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Fossila drivmedel står idag för en överlägsen majoritet av den totala användningen av drivmedel som dagligen förburkas. Alternativ till de fossila drivmedlen krävs för att säkerställa tillgång i framtiden. Försvarsmakten har fått uppdrag från regeringen att utforska möjligheten att övergå till att driva sina fordon på förnyelsebara bränslen.Militära organisationer strävar efter ett enhetsdrivmedel, alltså ett gemensamt drivmedel som driver samtliga fordon och enheter. Största anledningen är den förenklade logistik som kan uppnås om endast ett drivmedel används.Detta arbete har sökt efter ett alternativt drivmedel som skulle kunna användas som enhetsdrivmedel inom Försvarsmakten. Detta för att lösa problematiken med att både byta till ett förnyelsebart drivmedel och ett enhetsdrivmedel i samma fas.Slutsatserna som dragit i detta arbete är att FT-bränslen har potential att användas som enhetsdrivmedel ur ett tekniskt perspektiv. Den höga flampunkt som FT-bränslen har skulle kunna innebära att även sjöfarkoster kan använda samma drivmedel som mark- och luftfarkoster. Dock saknas i dagsläget tillräcklig tillgänglighet och framställningen är i utvecklingsfasen. / Fossil fuels currently account for the vast majority of the total amount of fuel that isconsumed globally every day. Alternatives to fossil fuels are needed to ensuresufficient supply in the future. The Swedish Armed Forces have been tasked by theGovernment to investigate and examine the possibility of operating their vehicles onrenewable fuels.Military organizations strive for the use of a single fuel concept. A single fuel conceptmeans that only one kind of fuel is used in all vehicles and machines. The majorreason for this is the simplified logistics that can be achieved if only one fuel is used.This paper has sought an alternative fuel that can also be used as a single fuel in theSwedish Armed Forces. In order to solve the problem of changing to a renewable andto a single fuel in one single step.The main conclusion drawn in this paper is that Fischer-Tropsch fuels have thepotential to be a single fuel from a technical perspective. The high flashpoint ofFischer-Tropsch fuels could mean that they might also be used in navy vessels.However, there is currently insufficient availability and production is in thedevelopment stages.

Atomization of fuel is an important pre-requisite for efficient combustion in devices such as gas turbines, liquid propellant rocket engines, internal combustion engines and incinerators. The overall objective of the present work is to explore air-assisted atomization strategies for high viscosity fuels and liquids. Air-assisted atomization is a twin-fluid atomization method in which energy of the gas is used to assist the atomization of liquids. Broadly, three categories of air-assisted injection, i.e., effervescent, impinging jet and pre-filming air-blast are studied. Laser-based diagnostics are used to characterize the spray structure in terms of cone angle, penetration and drop size distribution. A backlit direct imaging method is used to study the macroscopic spray characteristics such as spray structure and spray cone angle while the microscopic characteristics are measured using the Particle/droplet imaging analysis (PDIA) technique. Effervescent atomization is a technique in which a small amount of gas is injected into the liquid at high pressure in the form of bubbles. Upon injection, the two-phase mixture expands rapidly and shatters the liquid into droplets and ligaments. Effervescent spray characteristics of viscous fuels such as Jatropha and Pongamia pure plant oils and diesel are studied. Measurements are made at various gas-to-liquid ratios (GLRs) and injection pressures. A Sauter Mean Diameter (SMD) of the order of 20 µm is achieved at an injection pressure of 10 bar and GLR of 0.2 with viscous fuels. An image-based method is proposed and applied to evaluate the unsteadiness in the spray. A map indicating steady/unsteady regime of operation has been generated. An optically accessible injector tip is developed which has enabled visualization of the two-phase flow structure inside the exit orifice of the atomizer. An important contribution of the present work is the correlation of the two-phase flow regime in the orifice with the external spray structure. For viscous fuels, the spray is observed to be steady only in the annular two-phase flow regime. Unexpanded gas bubbles observed in the liquid core even at an injection pressure of 10 bar indicate that the bubbly flow regime may not be beneficial for high viscosity oils. A novel method of external mixing twin-fluid atomization is developed. In this method, two identical liquid jets impinging at an angle are atomized using a gas jet. The effect of liquid viscosity (1 cP to 39 cP) and surface tension (22 mN/m to 72 mN/m) on this mode of atomization is studied by using water-glycerol and water-ethanol mixtures, respectively. An SMD of the order of 40 µm is achieved for a viscosity of 39 cP at a GLR of 0.13 at a liquid pressure of 8 bar and gas pressure of 5 bar. It is observed that the effect of liquid properties is minimal at high GLRs where the liquid jets are broken before the impingement as in the prompt atomization mode. Finally, a pre-filming air-blast technique is explored for transient spray applications. An SMD of 22 µm is obtained with diesel at liquid and gas pressures as low as 10 bar and 8.5 bar, respectively. With this technique, an SMD of 44 µm is achieved for Jatropha oil having a viscosity 10 times higher than that of diesel.

