  The Piston-Ring-Liner system is the main tribological component of internal
combustion engines. The Elrod-Adams model is customarily used to numerically
assess the hydrodynamics of different ring designs and liner surface
treatments. However, that model does not incorporate the backpressure boundary
condition, which in this case corresponds to the combustion chamber pressure
and is quite significant. In this contribution a model is proposed that imposes
the combustion-chamber pressure in a mass-conserving way, together with an
effective algorithm for its numerical approximation. The new model incorporates
the pressure difference across the ring, which is shown to have a substantial
effect on the predicted friction force and MFT. The model is further elaborated
so as to provide a criterion for predicting blow-by inception.
