Experimental Study on the Propagation Characteristics of Gas-Coal Dust Coupled Explosion in Variable Cross-Section Pipelines

To investigate the propagation characteristics of gas-coal dust coupled explosions in a confined space with varying cross-sections, this study independently constructed an explosion test pipeline system featuring expansion and contraction structures. Explosion tests were conducted at different gas concentrations (8.5% and 10.5%) with the participation of 100 g/m3 coal dust. Using high-speed photography and pressure measurement systems, the flame propagation behavior, evolution of the flame front velocity, distribution of shock wave overpressure, and dynamic pressure fluctuation characteristics were systematically analyzed. The results indicate that gas concentration significantly affects the flame’s response to changes in the cross-section. Under the 10.5% gas condition, flame propagation is more continuous and the exit velocity reaches 170.15 m/s, which is approximately 42% higher than that under the 8.5% condition. The involvement of coal dust releases substantial energy during the middle and later stages of combustion, forming a multipeak pressure structure. This induces pressure reconstruction and flame acceleration in the cross-sectional contraction zone. Under the 10.5% gas condition, a significant overpressure rebound occurs in the region with abrupt cross-sectional changes, reflecting the combined modulation effect of the gas-coal dust coupled explosion and geometric discontinuity on the explosion dynamics. This study reveals the propagation mechanism of gas-coal dust coupled explosions in variable cross-section pipelines, providing a theoretical basis for explosion risk assessment and prevention in tunnels with complex structures.