Investigation of cavitation development in the lubricant film of piston-ring assemblies

The piston-ring assembly is one of the most loaded internal combustion engine subsystems. Inadequate film characteristics between the ring and the liner may result due to a number of reasons. The relative motion between these components replenishes the lubricant, but it also generates cavitation conditions at the outlet of the ring-liner conjunction. The onset as well as the development of cavities is heavily dependent of the relative velocity. At higher velocity the cavitation region develops later and lasts longer. Therefore, to predict the cavitation behaviour, the mechanisms of oil film formation and pressure distribution should also be considered. Cavitation conditions are expected to occur when the local lubricant pressure drops below the vapour saturation pressure. Ideally such experiment is performed in a combustion engine under firing conditions. However, the main disadvantage of such an approach is the complexity required to decouple individual contribution of separate physical phenomena. The current research proposes an experimental technique where the cavitation is monitored in a test rig which simulates the lubrication conditions in a piston-ring assembly. Simultaneous measurements of the oil film pressure and oil film thickness are compared with fast speed camera recordings.