La compréhension des phénomènes se déroulant lors de l’impact d’une goutte sur une paroi chaude est essentielle à l’optimisation des systèmes de refroidissement par sprays. Lorsque la température de paroi est élevée, un film de vapeur se forme quasi-instantanément entre la goutte et la paroi chaude. Ce film modifie le comportement hydrodynamique des gouttes et réduit considérablement les échanges de chaleur et de masse par rapport à un impact mouillant. La modélisation de ces phénomènes est complexe en raison des nombreux couplages entre les transferts de chaleur et de masse et la dynamique d’impact de la goutte. Pour aborder ce sujet, des techniques de mesure optiques ont été développées spécifiquement. L’imagerie de fluorescence induite par plan laser à deux couleurs permet de caractériser la distribution de la température à l’intérieur des gouttes. Des images du champ de température, résolues à la fois spatialement et temporellement, sont rendues possible grâce à l’utilisation d’un nouveau couple de colorants fluorescents conservant une grande sensibilité à la température quand ils sont excités par un laser pulsé nanoseconde d’une énergie de plusieurs centaines de mJ. En parallèle, la thermographie infrarouge a été utilisée pour déterminer la température de la surface d’impact en saphir. Pour cela, cette dernière est recouverte d’une couche de quelques centaines de nanomètres de TiAlN, émissif dans l’IR alors que le saphir est transparent. Les images haute cadence sont analysées par un modèle d’inversion, prenant en compte la conduction thermique dans le saphir, afin d’estimer la densité de flux thermique au niveau de la surface d’impact. L’épaisseur du film de vapeur est également déduite de ces mesures sous l’hypothèse, justifiée a posteriori, d’une conduction thermique prépondérante dans le film de vapeur. Une étude de l’impact de gouttes d’eau est réalisée en faisant varier la vitesse d’impact et la température des gouttes avant impact, ainsi que la température de paroi. Dans la plupart des cas, la chaleur extraite à la paroi est comparable à celle transférée au liquide pour l’échauffer. Lorsque la température de paroi se rapproche et dépasse la température de Leidenfrost, les transferts de chaleur deviennent de plus en plus sensibles au nombre de Weber, et de moins en moins dépendant de la température de paroi. L’épaisseur du film de vapeur est affectée par des instabilités, dont les caractéristiques (longueur d’onde, amplitude) sont étudiées à partir des images IR. Finalement, un modèle 1D semi empirique est proposé pour décrire l’échauffement des gouttes et la croissance du film de vapeur. La pression exercée par la goutte sur le film de vapeur se dissipe très vite à l’impact, si bien que la croissance du film de vapeur est gouvernée par la conduction de la chaleur vers la goutte et non par la dynamique de l’impact / The understanding of phenomena occurring at the impact of a droplet onto a hot wall is crucial for the optimization of spray cooling systems. When the temperature of the wall is high, a vapor layer appears quasi-instantaneously between the droplet and le wall. This film of vapor modifies the hydrodynamic behavior of the droplet and highly reduce the heat and mass transfers in comparison with a wetting impact. Modelling these phenomena is complex because of the numerous coupling between the heat and mass transfers and the fluids dynamic. To get some insights into this phenomenon, optical diagnostic techniques have been developed. Two color planar laser induced fluorescence imaging allows characterizing the distribution of the temperature inside the droplet. Images of the temperature fields, resolved both spatially and temporally, are recorded thanks to the use of a couple of fluorescent dyes keeping a high temperature sensitivity even when they are excited by a nanosecond pulsed laser with and an energy of hundreds m J. In parallel, the infrared thermography is used to determine the temperature of the impinged surface made of sapphire. For that, this surface is coated with a thin film (about 300 nanometers) of TiAlN, highly emissive in the IR domain as opposed to the sapphire which is transparent in it. High frame rate image sequences are analyzed thanks to an analytical inversion model, taking into account the thermal conduction in the sapphire, in order to estimate the heat flux density at the impact surface. The thickness of the vapor layer was also deduced from this measurements thanks to the hypothesis of a dominant thermal conduction in the vapor layer. A study of water drop impact was performed with different impact speeds, wall temperatures and different drop injection temperatures. In most of the cases, the heat flux extracted from the wall in close to the flux transferred to the liquid phase of the droplet. When the wall temperature approaches or exceeds the Leidenfrost temperature, the transfers become more sensitive to the Weber number and less sensitive to the wall temperature. The vapor layer thickness is affected by instabilities whose caracteristics (wavelengths, amplitude) were investigated from the IR images. Eventually, a 1-Dsemi-empirical model is given for describing the heating of the liquid part of the droplet and the growth of vapor layer. The effect of the pressure exerted by the droplet onto the vapor film rapidly decreases during the impact process, so that the growth of the vapor film is only driven by the heat transferred by conduction to the droplet and not by dynamical parameters such as the impact velocity

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. [...]

