Thermal mismatch between different components of a system could be sources of problems like residual stress induced cracking, thermal fatigue or even optical misalignment in certain high technology applications. Use of materials with tailored thermal expansion coefficient is a counter-measure to overcome such problems. With its negative thermal expansion coefficient zirconium tungstate (ZrW2O8) is a candidate component to be used in synthesis of composites with controlled thermal expansion coefficient (CTE). ZrW2O8 is typically produced by solid-state reaction between zirconium oxide and tungsten oxide at 1200oC. However, it has been demonstrated that ZrW2O8 can also be synthesized using wet chemical techniques, which provide a superior chemical homogeneity that often extents down to the atomic scale, and the convenient means of controlling nucleation and growth of the primary crystallites. With the commonly adopted wet chemical approaches, it is possible to crystallize particles with sizes in the submicrometer range at temperatures as low as 600 oC or even lower. In these studies, precursors are aged either below 100 oC (7 days &ndash / 3 weeks), or at 160-180 oC under hydrothermal conditions (1&ndash / 2 days). Besides the obvious disadvantage in the ageing steps, use of tungsten sources with high cost in all approaches, constitutes the other disadvantage. Production of composites with tunable controlled thermal expansion (CTE) has been achieved by blending negatively and positively expanding materials in different proportions. In majority of these studies composites have been produced by conventional sintering methods. Spark Plasma Sintering (SPS) is a recent technique / in which sintering can be achieved at relatively low temperatures in short durations. There is only one study made by Kanamori and coworkers on the use of SPS in sintering of a composite, in which ZrW2O8 is one of the constituents [1]. This study aims the synthesis of ZrW2O8 particles and composites that possess tunable or zero CTE. A novel precursor recipe for ZrW2O8 synthesis was developed. In preparation of the precursor a total of 2 days of ageing and a temperature less than 100 oC was used. It was developed using a cost-effective tungsten source, namely tungstic acid and its final pH was lower than 1. The particles obtained from &lsquo / unwashed&rsquo / procedure had sizes in micrometer range, while those obtained from &lsquo / washed&rsquo / case had sizes in the range of 400-600 nm. These precursors could readily be crystallized at 600 oC, which in turn provided the desired particle sizes for composite applications. Experimental details on the precursor development are hereby presented with a discussion on the effects of solution parameters (i.e. solubility of tungstic acid, adjustment of the stoichiometry, ageing time) on the phase purity of the fired product. Zirconium oxide (ZrO2) has positive vi thermal expansion, therefore ZrW2O8/ZrO2 was selected as the composite system, and for their synthesis both conventional and spark plasma sintering methods were experimented. Composition ranges that provide composites with almost zero CTE&rsquo / s were determined. The composite having a composition of containing 35% ZrW2O8, 65% ZrO2, and 35 w/o Al2O3 and sintered at 1200 oC for 24 hours had an expansion coefficient of 0.20 x 10-6/K for conventional method, while the one having a composition of 55% ZrW2O8, 45% ZrO2 and sintered at 1000 oC for 5 minutes had an expansion coefficient of 0.94 x 10-6/K for spark plasma sintering method. For characterization of the products X-ray diffraction (XRD), scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), and thermal and dilatometer analyses (DTA/TGA/DMA) were used.

<p>Ionic conductivity of metal oxides is critical for the function of a broad range of different components, such as electrolytes in solid oxide fuel cells and alloys designed for high temperature applications. In both cases the ionic conductivity can be studied by in situ impedance spectroscopy, which is also able to reveal information on the dielectric properties of the metal oxides, and in some cases the influence of their microstructure. The focus of this thesis is on impedance spectroscopy measurements of α-alumina in the temperature range 400-1000 °C. This metal oxide has found extensive use as the protective scale on heat resistant alloys. Some unpublished work on oxygen ion conductivity of yttria-stabilized zirconia is also included.</p><p>The low electrical conductivity of α-alumina can be a source for errors and misinterpretations during impedance spectroscopy measurements. A major disturbance originates from leakage currents that appear in the experimental setup. These leakage currents are due to conduction through the gas phase around the sample, conduction on the sample surface, or poor insulation in the sample holder. It was shown that below 700 °C, conduction on the sample surface could severely distort the measurement. The magnitude of the distortions appeared to be sensitive to the type of electrodes used. The use of a so-called guard electrode was shown to effectively block the surface conduction in the measurements.</p><p>Conductivity of metal oxides is known to be dependent on their microstructure. Generally it is believed that ionic conductivity is favoured along grain boundaries and dislocations. The influence of microstructure on conductivity was studied for α-alumina in the temperature range 400-1000 °C. The conductivity of a series of highly pure and dense samples with narrow grain size distributions was measured by impedance spectroscopy. It appeared that the activation energy for conduction increased with decreasing grain size.</p><p>Results based purely on impendence spectroscopy have some inherently weaknesses. For instance no information on the nature of the charge carrier can be found. Therefore the charge transport in single crystalline α-alumina was simulated by the molecular dynamics method. The results from the simulation were then compared to results from impedance measurements on single crystalline α-alumina. From the simulation it turned out that diffusion of aluminium ions had lower activation energy than diffusion of oxygen. The activation energy of oxygen was close to the measured activation energy, and the mobility of oxygen was higher than for aluminium. Therefore the dominating charge carrier was suggested to be oxygen ions.</p>

