Impact of Oxidation on Lubricating Properties of Biodiesel Blends

The lubricating efficiency is an important property of diesel fuel since several diesel engine parts, such as pumps and injectors, are lubricated by the fuel itself only. The evolution of oxidation products during oxidative deterioration may as well affect the lubricating properties of the biodiesel fuel blends and thus the proper functioning of a diesel engine. In this study Fatty Acid Methyl Esters were produced from various types of feedstock that significantly differentiate in their fatty acid profile. Each methyl ester was blended with an Ultra Low Sulphur Automotive Diesel (ULSD) at a concentration of 7% v/v which is currently the maximum acceptable FAME content according to the European Standard EN590. The B7 biodiesel blends were evaluated regarding fundamental physicochemical properties as well as their lubricating efficiency. Oxidation stability was examined on a Rancimat apparatus according to EN 15751 standard. Moreover, the samples were subjected to oxidative deterioration by employing a Rapid Small Scale Oxidation Test (RSSOT) unit in accordance to ASTM D7545 Test Methods. Subsequently, the oxidized samples were collected from the RSSOT apparatus for further analyses. Alterations in the tribological performance of the B7 blends were assessed by measuring the lubricity of the oxidized fuels in a High Frequency Reciprocating Rig apparatus. Differences in the acidity of the oxidized samples were examined, as well, by conducting acid value tests. Finally, FTIR measurements were performed in order to try to detect relative changes that occur in the blends under oxidizing conditions. Overall, a noticeable deterioration in the lubricating performance of the oxidized blends was exhibited and the analyses showed that this could be principally attributed to FAME degradation.