First-principles studies on oxide nanoclusters in bcc Fe

The worldwide growing demand for clean energy leads to necessity for new energy generation methods. Nuclear power generators are an excellent solution for these demands. The feasibility of nuclear power production depends on the performance of structural materials under the harsh conditions in nuclear reactors such as high radiation flux and high temperature. The development of structural materials to withstand such conditions is a big challenge and crucial for advanced nuclear fission and fusion reactors. Several materials are developed, amongst them Oxide Dispersion Strengthened (ODS) steels also called Nanostructured Ferritic Alloys (NFA). NFA consist of Fe-Cr based ferritic/martensitic steels that contain highly dispersed nanometer-size Y-Ti-O nanoclusters, and are manufactured via powder metallurgy. The presence of nanoclusters leads to high temperature stability and radiation resistance. Despite many research activities using advanced analytical techniques such as Transmission Electron Microscopy and Atom Probe Tomography as well as theoretical calculations many properties of the nanoclusters, such as the detailed atomic structure and composition as well as their efficiency for trapping He, vacancies and self-interstitial atoms (SIA), are still not completely understood. In the first part of this thesis work, six different structural models for atomic clusters in bcc Fe which may contain O, Y, Ti, and vacancies (v) are investigated by Density Functional Theory (DFT) calculations. Results for clusters with identical numbers of constituents (O, Y, Ti, and v) are compared. The most important finding consists in the statement that the data on the stability or energetics of the relaxed clusters are comparable although their atomic configurations are often different. This contradicts the prevailing opinion in the related theoretical literature that favors the so-called structure-matching model, which is also investigated in this work. In all studied cases, the absolute value of the total binding energy per cluster constituent becomes lower if Y is partially replaced by Ti, i.e. the driving force for the growth of O-Y clusters is higher than that of O-Y-Ti clusters. This may be correlated with the experimental observation that the presence of Ti leads to a reduction of the size of the oxide clusters in NFA and to a higher dispersion. A further major result is the finding that cage-like (CL) clusters and clusters with an oxygen atom in the center (cage) have a similar total binding energy. If Ti is not present such clusters are slightly more stable than the corresponding CL clusters. The opposite holds for clusters with Ti. It is also shown that adding O atoms to CL cluster leads to structures with O in the center. Vacancies are an important for the stabilization of the cluster due to the very strong binding with O. We infer that the Ov pair may be the origin for cluster nucleation growth. Because of limited computational resources, the dimension of clusters investigated by DFT is still below or close to the limit of the experimental resolution of methods allowing for a simultaneous determination of atomic structure and composition of the clusters. These small clusters may be considered as nuclei for further structural evolution and growth during which a selection of the most favored cluster structures could occur. In the second part of the work four different cluster structures are used to investigate their ability to trap irradiation defects He, v and SIA. These defects are inserted on different positions inside and in the environment of the clusters, the total energy of the corresponding supercell is minimized by DFT, and the binding and incorporation energy of the three kinds of defects is determined. He in the center of a CL cluster is more stable than on interfacial vacant sites (IVS). In CL O-Y clusters, He on an IVS is more stable than in clusters with oxygen in the center, whereas there is no significant difference between the two kinds for clusters with Ti. Up to a distance of 1.5 times the iron lattice constant from the cluster center He is not stable on most of the octahedral and tetrahedral interstitial sites in the Fe matrix. Instead, He is shifted towards positions closer to the cluster. Relaxation occurs to known IVS as well as to previously unknown interfacial interstitial sites (IIS). Moreover, two or three He atoms are placed on sites found to be stable after adding a single He. The corresponding binding and incorporation energies obtained after relaxation are nearly equal to the sum of the values for the interaction with a single He atom. However, placing He dimers or trimers in the environment of a vacancy that belongs to the cluster may also lead to relatively low values of the incorporation energy. Also, He jump barriers between interfacial sites and the center of CL clusters are determined. In the CL O-Y cluster, the barriers are lower than in the CL O-Y-Ti cluster, i.e. trapping and release of He is easier in the former than in the latter. The main reason for the high He trapping efficiency is the low electron density in the empty regions of the oxide-like structure of the clusters. Vacancy and SIA interaction with the clusters is also attractive. The binding energy of a vacancy strongly depends on the site where the vacancy is inserted while in all the studied cases the SIA is annihilated at the cluster-iron interface. Present results clearly demonstrate that the oxide-based nanoclusters are strong traps for irradiation-induced defects, which is in agreement with experimental findings

