Abstract:
The coating of low coefficient of friction protects the lubricant-starved dry surface of the
piston skirts against wear in a low-load and low-speed initial engine start-up. Despite a
relatively large radial clearance, a physical contact between the skirts and the cylinder liner
causes an elastic deformation. A hydrodynamic or elastohydrodynamic (EHL) film may also
break due to unusual operating conditions. This study develops the numerical piston
dynamics model by incorporating the secondary piston displacements of the skirts during the
720-degree crank rotation cycle. The study also models the 2-D hydrodynamic and EHL of
the un-coated and the solid lubricant coated piston skirts separately. The numerical models
couple the secondary piston dynamics with the hydrodynamic and EHL models. The contact
zone in the boundary-value problem is discretized using the finite difference method and
solved Navier /Lame equation numerically by successive-over-relaxes (SOR) method. The
secondary piston and oil lubrication parameters are plotted as function of 720-degree (04
stokes) crank rotation cycle. The simulation results show that the dry piston skirts establish a
physical contact with the liner during the compression stroke that remains in the expansion
and exhaust strokes. The elastic displacements of coating prevent the stress accumulation on
the substrate and protect it from adhesive wear. The solid lubricant film facilitates towards
achieving an effective lubrication of the skirts and a more uniform pressure distribution to
prevent adhesive wear in the low-speed initial engine start up