Com clima diversificado e terras férteis, o Brasil tem vocação natural para o desenvolvimento agropecuário e todas as suas vertentes. Assim, o agronegócio é hoje a principal locomotiva da economia brasileira, representando cerca de um terço do nosso Produto Interno Bruto (PIB). Nesse contexto, o Brasil é o terceiro maior produtor de frutas do planeta, com destaque para a produção de laranjas. Particularmente, o país lidera a produção mundial de suco de laranja e conta com uma participação de 85% nas exportações deste produto. Porém, um dos principais fatores atuais que restringem os lucros e a expansão da citricultura é o controle fitossanitário. Atualmente, dentre as principais doenças podemos destacar o HLB e o cancro cítrico. Ambas, doenças bacterianas que não têm cura comprometem a produção e desenvolvimento da fruta e levam à morte da árvore. Dessa maneira, o monitoramento destas é fundamental para evitar danos aos frutos e a necessidade da erradicação de plantações inteiras. O presente trabalho avaliou o emprego das técnicas de Espectroscopia de Fluorescência Induzida por Laser (LIFS) e Espectroscopia de Emissão Óptica com Plasma Induzido por Laser (LIBS) como forma de diagnóstico destas doenças, se apresentando como uma alternativa às inspeções visuais e ao PCR utilizados atualmente. Para isso, folhas de citros in natura provenientes de plantas sadias, com HLB ou com cancro foram amostradas e medidas com ambos os sistemas. Através do sistema LIFS foi realizado um estudo de precocidade no diagnóstico do HLB. Este sistema fotônico pôde detectar a doença até 21 meses antes do aparecimento dos primeiros sintomas visuais. Foram utilizados classificadores sazonais, criados a partir de Regressão por Mínimos Quadrados Parciais (PLSR) e conjuntos de calibração previamente avaliados. Quanto ao cancro cítrico e o sistema LIFS, taxas de acerto superiores a 90% foram alcançadas nos melhores casos de validação cruzada dos dados. A diferenciação do cancro e do HLB também foi possível pela mesma técnica ao avaliar um conjunto pequeno de dados, que atingiu uma taxa de acerto de 82%. Através dos espectros obtidos pelo sistema LIBS, avaliou-se as variações nutricionais causadas na planta devido à doença. Por meio de tais variações e métodos de PLSR foi construído um modelo para o diagnóstico de HLB alcançando taxas de acerto da ordem de 75%. Em relação ao cancro cítrico e o sistema LIBS, um estudo preliminar foi realizado, e uma taxa de acerto superior a 90% foi atingida. Por fim, os resultados corroboraram com a ideia inicial de se realizar o diagnóstico do HLB e do cancro cítrico através de técnicas fotônicas. Dentre outras vantagens estas permitem uma análise rápida, in loco, sem a necessidade de preparo de amostra. Além disso, para o HLB, as técnicas fotônicas demonstraram menor sensibilidade à distribuição não homogênea da doença, quando comparada com a técnica de referência (qPCR). / The diverse climate and fertile soils make Brazil a country with a natural vocation for agricultural development. Thus, agribusiness is now the main locomotive of the Brazilian economy, accounting for about one-third of our Gross Domestic Product (GDP). In this context, Brazil is the third largest fruit producer in the world, with emphasis on the orange production. Particularly, the country leads the world production of orange juice, and with a stake of 85% in exports of this product. However, one of the main factors that restrict current profits and the expansion of citrus production is phytosanitary control. Currently, among the major diseases we highlight the HLB (Greening) and Citrus Canker, two bacterial diseases that have no cure and affect production and fruit development. Therefore, monitoring is essential to prevent damage to the fruits and the complete eradication of infected orchards. The present study evaluated the use of Laser-Induced Fluorescence Spectroscopy (LIFS) and Laser-Induced Breakdown Spectroscopy (LIBS) techniques as alternative diagnostic methods to visual inspection and PCR technique, currently used. For that, citrus leaves from healthy, HLB or citrus canker infected plants, were sampled and measured with both systems. Through LIFS system, a study of the HLB early diagnosis was done. This photonic system could detect the disease up to 