Numerical simulation of dilute and dense layered coal-dust explosions

Multidimensional time-dependent simulations were performed to study the interaction of a shock wave and resulting shear layer with layers of coal dust. The simulations used a high-order compressible numerical method for fluid dynamics and included a Eulerian kinetic-theory-based granular multiphase model applicable over a range from dense to dilute particle volume fractions. Two cases were considered: a loose dust layer with an initial volume fraction of 1%, and a dense dust layer with an initial volume fraction of 47%. For both cases, the final result is a coupled complex consisting of a shock leading a coal-dust flame. In the simulations presented here, a shock is initially produced from remnants of a natural gas detonation, which has decayed into a shock once it passes into a region containing no gaseous fuel. This shock weakens further due to mechanical and thermal losses from lifting and entraining the coal dust. The lifted dust subsequently ignites in the shock-heated air and produces a structure similar to a mixing-limited, nonpremixed flame. The flame consists of a burning coal dust wave that follows the shock. The distance between the shock and ignition point is determined by the induction length of carbon char, which is similar to 170 cm and similar to 15 cm for the 47% and 1% cases, respectively. The burning of coal particles is predominantly from heterogeneous reactions with carbon char, and volatilized methane combustion is a secondary effect. Air and particles are mixed by relative velocity between the gas and solid phases. Coal particles burn and produce pressure waves that accelerate the shock from Mach 2.2 to 2.6 for the dilute layer, and from Mach 1.7 to 1.8 in the dense layer. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.