Anders Vølund

Development of a model capable of predicting the performance of piston ring—cylinder liner-like tribological interfaces

Abstract Friction in the piston ring package (piston, piston rings, and liner) is a major source of power consumption in large two-stroke marine diesel engines. In order to improve the frictional and wear performance, knowledge about the tribological interface between piston rings and liner is needed. The work described in this article addresses the subject from both an experimental and a theoretical perspective. First, a one-dimensional numerical model based on the Reynolds equation is presented. It uses a pressure—density relation for the modelling of cavitation. The viscosity is assumed to depend on a measured temperature only; thus, it is not necessary to include the energy equation. Conservation of oil is ensured throughout the domain by considering the amount of oil outside the lubricated interface. A model for hard contact through asperities is also included. Second, a laboratory-scale test rig is described. Results from a number of experimental tests with different geometries and running speeds are presented. Finally, a comparison between the measured friction force and simulated values is given. Good correlation between the measurements and the simulations has been observed, especially when running at a high speed. This article represents the first steps in the pursuit of being able to accurately model the interface between a piston ring and the cylinder liner in large two-stroke diesel engines.

Lubricant transport across the piston ring with flat and triangular lubrication injection profiles on the liner in large two-stroke marine diesel engines

A theoretical investigation of the lubricant transport across the top compression piston ring in a large two-stroke marine diesel engine is presented. A numerical model for solving Reynolds equation between the piston ring and cylinder liner based on the finite difference method in one dimension has been made. The model includes force equilibrium of the piston ring, perturbation of Reynolds equation, and transient mass conservation. The model represents a new method of achieving mass conservation across the piston ring and between different time-dependent positions. For analyzing the lubricant transport across the piston ring, two different kinds of initial lubricant profile on the liner and two different kinds of load are investigated i.e. a flat profile and an approximated triangular profile as well as no load and a combustion load based on a combustion pressure profile. The impact from the different load conditions and different lubricant profiles on the liner are presented for film thicknesses, development in the lubricant profiles on the liner as well as the lubricant consumption at each stroke.

Investigation of different piston ring curvatures on lubricant transport along cylinder liner in large two-stroke marine diesel engines:

A theoretical investigation of the hydrodynamic lubrication of the top compression piston ring in a large two-stroke marine diesel engine is presented. The groove mounted piston ring is driven by the reciprocal motion of the piston. The ring shape follows a circular geometry and the effect of changes in radii is analysed. A numerical model based on the finite difference method in 1D has been developed for solving Reynolds equation in combination with the load equilibrium equation together with flow continuity between the piston ring surface and liner for analysis of the lubricant transport. The cyclic variation throughout one stroke is presented for the minimum film thicknesses at different interesting locations of the piston ring surface together with the friction and the pressure distribution history. The aforementioned parameters have been investigated numerically. The numerical results are presented and discussed.

Discontinuity effects in dynamically loaded tilting pad journal bearings

This article describes two discontinuity effects that can occur when modelling radial tilting pad bearings subjected to high dynamic loads. The first effect to be treated is a pressure build-up discontinuity effect. The second effect is a contact-related discontinuity that disappears when a contact force is included in the theoretical model. Methods for avoiding the pressure build-up discontinuity effect are proposed.

Shaft Center Orbit in Dynamically Loaded Radial Bearings

The bearing damping coefficients may be utilized to estimate the orbit for a dynamically loaded journal bearing. The classical method for this analysis was developed by Booker [1] in 1965. Several authors have refined this method over the years. In 1966 Jorgen W. Lund [2] published an approach to find the dynamic coefficients of a journal bearing by a first order perturbation of the Reynold’s equation. These coefficients made it possible to perform a rotor-bearing stability analysis for a statically loaded bearing. In the mid seventies Jorgen W. Lund pointed out in lecture notes that the dynamic damping coefficients of the bearing could be used to find the shaft orbit for dynamically loaded bearings. The connection between the “Booker Mobility Method” and the “Lund Damping Coefficient Method” will be explained.Copyright