Superior tribological performance of graphene-enhanced lubrication in the piston ring -cylinder liner interface of internal combustion engine

Friction and wear at the interface between the piston ring and the cylinder liner of an internal combustion engine remain critical challenges in improving engine efficiency and durability. To address this issue, continuous efforts have been made to enhance the tribological performance of the liner/ring pair using various anti-wear and extreme pressure additives in engine oil. This study explores the synergistic impact of graphene nanoplatelets (GNPs) as nano-additives in polyalphaolefin (PAO) oil lubrication with T6-tempered, rapidly solidified hypereutectic Al-25Si alloy as cylinder liner. Testing was performed under an applied normal load of 50 N and a sliding frequency of 5 Hz, using 0.5 wt% GNPs as a nano-additive in PAO oil. The incorporation of GNPs into PAO oil led to an ultra-low coefficient of friction (CoF ∼ 0.04) and wear (2 × 10 −15 m 3 /Nm), corresponding to a 51.8% and 94.9% reduction, respectively, compared to dry sliding conditions. Analysis revealed that this improvement in tribological performance is attributed to the adsorption of GNPs at the contact surfaces, minimizing direct asperity interactions and enhancing load-bearing capacity by forming a protective tribofilm. Additionally, the shearing and exfoliation of GNPs contribute to a reduction in the coefficient of friction. These findings highlight the effectiveness of GNPs as oil additives, offering a promising approach to enhancing the durability and performance of highly stressed automotive components.