Mass-Conserving Numerical Simulation of Piston Ring/Liner Contact Along a Full Engine Cycle

Abstract

Of great concern for the automotive industry is the power lost to friction in the reciprocating components, in particular at the piston ring/liner contact. The piston rings seal the space between the piston and the liner, and act essentially as slider bearings subject to alternating motion. The numerical assessment of the ring/liner contact is very challenging due to the dynamical interaction of the oil film with the elastic rings, and the significant effect of cavitation and starvation phenomena. Important precedents can be found in the work of Priest and coworkers (e.g.; Proc. Inst. Mech. Engrs. 214:435-447, 2000).
In this article we report, to our knowledge for the first time, numerical simulations of the pistonring assembly along a full engine cycle with a conservative formulation that is not restricted to onedimensional configurations. We consider realistic applied loads on the rings, the actual crankshaftconnecting rod kinematics, and study both untextured and striated liners. It is shown that the rings’ dynamics is strongly affected by starvation along the downwards strokes of the piston (intake, blow), leading to solid-solid contact of the compression ring. The effect of both transverse and oblique striations on this dynamics is assessed. The former induces an unstable behavior of the wiper ring, while the effect of the latter is more benign and indeed brings improvement at some parts of the cycle.
A brief discussion on the work that is still needed to accurately compute ring/liner lubrication is included as closure, with emphasis on the pitfalls of available mathematical models and on the numerical difficulties involved.