## 3 Results and Discussion  
### Introduction of Experimental Instruments  
In this study, according to Chinese national standard GB/T 16425, a standard 20 L spherical explosion system was used to carry out the explosion suppression experiment, as shown in Figure 6. The device consisted of three main parts: a main sphere, a control system, and a data acquisition system [28]. During the experiment, a 10 KJ chemical igniter was installed at the center of the ignition electrode in the 20 L spherical tank, and then the 20 L spherical tank was closed. A given weight of dust was placed in the dust bin, the explosion chamber was vacuumed to 0.06 MPa, and the dispersion pressure was set to 2.0 MPa. When the solenoid valve between the dust storage container and the test chamber opened automatically, air and dust were sprayed into the explosion chamber and ignited after a delay of 60 ms. An oil shale dust concentration of 500 g/m\({}^{3}\), which had the strongest explosion index, was chosen as the experimental explosion suppression concentration. During the experiment, 10 g of oil shale were mixed with MSA, MSA-NaHCO\({}_{3}\), and NaHCO\({}_{3}\) and tested according to the material ratio and experimental parameters  
Figure 5: The nitrogen adsorption–desorption results of composite powder explosion inhibitors. shown in Table 4. The experiment started with the smallest dose of the inhibitor and increased thereafter at regular intervals. Each experiment was repeated three times. The results of the group of 20 L spherical explosion characterization experiments with the largest maximum explosion pressure (\(P_{\text{max}}\)) and the largest maximum explosion pressure rise rate (\(dP/dt\))\({}_{\text{max}}\) were further analyzed. The explosion flame propagation was characterized with a transparent pipeline explosion propagation test system. The main pipe of the experimental system was 3 m long and 0.15 m in diameter. The entire test system included a powder sprayer system, an igniter system, a data collection system, a high-speed camera, and a pipeline system, as shown in Figure 7. The air transmission switch was turned on to let compressed air into the air cylinder until the rated power injection pressure (1 MPa) was reached. The ignition energy parameter (E = 20 J) and ignition delay time (t = 25 ms) were set. When the control system began to work, the solenoid valve was opened. The compressed air sprayed the dust in the dust bin into the pipeline through the dispersion valve and evenly dispersed the dust into the pipeline space. After the time delay, the ignition system excited ignition, and the target powder was ignited. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Material Proportion**} & \multicolumn{5}{c}{**Mass/g**} & \multirow{2}{*}{**E/J**} & \multirow{2}{*}{**t/ms**} & \multirow{2}{*}{**P/MPa**} \\ \cline{2-2} \cline{5-6}  & **Oil Shale** & & & & & & \\ \hline
0 & 10 & 0 & 0 & 0 & 10 KJ & 60 ms & 2 MPa \\
10\% & 10 & 1 & 1 & 1 & 10 KJ & 60 ms & 2 MPa \\
20\% & 10 & 2 & 2 & 2 & 10 K  
As the mass of mixed dust changed with the addition of the inhibitor, it was necessary to use a high-speed photography to debug various parameters (primarily the initial ignition energy E, ignition time delay t, and initial spray pressure P\({}_{0}\)) to keep the mass concentration of the dust unchanged while exploding in the pipeline. As shown in Figure 8, before ignition, the dusting length of pure oil shale dust at 20 ms reached 1 m. After 20 ms, the dust cloud began to segment in the pipeline and a lot of dust was deposited at the bottom of the pipeline. Thus, if ignition began at that time, the dust cloud could not fully participate in the explosion reaction. Therefore, experimenting with parameters for complete dust cloud state could ensure the best state of dust explosion. As calculated, the explosion concentration of 9 g of oil shale dust in the pipeline at 20 ms was 509 g/m\({}^{3}\).