The currently reported thesis was concerned with visualisation of the charge homogeneity and cyclic variations within the planar fuel field near the spark plug in an optical spark ignition engine fitted with an outwardly opening central direct fuel injector. Specifically, the project examined the effects of fuel type and injection settings, with the overall view to understanding some of the key mechanisms previously identified as leading to particulate formation in such engines. The three fuels studied included a baseline iso-octane, which was directly compared to two gasoline fuels containing 10% (E10) and 85% (E85) volume of ethanol respectively. The engine was a bespoke single cylinder with Bowditch style optical access through a flat piston crown. Charge stratification was studied over a wide spectrum of injection timings using the Planar Laser Induced Fluorescence (PLIF) technique, with additional variation in charge temperature due to injection also estimated when viable using a two-line PLIF approach. Overall, both gasoline-ethanol fuels generally exhibited a higher degree of stratification, albeit at least partly alleviated with elevated rail pressures. Under both warm and cold liner conditions the E10 fuel showed clear evidence of fuel droplets persisting up until ignition. Interestingly, with late injection timing the repeatability of the injection was superior (statistically) with higher ethanol content in the fuel, which may have been associated with the higher charge temperatures aiding control of the evaporation of the main mass of alcohol. The findings were corroborated by undertaking a comprehensive study of the influence of varying fuel type and injection settings on thermodynamic performance and engine-out emissions during firing operation, with additional gas exchange effects also influencing the optimum fuel injection timings.

Nas últimas décadas, questões sobre o controle de emissões em motores à combustão interna e sobre a redução de consumo de combustível vêm sendo debatidas globalmente, com claros desdobramentos em especificações de controles mais restritos, a fim de permitir a comercialização de novos motores à combustão interna a consumidores mais exigentes, que presam pela qualidade de vida e meio ambiente. Mesmo com a introdução de novas tecnologias, os motores ainda apresentam uma grande perda da energia gerada por conta do atrito mecânico. Com base neste contexto, os projetos dos novos motores visam uma melhor eficiência térmica e mecânica, com auxílio de soluções de engenharia que possam beneficiar o desempenho dos motores, resultando em uma melhor queima do combustível e menor atrito. Um dos contribuintes mais relevantes para o atrito num motor é o sistema pistão-anel de pistão-camisa de cilindro que é o foco de muitos trabalhos em busca da redução das perdas por atrito. As propriedades dos filmes à base de carbono tipo diamante (Diamond-Like Carbon - DLC) são bem conhecidas por apresentam alta resistência ao desgaste e baixo coeficiente de atrito, tornando-se adequados para diferentes aplicações tribológicas. O presente trabalho discute a viabilidade técnica de se aplicar um filme DLC amorfo hidrogenado, com gradiente de composição química, sobre a superfície interna brunida de camisas de cilindro para redução do atrito. A metodologia aborda duas espessuras de filme: 2,5 e 12,5 μm, depositadas pelo processo de deposição química em fase vapor assistida por plasma (PACVD), como alternativa para redução do atrito do motor e, consequentemente, redução no consumo específico de combustível, e ainda na redução do desgaste dos anéis de pistão e da superfície de trabalho da camisa de cilindro. Comparando camisas de cilindro com mesma rugosidade na superfície interna, denominadas camisas de referência (sem revestimento interno) e camisas recobertas com filme DLC, testes de bancada com movimento recíproco de contato mostraram redução do coeficiente de atrito (COF) em até 19%. Testes de motor ciclo Otto e Diesel em banco de prova com dinamômetro conferiram, respectivamente, uma redução da pressão média efetiva de atrito (FMEP) do motor em até 12% e consumo específico de combustível (BSFC) em até 2,5% em rotações de 1000 a 1400 rpm. / In the last few decades questions about emissions level control for internal combustion engines as well as fuel consumption reduction have been debated in a global bases with clear deployments in more restricted control specifications to allow the commercialization of new internal combustion engines to more restrictive markets that look for a better life quality and environment. Even with the introduction of new technologies the engines still present a significant loss of energy due to the mechanical friction. With base in this context, the new development projects seek for high mechanical-thermal efficiency linked with engineer that can benefit the engine performance with a better combustion process and reduced friction as well. One of the most relevant contributors for the friction in an engine is the piston-piston ring-cylinder liner system which has been the focus of many research works with focus on reduce engine friction losses. The properties of Diamond-Like Carbon films (DLC) are well-known such as superior wear resistance and low friction coefficients that makes suitable for many different tribology applications. This work evaluates the application of a graded hydrogen amorphous DLC film with applied over cylinder liner running surface. The methodology approach two coating thickness: 2.5 and 12.5 μm, deposited by the plasma assisted chemical vapor deposition process (PACVD) as the alternative solution for engine friction reduction and thus a reduction on brake specific fuel consumption (BSFC), and a improved wear resistance behavior of the piston rings and cylinder liner contact surfaces as well. By using baseline parts without inner DLC coating and DLC coated parts with similar running roughness surfaces, comparative reciprocating bench tests showed a tendency of coefficient of friction (COF) reduction in up to 19%. In a same trend, fired gasoline and diesel engine tests showed a friction mean effective pressure reduction (FMEP) in to 12% and small brake specific fuel consumption (BSFC) in up to 2.5% at low engine speed range respectively.

