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Increasing fuel prices, stricter government policies, and technological developments made it possible to seek for renewable alternatives, called biofuels, to petroleum fuel. Biodiesel, a biofuel that is produced from chemically mixing animal fat, vegetable oils, or recycled restaurant grease with alcohol and catalyst, is gaining popularity in recent years as a substitute for petroleum diesel. Ninety percent (90%) of U.S. biodiesel industry makes use of soybean oil as its feedstock. However, soybean oil alone cannot meet such a huge demand on biofuel production. Hence, it is important to identify and get more information about other feedstocks, specifically on its effects on the performance and exhaust emissions of diesel engines. The purpose of this study is to investigate the performance and emissions of two diesel engines operating on different biodiesel fuels (i.e. canola oil, sunflower oil, safflower oil, peanut oil, and chicken fat) and compare them to the performance and emissions when the engine is operated on soybean oil-based biodiesel and petroleum-based diesel. Results indicated that an engine operating on biodiesel generates a little less power and torque at any given speed than one running on diesel. Such power and torque loss were attributed to the biodiesel's lower energy content. The lower heating value (energy content) of biodiesel can be reflected in the specific fuel consumption, i.e., to generate the same power, more biodiesel is needed. The reduction in torque and power of less than 10% indicates that in some cases biodiesel has better combustion than diesel. Unfortunately, the high efficiency of combustion may give rise to increased combustion temperature which may lead to higher exhaust emissions. The gradual decrease in the total hydrocarbon and CO2 emissions, as blends were increased from B20 to B100, was also found to be an indication of better combustion using biodiesel fuels than petroleum diesel. However, NOx emissions were higher, predominantly at low speeds for most biodiesel and blends and therefore may require some additives or engine modifications/or adjustments to equalize the NOx emissions of diesel. Other emissions particularly SO2 were lower than standards require.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

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Introduction: Single sample TWA samples collected over an 8-hour shift have the potential to mask elevated exposures, excursions or “peaks” that may have occurred thus permitting situations where workers are over-exposed or indeed over-dosed. The objectives of this study, undertaken in a small acrylic sheet manufacturing plant, are therefore to identify tasks that have the potential to exceed short-term occupational exposure levels and then simultaneously monitor employees undertaking these tasks for 8-hour TWA and Short-Term exposure concentrations. The results obtained from this sampling are then compared to their respective legal limits and then finally correlated to establish their statistical significance. Materials and Methods: The study setting comprises a syrup room wherein two employees are assigned per shift. Employees in this setting manufacture an acrylic “syrup” which is achieved by dosing raw materials into any one of 13 mixing vessels. Whilst mixing, these vessels also heat the ingredients until the required viscosity is reached. This “syrup” comprising mostly of liquid methyl methacrylate, is then decanted into a pressure vessel from where it is pipe-fed into a casting chamber and finally poured between two glass sheets. When cured, the final product is stored and sold as a clear or tinted acrylic sheet. All operations with this area are therefore associated with facilitating the syrup manufacture. Personal 8-hour TWA and Task- Based measurements of methyl methacrylate vapour were simultaneously obtained from the breathing zones of six employees over five separate shifts. These employees routinely work within the setting and also undertake tasks that have the potential to exceed the Short-Term Occupational Exposure Limit (ST-OEL) for methyl methacrylate vapour. Tasks were studied and those selected for quantitative monitoring were captured using a qualitative risk assessment tool. These selections were based on studying each task to establish the employee’s exposure probability and severity i.e. whether performing the task could indeed lead to excessive Short-Term exposures. Eight-hour TWA monitoring was undertaken using activated carbon 3M 3500 passive monitoring badges which were attached to each of the subject’s breathing zone and left over 80 % of the shift. The task-based measurements were obtained by using a Drager PAC III electro-chemical monitoring instrument, which was also placed in each each 4 subject’s breathing zone, and provided real-time exposure data whilst the employees were undertaking the various tasks. Results: All measurements (N = 116) were obtained over a series of 5 full-shift monitoring periods. When analysed, 8 of the 10 of the TWA samples returned results that were below the 8-hour TWA OEL. Of the 106 task-based measurements obtained for the nine identified tasks, when averaged, 89.1 % of results exceeded the ST-OEL. When the TWA and ST measurements were correlated, only one of the nine tasks were statistically significant in their correlation. This correlation coefficient was however highly statistically significant (r = 0.339, p = 0.032 and r = 0.337, p = 0.022 respectively). Both negative and positive correlations were obtained however these were statistically insignificant. Discussion: A significantly higher proportion of the sample results were above the STOEL than the 8-hour TWA OEL concentrations contributing to the argument that ST exposure monitoring may add additional insight to employees’ exposure profiles. A major limitation of the study is however the small sample size, which makes it difficult, due to inter-worker variability amongst other factors, to extrapolate the results and their corresponding interpretations to larger, more generalised occupational hygiene monitoring scenarios. Conclusion: The results obtained therefore support the assertion that the inclusion of short-term monitoring is important in characterising employee exposures in situations where these tasks are themselves potential sources of significant chemical exposures. Recommendations: As a basis for undertaking any form of monitoring and particularly in settings where short-term, task-based exposures may exist, the importance of undertaking a systematic approach to hazard identification and risk profiling via the use of a known risk assessment tool to compile a air sampling programme, has been demonstrated in the results of this research. Further research that specifically addresses the problem of characterising workplace exposures would be useful in larger study populations as well as occupational settings which expose employees to the various types of airborne contaminant e.g. fume, mists, particulates and gases.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 140-164). Available also in a digital version from Dissertation Abstracts.