Influence of Gas Compression on the Process of an Accidental Methane/Air/Coal Dust Fire in a Coalmine

摘要

Coalmining keeps experiencing one the highest fatality and injury rates for employees among the industries dealingrnwith flammable gases and explosive dust. To reduce such a high level or risks, novel preventive mining/fire safetyrnstrategies have recently been developed by Demir et al. [http://dx.doi.org/10.1080/13647830.2017.1328129], whornhas identified and scrutinized the keys stages of the premixed flame front evolution and quantified its majorrncharacteristics such as the flame shape and its propagation velocity, acceleration rate, run-up distance and flamegeneratedrnvelocity profile. However, that analysis adopted the approach of incompressible flows, which made it arnlittle far from the practical reality. To fix this discrepancy, in the presented study, the effect of gas compression isrnincorporated into Demir’s predictive scenario of methane/air/coal dust fire in a coalmining passage, for a twodimensionalrngeometry. Among various mechanisms responsible for the flame acceleration such as combustionrninstability, turbulence, acoustics, and wall friction, acceleration due to a finger-shaped flamefront plays a dominantrnrole in coalmines, because this mechanism is scale-invariant and, thereby, Reynolds-independent. This finger-flamernacceleration is very powerful, promoting the flame speed by an order of magnitude. Starting with gaseous fuels, thernformulation is then extended to gaseous-dusty flows, with combustible and inert dust as well as their mixturernstudied. Specifically, the effects of equivalence ratio on the flame evolution, as well as that of the size andrnconcentration of the dust particles, are systematically investigated. It is shown that gas compression generallyrnmoderates flame acceleration, and its impact depends on various thermal-chemical parameters. While the effect ofrncompression is minor (yielding 3-5% reduction) for lean and rich flames, thereby justifying the incompressiblernformulation in that case, it appears significant (up to the reduction of 22%) for near-stoichiometric methane-airrncombustion, and therefore should be accounted in a rigorous formulation. Furthermore, it is demonstrated that gasrncompression may control acceleration of slightly-reach flames.