Current and future pollutant enussion legislation calls for decreased NOx emissions from combustion systems. A review of techniques used for NOx abatement led to the choice of combustor redesign to be the most cost effective method available. This led to the design, construction and development of a combustion system that utilised a Coanda ejector to generate recirculation of the exiting high temperature combustion products to mix with the air supply. Cooling of the burner was integrated into the design through the use of the air and fuel supplies. Computational fluid dynamics was used to model and aid development of the design. The model was used to predict NOx and CO emissions and the fuel-air mixing pattern. This, along with an analysis of experimental results and observations led to an understanding of the burner operation with respect to pollutant emissions and stability. NOx emissions from the Coanda burner were found to be lowest when using a 0.2 mm Coanda gap width, resulting in 16 ppm NOx being emitted at an air to fuel ratio of 1.5. However, the use ofa 0.2 mm Coanda gap width required an air supply pressure of up to 4 bar. The use of a 0.5 mm Coanda gap width enabled burner operation at lower air supply pressures. The resulting NOx emissions were measured as 23 ppm at an air to fuel ratio of 1.I, with a corresponding exit gas temperature of 2200 K. Flue gas recirculation quantity, flame stability, flame stabiliser shape and operational limits proved to be inter-linked in the reduction of NOx emissions. It was found that fuel-air mixing was controlled by the entrainment properties of the Coanda ejector and the flame stabiliser. The average oxygen concentration entering the combustion chamber when using a 0.2 mm and 0.5 mm Coanda gap width was 13.7 % and 16.6 %, respectively. Due to the position of the fuel injector, a fuel rich region formed behind the flame stabiliser. With a suitable flame stabiliser geometry and the use of 'fingers', low NOx combustion and flame stability was achieved near stoichiometric conditions. It was shown that the design of the burner enabled very low pollutant emissions near stoichiometric conditions, resulting in high exit gas temperatures. Conceivable applications of this type of burner could lie in small and intermediate furnaces where low NOx emissions are required. Additionally, very high temperature applications, such as glass furnaces could benefit in both cost and pollutant emissions from such a burner.

Nowadays, in the field of energy production, particular attention must be paid to improving efficiency, reducing pollutants and fuel flexibility. To reach those goals, cogenerative systems represent an appealing solution. One of the most promising cogenerative systems available nowadays is the micro turbine, which provides reasonable electrical efficiency of about 30%, multi-fuel capability, low emission levels and heat recovery potential, and need minimum maintenance. Among the several options, micro gas turbines (mGT) are particularly interesting. Beside theuse of natural gas, other fuels like landfill gas, ethanol, industrial waste off-gases and other bio-based gases can be used. Moreover, it is possible to further improve the efficiencies and reduce the emissions for mGTs by paying particular attention at the design of the combustion chamber. To this goal, flameless combustion could be an interesting solution. Flameless combustion is able to provide high combustion efficiency with low NOx and soot emissions. The increasing interest in flameless combustion is motivated by its large fuel flexibility, representing a promising technology for low-calorific value fuels, high-calorific industrial wastes as well as in presence of hydrogen. Moreover, flameless combustion is very stableand noiseless, so it is suited for gas turbine applications where conventional operations may lead to significant thermo-acoustic instabilities (“humming”) and stresses. Flameless combustion needs the reactants to be preheated above their self-ignition temperature and enough inert combustion products to be entrained in the reaction region, in order to dilute the flame. As a result, the temperature field is more uniform than in traditional combustion systems, and it does not show high temperature peaks. Hence, NOx formation is suppressed as well as soot formation,due to the lean conditions, low temperatures and the large CO2 concentration in the exhausts.mGTs operating in flameless combustion regime represent a promising technology for the combined production of heat and power with increased efficiency, reduced pollutants emission and high fuel flexibility. The objective of the present Thesis is the design of a combustion chamber for amGT for residential applications. The design is performed employing CFD-tools. Thus, it is necessary to develop a reliable numerical model to use in the design process. Therefore, the first step of the Thesis consists in a series of validation studies, with the goal of selecting the most appropriate and reliable models to describe flameless combustion. The validation will be carried on three differenttest cases, which have different nominal powers and employ different gaseous fuels. The second part of the Thesis focuses on the design and optimization of the combustion chamber. Finally, the third part shows the experimental investigation of the aforementioned chamber.The study of those three cases shows that, to correctly predict the behavior of those systems, it is necessary to take into account both mixing and chemical kinetics. The best results have been obtained with the Eddy Dissipation Concept model, coupled with detailed kinetic schemes. As far as the NOx emissions are concerned, it is fundamental