics of buoyant gas dispersion into ambient air. Also, from a practical engineering stand-point, flow patterns and dispersion of gas originating from orifices in the side wall of circular pipe or storage tank need to be studied. In this thesis, novel configurations were considered to investigate the evolution of turbulent jets issuing from realistic pipeline geometries. First, the effect of jet densities and Reynolds numbers on vertical jets were investigated, as they emerged from the side wall of a circular pipe, through a round orifice. The resulting jet flow was thus issued through a curved surface from a source whose original velocity components were nearly perpendicular to the direction of the ensuing jets. Particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques were employed simultaneously to provide instantaneous and time-averaged flow fields of velocity and concentration. The realistic flow arrangement resulted in an asymmetric flow pattern and a significant deflection from the vertical axis of jets. The deflection was influenced by buoyancy, where heavier gases deflected more than lighter gases. These realistic jets experienced faster velocity decay, and asymmetric jet spreading compared to round jets due to significant turbulent mixing in their near field.
In addition to that, horizontal multi-component jets issuing from a round orifice on the side wall of a circular tube were also investigated experimentally by the means of simultaneous velocity and concentration measurements. A range of Reynolds numbers and gas densities were considered to study the effects of buoyancy and asymmetry on the resulting flow structure. The realistic pipeline jets were always exhibited an asymmetry structure and found to deflect about the jet's streamwise axis in the near field. In the far field, the buoyancy dominated much closer to the orifice than expected in the axisymmetric round jet due to the realistic leak geometry along with the pipeline orientation considered in this study. In general, significant differences were found between the centreline trajectory, spreading rate, and velocity decay of conventional horizontal round axisymmetric jets issuing through flat plates and the pipeline leak-representative jets considered in the present study.
Finally, the dispersion of turbulent multi-component jets issuing from high-aspect-ratio slots on the side wall of a circular tube were studies experimentally by employing simultaneous PIV and PLIF techniques. Two transversal & longitudinal oblong geometries in respect to the longitudinal axes of the tube , and with an aspect ratio of 10 were considered in this study. Both horizontal and vertical orientations along with broad range of Reynolds numbers and gas densities were considered to investigate the effects of buoyancy and asymmetry on the resulting flow structure. The ensuing jets were found to deflect along the jet streamwise axis, once more, due to the realistic pipeline leak-representative configuration. It was also found that increases in aspect ratio of these realistic jets caused a reduction in the angle of deflection, jet centreline decay rates and the width growth on both velocity and scalar fields compared to their round jets counterparts, most notably in the far field.
These findings indicate that conventional jets (those that are issuing through flat surfaces) assumptions are inadequate to predict gas concentration, entrainment rates and, consequently, the extent of the flammability envelope of realistic gas leaks. Thus, extreme caution is required when using conventional jet assumptions to describe the physics of a buoyant jet emitted from realistic geometries. / Graduate
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Application de la LIF de molécules aromatiques au dosage de carburants fossiles et biocarburantsLedier, Constantin 13 December 2011 (has links) (PDF)
Les industries automobile et aéronautique sont confrontées dans le futur proche à une raréfaction des carburants fossiles, ainsi qu'au problème de pollution de l'environnement émis par les systèmes propulsifs. Pour s'affranchir de ces problèmes, l'utilisation de carburants alternatifs censés apporter rendement et préservation de l'environnement, s'est considérablement développée ces derniers temps. Cependant, leurs impacts sur la pollution, consommation et rendement de combustion ne sont toujours pas clairement établis. En particulier, il est nécessaire de quantifier leurs effets sur les phénomènes physiques clés à la base des processus que sont l'évaporation du carburant liquide et le mélange carburant vapeur/air. L'analyse expérimentale de ces processus physiques nécessite alors l'emploi de diagnostics lasers non-intrusifs et quantitatifs, permettant de mesurer des grandeurs physiques comme les distributions spatiales instantanées de température et de concentration du carburant en phase vapeur. Parmi les techniques optiques les plus attrayantes, l'imagerie de fluorescence induite par laser (PLIF) offre de nombreux avantages. L'objectif de la thèse a été, dans un premier temps, de caractériser les propriétés spectroscopiques de quatre carburants multi-composants, le kérosène (Jet A1), le Biomass-to-Liquid (BtL), le Diesel et l'Ester Méthylique Huile Végétale (EMHV) qui, mis à part le premier, possèdent des propriétés spectroscopiques encore peu connues. L'exploitation de leurs propriétés de fluorescence a ensuite permis d'évaluer leurs capacités à fournir des signaux autorisant la