Effects of Lubricant and Piston Design on Reciprocating Engine Friction

Abstract

The piston and rings generate a significant fraction of the total friction in a reciprocating engine, with comparable contributions from the rings and from the piston. In order to develop strategies to reduce overall engine friction, a piston model was used to examine the effects of lubricant, piston design, and material surface characteristics on piston friction. The analysis was performed on a large-bore reciprocating natural-gas engine. First, opportunities in friction reduction via lubricant supply and lubricant formulation were evaluated. This was done by studying how oil film thickness, viscosity, and its temperature dependence affect piston hydrodynamic and boundary-contact friction. Piston design parameters investigated include piston skirt profiles that are more realistic and varied than those previously studied. The piston material was also analyzed in terms of surface waviness. The results show how individual design parameters can be combined to generate the aggregate benefit in engine friction reduction.