to include all the formation routes, i.e. thermal, prompt, via N2O and NNH route, to estimate properly the NOx production in flameless conditions.The aforementioned models have been used for the design and optimization of a combustion chamber for a mGT operating in flameless combustion regime. Both the design and the optimization have been carried out by means of CFD simulations and both are goal-oriented, meaning that they are carried out with the purpose of improving one or more performance indicators of the chamber, such as pollutants emissions, efficiency or pressure losses. The configuration that satisfies the criteria on the performance indicators has been built and investigated experimentally. The combustion chamber is stable and performs well in terms of emissions for a wide range of air inlet temperature and air-fuel equivalence ratio, lambda, values. Except for the condition closer to the stoichiometric one, both CO and NOx emissions are extremely low for all !and air inlet temperatures. Thechamber performs the best at its nominal operating condition, i.e. lambda = 3.5 and air inlet temperature 730 °C, In this case CO is 0 ppm and NOx is 5.6 ppm. The numerical model employed to describe the combustor performs quite well, except for the CO prediction, for all the conditions investigated. The final step of the present work is the application of a different kind of fuel, namely biogas. First the feasibility of such application has been evaluated using CFD calculations, and then the experimental evidence has been discussed. Due to a calibration error on the gas flow meter, it has not been possible to investigate the conditions of the design point (lambda = 3.5). Three other conditions have been examined,characterized by lower values of !closer to the stoichiometric conditions. Despite the relatively high values of NOx emissions due to the lower air excess and to the consequently higher temperatures, the combustion chamber has proven to be fuel flexible. Both ignition and stable combustion can be achieved also when biogas is burnt. Numerical simulations have also been performed; the results are in good agreement with the experimental evidence. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Cette thèse vise à comprendre et à modéliser les mécanismes chimiques de combustion de la biomasse dans les appareils de chauffage domestiques afin de réduire les émissions polluantes. Dans ce but, un modèle global de combustion a été développé. Ce modèle considère à la fois une cinétique chimique détaillée et le transfert thermique. La première partie de ce travail a consisté à développer un modèle cinétique permettant de représenter la dévolatilisation de la biomasse ainsi que les réactions secondaires de combustion en phase gazeuse des espèces émises au cours de la pyrolyse primaire. Selon le modèle cinétique de pyrolyse utilisé, la biomasse est caractérisée comme étant un mélange de trois constituants dits de référence : la cellulose, l’hémicellulose et la lignine. Pour connaître les limitations du modèle étudié, il a été testé sur plusieurs cas de pyrolyse primaire. Un modèle de pyrolyse secondaire et de combustion a été ajouté au modèle représentant la pyrolyse primaire. Ce modèle secondaire est composé de mécanismes d'oxydation pour les produits formés par la pyrolyse, comme l’hydroxyacétaldéhyde, le furane et ses dérivés, l’anisole, le furfural, le gaïacol… Ce modèle secondaire, ainsi que le nouveau modèle global développé, BioPOx (Biomass Pyrolysis and Oxidation), ont été testés sur un grand nombre de points expérimentaux. Dans une seconde partie, le modèle cinétique considérant à la fois la pyrolyse primaire et le craquage thermique des espèces gazeuses émises, est couplé à un modèle de transfert de chaleur simplifié afin de modéliser la combustion d’une bûche de bois dans un poêle représenté par un réseau de réacteurs chimiques idéaux. Le modèle global, couplant les parties cinétique et thermique, permet de reproduire des résultats expérimentaux sur des émissions gazeuses (CO, CO2, NO) obtenues dans un poêle à bois. / This thesis aims to understand and model the chemical mechanisms of biomass combustion in domestic heating appliances to reduce polluting emissions. For this purpose, a global model of combustion has been developed. This model considers both detailed chemical kinetics and heat transfer. The first part of this work consisted of developing a kinetic model to represent the devolatilization of biomass as well as the secondary gas phase combustion reactions of the species emitted during primary pyrolysis. According to the used kinetic model of pyrolysis, the biomass is characterized as a mixture of three so-called reference constituents: cellulose, hemicellulose and lignin. To know the limitations of the studied model, it has been tested on several cases of primary pyrolysis. A model of secondary pyrolysis and combustion was added to the model representing primary pyrolysis. This secondary model is composed of oxidation mechanisms for products formed by pyrolysis, such as hydroxyacetaldehyde, furan and its derivatives, furfural, anisole, guaiacol ... This secondary model, as well as the new global model developed BioPOx (Biomass Pyrolysis and Oxidation) have been tested on a large number of experimental results. In a second part, the kinetic model considering both the primary pyrolysis and the thermal cracking of the emitted gaseous species, is coupled to a simplified model of heat transfer to model the combustion of a log of wood in a stove represented by a network of ideal chemical reactors. The global model, coupling the kinetic and thermal parts, reproduces experimental results on gaseous emissions (CO, CO2, NO) obtained in a wood stove.

