Biodiesel-blended fuel is increasingly becoming available for diesel engines. Due to seasonal and economic factors, biodiesel available in filling stations can be sourced from varying feedstocks. Moreover, biodiesel may not contain the minimum oxidative stability required by the time it is used by the automotive consumer. With fuel dilution of engine oil accelerated by post-injection of fuel for regeneration of diesel particulate filters, it is necessary to investigate whether different biodiesel feedstocks or stabilities can affect engine oil properties. In this work, SAE 15W-40 CJ-4 is diluted with B20 fuel, where the B20 was prepared with soy methyl ester (SME) B100 with high Rancimat oxidative stability, SME B100 with low oxidative stability, and lard methyl ester (LME). The oils were then subjected to laboratory aging simulating severe drive cycles. At intermediate aging times, samples were obtained and additional B20 was added to simulate on-going fuel dilution. Gas chromatographic and FTIR analyses were performed to monitor fatty acid methyl ester (FAME) content and oil degradation, respectively, while ball-on-flat sliding tests (HFRR) were run to assess friction, antiwear film formation, and wear protection capability under boundary lubrication conditions.
The results generally showed no differences in film formation, friction, and degree of wear with these three different sources. Friction, film formation, and wear were very similar before, during, and after aging. Oxidation of polyunsaturated FAMEs in SME and LME occurred, but did not appear to adversely impact the tribological results. Oil degradation as measured by FTIR was also similar for the different B20s.
