Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Idaho, 2005. / Abstract. "December, 2005." Includes bibliographical references. Also available online in PDF format.

<p>This essay is written within my education for Technical Officer in the Swedish armed forces. The essay describes the alternative fuels that the Swedish armed forces can make use of if the supply of fossil fuels is insecure. The alternative fuels that are described and compared are; Synthetic diesel, Organic diesel, Methanol and Ethanol. The essay describes the process of producing the alternatives, the need for modification and the economics for each alternative. The alternatives are compared and assessed for their ability to secure the supply of fuel to the Swedish Armed Forces. The result of the study is that, while synthetic diesel has the best chemical constitution but is not produced in Sweden, the best alternative fuel for the Swedish armed forces at this moment is organic diesel.</p>

This essay is written within my education for Technical Officer in the Swedish armed forces. The essay describes the alternative fuels that the Swedish armed forces can make use of if the supply of fossil fuels is insecure. The alternative fuels that are described and compared are; Synthetic diesel, Organic diesel, Methanol and Ethanol. The essay describes the process of producing the alternatives, the need for modification and the economics for each alternative. The alternatives are compared and assessed for their ability to secure the supply of fuel to the Swedish Armed Forces. The result of the study is that, while synthetic diesel has the best chemical constitution but is not produced in Sweden, the best alternative fuel for the Swedish armed forces at this moment is organic diesel.

No description available.

No description available.

To ran a DMFC without methanol crossover is the aim of this study.It is done by supplying fuel no more than what the anode can consume. The first is to explore the factors that may affect the time constant of vapor feed DMFC. In order to reduce the time constant of current decline, first, we decrease store tank¡¦s space of methanol with different structure of unipolar plate. Second, we reduce the thickness of anode stack and the space above the air bleed valve. Using slide plate instead of air bleed valve can shorten the diffuse distance effectively and reduce the time constant of current rise curve. The second is to explore the impact of supply of methanol on steady-state current of system. Using air bleed valve, because of its high gas tightness, the utilization rate of methanol can exceed 94% without crossover. It was found that in the slide plant experiment, steady-state current value depends mainly on the pore size of slide plate, and resistance value has nothing to do. However, the resistance value is lower, the time required to reach steady-state current is shorter. The third is to explore if the performance decay after long time test of steady-state current. It was found that the performance of MEA will decay while the water content of membrane decreased.

Perfluororated proton exchange membrane Nafion is the mostly used type of ion exchange membrane in fuel cells. Over the past decades, various studies have been carried out on their structures at different scales, proton conduction mechanism, electrochemical performance, thermal and mechanical properties etc, but many problems are still open, such as the precise picture of proton conduction, degradation and aging of the membrane, even the distribution of pores and channels etc. Because membrane degradation is crucial for practical operation of fuel cells and its understanding offers insights for developing new generation membranes, more and more attention is paid to this issue. Methanol is used in direct methanol fuel cells (DMFC) and alcohols are sensitive to the structure and dynamics of Nafion. In addition, aqueous solutions of alcohols are known to have special mesoscopic structures. Therefore, this thesis employs the aqueous solution of methanol as a probe and investigate the physicochemical mechanism of the degradation of Nafion 117 by means of solid state NMR spectra, relaxation, exchange, diffusion and micro-imaging. A series of methanol-water binary solution samples covering the entire range of concentration (0% ~ 99%(w/w)) were prepared and the 1H,17O NMR spectra,T1¡BT2, exchange rate, diffusion coefficient of these samples in bulk and in Nafion were measured. In bulk samples, the OH peak of water and that of methanol could be resolved with concentration at or above 40% (w/w). The microscopic and mesoscopic structure and dynamics of methanol solutions (in bulk) were subsequently investigated with variable temperature and diffusion experiments. By measuring the variable temperature 1H and 17O spectra, T1, T2, diffusion and micro-images of the methanol solutions in Nafion 117, the structure and dynamics of methanol solutions in bulk and in Nafion 117 were then compared. Based on these data, the structure an dynamics of Nafion 117 and the correlations between methanol and proton conduction and membrane degradation are discussed. The results of this work provides valuable reference for further understanding the structure, dynamics and degradation of Nafion and their relationship with proton conduction.

A theoretical model and numerical simulation of a direct methanol fuel cell (DMFC) is developed to simulate the reaction mechanisms and the cell voltage under several different designing parameters and operational conditions. The results of a numerical simulation include the distributions of the proton current density, the concentration of methanol, the electrochemical reaction rates, the overpotential losses, and the pressures within proton exchange membrane layer, catalyst layer and diffusion layer. In addition, the influence of aforementioned operational conditions on methanol crossover in a direct methanol fuel cell is also investigated. Finally, the results of the model are compared to the results from the experimental work. The results show that increasing of temperature, pressure and anode catalyst loading can enhance the performance of a direct methanol fuel cell, and the concentration of methanol plays an important role in its performance. The optimal concentration of methanol for a direct methanol fuel cell is about 2M. Methanol crossover can be suppressed by decreasing methanol concentration and increasing thickness of polymer electrolyte membrane (PEM). However, under operating condition of high current density, thick PEM and low methanol concentration will cause large concentration overpotential and ohmic losses, respectively.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2000. / Includes bibliographical references.