In this study, tribological properties of custom formulated and stabilized nano lubricant are investigated. Spherical CuO nanoparticles are suspended in 20W-50 mineral base lubricant using Oleic Acid (OA) as a surfactant. Three different nano lubricant concentrations with 0.2, 0.5, and 1 wt.% were analyzed through ASTM G-99 pin-on-disc tribometer standardized test under boundary/mixed lubrication regimes. The generated friction and wear analyses confirm a consolidation of tribological properties with a reduction in friction coefficient in the range of 14.59–42.92%, compared with the base lubricant. Analysis of worn surfaces (SEM/EDX) as well as (AFM) was conducted. Combined hypotheses were proposed from the analysis of worn surfaces; these hypotheses suggested that CuO nanoparticles exhibit an integrated effect of two phenomenal lubrication mechanisms. Additionally, dispersion stability evaluation of the suspended nanoparticles was performed through Zeta potential, (FTIR), and sedimentation analyses. Stability results showed that steric stabilization is the dominating effect of the repulsive forces between nanoparticles, surpassing the electrostatic repulsive forces.

Reducing power losses in engines is considered a key parameter of their efficiency improvement. Nanotechnology, as an interface technology, is considered one of the most promising strategies for this purpose. As a consumable liquid, researchers have studied nanolubricants through the last decade as potential engine oil. Nanolubricants were shown to cause a considerable reduction in the engine frictional and thermal losses, and fuel consumption as well. Despite that, numerous drawbacks regarding the quality of the processed nanolubricants were discerned. This includes the dispersion stability of these fluids and the lack of actual engine experiments. It has been shown that the selection criteria of nanoparticles to be used as lubricant additives for internal combustion engines is considered a complex process. Many factors have to be considered to investigate and follow up with their characteristics. The selection methodology includes tribological and rheological behaviours, thermal stability, dispersion stability, as well as engine performance. Through the last decade, studies on nanolubricants related to internal combustion engines focused only on one to three of these factors, with little concern towards the other factors that would have a considerable effect on their final behaviour. In this review study, recent works concerning nanolubricants are discussed and summarized. A complete image of the designing parameters for this approach is presented, to afford an effective product as engine lubricant.

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In internal combustion engines, significant power losses are directly related to the mechanical friction of engine parts. Therefore, controlling tribological performance for engine lubricants has a major role in limiting those losses. In this study, the tribological properties of traditional engine oil with nano ZnO and oleic acid (OA) as a surfactant have been analyzed. Three different concentrations of 0.2, 0.5 and 1 wt.% were investigated using a pin-on-disc tribometer, according to ASTM G-99 with boundary/mixed lubrication regimes. The generated friction and wear characteristics revealed a remarkable reduction in friction coefficient with a range of 8–10%. Analysis of SEM and EDX was conducted on the worn surfaces. Additionally, the colloidal stability of nano dispersion was performed through sedimentation, FTIR, and Zeta analyses.