By 2050, Europe needs to have drastically decoupled its economic growth from its emissions of CO2. This is a direct response to the compelling evidence from the increasing risks of climate change brought about by the anthropogenic Greenhouse Gas (GHG) emissions and pollutant emissions (NOx). A replacement of significant percent of fossil fuels with renewable energy sources will be needed. However, energy production from most renewable energy sources, is typically intermittent and unpredictable. This requires a reliable mid-long term energy storage to synchronize production and demand. The Power-to-Fuel option or chemical storage can be the key for a sustainable energy system. Indeed, converting the excess of renewable energy into second generation fuels will unlock a long-term and high-density energy storage, ensuring also a reduction of the carbon footprint. These ”green” non-conventional fuels are blends of CH4, H2, CO and NH3. However, to achieve Power-to fuel, the development of an efficient combustion technology, coupled with virtually zero pollutant emissions, stable working conditions with different load and fuel and significant energy saving is required. In the last years, a so-called MILD or flameless combustion has drawn attention for its ability of meeting the mentioned targets. However, the studies available in literature are conducted on Jet in hot co-flow-like systems or they face conventional fuels, such as natural gas or methane. The examples using non-conventional fuels are scarce and limited to few operating conditions. In this framework, this PhD thesis focuses on a threefold aspect. Experimental campaigns investigated fuel flexibility of flameless combustion in the ULB furnace. A progressive addition of hydrogen in methane enhanced combustion features, reducing the ignition delay time and increasing the reactivity of the system, possibly losing its flameless behavior. Indeed, a threshold of 25% H2 was defined for reaching flameless/MILD conditions, characterized by still low pollutant emissions and temperature peak. This is in line with the goal of introducing “green” hydrogen into the natural gas pipeline (up to 20%) to reduce CO2 emissions. Further experimental campaigns tested the role of the injection geometry (varying the air injector ID) and fuel lance length to reduce NO emissions and retrieve flameless/MILD conditions for high hydrogen content. Finally, ammonia/hydrogen blends were tested. Results suggests that stoichiometry has a major impact on NO emissions. An optimal window, minimizing both NO and NH3-slip emissions was defined using an equivalence ratio of 0.9. To qualitatively describe the observed trends, a simplified reactors network was considered. The analysis highlighted the most important reactions correlated to NO formation and the reason of the NO reduction at stoichiometry condition. On the other side an affordable and reliable numerical model was optimized and tested in the Adelaide Jet in Hot Co-flow burner. The latter is a simplified burner capable of mimicking MILD combustion conditions. A set of RANS simulations were run using the Partially Stirred Reactor (PaSR) approach, investigating different mixing model formulations: a static, a fractal-based and a dynamic formulation, based on the resolution of transport equations for scalar variance and dissipation rate. A study about the role of combustion models and kinetic mechanisms on the prediction of NO formation was also conducted. Finally, an analysis of the choice of a Heat Release Rate (HRR) marker for MILD (HM1 flame) and not MILD (HM3 flame) conditions was carried out. Once having awareness of the capability of the proposed numerical model, simulations were conducted to define the key aspects in simulating a flameless furnace, varying the composition of the fuel, considering methane/hydrogen and ammonia/hydrogen blends. In particular, for the latter case, existing kinetic schemes showed a major over-estimation of NO emissions, reason why an optimization study was conducted in a simplified reactor (well stirred reactor) using a Latin Hypercube Sampling. Finally, the first-of-its-kind digital twin based on CFD simulations for a furnace operating in flameless combustion conditions was created. A reduced- order model (ROM) based on the combination of Proper Orthogonal Decomposition (POD) and Kriging was developed for the prediction of spatial fields (i.e. temperature) as well as pollutant in the exhausts. / D’ici 2050, l’Europe devra découpler sa croissance économique de ses émissions de CO2. Il s’agit d’une réponse nécessaire au changement climatique et à la pollution de