Orientador: Amilcar Porto Pimenta / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-16T14:56:57Z (GMT). No. of bitstreams: 1 Soares_SergioLeal_M.pdf: 10822438 bytes, checksum: bf38004d90969d8ce0aa87842d2431f9 (MD5) Previous issue date: 2010 / Resumo: Da constante necessidade de aperfeiçoar a fabricação de produtos, as indústrias têm introduzido em suas linhas de fabricação diversos conceitos já consagrados para estabelecer a qualidade otal nas suas concepções, garantindo que seus produtos estejam dentro das especificações e que todos enham o mesmo resultado funcional. Na fabricação de motores ocorre a mesma tendência. Eles necessitam de processos confiáveis na concepção, buscando repetibilidade dos resultados, onde o motor tem grande influencia nos veículos que os equipa, sendo esses grandes fontes de emissões de poluentes. Dessa forma, é muito importante aperfeiçoar o funcionamento dos motores, para que haja redução nas emissões. Além disso, é necessário efetuar melhorias funcionais, atendendo as exigências feitas pelo mercado, reduzindo as perdas de potência e o consumo de combustível. Uma das formas para aumentar o rendimento funcional do motor é aperfeiçoar a passagem do ar de admissão dentro do motor. Isto pode trazer como resultado redução do consumo de combustível, aumento de potência, redução de temperaturas e pressões internas no motor, redução de desgaste dos componentes, aumento de vida útil, redução dos níveis de emissões e melhorias na condução do veículo, principalmente na partida do veículo. Porém, mesmo tendo um bom projeto, é necessário conhecer as conseqüências quando ocorrem dispersões no processo de fabricação, sabendo também o quanto o produto é susceptível a possíveis falhas de fabricação. Na produção dos cabeçotes existem diversos pontos críticos que podem gerar falhas de posicionamento da peça durante o processo de usinagem. Para reduzir essas falhas foi construído um dispositivo de fixação da peça na operação de usinagem dos primeiros furos. Mesmo com esse dispositivo, algumas peças ainda ficam fora da especificação dimensional. O grande interesse desse trabalho é conhecer, através de avaliações dimensionais, testes funcionais em bancada de fluxo e em dinamômetro (ensaio de desempenho a plena carga e emissões), se existe alguma influência gerada pela dispersão da usinagem dos furos das guias no cabeçote de um certo motor e quantificar essa diferença. Para isso, foram confeccionados três grupos de quatro cabeçotes cada onde o primeiro grupo tem suas dimensões dentro da especificação, escolhido como padrão, o segundo grupo tem a cota de posicionamento do furo da válvula de admissão 1,5 mm fora do especificado a esquerda e o terceiro grupo tem esta mesma cota 1,5 mm fora do especificado a direita. Todos os cabeçotes foram testados no mesmo conjunto motor-dinamômetro e com mesma instrumentação, para aumentar a confiabilidade dos resultados. Constatou-se uma variação de 4% em média no número de swirl nos cabeçotes alterados em relação ao grupo padrão. Foi mostrado ainda que a influência provocada pelas dispersões dimensionais não afetaram significantemente o desempenho do motor / Abstract: The constant need to improve the manufacturing of products, industries have introduced into their production lines several existing concepts to estabilish total quality in their designs, ensuring that their products are within specifications and that they all have the same functional outcome. In the engines manufacturing, the same trend can be seen. They need reliable processes in the design, seeking repeatability of results, since they have great influence in vehicles (large sources of emissions). Thus, it is very important to improve the engine's functioning, in order to reduce emissions. Furthermore, it is necessary to make functional improvements, meeting the requirements made by the market, reducing power losses and fuel consumption. One way to increase the engine functional efficiency is to improve the airflow intake inside the engine. This