Orientador: Janito Vaqueiro Ferreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-25T19:22:38Z (GMT). No. of bitstreams: 1 Cro_NelsonPradoRodrigues_M.pdf: 2904462 bytes, checksum: 1e944d316e2e4ec4ca0a4e8ba01ae4a2 (MD5) Previous issue date: 2014 / Resumo: Este trabalho descreve o desenvolvimento de um modelo de simulação computacional para motores de combustão interna com ignição por centelha que inclui o processo de combustão com duração finita, a transferência de calor instantânea entre o fluído operante e as paredes dos cilindros e os processos de admissão e de escape. O modelo de simulação desenvolvido realiza os cálculos de propriedades termodinâmicas de cada uma das substâncias envolvidas no processo a cada instante discretizado do ciclo termodinâmico do motor a partir de dados de entrada relacionados ao motor e ao regime de operação que se deseja avaliar. O algoritmo tem por resultado os perfis de temperatura e pressão instantâneas dos gases no interior dos cilindros em função do ângulo do eixo de manivelas e o diagrama da pressão instantânea pelo volume instantâneo no intervalo de um ciclo do motor. O algoritmo também contempla campos para inserção de dados relativos a determinados parâmetros de projeto de motor que permitem a avaliação da influência da variação dos referidos parâmetros nas características de desempenho do motor simulado / Abstract: This work describes the development of a computational simulation model for internal combustion engines with spark ignition which includes the combustion process with finite duration, the instantaneous heat transfer between the working fluid and the cylinder walls and the intake and exhaust processes. The simulation model developed calculates the thermodynamic properties of each element involved in the process at every discretized instant of the engine cycle using as input the data related to the engine and to its intended operating regime. The simulation model has as a result the instantaneous temperature and pressure profiles inside of the cylinder as a function of the crankshaft angle and the diagram of instantaneous pressure by instantaneous volume in the range of one cycle. The algorithm also includes a variation range of certain parameters of the engine project to evaluate the influence of each one of these parameters in its performance characteristics / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

We characterize finite-time thermodynamic processes of multidimensional quadratic overdamped systems. Analytic expressions are provided for heat, work, and dissipation for any evolution of the system covariance matrix. The Bures-Wasserstein metric between covariance matrices naturally emerges as the local quantifier of dissipation. General principles of how to apply these geometric tools to identify optimal protocols are discussed. Focusing on the relevant slow-driving limit, we show how these results can be used to analyze cases in which the experimental control over the system is partial.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23691号 / 理博第4781号 / 新制||理||1684(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 佐々 真一, 准教授 武末 真二, 講師 DECHANT Andreas / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The work was concerned with experimental study of the turbulent flame development process of alcohol fuels, namely ethanol and butanol, in an optically accessed spark ignition research engine. The fuels were evaluated in a single cylinder engine equipped with full-bore overhead optical access operated at typical stoichiometric part-load conditions with images captured using high-speed natural light imaging techniques (or chemiluminescence). The differences in flame development between the fuels was analysed to understand better the impact of high and low alcohol content fuels on combustion. Advanced image analysis, in conjunction with Ricardo WAVE simulation, allowed for the conclusion that the faster burning exhibited by ethanol was the result of the marginally higher laminar burning velocity providing a faster laminar burn phase and accelerating the flame into the turbulent spectrum thus reducing bulk flame distortion and better in-cylinder pressure development. Such physical reactions are often over-looked in the face of chemical differences between fuels. A further study into the variation of maximum in-cylinder pressure values was conducted focussing on iso-octane and ethanol. This study identified two phenomena, namely “saw-toothing” and “creep” in which cluster of cycles feed into one another. From this it became clear that the presence of high pressure during the exhaust process had a large influence on the following cycles. This is another often overlooked phenomenon of direct cycle-to-cycle variation whereby incylinder pressures during blowdown can dictate the duration, load or stability output of the following cycle. Finally the work investigated the impact on flame development of alcohol fuels when the overlap duration was altered. While the engine produced counterintuitive figures of residual gas, ethanol was confirmed as having greater synergy with EGR by displaying less impacted combustion durations c.f. iso-octane. Care should be taken however when analysing these results due to the unique valve configuration of the engine.

Dissertation research involves development of Mobile Order Theory thermodynamic models to mathematically describe and predict the solubility, spectral properties, protonation equilibrium constants and two-phase partitioning behavior of solutes dissolved in binary solvent mixtures of analytical importance. Information gained provide a better understanding of solute-solvent and solvent-solvent interactions at the molecular level, which will facilitate the development of better chemical separation methods based upon both gas-liquid and high-performance liquid chromatography, and better analysis methods based upon complexiometric and spectroscopic methods. Dissertation research emphasizes chemical equilibria in systems containing alcohol cosolvents with the understanding that knowledge gained will be transferable to more environmentally friendly aqueous-organic solvent mixtures.