l’air induits par les émissions atmosphérique de gaz à effet de serre (GES) et de polluants (NOx). Un remplacement d’un pourcentage significatif des combustibles fossiles par des sources d’énergie renouvelables sera nécessaire. Cependant, la production d’énergie à partir des sources renouvelables est généralement intermittente et imprévisible. Cela nécessite un stockage d’énergie fiable à moyen et long terme, pour synchroniser la production et la demande d’énergie. L’option Power-to-Fuel, ou stockage chimique, peut être la clé d’un système énergétique durable. En effet, la conversion de l’excès d’énergie renouvelable en carburants de deuxième génération permettra de débloquer un stockage d’énergie à long terme et à haute densité, en assurant également une réduction de l’empreinte carbone. Ces carburants non conventionnels « verts » sont des mélanges de CH4, H2, CO et NH3. Cependant, pour exploiter le potentiel du Power-to-Fuel, il est nécessaire de développer une technologie de combustion efficace, avec des émissions de polluants pratiquement nulles, assurant des conditions de travail stables avec une charge et des carburants différents et des économies d’énergie significatives. Au cours des dernières années, une combustion dite « MILD », ou sans flamme, a attiré l’attention pour sa capacité à atteindre les objectifs mentionnés. Cependant, les études disponibles dans la littérature sont menées sur des systèmes de laboratoire (jet in hot co-flow) et avec des carburants conventionnels comme le gaz naturel ou le méthane. Les exemples utilisant des carburants non conventionnels sont rares et limités à quelques conditions de fonctionnement.Dans ce cadre, cette thèse de doctorat se concentre sur un triple aspect.Des campagnes expérimentales ont étudié la flexibilité du combustible dans un four sans flamme installé à l'ULB. L’ajout progressif d’hydrogène dans le méthane permet d’améliorer les caractéristiques de combustion, en réduisant le délai d’allumage et augmentant la réactivité du système, ce qui, par contre, cause un éloignement du système des conditions sans flamme. En effet, un seuil supérieur de 25% H2 a été identifié pour les mélanges méthane/hydrogène, pour travailler dans des conditions sans flammes (MILD), caractérisées par une faible augmentation de température et des émissions de polluants amoindries .Cela est conforme à l’objectif d’introduire de l’hydrogène « vert » dans le gazoduc (jusqu’à 20%) afin de réduire les émissions de CO2. D’autres campagnes expérimentales se sont focalisées sur le rôle de la géométrie d’injection (variation du diamètre de l’injecteur d’air) et de la longueur de la lance du carburant pour réduire les émissions des oxydes d’azote et récupérer les conditions sans flamme/MILD pour une teneur élevée en hydrogène. Enfin, des mélanges ammoniac/hydrogène ont été testés. Les résultats suggèrent que la stœchiométrie a un impact majeur sur les émissions d’oxydes d’azote. Une fenêtre optimale minimisant les émissions de NO et d’ammoniac imbrulées a été définie en utilisant un rapport d'équivalence de 0,9. Pour tracer qualitativement les tendances observées, un réseau de réacteurs simplifié a été construit. L’analyse a mis en évidence les réactions les plus importantes pour la formation des NOx et elle a permis de justifier la réduction des oxydes d’azote à l’état stœchiométrique.De l’autre côté, un modèle numérique robuste et fiable a été optimisé et testé pour le brûleur Jet in Hot Co-flow de l’Université d’Adelaide. Ce dernier est un brûleur simplifié capable de simuler les conditions de combustion MILD/sans flamme. Un ensemble de simulations RANS ont été effectuées à l’aide de l’approche du réacteur partiellement agité (Partially Stirred Reactor – PaSR - en anglais), en examinant les différentes formulations de modèles de mélange :une formulation statique, fractale et dynamique, basée sur la résolution des équations de transfert pour la variance scalaire et le taux de dissipation. Une étude sur le rôle des modèles de combustion et des mécanismes cinétiques dans la prédiction de la formation des oxydes d’azote a également été réalisée. Enfin, une analyse sur le choix d’un marqueur de taux de dégagement de chaleur (Heat Release Rate – HRR – en anglais) pour les conditions MILD et non MILD a été réalisée. Après validation, les modèles développés ont été utilisés pour définir les aspects clés de la simulation d’un four sans flamme, en variant la composition du combustible, pour des mélanges méthane/hydrogène et ammoniac/hydrogène. En particulier, pour ce dernier cas, les schémas cinétiques existants ont montré une surestimation importante des émissions d’oxydes d’azote, raison pour laquelle une étude d’optimisation a été menée dans un réacteur simplifié.Enfin, le premier jumeau numérique en son genre, basé sur des Simulations numériques de Dynamique de Fluides (CFD – Computational Fluid Dynamics en anglais) pour un four fonctionnant dans des conditions de combustion sans flamme, a été créé. Un modèle à ordre réduit (ROM – Reduced Order Model en anglais) basé sur la combinaison de la Décomposition Orthogonale aux valeurs Propres (POD) et du Kriging a été développé pour la prédiction des variables d’intérêt (température et espèces chimiques majeures) ainsi que des polluants dans les fumées. