Modern spark ignition engines are downsized and boosted to meet stringent emission standards and growing customer demands on performance and fuel economy. They operate under high intake pressures and close to their limits to engine knock. As the intake pressure is increased knock becomes the major barrier that prevents further improvement on downsized boosted spark ignition engines. It is generally accepted that knock is caused by end gas autoignition ahead of the propagating flame. The propagating flame front has been identified as one of the most influential factors that promote the occurrence of autoignition. Systematic understanding and numerical relation between the propagating flame front and the occurrence of knock are still lacking. Additionally, knock mitigation strategy that minimizes compromise on engine performance needs further researching. Therefore the objectives of the current research consist of two steps: 1). study of turbulent flame propagation in both naturally aspirated SI engine. 2) study of the relationship between flame propagation and the occurrence of engine knock for downsized and boosted SI engine. The aim of the current research is, firstly, to find out how turbulent flames propagate in naturally aspirated and boosted S.I. engines, and their interaction with the occurrence of knock; secondly, to develop a mitigation method that depresses knock intensity at higher intake pressure. Autoignition of hydrocarbon fuels as used in spark ignition engines is a complex chemical process involving large numbers of intermediate species and elementary reactions. Chemical kinetics models have been widely used to study combustion and autoignition of hydrocarbon fuels. Zero-dimensional multi-zone models provide an optimal compromise between computational accuracy and costs for engine simulation. Integration of reduced chemical kinetics model and zero-dimensional three-zone engine model is potentially a effective and efficient method to investigate the physical, chemical, thermodynamic and fluid dynamic processes involved in in-cylinder turbulence flame propagation and knock. The major contributions of the current work are made to new knowledge of quantitative relations between intake pressure, turbulent flame speed, and knock onset timing and intensity. Additionally, contributions have also been made to the development of a knock mitigation strategy that effectively depresses knock intensity under higher intake pressure while minimizes the compromise on cylinder pressure, which can be directive to future engine design.

O objetivo deste trabalho é estudar as reações de isomerização e cisão dos isômeros C2F2Cl2, e determinar entalpias de formação e potenciais de ionização para derivados halogenados do eteno, através de cálculos ab initio, e ainda, para algumas reações determinar a constante de velocidade microcanônica k(E*), segundo o formalismo da teoria RRKM. Foram obtidas a barreira energética e a estrutura do estado de transição para a reação de isomerização do (Z)-CFCl=CFCl ao isômero (E)-CFCl=CFCl, que ocorre através de um estado de transição com uma barreira de energia calculada de 54,223 kcal/mol com o método CASSCF. Foi analisada a possibilidade de a isomerização ocorrer via intermediários etilidenos halosubstituídos, porém as barreiras de energia para estas reações e resultados obtidos para a constante de velocidade k(E*) indicam que a reação direta predomina sobre as vias de formação de etilideno halosubstituído em baixas energias, até cerca de 154 kcal/mol pelo menos. A não observação, experimentalmente, de formação do isômero CF2=CCl2 a partir desses intermediários também corrobora com os resultados obtidos através dos cálculos. Para as reações de cisão de ligação C=C dos compostos CF2=CCl2, (Z) e (E)-CFCl=CFCl e CF2=CCl, as curvas de energia em função do comprimento desta ligação mostram que a cisão do CF2=CCl ocorre a uma energia menor do que para as demais substâncias. Porém, a cisão da ligação C-Cl na substância CF2=CCl2 é a que possui a menor barreira energética. Utilizando a teoria variacional do estado de transição, determinamos a estrutura do estado de transição para esta reação e a constante de velocidade microcanônica, k(E*), sendo esta maior que as determinadas para a formação dos etilidenos halosubstituídos. Potenciais de ionização adiabáticos (PIA) e verticais (PIV) de haloetenos foram obtidos utilizando as teorias G2 e G3. Os resultados