Experimental and numerical investigation of novel pine oil biofuel in a diesel engine

Ph.DDOCTOR OF PHILOSOPH

Control System of Smart Factory Model

Konstrukce inteligentní továrny obnáší při instalaci mnoho komplikací. Tato práce si klade za cíl vytvořit vylepšený a zjednodušený komunikační a řídicí systém pro inteligentní model chytré továrny. Model chytré továrny je se skládá z těchto komponent: vozík, zásobníky korálků, server a řídicí aplikace. Jednotlivé komponenty spolu komunikují pomocí Wi-Fi. Vozík se pohybuje pomocí sledování černé čáry mezi zásobníky korálků tak, aby automaticky získal ze zásobníků korálky správných barev podle objednávky od uživatele. Komunikační protokol mezi jednotlivými komponenty továrny, který byl vytvořen panem Jansou [10], měl mnoho nevýhod. Řídicí systém s Arduinem pracoval pomaleji, protože řídicí algoritmus, spočívající v testování příliš mnoho podmínek v hlavní smyčce, byl příliš složitý. Komunikace je zefektivněna použitím struktury automatů. Pro každou komponentu byly navrženy grafy automatu, aby se podmínky testovaly ve fázích. Na inteligentní továrně jsou dale vytvářeny a testovány nové řídicí strategie. Po začlenění pracovních diagramů automatů do programu s využitím několika nových strategií se tedy v modelu chytré továrny podařilo vytvořit jednoduchý a poměrně dobrý řídicí systém.The construction of a smart factory involves many complications in installing it. This thesis aims at establishing an enhanced and simplified communication and control system for a smart factory model. A smart factory model is made with components like, vehicle, stacks with beads, server and control application, which, communicates using Wi-Fi communication. A vehicle is navigated in a controlled path of the system, to collect beads from the stacks automatically on getting order from user. The communication relationship between the components was made by Mr. Jansa [10], but had many cons in it. The control system with Arduino worked slower, as those codes were complicated in testing too many conditions in main loop. The communication is possibly made efficient, by drawing working diagrams of automaton for each smart component to split up the conditions checked at stages. New strategies for the communication model are made and tested on the smart factory. Hence, after implicating the work diagrams into the program and using new strategies, simple and comparatively good control system in the smart factory model is exercised

An Investigation of Viscosities, Calorific Values and Densities of Binary Biofuel Blends

Straight vegetable oil (SVO) biofuel is a promising alternative to petroleum diesel fuel primarily due to its comparable physical properties to that of petroleum diesel fuel. However, the relatively higher viscosity of SVO limits its direct application in diesel engine. To resolve this issue, binary biofuel blends was introduced in this study to reduce the viscosity of SVO. In this work, a novel biofuel namely Melaleuca Cajuputi oil (MCO) was used and blended with refined palm oil (RPO). A total of four blends with the mixing ratios of 20%, 40%, 50% and 60% of MCO were prepared. Various key properties of dynamic viscosity, calorific value and density of the blends were measured and benchmarked against the biodiesel standards based on ASTM D6751. It was found that viscosity and density of the blends decreased with the increase of MCO fraction. Meanwhile, the calorific value of the blends increased linearly as the MCO fraction increased. The blend of 40RPO60MCO was found to have comparable key properties of viscosity, calorific value and density to those of petroleum diesel fuel and ASTM D6751 standard

Impact of biodiesel fuel on cold starting of automotive direct injection diesel engines

