Effect of partitioned thermal barrier coating on performance and exhaust emissions in a diesel engine and thermal and pressure stress analysis of combustion chamber elements

Different methods can be applied in order to increase the efficiency of internal combustion engines and improve their emissions. Due to the ease of application and developments in material technology, the thermal barrier coating is one of the methods used in recent years. It is aimed to reduce heat losses and increase engine performance by coating the piston surface with low heat transfer coefficient materials. Alumina, zirconia, magnesia, Berrillia, Lantanat and Gadalium can be used as coating material. In the present study, the engine piston was coated with Yttria stabilized zirconia by plasma spray coating technique. Engine performance and exhaust emission tests, heat transfer, and combustion analyzes were carried out with four piston models with uncoated (reference model), fully coated, and two different partially coated. It is aimed to increase the strength of the coating layer and at the same time reduce NOx emissions by applying a partial coating process on the piston surface. Six different load levels were used in the engine performance and exhaust emission experiments. Six different thermocouples were used to read the temperature change in, the intake line, exhaust manifold, air cooling fin tip, air cooling fin bottom, top cover, and engine oil during the experiments. Piston models were designed using Solidworks 2022 software for using finite element simulations. Piston models were imported to Ansys Workebench 2021 R1 for transient thermal and transient structural analysis. As a result of transient thermal and structural analyzes, temperature distribution, heat flux, von-Mises stress values, and total strain for the piston, lining layer, and coating surface was obtained. For the combustion analysis, the piston model was created in the ANSYS Forte software, and as a result of the analysis, internal piston temperature, internal piston pressure, exhaust emission, and heat transfer data were obtained. As a result of the experiments, it was determined that the NOx exhaust emission values decreased but the fuel consumption increased in the partially coated piston models compared to the fully coated piston model. In the HC exhaust emission values, values close to 50% loading conditions were determined for the four piston models, while the highest value was determined in the whole surface-covered piston model at the 62.5% loading condition. As a result of transient thermal analysis, the highest piston surface temperature was obtained for the fully coated piston model. It has been observed that the heat losses in the fully coated piston model are lower than the other piston models. It has been determined that the amount of heat flux in the partially coated piston models is low on the coated surface, while it is higher in the uncoated combustion chamber area. As a result of the combustion analyses carried out, the in-cylinder temperature and pressure values were found to be the highest in the fully coated piston, the lowest in the uncoated piston model, and in these two value ranges and close to each other in the partially coated piston models. As a result of the combustion analysis, when the heat transfer rates on the wall were compared, the highest transfer was observed in the uncoated piston model, while the lowest heat transfer was detected in the fully coated piston model. The highest combustion efficiency was observed in the fully coated piston, but the NOX exhaust emission is higher compared to other piston models.