obtidos com a teoria G3 são mais próximos dos valores experimentais, ou tão exatos quanto, comparados aos valores calculados encontrados na literatura. As mudanças na energia de correlação eletrônica e energia de relaxação dos orbitais são importantes para a obtenção de resultados de PIV quantitativamente melhores em comparação com os resultados obtidos a partir da energia do HOMO. Também foram feitos cálculos de entalpias de formação para etilenos halogenados utilizando as teorias G2 e G3 utilizando reações isodésmicas. A comparação entre os valores calculados por nós e outros valores calculados encontrados na literatura mostram que apesar das reações isodésmicas serem um método capaz de gerar bons resultados, devido ao cancelamento dos erros nos valores calculados, o resultado final é dependente dos valores experimentais escolhidos. / We report ab initio calculations on the isomerization and fission reactions of C2F2Cl2 isomers and also the enthalpies of formation and the ionization potentials of halogenated ethylenes. We have also evaluated the microcanonical rate constant k(E*) using the RRKM formalism to gain more insight into mechanistics details of some reactions. The energy barrier and the structure of the transition state for the isomerization reaction of (Z)-CFCl=CFCl to (E)-CFCl=CFCl, occurs by a transition state with a calculated barrier of 54,223 kcal/mol using the CASSCF method. The isomerization reactions through ethilidene halosubstituted intermediates was also tested, however the energy barriers to these reactions showed be greater and the results obtained for the rate constant k(E*) stated that the direct reaction predominates over the formation of the halosubstituted ethilidene at low energies, until 154 kcal/mol at least. The experimentaly unobserved formation of CF2=CCl2 from intermiaries confirms the calculated results. For the fission reaction of the C=C bond on CF2=CCl2, (Z) and (E)-CFCl=CFCl and CF2=CCl , the plots of energy as a function of the bond length show that the fission of CF2=CCl occurs with the lowest energy of all these reactions. However, the fission of C-Cl on the CF2=CCl2 shows to have the lowest energy barrier. By the variational transition state theory, we have determined the structure of the transition state for that reaction and the rate constant k(E*), beeing this higher than that determined to the halosubstituted ethylenes. Adiabatic ionization potentials (AIPs) and vertical ionization potentials (VIPs) for haloethylenes were obtained applying G2 and G3 theories. The results obtained with G3 theory are the nearest within the experimental values or, at least, with the same exactness, compared with other earlier calculated methods. The changes in eletronic correlation energy and orbital relax energy are important to achieve quantitatively better results comparativily with results obtained from HOMO energy. Moreover, we have done calculations of enthalpies of formation of haloethylenes using G2 and G3 theories using isodesmic reactions. The comparison among the values calculated by us and other values found in the literature shows that, however the use of isodesmic reactions may be a method able to achieve good results, because the calculated errors in the energy values are being cancelled , the final result is very dependent on the choosen experimental values.

研究證實，助焊劑能將溶融合冷卻至其溶點之下，仍保持溶液態，亦即達到過冷態。這些溶液因而能夠進液態調幅分。它們凝固之後，會有種互相接的相。在這篇文，這種結構的合簡稱為網絡合。近期研究顯示，白鑄鐵Fe₈₀C₂₀ 亦可憑上述方法，冶成網絡合。其網絡合由種相構成。它們分別是αFe 子網絡及Fe₃C 子網絡，前者柔韌後者堅硬，因此這種網絡合有很優越的機械性能。 / 久之前，有報告研究Fe₇₉.₅B₆.₅C₁₄ 及Fe₈₄B₁₆ 網絡合的結晶過程。這篇文中，研究會集中在過冷Fe₈₀C₂₀ 的結晶過程。其微觀結構分為三區：區由無序網絡構成，十分細小。區之外遍佈高碳的Fe₃(C,B)，由於成份上與Fe₇₉.₅B₆.₅C₁₄的C區相，因此Fe₈₀C₂₀A區外的區稱作C₁ 區及C₂ 區，以相對照。C₁ 區的種子網絡成棒。C₂ 區與Fe₇₉.₅B₆.₅C₁₄ 的C 區一樣，網絡有明顯方向性，且長成樹幹圖案，其Fe₃(C,B) 子網絡屬多晶結構。 / 我們認為合的碳含是引致Fe₈₄B₁₆，Fe₇₉.₅B₆.₅C₁₄，Fe₈₀C₂₀ 三種網絡合，於微觀結構上有差別的原因。高碳的Fe₃(C,B)比低碳的Fe₃(C,B)難生長。以此，我們解釋上述三個合的結晶過程。在Fe₈₀C₂₀ 系統，大碳原子堆積於生長中的固體/液體界面前，這引致細小的A區､C₁ 區的高碳Fe₃(C,B)枝晶出現。 / By employing a fluxing technique, molten alloys can be undercooledsubstantially below its liquidus. The melts carry out phase separation by liquid state spinodal decomposition. After crystallization, solids with interconnected phases are obtained. They are called network alloy in this work. Recently, it is reported that a Fe₈₀C₂₀ eutectic ingot can be cast into a network alloy. The network alloy has two constituent phases. One of which is a ductile αFe subnetwork and the other one is a strong Fe₃C subnetwork. Therefore the network alloy has attractive mechanical properties. / The kinetics of crystallization in undercooled Fe₇₉.