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Στην παρούσα διπλωματική εργασία επιχειρείται μια προσπάθεια προσδιορισμού του ευρωπαϊκού μητρώου έκλυσης και μεταφοράς ρύπων καθώς και μια προσέγγιση προσαρμοσμένη σε δεδομένα της ελληνικής πραγματικότητας. Δηλαδή σε δεδομένα που αφορούν ελληνικές επιχειρήσεις που συμμετέχουν στο συγκεκριμένο μητρώο. / --

Made available in DSpace on 2014-12-17T15:01:52Z (GMT). No. of bitstreams: 1 ManoelRF_TESE_PARCIAL.pdf: 3699462 bytes, checksum: 4db868ae1dcdf8497e51d1aa5771684c (MD5) Previous issue date: 2011-05-16 / The industry, over the years, has been working to improve the efficiency of diesel engines. More recently, it was observed the need to reduce pollutant emissions to conform to the stringent environmental regulations. This has attached a great interest to develop researches in order to replace the petroleum-based fuels by several types of less polluting fuels, such as blends of diesel oil with vegetable oil esters and diesel fuel with vegetable oils and alcohol, emulsions, and also microemulsions. The main objective of this work was the development of microemulsion systems using nonionic surfactants that belong to the Nonylphenols ethoxylated group and Lauric ethoxylated alcohol group, ethanol/diesel blends, and diesel/biodiesel blends for use in diesel engines. First, in order to select the microemulsion systems, ternary phase diagrams of the used blends were obtained. The systems were composed by: nonionic surfactants, water as polar phase, and diesel fuel or diesel/biodiesel blends as apolar phase. The microemulsion systems and blends, which represent the studied fuels, were characterized by density, viscosity, cetane number and flash point. It was also evaluated the effect of temperature in the stability of microemulsion systems, the performance of the engine, and the emissions of carbon monoxide, nitrogen oxides, unburned hydrocarbons, and smoke for all studied blends. Tests of specific fuel consumption as a function of engine power were accomplished in a cycle diesel engine on a dynamometer bench and the emissions were evaluated using a GreenLine 8000 analyzer. The obtained results showed a slight increase in fuel consumption when microemulsion systems and diesel/biodiesel blends were burned, but it was observed a reduction in the emission of nitrogen oxides, unburned hydrocarbons, smoke index and f sulfur oxides / A ind?stria, ao longo dos anos, vem trabalhando no sentido de melhorar a efici?ncia dos motores. Mais recentemente surgiu, tamb?m, a necessidade de reduzir as emiss?es de poluentes para se adequar ?s severas leis ambientais. Isto tem despertado o interesse de desenvolver pesquisas no sentido de substituir os combust?veis derivados do petr?leo por diversos tipos de combust?veis menos poluentes, tais como: misturas de ?leo diesel com ?steres de ?leos vegetais e ?leo diesel com ?leos vegetais e ?lcool, emuls?es e microemuls?es. Este trabalho tem como objetivo desenvolver sistemas microemulsionados a partir de tensoativos n?o i?nicos dos grupos nonilfenois etoxilados e ?lcoois l?uricos etoxilados, misturas com etanol/diesel e misturas diesel/biodiesel para uso em motores diesel. Em uma primeira fase, visando selecionar os sistemas microemulsionados, foram obtidos diagramas tern?rios das misturas, sendo os sistemas compostos por: tensoativos n?o-i?nicos, ?gua como fase polar e como fase apolar o diesel e/ou misturas diesel/biodiesel. Os sistemas microemulsionados e as misturas, que representam os combust?veis estudados, foram caracterizados quanto ? massa espec?fica, a viscosidade, o ?ndice de cetano e o ponto de fulgor. Tamb?m foram avaliados o efeito da temperatura nos sistemas microemulsionados, o desempenho do motor, e as emiss?es de mon?xido de carbono, ?xidos de nitrog?nio, hidrocarbonetos n?o queimados e fuma?a de todos os sistemas. Os ensaios de consumo espec?fico e das emiss?es em fun??o da pot?ncia foram realizados em um motor de ciclo diesel em uma bancada dinamom?trica e o analisador de emiss?es GreenLine 8000. Os resultados mostraram um pequeno aumento no consumo espec?fico para os combust?veis microemulsionados, nas misturas diesel/biodiesel em rela??o ao diesel puro, por?m com uma redu??o nas emiss?es de ?xidos de nitrog?nio, hidrocarbonetos n?o queimados, ?ndice de fuma?a e ?xidos de enxofre

