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Tribology for Greener Combustion Engines: Scuffing in Marine Engines and a Lubricating Boric Acid Fuel Additive
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Ångström Tribomaterialgrupp)ORCID iD: 0000-0003-2704-5447
2018 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Tribologi för grönare förbränningsmotorer : Skuffning i fartygsmotorer och ett smörjande borsyrabaserat bränsleadditiv (Swedish)
Abstract [en]

This thesis aims at increased knowledge in two fields of tribological research; both related to making currently used combustion engines greener. The first field regards the possibilities of using a boric acid fuel additive to increase fuel efficiency. The second field is about the severe wear phenomenon scuffing, which can become problematic when cargo ships are operated on low-sulphur fuel to reduce sulphuric emissions.

Tribological tests were developed and performed to simulate the applications. Advanced surface analysis was performed to understand changes occurring on the outermost surface of sliding components, which affect friction and wear. Samples from engines were studied to verify the relation between the lab tests and the applications.

In the case of boric acid, the coefficient of friction was below 0.02 for large parts of the tests, but varied with test parameters. The corresponding reduction in friction was up to 78% compared with tests without the additive. As an attempt to assess if the substantial fuel savings found in field tests with passenger cars (6%) can be explained by friction reduction in boundary and mixed lubricated parts of the piston assembly, assumptions were presented that would lead to fuel savings close to these 6%. Boric acid was detected on surfaces after the tests, and the tribofilm appearance depended on test parameters. The tribofilms were shown to be affected by storage time and test temperature; a finding that is vital for future studies.

In the case of scuffing, mechanisms were studied and accumulation of wear debris had a significant role on scuffing initiation in the lab scale scuffing tests. Regarding the possibility to test materials scuffing resistance, there was a large scatter in the results, and thereby difficult to draw conclusions. Two new piston ring materials were identified to perform somewhat better than the currently used.

In conclusion, findings that could facilitate immediate improvement of fuel efficiency of today’s combustion engine vehicles as well as findings that strengthen available hypotheses on scuffing mechanisms are presented. The latter offers improved understanding of scuffing and thereby give possibilities to counteract the higher risk associated with operation on cleaner fuel.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 97
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1607
Keyword [en]
Friction, wear, lubrication, energy loss, atmospheric emissions, fuel efficiency, transport.
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Other Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-333430ISBN: 978-91-513-0174-7 (print)OAI: oai:DiVA.org:uu-333430DiVA, id: diva2:1161025
Public defence
2018-01-19, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2017-12-21 Created: 2017-11-29 Last updated: 2018-03-08
List of papers
1. Boric acid as a lubricating fuel additive - Simplified lab experiments to understand fuel consumption reduction in field test
Open this publication in new window or tab >>Boric acid as a lubricating fuel additive - Simplified lab experiments to understand fuel consumption reduction in field test
2017 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376, p. 822-830Article in journal (Refereed) Published
Abstract [en]

In field tests, a boric acid based fuel additive has led to reduced fuel consumption. The reduction was substantial, an average of 6 and 10% in passenger cars and diesel generators respectively. Aiming towards improved understanding of mechanisms behind the fuel saving, three methods to mimic the effect of the additive in the piston-ring/cylinder contact have been evaluated. A reciprocating cylinder/flat configuration with ball bearing steel against grey cast iron was used, and it was lubricated with base oil. The different methods were as following: A) repeated spraying of a small amount of the boric acid solution onto the surfaces, B) predeposition of a boric acid layer on the flat surface and C) a combination of method A) and B). The three methods all showed effects of the additive, spanning from about 20% to 50% reductions (in the latter case, from roughly 0.1 to 0.05 in coefficient of friction averaged over the stroke). The greatest potential of the additive was seen with local coefficient of frictions lower than 0.020 in tests at room temperature with Method C. This means a reduction of around 75% compared to the lowest levels measured for the reference tests run without the additive. The most stable friction test was Method A, where a small amount of boric acid solution was repeatedly sprayed onto the lubricated sliding surfaces. In this type of test, friction reductions of roughly 20% and 40% were found at 100 C and room temperature respectively. The tribological and chemical mechanisms of boric acid in this test configuration are yet not fully understood and more studies are needed. However, the observed poor stability of the tribofilms containing boron and oxygen complicates such activities.

Keyword
Boric acid, Lubrication, Friction, Fuel consumption, Fuel additive
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-329131 (URN)10.1016/j.wear.2017.01.105 (DOI)000403904000093 ()
Conference
21st International Conference on Wear of Materials (WOM), MAR 26-30, 2017, Long Beach, CA, USA
Funder
VINNOVA
Available from: 2017-10-10 Created: 2017-10-10 Last updated: 2017-11-29Bibliographically approved
2. Boric acid as fuel additive: Friction experiments and reflections around its effect on fuel saving
Open this publication in new window or tab >>Boric acid as fuel additive: Friction experiments and reflections around its effect on fuel saving
(English)Manuscript (preprint) (Other academic)
National Category
Other Materials Engineering Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-333429 (URN)
Available from: 2017-11-29 Created: 2017-11-29 Last updated: 2018-01-13
3. Piston ring and cylinder liner wear aggravation caused by transition to greener ship transports: Comparison of samples from test rig and field
Open this publication in new window or tab >>Piston ring and cylinder liner wear aggravation caused by transition to greener ship transports: Comparison of samples from test rig and field
2013 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, no 1-2 SI, p. 1345-1350Article in journal (Refereed) Published
Abstract [en]