21 months before the tree show the visual symptoms. Seasonal classifiers were used, which were designed from Partial Least Square Regression (PLSR) methods and calibration database previously acquired. Regarding citrus canker and LIFS system, success rates higher than 90% were achieved in the best cases. The differentiation between citrus canker and HLB was also possible using the same technique reaching a success rate around 82%. Through the spectrum obtained by LIBS system, it was evaluated the nutritional variations caused in the plant due to HLB, and based on these data, the diagnosis was done. The average success rate was 75%, which was achieved by PLSR model. Regarding on citrus canker and LIBS system, a preliminary study was carried out and a success rate greater than 90% was achieved. Finally, the results corroborated with the use of photonic techniques for the HLB and citrus canker diagnosis. Among other advantages, they allow rapid analysis, in loco and without the need of sample preparation. In addition, for the HLB, photonics techniques showed lower sensitivity to the non-homogeneous distribution of the disease when compared with the reference technique (qPCR).

Les impacts de gouttes sur paroi chaude sont présents dans de multiples domaines, tels que l'injection de diesel sous forme de spray dans des moteurs à combustions internes, ou le traitement thermiques de l'acier dans le domaine de la sidérurgie. L'étude de l'interactions goutte/paroi permet de mieux comprendre les phénomènes thermiques mis en jeu, et ainsi d'aboutir à des économies d'énergies et d'eau. De nombreux travaux portent sur cette thématique, mais ils présentent des résultats divergents et uniquement basés sur l'étude de la paroi chaude. Cette thèse a pour but d'apporter des mesures expérimentales sur les caractéristiques inconnues en étudiant les gouttes. Pour cela, un dispositif expérimental a été mis au point afin de mener à bien l'ensemble des mesures souhaitées. Les diverses techniques de mesures de température utilisées sont présentées, et une attention plus particulière a été portée sur le développement de la technique de fluorescence induite par plan laser qui permet d'accéder au champ de température des gouttes durant leur impact. Cette méthode, combinée à une technique de thermographie par caméra infrarouge couplée à un modèle de conduction inverse, permet d'extraire les paramètres concernant l'aspect thermique, et de déterminer de nouvelles caractéristiques inédites, telles que l'échauffement des gouttes, l'évaporation relative de celles-ci ou encore l'efficacité de refroidissement. Les parts respectives jouées par la chaleur sensible et l'évaporation des gouttes sont tirées de cette dernière. Enfin, l'aspect dynamique est également abordé aboutissant au développement d'une technique d'ombroscopie rapide. Cette dernière a permis, grâce à la combinaison de mesures de diamètres précises et d'une fréquence d'acquisition élevée, d'extraire les paramètres dynamiques de l'impact tels que la vitesse et taille des gouttes, ou d'autres paramètres relatif au type d'impact rencontrés à l'aide d'un algorithme de suivi de particules développé durant la thèse / The droplet impact onto a heated wall interaction can be found in mutiples fields, such as internal combustion engines or the steel industry, specially in the thermal treatment of the steel where high energy dissipation rate is required. The study of this interaction should grant a better understanding of this phenomena, and thus, allow the enhancement of these processes and reduce the energy and water consumption. Several studies have already been carried out on this subjet but a great majority of them, whose results present great divergence, only consider the heated wall, neglecting the outgoing of the droplet. This thesis put the emphasis on the liquid phase where currently no data exist to our knowledge, with the help of multiples experimental technics that have been developped. A general experimental setup has been made in order to make all the wanted measurements. The measurement techniques used in this study are first presented, to begin with the planar laser induced fluorescence, which allow us to know the droplet temperature during the impact. Used with an infrared thermography technique coupled with an inverse conduction model, it is possible to extract some important parameter regarding the thermal aspect, such as the droplet heating, the relative evaporation ratio or the cooling efficiency. This latter can be written as the sum of the two major contributions of the cooling: the sensible heat and the evaporation of the droplet. Finally, a high speed shadow imagery technique is presented. It has been developped in order to study the dynamic aspect of the droplet impact. This technique can determine several dynamic parameters such as the droplet speed and diameter, or other parameter regarding the type of impact encountered

