This paper presents two piston ring and cylinder liner lubrication models and compares the friction predictions against the experimental results from a corresponding bench test. The first model aims to solve the average Reynolds equation with corrective flow factors, which describe the influence of surface irregularities on the lubricant flow under mixed lubrication condition. The second model takes account of the lubricant film rupture and cavitation. Meanwhile, a stochastic rough contact sub-model quantifies the relation between contact pressure and mean surface separation in both cases. Numerical results on the top compression ring simulation show that both models capture hydrodynamic, mixed, and boundary lubrication regimes, which depend on the real surface topographies of the piston ring and the cylinder liner. Whenever hydrodynamic action is insufficient to maintain the equilibrium position of the ring, the restoring force will be augmented by multi-asperity contacts lubricated by a thin boundary film. Total friction will originate mainly from shearing of viscous lubricant and shearing of asperity conjunctions. The purpose of this modeling effort is to compare both lubrication models to data from an experimental test-rig. This test rig eliminates many of the factors that can make analysis of predictions for real engine operating conditions difficult.

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