Effect of C60-SiO2 hybrid nanoparticles on thermophysical and tribological properties of a multigrade engine oil: an experimental study

In this study, the thermophysical and tribological properties of a hybrid nanofluid containing fullerene-silica nanoparticles in a multigrade engine oil have been investigated. The nanoparticles were suspended in SAE 5W30 engine oil with a volume fraction of 0.1 to 1% using the two-step method. The results showed that thermal conductivity of nanofluid increased by approximately 9% at 1% volume fraction, and at ambient temperature, rather than the base oil. Investigation of shear stress variations for base fluid and nanofluids at different concentrations revealed that the rheological behavior of the nano-oil is non-Newtonian and shear thinning. Also, the results represented that by increasing the concentration, the nanofluid dynamic viscosity had an erratic trend. The highest increase was 14% and occurred at 1% volume fraction and 5 °C. Also, the behavior of nanofluids against temperature was in accordance with the conventional fluids. Besides, viscosity decreased after the enhancement of temperature in all volume fractions. The wear test was carried out using a pin-on-disk device based on the ASTMG99 standard. The results revealed that the wear rate decreased by 18% in comparison with the base oil at concentration of 1% and temperature of 25 °C. Finally, in order to predict the viscosity of nanofluid, a precise equation was presented based on the experimental data in terms of three variables of temperature, volume fraction and shear rate by using response surface methodology (RSM). Two-degree polynomial function with R2 = 0.9983 has been employed as the optimal function to model the viscosity of nanolubricant.