O objetivo do desenvolvimento do projeto foi minimizar uma das principais desvantagens no uso do gás natural veicular, que é a perda de potência, e aumentar sua eficiência volumétrica através da construção de um circuito eletrônico capaz de gerenciar de forma eficiente a injeção do gás. O aumento do rendimento é obtido através do gerenciamento eficiente da mistura ar-combustível utilizando um sistema de malha fechada. O gerenciamento da relação de potência e economia é conseguido com o uso simultâneo de gás natural e o combustível líquido. Nos sistemas de conversão atuais e nos veículos originais a gás natural, a perda de potência é compensada desligando o sistema de gás e utilizando somente o combustível líquido, sendo esta seleção feita de forma manual na maioria dos sistemas de conversão e de forma automática no Fiat Siena tetrafuel, não possibilitando o uso simultâneo do gás com o combustível líquido. A exigência de potência é medida através do ângulo do pedal do acelerador. Quando a exigência de potência é baixa, o sistema opera apenas com gás. No momento em que há solicitação de potência intermediária, o sistema opera com diferentes proporções de etanol e gás. Na situação de solicitação de potência máxima, é utilizado apenas o combustível líquido. Foram feitas comparações entre o sistema convencional e o sistema proposto, através de ensaios dinamométricos, rodoviários e emissão de poluentes. O veículo Volkswagen Gol com seu sistema original utilizando somente etanol possui potência máxima de 64,06 cavalos, (47,77 Kilowatts) e consumo de 12,6 quilômetros por litro de etanol. Com o sistema convencional de gás natural aspirado, o consumo foi de 21 quilômetros por metro cúbico e a potência não ultrapassou 51,82 cavalos (38,64 Kilowatts), com o protótipo desenvolvido a eficiência volumétrica aumentou 25% com consumo de 26,4 quilômetros por metro cúbico. O gerenciamento de potência proporciona potências intermediárias acima de 51,82 cavalos (38,64 Kilowatts), até a potência máxima de 64,06 cavalos (47,77 Kilowatts) em situações que uma maior potência é requerida. O sistema desenvolvido proporciona o benefício da flexibilidade no abastecimento disponível nos sistemas atuais, com a flexibilidade na potência não disponível nos sistemas atuais. / This project intended to minimize one of the main disadvantages of using natural gas vehicles, which was the loss of power, and increase their volumetric efficiency by building an electronic circuit able to efficiently manage the gas injection. The increase in volumetric efficiency is obtained through the efficient management of air-fuel mixture using a closed loop system. The management of the power and economy ratio is achieved with the simultaneous use of natural gas and liquid fuel. In the current conversion systems and original vehicles that use natural gas, the power loss is compensated by turning off the gas system and using only the liquid fuel. This selection is done manually in most conversion systems, and automatically at Fiat Siena Tetrafuel, not allowing the simultaneous use of gas to liquid fuel. The demand for power is measured by the angle of the accelerator pedal. When the power demand is low, the system operates only with natural gas. When intermediate power is required, the system operates with different proportions of ethanol and natural gas. For maximum power, only ethanol is used. Comparisons were made between the conventional and the proposed system through dynamometer tests, road tests and emission analyses. The Volkswagen Gol with original system using only ethanol has a maximum power of 64.06 horses (47.77 Kilowatts) and consumption of 12.6 kilometers per liter of ethanol. With conventional aspirated natural gas system, the consumption was 21 km per cubic meter and the power did not exceed 51.82 horses (38.64 Kilowatts). With the prototype, volumetric efficiency increases by 25%, with consumption of 26.4 kilometers per cubic meter. The power management provides intermediate powers up to 51.82 horses (38.64 Kilowatts) until the maximum power of 64.06 horses (47.77 Kilowatts) in situations where more power is required. The developed system provides the benefit of refueling flexibility found in the original system, with power flexibility not available in original systems.