This master thesis covers the development of a high-pressure fuel system for compression ignitedfuels such as diesel and diesel-like fuels that will be deployed into a single cylinder test cell at AVLMTC Södertälje, Sweden. The test cell is used by AVL to conduct research and testing of new fuelsfor their customers and this new fuel system will widen the span of fuels able to be tested by theequipment.This thesis focuses on pumping and pressurizing of the fuel, ensuring that all ingoing materialsare non-corrosive in this environment and compatible with the necessary fuels and lastly a safetyanalysis of the system with respect to operator and process safety. Other aspects of the projectsuch as mass flow measurements and fuel conditioning is covered in a sister thesis Mass flowrate measurement of compression ignition fuels in high-pressure stand-alone pump unit for singlecylinder test cell written by C. Aksoy [1].The goal of this thesis project was to deliver a finished manufactured fuel system and if the timeallowed for it, also validate its performance and finally installing and incorporating it into the singlecylinder test cell. The development process started with the writing of a product specificationoutlining the requirements and request on the product in a specification of requirements matrix andrelate these to product properties of the system using a quality function deployment (QFD) matrix.This document was then used as a base for further advancement in developing concepts to solveeach product property and weighing these concepts against each other using Pugh’s matrices. Thechosen concepts were then further developed, a flow chart for the system was developed as well asfuel lines and other supporting components were analyzed and chosen.In the end the high-pressure fuel pump from Scania’s XPI fuel system were chosen as well asa pressure transducer in the HP1000 series from ESI. Within the time frame of this thesis, theproject did not end up getting finished to the degree planned, but due to time constraints werehalted before starting manufacturing of the system. Some minor component choices remained aswell as documentation such as drawings and finalizing the physical layout of the system remained.All information regarding the remaining work needed to finalize the project and deploying thesystem in the test cell were outlined and with more time, the fuel system should fulfill its purposeof allowing testing and research of compression ignited fuel to be possible in the test cell. / Kontentan för denna mastersavhandling är utvecklingsprocessen för ett högtrycksbränslesystemför kompressionsbränslen såsom diesel och diesellika bränslen som kommer att installeras i enencylindertestcell hos AVL MTC Södertälje, Sverige. Testcellen används av AVL för forskningoch testning av nya bränslen åt deras kunder och detta nya bränslesystem kommer att utöka typernaav bränslen som kan testas med utrustningen till att inkludera kompressionsantända bränslen.Denna avhandling fokuserar på utvecklingen av tillförseln och trycksättnigen av bränslet, säkerställnigenav att ingående material är icke-korrosiva i den avsedda miljön och kompatibla med allanödvändiga bränsletyper och slutligen en säkerhetsanalys av systemet med avseende på operatörsochprocessäkerhet. Andra aspekter såsom massflödesmätning och bränslekonditionering presenterasi systeravhandlingen Flödesmätning och konditionering av högtryckantända bränslen för encylindertestcellskriven av C. Aksoy [1].Målet med denna avhandling var att leverera ett färdigtillverkad bränslesystem och om tiden tillät,även validera systemets prestanda och slutligen integrera och installera systemet i testcellen. Utvecklingsprocesseninleddes med att skriva en produktspecifikation som innehöll en sammanställningav kundens krav och önskemål för produkten och relaterade dessa till produktegenskaper med hjälpav en quality function deployment (QFD) matris. Detta dokument användes vidare som en bas förfortsatt utveckling av produkten i konceptgenereringsprocessen och för att väga de olika konceptenmot varandra med hjälp av Pugh’s matriser. De valda koncepten blev sedan analyserade ytterligare,ett flödesschema för de ingående komponenterna framtaget och övriga sekundära komponenteranalyserade och valda.Till slut valdes högtrycksbränslepumpen från Scanias XPI system och en tryckgivare från HP1000-serien från ESI. Inom tidsramen för avhandlingen färdigställdes aldrig projektet till den grad somhade planerats, men blev istället avbrutet innan tillverkningen av systemet han påbörjas på grund avtidsbegränsningar. Vissa sekundära komponentval, dokumentation såsom ritningar och färdigställningav den fysiska layouten av systemet kvarstod vid avhandlingens slut. All information angåendeallt nödvändigt fortsatt arbete för att färdigställa projektet och integrera systemet i encylindertestcellendokumenterades och med mer tid borde bränslesystemet kunna uppfylla sitt syfte att möjliggöratestning och forskning av kompressionsbränslen i testcellen.

