Application of Stribeck curve in development of engine lubricants containing Cu and TiO2 nanoparticles as additives

Nanofluids are engineered colloidal suspensions of nanoparticles (NPs) in a base fluid which can exhibit enhanced physical properties compared to the base fluid. The main purpose of this investigation has been to study the tribological performance and anti-wear mechanism of metal and oxide NPs as lubricating oil additives, through fabrication and characterization of nanolubricants containing 0.005%vol, 0.01%vol and 0.02%vol nanoparticles in commercial motor oils. Metal NPs are synthesized in the lab by using a polyol method, while oxide NPs are commercially available. NPs structure, morphology and size are investigated by UV-Vis spectrometry, scanning electron microscopy and X-ray diffraction while thermo-gravimetric analysis is carried out to quantify the final amount of organic ligand. The friction coefficient for raw oil and NPs-added oils is investigated by using a ball-on-disc tribotester. Moreover, to establish the different lubrication regimes and detect the transition among them, Electrical Contact Resistance (ECR) is measured to get a qualitative characterization of the surface interaction. Stribeck tests are carried out to describe different lubrication regimes for lubricated sliding contacts, to estimate performances of different suspensions, compared to raw oil, and to study their response to the variation of the operating conditions. It comes out that both metal and oxide NPs give an improvement to tribological properties of raw oil. The results presented in this communication enters within an industrial project funded by the Italian Ministry of Economic Development for the implementation of a cogeneration device where nanolubricants can effectively contribute to reduce friction and wear and increase lifetime and fuel efficiency of mechanic components.