₅B₆.₅C₁₄ and Fe₈₄B₁₆ are latelyreported. In this thesis, the kinetics of crystallization in undercooled Fe₈₀C₂₀ alloy was studied. The microstructure can be classified into three zones. Zone A is a small random network. Outside zone A, the microstructure contains high-carbon Fe₃(C,B). In terms of the composition of Fe₃(C,B), they are analogous to the zone C inFe₇₉.₅B₆.₅C₁₄ system. Therefore the two zones outside zone A are named zone C₁ and C₂. Zone C₁ contains dendrites of the two subnetworks. Zone C₂ is the same as thezone C in Fe₇₉.₅B₆.₅C₁₄ systems, which is an aligned network structure showing patterns. The structure of Fe₃(C,B) subnetwork is polycrystalline. / The difference in microstructures between Fe₈₄B₁₆, Fe₇₉.₅B₆.₅C₁₄ and Fe₈₀C₂₀ isattributed to the carbon concentration. The formation of high carbon Fe₃(C,B) is less favoured than low carbon Fe₃(C,B). By this, the kinetics of crystallization in the 3 systems is explained. In Fe₈₀C₂₀, a high concentration of carbon atoms is established in front of the growing solid/liquid interface. This results in the presence of a small zone A and high carbon Fe₃(C,B) dendrites (zone C₁). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Yip, Kai Hou = 因過冷引致相分離的網絡結構Fe₈₀C₂₀合金的結晶動力學 / 葉繼豪. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / Yip, Kai Hou = Yin guo leng yin zhi xiang fen li de wang luo jie gou Fe₈₀C₂₀ he jin de jie jing dong li xue / Ye Jihao. / Abstract --- p.i / Acknowledgements --- p.v / List of Figures --- p.ix / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Composites --- p.1 / Chapter 1.2.1 --- Different Types of Composites --- p.1 / Chapter 1.2.2 --- Fabrication of Composites --- p.3 / Chapter 1.3 --- Phase Transformation --- p.3 / Chapter 1.4 --- Nucleation --- p.5 / Chapter 1.4.1 --- Homogeneous Nucleation --- p.5 / Chapter 1.4.2 --- Heterogeneous Nucleation --- p.6 / Chapter 1.5 --- Growth --- p.7 / Chapter 1.5.1 --- Solidification in Pure Metals --- p.8 / Chapter 1.5.2 --- Solidification in Alloys --- p.9 / Chapter 1.5.2.1 --- Growth of Single-Phase Alloys --- p.9 / Chapter 1.5.2.2 --- Solidification in Eutectic Binary Alloys --- p.11 / Chapter 1.6 --- Phase Separation by Spinodal Decomposition --- p.12 / Chapter 1.6.1 --- Spontaneous Phase Separation --- p.12 / Chapter 1.6.2 --- Uphill Diffusion --- p.13 / Chapter 1.6.3 --- Modified Diffusion Equation --- p.14 / Chapter 1.6.4 --- Solution to the Equation --- p.16 / Chapter 1.6.5 --- Morphology Resulted from Spinodal Decomposition --- p.17 / Chapter 1.7 --- Aim of This Project --- p.18 / Figures --- p.20 / References --- p.28 / Chapter Chapter 2: --- Experiment --- p.30 / Chapter 2.1 --- Introduction --- p.30 / Chapter 2.2 --- Preparation of Fused Silica Tube --- p.30 / Chapter 2.3 --- Sample Preparation --- p.31 / Chapter 2.3.1 --- Preparation of Eutectic Fe₈₀C₂₀ ingots --- p.31 / Chapter 2.3.2 --- Fluxing with Dehydrated B₂O₃ --- p.32 / Chapter 2.4 --- Optical Microscopy Analysis --- p.33 / Chapter 2.5 --- Scanning Electron Microscopy (SEM) Analysis --- p.34 / Chapter 2.6 --- Transmission Electron Microscopy (TEM) Analysis --- p.34 / Chapter 2.6.1 --- TEM Specimen Preparation --- p.34 / Chapter 2.6.1.1 --- Polishing --- p.35 / Chapter 2.6.1.2 --- Ion Milling --- p.35 / Chapter 2.6.2 --- TEM Characterization: Indexing Diffraction Patterns --- p.36 / Chapter 2.6.3 --- TEM Characterization: Electron Energy Loss Spectrum (EELS) --- p.37 / Figures --- p.39 / References --- p.43 / Chapter Chapter 3: --- Kinetics of crystallization in undercooled phase-separated molten Fe₈₀C₂₀ alloys --- p.44 / Chapter 3.1 --- Introduction --- p.45 / Chapter 3.2 --- Experimental --- p.45 / Chapter 3.3 --- Results --- p.46 / Chapter 3.3.1 --- SEM studies --- p.47 / Chapter 3.3.2 --- TEM studies --- p.49 / Chapter 3.4 --- Discussion --- p.55 / Chapter 3.5 --- Conclusion --- p.61 / Figures --- p.62 / References --- p.92 / Bibliography --- p.93

