In order to mitigate the effect of fossil fuels on global warming, biodiesel is used as drop in fuel. However, in the mixture of biodiesel and diesel, soft particles may form. These soft particles are organic compounds, which can originate from the production and degradation of biodiesel. Further when fuel is mixed with unwanted contaminants such as engine oil the amount soft particles can increase. The presence of these particles can cause malfunction in the fuel system of the engine, such as nozzle fouling, internal diesel injector deposits (IDID) or fuel filter plugging. Soft particles and the mechanism of their formation is curtail to understand in order to study and prevent their effects on the fuel system. This paper focuses on one type of soft particles, which are metal soaps. More precisely on the role of the short chain fatty acids (SCFA) during their formation. In order to do so, aged and unaged B10 was studied. The fuel matrixes were mixed with a calcium source such as calcium oxide (CaO), calcium carbonate (CaCO3) and engine oil. The importance of SCFA was studied by influencing the presence of the acids, by degrading the fuel, by the addition of formic acid and by inert gas bubbling. The created deposits and fuels mixtures were examined with the use of pH measurements, Fourier-transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS) and ion chromatography (IC). Opposed to the expectations, the results indicate that SFCA in not the most important factor for the formation of soft particles. It is shown that the calcium sources influenced the consistency and amount of the created soft particles. From the tested contaminants, CaO showed the highest yield towards precipitates. While degradation of the fuels showed to be the most important factor to form soap type soft particles.