[pt] O presente trabalho apresenta um estudo experimental da distribuição da fuligem e de hidrocarbonetos aromáticos policíclicos (PAH) em chamas laminares não pré-misturadas de etileno e ar, mediante o uso de técnicas de diagnóstico espectroscópico, num queimador tipo co-flow. Para este fim são aplicadas as técnicas de fluorescência induzida por plano laser e incandescência induzida por plano laser, com excitação no espectro ultravioleta. Bandas espectrais de detecção centradas em 340, 400, 450, 500, 550 nm são empregadas para caracterizar diferentes PAH, aproveitado o fenômeno do deslocamento do espectros de fluorescência para o infravermelho, conforme se incrementa sua massa molecular. A técnica de extinção laser é utilizada para calibrar os resultados de incandescência e obter a fração volumétrica de fuligem. A radiação espontânea emitida pela fuligem é utilizada para medir a temperatura pela técnica de termometria em duas cores. A comparação dos resultados obtidos com uma detecção simultânea (0 ns) e atrasada (50 ns) com respeito ao pulso laser permite discriminar entre as regiões onde estão presentes PAHs e fuligem ou apenas fuligem. Os resultados mostram que na região mais fria, perto da entrada de combustível, apenas existem PAH. Seguindo esta região, numa zona de altura intermediária e mais quente, tanto a fuligem como o PAHs coexistem até a o ponto de máxima fração volumétrica integrada de fuligem. O deslocamento no sentido vertical da distribuição de fluorescência é observado com o aumento do comprimento de onda de detecção, o que é consistente com o crescimento do tamanho de PAH e sua progressiva transformação em fuligem. A distribuição de PAH e da fuligem é investigada como função da vazão de combustível. A fração volumétrica de fuligem apresenta uma distribuição clássica, cujo valor se incrementa com a vazão de combustível, enquanto que a temperatura medida diminui. / [en] This work presents an experimental study of soot and polycyclic aromatic hydrocarbons (PAH) distribution in axisymmetric ethylene-air non-premixe laminar flames using spectroscopic diagnostic in a co-flow target burner. For this purpose, are applied laser-induced fluorescence and laser-induced incandescence techniques with UV excitation. Spectral detection bands centered at 340, 400, 450, 500, 550 nm are employed to characterize PAH, using the infrared fluorescence spectra displacement phenomenon with the molecular mass increase. The incandescence is captured at 400 nm and the laser extinction technique is used to calibrate the signal, and, thus to obtain the soot volume fraction at the reaction zone. The soot spontaneous emitted radiation is used to measure the temperature by the two-color pyrometry technique. The comparison between results with prompt (0 ns) and delayed (50 ns) detection, with respect to the laser pulse, allows to discriminate the regions between soot precursors (PAH) and soot. The results show that, in the colder region, near the fuel inlet, PAH exist only. Following this region, in an intermediate warmer zone, both soot and PAH appear to coexist until the point of maximum integral soot volumetric fraction. A vertical displacement of the fluorescence distribution with increasing detection wavelength is observed, which is consistent with PAH size growth and with its progressive transformation into soot. PAH and soot distribution are investigated as a function of the fuel flow rate. The soot volumetric fraction exhibits a classical distribution, whose value increases with the fuel flow rate, whereas the measured temperature decreases, exhibiting a singular behavior in the region where the soot is formed.

