Piston friction analysis using a direct-injection single-cylinder gasoline engine

Reducing piston friction is an effective means for engine friction improvement. A recent report indicated that, indirect-injection engines, the fuel sprayed on the cylinder bore surface (which "wets" the cylinder) affects piston lubrication. The analyses of piston friction together with lubrication behavior will accordingly become increasingly important. This study focused on the influences of cylinder wetting on piston friction characteristic through the use of a direct-injection single-cylinder engine. The study revealed that cylinder wetting reduces piston friction during the compression stroke, and that this phenomenon can be explained by the lowered oil viscosity on the cylinder bore surface caused by fuel wetting. (C) 2003 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.