Investigation into the Tribological Properties of Biodiesel-Diesel Fuel Blends Under the Run-In Period Conditions

Lubricity is a very important issue for diesel fuel injectors and pumps (of an engine) that are lubricated by the fuel itself. Biodiesel as an alternative fuel has a number of technical advantages compared to conventional diesel. It is required to perform more research about the tribological behavior of biodiesel blends under run-in period conditions at different rotational speeds. Friction characteristics of biodiesel (mixture of sunflower and soybean methyl ester) were studied by using a four-ball wear testing machine. Results indicated that the friction was reduced with the increase in rotational speed under the run-in period conditions. Moreover, the results showed that the friction coefficient decreases at rotational speeds of 600 and 900 rpm as the proportion of biodiesel increases in the fuel blend. This is due to higher viscosity of biodiesel and the presence of free fatty acids and monoglyceride and diglyceride components in this fuel, which improve the lubricity properties of the fuel blends. However, the coefficient of friction of the fuel blends that contained more biodiesel (B50 and B100) increased at rotational speeds of 1200 and 1500 rpm as a result of reduced fuel viscosity, oxidation, and moisture absorption in a higher temperature condition. So it was concluded that the better tribology performance belongs to B20 at higher rotational speeds.