Semiconductor nanocrystals have immense potential to make an impact in consumer products due to their narrow, tunable emission linewidths. One factor limiting their use is the ease and reproducibility of core/shell nanocrystal syntheses. This thesis aims to address this issue by providing chemical control over the formation of core/shell nanostructures by replacing engineering controls with kinetic controls. Chapter 1 contextualizes our study on nanoparticle synthesis with a brief discussion on the physics of quantum confinement and the importance of narrow size dispersities, core/shell band alignments, and low lattice mismatches and strain at core/shell nanocrystal interfaces. Next, the evolution of cadmium chalcogenide nanocrystal reagents is described, ranging from the original organometallic reagents used in the 1980s to modern approaches involving cadmium phosphonates and carboxylates. This is followed by a description of chalcogen precursors, highlighting the recent introduction of molecules whose well-controlled and tunable reaction rates allow for the size tuning of nanocrystals at 100% yield, and accompanying theories on nanocrystal nucleation. Chapter 2 covers work to expand the library of available sulfur precursors to a wider range of molecules relevant for the synthesis of cadmium sulfide nanocrystals. Using thioureas alone, only very fast or very slow precursor conversion rates can be accessed. This limits the accessible sizes of cadmium sulfide nanocrystals using a single hot injection of precursor at standardized reaction conditions. We observe that thiocarbonate and thiocarbamate precursors with varying electronic substituents allow access to intermediate precursor conversion rates and cadmium sulfide nanocrystal sizes. Interestingly, we note that these new precursor classes nucleate particles with higher monodispersity than ones synthesized from thioureas. These results indicate that in addition to precursor structure controlling precursor conversion rate, precursor structure additionally impacts nanocrystal monodispersity. Chapter 3 expands the library of sulfur and selenium precursors to include cyclic thiones and selenones which extends chemical control of precursor conversion kinetics to cover five orders of magnitude. This unprecedented breadth of rate control allows for the simultaneous hot injection of multiple precursors to generate core/shell or alloyed nanoparticles using precursor reactivity. Using this new synthetic strategy, we observe that kinetic control runs into several issues which we partially attribute to differences in cadmium sulfide and cadmium selenide critical concentrations and growth rates. Nevertheless, combined with a syringe pump shelling method, we are able to access core/shell and alloyed nanocrystals with photoluminescence quantum yields of 67-81%. Chapter 4 applies the concept of nanostructure control via precursor conversion kinetics to a better model system: two-dimensional nanoplatelets. Cadmium chalcogenide nanoplatelets are highly desirable materials due to their exceptionally narrow emission full width half max (FWHM) values which make them pure emitters relative to quantum dots or organic dyes. We synthesize 3 monolayer thick nanoplatelets whose lateral dimensions vary from 10 nm x 10 nm to 186 x 100 nm and demonstrate compositional control on the smallest platelet sizes with STEM EELS.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 268-376. / by Rakesh Agrawal. / Sc.D.

Han, Zuoyan. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 75-81). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

No description available.

Light intensity distribution studies in the heterogeneous photocatalytic reactors were carried out successfully with potassium ferrioxalate chemical actinometry, reproducible light intensity estimates of the irradiation source were obtained. The increased light intensity in the reactor system increased the absorption as determined by actinometry. It was found that reflectivity was a dependent variable but mesh opening area was an independent variable. The photocatalytic mineralization of dichoroacetic acid DCAA, in the presence of TiO2 immobilized on a plate in an externally irradiated bubble column photoreactor had been investigated. The mass transfer and activity evaluation were measured. It was found that increasing the catalyst thickness, increased the photoactivity until it reaches the optimum loading, further loading increase caused the reaction rate to remain constant. This phenomenon was observed with increased lamp power (intensity) and initial solute concentration. However, the catalyst activity was not influenced by the increasing concentration of dissolved oxygen. The reaction rate for DCAA photomineralization was expressed using the Langmuir-Hinsheldwood model.

