Molecular dynamics simulation on engine oil nanolubricant boundary lubrication conditions

Abstract

AbstractThe employment of nanoparticle additives in engine oil provides an effective technique for improvement in engine performance and emission. In this study, graphene, graphene–MWCNT, and graphene–SiO2 hybrid nanoparticles have been dispersed in engine oil (n‐decane) to measure the effects of microscopic characteristics of interfacial layer between the carbon–carbon, carbon–hydrogen, carbon–oxygen, and hydrogen–oxygen molecules under fixed shear rate 600 s−1. The boundary lubrication conditions are depicted with nanoindentation operation, in which interaction between the atoms generates the molecular forces under indentation and scratching operation that provide the nucleation and propagation of dislocation in the planes. The result shows that in an early stage of nanoindentation, plastic deformation occurs in the lubricant substrate around the indenter. Furthermore, forces generated in the z‐direction have a significant effect as compared with the forces x‐ and y‐directions. Nanoindentation results concluded that for graphene–MWCNT/engine oil (n‐decane) nanoparticles, at a volume fraction of 1.8%, the nanoparticles outperformed all other nanolubricants. At a volume fraction of 0.3%, the adhesion between the solid and liquid interface was increased by 2.5% graphene nanolubricant, 4% graphene–MWCNT nanolubricant, and 8% graphene–SiO2 nanolubricant. At 1.8% volume fraction, 240% increase in graphene–MWCNT nanolubricant, 72% increase in graphene nanolubricant, and 20% increase in graphene–SiO2 nanolubricant. This trend indicates that the performance of graphene SiO2 nanolubricants is superior at low‐volume fractions, whereas the performance of graphene nanolubricants and graphene–MWCNT nanolubricants is superior at high‐volume fractions. Also we observed the scratching effect of indenter on nanolubricants.