| Summary: | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012. === Cataloged from PDF version of thesis. === Includes bibliographical references (p. 187-192). === In piston ring pack design, there is a tradeoff between reducing friction and increasing oil consumption. While friction reduces engine efficiency, oil consumption can poison exhaust aftertreatment systems. The primary method in studying the balance between friction and oil consumption is by understanding and modeling oil transport. This study used Two-Dimensional Laser Induced Fluorescence (2D LIF) on a one-cylinder spark ignition research engine to view real-time oil transport in the power cylinder. The Lower Region, comprised of the 3' Land, skirt chamfer, the oil control ring (OCR), and the OCR groove, was the focus of this study for a number of real-world engine operating conditions. Previous studies noted that the interaction between oil and blowby gas flow is complex and important. What this research study attempted was a characterization and decoupling of the mechanisms governing oil transport into and out of the groove. This was accomplished by testing multiple piston ring pack configurations, thereby analyzing the effects of OCR and groove design. Namely a piston with no drain holes, a "Multi-Enlarged Hole" piston, and a baseline/production piston were used in conjunction with a U-Flex and Two-Piece OCR. In carrying out this analysis, a gross scaling relationship was created, utilizing the obtained LIF videos as a connection between the scaling model and the experiments' results. Mechanisms were classified into three types of oil transport: supply, release, and leakage. The primary mechanism of oil supply to the groove occurred during the intake stroke due to OCR downscraping. Oil's release from the groove was via the drain holes due to viscous shearing by blowby gases during the expansion stroke. It was found necessary that the releasing mechanism properly utilize the gas flow as well as the drainage area. Oil leakage out the groove was shown to be caused by inertia forcing oil out through the OCR gap during the intake, compression, and exhaust strokes. It was revealed that this leakage supplied oil to the Upper Region under throttled conditions. Additionally, the leakage locally affected the oil patterns of the 3rd Land and skirt. This study is the first to document many phenomena involved in oil transport within the Lower Region. The scaling relationships that resulted from such analysis created a framework that is an initial step towards a more complete model of oil transport in the Lower Region. === by Eric B. Senzer === Ph.D.
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