Ultrasonic Piston Lubrication Monitoring and the Effects of Distortion and Deterioration

Lead Research Organisation: University of Sheffield
Department Name: Mechanical Engineering


Modern design of automotive engines focuses primarily on raising efficiency to meet increasingly stringent legislation on vehicular emissions. A viable route for this is to study the oil films between interacting components to optimise the film thickness. This leads to reductions in frictional losses through the powertrain which in turn raises the overall efficiency. Research into automotive lubrication encompasses numerous other aspects of engine design that affect efficiency primarily being; lubricant deterioration, surface geometry, bulk structural deformation and surface specification.
This project is aimed to develop a series of sensing techniques to study the oil films formed in various contacts in internal combustion engines. This is achieved by the design and assembly of an electric motor driven engine that allows for the effect of degraded lubricant and component distortions to be studied. With the potential to incorporate the most promising techniques into a fired engine.
These films are being researched using ultrasonic transducers that are based upon the piezoelectric effect. The base principle for a longitudinal piezoelectric transducer is based upon a reflection of an ultrasonic wave from a change in medium that the wave is propagating through. The time in which it takes for a signal to be pulsed and received can provide the distance the wave has travelled and therefore thickness of a medium. Similar approaches can be used with shear transducers to quantify the oil viscosity. The most beneficial characteristic of these sensors is their non-invasive nature. That the surface either side of the oil film being considered does not require direct modification that most alternative approaches require. This therefore enables films closer to real world applications to be developed in motored rigs compared to their invasive method counterparts.
The automotive oil films are studied using longitudinal and shear wave piezoelectric transducers in conjunction with methodologies previously developed by the Leonardo Centre for Tribology at the University of Sheffield. An example of a contact of interest is the piston ring-liner contact. This can be studied by the instrumentation of piezoelectric transducers on the thrust, anti-thrust and neutral sides of a cylinder, which can provide data on; piston tilt, lubrication regime, cyclic variation and performance of each ring.


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Description The work involved using ultrasonic sensors to monitor the oil film thickness between piston rings and cylinder liners in various engines. One engine was a large diesel marine engine, sensors were instrumented close to top dead centre of the engine (when the piston is at the top of its stroke). Testing was completed for three differing engine configurations, each varying how lubricant was injected into the cylinder liner. The ultrasonic measurements showed that the oil film thickness first piston ring varied with each engine configuration. The engine configuration that had the lowest rate of lubricant atomisation led to a greater oil film thickness between the piston ring and liner. Providing a clear measurement that a redesign of the lubricant injection system, reducing the rate at which lubricant is lost to the exhaust manifold, leds to a significant increase in the lubricating film thickness between the piston ring and liner, therefore improving the lubrication regime of the piston ring.
Exploitation Route The current findings in this project provide a clear indication for large diesel marine engine manufacturers that through the use of ultrasonic transducers the oil film thickness between piston rings and the cylinder liner can be measured. Through the combination of this with prototype system designs such as cylinder lubricant injection systems it can provide experimental data on how lubricated the piston rings are. This can therefore be applied to improve the operational efficiency of various engines to meet their respective emission legislation.
Sectors Aerospace, Defence and Marine,Transport

Title Advanced signal processing methods to measure piston ring lubrication 
Description The ultrasonic signal recieved from the piston ring liner contact has been analysed using a series of different processing methods to provide an overview of the applicability of different processing methods. 
Type Of Material Improvements to research infrastructure 
Year Produced 2021 
Provided To Others? No  
Impact The more traditional approach of producing an FFT of each AScan and indexing at the transducer central frequency has been furthered developed by a series of additional data processing steps. BScans have shown a time delayed reflection being recorded by the ultrasonic sensors that was previously hidden within the AScans. This has shown that analysis of the whole recorded reflection is not appropriate at all points as there is a crank angle range in which reflection from the piston ring are being measured without it being inline with the sensor. The hilbert envelope peak of the reflection has also been considered as this method focuses on the peak of the envelope it is not subject to time delayed factors in the reflection. Through study of differing portions of the envelope it provides a visualisation of which sections of the reflection led to the complex reflection coefficient plots produced in the traditional data processing of the FFT. The BScans showed that it is unrepresentative of the true piston ring reflection to use the whole AScan to produce an FFT in the traditional analysis technique. This has led to an AScan window selection technique being developed to optimise the length of the AScan selected to minimise the impact of these time delayed reflections while not removing the true reflection of interest. Through an independence study between the AScan window size and the frequency of the maximum amplitude response of the FFT. The optimised AScan windows enable refinement of the traditional approach to process the reflection coefficient from the piston ring. These optimsed windows have also been used to produce spectrograms of the reflection coefficient and oil film thickness to indicate the variation in both factors over the bandwidth of the transducer. 
Description Jaguar Land Rover 
Organisation Jaguar Land Rover Automotive PLC
Department Jaguar Land Rover
Country United Kingdom 
Sector Private 
PI Contribution Ultrasonic transducers have been used on a Jaguar Land Rover Ingenium engine to provide information on the oil films on various lubricated automotive components.
Collaborator Contribution Jaguar Land Rover have provided the engine in which this work is based on and provide technical support through the project.
Impact The project is still underway and therefore does not have any outputs yet.
Start Year 2017
Description Winterthur Gas & Diesel 
Organisation Winterthur Gas & Diesel
Country Switzerland 
Sector Private 
PI Contribution Ultrasonic transducers have been used on a WinGD Diesel Marine engine to provide information on the oil films on various lubricated automotive components.
Collaborator Contribution Provided technical support to enable the work to take place.
Impact The data gathered from this testing is being used for two papers that are in process of being written.
Start Year 2018