A study of the friction of the power cylinder system in internal combustion engines using a floating liner engine

Abstract

The recent worldwide quest to increase the fuel efficiency of internal combustion engines has led to great effects to reduce friction of many of the components in these engines. One area of major concern pertaining to this area is the friction of the piston/ring pack assembly. Because of the importance and necessity of this component to the internal combustion engine, any improvements can have relatively large implications for friction reduction. The purpose of this paper is to investigate several key components of the piston/ring pack assembly and how they influence friction levels. Specifically, experimental friction trends related to the oil control ring, piston skirt, liner surface and lubricant will be discussed. The Floating Liner Engine is used in this study in both the motored and fired configuration to isolate results from components and provide data for comparative analysis. The oil control ring (OCR) controls the supply of lubricating oil to the top two rings of the ring pack and has a significant contribution to friction of the system. This study investigates the two most prevalent types of OCR in the automotive market: the twin land oil control ring (TLOCR) and three piece oil control ring (TPOCR). The effect of changing the land width and spring tension on different liner surfaces for the TLOCR is investigated, and distinct trends are identified. A comparison is then done between the TLOCR and TPOCR on different liner surfaces. Results showed the TPOCR displayed different patterns of friction compared the TLOCR in certain cases. The piston skirt is also an important contributor of friction in the piston assembly. This thesis discusses the investigation into low friction coatings on the piston skirt. A brief study of piston skirt patterns is presented, with little gains being made by applying patterns the piston skirt coating. Next the roughness of the piston skirt coating is analyzed, and results show that reducing piston skirt roughness can have positive effects on friction reduction. Finally, an introductory study into the profile of the piston skirt is presented, with the outcome being that friction reduction is possible by optimizing the skirt profile. The final section of this thesis discusses the effects of lubricants pertaining to friction in the piston assembly. The effects of changing lubricant viscosity through both temperature and formulation are presented, as well as results from testing the effects of select anti-wear additives in the oil. The results identify new developments related to lubricant/additive effects on the liner surface, and how these effects can influence friction.