The photocyclization and photosolvolysis of a series of hydroxy-substituted biaryl methanols [special characters omitted] have been studied. The proposed mechanism involves deprotonation of the HOAr moiety and heterolytic cleavage of the C-O bond of the hydroxymethyl group [special characters omitted] in the first excited singlet state (S1), to give biaryl quinone methide intermediates, which subsequently cyclize to the corresponding chromene product and/or react with solvent to give the solvolysis product. The formation of these quinone methide intermediates is facilitated by the excited state planarization and the subsequent charge polarization (negative charge transferred from the HOAr ring into the [special characters omitted] ring) of the biaryl. Although both of these processes are influenced by steric and electronic factors, the latter turns out to have a more significant effect on reaction efficiency. When the geometry of the molecule goes from a twisted conformation to a more planar form, the molecule becomes more conjugated and thus gains delocalization energy. This energy is generally larger for the planarization in the S1 state than in the ground state. When it is large enough to overcome the steric repulsion for twisting, biaryls can planarize efficiently in the excited state, which is true for most biphenyl systems. However, it is shown that the deprotonated forms [special characters omitted] of these biaryls have an even larger driving force for S1 planarization than the neutral forms [special characters omitted]. Thus, biaryls with naphthalene ring(s) joined at the 1-position which do not planarize efficiently in the neutral form can still reach a more planar geometry after adiabatic deprotonation of the phenolic hydroxy group in S1. That is, the photocyclization of these molecules proceeds via initial adiabatic deprotonation from the twisted S1 state, followed by twisting (to the planar form) and subsequent charge polarization which expels the hydroxy group at the benzylic position [special characters omitted], to give the required quinone methide intermediate. The o,o'-biaryl quinone methides derived from the o,o'-substituted biaryl methanols are very short-lived due to rapid intramolecular ring closure and are therefore not detectable by nanosecond laser flash photolysis. The o,p’- and p,p'-biphenyl quinone methides, however, do not cyclize and as expected, are readily observable by nanosecond laser flash photolysis. When the benzylic hydroxy group is replaced by other leaving groups, the reaction can be used, in principle, as a photodeprotecting reaction and also to photogenerate acid. These and other results of the Thesis have uncovered many interesting mechanistic details of this new class of reaction and hence have increased our general knowledge of the excited state behavior of aromatic molecules. / Graduate

Against the backdrop of rising fuel prices and increasing demand for transport fuels, coupled with government’s imperative to reduce high unemployment levels by developing the agricultural sector to support a bio-fuels sector, it was considered necessary to conduct research to determine the factors that would influence the success of bio-ethanol production for use in liquid transport fuels. The literature review highlighted five key factors that were developed into research questions to establish whether these factors are relevant to the South African context and which are considered more important. The research was conducted using a combination of face-to-face interviews and telephonic interviews to gather opinions from 16 subject matter experts in the field of bio-fuels. A questionnaire was used to drill down into each of the factors individually, to determine the importance of that factor as it relates to bio-ethanol production. The findings reveal that the absence of clear and sound government policy poses the biggest hindrance to the establishment of the industry. Furthermore, that agricultural development is a major factor for the success of bio-ethanol production as the industry is dependant on the availability of competitive feed stocks in order to be sustainable. Finally, that job creation is the motivating factor for the establishment of the industry since it addresses a government imperative to reduce unemployment levels in South Africa. / Dissertation (MBA)--University of Pretoria, 2007. / Gordon Institute of Business Science (GIBS) / unrestricted