Spatially-resolved measurements of flame temperature have been demonstrated with diode lasers for the first time. The technique is based on the use of blue diode lasers to perform laser-induced fluorescence on indium atoms seeded to the flame. Temperature measurements have been carried out in laminar flames both by the two-line atomic fluorescence technique, and also by a novel line-shape thermometry method that requires the use of only a single diode laser. The first part of this work involved the development of blue extended cavity diode lasers with favourable tuning properties. Two custom-designed extended cavity diode lasers (ECDL) have been built, emitting at wavelengths of around 410 nm and 451 nm respectively. These devices are capable of mode-hop free tuning over ranges greater than 90 GHz. The performance of these devices exceeds that of commercially available systems and a patent application has been filed. High resolution fluorescence spectroscopy has been performed on both the 52P1/2→62S1/2 and 52P3/2→62S1/2 transitions of indium atoms seeded at trace quantities into atmospheric pressure flames. In both cases, the spectra obtained show excellent agreement with a theoretical fit based on the individual hyperfine components of the transition. The two ECDLs have been used to build a sensor for the measurement of temperature in combustion systems. It is much simpler, more compact, less expensive, and more versatile than any previously existing device. The two lasers were used sequentially to probe indium atoms seeded to the flame. The ratio of the resulting fluorescence signals is related to the relative populations in the two sub-levels of the spin-orbit split ground state of indium, and thus to the temperature. Temperature measurements have been successfully performed in a laminar flame and the data thus obtained do not need to be corrected by any ‘calibration constant’. This novel thermometry technique offers a robust alternative to traditional methods involving bulky high power lasers. A further development has been made by demonstrating a fluorescence line-shape thermometry technique requiring only a single diode laser excitation source. Progress has been made towards the goal of rapid temperature measurements appropriate to the study of turbulent flames. This involved the development of a simple technique for actively locking the wavelength of the blue diode laser to a resonance line of the tellurium molecule. A high-speed thermometry system would work by rapidly switching between the two locked laser beams using an optical modulator.

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.

Les motoristes aéronautiques misent sur le développement de systèmes d’injection de carburant innovants pour réduire la consommation de carburant et les émissions de polluants. L’objectif de la thèse est de contribuer à l’étude expérimentale d’un injecteur « Lean Premixed » par le développement de diagnostics lasers couplant des approches basées sur la diffusion de Mie et l’émission fluorescente de traceurs. Les mesures ont été réalisées sur le banc de combustion haute pression HERON. Une approche novatrice avec l’imagerie de fluorescence du kérosène a permis d’obtenir une quantification du mélange kérosène/air. La structure de flamme a été mesurée simultanément par PLIF-OH et des mesures PIV de vitesse ont complété cette analyse. Un développement préliminaire de la PLIF-CO a également été mené. Les nombreuses mesures permettent de fournir une analyse détaillée des interactions flamme/spray/aérodynamique lors d’une combustion swirlée stabilisée kérosène/air à haute pression. / Aeronautical engine manufacturers are banking on the development of innovative fuel injection systems to reduce fuel consumption and pollutant emissions. The aim of the thesis is to contribute to the experimental investigation of a "Lean Premixed" injector by developing laser diagnostics coupling approaches based on Mie scattering and fluorescent emission of tracers. Measurements are performed at high pressure on the HERON combustion test bench. An innovative approach with fluorescence imaging of kerosene has resulted in the quantification of the kerosene/air mixture. The flame structure was analyzed simultaneously by OH-PLIF and velocity PIV measurements were performed to complete this analysis. A preliminary development of CO-PLIF was also conducted. The numerous measurements provided a detailed analysis of the mechanisms of flame/spray/aerodynamic interactions during a swirl-stabilized kerosene/air combustion at high pressure.

