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Thermal barrier coatings for diesel engines
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0002-6619-8799
2022 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Termiska barriärbeläggningar för dieselmotorer (Swedish)
Abstract [en]

The upward trend in internal combustion engine efficiency is driven by the demands for emission reduction and fossil fuel depletion. No present alternative fuel can produce energy comparable to that produced by conventional oil; this necessitates the reasonable, efficient usage of oil. For several decades, thermal barrier coatings (TBCs) have been studied as an answer for increasing the thermal efficiency of gas turbine engines. However, TBCs have not been extensively evaluated for application to internal combustion engines owing to their emissions, costs, and demanding working conditions. Much effort is needed to simultaneously address this problem and expand the applicability of thermal barrier coatings.The objective of this study is to investigate the relationships between the spraying parameters, microstructural variations, thermal properties, and performance of TBCs applied to diesel engines. The further objective is to harness this knowledgeto fabricate coatings that result in high automotive engine efficiencies. Different feedstock materials were used with various spraying methods and classified into separate TBC types. The first TBC type had a lamellar bond coat deposited by atmospheric plasma spray (APS) and lamellar yttria-stabilized zirconia (YSZ) APS top coat. The second TBC type was derived from the first TBC type and had a lamellar APS bond coat, and the top coat was deposited by APS using a feedstock along with a porosity former, resulting in high-porosity top coats. The third TBC type had a dense bond coat deposited with high velocity air fuel (HVAF) and a columnar top coat deposited by suspension plasma spray (SPS) using a feedstock of YSZ or gadolinium zirconate (GZO). The SPS technique can generate a variety of microstructures, and the TBCs containing these microstructures were tested in an internal combustion engine for the first time. The fourth TBC type had a dense bond coat deposited HVAF, a columnar top coat produced with SPS and an additional top layer, which functioned as the sealing layer.

For the thermophysical property investigation of all coating types, experimental and modeling techniques—laser flash analysis (LFA) and object-oriented finite element (OOF) analysis, respectively—were employed. To evaluate the optical properties of the coatings, two methods were adopted, namely, spectral normal hemispherical reflectivity at room temperature (SNHRRT) and spectral normal emissivity at high temperature (SNEHT). The functional performance of the coatings was evaluated on the basis of the TBC behavior under cyclic thermal loads; thermal cyclic furnace test, flame rig test, thermal swing test, and a single cylinder engine experiment were conducted. The coatings were characterized by scanning electron microscopy (SEM) before and after the functional performance test. The coating performance was correlated to the microstructural, thermophysical, and optical properties of the coatings.

The results of this study infer that the TBC type significantly influences the thermal properties and thermal cyclic performance, which can be correlated with the porosity levels and the pore types. The complex substrate geometry of the piston resulted in inherent variations in spray angle and spray distance, leading to different coating microstructures and porosities owing to the changes in the particle trajectory and in-flight characteristics. Further, the single-cylinder engine evaluation demonstrated that the high-emissivity second TBC type or the third TBC type with a porous microstructure and a low thermal effusivity resulted in a high engine efficiency.

Abstract [sv]

En ökad effektivitet i förbränningen hos dieselmotorer krävs för att kunna uppfylla de allt högre kraven på minskad miljöpåverkan och ett minskat användande av fossila bränslen. Inget alternativt bränsle finns idag som kan producera energi som är jämförbar med den som produceras av konventionell olja, vilket förutsätter en effektiv användning av olja. Under flera decennier har termiska barriärbeläggningar (TBC) varit en lösning för att öka den termiska effektiviteten hos gasturbinmotorer. Beläggningarna har dock inte utvärderats i tillräcklig omfattning för dieselmotorer. Forskning är av detta skäl nödvändig för att skapa förutsättningar för att denna typ av beläggningar kommersiellt skall kunna tillämpas i dieselmotorer.

Syftet med detta arbete är att utforska sambandet mellan processparametrar, beläggningsmikrostruktur, termiska egenskaper och prestanda hos termiska barriärbeläggningar för dieselmotorer. Målet med arbetet är att skapa beläggningar som resulterar i hög förbränningsverkningsgrad. Olika beläggningsmaterial utvärderades och kategoriserades med olika spruttekniker. Det första materialet som utvärderades var yttriumoxidstabiliserad zirkoniumdioxid (YSZ) som sprutades med atmosfärisk plasmassprutning (APS). Denna beläggning användes som referensprov. Det andra materialet var en vidareutveckling av den första beläggningen där porositet i beläggningen skapades med hjälp av ett tillsatsmaterial, vilket resulterade i beläggningar med hög porositet. Den tredje typen var en så kallad kolumnär mikrosstrukturbeläggning som skapades med suspensionsplasmasprutning (SPS) och tillsatsmaterialet YSZ. SPS tekniken valdes även för gadoliniumstabiliserad zirkoniumdioxid. Anledningen till att tekniken SPS utvärderades var att denna teknik i gasturbinapplikationer visat sig kapabel till att producera ett stort antal olika typer av mikrostrukturer. Den fjärde typen av beläggning som utvärderades var ett SPS producerat beläggningssystem där ytterligare ett så kallat toppskikt som tätskikt sprutades.

