Fang, T. and Tian, T., "Oil Transport from Scraper Ring Step to Liner at Low Engine Speeds and Effect of Dimensions of Scraper Ring Step," SAE Int. J. Fuels Lubr. 9(1):48-58, 2016, doi:10.4271/2016-01-0495.
In gasoline engines, a scraper ring with a step on the bottom outer edge is widely used as a second ring. However, there lacks a fundamental understanding on the effects of this feature and its dimensions on oil transport. Inspired by observations from visualization experiments, this work combining computational fluid dynamics (CFD) and theoretical analysis shows that oil can be trapped in the space bordered by a second ring step and the chamfer of a piston third land. The trapped oil can be released to a liner when the piston is approaching the top dead center (TDC). This additional oil on the liner becomes a potential source of oil consumption. Such oil transport has been observed at typically less than 1500rpm. Since road vehicles often operate in this speed range, the newly-observed oil trapping and release can be closely associated with oil consumption in gasoline engines. In this work, a comprehensive study on oil trapping and release will be demonstrated. Computational simulations indicated that oil trapping resulted from the balance between surface tension and inertia. A theoretical model based on the primary physics will be demonstrated. The modeling results satisfactorily matched with experiments and computational simulations. The model indicated that oil trapping in a scraper ring step, as well as oil release to a liner, can be controlled by the geometry of the step. Effects of a few dimensions of a scraper ring step will be described.