Oil transport mechanisms in piston ring assembly: CFD analysis with consideration of ring motion and deformation

Abstract

The dynamic design of piston rings and cylinder liners critically influences engine performance, durability, and reliability. While experimental validation of blow-by gas and oil transport remains challenging due to high costs and limited visualization capabilities, numerical analysis has emerged as a robust alternative. This study investigates oil transport in the piston ring assembly using a fluid model driven by prescribed ring deformation and motion. A refined 2D CFD framework, incorporating piston ring dynamics, deformations, and localized mesh refinement, was developed and validated using a 4.5L diesel engine under rated conditions. Key findings reveal: (1) During ring flutter, intensified gas flow through the back clearance facilitates oil renewal, removing carbon deposits. (2) Ring collapse disrupts the oil wedge on the ring-liner interface, increasing oil stripping and degrading lubrication. (3) Ring twist enhances axial stability by promoting line contact with the liner and oil wedge formation at angular regions, improving run-in and lubrication. (4) Further analysis of a throttle-equipped diesel engine under low load demonstrates that in-cylinder negative pressure induces a 6.3% rise in oil accumulation during intake, directly linking throttling-induced vacuum to elevated oil consumption. This study establishes a fluid modeling methodology driven by prescribed deformation and motion of the piston ring assembly, aiming to optimize ring dynamic characteristics and address critical challenges in oil control and lubrication for advanced engine designs.