Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references. Also available on the Internet.

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This thesis reports the investigation of liquid-to-gas and liquid-to-solid phase transitions of liquid hydrocarbon fuels and their ethanol blends, both in the bulk phase and as single droplets. The key point has been to develop an understanding of the fuels' macroscopic behavior by studying them at the molecular and at the single droplet level. A key work in this thesis is the investigation of different ratio ethanol/gasoline blends at the molecular level. At the macroscopic level, the vapor pressure, and hence the evaporation of the blends, is influenced by the strength of intermolecular interactions. Thus, information on the molecular interactions between ethanol and gasoline are inferred by using IR and excess IR spectroscopy. The spectroscopic data suggest that the hydrogen bonding between ethanol molecules is weakened upon gasoline addition, but the hydrogen bonds do not disappear. This can be explained by a formation of small ethanol clusters that interact via Van der Waals forces with the surrounding gasoline molecules. In addition, Raman spectroscopy is performed on the same blends, and the Raman spectra are compared with the IR ones. Two different approaches for data evaluation, with the scope of determining the ethanol content in the blends, are tested and compared: Firstly, the calibration of the intensity ratio of characteristic peaks as function of composition; secondly, a principal component regression (PCR). Both methods are found to have comparable uncertainty. For the evaluation of the Raman spectra, the PCR method yielded better accuracy than the intensity ratio approach. In addition, a detailed investigation of the influence of noise in the signal is presented. When the full IR spectra were evaluated by PCR, even high noise levels did not reduce the measurement accuracy significantly. Later, with the aim of studying the evaporation dynamics of fuel blends, at the single droplet level, electrodynamic balance (EDB) and optical tweezers are used to trap ethanol/gasoline droplets, containing different ethanol percentages. A longer lifetime is observed for droplets containing a greater fraction of ethanol. In order to explain the experimental evaporation trends obtained, a theoretical model is used to predict the evaporation rates of pure ethanol and pure gasoline droplets in dry nitrogen gas. Also a theoretical estimation of the saturation of the environment, with other aerosols, in the tweezers is carried out. Lastly, the liquid-to-solid phase transition of some long chain alkanes, commonly present in diesel or gasoline, is investigated both at the molecular and at the single droplet level. Firstly, by using Raman spectroscopy the solidification of these hydrocarbons in the bulk phase is observed. Distinctive features associating the solid even hydrocarbons to a triclinic structure and the odd ones to an orthorhombic structure can be observed in the spectra. Secondly, the liquid-to-solid phase transition of single hydrocarbons droplets is investigated. Freezing time and surface area resulted to be inversely proportional in dodecane droplets. This might suggest a surface freezing mechanism. Furthermore, differences in the scattering patterns, depending on the freezing mechanism, are pointed out. Droplets freezing homogeneously show a different scattering pattern with respect to droplets that froze heterogeneously.

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Includes bibliographical references. / This project involves an investigation of combustion image analysis by the two-colour method as a technique for comparing diesel fuels. The purpose is to master the technique of combustion imaging in both an engine and a Combustion Bomb, with a view to determine the suitability of the two-colour method for fuel comparisons. To evaluate the abilities of the method, an intensive range of testing was conducted on two diesel fuels with slightly different fuel properties.

Due to the numerous disadvantages associated with the use of fossil fuels, focus has been drawn on the environmentally friendly, renewable and carbon-neutral alternative, algalbased biofuels. Many microalgal species have been studied due to their ability to produce significant lipid yields which may be converted to biodiesel. In the present study three microalgal species were screened and a model organism that produced maximal lipid yields, had the greatest lipid productivity and showed potential to be used on a large scale basis, was selected. The selected species was identified, using both morphological and molecular methods, as Isochrysis galbana U4. Nitrogen (N) limitation and depletion studies showed that an internal N reservoir determines cell growth and eventual lipid accumulation in I. galbana when the external N reserves are deplete. Intracellular N depletion was associated with a decrease in the pyrenoid size and chlorophyll content, a breakdown of the chloroplast and the production of large lipid bodies which is advantageous in terms of lipid sequestration for biodiesel production. Cost reduction approaches for the mass culture of I. galbana were investigated. Factors that were proven to reduce costs, without altering the final lipid yield, included the use of urea as a N source and the supply of lower phosphorus (P) levels since this species is capable of growing optimally with as little as 0.25 ppm P. Furthermore, I. galbana cells demonstrated spontaneous flocculating abilities when cultured for prolonged periods. This is advantageous in the cost reductions of downstream harvesting processes. Both, 7 L and 16 L photobioreactors (PBR) were tested. Culture upscale resulted in the concomitant decrease in algal growth rate which was attributed to the limitations on the carbon dioxide and light supply in scaled up systems. Hence, it is suggested that multiple smaller units be used in an industrial setup. Overall, I. galbana is a promising candidate for biodiesel production, due to its ability to produce large amounts of lipid, its elevated growth rates and low P demand. The use of a two-phase PBR (The first phase being nutrient replete, promoting cell growth and division, and the second phase nutrient deplete, promoting lipid production) for the mass culture of this species in industry is recommended.

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