## 4 Results and Discussion
### Explosive Pressure Change Analysis  
Overpressure is an important indicator for evaluating explosive hazards. Obstructions can affect the distribution and peak of overpressure generated by an explosion, especially in pipelines or vessels. The deflagration phenomenon of premixed combustible gases is a non-pressurized combustion, which may lead to localized overpressure, generating pressure waves and increasing the destructive force of the explosion. During the explosion, the obstacle absorbs heat from the flame and transfers it to the surrounding gas by heat conduction and thermal radiation [34], which raises the temperature and volume expansion, thereby increasing the pressure. Explosive overpressure shows a tendency to rise and then fall. The pressure relief and deflagration generated by overpressure alternately play a major role because, as the intensity of the deflagration increases, the deflagration generated by the overpressure becomes greater than the overpressure released from the vent. The overpressure rapidly accumulates and rises until it reaches the peak overpressure. Subsequently, the rate of release of overpressure exceeds the rate of generation, and the release is dominated by the gradual decrease in overpressure. As shown in Figure 10, the premixed flame propagated in a laminar combustion state with relatively slow combustion until the flame crossed the obstacle at 200 mm. During the flame crossing the obstacle, the turbulence caused by the obstacle perturbs the flow field, resulting in a change in the momentum distribution of the combustion gases. This perturbation effect reduces the momentum transfer efficiency of the combustion products, which slows down the growth of the pressure wave in the deflagration process to a certain extent and reduces the overpressure peak generated by the deflagration. It was observed  
Figure 9: Flame evolution at 800 mm for obstacles of different angles. that when the obstacle position was increased from 200 mm to 500 mm, the pressure peak did not reduce the explosion pressure by moving away from the ignition source. The 800 mm point has some relief effect on the pressure due to its proximity to the vent. For premixed gas combustion throughout the weakly constrained structure, at this point, the combustion is already halfway through, and the already-fired gas in the vicinity of the ignition source is beginning to cool down due to the small amount of fuel left to burn. Thermal expansion not only drove the unburned gas but also maintained the heat loss of the burned gas. At the same time, the obstacle at 800 mm made it difficult for the returning pressure wave to act on the pressure sensor near the ignition source, resulting in the pressure at the location being much smaller than that at other positions. The peak pressure at 800 mm with the angle decreases with the decrease of the angle (a decrease in angle favors the flame rushing out of the pipe pressure relief port). Observe Figure 10: when the obstacle was placed at 200 mm, the maximum and minimum explosion overpressure peak difference was nearly 13 kPa. Obstacle_30\({}^{\circ}\) had the greatest impact on the deflagration, as the flame was in the forced acceleration period. Obstacle_30\({}^{\circ}\) upwind on the flame obstruction effect was the weakest, and the flame speed impact was small. Obstacle_90\({}^{\circ}\) had the largest interference with flame acceleration, so the explosion pressure under this condition was the lowest. It can be seen that increasing obstacle interference near the ignition source is beneficial for reducing the explosion effect. However, Obstacle_90\({}^{\circ}\) produced the maximum peak overpressure at 500 mm and 800 mm. The reason for this may be that after the flame passes through the right-angle obstacle, the degree of flame fragmentation and turbulence is significant, leading to an increase in the surface area of the combustion region. This increases the contact area with oxygen, thus speeding up the combustion rate and releasing more heat, which leads to the rise in pressure.