Friction and wear analysis of palm kernel methyl ester containing a polymeric viscosity index improver

Abstract

The search for renewable resources and the development of bio-lubricants as a substitute for mineral oils are being considered as a top priority in the fuel and energy fields. Bio-lubricants derived from vegetable oils are an attractive alternative to conventional petroleum-based lubricants due to their renewability, biodegradability, high lubricity and high flash point. Nevertheless, some types of vegetable oils have a few issues with regard to their low viscosity that limit their potential to be used as biolubricants in automotive applications. Thus, the present work featured a specific study on the application of ethylene-vinyl acetate (EVA) copolymer as a viscosity index improver (VII) additive inside vegetable oils. The lubrication performance of palm kernel methyl ester (PKME) with the added EVA copolymer was experimentally evaluated using a four-ball tribotester and modified pin-on-disc tester. Tests were performed with 2%, 3% and 4% concentrations of EVA copolymer at various loads, temperatures and sliding speeds. The results obtained were compared to the commercial mineral engine oil, SAE 40, for reference purposes. The present research revealed that the addition of 4% EVA copolymer managed to enhance the viscosity index of PKME by up to 61% of its original value. Based on the four-ball test, it was found that the PKME formulated with 4% EVA copolymer produced slightly better friction-reducing properties and smoother worn surfaces than SAE 40. Meanwhile, the results of the modified pin-on-disc test showed that the application of EVA copolymer successfully minimized the coefficient of friction (COF) of PKME and also enabled it to give a better performance than SAE 40. Thus, the reduction of frictional force by using this formulated bio-lubricant will contribute to the efficiency of internal combustion engine in the future. However, the anti-wear performance of PKME added with EVA copolymer is slightly lower than SAE 40. Therefore, further improvisation method should be taken in order to solve this issue. Finally, it is suggested that the EVA copolymer shows good potential as a VII for enhancing the tribological performance of vegetable oils.