Polyalphaolefin-based SiO₂ nanolubricants: Thermo-physical and tribology investigations for electric vehicle air-conditioning system

The polyalphaolefins (PAO) lubricant oil exhibits promising potential as a substitute for lubricants used in electric vehicle air-conditioning systems employing R134a and R1234yf. This paper presents an experimental study on PAO lubricant's thermo-physical and tribological properties when dispersed with SiO₂ nanoparticles. The dispersion of SiO₂ nanoparticles in the PAO lubricant was achieved using a two-step method, with volume concentrations ranging from 0.01 % to 0.10 %. The SiO₂/PAO nanolubricants were visually observed, and their thermal conductivity, dynamic viscosity, coefficient of friction (COF), and wear scar diameter (WSD) were evaluated using appropriate instruments. The study found that the SiO₂/PAO nanolubricant exhibited excellent stability, as indicated by a zeta potential value of over 60 mV. Additionally, a minimal amount of sedimentation was observed during the visual examination after 30 days of preparation. The SiO₂ nanolubricant exhibited a thermal conductivity of 4.42 % higher and a viscosity that is 8.72 % higher compared to pure PAO lubricant. The COF reduction exhibited the maximum value at 17.33 %, while the friction torque reduction reached its lowest value at 1.47 %. In conclusion, the SiO₂ nanoparticles significantly impact the PAO lubricant's tribological properties, reducing friction and wear while improving the thermal conductivity with little drawback with viscosity increment.