could bring as a result a reduction in fuel consumption, increased power, lower temperatures and pressures inside the engine, reduced wear of components, increased life cycle, reduced emission levels and improved vehicle drivability, especially at the vehicle startup. However, even with a good design, it is necessary to know the consequences when dispersions occur in the manufacturing process, also knowing how the product is susceptible to possible manufacturing faults. In the cylinder-heads production, there are several critical points that can generate position failure of the working piece during the machining process. To reduce these failures, a fixing device was built in the operation of machining the first holes. Even with this device, some parts are still out of dimensional specification. The great interest of this work is to know, through dimensional assessments, functional testing flow and dynamometer in lab scale (performance at full load and emissions tests), if there is any influence caused by the dispersion of an engine cylinder-head guide holes machining and quantify this difference. For so, three groups of four cylinder-heads each were created, where the first group has its dimensions within the specification, chosen as standard; the second group has a quota of positioning hole inlet valve of 1.5 mm out of specification at left; and the third group has the same dimension of 1.5 mm out of specification at right. All cylinder-heads were tested in the same engine-dynamometer set and with the same instrumentation, in order to increase the reliability of results. There was an average variation of 4% in the number of swirl in the cylinder-heads changed regarding the standard group. It was also shown that the influence caused by the dimensional dispersions did not significantly affect the engine performance and emission level / Mestrado / Motores / Mestre em Engenharia Mecânica

O presente trabalho é o início de um estudo da aplicação do método de otimização conhecido como adjunto em escoamentos incompressíveis, viscosos e periódicos, envolvendo um problema de bastante interesse: a análise da aplicação de splitter plates em cilindros de seção circular. Conhecido por sua simplicidade, o splitter plate, que consiste em uma placa plana alinhada ao escoamento e colocada a jusante do corpo, é um dispositivo efetivo na mudança de comportamento da esteira de vórtices de Von Kárman. A partir da revisão bibliográfica foi possível entender a dinâmica do escoamento, proporcionando uma calibração dos modelos numéricos. Complementando esta etapa, foi efetuada uma análise da qualidade das malhas computacionais. Através de uma geração de diversas malhas computacionais, o espaço de soluções foi explorado buscando encontrar o mínimo arrasto para diversos comprimentos de splitter plate e diferentes números de Reynolds (Re). Foi observada a influência da placa na formação da esteira de vórtices, obtendo uma redução dos coeficientes de força do cilindro. Com esses dados, foi possível desenvolver o método de otimização voltado para análise do gradiente de sensibilidade conhecido como método adjunto baseado nas equações de Navier Stokes utilizando o problema descrito como base para validação dos resultados. A abordagem do método adjunto caracteriza-se pela busca dos extremos de funções conhecidas como medidas de mérito. Essas funções podem ser integrais de sustentação e arrasto por exemplo. Na literatura, o método adjunto é apresentado como possuindo duas grandes vantagens: a primeira é a imposição das equações do escoamento como restrições do problema, o que sempre confinará as variações da medida de mérito dentro do universo de soluções realizáveis; já a segunda é conseqüência da primeira, pois as restrições permitem uma simplificação no cálculo do gradiente de sensibilidade, reduzindo o custo computacional. Para o cálculo do gradiente de sensibilidade, o objetivo é otimizar o arrasto do cilindro sob efeito do splitter plate variando os parâmetros de controle (comprimento e posicionamento do splitter plate). A direção de busca e o cálculo do passo da geometria são obtidos a partir da relação entre a solução numérica do escoamento e as variáveis adjuntas calculadas. Nesta dissertação, será apresentada a pesquisa bibliográfica, os resultados do método tentativa e erro, a formulação do método adjunto baseado nas equações de Navier Stokes e um exemplo de sua solução numérica, demonstrando sua existência. / The report is the beginning of a research about the application of the so called adjoint method in the optimization of incompressive, viscous and periodic flows. The study involves a problem of great interest: an analysis of the implementation of splitter plates in the flow around cylinders with circular section. Widely recognized for its simplicity, the splitter plate consists of a flat plate, which is placed in the wake of a cylinder, in the stream wise direction, and it works by changing the way the shear layers interact with one another. Based on a literature survey, it is possible to understand the physics of this class of flows. As a better result, one learns what to expect from the numerical solutions and hence, one can calibrate its parameters. Moreover, we study the best configuration of the computational mesh, thus reducing the computational cost. After the generation of meshes, the universe of solutions was explored to find the minimum drag for various lengths of splitter plate and Reynolds number (Re). The influence of the plate in the interaction of the shear layers was observed in the reduction of drag coefficient. These results form a the basis for comparison, upon one can develop the optimization by the adjoint method. The adjoint method can be used to search the extreme of objective functionals. These functionals can be the lift and drag integrals for example. The theory presents two advantages to the method: first, the imposing the equations that govern the flow as variational constraints one limits the variations to the universe of realizable solutions; second, these constrains simplify the computation of the sensitivity gradient, by reducing its computational cost. To compute the sensitivity gradient, the objective functional can be defined as the average drag coefficient of the circular cylinder with a splitter plate. The control parameters are the length of the plate and the distance between it and the body, which known as gap. The search direction and the variation of geometry can be obtained by the relationship between the solutions to the flow and the adjoint equations. This final report shows the literature survey, the results of trial and error method and the formulation and one result of adjoint equations based on the incompressible NavierStokes equations.

Este trabalho apresenta a demonstração de dois teoremas sobre a caracterização de hipersuperf ícies maximais no espaço anti-de Sitter. Ambos os Teoremas 4.0.1 e 4.0.2 caracterizam hipersuperf ícies maximais isométricamente imersas no espaço anti-de Sitter Hn+1 1 com (n-1) curvaturas principais de mesmo sinal, com curvatura escalar constante e curvatura de Gauss-Kronecker constante não-nula, respectivamente, como sendo isométricas ao cilindro hiperbólico H1(c1)Hn1(c2). Também é feito um breve estudo do artigo [17], onde o Teorema 3.0.3 é ferramenta chave para a obtenção dos resultados demonstrados nos Teoremas 4.0.1 e 4.0.2. / This work presents, the demonstration of two theorems about the characterization of maximal hypersurfaces on the anti-de Sitter space. Both Theorems 4.0.1 and 4.0.2 characterize maximal hypersurfaces isometrically immersed in the anti-de Sitter space Hn+1 1 with (n-1) principal curvatures with the same sign, with constant scalar curvature and nonzero constant Gauss-Kronecker curvature, respectively, as being isometric to the hyperbolic cylinder H1(c1) Hn1(c2). Is also done a brief study of the article [17], where the Theorem 3.0.3 is key piece to obtain the results demonstrated in Theorems 4.0.1 and 4.0.2.

