Thermal barrier coatings for efficient combustion
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
A reduction of the Greenhouse Gases (GHG) emissions is of highest importance in all industrial sectors around the world in order to prevent unwanted climate changes. Among EU countries in the last years, a number of international and national procedures and commitments have already been implemented in different sectors. However, in the transport sector however, due to its rapid growth, the overall GHG emission is still increasing. In the IEA technology roadmap for transportation it is stated that today over 50% of oil use is for transportation, three-fourths of it is consumed on the roads. If no preventative steps are taken, the total oil consumption in this sector will double by 2050. The most cost effective way to reduce the oil consumption is to develop more efficient combustion engines.
Today, about 40-45% of fuel energy is converted into a useful work, while remaining fuel energy in form of heat losses is transferred to environment. One of the possible solutions of decreasing heat losses from the engine is by insulation of combustion chamber walls with the Thermal Barrier Coating (TBC). For Scania, as a leader in fuel efficiency, all possible measures of improvements are in the scope of interest. Therefore this master thesis was carried out. The theoretical study was focused on about appropriate materials, industrial applications and the state of the art research in the area of combustion chamber insulation. For the experimental studies three materials with documented performance in the engine and turbine industry were chosen. Piston prototypes and samples for material study were coated using two thicknesses 500 μm and 1000 μm and a coating of Metco 143 ZrO218TiO210Y2O3, Metco 204C-XCL ZrO28Y2O3 (porous) and Metco 204F ZrO28Y2O3 (segmented) powders. The heat capacity, apparent thermal diffusivity and microhardness were measured for each coating. The durability under high temperature variation was tested in a specially designed rig for thermal cycling. Coated pistons were tested in a single cylinder research engine, to verify the insulation potential. TBC samples were investigated with light optical (LOM) and scanning electron microscopy (SEM), both before and after tests. Experiments showed that there was a reduced heat transfer during engine testing with TBC. However, due to negative influence of insulation on the combustion process and lower overall engine efficiency, it was hard to quantify the results. A trend showing decreased heat losses with increased insulation thickness was noticed. During both engine and thermal cycling tests the Metco 143 coating failed mechanically. LOM observations revealed cracks on the top coat/bond coat interface for all the samples after engine testing. Only the Metco 204C-XCL coating showed no changes after a thermal cycling test. Also the porosity proved to be an effective factor decreasing thermal diffusivity as well as to improve the coating tolerance for residual stress. The SEM study revealed cracks in the samples after engine testing in Metco 143 and Metco 204F materials.
Place, publisher, year, edition, pages
EES Examensarbete / Master Thesis
Thermal Barrier Coatings, Yttria stabilized zirconia, titanium oxide, Diesel engine combustion
IdentifiersURN: urn:nbn:se:kth:diva-155055OAI: oai:DiVA.org:kth-155055DiVA: diva2:759397
Master of Science - Materials Science and Engineering
Gramatyka, MichalJönsson, Pär