## 3 Results and Discussion
### Introduction of Experimental Instruments
In order to control the explosion concentration of mixed dust in the pipeline to around 500 g/m\({}^{3}\), the experimental parameters of mixed dust were debugged using high-speed photography, and experimental parameters shown in Table 2 were obtained. Figure 7: The transparent pipeline explosion propagation system. During the experiment, the oil shale was mixed with MSA, MSA-NaHCO\({}_{3}\), and NaHCO\({}_{3}\), and these mixtures were tested according to the material ratio and experimental parameters shown in Table 5. The experiment started with the smallest dose of the inhibitor and increased thereafter at regular intervals. Each experiment was repeated three times. The result of the group of flame propagation characterization experiments with the longest flame was further analyzed. Figure 8: The oil shale powder spraying process. Experimental Study on Suppression Characteristics of Explosion Pressure of Oil Shale Dust by 20 L Spherical Explosion System in Enclosed Space  
In this experimental study, the explosion dust was oil shale dust. The explosion inhibitors were MSA, NaHCO\({}_{3}\), and MSA-NaHCO\({}_{3}\) composite powder explosion inhibitors at inhibitor equivalents of 0%, 10%, 20%, 30%, 40%, 50%, 60%, etc., until the explosion stopped. The mixing methods were the grinding and screening mixing methods. The dust was poured into the grinding apparatus in proportion and ground in a Chinese planetary ball mill (TC-XQM4) at 400 r/min for 4 min. Then, according to the Taylor standard screening method, the ground dust was screened and the mixed dust with a particle size of less than 75 \(\upmu\)m was prepared. Using the air conditioning system of the laboratory, the environmental conditions of the experiment were limited to: a room temperature of 27 \({}^{\circ}\)C, an relative air humidity of 67%, and an atmospheric pressure of 99.1 KPa. An explosion pressure change curve was obtained, as shown in Figure 9. Adding more than 30% MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor was able to completely inhibit the explosion of oil shale dust. Adding 30% MSA or NaHCO\({}_{3}\) was less effective in suppressing the explosion pressure of oil shale dust than adding a 30% MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor, with a maximum pressure drop of 53.2% for the MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor, 50.6% for NaHCO\({}_{3}\), and 47.8% for MSA. Under the same proportion, the inhibition effect of the three substances on oil shale dust explosion was ranked as: MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor >NaHCO\({}_{3}\) > MSA. Experimental Study on Flame Suppression Characteristics of Oil Shale Dust Explosion by Explosion Inhibitor in Semi Open Space  
Dust explosion behavior tests were conducted in a transparent pipeline explosion propagation system by mixing oil shale dust with an MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor, MSA, and an NaHCO\({}_{3}\) composite powder explosion inhibitor. \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}{*}{**Po/MPa**} \\ \cline{2-2} \cline{6-7}  & **Oil Shale** & & & & & \\ \hline
0 & 9 & 0 & 0 & 0 & 20 & 20 & 1 \\
10\% & 9 & 0.9 & 0.9 & 0.9 & 20 & 22 & 1 \\
20\% & 9 & 1.8 & 1.8 & 1.8 & 20 & 24 & 1 \\
30\% & 9 & 2.7 & 2.7 & 2.7 & 20 & 22 & 1.2 \\
40\% & 9 & 3.6 & 3.6 & 3.6 & 20 As shown in Figure 10, the maximum explosion flame length of the pure oil shale dust was 2.2 m; the flame front was regularly shaped, continuous, and clearly outlined, and the flame was highlighted [29; 30; 31]. After adding explosion inhibitors, the flame length was obviously shortened, the flame speed decreased, and a little explosion delay occurred. As the amount of slag-based composite powder explosion inhibitor increased, the explosion flame front of the oil shale dust changed from parabolic to discrete.