Oil Film Thickness Measurements Combined with High Temperature Friction Investigations in a Simplified Piston-Ring Lubrication Test Rig

Abstract

The effect of lubricants properties in oil film thickness was evaluated and linked to performance limitations in view of cavitation appearance, its initia Ccapacitance tion and development. The piston-ring and the cylinder liner interface are characterized in terms of oil film thickness measurements. Study of cavitation in lubricants and its rheology were presented in previous studies and results of different lubricants, speed, load, temperature and piston-ring curvatures were assessed to achieve useful tribological engine data that apply to the piston-cylinder assembly. The evaluation of new designs that can be applied to the ring/liner interface and many future parametric studies that can be combined with surface modifications in both parts of the assembly are under examination. The use of a simplified single-ring test rig that utilizes a steady piston-ring section of overall width 5 mm placed under a flat liner surface that reciprocates instead, takes advantage of significantly less uncertainties when compared to engine experiments. Minimum oil film thickness measurements (MOFT) is studied for different lubricants as a variation of temperature and simultaneously friction high temperature results for the whole stroke length are presented. Measurement transducers for the separation of the metal surfaces (liner and piston-ring) and the friction force developed in the contact surfaces were the conventional methods used. Within certain parts of the stroke where friction reaches its maximum value, a greater focus is given to evaluate the effect of different operating conditions. Useful conclusions are drawn regarding lubricants behavior under cavitation that can be used to new additives design and enhancement of lubricant physical-chemical properties that have the potential to conform to the even stricter emission regulations that will apply in the future.

Keywords

• piston-ring lubrication
• single-ring test rig
• oil film thickness
• friction force measurements
• capacitance
• cavitation