mesure de la température et de la concentration du carburant en phase vapeur. Dans un second temps, un étude exhaustive des propriétés de fluorescence de plusieurs cétones (3-pentanone, benzophénone) et aromatiques (fluoranthène, acénaphtène, naphtalène, 1,2,4-triméthylbenzène...) en fonction de la température et du quenching de l'oxygène moléculaire, a été réalisée à pression atmosphérique pour identifier les traceurs fluorescents potentiellement adaptés au dosage optique des quatre carburants. Les données photophysiques collectées ont ensuite été utilisées pour parfaire l'établissement des couples carburants/traceurs fluorescents ainsi que les stratégies de mesures de température et de concentration de carburant associées. L'exploitation des données acquises lors de différentes campagnes de mesures a ainsi mis en évidence la possibilité de détecter simultanément la fluorescence de plusieurs molécules aromatiques (mono-, di- et/ou tri-aromatique) naturellement présentes ou ajoutées artificiellement dans les carburants. Le cas du Diesel a nécessité le développement d'un carburant modèle pour permettre une étude de son évaporation. L'application de cette nouvelle approche PLIF a été validée sur un injecteur hélicoptère LPP de nouvelle génération fonctionnant avec trois carburants spécifiques que sont le Jet A1, le BtL et un mélange Jet A1/BtL
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Analyse de la topologie des flammes prémélangées swirlées confinées / Analysis of the topology of premixed swirl-stabilized confined flamesGuiberti, Thibault 04 February 2015 (has links)
Ce travail porte sur la stabilisation de flammes prémélangées et swirlées de mélanges combustibles méthane/hydrogène/air avec différents taux de dilution d’azote et de dioxyde de carbone. Une tige centrale permet de stabiliser des flammes pour de faibles nombres de swirl. Le sommet de la flamme interagît éventuellement avec les parois de la chambre de combustion. L’objectif ces travaux est d’améliorer la connaissance des mécanismes qui gouvernent la stabilisation et la topologie de ces flammes. Ces travaux démontrent que le nombre de swirl, la composition du mélange combustible, la géométrie de la chambre de combustion ainsi que les conditions aux limites thermiques ont une grande influence sur la forme prise par la flamme. Le dispositif expérimental permet de modifier la forme et la taille de la chambre de combustion, le diamètre du tube d’injection et le nombre de swirl. Des conditions opératoires propices aux transitions de forme de flamme sont ensuite étudiées pour différentes configurations de brûleur. Une caractérisation expérimentale fouillée d’un point de fonctionnement est réalisée grâce à la Fluorescence Induite par Laser sur le radical Hydroxyle (OH-PLIF), la Vélocimétrie par Images de Particules (PIV) et la Phosphorescence Induite par Laser de phosphores sensibles à la température (LIP). Une base de donnée de l’écoulement et des conditions aux limites associées est obtenue sans et avec combustion. Les mécanismes qui contrôlent les transitions de formes de flamme sont ensuite analysés lorsque la flamme interagit avec les parois de la chambre de combustion. L’influence de la composition du mélange combustible, de la vitesse débitante et du nombre de swirl est caractérisée et il est démontré que la transition d’une flamme en V vers une flamme en M est déclenchée par un retour de flamme dans la couche limite le long d’une des parois latérales de la chambre de combustion. Les nombres sans dimension contrôlant ces transitions sont identifiés et un modèle de prévision de la forme de ces flammes est développé. La physique déterminant les transitions de forme de flammes est différente lorsque celles-ci n’interagissent pas avec les parois de la chambre de combustion. En utilisant le signal de chimiluminescence OH* et la OH-PLIF, il est montré que la teneur en hydrogène dans le combustible a une grande influence sur la forme de flamme. L’utilisation de la LIP et de thermocouples a également permis de montrer que les conditions aux limites thermiques jouent un rôle prépondérant sur la forme de flamme. Les effets combinés de l’étirement et des pertes thermiques sont examinés par l’utilisation conjointe de la PIV et de la OH-PLIF. Il est montré que les limites d’extinction de flammes pauvres prémélangées sont réduites par les pertes thermiques et que la transition d’une flamme en M vers une flamme en V est consécutive à l’extinction du front de flamme situé dans la couche de cisaillement externe du jet soumis à un étirement trop important. Ces expériences sont complétées par une analyse de la dynamique de ces flammes. Des modulations de la vitesse débitante à basse fréquence et à haute amplitude modifient la forme de flamme. La stabilisation de flammes CH4/H2/air diluées par du N2 ou du CO2 est finalement examinée. La zone de recirculation produite par la tige centrale permet d’alimenter la base de la flamme avec des gaz brûlés chauds et de stabiliser des flammes fortement diluées. Augmenter la fraction molaire de diluant dans le combustible réduit l’intensité de lumière émise par le radical OH*. Il est également montré que la composition du diluant a un impact sur le champ de température des gaz brûlés et des surfaces de la chambre de combustion. La dilution par du CO2 augmente les pertes thermiques par rayonnement des gaz brûlés. Cela réduit l’efficacité de la chambre de combustion équipée de quatre parois transparentes. [...] / This