<p>Quenching distance is a fundamental property of hydrocarbon fuel-air mixtures and is a crucial parameter guiding process and equipment design for fire hazard mitigation. Many industrial equipment such as flame arrestors and burners rely on the fundamental principle of flame quenching, i.e., a premixed flame cannot pass through confined spaces below a critical width, given by the Quenching Distance (QD) of the fuel-air mixture. Through the efforts spanning over more than a century, QD is found to depend on various parameters such as temperature, pressure, fuel-air equivalence ratio, and the characteristics of hydrocarbons comprising the fuel. Many investigations on flame quenching behavior have focused on simple fuels such as Hydrogen, Methane, and hydrocarbons upto n-Decane. However, there is a lack of quenching distance data on aviation fuels like Jet-A likely due to the fact that QD property of these fuels is less relevant in practical combustor applications. But in this era of miniaturization, there are several upcoming technologies that will utilize jet fuels or kerosene in confined spaces. For example, a recently proposed Printed Circuit Heat Exchanger (PCHE) is being considered for jet engine performance enhancement by cooling down the compressor discharge air using fuel prior to injection. The cooled air can be used to improve turbine cooling allowing for improvement of the thermal efficiency of the jet engine. However, a major cause of concern during the PCHE operation is the accidental internal fuel leakage from high pressure fuel microchannels into the surrounding air microchannels. Under the severe operating conditions of a jet engine (T >800K, P >10bar), the leaking fuel upon mixing with air pose ignition and sustained combustion risks. This must be evaluated against the competing phenomenon of flame arrestment, since the channel sizes in PCHEs are very small (in the order of a few hundred micrometers). Thus, it becomes imperative to measure the quenching distance of jet fuels to design the microscale passages, predict and mitigate fire hazards to ensure safe operation.</p><p> </p><p>In the present work, the quenching distance of homogeneous, quiescent Jet-A/air mixtures at 473K, 1atm under various equivalence ratios (lean to rich) have been studied. For this purpose, experiments were setup using the ASTM Standard Method that involves using flanged electrodes to measure the parallel-plate QD of quiescent, pre-vaporized fuel-air mixtures under various conditions. Validation tests were carried out with Methanol/air mixtures at 373K, 1atm for different equivalence ratios. For tests with Jet-A/air mixtures, the QD variation with equivalence ratio follows similar trends as that of n-Decane/air. On further analyzing the QD variation with equivalence ratio, we see that the QD minimizes on fuel rich conditions with increasing molecular weight of the fuel which is consistent with the trend shown in literature. The flame propagation behavior shows considerable differences on the lean and the rich sides.</p><p> </p><p>Moreover, the quenching distance of quiescent Methanol/air and Jet-A/air mixtures have been estimated using three different models taken from literature. Model parameters were calculated using Chemkin Pro simulations of the premixed flames at the similar initial conditions as the experiments. On comparing the experiment data with model predictions, we observe that the models agree well with experiment data for Methanol/air mixtures, whereas they fail to capture the QD variation with equivalence ratio for Jet-A/air mixtures. The disagreement may arise because of the high molecular weight of Jet-A that causes the Lewis number to be non-unity unlike Methanol/air mixtures. Therefore, an empirical power law relation has been developed for estimating the QD of hydrocarbon/air mixtures to the incorporate the Lewis number effect. The model agrees well with Jet-A/air QD data from experiments over the entire equivalence ratios. This will help to further our understanding of the complex fuel combustion and flame quenching for better risk mitigation.</p>

