Experimental evaluation of tribological behavior in engine lubricants with trace additions of CuO and TiO₂ nanoparticles

The performance and longevity of engine components are critically dependent on the tribological behavior of lubricants. Nanoparticle additives have emerged as a promising solution for enhancing lubrication by reducing wear and friction, improving fuel efficiency and extending service life. However, most studies have focused on concentrations exceeding 0.1 wt%, with limited exploration of the effects at lower dosages. This study systematically investigates the tribological performance of SAE 20 W-50 engine oil modified with CuO and TiO2 nanoparticles at 0.02, 0.06, and 0.12 wt%. Pin-on-disc tribometry reveals that CuO nanoparticles at 0.02 wt% achieve a 25% reduction in the coefficient of friction (COF), while TiO2 nanoparticles at 0.12 wt% lead to a 90% reduction in wear volume. These improvements are attributed to distinct tribomechanical mechanisms: CuO facilitates tribofilm formation and third-body interactions, whereas TiO2 acts as nano-bearings, promoting a rolling-sliding motion that mitigates surface damage. Viscosity measurements revealed a concentration-dependent reduction, with a maximum decrease of 31%, attributed to nanoparticle-induced disruption of intermolecular friction in the base oil. This modification enhances fluidity without compromising the lubricant performance, indicating enhanced flow characteristics. The findings underscore the potential of low-concentration nanoparticle additives in engine lubrication, offering a scalable and energy-efficient strategy for minimizing frictional losses and wear in high-load tribosystems.