## 3 Results and Discussion
### Combustion Analysis Results  
The variations in pressure values obtained as a result of experiments and simulations for the NC and FC pistons are given in Figure 12. The in-cylinder pressure values of the engine were read using the FEBRIS combustion analysis program. In-cylinder pressure values obtained as a result of experiment and simulation for the NC and FC pistons were determined as confirming each other. The application of a thermal barrier coating on the  
Figure 11: The total deformation distribution for (**a**) NC assembly model, (**b**) FC assembly model, (**c**) PC-5 assembly model, and (**d**) PC-10 assembly model. Figure 10: (**a**) von Mises stress variation. (**b**) von Mises stress variation at the coating surface. (**c**) von Mises stress variation on the piston surface. piston surface led to an increase in the in-cylinder pressure value. The FC piston reached a higher in-cylinder pressure value due to the insulating feature of the TBC. The variations in the heat release rate (HRR) and in-cylinder pressure for different piston models are given in Figure 13. The highest in-cylinder pressure values were determined as 12.24 MPa for the NC piston, 12.6 MPa for the PC-5 piston, 12.5 MPa for the PC-10 piston, and 12.8 MPa for the FC piston. A higher in-cylinder pressure value was observed for the FC piston compared to the NC piston. The increase in the amount of coating surface caused an increase in the in-cylinder pressure values. The highest HRR values were observed for all piston models at \(-2\)\({}^{\circ}\)CA. The HRR values were determined as 357.9 J/deg, 351.6 J/deg, 350.7 J/deg, and 313.1 J/deg for the NC, PC-10, PC-5, and FC pistons, respectively. Due to the higher cylinder temperature of the FC piston compared to the other pistons, the ignition delay was shorter, and combustion started earlier. Therefore, the FC model was identified as the model with the lowest HRR rate. Figure 12: Comparison of experimental and simulation pressure values for NC and FC piston models. Figure 13: In-cylinder pressure and HRR values for different piston models. In-cylinder temperatures and the heat transfer rate on the wall divided by the crank angle are given for the four piston models in Figure 14. The highest in-cylinder temperature values were determined as 1225.4 K, 1261 K, 1265.2 K, and 1287 K for the NC, PC-10, PC-5, and FC pistons, respectively. The in-cylinder temperature was the lowest in the NC piston because the heat losses in the NC piston were higher than in the other piston models. While the in-cylinder temperatures of the PC-5 and PC-10 pistons were close to each other, the highest in-cylinder temperature value was obtained for the FC piston model. The heat transfer rate on the wall corresponding to 0 \({}^{\circ}\)CA was observed as 33 J/deg, 29.6 J/deg, 28.6 J/deg, and 23.6 J/deg for the NC, PC-10, PC-5, and FC pistons, respectively. The heat transfer rate on the wall corresponding to 16 \({}^{\circ}\)CA was observed as 11.3 J/deg, 10.8 J/deg, 10.7 J/deg, and 9.2 J/deg for the NC, PC-10, PC-5, and FC pistons, respectively. A decrease in the heat transfer rate on the wall was observed after 0 \({}^{\circ}\)CA. Similar variations in the amount of heat transfer from the wall were observed for the PC-5 and PC-10 models. The highest heat transfer amount was observed in the NC model. At 40 \({}^{\circ}\)CA, the values of 1.56 J/deg, 1.43 J/deg, 1.44 J/deg, and 1.36 J/deg were observed for the NC, PC-10, PC-5, and FC models, respectively. The highest amount of heat transfer on the wall was determined in the uncoated model, and the lowest amount in the model with full surface coating. A decrease was observed in the in-cylinder temperatures with the decrease in the coating surface area in the models with the coating process. The decrease in the in-cylinder temperature values was due to the higher heat transfer losses. Figure 15 demonstrates the effect of TBC on exhaust emissions. The EVO (exhaust valve open) emission represents the simulation results, while the Exp. represents the experimental results.