Les balances manométriques sont utilisées en métrologie des pressions statiques.Des projets européens tel qu'Euromet 463 ont mis en évidence des écarts systématiques entreles mesures expérimentales et les calculs des paramètres nécessaires à la caractérisation desbalances de référence. La vitesse de chute du piston est l'un d'eux pourtant essentiel dans laprocédure d'étalonnage. L'objectif des travaux de thèse est l'ajustement des méthodesd'estimation de cette vitesse de chute. Cela permettra d'améliorer la caractérisation du jeuinterne de la balance, de déterminer plus précisément la section effective de ce jeu et parconséquent d'améliorer l'incertitude portant sur le coefficient de déformation, paramètre clé del'étalonnage par comparaison. Jusqu'à présent le modèle de calcul de l'écoulement du fluidedans la balance était quasi unidimensionnel. Il assimilait le jeu entre le piston et le cylindre àdeux parois parallèles. Dans cette étude, les équations de l'écoulement du flu ide sont modifiéespour évaluer l'influence du modèle dans un jeu annulaire. Les corrections dues à la vitesse dechute du piston sont également prises en compte. Les calculs des déformations des structuressont réalisés en utilisant la méthode des éléments finis. Les travaux expérimentaux portent surdes ensembles piston-cylindre 50, 200 et 1000 MPa du Laboratoire National de Métrologie etd'Essais (LNE). Une confrontation calcul-expérience est réalisée en prenant en compte lesparamètres de variabilités tels que la géométrie ou les propriétés du fluide. / The pressure balances are utilized in the metrology of the static pressure. TheEuropean project as "Euromet 463" has underlined the lack of agreement between experimentalmeasurements and calculations of the parameters necessary for the pressure balance. Thepiston fall rate is, in particular, an essential parameter in the calibration procedure. The aim ofthe thesis is the adjustment of methods for estimating the piston fall rate. This will improve thecharacterization of the gap, determine the effective area more precisely and consequentlyimprove the uncertainty on the pressure distortion coefficient, a key parameter for the calibrationby comparison. lndeed, the former quasi one-dimensional madel assimilates the gap betweenpiston and cylinder as formed by two parallel walls, which is an approximation. ln this study, theequations of the fluid flow are modified to evaluate the influence of the model in an annular gapmadel. ln addition, corrections due to the velocity of the piston wall are taken into account. Thisresearch work is applied on the piston-cylinder units 50, 200 and 1000 MPa of the Laboratoirenational de métrologie et d'essais (LNE). Taking into consideration the variability of parameterssuch as geometry or fluid properties, a comparison between the experiment and the calculationis carried out.

Dans une optique d'allègement, les alliages d'aluminium de fonderie représentent une excellente solution technique. Ainsi, pour les culasses automobiles, les alliages d'aluminium Al-Si-Cu (Aluminium-Silicium-Cuivre) sont souvent choisis pour leurs performances mécaniques ainsi que leur bonne coulabilité. L'objectif de cette étude est d'améliorer la compréhension des mécanismes en fatigue oligocyclique pour définir un critère de fatigue adapté. Cet objectif est réalisé en combinant des essais (en fatigue oligocyclique à température ambiante et élevée), de nombreuses observations (microscopie à balayage électronique, microtomographie 3D rayons-X de laboratoire, suivi de fissure) et des simulations (génération de population de défauts et calculs éléments finis). À l'aide d'outils spécialement développés, la population de défauts (défauts de fonderie) est analysée en détails : la taille de défaut est modélisée par une distribution de Pareto généralisée et leurs positions par un processus ponctuel de type agrégé (démontrant que les défauts ne sont pas spatialement distribués de manière totalement aléatoire). Les processus ponctuels marqués permettent de montrer que tailles et positions de défauts ne sont pas corrélées. En utilisant ces informations statistiques, il est démontré que seuls les défauts proches de la surface sont critiques pour la fatigue oligocyclique. Un critère de fatigue basé sur l'énergie de déformation est utilisé pour prévoir la durée de vie en fatigue. Par la suite, un modèle de propagation de fissure permet de prendre en compte la taille de défaut dans la prévision de la durée de vie. Combiné à la statistique des défauts, ce modèle permet d'estimer la dispersion des essais. En dernier lieu, des essais et des simulations sur éprouvettes entaillées montrent que l'étude de la population de défauts est d'autant plus critique que le volume fortement sollicité mécaniquement devient plus faible. / In a search for lightweight materials, cast aluminium alloys have become an efficient solution for the automotive industry. For cylinder heads, cast aluminium alloys (Aluminium-Silicon-Copper based) are often chosen for their mechanical performances combined with their good casting abilities. This study aims at better understanding the damage mechanisms of Low-Cycle Fatigue (LCF) to help define a suitable design criterion. This is achieved by combining experiments (LCF tests at ambient and high temperature), various observations (Scanning electron microscopy, laboratory 3D X-ray microtomography, crack propagation monitoring) and numerical techniques (Finite element method simulations and defect population generation). Specifically designed statistical tools allow clearly identifying the defect (casting defects) population: the defect size can be modelled by a generalized Pareto distribution and their positions by a clustered point process (thus showing the defect locations are not completely random). Using marked point processes, it is also shown that defect size and defect position are uncorrelated. Using this statistical information and by systematic observations, it is proven that only defects close to the surface are critical for the fatigue life. The different interactions between cracks and defects are also studied, especially with respect to temperature. A strain energy based fatigue criterion is introduced and allows estimating the fatigue life. Then, a crack propagation model provides a mean of taking the defect size into account, which combined with the statistics of defects, gives an estimate of the fatigue life dispersion. Finally, notched specimens tests and simulations show the study of the defect population is even more critical as the highly loaded volume becomes smaller.

