Lubrication analysis of the piston ring of a two-stroke marine diesel engine considering thermal effects

Abstract

Thermal deformation of the cylinder liner (TDCL) and the temperature–viscosity effect (TVE)of the lubricating oil are two common thermal effects which impact the lubrication properties of the piston-ring–liner tribological pair. In this study, the influence of these two thermal effects in a low-speed two-stroke diesel engine on piston ring lubrication performance are discussed in detail. For the TDCL, a steady-state heat-transfer model based on sequential fluid–solid coupling is used to solve for the heat-transfer coefficient and temperature on the coupling surface between the cylinder liner and the cooling water jacket. The boundary condition used to calculate the TDCL is the temperature distribution on the inner surface of the cylinder liner calculated empirically and verified experimentally. For the TVE, experimental data measured using capillary viscometers are used to determine the coefficients in four different empirical viscosity–temperature formulas, then the experimental and simulation results for TVE are compared using correlation coefficients and average absolute relative errors. Ultimately, the American Society for Testing and Materials (ASTM) model is selected to describe the viscosity–temperature characteristics of the lubricating oil used in this research. The results of the TDCL and the ASTM model are used in the lubrication model to analyze how the thermal effects influence the lubrication performance of the piston-ring–liner tribological pair.