Effect of scale on the explosion of methane in air and its shockwave

Explosion experiments using premixed gas in a duct have become a significant method of investigating methane-air explosions in underground coal mines. The duct sizes are far less than that of an actual mine gallery. Whether the experimental results in a duct are applicable to analyze a methane-air explosion in a practical mine gallery needed to be investigated. This issue involves the effects of scale on a gas explosion and its shockwave in a constrained space. The commercial software package AutoReaGas, a finite element computational fluid dynamics (CFD) code suitable for gas explosions and blast problems, was used to carry out the numerical simulation for the explosion processes of a methane-air mixture in the gallery (or duct) at various scales. Based on the numerical simulation and its analysis, the effect of scale on the degree of correlation with the real situation was studied for a methane-air explosion and its shockwave in a square section gallery (or duct). This study shows that the explosion process of the methane-air mixture relates to the scales of the gallery or duct. The effect of scale decreases gradually with the distance from the space containing the methane-air mixture and the air shock wave propagation conforms approximately to the geometric similarity law in the far field where the scaled distance (ratio of the propagation distance and the height (or width) of the gallery section) is over 80.