Une étude expérimentale a été menée sur le sillage d’un cylindre circulaire stratifié dans le but de décrire l’effet de l’inclinaison et de la stratification sur les instabilités tridimensionnelles d’un sillage. Principalement 4 modes instables ont été trouvés.Ces résultats mettent ainsi en évidence le fait que la stratification et l’angle d’in- clinaison modifient fortement la transition d’un écoulement 2D à 3D du sillage d’un cylindre avec la présence de nouveaux modes instables. / An experimental study has been delineated of a stratified wake of a circular cy- linder in order to describe the effect of the tilt and of the stratification on the 3D instabilities of the wake. Principally, four unstable modes have been figured out.These results highlight the fact that the stratification strongly modifies the transition from a 2D to a 3D flow in a cylinder wake, with the presence of new unstable modes. The tilt of the cylinder with respect to the vertical plays a major role, such that a study limited to a vertical or a horizontal cylinder misses a lot of the rich dynamics of the tilted wake.

Sea water intake structures submerged in the surf zone are used to provide water for cooling processes in large facilities such as power plants and refineries. Structures submerged in the surf zone are subject to large forces from breaking waves. To study these forces induced from realistic sea state conditions, a physical model of an intake structure submerged in the wave breaking zone was constructed and subjected to a wide spectrum of regular and irregular waves. The model structure was designed in a manner so force measurement could be isolated to separate components of the structure. The data of peak forces on the structure was analyzed for correlations with varying irregular wave properties. Using the results of forcing on the structure from regular wave tests, drag and inertia coefficients for use in the Morison equation were determined for each separate component and configuration of the structure. These force coefficients were plotted against various wave properties to analyze correlations with wave conditions. Finally, the force coefficients for the structure were used with the Morison equation and current data from the experiments to successfully model forcing on the structure during irregular wave tests.

Large-eddy simulations of turbulent flows past a circular cylinder have been performed at sub-, critical and super-critical Re using an orthogonal curvilinear grid solver, CFDship-Iowa version 6.2. An extensive verification and validation study has been carried out. Various aspects of the flow field have been investigated. The aspect ratio of the computational domain has major effects on the results. In general, large aspect ratio produced best results for the sub-critical Re. Small dependency on both aspect ratio and grid resolution was observed for the critical Re. Small aspect ratio and conservative scheme produced best results for the super-critical Re. Overall flow features and the drag crisis phenomenon have been correctly predicted. A lot of experimental and numerical studies of flow past a circular cylinder were collected and used for the validation of the present LES study. Integral and local variables were in fairly good agreement for the sub-critical Re. Sharp behavior including drag crisis was predicted for the critical Re. Although some discrepancy including early formation of turbulent separation was observed, local flow structures including separation bubble were observed for the super-critical Re. The formation of secondary vortex near the cylinder wall and its evolution into separation bubble were observed. The spectral analysis showed that the separation bubble had the instabilities close to the shear layer frequency. The proximity of shear layer to the cylinder enhanced the mixing process of boundary layer and shear layer and led to the formation of separation bubble. A snapshot POD method was used to extract flow structures in the boundary layer, shear layer and wake. In the boundary layer, the secondary vortices and separation bubble were successfully extracted. Due to the weak TKE distribution, specific flow structures were hard to find in the shear layer. Large two-dimensional flow structures representing the Karman shedding vortices were extracted for the sub- and super-critical Re.