Prestanda och egenskaper utvärderades för samtliga skapade beläggningar genom såväl experimentella tekniker som modellering där laser flash analysis (LFA) och finita elementanalys är exempel. För att utvärdera beläggningarnas optiska egenskaper användes två metoder, spektral normal hemisfärisk reflektivitet vid rumstemperatur (SNHRRT) och spektral normal emissivitet vid hög temperatur (SNEHT). Beläggningarnas livslängd utvärderades indirekt med hjälp av termisk utmattning i ugn, termisk utmattning med förbränningslåga och med ett motorexperiment. Beläggningarnas mikrostruktur analyserades genom svepelektronmikroskopi (SEM) före och efter prestandautvärderingarna. Beläggningsprestanda korrelerades därefter till beläggningarnas mikrostruktur, termiska och optiska egenskaper samt de funktionella egenskaperna.

Resultaten av studien visar att valet av TBC-typ signifikant påverkar de termiska egenskaperna och de termiska utmattningsegenskaperna, och att dessa skillnader kan korreleras med porositetsnivåerna och portyperna i beläggningarnas mikrostruktur. Motorkolvens komplexa substratgeometri orsakade variationer i sprutvinkel och sprutavstånd, vilket ledde till olika beläggningsmikrostrukturer på kolvens olika ytor. Motorutvärderingen visade att den andra TBC-typen med hög emissivitet och den tredje TBC-typen med en porös mikrostruktur och en låg termisk effusivitet resulterade i hög motoreffektivitet.

Place, publisher, year, edition, pages
Trollhättan: University West , 2022. , p. 107
Series
PhD Thesis: University West ; 49
Keywords [en]
Thermal Barrier Coatings; Suspension Plasma Spraying; Gadolinium Zirconate; Internal Combustion Engines; Engine Efficiency, Termiska barriärbeläggningar; Plasmasprutning; Suspensionssprutning; Gadolinium; Zirkoniumdioxid; Förbränningsmotorer; Motoreffektivitet
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-18369ISBN: 978-91-89325-23-4 (print)ISBN: 978-91-89325-22-7 (electronic)OAI: oai:DiVA.org:hv-18369DiVA, id: diva2:1657643
Public defence
2022-06-17, F131, Gustava Melins gata, Trollhättan, 10:00 (English)
Opponent
Supervisors
Note

Delarbeten är endast i tryckt form tillgängliga och finns inte med i den elektroniska versionen.

Available from: 2022-05-25 Created: 2022-05-11 Last updated: 2022-06-21Bibliographically approved
List of papers
1. Suspension Plasma-Sprayed Thermal Barrier Coatings for Light-Duty Diesel Engines
Open this publication in new window or tab >>Suspension Plasma-Sprayed Thermal Barrier Coatings for Light-Duty Diesel Engines
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2019 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 7, p. 1674-1687Article in journal (Refereed) Published
Abstract [en]

Demands for improved fuel efficiency and reduced CO2 emissions of diesel engines have been the driving force for car industry in the past decades. One way to achieve this would be by using thermal spraying to apply a thermal insulation layer on parts of the engine’s combustion chamber. A candidate thermal spray process to give coatings with appropriate properties is suspension plasma spray (SPS). SPS, which uses a liquid feedstock for the deposition of finely structured columnar ceramic coatings, was investigated in this work for application in light-duty diesel engines. In this work, different spray processes and materials were explored to achieve coatings with optimized microstructure on the head of aluminum pistons used in diesel engine cars. The functional properties of the coatings were evaluated in single-cylinder engine experiments. The influence of thermo-physical properties of the coatings on their functional properties has been discussed. The influence of different spray processes on coating formation on the complex piston head profiles has been also discussed. The results show that SPS can be a promising technique for producing coatings on parts of the combustion chamber, which can possibly lead to higher engine efficiency in light-duty diesel engines.

