## 4 Results and Discussion
Subsequently, the magnetron output power was adjusted to 50%, 75%, and 100% of the total power, and the corresponding temperature values recorded by the thermocouple at the burner outlet were documented. The secondary air flow rate of 500 Nm\({}^{3}\)/h, measured in the M4 measurement as presented in Table 1, reached a maximum temperature of 474 \({}^{\circ}\)C at 100% magnetron output power. Moreover, when different magnetron output powers were applied to the air flow rates corresponding to M5, M6, M7, and M8 measurements, the temperature values were recorded at the burner outlet and are illustrated in the graph shown in Figure 6.  
Figure 5: (**a**) Camera setup for observing secondary air transformation; (**b**) plasma formation at 500 Nm\({}^{3}\)/h air flow rate after ignition. As shown in Figure 1, which illustrates the burner structure, the damper labeled as number 9 on the pipe where primary air enters the burner was adjusted to direct a portion of the mixture to channel 4, while the remaining part is directed to channel 5. The damper was adjustable between 0 and 180 degrees. During the tests, the damper was gradually rotated counterclockwise to perform the experiments. The fan was activated, which delivered the primary air to the burner through a 300 mm diameter pipe. At the time the tests were conducted, the ambient temperature of the air was 33 \({}^{\circ}\)C. Although the fan has automatic control, it was set to operate with a maximum capacity of 6000 m\({}^{3}\)/h airflow. After the damper was set to 25\({}^{\circ}\), measurements were taken at the port on the pipe leading to the burner and separately at the ports in channels 4 and 5. In this way, the data obtained from each port were thoroughly examined and compared. These measurements were conducted to understand how the damper position influences and affects the primary airflow. The M9 measurement in Table 2 was conducted at the port on the 300 mm diameter pipe at the burner inlet. The M\({}_{4}\)10 and M\({}_{5}\)11 measurements were taken on channels 4 and 5. Both channels have a diameter of 150 mm. After the damper was set to 50\({}^{\circ}\), measurements were taken at the ports in channels 4 and 5. Finally, the damper was adjusted to 75\({}^{\circ}\), and measurements taken at the same ports are shown in Table 2, along with the previous measurements. After the measurements were completed, the secondary air flow rate was adjusted to 500 Nm\({}^{3}\)/h, and the ignition process was carried out. Once the plasma flame was established, the damper at the burner inlet was adjusted to 25\({}^{\circ}\), and then to 50\({}^{\circ}\) and 75\({}^{\circ}\), with primary air being introduced into the burner. It was observed that the plasma flame remained stable at 25\({}^{\circ}\) but extinguished when the damper was set to 50\({}^{\circ}\) and 75\({}^{\circ}\). Consequently, the damper was set back to 25\({}^{\circ}\), and tests were conducted with pulverized coal and primary air mixtures. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Parameters** & **M9** & **M\({}_{4}\)10** & **M\({}_{5}\)11** & **M\({}_{4}\)12** & **M\({}_{5}\)13** & **M\({}_{4}\)14** & **M\({}_{5}\)15** \\ \hline damper position [\({}^{\circ}\)] & 25 & 25 & 25 & 50 & 50 & 75 & 75 \\ static pressure [Static, Pa] & 325 & 362 & 410 & 384 & 367 & 399 & 341 \\ temperature [T, \({}^{\circ}\)C] & 33 & 33 & 33 & 33 & 33 & 33 & 33 \\ density [\(\rho\), kg/m\({}^{3}\)] & 1.14 & 1.14 & 1.14 & 1.14 & 1.14 & 1.14 & 1.14 \\ \({}^{*}\) differential pressure [APdifferential, Pa] & 292 & 190 & 297 & 591 & 1923 & 962 & 1381 \\ velocity [V, m/s] & 23.57 & 19.02 & 75.30 & 33.58 & 60.57 & 42.84 & 51.31 \\ secondary air flow [Q, Nm\({}^{3}\)/h] & 5998 & 1210 & 4790 & 2140 & 3860 & 2730 & 3270 \\ \hline \end{tabular} \({}^{*}\) The differential pressure values represent the average values measured at each port.  
\end{table} 
Table 2: Primary air measurements. Figure 6: Plasma flame temperatures were measured at the burner outlet under different secondary air flow rates and magnetron output power levels.