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To elucidate the behavior of oil film on the piston land, the visualization experiments around the piston using an optical engine with a glass liner was conducted. The photochromic visualization technique was successfully applied. The oil film above the top ring gap moved toward the piston head under each throttle condition. The oil film velocity in each engine stroke was successfully calculated from the image processing, and it was confirmed that the direction of movement and the velocity is different with the throttle condition and the engine stroke. The rapid transport of oil film on the 2nd land under the engine brake like condition was captured and it was supposed that this type of oil transport phenomena is the cause of high oil consumption under engine brake condition.

Offsetting the crankshaft axis with respect to the cylinder axis has been thought to be a method to reduce piston side force[1]. Hence the piston friction is expected to be reduced. An automotive manufacturer has already used the crankshaft offset for a production gasoline engine to improve fuel economy. The authors have conducted research into the effect of crankshaft offset on the piston friction. A single-cylinder engine was modified to have a crankshaft offset. Piston frictional force was measured in real-time by using a floating liner method. In addition, laser-induced fluorescence (LIF) technique was employed to measure oil film thickness on the piston skirt area, and a gap sensor was used to measure piston motion. As a result, the authors concluded that the effect of crankshaft offset on piston friction could not be explained only by its effect on the piston side force. In accordance with the measurement results, crankshaft offset changed piston slap motion.