Experimental Investigation of the Thermophysical and Tribological Properties of Nano-TiO₂-MnO₂-Doped Graphene Oxide/Base Oil Ternary Hybrid Nanofluids

Nanolubricants (NLs) are the preferred choice for enhancing the anti-wear property of moving machine components. This study introduces a novel approach by incorporating a nanocomposite made of TiO₂ (T) and MnO₂-doped graphene oxide (MGO) into paraffinic base oil. Additionally, the essential properties of the NLs that indicate oil quality were experimentally investigated, including stability (ISO 22412:2008), viscosity index (ASTM D2270), viscosity (ASTM D445), flash point (ASTM D92), thermal conductivity coefficient, specific heat capacity (ASTM D5334-08), coefficient of friction (COF), and pin weight loss (ASTM G99). A significant advantage of these ternary nanoadditives is their enhanced thermal conductivity and lubricating properties, resulting from the synergistic interaction between TiO₂ and MGO. GO nanosheets were synthesized using a modified Hummer’s method; MGO nanoadditives were synthesized through the co-precipitation method. NLs containing 0.075T + 0.225MGO and 0.15T + 0.15MGO nanomaterials demonstrated the most significant improvements, with the thermal conductivity coefficient increasing by 35.74% and the COF decreasing by 21.73% (at 100 N and 180 rpm). Incorporating varying concentrations of 0.225T + 0.075MGO, 0.075T + 0.225MGO, and 0.15T + 0.15MGO into the engine oil (EO) at 100 N and 180 rpm resulted in a reduction in the COF between the two surfaces, thereby preventing an average weight loss by approximately 38.46%, 51.04%, and 60.83%, respectively.