United States Department of Transportation
i
Combustion Chemistry of Biodiesel for Use in Urban Transport Buses: Experiment and Modeling
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2014-10-01
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[PDF-2.17 MB]
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TRIS Online Accession Number:01552185
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Edition:Final Report
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Abstract:Biofuels, such as biodiesel, offer benefits as a possible alternative to conventional fuels due to their fuel source sustainability and reduced environmental impact. Before they can be used, however, it is essential to understand their physical properties, combustion chemistry, and characterization of the exhaust due to a number of issues associated with fuel properties. High viscosity of biodiesel may lead to poor atomization of the fuel spray and inaccurate operation of the fuel injectors. Biodiesel may produce high NOx emissions and variations in chemical properties may also be an issue. During this study, physical properties such as flash point, cloud point, and kinematic viscosity of different blends (B0, B10, B20, B50, and B100) were measured on three different feedstocks (soybean methyl ester or SME, tallow oil, or TO, and waste cooking oil, or WCO) while ultra-low sulfur diesel (ULSD) was used as base fuel. The research applied the standard methods of the American Society for Testing and Materials (ASTM). For the study of combustion chemistry and characterization of the exhaust, various tests, such as gravimetric analysis, elemental analysis, elemental carbon/organic carbon (EC/OC) analysis, and gas chromatography (GC) analysis, were conducted for PM emission samples collected from buses, as well as from the laboratory setup. In the field, emission samples were collected for both hot and cold idle conditions. Gravimetric analysis showed a decrease of 17% in PM emissions from the transit buses running on B20 compared to ULSD (B0). Eleven elements were detected in the exhaust samples collected from the laboratory experiments, and fifteen from the field experiments. Results also indicated that the use of biodiesel could effectively reduce EC and increase the portion of OC/EC emissions. Positive matrix factorization (PMF) was used to identify all possible sources of the elements from the transit buses. A simple chemical model was also proposed on PM formation from transit buses, as well as the emission from the laboratory experiments. The emission of carbon was also investigated, and the results confirmed that lower emissions of CO and CO2 are related to lower ratios of carbon to oxygen in biodiesel fuels compared to ULSD.
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