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2007. / Biodiesel, a fatty acid alkyl ester, derived from the transesterfication of vegetable oil, is considered a renewable fuel that can be used as a replacement for fossil diesel. The urgency for biofuel production in South Africa is motivated by the vulnerability of crude oil prices, high unemployment, climate change concerns and the need for the growing economy to use its resources in a sustainable manner. The technical feasibility of biodiesel production has been proven and this study investigates its preliminary economic feasibility in South Africa by looking at the market, financial and agricultural feasibility of commercial biodiesel production. / ENGLISH ABSTRACT: Biodiesel, a fatty acid alkyl ester, derived from the transesterfication of vegetable oil, is considered a renewable fuel that can be used as a replacement for fossil diesel. The urgency for biofuel production in South Africa is motivated by the vulnerability of crude oil prices,high unemployment, climate change concerns and the need for the growing economy to use its resources in a sustainable manner. The technical feasibility of biodiesel production has been proven and this study investigates its preliminary economic feasibility in South Africa by looking at the market, financial and agricultural feasibility of commercial biodiesel production. The market feasibility. The potential market size for biodiesel in South Africa is about 1 billion litres if it is to replace 10% of its diesel consumption by 2010. However, governmental legislation and policies are needed to create a predictable and growing market for biodiesel in South Africa. These policies or regulations could be in the form of subsidising feedstock for biodiesel production, subsidising the biodiesel itself, using government purchasing power, mandatory blending legislation, tax incentives or price compensation agreements. The financial feasibility. Calculations to asses the financial feasibility of commercial biodiesel production are based on a 2500 kg/h (22.5 million litres/annum) containerized plant. This size is based on findings of Amigun & von Blottnitz (2005) that the optimum biodiesel plant size in South Africa ranges between 1500 and 3000 kg/h. Two types of plants were considered, namely a seed extraction biodiesel production (SEBP) plant using locally produced oilseeds as feedstock and a crude oil biodiesel production (COBP) plant using imported crude vegetable oil as feedstock. The capital investment for a SEBP plant ranges between R110 and R145 million while a COBP plant would require a capital investment of about R45 to R50 million. These amounts include a working capital of about R35 million due to money that is fixed in a 3 month stock supply.Feedstock and raw material contribute to about 80% of the manufacturing cost while transport costs are the second biggest contributor. These results point to the fact that the plant location is very important in order to minimize production costs. Thus, commercial biodiesel production should not be centralized, but should rather happen through greater number of relatively small plants located in oilseed producing regions. (South Africa would require about 46 plants each producing 2500 kg/h to produce 10% of its diesel by 2010). The sensitivity analyses showed that the manufacturing costs of a SEBP plant are very sensitive to changes in oilseed and oilcake prices while the manufacturing costs of a COBP plant are very sensitive to a change in crude vegetable oil price. The fluctuating nature of the agricultural commodity prices makes biodiesel manufacturing costs predictable. Soybean biodiesel costs are the most sensitive to price changes while sunflower biodiesel costs are the least affected. An increase in glycerol price would decrease the manufacturing costs of biodiesel by about 12 cents/litre for every R1000/ton increase in price. Glycerol prices are currently too low to consider in the calculations due to a global oversupply as a result of biodiesel production. The break even price of biodiesel is calculated by adding R1.01/litre fuel tax to the manufacturing cost, which means that biodiesel produced from oilseeds (except canola) will not be able to compete with the current price of fossil diesel (30 August 2006) without subsidies or legislation. The agricultural feasibility. Producing 10% of South Africa’s diesel using oilseeds would require a major production increase.Biodiesel production will also increase the local oilcake supply which means South Africa will change from being a net-importer of oilcake (730 thousand tons/year) to a net-exporter of oilcake (1.7 million tons/year). Land availability for such a production increase is not a problem which means that the agricultural resources and potential market are available to produce and absorb 10% of the countries diesel in the form of biodiesel. However, at the moment the commercial production of biodiesel does not seem financially feasible without any government imposed legislation or subsidies. / AFRIKAANSE OPSOMMING: Biodiesel, ‘n hernubare brandstof wat uit groente olie vervaardig word, is ‘n moontlike plaasvervanger vir petroleum diesel. Biodiesel vervaardiging in Suid Afrika word aangespoor deur hoë kru olie pryse, hoë werkloosheid syfers, toenemende bewustheid van klimaatveranderings en druk op ‘n groeiende ekonomie om sy bronne volhoubaar te gebruik. Die vervaardiging van biodiesel is relatief maklik en hierdie studie is ‘n voorlopige ondersoek in die ekonomiese lewensvatbaarheid van