A computational chemistry approach for friction reduction of automotive engines

To improve the fuel efficiency of automobile internal combustion engines, the friction reduction of each engine moving part is important. Recently, carbon films have been attracting much interest as surface-coating materials due to its excellent properties such as low friction and good wear resistance. In this study, the low-friction mechanisms of carbon films were analyzed using molecular dynamics simulations and density functional theory calculations. Molecular dynamics simulation results showed that the termination of OH groups on the surface of the diamond substantially reduced the friction coefficient from 0.07 to 0.01. This reduction was achieved because termination of OH groups weakened the covalent interaction between Fe and C atoms, which was indicated by density functional theory calculations. Additionally, based on the concept of terminating the OH groups on the surface of diamond-like carbon films, we carried out the reciprocating friction experiment between hydrogen-free diamond-like carbon surface and glycerin, which contains large number of OH groups. The friction coefficient of the glycerin was 0.028, much lower than that of the base oil, which was 0.075. The experiments confirmed that OH groups on the surface of hydrogen-free diamond-like carbon films greatly improved the friction properties of its films.