O objetivo do desenvolvimento do projeto foi minimizar uma das principais desvantagens no uso do gás natural veicular, que é a perda de potência, e aumentar sua eficiência volumétrica através da construção de um circuito eletrônico capaz de gerenciar de forma eficiente a injeção do gás. O aumento do rendimento é obtido através do gerenciamento eficiente da mistura ar-combustível utilizando um sistema de malha fechada. O gerenciamento da relação de potência e economia é conseguido com o uso simultâneo de gás natural e o combustível líquido. Nos sistemas de conversão atuais e nos veículos originais a gás natural, a perda de potência é compensada desligando o sistema de gás e utilizando somente o combustível líquido, sendo esta seleção feita de forma manual na maioria dos sistemas de conversão e de forma automática no Fiat Siena tetrafuel, não possibilitando o uso simultâneo do gás com o combustível líquido. A exigência de potência é medida através do ângulo do pedal do acelerador. Quando a exigência de potência é baixa, o sistema opera apenas com gás. No momento em que há solicitação de potência intermediária, o sistema opera com diferentes proporções de etanol e gás. Na situação de solicitação de potência máxima, é utilizado apenas o combustível líquido. Foram feitas comparações entre o sistema convencional e o sistema proposto, através de ensaios dinamométricos, rodoviários e emissão de poluentes. O veículo Volkswagen Gol com seu sistema original utilizando somente etanol possui potência máxima de 64,06 cavalos, (47,77 Kilowatts) e consumo de 12,6 quilômetros por litro de etanol. Com o sistema convencional de gás natural aspirado, o consumo foi de 21 quilômetros por metro cúbico e a potência não ultrapassou 51,82 cavalos (38,64 Kilowatts), com o protótipo desenvolvido a eficiência volumétrica aumentou 25% com consumo de 26,4 quilômetros por metro cúbico. O gerenciamento de potência proporciona potências intermediárias acima de 51,82 cavalos (38,64 Kilowatts), até a potência máxima de 64,06 cavalos (47,77 Kilowatts) em situações que uma maior potência é requerida. O sistema desenvolvido proporciona o benefício da flexibilidade no abastecimento disponível nos sistemas atuais, com a flexibilidade na potência não disponível nos sistemas atuais. / This project intended to minimize one of the main disadvantages of using natural gas vehicles, which was the loss of power, and increase their volumetric efficiency by building an electronic circuit able to efficiently manage the gas injection. The increase in volumetric efficiency is obtained through the efficient management of air-fuel mixture using a closed loop system. The management of the power and economy ratio is achieved with the simultaneous use of natural gas and liquid fuel. In the current conversion systems and original vehicles that use natural gas, the power loss is compensated by turning off the gas system and using only the liquid fuel. This selection is done manually in most conversion systems, and automatically at Fiat Siena Tetrafuel, not allowing the simultaneous use of gas to liquid fuel. The demand for power is measured by the angle of the accelerator pedal. When the power demand is low, the system operates only with natural gas. When intermediate power is required, the system operates with different proportions of ethanol and natural gas. For maximum power, only ethanol is used. Comparisons were made between the conventional and the proposed system through dynamometer tests, road tests and emission analyses. The Volkswagen Gol with original system using only ethanol has a maximum power of 64.06 horses (47.77 Kilowatts) and consumption of 12.6 kilometers per liter of ethanol. With conventional aspirated natural gas system, the consumption was 21 km per cubic meter and the power did not exceed 51.82 horses (38.64 Kilowatts). With the prototype, volumetric efficiency increases by 25%, with consumption of 26.4 kilometers per cubic meter. The power management provides intermediate powers up to 51.82 horses (38.64 Kilowatts) until the maximum power of 64.06 horses (47.77 Kilowatts) in situations where more power is required. The developed system provides the benefit of refueling flexibility found in the original system, with power flexibility not available in original systems.