The need for cleaner and more efficient alternative energy sources is becoming urgent as concerns mount about climate change wrought by greenhouse gas emissions. Solid oxide fuel cells (SOFCs) are one of the most efficient options if the goal is to reduce emissions while still operating on fossil energy resources. One of the foremost problems in SOFCs that causes efficiency loss is the polarization resistance associated with the oxygen reduction reaction(ORR) at the cathodes. Hence, improving the cathode design will greatly enhance the overall performance of SOFCs. Lanthanum nickelate, La2NiO4+δ (LNO), is a mixed ionic and electronic conductor that has competitive surface oxygen exchange and transport properties and excellent electrical conductivity compared to perovskite-type oxides. This makes it an excellent candidate for solid oxide fuel cell (SOFC) applications. It has been previously shown that composites of LNO with Sm0.2Ce0.8O2-δ (SDC20) as cathode materials lead to higher performance than standalone LNO. However, in contact with lanthanide-doped ceria, LNO decomposes resulting in free NiO and ceria with higher lanthanide dopant concentration. In this study, the aforementioned instability of LNO has been addressed by compositional tailoring of LNO: lanthanide doped ceria (LnxCe1-xO2,LnDC)composite. By increasing the lanthanide dopant concentration in the ceria phase close to its solubility limit, the LNO phase has been stabilized in the LNO:LnDC composites. Electrical conductivity of the composites as a function of LNO volume fraction and temperature has been measured, and analyzed using a resistive network model which allows the identification of a percolation threshold for the LNO phase. The thermomechanical compatibility of these composites has been investigated with SOFC systems through measurement of the coefficients of thermal expansion. LNO:LDC40 composites containing LNO lower than 50 vol%and higher than 40 vol% were identified as being suitable to incorporate into full button cell configuration from the standpoint of thermomechanical stability and adequate electrical conductivity. Proof-of-concept performance comparison for SOFC button cells manufactured using LNO: La0.4Ce0.6O2-δ composite to the conventional composite cathode materials has also been provided. This thermodynamics-based phase stabilization strategy can be applied to a wider range of materials in the same crystallographic family, thus providing the SOFC community with alternate material options for high performance devices.

It has been generally recognized that the surface phenomena of the solid particles such as shrinking and swelling, water- holding capacity, water' movement, and cation exchange are important in understanding the physical properties of the soil. Clay is the most prevalent material in the colloidal fraction of many soils. Because of the complex nature of the surface of clays and the small size of the particles, the direct study of surface phenomena is difficult. Thermodynamic functions change in accordance with changes and organization within the system. Thus, an examination of the thermodynamics of surface phenomena provides some understanding of the reactions.

The retention of water in soils is a very interesting subject. Soil-water research presents a great challenge to research workers. The challenge is broad in scope and extends from the field problems of large irrigation projects to the atomic scale of the solid-liquid interface. If scientists are going to describe scientifically soil-water relations, they must ultimately utilize the instruments of science and the language of mathematics. To the end of the latter the mathematics of thermodynamics has been applied in these studies of water retention in soils.

The movement of water in soil presents many interesting problems to the research worker. It is also a subject which finds wide and important application in agriculture and several branches of engineering. The object of this work was to examine the usefulness of a new equation of flow of water in unsaturated soil. If valid, this new approach may be able to eliminate some of the gaps in our present knowledge of the subject. All soil lying above the capillary fringe of a water table is in the unsaturated state with respect to water. This means that in any macroscopic volume element of soil three phases are present-- solid, liquid and gas. The volume fraction of each of these phases show wide variation in both space and time in field soils. The variation in both space and time in field soils. The variation in the volume fraction of the liquid or water phase is accompanied by a considerable change in the physical properties of the water. In the strictest sense the unsaturated state covers all intermediate conditions between saturation and an incomplete monomolecular layer of absorbed water. It is important to recognize that the solid phase is also dynamic. It consists of unconsolidated particles with great variation of size and shape. Many solid phase properties show a complex dependence upon the amount of water present. Swelling and shrinking are well known in soils and these changes affect water movement.

Martensitic steels have become very important engineering materials in modern society. Crucial parts of everyday products are made of martensitic steels, from surgical needles and razor blades to car components and large-scale excavators. Martensite, which results from a rapid diffusionless phase transformation, has a complex nature that is challenging to characterize and to classify. Moreover the possibilities for modeling of this phase transformation have been limited, since its thermodynamics and kinetics are only reasonably well understood. However, the recent development of characterization capabilities and computational techniques, such as CALPHAD, and its applicability to ferrous martensite has not been fully explored yet. In the present work, a thermodynamic method for predicting the martensite start temperature (Ms) of commercial steels is developed. It is based mainly on information on Ms from binary Fe-X systems obtained from experiments using very rapid cooling, and Ms values for lath and plate martensite are treated separately. Comparison with the experimental Ms of several sets of commercial steels indicates that the predictive ability is comparable to models based on experimental information of Ms from commercial steels. A major part of the present work is dedicated to the effect of carbon content on the morphological transition from lath- to plate martensite in steels. A range of metallographic techniques were employed: (1) Optical microscopy to study the apparent morphology; (2) Transmission electron microscopy to study high-carbon plate martensite; (3) Electron backscattered diffraction to study the variant pairing tendency of martensite. The results indicate that a good understanding of the martensitic microstructure can be achieved by combining qualitative metallography with quantitative analysis, such as variant pairing analysis. This type of characterization methodology could easily be extended to any alloying system and may thus facilitate martensite characterization in general. Finally, a minor part addresses inverse bainite, which may form in high-carbon alloys. Its coupling to regular bainite is discussed on the basis of symmetry in the Fe-C phase diagram. / <p>QC 20120824</p> / Hero-m