Ultrasonic measurement of lubricant films generated at the piston-cylinder interface of internal combustion engines

• Main Author: Mills, Robin
• Published: University of Sheffield 2012
• Subjects: 621.43
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.577537

Internal combustion engines are perhaps the most ubiquitous power source in the modern world. Their heavy use in the vehicle industry and the current impetus to improve efficiency whilst reducing emissions means that OEMs are driving research to provide cleaner and 'greener' engines. Though significant effort is being channelled into teasing out improvements in thermodynamic Efficiency by such methods as pressure boosting and power management. the nature of an engine means many moving parts contribute to parasitic frictional loss. Of these interfaces. the reciprocating contacts between cylinder. piston rings and skirt are arguably subject to the most demanding tribological conditions within an engine. required to seal against the high temperature' combustion gases whilst supporting the large side loading inherent to the system. Given that the piston of an engine may perform this action hundreds of millions of times in its lifespan. the lubrication strategy and component design is of key importance in minimising wear frictional losses. Though the use of numerical simulation tools for improving design has seen significant growth as computational capabilities improve and provide cost advantages to full scale testing. robust validation methods are required to guide the development of the underlying models. The aim of this project was to assess the suitability of an ultrasonic method to monitor the condition of lubrication at the aforementioned contacts by measuring film thickness. Though various techniques involving optical and electrical principles have been employed in the past they generally require the cylinder of the engine to be penetrated and implementation. for the most part. is limited to the test cell. The results of investigations at the piston ring contact have shown that the ultrasonic technique can be used to measure lubricant film thickness and have shown the influence of cylinder pressure and reciprocating speed. Measurements correlate well with work by other authors using the alternative methods mentioned. giving confidence in the robustness of the method. Film measurements at the skirt have been also been successful. not only in quantifying the minimum films present. but also in detailing the profile of the film over its surface and enabling some of the secondary motions of the piston to be deduced. It has been shown that the ultrasonic technique offers the ability and freedom to measure film thickness within an operational engine whilst having the distinct advantage of limiting the degree structural modification required. It shows promise as a research tool and with further development. offers the potential to be incorporated into a lubricant monitoring and control System to help reduce friction losses and emissions.