Influence of Fatty Acid Composition on the Tribological Performance of Methyl Esters Under Boundary Lubrication Regime

Plant-based oil is a better alternative for replacing petroleum-based oil on account of its good lubricity, biodegradability, availability and low manufacturing cost. The methyl esters obtained from plant-based oils could be used as potential biolubricants in diverse applications, based on their fatty acid profile and properties. The present research investigates the influence of fatty acid composition of three different methyl esters on the physicochemical, thermal and tribological characteristics. Jatropha, Karanja and Cottonseed methyl esters are chosen and important properties viz. fatty acid profile, viscosity, density, TAN and flashpoint are measured. Using a reciprocating wear tester, a sliding contact pair is established between AISI E52100 steel and SS-301. The tribo-tests are carried out under different loads (50, 75 and 100 N) and sliding frequencies (15 and 30 Hz) while keeping the contact pair at 160 degrees C, simulating the boundary lubrication regime. The output responses such as frictional force, coefficient of friction and wear scar diameter are measured at the end of every trial. The relationship between the fatty acid composition of all investigated methyl esters to their tribological behaviour is deduced and pictorially presented. The test results revealed the supremacy of Jatropha methyl ester over Cottonseed and Karanja. A maximum reduction of about 31% in frictional force and 39% in wear scar diameter are observed with Jatropha methyl ester. The results are substantiated by the microscopic examination of the worn-out surfaces.