The use of biodiesel fuels in diesel engines is gaining attention as a promising solution to control CO2 emissions. Great research efforts have been carried out to identify the impact of biodiesel physical and chemical properties on engine systems and processes. Most of these investigations were performed in warm conditions, but the suitability of biodiesel for starting the engine at under-zero ambient temperatures has not widely evaluated. The surface tension and the viscosity of biodiesel fuels are higher compared to those of standard diesel and, in cold conditions, these differences become critical since the injection fuel rate is largely affected and consequently the combustion process can be deteriorated. In order to improve its flow characteristics at cold temperatures and make them more suitable for low temperatures operation, additives are used in biodiesel fuels. In this paper the suitability of different biodiesel fuels, with and without additives, for cold starting of DI (direct injection) diesel engines has been evaluated. The results have shown that the engine start-ability with pure biodiesel fuels can be largely deteriorated. However, using diesel/biodiesel blends the start-ability of the engine can be recovered with the additional benefit of reducing the opacity peak of the exhaust gasesBroatch Jacobi, JA.; Tormos Martínez, BV.; Olmeda González, PC.; Novella Rosa, R. (2014). Impact of biodiesel fuel on cold starting of automotive direct injection diesel engines. Energy. 73:653-660. doi:10.1016/j.energy.2014.06.062S6536607

Biofuels and thermal barrier:a review on compression ignition engine performance, combustion and exhaust gas emission

The performance of an internal combustion engine is affected when renewable biofuels are used instead of fossil fuels in an unmodified engine. Various engine modifications were experimented by the researchers to optimise the biofuels operated engine performance. Thermal barrier coating is one of the techniques used to improve the biofuels operated engine performance and combustion characteristics by reducing the heat loss from the combustion chamber. In this study, engine tests results on performance, combustion and exhaust emission characteristics of the biofuels operated thermal barrier coated engines were collated and reviewed. The results found in the literature were reviewed in three scenarios: (i) uncoated versus coated engine for fossil diesel fuel application, (ii) uncoated versus coated engine for biofuels (and blends) application, and (iii) fossil diesel use on uncoated engine versus biofuel (and blends) use on coated engine. Effects of injection timing, injection pressure and fuel properties on thermal barrier coatings were also discussed. The material type, thickness and properties of the coating materials used by the research community were presented. The effectiveness and durability of the coating layer depends on two key properties: low thermal conductivity and high thermal expansion coefficient. The current study showed that thermal barrier coatings could potentially offset the performance drop due to use of biofuels in the compression ignition engines. Improvements of up to 4.6% in torque, 7.8% in power output, 13.4% in brake specific fuel consumption, 15.4% in brake specific energy consumption and 10.7% in brake thermal efficiency were reported when biofuels or biofuel blends were used in the thermal barrier coated engines as compared to the uncoated engines. In coated engines, peak cylinder pressure and exhaust gas temperature were increased by up to 16.3 bar and 14% respectively as compared to uncoated condition. However, changes in the heat release rates were reported to be between −27% and +13.8% as compared to uncoated standard engine. Reductions of CO, CO2, HC and smoke emissions were reported by up to 3.8%, 11.1%, 90.9% and 63% respectively as compared to uncoated engines. Significant decreases in the PM emissions were also reported due to use of thermal barrier coatings in the combustion chamber. In contrast, at high speed and at high load operation, increase in the CO and CO2 emissions were also reported in coated engines. Coated engines gave higher NOx emissions by about 4–62.9% as compared to uncoated engines. Combined effects of thermal barrier coatings and optimisation of fuel properties and injection parameters produced further performance and emissions advantages compared to only thermal barrier coated engines. Overall, current review study showed that application of thermal barrier coatings in compression ignition engines could be beneficial when biofuels or biofuel blends are used instead of standard fossil diesel. However, more research is needed combining coatings, types of biofuels and other engine modifications to establish a concrete conclusion on the effectiveness of the thermal barrier when biofuels are used in the compression ignition engine. Reduction of NOx emissions is another important R & D area