komersiële biodiesel produksie in Suid Afrika deur te kyk na die mark, finansiële en landbou lewensvatbaarheid daarvan. Die mark lewensvatbaarheid. Die potensiële grote vir ‘n biodiesel mark in Suid Afrika is omtrent 1 miljard liter indien dit 10% van sy petroleum diesel teen 2010 wil vervang, maar wetgewing sal nodig wees om ‘n voorspelbare en groeiende mark te skep. Hierdie wetgewing kan in die vorm van subsidies vir boere of biodiesel produsente wees, gebruik maak van regerings koopkrag, verpligtende inmeng maatreëls, belasting voordele of prys vergoeding ooreenkomste. Die finansiële lewensvatbaarheid. Berekeninge om die finansiële lewensvatbaarheid te bepaal is op ‘n 2500 kg/uur (22.5 miljard liter/jaar) gedoen. Hierdie aanleg grote is gebaseer op inligting verkry deur Amigun & von Blottnitz (2005) wat sê dat die optimale grote biodiesel aanleg in Suid Afrika tussen 1500 en 3000 kg/uur is. Daar is na twee tipe aanlegte gekyk, naamlik na ‘n saad ekstraksie biodiesel vervaardigings (SEBP) aanleg wat plaaslike oliesade as voer materiaal gebruik en ‘n kru olie biodiesel vervaardigings (COBP) aanleg wat ingevoerde groente olie as voer materiaal gebruik. 'n SEBP aanleg het ‘n kapitale belegging van tussen R100 en R145 miljoen nodig terwyl ‘n COBP aanleg slegs tussen R45 en R50 miljoen nodig het. Hierdie bydrae sluit werkende kapitaal van omtrent R35 miljoen in wat vas is in 3 maande se voer materiaal kostes. Die onderstaande tabel wys die vervaardigings kostes vir albei tipe aanlegte en verskillende voer materiale. Omtrent 80% van die kostes is voer materiaal terwyl vervoerkostes die tweede hoogste bydraer is. Hierdie resultaat wys na die feit dat die aanleg ligging ‘n baie belangrike rol speel om vervaardigins kostes te minimeer. Dus word die stelling gemaak dat kommersiële biodiesel vervaardiging nie in ‘n paar sentrale aanlegte moet plaasvind nie, maar eerder in ‘n klomp verspreide relatief kleiner aanlegte moet plaasvind. Hierdie kleiner aanlegte sal in die oliesaad produserende streke versprei moet wees. (Suid Afrika sal omtrent 46 aanlegte nodig hê wat elk 2500 kg/uur produseer om 10% van sy diesel teen 2010 te kan vervaardig). Die sensitiwiteits analise het gewys dat die kostes van ‘n SEBP aanleg baie sensitief vir veranderings in oliesaad en oliekoek pryse is. Die kostes van ‘n COBP aanleg is baie sensitief vir veranderinge in groente olie pryse. Wisselvallige landbou pryse maak die kostes van biodiesel baie wisselvallig en onvoorspelbaar. Sojaboon biodiesel kostes is die sensitiefste vir prys veranderings terwyl sonneblom saad die minste geaffekteer word deur sulke prys veranderings. Vir elke R1000/ton wat die glyserol prys styg sal die vervaardigings kostes van biodiesel met 12 sent/liter daal. Die glyserol prys is op die oomblik te laag om in ag te neem weens ‘n oormaat glyserol in die wêreld mark as gevolg van biodiesel produksie. Die gelykbreek prys van biodiesel word uitgewerk deur R1.01/liter brandstof belasting by die vervaardigings kostes by te tel. Op die oomblik (30 Augustus 2006) kan biodiesel van oliesade (behalwe kanola) nie met die petroleum diesel prys meeding nie sonder enige subsidies of wetgewing. Die landbou lewensvatbaarheid. Die landbou implikasies om 10% van die land se diesel uit oliesade te vervaardig word in die onderstaande tabel uiteengesit. Hierdie resultate is gebaseer op die feit dat al drie oliesade gebruik word vir biodiesel vervaardiging en dat die oppervlak verhouding van die drie oliesade konstant bly soos die produksie vermeerder. Biodiesel vervaardiging sal ook die plaaslike oliekoek produksie vermeerder sodat Suid Afrika sal verander van ‘n netto-invoerder (730 duisend ton/jaar) tot ‘n netto-uitvoerder (1.7 miljoen ton/jaar) van oliekoek. Land beskikbaarheid vir so ‘n vermeerderde produksie is nie ‘n probleem nie wat beteken dat Suid Afrika wel die landbou bronne en potensiële mark het om 10% van sy diesel te vervaardig en te absorbeer in die vorm van biodiesel. Uit `n finansiële oogpunt lyk dit egter asof die kommersiële vervaardiging van biodiesel in Suid Afrika nie lewensvatbaar sal wees, sonder enige wetgewings of subsidies, nie. / Centre for Renewable and Sustainable Energy Studies

