Thermo-mixed lubrication analysis of coated compression rings with worn cylinder profiles

Abstract

Purpose Compression rings are the main sources of frictional losses in internal combustion engines. The present paper aims to present a thermo-mixed hydrodynamic analysis for coated top compression rings. To understand the coating effects, the main tribological parameters are investigated into a ring-cylinder conjunction in a motorbike engine. Furthermore, flow simulations have been carried out on how different worn profiles on the cylinder inner liner affects friction, lubricant film and localized contact deformation of the coated compression rings. Design/methodology/approach In this paper, the basic geometrical dimensions of the top compression ring-cylinder system are obtained from a real motorbike engine. A 2D axisymmetric CFD/FLOTRAN model is created for coated compression rings. Flow simulations are performed by solving the Navier-Stokes and the energy equations. The load capacity of the asperities is also taken into account by Greenwood and Tripp contact model. Realistic boundary conditions are imposed to simulate the in-plane ring motion. The simulation model is validated with analytical and experimental data from the literature. Under thermal considerations, the contribution of worn cylinder profiles in conjunction with different coated compression rings is presented. Findings This research shows that because of thermal effects, the boundary friction is higher at reversals and the viscous friction is lower because of reduced oil viscosity. As regards to the isothermal case, the viscous friction is greater because of a higher lubricant viscosity. In the case of chromium-plated ring, boundary friction was 16 per cent lower than a grey cast iron ring taking into account thermal effects. Regarding the localized contact deformation, the coated compression rings showed lower values under different worn cylinder shapes. In particular, hard wear-resistant (Ni-Cr-Mo) coating showed the slighter local deformation. Therefore, the worn cylinder profiles promote boundary/mixed lubrication regime, whereas the lobed profile of cylinder inner liner becomes more wavy. Originality/value The solution of the thermo-mixed lubrication model, concerning the piston ring and worn cylinder tribo pair by taking into account the coating of the top compression ring.

An Improved Lubrication Model between Piston Rings and Cylinder Liners with Consideration of Liner Dynamic Deformations

“…Reipert and Voigt [6] proposed that the magnitude of the thermal expansion is greater by far than the distortion caused by the clamping of cylinder head bolts. Zavos and Nikolakopoulos [3] have suggested that small thermal deformation will lead to less friction and wear in the cylinder liner. However, the thermal expansion is primarily a quasi-static deformation, with good radial continuity, which cannot cause obvious dynamic localised deformation on the liner surface, and therefore cannot cause direct impact on the friction and lubrication behaviour between piston rings and liner surface.…”

“…wherein η 0 is the lubricant viscosity at atmospheric pressure and ambient temperature 40 • C, p is the pressure, and Z and S are the dimensionless viscosity-pressure coefficient and viscosity-temperature coefficient, respectively, which can be calculated according to the literature [3,23]. T 0 is the ambient Energies 2017, 10, 2122 9 of 22 lubricant temperature, and the lubricant temperature T is calculated based on a series of heat flow balance equations [1,3,24].…”

“…T 0 is the ambient Energies 2017, 10, 2122 9 of 22 lubricant temperature, and the lubricant temperature T is calculated based on a series of heat flow balance equations [1,3,24].…”

“…Research on modelling of cylinder liner and piston ring tribological behaviours has been developed for decades. In modelling oil film formation and distribution on the cylinder liners, the cylinder wall is often taken as being a perfect cylindrical surface by the majority of researchers [1][2][3]. These studies believe that the deformation of cylinder liner does not directly affect the formation and distribution of the oil film, and thus does not affect the friction and lubrication behaviours.…”

Wear Analysis of Top Piston Ring to Reduce Top Ring Reversal Bore Wear

“…The effect of wear on tribological characteristics were also included in the study. Zavos et al [31] used Navier Stokes equation and experimental data from 2 Stroke engine. Surface irregularities are measured by using Coordinate Measuring machine (CMM).…”