## 4 Results and Discussion  
### Formation and Dissipation of Reactants and Reaction Products  
The multistep elementary reaction of methane deflagration is a very short process. Figure 71 shows the mass fraction changes in the intermediate products CH\({}_{3}\) and CH\({}_{2}\)O and final product CO\({}_{2}\) when methane reactants are consumed whereas Figure 71 shows the changes in overpressure and temperature during methane combustion. The initial reaction rate of methane is slow, but the chain reaction starts after generating CH\({}_{3}\), the product of the initial elementary reaction, and CH\({}_{2}\)O, the oxidation product of CH\({}_{3}\). As a result, the methane combustion reaction rate sharply increases, and the final product CO\({}_{2}\) starts to be generated. At the same time, the pressure and temperature of the mixed gas sharply increase. The mass fraction of intermediate products reaches its peak during the intense consumption of methane. The components rapidly participate in the next reaction after generation because of the unstable chemical properties of intermediate products. Moreover, the peak mass fraction is significantly lower than the initial reactants and final products. At this time, the distribution of intermediate products CH\({}_{3}\) and CH\({}_{2}\)O is a thin circle, representing the region of intense methane reaction. The final product CO\({}_{2}\) is inside the circle whereas methane that has not participated in the reaction is outside the circle. When methane is completely consumed, the intermediate products are almost simultaneously consumed. However, the mass fraction of the final product CO\({}_{2}\) still slowly increases, indicating the remaining CO that still continues the reaction at this time. Therefore, the pressure and temperature of the mixed gas slowly increase for a short period of time after the complete consumption of methane. Subsequently, the formation and diffusion of harmful gases CO and CO\({}_{2}\) after explosion were analyzed, as shown in Figure 8,II. At 0.5 ms, the CO mass fraction at points P1 and P2 at the centers of tunnel sections A and B reached 4.77% and 3.07%, respectively, and the CO mass fraction decreased sharply after reaching the peak. The trend of CO mass-fraction time curves at the P3 and P4 points, which are 3 m apart from the P1 and P2 points, is similar to that of the P1 and P2 points, but the peak value is less than 0.09%, and the CO mass fraction at points P5 and P6 (with an interval of 7.5-10.5 m from the ignition source) is less than 0.02%. This finding shows that the CO produced via methane deflagration is consumed in a large amount before it diffuses to the distance. The CO\({}_{2}\) mass fraction at the P1 and P2 points reached 11.98% and 12.11%, respectively. After reaching the peak value, the CO\({}_{2}\) gas began to diffuse slowly to the distance. At 35 ms, the CO\({}_{2}\) gas mass fraction at P1 and P2 decreased to 8.49% and 5.89%, respectively. At the same time, the CO\({}_{2}\) mass fraction at the P3-P8 points in the further distance (4.5-10.5 m from ignition point) increased to 1.29-5.54%. Figure 7: Methane deflagration reaction. Propagation Characteristics of Shock Wave in Approximate Real Tunnel Model and Tunnel Model with Smooth Walls  
In real coal mine gas explosion scenarios, the unevenness of the tunnel walls and floor caused by coal mining has a significant im-pact on the propagation of shock waves in the tunnel. Therefore, we compared and analyzed the propagation and attenuation processes of gas explosion shock waves in ap-proximately real tunnel models with uneven walls and floors, as well as in smooth tunnel models with smooth walls and floors, as shown in Figure 9.  
During the time period from 1.5 ms to 10 ms, the explosion shock wave propagates in the straight tunnels on both sides simultaneously. At 1.5 ms, the initial shock wave is superimposed with the reflection wave from the tunnel wall, and the overpressure reaches the maximum value of 884.5 kPa.