Autoignition characteristics of pre-vaporized iso-octane, primary reference fuels, gasolines, and dimethyl ether (DME) have been investigated experimentally in a coflow with elevated temperature of air. With the coflow air at relatively low initial temperatures below autoignition temperature Tauto, an external ignition source was required to stabilize the flame. Non-autoignited lifted flames had tribrachial edge structures and their liftoff heights correlated well with the jet velocity scaled by the stoichiometric laminar burning velocity, indicating the importance of the edge propagation speed on flame stabilization balanced with local flow velocity. At high initial temperatures over Tauto, the autoignited flames were stabilized without requiring an external ignition source. The autoignited lifted flames exhibited either tribrachial edge structures or Mild combustion behaviors depending on the level of fuel dilution. For the iso-octane and n-heptane fuels, two distinct transition behaviors were observed in the autoignition regime from a nozzle-attached flame to a lifted tribrachial-edge flame and then a sudden transition to lifted Mild combustion as the jet velocity increased at a certain fuel dilution level. The liftoff data of the autoignited flames with tribrachial edges were analyzed based on calculated ignition delay times for the pre-vaporized fuels. Analysis of the experimental data suggested that ignition delay time may be much less sensitive to initial temperature under atmospheric pressure conditions as compared with predictions. For the gasoline fuels for advanced combustion engines (FACEs), and primary reference fuels (PRFs), autoignited liftoff data were correlated with Research Octane Number and Cetane Number. For the DME fuel, planar laser-induced fluorescence (PLIF) of formaldehyde (CH2O) and CH* chemiluminescence were visualized qualitatively. In the autoignition regime for both tribrachial structure and mild combustion, formaldehyde were found mainly between the fuel nozzle and the lifted flame edge. On the other hand, they were formed just prior to the flame edge for the non-autoignited lifted flames. The effect of fuel pyrolysis and partial oxidation were found to be important in explaining autoignited liftoff heights, especially in the Mild combustion regime. Flame structures of autoignited flames were investigated numerically for syngas (CO/H2) and methane fuels. The simulations of syngas fuel accounting for the differential diffusion have been performed by adopting several kinetic mechanisms to test the models ability in predicting the flame behaviors observed previously. The results agreed well with the observed nozzle-attached flame characteristics in case of non-autoignited flames. For autoignited lifted flames in high temperature regime, a unique autoignition behavior can be predicted having HO2 and H2O2 radicals in a broad region between the nozzle and stabilized lifted flame edge. Autoignition characteristics of laminar nonpremixed methane jet flames in high- temperature coflow air were studied numerically. Several flame configurations were investigated by varying the initial temperature and fuel mole fraction. Characteristics of chemical kinetics structures for autoignited lifted flames were discussed based on the kinetic structures of homogeneous autoignition and flame propagation of premixed mixtures. Results showed that for autoignited lifted flame with tribrachial structure, a transition from autoignition to flame propagation modes occurs for reasonably stoichiometric mixtures. Characteristics of Mild combustion can be treated as an autoignited lean premixed lifted flame. Transition behavior from Mild combustion to a nozzle-attached flame was also investigated by increasing the fuel mole fraction.

We study the expansion velocity and ion temperature evolution of ultracold neutral plasmas (UNPs) of calcium atoms under the influence of a uniform magnetic field that ranges up to 200 G. In the experiments, we use a magneto-optical trap (MOT) to capture the neutral atoms and laser-induced fluorescence (LIF) to take images of the plasma. We vary the magnetic field strengths and the initial electron temperatures and observe the plasma evolution in time. We compare the ion temperature evolution to the theory introduced in the paper by Pohl et. al. [Phys. Rev. A 70, 033416 (2004)]. The evolution of the gradient of expansion velocity suggests the presence of ion acoustic waves (IAWs). We speculate that our measurements showing that the ion temperature remains relatively high throughout the evolution is a biproduct of the IAW.