Performance evolution of a worn piston ring

Abstract

Abstract Reducing the fuel consumption of a combustion engine has been an important design issue. Engine friction has to be reduced and the piston ring - cylinder liner contact is a major source of friction. However, the piston ring geometry can evolve due to wear, and the ring can acquire a flat part. The current work analytically studies the hydrodynamic friction and load carrying capacity of a twisted parabolic - flat (worn) piston ring. The outcome is presented as a function of twist angle, total width and flat width. With the chosen functional parameters of the piston ring, the evolution of stroke-averaged friction and film thickness with wear (increasing flat width) is studied. One finds that the hydrodynamic friction increases with initial piston ring wear, but the minimum thickness of the generated film increases as well. This ensures the ring can continue to operate safely and last. Imposing a constant film, the hydrodynamic friction can be reduced a little for wide rings by using a narrower parabolic-flat ring. No such reduction is possible for narrow rings.