Detonative wavelets in quasi-detonations with fine coal char particles

Direct initiation and propagation of cylindrical detonation in fine coal char particle suspensions with varying concentrations are simulated using the Eulerian-Lagrangian method. The kinetic surface reaction model and GRI-Mech 3.0 mechanism are adopted to model the heterogeneous and homogeneous reactions, respectively. The results show that stable detonation occurs at initial particle concentrations from 40 to 620 g/m 3 , while quasi-detonation can be observed when the concentration exceeds 620 g/m 3 , which is featured by relatively low detonation speed and overpressure. In the quasi-detonations, a series of azimuthally propagating detonation wavelets exist along the leading shock front, with localized subsonic regions behind them. This results in different hydrodynamic structures compared to that of conventional detonations with multiple transverse waves. As the detonation wave expands, the number of azimuthal detonation wavelets (ADW) increases. It is also seen that the ADW plays a key role in sustaining quasi-detonation and the cellular trajectories are primarily from ADW collisions. Compared to stable detonation, quasi-detonation generates high pressure and heat release behind the ADW regions. Meanwhile, detonation cell bifurcation generates additional ADWs to maintain the quasi-detonation propagation towards large radii. It is also shown that under near-stoichiometric particle concentrations the wave is intensified and accelerated, resulting in small, regular detonation cells. In contrast, excessively high concentrations generate large, irregular cells, mainly due to oxygen depletion. Furthermore, strong shear-induced flow jets and vortices lead to non-uniform particles behind the leading shock. Sparse and aggregated regions can therefore further result in highly uneven reaction zones. In the quasi-detonations, sparse regions exhibit higher temperatures due to lower energy absorption, while aggregated regions experience significant interphase heat transfer, different from the behaviors under near-stoichiometric conditions.