Propagation characteristics of flame and shock wave in gas–coal dust coupled explosions in a variable-cross-section pipeline

To reveal the evolution characteristics of flame and shock waves in gas-coal dust coupled explosions under conditions of sudden cross-sectional changes, this paper designs and builds a transparent plexiglass pipeline test system with three different cross-sectional sizes. Comparative experiments were conducted on coupled explosions with 8.5 and 10.5% gas concentrations and 100 g/m³ coal dust. By combining high-speed camera technology and a high-frequency pressure acquisition system, a systematic analysis was performed on the morphological evolution of the explosion flame, changes in flame front velocity, shock wave overpressure distribution, and its dynamic fluctuation behavior. The results indicate that gas concentration has a decisive impact on the flame propagation speed, acceleration timing, and pressure peak value of the coupled explosion. Under the condition of 10.5% gas, the time taken for the flame to develop from ignition to the outlet is shorter (31 ms vs. 42 ms), the peak velocity is higher (348.6 m/s vs. 260.66 m/s), and the pressure peak occurs earlier and is more intense (812.05 mbar vs. 509.97 mbar). The sudden cross-sectional change structure significantly affects the flame morphology and shock wave propagation, with small cross-sectional pipelines inducing flame stretching and acceleration, while large cross-sectional areas lead to rapid pressure decay. Under low gas concentration conditions, the shock wave exhibits stronger nonlinear fluctuations and reflection superposition characteristics. The study reveals the coupling mechanism of gas concentration and pipeline structure in regulating the propagation of coupled explosions, providing a theoretical basis for the prediction and prevention of explosion disasters under complex mine conditions.