New and upcoming emission regulations for ships will push towards greener sea based transports. Changing the fuel, from heavy fuel oil to natural gas, is a promising approach to fulfil these regulations, but tribological problems are expected to appear when the sulphur-free gas replaces the sulphur-rich heavy fuel oil. The aim of this study was to investigate the role of sulphur for the high performance of current tribosystem in the cylinder. Field worn samples were examined and no tribofilm containing sulphur was detected, but grain refinement and plastic deformation was found below the sliding surfaces. A reciprocating test rig was used in order to simulate the tribological conditions for the piston rings and cylinder liner. Tests were run with fresh cylinder oil as well as with used cylinder oil, where the latter was used in order to simulate the chemical environment in the cylinder of an engine. Tribofilms were formed on the surfaces during these tests, and the tribofilms formed on samples run with used cylinder oil contained more sulphur than tribofilms formed on samples run with fresh cylinder oil. So far, we have not been able to see any beneficial effects of higher sulphur content in the oil.

Keyword
Piston ring/cylinder liner, Marine diesel engine, Sulphur, Tribofilm, Laboratory test
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-201977 (URN)10.1016/j.wear.2012.12.028 (DOI)000322682800057 ()
Conference
19th International Conference on Wear of Materials; Portland, OR, USA; April 14-18, 2013
Projects
Helios
Funder
EU, FP7, Seventh Framework Programme, 265861
Available from: 2013-06-18 Created: 2013-06-18 Last updated: 2018-01-11
4. Testing scuffing resistance of materials for marine 2-stroke engines: Difficulties with lab scale testing of a complex phenomenon
Open this publication in new window or tab >>Testing scuffing resistance of materials for marine 2-stroke engines: Difficulties with lab scale testing of a complex phenomenon
Show others...
2015 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 340-341, no SI, p. 9-18Article in journal (Refereed) Published
Abstract [en]

Optimising sliding materials of marine two-stroke diesel engine cylinders for reduced risk of scuffing is imperative because of the high costs associated with replacing the cylinder liner. But how can a complex and poorly understood phenomenon such as scuffing be tested? This study investigates the potential of material selection based on lab tests. Experience from ship operation is combined with analysis of lab scale scuffing tests to evaluate the possibilities of gaining applicable knowledge from scuffing testing. Two piston ring materials, a grey cast iron and a plasma sprayed cermet coating, both currently used in engines, were tested. Each of the materials was tested with two surface characters, achieved by run-in in a real engine and by fine grinding respectively. The ranking of the two materials proved to differ between the two surface characters. In the tests, scuffing could only be detected when all oil had become removed from the contact by being adsorbed by agglomerated wear debris and scraped away. This and other critical mechanisms behind scuffing in the tests are thoroughly discussed and compared to possible mechanisms taking place in the engine.

Keyword
Cylinder liner; Lubricated wear including scuffing, Marine two-stroke diesel engine, Materials, Piston ring
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-265177 (URN)10.1016/j.wear.2015.06.015 (DOI)000362926400003 ()
Conference
16th Nordic Symposium on Tribology - NORDTRIB 2014, 10-12 june 2014, Aarhus, Denmark
Funder
EU, FP7, Seventh Framework Programme, 265861
Available from: 2015-10-23 Created: 2015-10-23 Last updated: 2018-01-11Bibliographically approved
5. Scuffing resistance testing of piston ring materials for marine two-stroke diesel engines and mapping of the operating mechanisms
Open this publication in new window or tab >>Scuffing resistance testing of piston ring materials for marine two-stroke diesel engines and mapping of the operating mechanisms
2015 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 330, p. 42-48Article in journal (Refereed) Published
Abstract [en]

The incentive is strong for optimising sliding materials to reduce the risk for scuffing. In this study, scuffing tests were performed aiming towards finding new piston ring materials for greener marine diesel engines and also towards understanding scuffing mechanisms better. The tested ring materials where grey iron, Stellite 6, plasma sprayed cermet and high velocity oxy fuel (HVOF) cermet (both cermets with the same compounds: Cr-carbide, Ni, Cr, Mo). The Stellite 6 and HVOF cermet performed somewhat better than the other two materials. Microscopic and spectroscopic studies of failed sample surfaces revealed several characteristic features. It was clear that different mechanisms are active simultaneously, at different parts of the samples. Based on these results, we propose a hypothesis for a scuffing process involving several stages with distinctive mechanisms. Further studies are needed to strengthen this hypothesis and to relate these findings to actual deterioration mechanisms in the engine.

Keyword
Scuffing, Boundary lubrication, Marine diesel engines, Cast iron, Cermet, Stellite
National Category
Materials Engineering Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:uu:diva-260160 (URN)10.1016/j.wear.2015.01.074 (DOI)000357438000006 ()
Funder
EU, FP7, Seventh Framework Programme, 265861
Available from: 2015-08-17 Created: 2015-08-17 Last updated: 2018-01-11Bibliographically approved

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