Les systèmes de refroidissement des véhicules continuent à se développer et devenir de plus en plus complexes. Ceci introduit des nouveaux problèmes dus aux interactions des composants et les perturbations du système. Avec la montée des prix des carburants; les développeurs et les compagnies cherchent à améliorer la consommation en respectant les normes d’émission. Une partie de l’énergie produite par le moteur est utilisé par les composants du circuit de refroidissement. L’utilisation d’auxiliaires électriques est une manière de réduire ces pertes parasites, mais ce n’est pas la seule solution. Des études récents proposent que un control plus adaptes des composants peux réduire la consommation de carburant. Actuellement, le groupe Volvo en essayant d’améliorer la performance du système de refroidissement des camions a installe des nouveaux composants pour la gestion thermique du moteur. Néanmoins, des problèmes ont été identifie lors d’essais véhicule. Une meilleure compréhension du système et de l’implémentation de composants est nécessaire pour limiter les effets non voulus. Le système de refroidissement d’un poids lourd a été étudié grâce à l’outil Bond Graph. Puis des nouvelles stratégies de control sont introduites : commande prédictive, commande par platitude, commande sans model et commande avec model réduit. Ces méthodes ont été implémentées dans une plateforme de simulation sur Matlab/Simulink. Les gains de consommation obtenue à partir de simulations sont entre 0.5 et 0.9%. Une analyse structurelle de l’architecture actuelle est présentée. D’après les conclusions de cette analyse, des propositions pour la modification de l’architecture du circuit sont évalués. / The increasing complexity of engine cooling systems results in added interactions and disturbances to the performance. Besides, non-propulsion loads (fan, water pump…) draw a significant percentage of the engine’s power thus lowering the vehicle’s fuel efficiency. Recent studies have shown that by controlling components the efficiency can be improved by adjusting fan speed according to cooling needs, coolant flow, and oil flow. Currently, the Volvo group in order to optimize the performance of their truck’s cooling systems had installed new thermal management components. However, problems were found while testing control strategies and a better understanding of the interaction between components is required to prevent this from happening again. In this work, the bond graph approach has been applied for the study of the cooling system of a Heavy duty vehicle and has enabled subsystem interactions to be identified. Based on a simplified model issued from the bond graph, several control strategies have been built. These controllers are based on different control approaches: model predictive control, flatness control, model free control and model free control with reduced order model. These controllers were implemented in a simulation platform in the Matlab/Simulink environment. Results of the implementation of the new advanced control strategies are given. Fuel economy gains ranged between 0.5 and 0.9 %. A structural analysis of the current architecture is also proposed aiming at the optimization of the system. Given the insights from the analysis, an assessment of new concepts for the cooling system architecture is proposed.

This thesis aims at improving our knowledge on swirl combustors. The work presented here is based on Large Eddy Simulations (LES) coupled to an advanced combustion model: the Conditional Moment Closure (CMC). Numerical predictions have been systematically compared and validated with detailed experimental datasets. In order to analyze further the physics underlying the large numerical datasets, Proper Orthogonal Decomposition (POD) has also been used throughout the thesis. Various aspects of the aerodynamics of swirling flames are investigated, such as precession or vortex formation caused by flow oscillations, as well as various combustion aspects such as localized extinctions and flame lift-off. All the above affect flame stabilization in different ways and are explored through focused simulations. The first study investigates isothermal air flows behind an enclosed bluff body, with the incoming flow being pulsated. These flows have strong similarities to flows found in combustors experiencing self-excited oscillations and can therefore be considered as canonical problems. At high enough forcing frequencies, double ring vortices are shed from the air pipe exit. Various harmonics of the pulsating frequency are observed in the spectra and their relation with the vortex shedding is investigated through POD. The second study explores the structure of the Delft III piloted turbulent non-premixed flame. The simple configuration allows to analyze further key combustion aspects of combustors, with further insights provided on the dynamics of localized extinctions and re-ignition, as well as the pollutants emissions. The third study presents a comprehensive analysis of the aerodynamics of swirl flows based on the TECFLAM confined non-premixed S09c configuration. A periodic component inside the air inlet pipe and around the central bluff body is observed, for both the inert and reactive flows. POD shows that these flow oscillations are due to single and double helical vortices, similar to Precessing Vortex Cores (PVC), that develop inside the air inlet pipe and whose axes rotate around the burner. The combustion process is found to affect the swirl flow aerodynamics. Finally, the fourth study investigates the TECFLAM configuration again, but here attention is given to the flame lift-off evident in experiments and reproduced by the LES-CMC formulation. The stabilization process and the pollutants emission of the flame are investigated in detail.