Indiana University-Purdue University Indianapolis (IUPUI) / Natural gas substitution for diesel can result in significant reduction in pollutant emissions. Based on current fuel price projections, operating costs would be lower. With a high ignition temperature and relatively low reactivity, natural gas can enable promising approaches to combustion engine design. In particular, the combination of low reactivity natural gas and high reactivity diesel may allow for optimal operation as a reactivity-controlled compression ignition (RCCI) engine, which has potential for high efficiency and low emissions. In this computational study, a lean mixture of natural gas is ignited by direct injection of diesel fuel in a model of the heavy-duty CAT3401 diesel engine. Dual-fuel combustion of natural gas-diesel (NGD) may provide a wider range of reactivity control than other dual-fuel combustion strategies such as gasoline-diesel dual fuel. Accurate and efficient combustion modeling can aid NGD dual-fuel engine control and optimization. In this study, multi-dimensional simulation was performed using a nite-volume computational code for fuel spray, combustion and emission processes. Adaptive mesh refinement (AMR) and multi-zone reaction modeling enables simulation in a reasonable time. The latter approach avoids expensive kinetic calculations in every computational cell, with considerable speedup. Two approaches to combustion modeling are used within the Reynolds averaged Navier-Stokes (RANS) framework. The first approach uses direct integration of the detailed chemistry and no turbulence-chemistry interaction modeling. The model produces encouraging agreement between the simulation and experimental data. For reasonable accuracy and computation cost, a minimum cell size of 0.2 millimeters is suggested for NGD dual-fuel engine combustion. In addition, the role of different chemical reaction mechanism on the NGD dual-fuel combustion is considered with this model. This work considers fundamental questions regarding combustion in NGD dual-fuel combustion, particularly about how and where fuels react, and the difference between combustion in the dual fuel mode and conventional diesel mode. The results show that in part-load working condition main part of CH4 cannot burn and it has significant effect in high level of HC emission in NGD dual-fuel engine. The CFD results reveal that homogeneous mixture of CH4 and air is too lean, and it cannot ignite in regions that any species from C7H16 chemical mechanism does not exist. It is shown that multi-injection of diesel fuel with an early main injection can reduce HC emission significantly in the NGD dual-fuel engine. In addition, the results reveal that increasing the air fuel ratio by decreasing the air amount could be a promising idea for HC emission reduction in NGD dual-fuel engine, too.

Very little information is available on domestic fuel consumption in African villages in Southern Africa. And yet, it is a problem that concerns a large number of people, and which is contributing to environmental deterioration. At three villages, 'in Lesotho, Transkei and KwaZulu, the collection and consumption of wood, dung and par2ffin were recorded. The larges~ quantities of energy are consumed . .in KwaZulu with the least in the Transkei (only slightly belong Lesotho). the total consumption of energy largely depends on the availability tv of wood. wood becorr.es scarce, is burnt for heat and cooking. Paraffin is used for light, and for cooking by some women. Wood and dung are burnt at efficiencies of below 3%. The most obvious short term solution, to shortages of energy, is to raise the effi8iency with which fuel is burnt, In the long term, alternative energy sources must be developed.

No description available.

No description available.

The application of a decomposition methodology to the synthesis/design optimization of a stationary cogeneration fuel cell sub-system for residential/commercial applications is the focus of this work. To accomplish this, a number of different configurations for the fuel cell sub-system are presented and discussed. The most promising candidate configuration, which combines features of different configurations found in the literature, is chosen for detailed thermodynamic, geometric, and economic modeling both at design and off-design. The case is then made for the usefulness and need of decomposition in large-scale optimization. The types of decomposition strategies considered are time and physical decomposition. Specific solution approaches to the latter, namely Local-Global Optimization (LGO) and Iterative Local-Global Optimization (ILGO) are outlined in the thesis. Time decomposition and physical decomposition using the LGO approach are applied to the fuel cell sub-system. These techniques prove to be useful tools for simplifying the overall synthesis/design optimization problem of the fuel cell sub-system. Finally, the results of the decomposed synthesis/design optimization of the fuel cell subsystem indicate that this sub-system is more economical for a relatively large cluster of residences (i.e. 50). To achieve a unit cost of power production of less than 10 cents/kWh on an exergy basis requires the manufacture of more than 1500 fuel cell sub-system units per year. In addition, based on the off-design optimization results, the fuel cell subsystem is unable by itself to satisfy the winter heat demands. Thus, the case is made for integrating the fuel cell sub-system with another sub-system, namely, a heat pump. / Master of Science

