Influence of Al2O3 nanoparticles in a lubricating oil for reciprocating engines

The improvement of reciprocating engine efficiency, together with the responsible use of worldwide energy resources and the reduction of pollutant emissions, are significant challenges to be addressed by the automotive industry. Friction and wear problems directly affect the engine efficiency and continue to motivate the study of more effective lubricants. The present work analyzes the contribution of the use of alumina nanoparticles (Al2O3) as additives in lubricating oil of SAE grade 5W30 to improve the efficiency of reciprocating engines. Sliding friction tests were carried out with varying concentrations and size of Al2O3 nanoparticles in the base oil, mimicking the motion between the piston rings and the cylinder liner via a universal tribometer and a High Frequency Reciprocating Rig (HFRR). Although the addition of Al2O3 nanoparticles always showed an improved tribological behavior compared to the base oil, the best strategy to get a better lubricating property was to add low concentration (0.05 wt.%) of larger sized nanoparticles (20 nm). A reduction in Coefficient of Friction (COF) up to 11% and 34%, compared to pure oil was achieved with the universal tribometer and the HFRR, respectively. The particularities of wear mechanisms and the lubricating properties of all samples under different test conditions are examined throughout this work.