Mechanism of Formation of Soft Particles in Biodiesel Fuel Blends
Abstract: The large environmental impact related to the use of fossil fuel has driven the shift toward renewable sourced alternatives. Fossil diesel can be nowadays replaced by biodiesel, obtained from vegetable oils and fats, mostly used as biodiesel blends. However, some drawbacks are related to the use of this bio-fuel, among which the formation of deposit in injectors and filters causing a reduction of engine performances or engine failure. This thesis project focuses on the analysis of the mechanism of formation of soft particles in biodiesel deposits. These particles are constituted mostly of carboxylic metal soaps, and were found in biodiesel engines after using aged biofuel with contaminants, such as engine oil. The role of short chain fatty acids (SCFAs) has been investigated, together with the use of three different calcium sources, to analyse the formation mechanism of calcium soaps. Artificial ageing of B10 and B100 test fuels was performed, and in some cases an inert gas was bubbled to remove the formed SCFAs. Calcium sources, namely calcium oxide, calcium carbonate and engine oil, were added to investigatethe formation of soft particles. Ion chromatography, pH measurements, NMR spectroscopy and oxidation stability tests have been performed on the liquid test fuel to verify the presence and effect of SCFAs, while FTIR spectroscopy and GC/MS analyses were used to verify the presence of calcium soaps in the deposit and in solution. In contrast to the expectation, it was found that the presence of SCFAs in the fuel not is fundamental for the formation of carboxylic soap. Moreover, the different calcium sources result in different amounts and textures of metal soaps in deposits and in solution.
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