Demand for liquid fuels (i.e., petroleum products) has burdened the U.S. with major challenges, including national security and economic concerns stemming from rising petroleum imports; impacts of global climate change from rising emissions of CO2; and continued public health concerns from criteria and hazardous (i.e., toxic) air pollutants. Over the last decade or so, biofuels have been touted as a supply-side solution to several of these problems. Biofuels can be produced from domestic biomass feedstocks (e.g., corn, soybeans), they have the potential to reduce GHG emissions when compared to petroleum products on a lifecycle basis, and some biofuels have been shown to reduce criteria air pollutants. Today, there are numerous policy incentives—existing and proposed—aimed at supporting the biofuels industry in the U.S. However, the Renewable Fuel Standard (RFS) Program stands as perhaps the most significant mandate imposed to date to promote the use of biofuels. Overall, the RFS stands as the key driver in a transition to biofuels in the near term. By mandating annual consumption of biofuels, increasing to 36 bgy by 2022, the program has the potential to significantly alter the state of the U.S. liquid fuels sector. Fuel transitions in the transportation sector are the focus of this thesis. More specifically, the increasing consumption of biofuels in the transportation sector, as mandated by the RFS, is examined. With a well-developed, efficient, and expensive, petroleum-based infrastructure in place, many barriers must be overcome for biofuels to play a significant role in the transportation sector. Identifying and understanding the barriers to a biofuels transition is the objective of this thesis. Although fuel transitions may seem daunting and unfamiliar, the U.S. transportation sector has undergone numerous transitions in the past. Chapter 2 reviews major fuel transitions that have occurred in the U.S. liquid fuels sector over the last half century, including the phasing out of lead additives in gasoline, the transition from MTBE to ethanol as the predominant oxygenate additive in gasoline, and the recent introduction of ULSD. These historical transitions represent the uncertainty and diversity of fuel transition pathways, and illustrate the range of impacts that can occur across the fuel supply chain infrastructure. Many pertinent lessons can be derived from these historical transitions and used to identify and assess barriers facing the adoption of alternative fuels (i.e., biofuels) and to understand how such a transition might unfold. Computer models can also help to explore the implications of fuel transitions. In order to better understand the barriers associated with fuel transitions, and to identify options for overcoming these barriers, many recent research efforts have used sophisticated modeling techniques to analyze energy transitions. Chapter 3 reviews a number of these recent modeling efforts with a focus on understanding how these methodologies have been applied, or may be adapted, to analyzing a transition to biofuels. Four general categories of models are reviewed: system dynamics, complex adaptive systems, infrastructure optimization, and economic models. In chapter 4, scenarios created from a high-level model of the liquid fuels sector (the Liquid Fuels Transition model) are presented to explore potential pathways and barriers to a biofuels transition. The scenarios illustrate different pathways to meeting the requirements of the RFS mandate, and differ based on the overall demand of liquid fuels, how the biofuels mandate is met (i.e., the mix of biofuels), and the status of the ethanol blend limit in the motor gasoline sector. The scenarios are used to evaluate the infrastructure implications associated with a biofuels transition, and illustrate the uncertainty that exists in assessing such a transition. / text

An experimental study of the effects of turbulent flow regime on the flame structure is conducted by using perforated-plate-stabilized hydrogen-piloted lean premixed methane/air turbulent flames. The underlying non-reacting turbulent flow field was investigated using two-dimensional three-components particle imaging velocimetry (2D3C-PIV) with and without three perforated plates. The non-reacting flow data allowed a separation of the turbulent flow regime into axial velocity dominated and vortex dominated flows. A plate with 62\% blockage ratio was used to represent the stream-dominant flow regime and another with 86\% blockage ratio was used to represent the vortex-dominant flow regime. OH laser-induced fluorescence was used to study the effects of the turbulent flow regime on the mean progress variable, flame brush thickness, flame surface density, and global consumption speed. In comparison with the stream-dominant flow, the vortex-dominant flow makes a wider and shorter flame. Also, the vortex-dominant flow has a thicker horizontal flame brush thickness and a thinner longitudinal flame brush thickness. Especially, the horizontal flame brush thickness for the vortex-dominant flow does not follow the turbulence diffusion theory. Then, the vortex-dominant flow shows a relatively constant flame surface density along the stream-wise direction, while the stream-dominant flow shows a decreasing flame surface density. Lastly, the vortex-dominant turbulent flow improves the consumption speed in comparison to the stream-dominant turbulent flow regime with the same velocity fluctuation level.

