Flammability and Explosion Risk of Post-explosion CH4/air and CH4/coal dust/air Mixtures

The post-explosion gaseous environment in a coal mine influences the occurrence of secondary explosions. The flammable and explosion risk of post-explosion gases (CH4/air and CH4/coal dust/air mixtures) was evaluated. Explosion tests were carried out in a 20-L spherical explosion device under conditions with different air-fuel ratios. The composition and volume fraction of post-explosion gases were collected and analyzed. CO and H2 are two main possible flammable gas products with increasing initial fuel-air ratio. Unexpectedly, H2 was generated after a CH4/air explosion when the initial φ(CH4) ≥ 13%, in which condition the concentration of O2 was far from sufficient to oxidize CH4. The volume fraction of flammable gas in residual gases of CH4/coal dust/air mixture explosions was higher than that of CH4/air mixtures. It was found that the secondary explosion risk increased significantly when coal dust was involved in a methane explosion. The lower explosion limit (LEL) of post-explosion flammable gases decreased with the increasing mass concentration of coal dust. The flammable component of such post-explosion gases affected the secondary explosion.