Tribological enhancement of synthetic compressor lubricants using SiO₂ nanoparticles

Abstract

Electric-vehicle (EV) air-conditioning compressors operate under stringent thermal and tribological demands, necessitating lubricants that ensure high stability, low friction, and reliable thermal management. Despite increasing interest in nanoparticle-enhanced lubricants, the influence of base-lubricant chemistry on nanoparticle stability, thermal conductivity, and tribological performance remains insufficiently understood. This study evaluates the stability, thermal behaviour, and tribological performance of SiO 2 nanolubricants formulated in POE, PVE, and PAO base lubricants to identify the most effective lubricant platform for EV air-conditioning compressors. SiO 2 nanoparticles were dispersed at concentrations of 0.005 to 0.030% volume concentration in POE, PVE, and PAO lubricants, and their colloidal behaviour was characterised. Thermal conductivity was assessed at 30-100°C to quantify heat-transport enhancement. Tribological performance was evaluated using four-ball tests to determine frictional torque, coefficient of friction (COF), operating temperature, and wear scar diameter (WSD). Tribologically, SiO 2 /PAO exhibited the largest reduction in frictional torque and the lowest steady COF, corresponding to a 37% decrease relative to the base lubricant. The SiO 2 /PAO nanolubricant also achieved the smallest WSD, representing a more than 19% reduction in wear, while PVE produced reductions of 1 to 5% and POE below 4%. The results collectively highlight PAO as the favourable base lubricant platform for maximising nanoparticle effectiveness.