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Combustion Valve Wear Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1058 Combustion Valve Wear A Tribological Study of Combustion Valve Sealing Interfaces PETER FORSBERG ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 ISBN 978-91-554-8715-7 UPPSALA urn:nbn:se:uu:diva-204636 2013 Dissertation presented at Uppsala University to be publicly examined in Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, Friday, September 20, 2013 at 10:15 for the degree of Doctor of Philosophy. The examination will be conducted in English. Abstract Forsberg, P. 2013. Combustion Valve Wear: A Tribological Study of Combustion Valve Sealing Interfaces. Acta Universitatis Upsaliensis. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1058. 57 pp. Uppsala. ISBN 978-91-554-8715-7. 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. Keywords: Combustion valves, wear, tribofilm, test rig, combustion residue Peter Forsberg, Uppsala University, Department of Engineering Sciences, Applied Materials Sciences, Box 534, SE-751 21 Uppsala, Sweden. © Peter Forsberg 2013 ISSN 1651-6214 ISBN 978-91-554-8715-7 urn:nbn:se:uu:diva-204636 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-204636) Till Jenny List of Papers This thesis is based on the following papers, which are referred to in the text by their Roman numerals. I Quantification of combustion valve sealing interface sliding - A novel experimental technique and simulations P. Forsberg, D. Debord, and S. Jacobson Submitted to: Tribology International II Wear mechanism study of exhaust valve system in modern heavy duty combustion engines. P. Forsberg, P. Hollman, and S. Jacobson Wear, 271 (2011) 2477– 2484 III Combustion valve simulation rig with particle flow P. Forsberg, P. Hollman, and S. Jacobson Submitted to: Lubrication Science – Tribo Test IV Wear study of coated heavy duty exhaust valve systems in an experimental test rig P. Forsberg, P. Hollman, and S. Jacobson SAE Technical Paper 2012-01-0546, (2012) V Comparison and analysis of protective tribofilms found on heavy duty exhaust valves from field service and made in a test rig. P. Forsberg, F. Gustavsson, P. Hollman, and S. Jacobson Wear, 302 (2013) 1351-1359 VI The importance of oil and particle flow for exhaust valve wear – An experimental study P. Forsberg, R. Elo, and S. Jacobson Submitted to: Tribology International Reprints were made with permission from the respective publishers. Related work Friction and wear behavior of low-friction coatings in conventional and alternative fuels F. Gustavsson, P. Forsberg, and S. Jacobson Tribology International 48 (2012) 22-28 Formation of a tribologically beneficial layer on counter surface with smart chemical design of DLC coating in fuel contact F. Gustavsson, P. Forsberg, V. Renman, and S. Jacobson Tribology – Materials, Surfaces & Interfaces, Vol. 6, No. 3 (2012) 102-108 Performance of DLC coatings in heated commercial engine oils P. Forsberg, F. Gustavsson, V. Renman, A. Hieke, and S. Jacobson Wear, 304(2013) 211-222 Author’s Contribution to the Publications Paper I Major part of planning, evaluation and writing. Part of experimental work. Paper II–V All experimental work. Major part of planning, evaluation and writing. Paper VI Major part of planning, evaluation and writing. Substantial part of experimental work. The author has performed all analyses, with the exception of the TEM analy- sis in Paper V. The author did not make the FEM simulations in Paper I. Contents 1 Introduction ................................................................................................ 11 1.1 The valve system of combustion engines ........................................... 11 1.2 Tribology – Friction, Wear and Tribofilms ........................................ 12 1.3 Environmental legislation changes ..................................................... 13 1.4 Research objectives ............................................................................ 15 2 Description of Valves and Valve Seat Inserts ............................................ 16 2.1 The Valves .......................................................................................... 16 2.2 The Valve Seat Insert ......................................................................... 18 2.3 Valve rotation ..................................................................................... 19 3 Wear of the valve system ........................................................................... 20 3.1 The wear problem ............................................................................... 21 3.2 The two major wear components ....................................................... 21 3.3 Quantification of the interface sliding ................................................ 23 3.4 Wear mechanisms .............................................................................. 26 4 Wear testing of valves ................................................................................ 30 4.1 Experimental valve wear tester .......................................................... 31 4.2 Wear progress monitoring .................................................................. 33 4.3 Rig development ................................................................................ 33 5 Wear experiments ...................................................................................... 35 5.1 Coated valves ..................................................................................... 35 5.2 Oil residue tribofilm generation and characterization ........................ 38 5.3 The influence of oil and particle flow on the wear mechanism.......... 44 6 Conclusions ................................................................................................ 47 7 Sammanfattning på svenska ....................................................................... 50 8 Acknowledgements .................................................................................... 54 9 References .................................................................................................. 55 Abbreviations CO Carbon Monoxide FEM Finite Element Method HC Hydro Carbons LOM Light Optical Microscopy NOx Nitrogen Oxides PAO Polyalfaolefine PM Particulate Matter ppm Parts per million rpm Revolutions Per Minute SEM Scanning Electron Microscopy TEM Transmission Electron Microscopy 1 Introduction 1.1 The valve system of combustion engines Combustion engines are used in many applications. The most common use is in the transportation sector where they propel the vast majority of the vehi- cles in the world. They operate by converting the expansion of high- temperature and high-pressure combustion gases into mechanical energy through displacement of a piston situated inside a cylinder. The piston is connected to a crank shaft that converts the displacement into rotational movement. An engine is generally – with exception of the smaller ones – built up of several cylinders connected to the same crankshaft. By adapting timing shifts, they deliver a smooth torque. In order to control the gas ex- change needed in a cylinder, a set of valves – typically two intake and two exhaust valves – are situated in the cylinder head above the piston. Due to their direct contact with the high combustion pressure and hot gases, they operate under severe conditions. During the induction
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