"September 2002" Includes as appendix: a list of publications by the author arising from this work; and, copies of some published journal articles Includes bibliographical references. Describes the synthesis, properties and reactions of transition metal complexes containing poly-ynyl ligands

This thesis is submitted as a portfolio of peer-reviewed publications. / For many geochemical systems, reaction kinetics determines the system's current status and evolution. It might also be the key to unraveling their thermal history. In metal sulfide systems, kinetic studies have been carried out on four sets of solid-state transitions/transformations in Fe-Ni-S and Ni-S systems. In this work, a new kinetic model, the Refined Avrami method, has been developed to account for reactions involving changes in reaction mechanisms. Nonstoichiometric compounds are commonly present in these reactions. The exsolution of pentladite from the monosulfide solid solution (mss) is an important reaction in the formation of nickel ores. For near equimolar mss compositions, the reaction rate is rapid even in the low temperature ranges. For bulk composition Fe₀.₇₇ Ni₀.₁₉ S, the experimental results show the reaction rates ( mss → pentlandite ) vary from 1.6x10⁻⁵ to 5.0x10⁻⁷ s⁻¹ at 200 °C and from 9.4x10⁻⁵ to 4.1x10⁻⁷ s⁻¹ at 300 °C. The activation energy, E [subscript a], varies during the course of reaction from 49.6 kJ.mol⁻¹ at the beginning of reaction (nucleation mechanism is dominant) to 20.7 kJ.mol⁻¹ at the end (crystal growth mechanism is dominant). Monosulfide solid solution (mss) is a common intermediate phase observed during the oxidation of nickel ores, such as violarite and pentlandite. The investigation of mss oxidation is of benefit in understanding the thermal behavior of economically important metal sulfides during smelting. The oxidation products of mss vary in our samples depending on their compositions. Apart from the common oxidation products hematite and Ni₁ ₇ S₁₈, Fe₂ (SO₄) ₃ was observed during the oxidation of Fe₇ . ₉ S₈ and pentlandite for Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ . The activation energy was determined using a model-free method. The oxidation of Fe₆.₄ Ni₁.₆ S₈ exhibited a higher E [subscript a] than Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ over the course of the reaction. The E [subscript a] increases with reaction extent (y) from 67.1 to 103.3 kJ.mol⁻¹ for mss composition Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ and from 76.1 to 195.0 kJ.mol⁻¹ for Fe₆.₄ Ni₁.₆ S₈ . The kinetic study of the α - Ni₁₋ ₓ S → β - NiS transition shows that initial compositions of α - Ni₁₋ ₓ S plays an important role in the kinetics of the transition. The activation energy ( E [subscript a] ) for this α - to β - phase transition is 16.0 ( ± 0.5 ) kJ.mol⁻¹ for NiS in the temperature range 70 to 150 °C, and 13.0 (± 0.5) kJ.mol⁻¹ in the temperature range 250 to 350 °C. For Ni₀. ₉₇ S, however, E [subscript a] deceases from 73.0 ( ± 0.5 ) to 17.0 ( ± 0.5 ) kJ.mol⁻¹ over the course of the reaction in the temperature range 300 to 320 °C. The relationship between E [subscript a] and extent of transition (y) for the initial bulk Ni₀. ₉₇ S was derived using the Refined Avrami method. For Ni deficient compositions, α - Ni₁₋ₓ S, the transformation to β-NiS is accompanied by the exsolution of either a progressively more Ni deficient α-Ni₁₋ₓ S and Ni₃ S₄ , and the reactions become more sluggish for more metal deficient compositions. The study of oxidation kinetics of α-NiS is of metallurgical interest, as α-NiS related phases may occur when nickel ores are flash smelted to produce nickel matte. In an open air environment, the oxidation mechanisms of α-NiS are constant at 670 and 680 °C, dominated by the direct oxidation of α-NiS → NiO. The dominant oxidation mechanism changes to a chain reaction : α-NiS → [superscript k] ₁ Ni₃ S₂ → [superscript k] ₂ NiO at 700 °C. Therefore, different kinetic models need to be applied to these two distinct reaction mechanisms. Activation energy for the oxidation, α-NiS → NiO, in the temperature range 670 to 680 °C was calculated to be 868.2 kJ.mol⁻¹ using Avrami/Arrhenius method. Rate constant k₁ and k₂ are approximated to be 3 x 10⁻⁴ s⁻¹ and 5 x 10⁻⁴ s⁻¹ for the first part and second part of the chain reaction respectively at 700 ° C. The study of the variation in reaction rate with oxidation time illustrates the optimum oxidation time zone for each temperature, where NiO can be produced at the fastest rate. / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2005.