Tribological evaluation of rice bran oil blended with Calophyllum inophyllum oil as a potential base stock for bio-lubricant formulation

This study investigates the feasibility of utilising a blend of rice bran oil (RBO) and Calophyllum inophyllum oil (CIO) as a bio-lubricant. The chemical properties, including acid value, peroxide value, and iodine value, were evaluated for pure RBO, CIO, and their blends at different ratios according to ASTM and IS standards. The results showed that with an increase in the CIO content in the blended sample, the acid and peroxide values also increased. Considering the chemical properties and the fact that RBO is a consumable oil, the 50:50 blend of CIO and RBO (RCIO) was selected for further analysis. The tribological properties, such as coefficient of friction and wear scar diameter, were determined using a four-ball tribo-tester following ASTM D 4172. The results revealed that RCIO exhibited the lowest coefficient of friction (0.0466) among the samples, suggesting superior lubrication performance and friction reduction capabilities. Conversely, RBO had the highest coefficient of friction (0.0582), implying relatively higher friction. Regarding wear scar diameter, RBO showed the largest value (595 micrometres), indicating increased wear and surface damage, likely due to its higher friction. CIO had a moderate wear scar diameter (537 micrometres), while RCIO demonstrated the smallest wear scar diameter (521 micrometres), indicating better wear protection and surface integrity. Additionally, the flash temperature parameter and energy consumption during the tribological tests were calculated to assess the lubricating capabilities. RCIO exhibited the highest flash temperature parameter value of 99.550, surpassing both RBO and CIO, implying superior lubrication performance under extreme conditions. The energy consumption analysis indicated that RCIO generated slightly less thermal energy than RBO but more than CIO. Overall, the study highlights the potential of the RCIO blend as a promising bio-lubricant formulation, offering enhanced tribological properties, improved lubrication performance, and better resistance to extreme operating conditions.