Effect of fuel contamination on tribological properties of flex-fuel engines lubricating oils

Abstract Engines that allow the use of any percentage of alcohol and gasoline are flex-fuel engines. These motors face significant tribological challenges that seem to be associated with inadequate lubrication and severe tribochemical wear. The present work aimed to understand flex-fuel engines’ lubrication, friction better, and wear phenomena. Therefore, the authors analyzed the effects of adding percentages of fuels (ethanol and gasoline) to synthetic oil, evaluating the tribological performance of these lubricants. The lubricants were tested in an HFRR (High Frequency Reciprocating Rig) in order to measure the lubricity, friction, and wear between surfaces in relative motion under load. During the test, the coefficient of friction (COF) was evaluated, as well as the wear characterization via SEM/EDS and AFM. The results showed that the contamination of the lubricant with the fuels studied in this work decreased its lubrication capacity. This effect was more pronounced for higher proportions of ethanol once it promoted a tribocorrosion on the surface.