work deals with the stabilization of premixed turbulent swirling flames of methane/hydrogen/air combustible mixtures with different dilution rates of nitrogen and carbon dioxide. A central bluff body helps stabilizing the flames at low swirl numbers. The flame tip eventually impinges the combustor peripheral wall. The general objective is to gain understanding of the mechanisms governing the stabilization and the topology of these flames. It is found that the swirl number, the combustible mixture composition, the geometry of the combustor, and the thermal boundary conditions have a strong impact on the shape taken by these flames. The experimental setup used to characterize flames topologies is first described. Flames prone to topology bifurcations are selected and are studied for different arrangement of the combustor when the combustion chamber shape and size, the injection tube diameter, and swirl number are varied. One operating condition is fully characterized under non-reactive and reactive conditions using Planar Hydroxyl Laser Induced Fluorescence (OH-PLIF), Particle Imaging Velocimetry (PIV), and Laser Induced Phosphorescence of thermographic phosphors (LIP) to generate a detailed database of the flow and the corresponding boundary conditions. An analysis is then conducted to understand the mechanisms controlling shape bifurcations when the flame interacts with the combustor peripheral wall. Effects of the combustible mixture composition, the bulk flow velocity, and the swirl number are analyzed. It is shown that the transition from a V to an M flame is triggered by a flashback of the V flame tip in the boundary layer of the combustor peripheral wall. Dimensionless numbers controlling these transitions are identified and a simplified model is developed to help the prediction of the flame shapes. The physics of these shape bifurcations differs when the flame does not interact with the combustor wall. The large influence of the hydrogen enrichment in the fuel on the flame shape is analyzed using flame chemiluminescence and OH-PLIF. LIP and thermocouple measurements demonstrate that the thermal boundary conditions still have a strong impact on the flame topology. The combined effects of strain and heat losses are investigated using joint OH-PLIF and PIV experiments. It is shown that flammability limits of premixed flames are reduced due to heat losses and the transitions from M to V shaped flames is consecutive to localized extinctions of flame front elements located in the outer shear layer of the jet flow that are submitted to large strain rates. These experiments are completed by an analysis of the dynamics of methane/hydrogen/air flames. It is shown that low frequency and high amplitude velocity modulations generated by a loudspeaker alter the shape taken by these flames. The stabilization of methane/hydrogen/air flames diluted by nitrogen and carbon dioxide is finally examined. It was possible to stabilize swirled flames featuring important dilution rates due to the presence of the bluff body, installed on the axis of the injection tube. The recirculation zone behind this element supplies hot burnt gases to the flame anchoring point. Using OH* chemiluminescence imaging, it is shown than increasing the molar fraction of diluent in the fuel reduces the light emission from excited OH* radicals. The influence of dilution on the flame chemistry is emphasized with experiments conducted at a fixed thermal power and fixed adiabatic flame temperature. It is also demonstrated that the composition of the diluent has a strong influence on the temperature field of the burnt gases and of the combustor wall surfaces. Dilution with carbon dioxide increases radiative heat losses from the burnt gases in comparison to dilution with nitrogen. This penalizes the combustor efficiency equipped with four transparent quartz walls. [...]
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Fuel Filim Visualization And Measurement In The Inlet Manifold Of A Carbureted Spark-Ignition EnginePrabhu, Nishikant Madhusudan 10 1900 (has links) (PDF)
In order to meet future emission norms for small carbureted SI engines, such as those
used on motorcycles in India, there is a need to study mixture preparation, specifically the two-phase flow exiting the carburetor and entering the inlet manifold. A fully functional, modular experimental rig is designed and erected for performing both
qualitative and quantitative flow visualization. The vibrations of the engine are minimized to reduce their effect on the flow. A special, optically accessible tube of
square cross-section is added between the carburetor and the inlet manifold, to enable
the visualization of flow at the exit of the carburetor. An electronic circuit to obtain a
signal for the engine crank angle and convert it to a standard TTL pulse, for use on standard imaging systems to capture cycle resolved-images is also designed.
The flow in the optical section is qualitatively visualized using high and low
speed cameras. The resulting images and movies show two modes of fuel transport
within the inlet manifold, one of which is in the form of a dense cloud of fine fuel
droplets during some part of the intake stroke. The second mode is in the form of a
film at all times in the cycle, along the lower surface of the inlet manifold during
idling and along vertical walls under loaded conditions. Recirculation is seen on the
vertical walls of the manifold during idling and under load.