A incorporação do gadolínio diretamente no combustível de reatores nucleares para geração de eletricidade é importante para compensação da reatividade e para o ajuste da distribuição da densidade de potência, permitindo ciclos de queima mais longos, com intervalo de recarga de 18 meses, otimizando-se a utilização do combustível. A incorporação do Gd2O3 sob a forma de pó homogeneizado a seco diretamente com o pó de UO2 é o método comercialmente mais atraente devido à sua simplicidade . Contudo, este método de incorporação conduz a dificuldades na obtenção de corpos sinterizados com a densidade niínima especificada, devido a um bloqueio no processo de sinterização. Pouca informação existe na literatura específica sobre o possível mecanismo deste bloqueio, restrita principalmente à hipótese da formação de uma fase (U,Gd)O2 rica em gadolínio com baixa difusividade. Este trabalho tem como objetivo a investigação do mecanismo de bloqueio da sinterização neste sistema, contribuindo para o esclarecimento da causa deste bloqueio e na elaboração de possíveis soluções tecnológicas. Foi comprovado experimentalmente que o mecanismo responsável pelo bloqueio é baseado na formação de poros estáveis devido ao efeito Kirkendall, originados por ocasião da formação da solução sólida durante a etapa intermediária da sinterização, sendo difícil a sua eliminação posterior, nas etapas finais do processo de sinterização. Com base no conhecimento deste mecanismo, possíveis propostas são apresentadas na direção da solução tecnológica do problema de densificação característico do sistema UO2-Gd203. / The incorporation of gadolinium directly into nuclear power reactor fuel is important from the point of reactivity compensation and adjustment of power distribution enabling thus longer fliel cycles and optimized fuel utilization. The incorporation of Gd2O3 powder directly into the UO2 powder by dry mechanical blending is the most attractive process because of its simplicity. Nevertheless, processing by this method leads to difficulties while obtaining sintered pellets with the minimum required density. This is due to blockages during the sintering process. There is little information in published literature about the possible mechanism for this blockage and this is restricted to the hypothesis based on formation of a low difiiisivity Gd rich phase (U,Gd)O2. The objective of this investigation has been to study the blockage mechanism in this system during the sintering process, contributing thus, to clarify the cause for the blockage and to propose feasible technological solutions. Experimentally it has been shown that the blocking mechanism is based on pore formation because of the Kirkendall effect. Formation of a solid solution during the intermediate stage of sintering leads to formation of large pores, which are difficult to remove in the final stage of sintering. Based on this mechanism, technical solutions have been proposed to resolve densification problems in the UO2-Gd2O3 system.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O combustível nuclear metálico tipo placa em dispersão é um combustível versátil que pode ser projetado para ser utilizado tanto em reatores de testes quanto em reatores de potência. A elevada densidade das ligas metálicas de urânio com elementos de transição, como, Zr, Nb, Mo, etc, propicia o emprego deste combustível utilizando urânio com baixo teor de enriquecimento, o que o torna mais seguro no sentido de conter a proliferação nuclear. Além disso, as excelentes propriedades mecânicas e a grande resistência à corrosão das ligas metálicas de U-Zr-Nb, tornam a escolha desta liga na forma de combustível tipo placa em um desenvolvimento de grande atratividade devido às possibilidades de se alcançar um combustível de alto desempenho. Neste trabalho foram investigadas as transformações de fases das ligas U-2,5Zr-7,5Nb e U- 3Zr-9Nb em diferentes condições de tratamentos térmicos, bem como foi desenvolvido o processo de cominuição destas ligas pelo processo de hidretação-desidretação. As transformações de fases foram obtidas realizando-se a homogeneização das ligas de U- 2,5Zr-7,5Nb e U-3Zr-9Nb em elevadas temperaturas (1000 oC, durante 1 e 16 h), seguido de têmpera em água, bem como de envelhecimento a 600 oC em diferentes tempos (0,5, 3 e 24h), também, seguido de têmpera em água. As fases obtidas foram caracterizadas por intermédio das técnicas de difração de raios X, microdureza, microscopia ótica, microscopia eletrônica e EDS. Nestas condições experimentais, foram obtidas duas microestruturas distintas. Uma microestrutura monofásica constituída da fase gama (&#61543;) martensítica de cristalinidade cúbica de corpo centrado. A outra com estrutura do tipo lamelar perlítica, constituída da mistura das fases alfa e gama (&#945; e &#61543;). A fase &#945; tem cristalinidade ortorrômbica. Diferentemente da fase gama martensítica de alta estabilidade mecânica e elevada resistência à corrosão, a estrutura do tipo perlita não possui boas propriedades mecânicas e é pouco resistente à corrosão. Os resultados da