On the role of friction modifier additives in the oil control ring & piston liner contact

In-cylinder internal combustion engine parasitic frictional losses continue to be an area of interest to improve efficiency and reduce emissions. This study investigates the frictional behaviour at the oil control ring-cylinder liner conjunction of lubricants with anti-wear additives, varying dispersant concentration and a range of friction modifiers. Experiments are conducted at a range of temperatures on a cylinder liner with a nickel silicon carbide coating. A novel motored reciprocating tribometer, with a complete three-piece oil control ring and cylinder liner, was used to isolate the friction at the segment-liner interfaces. Four lubricants were tested, three with the same 3% dispersant concentration and 1% ZDDP anti-wear additive: the first with no friction modifier, the second with inorganic friction modifier (molybdenum dithiocarbamates), and the third with organic friction modifier (amide). A fourth lubricant with organic friction modifier with a 9% dispersant concentration was tested to compare the effect of the level of dispersant with the friction modifier. Results indicate that the inorganic friction modifier reduces friction comparatively to the other lubricants, showing the importance of friction modifier selection with anti-wear additives.