Magister Scientiae - MSc (Chemistry) / The anode catalyst is one of the important parts of the direct alcohol fuel cell (DAFC); it is responsible for the alcohol oxidation reaction (AOR) takes place at the anode side. Pd has been reported to have good alcohol oxidation reactions and good stability in alkaline solution. Better stability and activity has been reported for Pd alloyed catalysts when compared to Pd. Choosing a suitable alcohol also has an effect on the activity and stability of the catalyst. This study investigates the best catalyst with better AOR and the best stability and also looks at the better alcohol to use between glycerol and ethanol for the five in-house catalysts (20% Pd, PdNi, PdNiO, PdMn3O4 and PdMn3O4NiO on multi walled carbon nanotubes) using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectrometry (EIS) and chronoamperometry. HR-TEM and XRD techniques were used to determine the particle size and average particle size, respectively while EDS used to determine elemental composition and ICP was used to determine catalyst loading. It was observed from LSV that PdNiO was the most active catalyst for both ethanol and glycerol oxidation, and it was the most stable in ethanol while PdMn3O4 proved to be the most stable catalyst in glycerol observed using chronoamperometry. The best alcohol in this study was reported to be glycerol having given the highest current densities for all the inhouse catalysts compared to ethanol observed using LSV. From XRD and HR-TEM studies, particle sizes were in the range of 0.97 and 2.69 nm for XRD 3.44 and 7.20 nm for HR-TEM with a little agglomeration for PdMn3O4 and PdMn3O4NiO.

Direct liquid fuel cells represent an interesting alternative to conventional hydrogen fuel cell technology. A novel analytical method for the monitoring of direct liquid fuel cells is presented. Employing a combination of chronoamperometric, gravimetric and Raman spectroscopic measurements this method allows a straightforward determination of the Faradaic efficiency of a fuel cell. This method was applied in a proof of concept study analysing the operational behaviour of a direct methanol fuel cell. A very low Faradaic efficiency was found for the fuel cell under study. This was attributed to loss of methanol from the fuel mixture due to methanol crossover, stripping of methanol by carbon dioxide as well as evaporation. It is known from the literature that a fuel change from methanol towards higher alcohols and other hydrocarbons can help to mitigate the effects of these loss processes. However, the behaviour of such alternative fuels and their mixtures in an operating fuel cell and hence the performance of the fuel cell depends at least in part on the intermolecular interactions present in those fuel mixtures. Therefore, the intermolecular interactions in binary and ternary mixtures of potential candidates for alternative fuels were investigated in the main part of this thesis. Studies on the intermolecular interactions in binary mixtures of acetone with ethanol and 1-butanol showed a tendency for self association of both compounds albeit in different concentration ranges. It was further found that the alkyl chain length of the alcohols did not have a significant effect on the intermolecular interactions in the binary and ternary mixtures. Further, the behaviour of the ternary mixture was found to closely resemble the effects found in the individual binary mixtures. Finally, binary mixtures of dimethyl sulfoxide (DMSO) and different alcohols did not show self association. It was rather found that alcohol molecules inserted into chains of DMSO molecules eventually leading to the formation of alcohol-DMSO dimers.

The fluoride-salt-cooled high-temperature reactor (FHR) is a novel reactor design benefitting from passive safety features, high operating temperatures with corresponding high conversion efficiency, to name a few key features. The fuel is a layered graphite plank configuration containing enriched uranium oxycarbide (UCO) tri-structural isotropic (TRISO) fuel particles. Fuel cycle cost (FCC) models have been used to analyze and optimize fuel plate thicknesses, enrichment, and packing fraction as well as to gauge the economic competitiveness of this reactor design. Since the development of the initial FCC model, many corrections and modifications have been identified that will make the model more accurate. These modifications relate to corrections made to the neutronic simulations and the need for a more accurate fabrication costs estimate. The former pertains to a MC Dancoff factor that corrects for fuel particle neutron shadowing that occurs for double-heterogeneous fuels in multi-group calculations. The latter involves a detailed look at the fuel fabrication process to properly account for material, manufacturing, and quality assurance cost components and how they relate to the heavy metal loading in a FHR fuel plank. It was found that the fabrication cost may be a more significant portion of the total FCC than was initially attributed. TRISO manufacturing cost and heavy metal loading via packing fraction were key factors in total fabrication cost. This study evaluated how much neutronic and fabrication cost corrections can change the FCC model, optimum fuel element parameters, and the economic feasibility of the reactor design.