Simultaneous Film Thickness and Friction Measurement for a Piston Ring-Cylinder Contact

A significant part of the total parasitic loss in an internal combustion (IC) engine is due to the piston ring and cylinder liner friction. In this work, a piston ring-liner reciprocating test rig combined with non-invasive ultrasonic film thickness measurement system was used to understand frictional characteristic of the lubricant and the lubrication regime in the contact. Two test procedures were performed for three lubricants with different viscosities. These procedures were a step load increment at a constant speed and a step speed increment at a constant load. The results showed that minimum oil film thickness under the ring increased with speed and decreased with load but friction coefficient followed various trends depending on the viscosity of the lubricant.