Friction Response of Piston Rings for Application-like Starvation and Benefit of Amorphous Carbon Coatings

The oil supply at the interface between the top ring and the cylinder liner (TRCL) plays a major role in an internal combustion engines efficiency. In particular, the interface forms a trade-off between the serving of enough lubricant for sufficient lubrication conditions and emissions through subsequent combustion. This can lead to deficient top ring lubrication conditions. In this study, a new developed reciprocating long-stroke tribometer, enabling the variation of oil supply, is used to investigate such application-like starved lubrication conditions of the TRCL interface. With the simulative investigations, a comparison with the fired engine is possible. The performance of diamond-like carbon coatings is compared to standard nitrided piston rings. It was found that the tetrahedral amorphous carbon (ta-C) coatings exhibit up to 31% reduced friction as well as a lower wear under starved lubrication conditions. Simulative investigations show a good correlation between engine friction and tribometer measurements for selected oil supply conditions.

Automated summary

Oil supply at the interface between the top ring and the cylinder liner (TRCL) is crucial for internal combustion engine efficiency, but insufficient lubrication conditions for the top ring can occur. This study found that tetrahedral amorphous carbon (ta-C) coatings perform better in terms of friction and wear under starved lubrication conditions.