A study of the influence of ring gap size on the lubrication of piston rings in an internal combustion engine

Abstract

The work presented in this thesis is largely concerned with developing a greater understanding of piston ring lubrication by measuring the thickness of hydrodynamic films developed between the piston ring and the cylinder wall of an internal combustion engine.
It begins with a review on oil film thickness (OFT) measurement methods describing how techniques have developed since the last decade and continues by describing how a well established OFT measurement method was used to gather data to compare to the OFT predictions of a computer model.
The investigation was focused on the influence of the size of the piston ring gap in the top two rings on the OFT between the piston ring and cylinder liner of a single cylinder diesel engine (Hatz lB2O). The project studied the power stroke (at 500 ATDC for the top ring and 40° ATDC for the middle ring TDC) at a range of engine speeds (1500, 2000 and 3000 r.p.m) and 50% of maximum engine load. Four sets of piston rings, with different ring gap combinations were used. A capacitance OFT measurement method was used for the experimental measurements at the University of Central Lancashire and the data collected was compared to the output of a computer model data generated by a research student at Leeds University.
The theoretical results were found to be much different to the experimental ones, both in terms of their absolute value and their characteristic behavior. The experimental results were unusually large. A review was conducted to find the reason for this. Several possible causes were identified including cylinder shape, transducer wear and transducer stability. It was concluded that experimental data could not be used to form any type of reliable comparison with theoretical oil film thickness predictions. Investigations were proposed as further work to collect data after engine modifications (re-machining of the cylinder liner and installation of a new OFT transducer), along with measurements of OFT on other similar engines for comparison.
It was concluded that although this project did not meet the expected technical aim it had value in delivering OF!' measurements on a distorted cylinder surface and in developing the research methods of the author required for the completion of the study.