A study of lubrication mechanisms using two-phase fluids with porous bearing materials

A potential, novel lubrication mechanism involving two-phase fluids and porous bearing materials is examined in this study both theoretically and experimentally. Lubricating oils with a secondary particulate phase have been considered operating in oil-saturated porous media with the elements of the particulate phase acting as one-way valves on the pores, blocking and unblocking them, depending on the direction of contact load. The goal is to enhance the lubrication, mainly in starved contacts and in some ‘difficult’ applications, as for example in big end bearings for marine engines. The theoretical part of this work deals with the mathematical analysis of an oil-saturated, porous slab, in contact with a solid sphere and lubricated with a two-phase oil containing thin and soft platelets. The problem is analysed using Biot's theory of consolidation in porous media. A subsequent study deals with the effects of the maximum contact load, size, and number of pores of the porous medium, elastic modulus of the medium, and the viscosity of the oil used to carry the particulate phase, on the lubrication performance of the system. Furthermore, a rig was built to study the concept on a macroscale and the results are reported in the paper. Both the theoretical and the experimental work gave good indications that the concept works, at least in some cases. Potential problems with application of this lubrication mechanism have also been identified and are briefly discussed in the paper.