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A theoretical model was developed to better understand the lubrication of piston rings. Models like this are important for studying oil consumption and its contribution to emission. The model suggests that temperature gradients and viscous heating in the oil film can be neglected if it is assumed the oil is the same temperature as the cylinder wall. A simple model suggests that vibrations will not affect the calculated film thickness significantly. Oil film thickness was measured in a Cameron Plint wear test rig and in a diesel engine. Evidence of oil starvation was observed in both tests. Measured and predicted film thickness correlated well on the wear test rig. Engine tests showed some unexpected trends, however the theory predicts oil film thicknesses of the same order of magnitude as the measured results. Measured results showed that separation occurs at the rear boundary of the ring. For modelling, the Reynolds boundary condition has the best correlation with experimental data.

Inter-ring gas pressures and blowby in a diesel engine were investigated analytically and compared to experimental data measured at three engine speeds. Coupled simulations of ring dynamics, ring lubrication and inter-ring gas dynamics were carried out using the RINGPAK software, a code for the integrated analysis of ring pack performance and tribology. Inter-ring pressures and ring dynamics are known to have an important effect on the “blowback” mechanism of in-cylinder oil consumption, i.e. that of oil-laden gas flow from the ring lands into the cylinder. Predicted land pressures matched the experimental results very well qualitatively as well as quantitatively. The coupling between ring motions and inter-ring gas pressures and blowby, a key feature of the methodology, was seen to be crucial in obtaining agreement with detailed features of the land pressure data.