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Wear protective capacity of tribofilms formed on combustion engine valves with different surface textures
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.ORCID iD: 0000-0003-1274-4974
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.ORCID iD: 0000-0002-3955-5746
2017 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376, 1429-1436 p.Article in journal (Refereed) Published
Abstract [en]

The valve system controls the flow of gases into and out of the cylinders of combustion engines. As the combustion chamber is repeatedly filled with air and emptied from combustion residues, the contacting surfaces of the valve and valve seat insert (VSI) are exposed to high temperatures, high speed impacts, corrosive environment and high closing forces. Since the expected wear life of the components is hundreds of millions of operational cycles, the wear rate has to be extremely low. Previous studies have shown that this is accomplished by the continual formation of protective tribofilms on the surfaces, formed from oil additive residues. For some stationary gas engines, seemingly random occurrence of severe wear, i.e. without correlation to special running conditions, calls for an improved understanding of the wear protective abilities of these tribofilms. Further, the potential of making the protection more robust by using simple textures on sealing surfaces is investigated. Real valves and VSI's were therefore run in a dedicated test rig, previously shown capable of forming tribofilms similar to those found in real engine valves. Two surface textures, turned or ground, were tested. After a running in phase where fully covering tribofilms were formed, the tests were continued without adding the oil residues needed for replenishing the tribofilm. The flow of oil residues was either completely stopped or only intermittently open. The resulting wear was monitored during testing and after finishing the tests remaining tribofilms were analysed with SEM and EDS. The severity of the wear was graded and the presence of tribofilm and localization of wear was correlated. The endurance of the tribofilms was surprisingly high for both textures. Typically the tribofilms exhibited better wear resistance than the underlying metals. Once fully formed, the tribofilms can therefore endure for a long time without addition of new tribofilm forming material. Both textures showed the first sign of wear after roughly the same time and then followed the same progression, when the flow of oil residues was cut. With the intermittent oil residue supply, both textures performed even better. Especially the turned texture showed only slow, mild wear.

Place, publisher, year, edition, pages
2017. Vol. 376, 1429-1436 p.
Keyword [en]
Combustion engine valves, Surface texturing, Protective tribofilms, Rig testing
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:uu:diva-329132DOI: 10.1016/j.wear.2016.12.060ISI: 000403902000057OAI: oai:DiVA.org:uu-329132DiVA: diva2:1148161
Available from: 2017-10-10 Created: 2017-10-10 Last updated: 2017-10-10Bibliographically approved

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Elo, RobinHeinrichs, JannicaJacobson, Staffan
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