Tribological evaluation of passenger car engine oil: Effect of friction modifiers

The tribo-performance of passenger car engine oil with three friction modifiers (organic and inorganic) has been experimentally evaluated using benchtop tribometers. Friction coefficient traces and wear and contact potential (qualitative measurement of lubricating film formation) were reported at varying contact pressures, speeds, and temperatures. The in situ film-forming characteristics of friction modifier in engine oil were also investigated and reported using SLIM (Spacer layer imaging) in a Mini traction tribometer. Overall, inorganic friction modifiers (MoDTC) yielded better tribological performances than organic friction modifiers. Typically, thicker protective tribo-film (180 nm) formed at the worn surface by MoDTC than organic friction modifiers (80–120 nm). Scanning electron microscopy (SEM), Raman spectroscopy and Atomic force microscopy (AFM) have been utilised to characterise the worn surfaces and understand the mechanism behind the protective tribo-film formation.