<p>This licentiate thesis concerns one dimensional flow simulation of turbocharged spark ignited engines. The objective has been to contribute to the improvement of turbocharged SI engines’ performance as well as 1 D simulation capabilities.</p><p>Turbocharged engines suffer from poor gas exchange due to the high exhaust pressure created by the turbine. This results in power loss as well as high levels of residual gas, which makes the engine more prone to knock.</p><p>This thesis presents an alternative gas exchange concept, with the aim of removing the high exhaust pressure during the critical periods. This is done by splitting the two exhaust ports into two separate exhaust manifolds.</p><p>The alternative gas exchange study was performed by measurements as well as 1-D simulations. The link between measurements and simulations is very strong, and will be discussed in this thesis.</p><p>As mentioned, turbocharged engines are prone to knock. Hence, finding a method to model knock in 1-D engine simulations would improve the simulation capabilities. In this thesis a 0-D knock model, coupled to the 1-D engine model, is presented</p>

For every operating condition of an internal combustion engine there exists an optimal spark timing, called maximum brake torque (MBT), which maximises the output torque and the efficiency of the engine. Traditionally MBT timing is implemented as an open-loop control where the ignition timing is found by using a combination of static lookup tables and sensor information. With a direct closed-loop control from the combustion process the performance of internal combustion engines could be improved. The thesis investigates if it is possible to estimate the MBT timing from the ionization current for every operating condition of a spark ignited engine where the operating conditions are defined by the engine parameters lambda, internal exhaust gas recirculation, engine load, engine speed and spark advance. First an investigation of how much loss of torque an error from the MBT position corresponds to is made. Then the influence of the engine parameters on the shape of the ionization current was studied. Last different peak pressure position (PPP) estimating algorithms are presented and a new technique is developed where an engine operating point dependant part of the ionization current is used depending on the current operating condition of the engine. Two of the presented PPP estimating algorithms are then complemented with this technique and the results look promising.

A gasoline direct injection engine was set-up to operate with a dynamometer in a test cell. Test cycle and emissions measurement procedures were developed for evaluating the regulated and non-regulated gaseous emissions. Equipment and techniques for particulate matter measurements were adapted for use with the gasoline direct injection engine. The particulate matter emissions produced by the engine were compared between two different fuels; gasoline and E10 (10% ethanol and 90% gasoline). The gaseous emissions generated by the engine when it was run on gasoline and E30 (30% ethanol and 70% gasoline) were also compared. Particle number decreased with E10 for hot start conditions, while the opposite was observed for cold start conditions. Particulate matter emissions were found to track with acetylene and ethylene emissions.

A gasoline direct injection engine was set-up to operate with a dynamometer in a test cell. Test cycle and emissions measurement procedures were developed for evaluating the regulated and non-regulated gaseous emissions. Equipment and techniques for particulate matter measurements were adapted for use with the gasoline direct injection engine. The particulate matter emissions produced by the engine were compared between two different fuels; gasoline and E10 (10% ethanol and 90% gasoline). The gaseous emissions generated by the engine when it was run on gasoline and E30 (30% ethanol and 70% gasoline) were also compared. Particle number decreased with E10 for hot start conditions, while the opposite was observed for cold start conditions. Particulate matter emissions were found to track with acetylene and ethylene emissions.

