Browse Publications Technical Papers 2019-01-0012
2019-01-15

Tribological performance of an engine mineral oil blended with a vegetable oil under approached long term use conditions 2019-01-0012

It has widely reported that tribological performance of engine mineral oils (EMOs) can be improved by blending them with vegetable oils (VOs) in certain concentrations since bio-oils exhibit friction coefficients much lower than those from EMOs. However, bio-oils are also known to be higher susceptible to oxidation by thermal ageing than EMOs, which could be an important drawback when they are used in engines comprising high variations of working temperature. In this research paper, a comparative analysis of tribological performance of a pure EMO and a blend made of 80% vol. of EMO and 20% vol. of a VO (B20) in fresh and aged conditions is given. The VO selected for the blend was Jatropha oil since various advantages reported as a viable lubricant by different research groups. EMO and B20 were thermally aged in laboratory approaching oxidation and additives depletion caused in EMO due to use in a gasoline-powered car for 7500km. The effects of thermal ageing in the oils were evaluated by means of oxidation (PAI value), Zinc dialkyldithiophosphates (ZDDPs) depletion and changes in kinematic viscosity. The tribological performance of the oils was determined by testing samples from engine cylinder liners in a pin-on-disk tester measuring the friction coefficients and wear rates generated. The thermal ageing caused increased viscosity in B20 contrary to EMO that presented a slight decrease. The friction coefficients of B20 were lower than EMO even when they were aged. The wear rate of fresh EMO and fresh B20 were similar; however, ageing caused an increased rate of EMO but a decreased rate of B20 meaning that B20 exhibited better tribological performance than EMO even in approached engine operation conditions with the long term use.

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