Piston Ring and Groove Side Wear Analysis for Diesel Engines

Abstract

Piston ring wear is a major factor determining a diesel engine’s life. A ring is subjected to wear between its front face and the cylinder wall as well as at the interfaces between the ring and groove top and bottom flanks. In many modern engines, ring and groove wear are becoming more of a limiting factor for ring durability than face wear. The focus of this paper is on ring to groove side wear only. In this paper two fundamental mechanisms for ring/groove side wear are identified: (1) wear due to piston secondary motion and (2) wear due to ring twist. The time in the cycle where each of these mechanisms results in maximum wear is shown. Then the effect of ring static twist and the resulting effect on the pressure distribution around the ring are studied. The pressure distribution affects the force acting on the ring that causes the ring/groove side wear. It is also shown that the pressure distribution and the resultant wear can be influenced by the land diameter below the piston ring. Progressive wear is also studied, showing a good correlation between predicted wear and measured wear on both ring sides and groove sides. It is noted that as the corner of the ring/groove wears, the ultimate wear of the ring side can accelerate by a phenomenon named pressure infiltration. Pressure infiltration occurs because the bottom side of the ring groove wears exposing more of bottom side of the ring to lower pressure force. This ultimately causes a higher difference between the high pressure above the ring and the low pressure below the ring. As a result, the net force acting on the ring increases and wear increases. In addition to the study of the first ring, the second ring wear was studied. A comparison was made between the top ring and second ring groove side wear (RGSW) predictions. Also the effect of the second ring static twist on both top and second ring/groove side wear is described in detail.