An Experimental Study on Relationship between Lubricating Oil Consumption and Cylinder Bore Deformation in Conventional Gasoline Engine

It is well known that lubricating oil consumption (LOC) is much affected by the cylinder bore deformation occurring within internal combustion engines. There are few analytical reports, however, of this relationship within internal combustion engines in operation. This study was aimed at clarifying the relationship between cylinder bore deformation and LOC, using a conventional in-line four-cylinder gasoline engine. The rotary piston method developed by the author et al. was used to measure the cylinder bore deformation of the engine’s cylinder #3 and cylinder #4. In addition, the sulfur tracer method was applied to measure LOC of each cylinder. LOC was also measured by changing ring tension with a view to taking up for discussion how piston ring conforms to cylinder, and how such conformability affects LOC. Their measured results were such that the cylinder bore deformation was small in the low engine load area and large in the high engine load area. In particular, it was shown that there was a different tendency in deformation between cylinder #3 and cylinder #4 around the top dead center. Whereas there was not a large difference between cylinder #3 and cylinder #4 in LOC, as ring tension was lowered and overall LOC was on the increase. We then made a calculation of ring oil film thickness, using a model to predict a ring’s conformability considered cylinder bore deformation. The results were used to calculate the rate of oil flow into a combustion chamber, and the rate of evaporation of oil from a cylinder wall. This verified that a low tension ring conformed to a cylinder less, while ring oil film got thicker. In addition, as oil film got thicker, the rate of oil flow increased, however, there was not a noticeable change in the rate of evaporative oil. From the above, we can conclude that changes in ring tension are affected when a ring conforms to a deformed cylinder, which in turn affects LOC.