City Research Online

Abstract

The interface between the piston, piston-rings and the cylinder liner represents one of the most hostile environments the crankcase lubricant experiences in reciprocating engines. The role of piston rings is also becoming more complex in line with the increasing requirements for lower oil consumption and friction. A test rig has been developed to simulate under idealised conditions the lubrication action between the piston-ring and the cylinder-liner in reciprocating engines. This approach attempts to separate the tribological conditions from some of the fundamental and unsteady conditions occurring in production engine piston assemblies such as lubricant starvation, ring and piston dynamics, thermal and elastic deformations and blow by, thus allowing the lubricant film characteristics to be examined in isolation. The current work proposes a methodology in assessing the rheological behaviour of various base oils and their additive chemistry with a view to establishing the likely field performance in formulated lubricating oil. The experiment comprised of testing different types of engine oils where the lubricant film thickness, oil film pressure and friction were simultaneously measured throughout the stroke as a function of speed, load and temperature. Furthermore, laser induced fluorescence (LIF) was used to identify the onset of cavitation occurring in the diverging part of the lubricant film between the piston ring specimen and the liner wall. Recognition that lubricant films under certain condition may cavitate opens up a new area for research, focusing on possible links between cavitation, oil consumption, friction and wear. Oil flow visualisation in the test rig using a high speed video camera allowed observation of cavitation in the diverging part of the ring through an optical liner. The high recording framing rates of the camera have permitted the initiation, development and disintegration of the cavities throughout the stroke to be revealed. An attempt was made to extend the oil film visualisation to a motored diesel engine, with parts of the liner cut and fitted with quartz windows, to confirm the presence of cavitation in the piston-rings interface. Moreover the identification of sub-atmospheric pressure in the rings provided additional support to the visualisation of cavitation found in the engine, albeit of much inferior resolution to that of the idealised piston-ring assembly.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology Doctoral Theses School of Science & Technology > School of Science & Technology Doctoral Theses

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