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Combustion Valve Wear: A Tribological Study of Combustion Valve Sealing Interfaces
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
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 [en]
Combustion valves, wear, tribofilm, test rig, combustion residue
National Category
Tribology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-204636ISBN: 978-91-554-8715-7 (print)OAI: oai:DiVA.org:uu-204636DiVA: diva2:639359
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
List of papers
1. Quantification of Combustion Valve Sealing Interface Sliding - A Novel Experimental Technique and Simulations
Open this publication in new window or tab >>Quantification of Combustion Valve Sealing Interface Sliding - A Novel Experimental Technique and Simulations
2014 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 69, 150-155 p.Article in journal (Refereed) Published
Abstract [en]

The rapid sharpening of the environmental legislation during the last decades has forced engine manufacturers to radical design modifications. It has been shown that the sliding in the sealing interface is one of the major reasons for wear. The sliding wear is expected to have an even more important role in modern engines. This paper presents unique experimental data, acquired using a dedicated technique in a test-rig. The experimental data is complemented by FEM-simulations. The simulations involve validation of the test-rig valve sealing interface sliding behaviour and investigations on how different parameters influence the sliding length. These parameters include combustion pressure, contact angle, contact length, valve head thickness, coefficient of friction, running-in wear, and change of elastic modulus due to temperature variations.

National Category
Tribology
Research subject
Engineering Science with specialization in Tribo Materials; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-204452 (URN)10.1016/j.triboint.2013.09.014 (DOI)000328183100017 ()
Available from: 2013-08-05 Created: 2013-08-05 Last updated: 2017-12-06Bibliographically approved
2. Wear mechanism study of exhaust valve system in modern heavy duty combustion engines
Open this publication in new window or tab >>Wear mechanism study of exhaust valve system in modern heavy duty combustion engines
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.

Keyword
Exhaust valve system, Wear, Oxidative, Corrosive, Adhesive
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-162392 (URN)10.1016/j.wear.2010.11.039 (DOI)000294590200162 ()
Available from: 2011-11-30 Created: 2011-11-30 Last updated: 2017-12-08Bibliographically approved
3. Combustion valve simulation rig with particle flow
Open this publication in new window or tab >>Combustion valve simulation rig with particle flow
(English)In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833Article in journal (Refereed) Submitted
National Category
Tribology
Identifiers
urn:nbn:se:uu:diva-201863 (URN)
Available from: 2013-06-17 Created: 2013-06-17 Last updated: 2017-12-06Bibliographically approved
4. Wear study of coated heavy duty exhaust valve systems in a experimental test rig
Open this publication in new window or tab >>Wear study of coated heavy duty exhaust valve systems in a experimental test rig
2012 (English)In: SAE International technical papersArticle in journal (Refereed) Published
National Category
Tribology
Research subject
Engineering Science with specialization in Tribo Materials; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-173681 (URN)10.4271/2012-01-0546 (DOI)
Available from: 2012-05-02 Created: 2012-05-02 Last updated: 2014-01-07Bibliographically approved
5. Comparison and analysis of protective tribofilms found on heavy duty exhaust valves from field service and made in test rig
Open this publication in new window or tab >>Comparison and analysis of protective tribofilms found on heavy duty exhaust valves from field service and made in test rig
2013 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, no 1-2 SI, 1351-1359 p.Article in journal (Refereed) Published
Abstract [en]

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 particulates which can build up a protective film are some of the increasing challenges which the system has to endure. Thick protective tribofilms found on heavy duty exhaust valve surfaces have been analysed with SEM, TEM, EFTEM, STEM-EDS, Nano-indenter and XPS in order to get a better understanding for the tribofilms properties. Two analysed samples are presented in this paper, from a field service truck and another from atest rig which uses vaporised engine oil to simulate the particle flow. The tribofilms are built upfrom several layers with varying compositions. Most of the material originates from oil additives, but also metallic oxides and other carbon compounds produced in the combustion system. The similarities between the rig generated tribofilm and the tribofilm found on the field tested valve verify the test rig behaviour and opens up for realistic wear testing where the importance ofthe protective tribofilm can be investigated in detail that is not possible in motor tests. 

Place, publisher, year, edition, pages
Elsevier, 2013
National Category
Tribology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-201859 (URN)10.1016/j.wear.2013.01.061 (DOI)000322682800058 ()
Available from: 2013-06-17 Created: 2013-06-17 Last updated: 2017-12-06Bibliographically approved
6. The importance of oil and particle flow for exhaust valve wear - An experimental study
Open this publication in new window or tab >>The importance of oil and particle flow for exhaust valve wear - An experimental study
2014 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 69, 176-183 p.Article in journal (Refereed) Published
Abstract [en]

Oil residue particles have a large impact in protecting the sealing surfaces of heavy duty exhaust valves. To increase the understanding of the mechanism behind this, the wear behavior of exhaust valves subjected to a flow of hot air with controlled amounts of oil particles of three different compositions has been investigated. Air flow without addition of oil was used as a reference. The degree and mechanisms of surface damage proved to be sensitive to the test parameters. Residues from the oils containing additives proved to form protective tribofilms, while the oil without additives promoted agglomeration of wear debris on the sealing surfaces. The dry reference showed severe wear with debris scattered over the surfaces.

National Category
Tribology
Research subject
Engineering Science with specialization in Tribo Materials; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-204467 (URN)10.1016/j.triboint.2013.09.009 (DOI)000328183100020 ()
Available from: 2013-08-06 Created: 2013-08-06 Last updated: 2017-12-06Bibliographically approved

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