A numerical study of piston ring lubrication in internal combustion engines

A comprehensive numerical simulation of piston ring lubrication in an internal combustion engine is presented. Both one-dimensional and two-dimensional numerical models are developed. Each numerical model includes cavitation with elastohydrodynamics to evaluate the lubricant film thickness and hydrodynamic pressure. Using the one-dimensional model the cavitation and elastohydrodynamic effects were found to lead to thicker oil films than predicted in previous studies. The thicker films were prominent when the gas pressure at the trailing edge of the piston ring is high, especially near the position of top dead center.; The basic one-dimensional model was extended to two-dimensions by including circumferential flow effects. An approach was developed which linearizes the governing equation to eliminate numerical oscillation and improve convergence. Two cases were investigated to simulate piston ring performance: a rigid ring and an elastic ring in a slightly worn elliptic cylinder. It was found that the circumferential flow induced by the worn cylinder causes a hydrodynamic pressure drop which reduces the piston ring load carrying capacity and the oil film thickness. The deflection analysis demonstrated that the piston ring was able to conform to the shape of the worn cylinder. However, the accommodation was not perfect and consequently creates the potential for the combustion chamber gases to escape through the piston ring clearance area.; The friction force between the piston rings and the cylinder liner was also investigated under starved conditions. A moderate friction force, induced by shearing resistance due to a thicker oil film thickness than the surface roughness of piston ring and cylinder liner, was found. However, a sharp increase of friction force around top dead center was predicted because of boundary lubrication domination due to severe reduction of the oil film thickness.; The numerical methods of this work can be used to better simulate piston ring and piston ring package lubrication and can lead to better piston ring design.