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Wear mechanism study of exhaust valve system in modern heavy duty combustion engines
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.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
2011 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, 2477-2484 p.Article in journal (Refereed) Published
Abstract [en]

The increasing demands from environmental legislations are changing the conditions that the valve system is exposed to in heavy duty engines. Increased pressures, higher temperatures and lower amounts of soot which can build up a protective film are some of the increasing challenges which the system has to endure.

Three pairs of valves and valve seat inserts with the same material and design properties but with different service condition have been analyzed with a variety of analytical instruments to gain information of how the wear occurs.

The wear mechanisms found were a combination of oxidation, where many different oxides were found, adhesive wear, which was seen both in form of material transfer and flow lines. On top of Sample Mild and Hard there were tribo films of thickness varying from 1 to 5 mu m consisting of Ca, O, P, S and Zn. The film has in all cases protected the underlying surface from wear but in some cases seems to have a corrosive impact instead.

Place, publisher, year, edition, pages
2011. Vol. 271, no 9-10, 2477-2484 p.
Keyword [en]
Exhaust valve system, Wear, Oxidative, Corrosive, Adhesive
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-162392DOI: 10.1016/j.wear.2010.11.039ISI: 000294590200162OAI: oai:DiVA.org:uu-162392DiVA: diva2:460439
Available from: 2011-11-30 Created: 2011-11-30 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Combustion Valve Wear: A Tribological Study of Combustion Valve Sealing Interfaces
Open this publication in new window or tab >>Combustion Valve Wear: A Tribological Study of Combustion Valve Sealing Interfaces
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The exhaust valve system of combustion engines experiences a very complex contact situation of frequent impact involving micro sliding, high and varying temperatures, complex exhaust gas chemistry and possible particulates, etc. In addition, the tribological situation in the exhaust valve system is expected to become even worse due to strict future emission regulations, which will require enhanced combustion and cleaner fuels. This will substantially reduce the formation of combustion products that might ease the contact conditions by forming tribofilms on the contacting surfaces. The lack of protective films is expected to result in increased wear of the contact surfaces.

The aim of the work presented in this thesis has been to increase the tribological understanding of the valves. The wear that takes place in the valve sealing interface and how the change in operating conditions affects it have been studied. Such understanding will facilitate the development of future valve designs.

A test rig has been developed. It has a unique design with the ability to insert ppm amounts of media into a hot air flow, in order to simulate different environmental changes, e.g. varying amount and composition of combustion residue particles.

PVD coated valves were evaluated in a dry atmosphere. It was concluded that although some of the coatings showed potential, the substrate could not support the thin, hard coatings.

Investigations with an addition of different oils have been performed. Fully formulated oils proved to build up a protective oil residue tribofilm. This tribofilm has been in-depth analysed and proved to have similar composition and appearance as tribofilms found on low wear field tested valves. With a non-additivated oil, wear particles from the valve seat insert formed a wear particle tribofilm on top of the valve sealing surface. Without any oil the surfaces showed severe wear with wear particles spread over the surfaces.

The results presented give a hint about what to be expected in the future, when the engine oils are replaced with ash less oils with reduced amount of additives and the consumed amount of oil within the cylinders are reduced. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 57 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1058
Keyword
Combustion valves, wear, tribofilm, test rig, combustion residue
National Category
Tribology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-204636 (URN)978-91-554-8715-7 (ISBN)
Public defence
2013-09-20, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2013-08-30 Created: 2013-08-07 Last updated: 2014-01-07

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Forsberg, PeterHollman, PatrikJacobson, Staffan

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