School of Mechanical Engineering (/mechanical)

Institute of Thermofluids (/thermofluids)

in Tribology and surface engineering (../index.shtml)

Current research (index.shtml)

The study of friction, lubrication and wear under the collective name "Tribology"has been an area of research and knowledge transfer in the School of MechanicalEngineering for over a century. Tribology has long been recognised a keycontributor in terms of controlling friction and wear to maximise the scientificbenefits and their application in industry and society. As such, tribological researchis extremely broad, covering basic, strategic and applied threads with bothanalytical and experimental contributions. Understanding the complexinterrelationship between surface materials and coatings, the lubricant and theoperating environment of mechanisms and machines is key to the way forward.

The automotive industry strives to meet the ever more stringent governmentlegislation and customer requirements, dictating the need for better fuel economyand to limit environmental pollution caused by vehicles. Tribology is a keycontributor to these efforts through the control of frictional energy losses, wear andoil consumption. The automobile consists of many hundreds of tribologicalcomponents, from bearings, pistons, transmissions, clutches, gears, to wiperblades, tyres, and electrical contacts, many of which rely on the interaction of theirsurfaces to function. Reduction of sulphur, phosphorous, CO, CO2 and NOx in

exhaust emissions has been the priority of automobile manufacturers withoutcompromising the desired tribological performance. In general, a reduction innoxious exhaust emissions from automobiles can be achieved through tribologyeither by developing new engine oils that reduce friction and have low or nosulphur, phosphorous and ash containing additives and/or by developing newsurface materials (alloys/coatings) that are less dependent on sulphur andphosphorous containing engine oils. The application of tribological principles isessential for the reliability of the vehicle, and even the smallest improvements inengine efficiency, emission levels, and durability can have a major effect on theworld economy and the environment in the medium to long term given the hugesize of the global vehicle population.

Automobile and oil manufacturers are under increasing pressure from consumersand competitors to design efficient engines capable of running on environmentallyfriendly engine oils. Increasing demand for improved fuel economy andenvironmental protection has meant that there has been increased focus on the useof novel non-ferrous surface materials and coatings which have excellenttribological properties. As engine lubricants have historically been formulated forferrous materials and react chemically with the surface, it is highly unlikely thatthey will perform well on alternative surfaces. It is therefore crucial to understandhow the existing lubricants interact with non-ferrous coatings to be able to sensiblyapproach the design of new additives for such surfaces.

Concerns over depleting fossil fuel reserves and energy security have resulted instringent legislation demanding automobiles use more renewable fuels, haveimproved fuel economy and generate less harmful exhaust emissions. As aconsequence, alternative and environmentally sustainable biofuels are being givensignificant attention on a global scale. Biofuel ethanol, the most viable and freelyavailable gasoline substitute, is being considered as a long term gasolinereplacement. The piston ring and cylinder wall interface is generally the largestcontributor to engine friction and this region of the engine also suffers the highestlevels of fuel dilution into the lubricant from unburnt fuel in the cylinder and watercontamination heightened by the presence of ethanol.

It is not just traditional machine elements require attention. Tribology problems arepervasive in health technologies and the performance of living tissue. As humanswe are living longer and our mechanical joints often require repair or replacementat a much earlier stage in our lives, such that the replacements must perform wellin more active younger individuals, must last longer and be capable of further repairor replacement later in life. Adequate performance of prostheses relies on surfaceinteractions taking place as designed. Studying the self-healing and self-lubricating

properties of biological surfaces can lead to the design of intelligent engineeredsurfaces.

Our laboratory facilities are extensive, with many basic tribometers, bespokesimulation rigs and devices to test real applications, supported by analyticalinstruments to characterise materials, surfaces and lubricants at the minute scalesrequired for this discipline. Alongside this sit theoretical studies of the tribology of awide range of engineering component systems to predict lubrication, friction andwear and simulate the complex interactions between lubrication, friction and wearduring their lifetime. We have recently installed a state-of-the-art PVD (physicalvapour deposition) system (Hauzer) and have established a multi-capability thinfilm coating partnership with Sheffield and Sheffield Hallam Universities.

We also lead and host the highly regarded annual international researchconference, the Leeds-Lyon Symposium on Tribology, with colleagues at theUniversity of Lyon in France. This event has become a regular annual feature in theinternational research calendar since its inception in 1974 and attracts researchersand practitioners in tribology from all around the world.

Current Research

Improved friction prediction for automobile engine valve trains (friction-prediction.shtml)

Impact of ethanol biofuel on automotive piston ring friction (impact-of-ethanol-biofuel.shtml)

Lubricant misting in the piston assembly of automotive engines: cause,effect and control (lubricant-misting.shtml)

Multiscale bearing design (bearing-design.shtml)

Fretting damage (fretting-damage.shtml)

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