Thermal insulation of the combustion chamber in a light duty diesel engine
Doktorsavhandling, 2024
Reduction of heat loss from the combustion chamber in an engine has great potential to decrease fuel consumption and CO2 emissions. Research on thermal barrier coatings (TBC) has been performed since the early eighties to address this potential. However, reported results for engine efficiency improvements with insulation show a large spread and there is no consensus on the actual benefits of TBCs. The purpose of this PhD project was to make an accurate assessment of state-of-the-art TBCs and establish what coating properties are required to improve indicated engine efficiency.
Cylinder pressure data and measured heat losses to the piston cooling oil in a light duty single cylinder engine formed the basis for the experimental research. A robust and automated measurement method was developed and combined with statistical modeling of the data.
Plasma sprayed yttria stabilized zirconia and anodized alumina were selected to establish the effectiveness of state-of-the-art TBCs. These coatings, applied on the piston top, did not improve indicated efficiency. The high surface roughness of the coatings was an important contributor to the poor performance.
Experiments with a novel coating technology: suspension plasma spraying and a new material gadolinium-zirconate, led to a slightly improved indicated efficiency. Details in the heat release analysis indicated that the high open porosity in this coating might lead to increased heat losses and fuel entrainment.
An investigation of possible charge entrainment effects in a standard plasma sprayed zirconia thermal barrier coating was performed, using a combination of engine experiments, CFD simulations and a 0D crevice model. The crevice model predicted the observed deviations of the apparent rate of heat release surprisingly well, which is strong evidence for the existance and significance of this crevice effect.
To significantly increase engine efficiency with thermal insulation, materials with further reduced thermal conductivity and volumetric heat capacity are needed, while negative effects such as high surface roughness and crevice effects from permeable porosity should be minimized.
Cylinder pressure data and measured heat losses to the piston cooling oil in a light duty single cylinder engine formed the basis for the experimental research. A robust and automated measurement method was developed and combined with statistical modeling of the data.
Plasma sprayed yttria stabilized zirconia and anodized alumina were selected to establish the effectiveness of state-of-the-art TBCs. These coatings, applied on the piston top, did not improve indicated efficiency. The high surface roughness of the coatings was an important contributor to the poor performance.
Experiments with a novel coating technology: suspension plasma spraying and a new material gadolinium-zirconate, led to a slightly improved indicated efficiency. Details in the heat release analysis indicated that the high open porosity in this coating might lead to increased heat losses and fuel entrainment.
An investigation of possible charge entrainment effects in a standard plasma sprayed zirconia thermal barrier coating was performed, using a combination of engine experiments, CFD simulations and a 0D crevice model. The crevice model predicted the observed deviations of the apparent rate of heat release surprisingly well, which is strong evidence for the existance and significance of this crevice effect.
To significantly increase engine efficiency with thermal insulation, materials with further reduced thermal conductivity and volumetric heat capacity are needed, while negative effects such as high surface roughness and crevice effects from permeable porosity should be minimized.
temperature swing
crevice effect.
porosity
heat transfer
surface roughness
efficiency
diesel engine
surface sealing
thermal barrier coating
HA4, Hörsalsvägen 4
Opponent: Prof. Zoran Filipi, Department of Automotive Engineering, Clemson University, USA
Författare
Joop Somhorst
Chalmers, Mekanik och maritima vetenskaper, Energiomvandling och framdrivningssystem
Swinging coatings for better engines
The modern diesel engine is a very efficient thermodynamic machine. In an almost magical way it transforms heat from combustion into mechanical motion. Still, there is potential for improvement: in theory up to 30% less fuel would be used if the heat loss from the combustion chamber could be eliminated completely. This PhD thesis is about understanding why this potential has not been realized and what is required for successful insulation. Accurate measurements supported by simulations showed that traditional thermal barrier coatings used in gas turbines are not suitable for intermittend combustion.
Effective insulation requires temperature swing coatings that follow the fluctuating temperature in the combustion chamber. This demands for materials with extremely low thermal conductivity and heat capacity. A way forward here could be to incorporate a high content of air. Application of a coating can also have negative effects on engine efficiency. Four of these effects - related to compression ratio, soot deposits, surface roughness and charge entrainment in the coating - have been investigated and quantified. With more knowledge about coating material requirements and potential negative side effects from coating application, better guidelines can be given for future coating material development.
The modern diesel engine is a very efficient thermodynamic machine. In an almost magical way it transforms heat from combustion into mechanical motion. Still, there is potential for improvement: in theory up to 30% less fuel would be used if the heat loss from the combustion chamber could be eliminated completely. This PhD thesis is about understanding why this potential has not been realized and what is required for successful insulation. Accurate measurements supported by simulations showed that traditional thermal barrier coatings used in gas turbines are not suitable for intermittend combustion.
Effective insulation requires temperature swing coatings that follow the fluctuating temperature in the combustion chamber. This demands for materials with extremely low thermal conductivity and heat capacity. A way forward here could be to incorporate a high content of air. Application of a coating can also have negative effects on engine efficiency. Four of these effects - related to compression ratio, soot deposits, surface roughness and charge entrainment in the coating - have been investigated and quantified. With more knowledge about coating material requirements and potential negative side effects from coating application, better guidelines can be given for future coating material development.
Ämneskategorier
Produktionsteknik, arbetsvetenskap och ergonomi
Energiteknik
Keramteknik
Farkostteknik
Strömningsmekanik och akustik
Reglerteknik
Drivkrafter
Hållbar utveckling
Styrkeområden
Transport
ISBN
978-91-7905-991-0
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5457
Utgivare
Chalmers
HA4, Hörsalsvägen 4
Opponent: Prof. Zoran Filipi, Department of Automotive Engineering, Clemson University, USA