## 5 Results and Discussion
### Results of Combustion Experiment  
The temperature and H\({}_{2}\)O concentration in the premixed CH\({}_{4}\)/air flame were derived from the two partially overlapped H\({}_{2}\)O absorption signals with high sensitivity, as confirmed by the multi-peak Voigt fitting method using an electric furnace (Figure 10). Figure 10a shows the two partially overlapped H\({}_{2}\)O absorption signals at an equivalence ratio of 1.00, for the premixed CH\({}_{4}\)/air flame. Similar as in the temperature analysis of the preliminary experiment, the integrated absorbance areas A1 and A2 were separated using a multi-peak Voigt fitting, and the flame temperature was derived by applying the separated integrated absorbance areas A1 and A2 to temperature equation [24]. Thereafter, the derived flame temperature was used to calculate the linestrength equation [26], and the obtained linestrength was used to calculate the H\({}_{2}\)O concentration using concentration equation [27]. Figure 10b shows the two partially overlapped H\({}_{2}\)O absorption signals at an equivalence ratio of 1.00, as shown in Figure 10a. The H\({}_{2}\)O concentration in the premixed CH\({}_{4}\)/air flame was calculated using the total integrated absorbance area (consecutive slashes), as shown in Figure 10b. That is, as shown in absorbance equation [27], the total linestrengths in the wavelength range in which the absorption signal occurs should be included in the two partially overlapped H\({}_{2}\)O absorption signals. Therefore, after applying the measured flame temperature to linestrength equation [24], the linestrength corresponding to the two partially overlapped H\({}_{2}\)O absorption signals was calculated. Then, it was applied to the calculation of the H\({}_{2}\)O concentration in the premixed CH\({}_{4}\)/air flame by using the integrated absorbance obtained from the total partially overlapped H\({}_{2}\)O absorption signals shown in Figure 10b. Figure 11 shows a graph comparing the flame temperature and H\({}_{2}\)O concentration measured by TDLAS with the temperature value measured by R-type T/C and the H\({}_{2}\)O concentration derived by Chemkin. Figure 10: Two partially overlapped H\({}_{2}\)O absorption signals (**a**) for measuring temperature, and (**b**) for measuring H\({}_{2}\)O concentration under an equivalence ratio of 1.00. Figure 9: Reconstruction method using half absorbance for measured data at (**a**) 1073.15 K and (**b**) 1473.15 K.  
Figure 11a shows the results of comparing the temperature measured using the R-type T/C and the temperature measured by the multi-peak Voigt fitting base TDLAS at a height of 5 mm above the surface of the metal fiber burner. The blue symbol in Figure 11a is the average temperature measured using R-type T/C corrected for heat loss (radiative, etc.) based on the internal length interval measurement in the flame, such as the laser path. As shown in Figure 11a, the temperature measured by the R-type T/C with various bead sizes (0.4, 0.8, and 1.0 mm) was derived by a linear function in which the temperature increased as the bead size decreased at the measured point in the flame. Then, the heat loss of R-type T/C was corrected [28]. The error bar of the blue symbol was caused by the temperature fluctuation measured by T/C in the region where the flame surface and the outside air react. That is, the temperature measured by the multi-peak Voigt fitting base TDLAS and the temperature measured by calibrated R-type T/C corrected for heat loss showed similar tendencies. In general, in the case of a premixed flame in which fuel-air is well mixed, the temperature near equivalence ratios of 1.00-1.05 has the highest value compared to when the fuel is rich or lean [29, 30]. As can be seen in Figure 11a, the temperatures measured by the multi-peak [PERSON] fitting-based TDLAS and the temperature measured by the R-type T/C were the highest at 1385.80 and 1384.90 K, respectively at the equivalence ratio of 1.00, and the temperature decreased in the fuel-lean condition less than the equivalence ratio of 1.00.