## 6 Conclusions  
In this study, an experiment was conducted to measure the H\({}_{2}\)O concentration and temperature in a premixed CH\({}_{4}\)/air flame using two partially overlapped H\({}_{2}\)O absorption signals based on TDLAS. It was confirmed that the two partially overlapped H\({}_{2}\)O absorption regions selected through the HITRAN database did not interfere with other combustion products, and the validity of the wavelengths selected from the optimal line selection method summarized by [PERSON] et al. was verified. The accuracy of the temperature measurement was confirmed in the set temperature range, including the flame temperature, through a preliminary experiment using an electric furnace. To analyze the change in the sensitivity of two partially overlapped H\({}_{2}\)O absorption signals according to the temperature, they were separated into integrated absorbance areas A1 and A2 via multi-peak Voigt fitting. The line-average temperature measured by the multi-peak Voigt fitting base TDLAS within 1073.15-1573.15 K set in the electric furnace exhibited a linear tendency when compared to the temperature measured by the T/C. Subsequently, the flame temperature and H\({}_{2}\)O concentration were derived from the premixed CH\({}_{4}\)/air flame based on the results of the confirmed sensitivity in the preliminary experiment. The temperature measured by the multi-peak Voigt fitting based on the TDLAS and the temperature measured by the T/C corrected for heat loss under lean fuel conditions showed the same tendency, and the highest temperature was measured at an equivalence ratio of 1.00. In the case of the H\({}_{2}\)O concentration in the premixed CH\({}_{4}\)/air flame, the H\({}_{2}\)O concentration derived using the GRI 3.0 mechanism of Chemkin was compared with the H\({}_{2}\)O concentration measured by TDLAS. The H\({}_{2}\)O concentration derived from the Chemkin simulation decreased sharply under fuel-lean conditions, and the highest H\({}_{2}\)O concentration was derived in the fuel-rich region 1.15. Hence, it was consistent with the tendency of H\({}_{2}\)O concentration measured by TDLAS. This study focused on whether it is possible to accurately measure the temperature and H\({}_{2}\)O concentration using two partially overlapped H\({}_{2}\)O absorption signals. In conclusion, \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Equivalence**} & **Measured** & **Standard** & **Measured Conc.** & **Standard** \\  & **Temp. Using** & **D****L****S****L** & **Deviation (\(\pm\)K)** & **Using TD****L****S****L** \\ \hline
0.70 & 1342.3 & 13.1 & 13.89 & 0.32 \\
0.85 & 1374.9 & 16.2 & 15.39 & 0.33 \\
1.00 & 1385.8 & 11.2 & 18.05 & 0.31 \\
1.15 & 1384.3 & 15.6 & 18.92 & 0.32 \\
1.30 & 1337.0 & 13.8 & 18.62 & 0.30 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of the temperature and concentration measured using a TDLAS-based multi-peak Voigt fitting in a premixed CH\({}_{4}\)/air flame, and the analyzed standard deviation corresponding to the measured temperature and concentration. the two partially overlapped H\({}_{2}\)O absorption signals can provide good results and are expected to be effective in measuring the internal temperature and H\({}_{2}\)O concentration of large combustion systems. Conceptualization, S.S.; methodology, S.S.; software, S.S.; validation, J.H., D.K. and C.L. ; formal analysis, S.S.; investigation, S.S., N.J.; resources, C.L. ; data curation, S.S.; writing--original draft preparation, S.S.; writing--review and editing, C.L. ; visualization, S.S., N.J. and A.S.; supervision, C.L. ; project administration, C.L. ; funding acquisition, C.L. All authors have read and agreed to the published version of the manuscript. This work was supported by the KIST Institutional Program (Project No. 2E31340-21-P012). Not applicable. The data presented in this study are available on request from the corresponding author. The authors declare no conflict of interest.