## 3 Results and Discussion
### Combustion Analysis Results
The simulation results for NO\(\chi\) emissions indicated values of 19.44 ppm for the NC piston model, 26.26 ppm for the PC-10 piston model, 25.36 ppm for the PC-5 piston model, and 31.14 ppm for the FC piston model. Both experimental and simulation results show that the highest NO\(\chi\) value was observed for the fully coated piston. Good agreement was observed between the simulation and experimental results in the emissions data for the different piston models. As the TBC surface area increased in the piston models, the NO\(\chi\) emissions obtained from both the EVO and experimental results increased, while the CO and HC emissions decreased. The simulation results for the CO emissions were determined as 0.015, 0.011, 0.010, and 0.009 for the NC, PC-10, PC-5, and FC models, respectively. Both experimental and simulation results indicated that the highest CO and HC values were observed for the uncoated piston. [PERSON] et al. [22] found that as the thermal conductivity of  
Figure 14: In-cylinder temperature values and variation in the heat transfer on the wall as a function of crank angle for different piston models. the TBC decreases, CO and HC emissions decrease, while NO\({}_{\chi}\) emissions increase. [PERSON] and [PERSON] [30] conducted a study and observed that as the thermal conductivity of the TBC decreases, NO\({}_{\chi}\) emissions increase, while smoke density, carbon monoxide, carbon dioxide, and hydrocarbon emissions decrease. Results similar to those of studies in the literature were obtained in this study. NO\({}_{\chi}\) emissions increased as the coating surface area increased, and it was observed that CO emissions decreased. [PERSON] et al. [31], in their experiments on a coated engine, found a decrease in CO, HC, and smoke emissions for all fuel types and an average increase of 12.48% in NO\({}_{\chi}\). The distribution of cylinder internal temperatures based on different piston models and crank angles is shown in Figure 16. The maximum cylinder internal temperature corresponding to \(-2\)\({}^{\circ}\)CA was observed to be 2307.8 K, 2323.9 K, 2328.2 K, and 2330 K for the NC, PC-10, PC-5, and FC pistons, respectively. For 0 \({}^{\circ}\)CA, the maximum cylinder internal temperature was observed to be 2326 K, 2350.8 K, 2352.5 K, and 2361 K for the NC, PC-10, PC-5, and FC pistons, respectively. It could be observed that the temperature distribution within the cylinder was wider and higher for the FC model. [PERSON] et al. [32] determined that applying thermal barrier coatings to the combustion chamber leads to an expansion of the high-temperature area within the piston. The temperature distribution in the combustion chamber differs between coated and uncoated piston models. For 8 \({}^{\circ}\)CA, the maximum cylinder internal temperature was observed to be 2283 K for the NC model, 2297.7 K for the PC-10 model, 2307 K for the PC-5 model, and 2318.5 K for the FC piston model. Figure 17 demonstrates the effect of the thermal barrier coating (TBC) applied to the piston surface on thermal efficiency and combustion efficiency. The thermal efficiency values for the NC, PC-10, PC-5, and FC piston models were determined as 0.285, 0.331, 0.336, and 0.364, respectively. An increase in thermal efficiency was observed as the coated area on the piston surface increased. The lowest thermal efficiency was observed in the uncoated piston, while the highest thermal efficiency was observed in the fully coated piston. The thermal efficiency values were found to be close for the PC-5 and PC-10 pistons. [PERSON] et al. [33] found that the thermal efficiency of the TBC-applied piston increased by 2% compared to the uncoated piston engine. The combustion efficiency values for the NC, PC-10, PC-5, and FC models were determined as 0.869, 0.919, 0.921, and 0.928, respectively. The lowest combustion efficiency was observed in the uncoated piston, while the highest combustion efficiency was observed in the fully coated piston.