No description available.

the 18th World Congress The International Federation of Automatic Control, Milano (Italy), August 28 - September 2, 2011

找尋新穎的熱電材料是現在許多物理、化學以及材料學家的熱門研究，熱電材料的益處在於可將生活中所產生的廢熱轉化成電能再度利用，可應用在於熱機或是冷凍機之上。 首先，在第一個研究之中，透過布理奇曼法在1050 ℃之下維持10個小時用以製作Cu0.01Bi2Te2.7Se0.3塊材，以及透過水熱法製造出Cu0.01Bi2Te2.7Se0.3奈米粒子，並且將兩種不同尺寸的粒子做不同比例的混合：奈米粒子(粒徑：20~100奈米)重量百分比0、10、20、30和100；接著探討火花電漿燒結法及奈米聚合物對熱電性質之影響。在實驗中發現材料中混入百分之三十的奈米粒子可提升熱電優質係數約一倍，由0.35提升至0.74。若是可以將起初塊材的熱電優質係數提升至較良好的0.7以上，再透過奈米聚合和燒結，其熱電係數在400 K左右是可以超過1的。由這個研究顯示出：火花電漿燒結以及奈米聚合是可以有效的提升熱電優質係數，其主要原因來自於成功的降低熱傳導係數並同時維持住原本所擁有的電阻率以及席貝克係數的提升，而熱傳導降低因於樣品中的奈米結構所造成的粒子邊界增加、晶格的不匹配導致抑制聲子的傳熱所形成的結果。 第二個研究為一樣是透過布理奇曼法在750 ℃之下維持12個小時用以製作BixSb2-xTe3塊材，其中x分別為0.4、0.45、0.5以及0.6，本實驗主要為探討Bi的量對於BiSbTe所造成的影響。由結果中顯示x高於0.5和低於0.5所呈現的熱傳性質的趨勢有些許不同。在x為0.45的塊材中，得到本實驗中在室溫之下，最佳的熱電優質係數1.5，獲得此結果的主要原因來自於相對較低的電阻率，並可觀察到x為0.45的載子濃度高於0.4、0.5和0.6的結果，其將可以佐證x=0.45塊材的低電組率所造成的優質係數提升。 / Physicists, chemists and material scientists at many major universities and research institutions throughout the world are attempting to create novel materials with high thermoelectric (TE) efficiency. It will be beneficial to harvest waste heat into electrical energy. Specialty heating and cooling are other major applications for this class of new TE materials. In the first study, bulk and nanoparticles of Cu0.01Bi2Te2.7Se0.3 were prepared separately. The Cu0.01Bi2Te2.7Se0.3 bulk was fabricated by Bridgeman method at 1050 ℃ for 10 hrs and the nanoparticles were made through hydrothermal method. Two kinds of powders were mixed with the ratios of NPs 0, 10, 20, 30 and 100 wt% and sintered by the SPS technique to form the composite specimens. The ZT value can be enhanced over 100% from 0.35 to 0.74 for specimen with 30 wt% nanoparticles. The consequence indicates that the SPS process and mixing nanocomposite can effectively enhance ZT value. The enhancements were caused mainly by the presence of nanostructured regions existing within the samples which lowered the thermal conductivity. The phenomenon is due to the presence of significant number of grain boundaries, shorten phonon mean free path and lattice mismatch. For another investigation, the BixSb2-xTe3 ingots with x=0.4, 0.45, 0.5 and 0.6. were fabricated by Bridgeman method at 750 ℃ for 12 hrs. We studied the effects of amount of Bi in BixSb2-xTe3 and the SPS process on the ZT enhancement. The experiment showed that for x >0.5, the thermal property changed from a curve to a relatively linear line at the end. The best ZT is 1.5 ingot at 300 K for x=0.45 specimen. The significant ZT improvement arises from the much-reduced electric resistivity. The lowest resistivity for x=0.45 specimen is mainly due to the highest carrier concentration than those with x=0.4, 0.5 and 0.6 ingots.

Homogeneously charged spark ignition (SI) engines are unable to stabilise the combustion in ultra lean mixtures, therefore they operate with a near stoichiometric air-fuel ratio (AFR) at all load points. This produces high engine out NOx and CO emissions with a compromise on fuel consumption. Moreover, stoichiometric operation is needed for effective operation of a three way catalyst, which is not adequate to meet future fuel consumption targets. (For complete abstract open document)