The operating environment for piston rings in modern diesel engines continues to become more severe. Engine manufacturers are not only making changes to the engine to meet the government mandated emissions standards, but at the same time they are increasing both engine efficiencies and specific power levels. In order to meet these performance demands, Peak Cylinder Pressures (PCP) are increasing and piston compression heights are being reduced. These changes require significant upgrades to the Power Cylinder Unit (PCU), including piston and piston ring pack, as historic solutions no longer provide the robustness required for the next generation high output diesel engines.

Much attention has already been paid to improving top compression ring technology [1]. This paper will instead focus on how the lower compression ring and oil control ring are impacted by these increasing demands; as well as how design changes to these rings can help the engine manufacturers meet their performance goals. Changes to ring base material, ring face coatings, and running surface geometries will be explained along with a brief discussion about the influence of the ring’s boundary conditions and the changes that are simultaneously being made to surrounding components. These recommendations will be supported with bench test, simulations using the MIT ring pack code [2], and engine test results using numerous MDD/HDD engines.

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