Finally, the thickness of the fuel film in the optical section at the exit of the
carburetor is measured, using PLIF. This part of the study also reveals that there is a film on upper surface of the optical section, at all loads and speeds. This film is lesser than the resolution of measurement for low loads, and increases to 0.5 mm in the case of highest load and speed attained at full throttle. In contrast to the loaded conditions, during idling, the film occurs on the lower surface of the manifold and its thickness is highest (1 mm.). The film is also present throughout the cycle during idling and all load-speed conditions, suggesting that the mixture that goes into the engine has a significant part of fuel in liquid form.
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Analyse von Strömungseffekten in SchichtenladersystemenBuhl, Marcus 01 October 2018 (has links)
Solarthermie trägt wesentlich zur Verbrauchsreduzierung fossiler Energieträger bei. Die für eine thermische Zwischenspeicherung verwendeten Warmwasserspeicher werden häufig mittels schwerkraftbasierten Schichtenladern beladen. Bisher sind die komplexen Strömungsvorgänge im Beladesystem und deren Auswirkungen auf die Speichereffizienz begrenzt bekannt. Im Rahmen dieser Arbeit erfolgt daher eine detaillierte Auseinandersetzung mit den hydrodynamischen Effekten in einem Schichtenlader.
Dreidimensionale CFD-Untersuchungen zeigen, dass im Belader Strömungsschwankungen auftreten, welche mit dem Ausströmverhalten korrelieren und den Schichtungsaufbau negativ beeinflussen. Variationen der Betriebsparameter und Beladergeometrie verdeutlichen deren Einflussnahme auf die Strömungseffekte im Beladesystem. Experimentelle PIV/PLIF-Untersuchungen bestätigen die mit der CFD gewonnenen Erkenntnisse wie z. B. Strömungsasymmetrien im Beladerrohr und ein teilweise periodisches Ausströmen. Zusätzlich identifizieren die experimentellen Messungen starke Instationaritäten der Strömung. / Solar thermal energy makes a significant contribution to reducing the consumption of fossil fuels. Hot water storage tanks are often equipped with gravity-based stratification devices. Up to now, the complex flow in the loading system and the effects on storage efficiency are only been rudimentarily known. In this Phd thesis, therefore, detailed examination of the hydrodynamic effects in a stratification device is conducted.
3D-CFD investigations show that a fluctuating flow exists in the device which correlate with the outflow behaviour and has a negative influence on the thermal stratification in the storages. Variations of the operating parameters and device geometry illustrates their influence on flow effects in the loading system.
Experimental PIV/PLIF investigations confirm the results obtained from the CFD, such as flow asymmetries in the stratification device and a temporally periodic outflow. In addition, the experimental measurements identify strong instationarities of the flow.
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Development and Application of Burst-Mode Planar Laser Diagnostics for Detonating and Hypersonic FlowsAustin M Webb (17543874) 04 December 2023 (has links)
<p dir="ltr">Burst-mode lasers and burst-mode optical parametric oscillators (OPOs) are applied and developed for planar laser induced fluorescence (PLIF) measurements of key species for high-speed combustion measurements. OH-PLIF in the rotating detonation engine was performed for the first time at wave structure visualization in two different planes and was 10 times faster than any other burst mode OH-PLIF measurements at the time. The same system was used to perform another OH-PLIF experiment at 1 MHz for ~200 pulses to compare key features of the detonation wave structure with computational fluid dynamic simulations and a fundamental detonation tube experiment. The system was also used for seedless velocity measurements in the exhaust by tracking a pocket of OH with a technique called FLASH. A similar OPO was built, aligned, and tuned to perform 1 MHz NO PLIF in a Mach 10 hypersonic tunnel to visualize second mode instabilities and calculate the frequency in the boundary layer transition of a 7-degree cone. A high-efficiency OPO was developed and characterized utilizing the KTP crystal to provide narrow bandwidth pulses for the fluorescence of multiple species. The OPO was pumped at repetition rates up to 1 MHz and was calculated to have a 1.9% UV efficiency from the fundamental 1064 nm output. This is 3 – 5 times increase in efficiency from previous custom and commercial built OPOs. The OPO was applied to the RDC for OH PLIF in the combustor channel and NO PLIF for injector dynamics and response studies. Lastly, a burst-mode laser was used to perform LII on the post detonation blast flow field to measure explosively generated soot. The data was taken at 1 MHz and compared and corrected with a separate set of experiments and computational simulations.</p>
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