Characteristics of methane-air explosions in large-scale tunnels with different structures

Abstract

To investigate the characteristics of methane-air explosions in large-scale tunnels with different structures, the CFD code for gas explosion modelling of FLACS was validated and used to model the explosions in tunnelling faces, coalfaces and crosscuts, where explosions mostly occurred in coalmines. The maximum overpressures were obtained as about 150–1400 kPa but varied for places with different cross-sections. The confinement degree and combustible mixture volume compete for controlling the overpressures, the space congestion degree influences the competition. For the tunnelling faces and crosscuts with low congestions, the increase of confinement degree caused by reducing cross-sections takes the dominant effect, which makes the overpressure in 3 m × 2 m cross-section tunnels higher. However, the 6 m × 4 m coalface produces the largest overpressure as the highly congested coalface strengthens the effect of increasing the mixture volume on pressure rise. Since the pressure reflection results from space constraints, a higher confinement degree causes a greater reflection. In crosscuts with both ends closed, the delayed combustion of the unburnt rich mixture after the seal’s failure generates a high pressure than assumed. Because of containing the same volume combustible mixtures in the crosscut modelling with the same cross-section, little difference exists in the overpressure regardless of sealing conditions. The flame is more inclined to propagate towards free spaces, and the flame of a larger volume combustible mixture fills a longer tunnel more comprehensively. In straight tunnelling faces, the flame length can be calculated as the product of the equivalent side length of the cross-section and its corresponding simulated constant.