microdureza revelaram uma boa correlação entre dureza e a estrutura cristalina da amostra. Observou-se que as ligas tratadas isotermicamente até 3 horas, as quais são constituídas predominantemente pela fase &#61543; cúbica, apresentaram baixos valores de dureza. Por outro lado, essas ligas tratadas isotermicamente por 24 horas transformaram-se majoritariamente em fase &#945; com estrutura ortorrômbica e elevados valores de dureza. Isso mostra que a estrutura do tipo perlita é mais dura do que a fase &#61543;. Os pós das ligas dúcteis de U-2,5Zr-7,5Nb e U-3Zr-9Nb foram obtidos pela cominuição das mesmas com uso do hidrogênio. A cominuição realizada pelo processo de hidretaçãodesidretação foi feita na temperatura de cerca de 200 oC, em diferentes tempos variando entre 20 minutos a 4 horas. Os pós assim obtidos foram caracterizados por intermédio de microscopia ótica, difração de raios X e determinação da distribuição do tamanho de partículas por meio do equipamento a laser CILAS. O processamento utilizado permitiu a obtenção de pós com duas classes de tamanhos dependendo do tipo de tratamento. Os pós de ambas as ligas envelhecidos a 600 oC durante 0,5 e 3 horas apresentaram pós com granulometria de 180 a 200 &#61549;m e, por outro lado, os pós de ambas as ligas envelhecidas a 600 oC durante 24 horas apresentaram pós com granulometria superior a 220 &#61549;m. Os pós de ambas as ligas homogeneizados a 1000 oC e envelhecidos até 3 horas a 600 oC com granulometria na faixa de 180 a 200 &#956;m são adequados para serem utilizados na dispersão do cerne para a obtenção de combustível tipo placa para uso em reatores de teste e de potência de pequeno e médio portes. / Plate-type dispersion metallic nuclear fuel is a versatile fuel that can be designed to be used in both test and power reactors. The high density of uranium alloys with transition elements, such as Zr, Nb, Mo, etc, allows the use of this fuel with low uranium enrichment, which makes it safer in order to prevent nuclear proliferation. Furthermore, the excellent mechanical properties and high corrosion resistance of U-Zr-Nb metallic alloys makes the choice of this alloy as plate type fuel in a development of great attractiveness due to the possibilities of achieving a high performance fuel. In this study, it was investigated the phase transformations of the U-2.5Zr-7.5Nb and U-3Zr- 9Nb in distinct heat treatments, as well as it was developed the process of comminution of these alloys by the hydriding-dehydriging process. The phase transitions were obtained by performing the homogenization of the U-2.5Zr-7.5Nb and U-3Zr-9Nb alloys at high temperatures (1000 oC for 1 and 16 h) followed by water quenching, as well as by aging at 600 oC at different times (0.5, 3 and 24 h). The obtained phase transitions were characterized through the X-ray diffraction, micro hardness, optical microscopy, electron microscopy and EDS techniques. Under these experimental conditions, it was obtained two different microstructures. A single phase microstructure consisting of the martensitic &#61543; phase of body centered cubic crystallinity. The other one with the lamellar pearlite type structure, consisting on a mixture of &#945; and &#61543; phases. The &#945; phase has orthorhombic structure. Unlike of the high stability and good corrosion resistance martensitic structure, the two phases pearlite type structure has poor mechanical properties and low corrosion resistance. The results of microhardness have revealed a good correlation between hardness and crystal structure of the sample. It was observed that alloys isothermally treated up to three hours, which are predominantly the &#61543; cubic phase showed lower hardness values. Moreover, these alloys isothermally treated for 24 hours were processed mostly in &#945;-phase with orthorhombic structure and high hardness values. This shows that the pearlite type structure is harder than the &#61543; phase. The powders from ductile U-2.5Zr-7.5Nb and U-3Zr-9Nb alloys were obtained by hydrogen comminution. The comminution process carried out by hydriding-dehydriding was performed at a temperature of about 200 oC, at different times ranging from 20 minutes to 4 hours according to the composition and phase of each alloy. The obtained powders were characterized by optical and electronic microscopy, X-ray diffraction and determination of particle size distribution by means of laser CILAS equipment. The utilized process allowed the production of powders with two particle size classes depending on the type of treatment. The powders of both alloys aged at 600 oC for 0.5 and 3 hours presented powders with particle sizes of about 180-200 &#956;m, on the other hand, powders of both alloys aged at 600 oC for 24 hours presented powders with particle sizes greater than about 220 &#956;m. The powders of both alloys homogenized at 1000 oC and aged up to 3 hours at 600 oC with particle size in the range from 180 to 200 &#956;m are suitable for use in the dispersion of the fuel core to be utilized in test and power of small and medium sizes reactors.