First-principles studies on oxide nanoclusters in bcc Fe

The worldwide growing demand for clean energy leads to necessity for new energy generation methods. Nuclear power generators are an excellent solution for these demands. The feasibility of nuclear power production depends on the performance of structural materials under the harsh conditions in nuclear reactors such as high radiation flux and high temperature. The development of structural materials to withstand such conditions is a big challenge and crucial for advanced nuclear fission and fusion reactors. Several materials are developed, amongst them Oxide Dispersion Strengthened (ODS) steels also called Nanostructured Ferritic Alloys (NFA). NFA consist of Fe-Cr based ferritic/martensitic steels that contain highly dispersed nanometer-size Y-Ti-O nanoclusters, and are manufactured via powder metallurgy. The presence of nanoclusters leads to high temperature stability and radiation resistance. Despite many research activities using advanced analytical techniques such as Transmission Electron Microscopy and Atom Probe Tomography as well as theoretical calculations many properties of the nanoclusters, such as the detailed atomic structure and composition as well as their efficiency for trapping He, vacancies and self-interstitial atoms (SIA), are still not completely understood. In the first part of this thesis work, six different structural models for atomic clusters in bcc Fe which may contain O, Y, Ti, and vacancies (v) are investigated by Density Functional Theory (DFT) calculations. Results for clusters with identical numbers of constituents (O, Y, Ti, and v) are compared. The most important finding consists in the statement that the data on the stability or energetics of the relaxed clusters are comparable although their atomic configurations are often different. This contradicts the prevailing opinion in the related theoretical literature that favors the so-called structure-matching model, which is also investigated in this work. In all studied cases, the absolute value of the total binding energy per cluster constituent becomes lower if Y is partially replaced by Ti, i.e. the driving force for the growth of O-Y clusters is higher than that of O-Y-Ti clusters. This may be correlated with the experimental observation that the presence of Ti leads to a reduction of the size of the oxide clusters in NFA and to a higher dispersion. A further major result is the finding that cage-like (CL) clusters and clusters with an oxygen atom in the center (cage) have a similar total binding energy. If Ti is not present such clusters are slightly more stable than the corresponding CL clusters. The opposite holds for clusters with Ti. It is also shown that adding O atoms to CL cluster leads to structures with O in the center. Vacancies are an important for the stabilization of the cluster due to the very strong binding with O. We infer that the Ov pair may be the origin for cluster nucleation growth. Because of limited computational resources, the dimension of clusters investigated by DFT is still below or close to the limit of the experimental resolution of methods allowing for a simultaneous determination of atomic structure and composition of the clusters. These small clusters may be considered as nuclei for further structural evolution and growth during which a selection of the most favored cluster structures could occur. In the second part of the work four different cluster structures are used to investigate their ability to trap irradiation defects He, v and SIA. These defects are inserted on different positions inside and in the environment of the clusters, the total energy of the corresponding supercell is minimized by DFT, and the binding and incorporation energy of the three kinds of defects is determined. He in the center of a CL cluster is more stable than on interfacial vacant sites (IVS). In CL O-Y clusters, He on an IVS is more stable than in clusters with oxygen in the center, whereas there is no significant difference between the two kinds for clusters with Ti. Up to a distance of 1.5 times the iron lattice constant from the cluster center He is not stable on most of the octahedral and tetrahedral interstitial sites in the Fe matrix. Instead, He is shifted towards positions closer to the cluster. Relaxation occurs to known IVS as well as to previously unknown interfacial interstitial sites (IIS). Moreover, two or three He atoms are placed on sites found to be stable after adding a single He. The corresponding binding and incorporation energies obtained after relaxation are nearly equal to the sum of the values for the interaction with a single He atom. However, placing He dimers or trimers in the environment of a vacancy that belongs to the cluster may also lead to relatively low values of the incorporation energy. Also, He jump barriers between interfacial sites and the center of CL clusters are determined. In the CL O-Y cluster, the barriers are lower than in the CL O-Y-Ti cluster, i.e. trapping and release of He is easier in the former than in the latter. The main reason for the high He trapping efficiency is the low electron density in the empty regions of the oxide-like structure of the clusters. Vacancy and SIA interaction with the clusters is also attractive. The binding energy of a vacancy strongly depends on the site where the vacancy is inserted while in all the studied cases the SIA is annihilated at the cluster-iron interface. Present results clearly demonstrate that the oxide-based nanoclusters are strong traps for irradiation-induced defects, which is in agreement with experimental findings