Performance evolution of a worn piston ring

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.