The effects of piston skirt profiles on secondary motion and friction

Piston skirt form deviating from a perfect cylinder is investigated numerically for an improved frictional performance. Three features defining the barrel and oval form of the skirt are compared in the search for lower friction power loss. Radius of curvature around the bulge of the barrel is changed to obtain a flatter or more-rounded lubricated area with respect to a hot-piston profile as well as the axial location of this bulge. On the other hand, the circumferential variation in the separation between the skirt and cylinder wall is represented by an elliptical piston and the aspect ratio is varied for comparison. These different skirt profiles are used in a developed piston secondary dynamics model solving for the lateral movement of the piston by calculating the hydrodynamic and boundary normal forces acting on the piston together with friction. Finally, an improved skirt profile is suggested to obtain better frictional efficiency.