## 5 Results and Discussion  
### Results of Preliminary Experiment  
Figure 5 shows the two partially overlapped H\({}_{2}\)O absorption signals measured at the center temperatures of 1073.15, 1273.15, and 1573.15 K in the electric furnace in the preliminary experiment. As shown in Figure 2b, the linestrengths of the two partially overlapped H\({}_{2}\)O absorption wavelengths with increasing temperature were compared. It was found that the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Equivalence Ratio (\(\blacklozenge\))** & **Fuel (L/min)** & **Air (L/min)** \\ \hline
0.70 & & 252.57 \\
0.85 & & 208.68 \\
1.00 & 8.46 & 176.44 \\
1.15 & & 154.58 \\
1.30 & & 137.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Operating conditions for the combustion experiment of premixed CH\({}_{4}\)/air flame. Figure 4: Schematic diagram of the measurement system applied to a metal fiber burner. Figure 5: (**a**) Two partially overlapped H\({}_{2}\)O absorption signals measured at 1073.15 K, (**b**) 1273.15 K, and (**c**) 1573.15 K in the electric furnace. magnitude of the two partially overlapped H\({}_{2}\)O absorption signals measured according to the temperature in the electric furnace corresponded to the tendency of the ratio of the linestrength analyzed in Figure 2b. Specifically, in the linestrength ratio in Figure 2b, S1 was larger than S2 below 1275.15 K. In contrast, it can be seen that S1 and S2 were the same at 1267.66 K. It was confirmed that S1 tended to be smaller than S2 above 1273.15 K. As shown in Figure 5a, the two partially overlapped H\({}_{2}\)O absorption signals measured at 1073.15 K showed that A1 was larger than A2, such as the ratio of the line strength in Figure 2b. Figure 5b shows that the absorption signals of A1 and A2 were almost the same at 1273.15 K. Finally, it was found that the absorption signal at 1573.15 K was larger in A2 than in A1. Thus, it was confirmed once again that the tendency of the two absorption signals and the line strength ratio analyzed in Figure 2b were the same. Figure 6 shows the result of internal temperatures measured by the T/C of the electric furnace set at 1473.15 K. TDLAS based on line of sight is a technology that provides the line-average information of a measurement target. Therefore, the temperature value measured by TDLAS in the electric furnace was compared with the temperature value measured by the T/C based on the internal length interval measurement. As the measurement range of temperature is different depending on the T/C type, K-type T/C was used for temperatures from 1073.15 and 1173.15 K, and R-type T/C was used for temperatures from 1273.15 to 1573.15 K. In particular, the temperatures were measured at 1-cm intervals in an electric furnace with a length of 170 cm. As shown in Figure 6, the average temperature of the internal length intervals using a T/C at a center temperature of 1473 K was measured at 1273.34 K. The average temperature of the internal length interval was lower than the set center temperature of the electric furnace because the mounts for fastening the CaF\({}_{2}\) windows on both sides of the electric furnace were far from the heating element. In addition, it was a region where heat exchange with the atmosphere occurred, and heat was not preserved at both ends of the electric furnace. As a result, the comparison between the average temperature of the internal length interval measured by the T/C and the set center temperature in the electric furnace was derived, as shown in Table 3.  
Figure 7 shows a comparison of the reconstruction method using half absorbance and the multi-peak Voigt fitting method proposed to analyze the two partially overlapped H\({}_{2}\)O absorption signals. From Equations (1) and (2), the reconstruction method using half absorbance focused on the spectral lineshape symmetry of lifetime broadening, which