National Category
Energy Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14511 (URN)10.1007/s11666-019-00923-8 (DOI)0000498221700001 ()2-s2.0-85074254826 (Scopus ID)
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2022-05-11
2. Thermal barrier coatings with novel architectures for diesel engine applications
Open this publication in new window or tab >>Thermal barrier coatings with novel architectures for diesel engine applications
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2020 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 396, article id 125950Article in journal (Refereed) Published
Abstract [en]

The increased demands for higher efficiency and environmentally friendly diesel engines have led to a continuous search for new coating processing routes and new ceramic materials that can provide the required properties when applied on engine components such as pistons and exhaust manifolds. Although successful in gas turbine applications, thermal barrier coatings (TBCs) produced by suspension plasma spraying (SPS) processes have not been employed so far in the automotive industry. This work aims to achieve a better understanding of the role of thermal conductivity and thermal effusivity on the durability of SPS TBCs applied to pistons of diesel engines. Three different coating architectures were considered for this study. The first architecture was yttria-stabilized zirconia (YSZ) lamellar top coat deposited by APS (Atmospheric Plasma Spray) and used as a reference sample in this study. The second architecture was a columnar SPS top coat of either YSZ or gadolinium zirconate (GZO) while the third architecture was an SPS columnar top coat, "sealed" with a dense sealing layer deposited on the top coat. Two types of sealing layers were used, a metallic (M) or a ceramic thermal spray layer (C). Laser Flash Analysis (LFA) was used to determine the thermal conductivity and thermal effusivity of the coatings. Two different thermal cyclic tests were used to test the TBCs behavior under cyclic thermal loads. Microstructure analysis before and after the thermal cyclic tests were performed using SEM in different microstructures and materials. The thermal cyclic test results were correlated with coatings microstructure and thermophysical properties. It was observed that the columnar coatings produced by SPS had an enhanced service life in the thermal cyclic tests as compared to the APS coatings.

Keywords
Suspension plasma spray, Diesel engine, Sealing coating, Yttria stabilized zirconia, Gadolinium zirconate
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-15197 (URN)10.1016/j.surfcoat.2020.125950 (DOI)000540175000022 ()2-s2.0-85085597713 (Scopus ID)
Funder
Swedish Energy Agency
Available from: 2020-06-10 Created: 2020-06-10 Last updated: 2022-05-11Bibliographically approved
3. Microstructural Changes in Suspension Plasma-Sprayed TBCs Deposited on Complex Geometry Substrates
Open this publication in new window or tab >>Microstructural Changes in Suspension Plasma-Sprayed TBCs Deposited on Complex Geometry Substrates
2020 (English)In: Coatings, E-ISSN 2079-6412, Vol. 10, no 7, article id 699Article in journal (Refereed) Published
Abstract [en]

Thermal barrier coatings (TBCs) are considered a promising solution for improving the efficiency of internal combustion engines. Among the thermal spray processes, the relatively newly developed suspension plasma spray (SPS) is an attractive candidate due to its unique microstructural features that have already demonstrated increased performance in gas turbine applications. To achieve these features, thermal spray conditions play an essential role. In specific uses, such as piston of diesel engines, parameters as spray angle and spray distance pose challenges to keep them constant during the whole spray process due to the complex geometry of the piston. To understand the effect of the spray distance and spray angle, a comprehensive investigation of the produced thermal spray microstructure on the piston geometry was conducted. Flat and complex geometry surfaces were coated using the same plasma parameters while the spray angle and distance were changed. Characterization was performed using scanning electron microscopy (SEM) combined with the image analysis technique to perceive the variation of the thickness and microstructures features such as pores, cracks, column density, and column orientation. The results showed that the changes in spray angles and spray distances due to the complex shape of the substrate have a significant influence on the microstructure and thermal properties (thermal conductivity and thermal effusivity) of the coatings. The thermal conductivity and thermal effusivity were calculated by modeling for the different regions of the piston and measured by laser flash analysis combined with modeling for the flat-surfaced coupon. It was shown that the modeling approach is an effective tool to predict the thermal properties and thus to understand the influence of the parameters on the coating properties. Connecting the observations of the work on the microstructural and thermal properties, the complex geometry’s influence on the produced coatings could be diminished by tailoring the process and generating the most desirable TBC for the internal combustion engines in future applications.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
complex geometry substrate, internal combustion engines, object-oriented finite element (OOF2), suspension plasma spraying, thermal barrier coatings
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-15726 (URN)10.3390/coatings10070699 (DOI)000554806700001 ()2-s2.0-85088257159 (Scopus ID)
Funder
Swedish Energy Agency
Available from: 2020-08-24 Created: 2020-08-24 Last updated: 2022-05-11
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