Modeling Piston-Ring Dynamics, Blowby, and Ring-Twist Effects

TLDR

A coupled ring‑dynamics and gas‑flow model for a three‑ring piston pack simulates ring contact, oil film thickness, and gas pressures, incorporating static and dynamic twists and keystone configurations to resolve events such as ring flutter. Experiments show that static twist and keystone ring‑groove configurations strongly affect ring contact, stability, blowby, and wear, with negative static twist inducing ring flutter in spark‑ignition engines and altering twist behavior in diesel engines.

Abstract

A ring-dynamics and gas-flow model has been developed to study ring/groove contact, blowby, and the influence of ring static twist, keystone ring/groove configurations, and other piston and ring parameters. The model is developed for a ring pack with three rings. The dynamics of the top two rings and the gas pressures in the regions above the oil control ring are simulated. Distributions of oil film thickness and surface roughness on the groove and ring surfaces are assumed in the model to calculate the forces generated by the ring/groove contact. Ring static and dynamic twists are considered, as well as different keystone ring/groove configurations. Ring dynamics and gas flows are coupled in the formulation and an implicit scheme is implemented, enabling the model to resolve detailed events such as ring flutter. Studies on a spark ignition engine found that static twist or, more generally speaking, the relative angle between rings and their grooves, has great influence on ring/groove contact characteristics, ring stability, and blowby. Ring flutter is found to occur for the second ring with a negative static twist under normal operating conditions and for the top ring with a negative static twist under high-speed/low-load operating conditions. Studies on a diesel engine show that different keystone ring/groove configurations result in different twist behaviors of the ring that may affect the wear pattern of the keystone ring running surfaces.