A Visual Study of Cylinder Lubrication 460084

A V-type engine provided with a glass cylinder was used to study visually the lubrication characteristics of an aircraft-type piston. Photographs and data were obtained with the engine motored at engine speeds up to 1000 rpm and constant cylinder-head pressure from 0 to 50 pounds per square inch.
A study was made of the orientation of the piston under various operating conditions, which indicated that the piston was inclined with its crown nearest the major-thrust cylinder face throughout the greater part of the cycle. The piston moved laterally in the cylinder under the influence of piston side thrust.
The data and photographs indicate that the lubrication of the piston skirt, under the conditions of the present experiments, is hydrodynamic in nature for at least a part of the stroke. Definitely wedge-shaped oil films were photographed and correlated with piston-orientation data.
The amount of lubricant present on the piston skirt was observed to be a function of two variables: one, the relative angular positions of the piston rings; the other, the lateral motion of the piston. Rate and direction of piston-ring rotation varied with cylinder-head pressure and engine speed. Piston rings were observed to rotate as rapidly as 1 rpm at an engine speed of 1000 rpm. The oil film on the face of a piston ring was estimated to be 0.0001 inch thick or less.


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