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Extinction and re-initiation of methane detonation in dilute coal particle suspensions

In this study, methane detonation propagation in dilute coal particle suspensions is studied based on Eulerian-Lagrangian method. Two-dimensional configuration is considered, and a skeletal chemical mechanism (24 species and 104 reactions) is applied for methane combustion. The gas and particulate phase equations are solved using an OpenFOAM code for two-phase compressible reacting flow, RYrhoCentralFOAM. The effects of char combustion on methane detonation dynamics are investigated and devolatized coal particles are modelled. The results show that propagation of the methane detonation wave in coal particle suspensions are considerably affected by coal particle concentration and size. Detonation extinction occurs when the coal particle size is small and concentration is high. The averaged lead shock speed generally decreases with increased particle concentration and decreased particle size. Mean structure of methane and coal particle hybrid detonation is analysed, based on the gas and particle quantities. It is found that char combustion proceeds in the subsonic region behind the detonation wave and heat release is relatively distributed compared to that from gas phase reaction. Moreover, for 1 μm particle, if the particle concentration is beyond a threshold value, detonation re-initiation occurs after it is quenched at the beginning of the coal dust suspensions. This is caused by hot spots from the shock focusing along the reaction front in a decoupled detonation and these shocks are generated from char combustion behind the lead shock. A regime map of detonation propagation and extinction is predicted. It is found that the re-initiation location decreases with the particle concentration and approaches a constant value when the concentration exceeds 1000 g/m3. The results from this study are useful for prevention and suppression of methane/coal dust hybrid explosion.