An Experimental Study of Friction and Wear Characteristics of Sunflower and Soybean Oil Methyl Ester Under the Steady-State Conditions by the Four-Ball Wear Testing Machine

According to that the fuel pump and injectors of the diesel engines are lubricated by the fuel itself, so the lubrication property of the fuels is an important issue in internal combustion engines. Biodiesel is one of the most famous biofuels that can be used in diesel engines. In this research, wear characteristics of biodiesel derived from sunflower and soybean oil blends were investigated. The five fuel blends were tested under steady-state conditions (with durations of 1500 and 3600 s) at four different rotational speeds of 600, 900, 1200, and 1500 rpm. An optical microscope was also applied to check out the worn surfaces of the balls. The results indicated that wear and friction as tribological properties were reduced with the increase in the rotating speed under the steady-state condition. It was found that with an increase in the biodiesel concentration, the friction coefficient was reduced at lower rotating speeds due to free fatty acids, monoglycerides, and diglycerides as the components of biodiesel which help improve the lubrication properties of biodiesel and reduce the friction more than that of other blends. However, in higher rotational speeds, friction and wear of fuel blends included biodiesel increased due to reduced viscosity as the causes of oxidation which helps in the exposure of biodiesel to air at higher temperature. So, B100 has better lubricity properties compared to other fuel blends at lower rotational speeds, and better performance belongs to B20 at higher rotational speeds.