## 3 Results and Discussion  
### Finite Element Analysis Results  
After applying the boundary conditions for the NC, FC, PC-5 and PC-10 piston models, the temperature distributions in the pistons were as given in Figure 6. The initial temperature, which was 299.6 \({}^{\circ}\)C for the NC piston model, increased to 527.19 \({}^{\circ}\)C at the piston top after 1500 cycles. As a result of the analysis, the highest temperature value was seen in the piston crown, and the lowest temperature value was seen in the piston skirt. The reason for the highest temperature in the piston crown is the heat flow to which the piston crown is exposed [25]. The maximum observed temperatures for coated pistons were 574.31 \({}^{\circ}\)C, 528.95 \({}^{\circ}\)C and 529.77 \({}^{\circ}\)C on the FC, PC-5, and PC-10 pistons, respectively. Maximum temperature locations also changed with coating type. While the maximum temperature was observed at the piston crown on the FC piston, it was observed at the top of the coating for the partially coated pistons. \begin{table}
\begin{tabular}{l r} \hline
**Fuel** & **Diesel** \\ \hline Rated speed (rpm) & 1500 \\ \hline Number of injection nozzle & 4 \\ \hline Injection spray angle & 140 \\ \hline Inlet temperature & 362 K \\ \hline Inlet pressure & 2.215 bar \\ \hline Fuel injection temperature & 368 K \\ \hline Turbulence model & RNG k-epsilon \\ \hline Wall heat transfer & Han and Reitz \\ \hline Soot emission model & Kinetic model \\ \hline Cylinder head temperature & 470 K \\ \hline Cylinder liner temperature & 420 K \\ \hline \end{tabular}
\end{table} 
Table 4: Simulation boundary conditions. Figure 5: Computational grid of combustion chamber. After the boundary conditions were applied to the surface of the fully coated (FC) piston, the temperature distribution on the coating surface was as presented in Figure 6b. The temperature, initially of 299.6 \({}^{\circ}\)C, reached its highest value of 574.31 \({}^{\circ}\)C on the piston crown at the end of 1500 cycles. The lowest temperature was observed in the region around the piston skirt. The highest temperature in the NiCoCrAlY lining layer was 504.01 \({}^{\circ}\)C on the piston crown, and the minimum temperature was 461.58 \({}^{\circ}\)C in the combustion chamber. The highest temperature on the piston surface was 503.91 \({}^{\circ}\)C at the piston crown, and the lowest temperature was 378.58 \({}^{\circ}\)C towards the piston skirt. The temperature difference between the PYSZ coating surface and the piston surface was approximately 70 \({}^{\circ}\)C.  
In this study, similar results were obtained, and the temperature of the lining layer and the substrate was determined at close values. [PERSON] and [PERSON] [10] investigated the effect of a PYSZ thermal barrier coating on an aluminum-alloy piston on the temperature distribution of the piston in a natural gas-fueled engine with transient analyses. As a result of their study, they determined the highest temperature in the intake parts of the combustion chamber on the coating surface. In the current study, the maximum temperature value was determined around the combustion chamber. In addition, the temperature values observed on the coating material, lining layer, and piston surface had proportionally similar results. Figure 7 shows the time-varying maximum temperature over a 60-s simulation period for the four piston models. The highest temperature values for the four piston models were determined on the coating surface. [PERSON] et al. [19] carried out a thermal analysis for a YSZ-coated piston in a diesel engine and determined the highest temperature on the coating surface as 217.66 \({}^{\circ}\)C on the piston head upper surface towards the combustion chamber. The analyses performed in this study were effective in determining the temperature on the coating surface due to the fact that the boundary conditions affecting the piston were different and the analyses were transient.