Physicochemical properties and tribological performance of motorbike lubricant dispersed with surface-modified WS2 nanoparticles

This paper investigates the effect of dispersion of surface-modified WS2 nanoparticles on the tribological performance and physicochemical properties of motorbike lubricant. Surface-assisted WS2 nanoparticles were dispersed in motorbike engine oil and an optimum amount of surfactant for best stability of the lubricant suspension was found by investigating the changes in the physicochemical properties of lubricant. The stability analysis using light scattering techniques confirmed the stability of nanoparticles dispersed in lubricant medium and surface-modified WS2 nanoparticles remained stable for 180 days. The physicochemical properties were evaluated as per ASTM standards over a period of two months to check the state of lubricant and observable changes in the properties during this period. The tribological performance of the lubricants was assessed by conducting endurance tests on a 100 cc motor bike. The performance was evaluated by checking the wear of the engine components and fuel consumption. It was found that there were no abnormal changes in the physicochemical properties of lubricant up to a certain surfactant to nanoparticle ratio indicating its utility in automotive engines. However, if the amount of surfactant was increased beyond optimum quantity abnormal changes are seen in the viscosity index, leading to the deterioration of key lubricant properties. Lubricant dispersed with WS2 nanoparticles gave good performance characterized by the reduction in both engine wear and fuel consumption. Worn surfaces of the oil rings after the endurance test were assessed for deposits and it was found that a layer of WS2 deposited on the oil ring surface that reduced friction and wear.