Modeling the piston ring behavior is crucial for the engine power cylinder system. The dynamic and thermal characteristics directly affect engine performance, e.g. frintion loss, wear, blowby loss, etc. This dissertation describes a numerical model of the power cylinder system focusing on the ring pack design. A three-dimensional piston ring model is developed using finite element method. The model predicts the piston ring conformability with the cylinder wall as well as the separation gap between the interfaces. In addition, the ring model also predicts the interaction between the ring and piston groove sides. This means, the ring axial lift, twist, contact with the groove sides along the circumferential direction are all calculated simultaneously with the radial conformability prediction. The numerical model is then verified through experiment measurement. This validation includes a ring tension force measurement as well as a light-tightness measurement. Good agreement has been found between the measured and calculated result. Thermal load is believed having significant influence on the ring pack performance, especially for the top compression ring, which is under the most severe operating condition. The thermal load influences are included in the model. In addition, a new lubrication model is implemented to the existing model with the consideration of flow factor for the ring pack lubrication and tribology analysis. A simulation study of the second ring dynamics for a modern diesel engine is presented. Two phenomena are focused for this study, one is the second ring fluttering and the other is ring collapse. Both these phenomena are closely related to gas dynamics and could result in engine blowby increase. The mechanism and the conditions at which these phenomena occur are given. The second ring dynamic behavior over an engine cycle is then studied considering 3D effect. The contact forces, in both radial and axial directions, and the twist angles can be found at each engine crank angle. The piston ring model provides the geometry for three-dimensional gas dynamics analysis. In addition to the gas flow paths that the current two-dimensional models predict, including through the ring end gap, through the ring-groove sides as ring flutters, through the ring front face when ring radially collapses, gas can flow through an additional path across the ring. This gas flow path is formed due to the variance of ring axial displacements along the circumference. The variant lift occurs for rings with asymmetric cross-sections. Even for rings with symmetric cross-section, the ring can also undergo different circumferential lift due to influences like piston secondary motion. When this different circumferential lift occurs, gas can flow from the piston land above the ring, through the crevice between the ring-groove sides, to the volume behind the ring for the ring segment that stays bottom seated. The gas can travel circumferentially through the volume behind the ring, until a point that the ring segments lift and stay top seated against the groove top side. Then the gas can flow from the volume behind the ring, through the crevice between the ring-groove bottom sides, to the piston land below the ring.
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