## 2 Materials and Methods
### Temperature Calibration Experiment  
The temperature field detection imaging in this study was mainly realized using visible light cameras, specifically two Tucsen Photonics DHYANA 400 BSI V2 sCMOS cameras [45] (Tucsen, Fuzhou, China), with image resolutions of 2048 \(\times\) 2048 and an image frame rate \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Wavelength Interval (nm)** & **10** & **20** & **30** & **40** & **50** & **60** \\ \hline Error (\%) & 3.80 & 2.41 & 1.52 & 0.79 & 0.80 & 0.80 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Error results of blackbody temperature measurement for 800 \({}^{\circ}\)C.  
Figure 4: Average spectrum of nitrocellulose residues. of 40 Hz. For spectral analysis based on energy-containing materials above, we choose \(\lambda_{1}=694\pm 10\) nm and \(\lambda_{2}=768\pm 10\) nm, two kinds of narrow-band filters installed in front of the camera lens for temperature field narrow-band filter detection. The temperature field detection imaging module is shown in Figure 5.  
Compared with other papers [22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38], the resolution of the temperature measurement image in this paper has been greatly improved, reaching 2048\(\times\)2048 image pixels with a spatial frequency of 76.92 Ip/mm. This method has the advantage of achieving higher-resolution two-dimensional imaging of flames. Before acquiring images of the temperature field using two high-precision scientific cameras, the DHYANA 400 BSI V2, it is essential to calibrate the cameras, as illustrated in Figure 6. The optical path employs a beamsplitter with a discrete beam splitter to facilitate simultaneous image acquisition by both cameras--one equipped with a 694 nm filter and the other with a 768 nm filter. Both cameras are configured with identical parameters: an exposure time of 100 microseconds, an aperture of f/1.4, and each camera utilizes a 2/3-inch lens with a focal length of 50 mm. The two cameras capture the same target temperature information through the beamsplitter, and a synchronous trigger device ensures that both cameras collect temperature data simultaneously, which is then transmitted to a computer for processing. In this study, we utilized the medium-temperature blackbody furnace SR20-32 from CI, Israel, as the standard temperature radiation source. This furnace features a blackbody cavity with an inner diameter of 25.4 mm, a length of 100 mm, and a spectral emissivity of approximately 0.99. We conducted a temperature calibration of the camera for the range of 600 to 1000 \({}^{\circ}\)C. The calibration experiment was arranged as illustrated in Figure 6, with the imaging system positioned 0.5 m away from the opening of the blackbody furnace cavity. The lens focus was adjusted to ensure a clear and stable image. Two sCMOS cameras were employed to capture images at intervals of 25 \({}^{\circ}\)C, starting from 600 \({}^{\circ}\)C, resulting in a total  
Figure 5: Two-color thermometry cameras. (**a**) Physical view of the sCMOS cameras; (**b**) Filter and mounting bracket. Figure 6: Schematic diagram of the calibration experiment. of 17 acquisitions. Upon completion of the image acquisition, the grayscale images at each temperature were processed in batches to extract the relevant luminescence data from the blackbody cavity. Subsequently, we averaged the grayscale values within the designated region and fitted the relationship between spectral irradiance and the average grayscale value at various temperatures of the blackbody.