Surface Effects on Engine Materials of Mineral Oil Dilution With Methyl Esters and Biodiesels

During ordinary internal-combustion engine operation, biodiesels partially mix in the engine-oil, leading to increased surface degradation, as premature wear. Biodiesels are blends of methyl esters as main components, which are dependent on the source feedstock and may lead to different surface effects on engine materials. In this preliminary study of surface change of SAE 1018 steel when adding pure methyl-esters to engine oil, a SAE 15W40 mineral oil was diluted with methyl-palmitate, -oleate, -stearate, -linoleate, -laurate and -myristate, and with two typical biodiesels, soybean oil and peanut oil biodiesel, each at six different dilutions, and tested in two different instruments. Biodiesel at just 5% in oil led to enhanced wear, but some larger fractions of methyl-oleate and -laurate produced negligible surface change enhancements. Addition of methyl-linoleate and -palmitate enhanced surface degradation. Methyl ester compositions of the two tested biodiesels and their wear trends, which are found in good agreement with previous studies, are used to explain the wear differences.