Effects of coal particle diameters and detonation-supporting gases on hybrid detonation characteristics

Solid powder detonation engines have a promising application prospect due to the high thermal efficiency of the detonation cycle and the unique advantages of solid powder fuels, such as high volumetric energy density , and so on. However, achieving a stable and efficient powder detonation remains a significant challenge. This study investigated the detonation onset and detonation structures of the pulverized coal-ethylene‑oxygen mixtures by conducting in-house detonation bomb experiments and the corresponding numerical simulations. The results indicate that: In ethylene‑oxygen mixtures, increasing ignition energy accelerates the chemical reaction rate, facilitating the transition from the ignition-induced shock wave (ISW) into the detonation wave (DW). However, even under high ignition energy, pulverized coal‑oxygen mixtures do not achieve detonation. In contrast, the addition of ethylene to pulverized coal‑oxygen mixtures generates additional chemical reaction heat, accelerating the temperature rise rates and burning rates of coal particles, thereby promoting the formation of the hybrid DW. The study further reveals that smaller coal particles shorten the induction and reaction zones, altering detonation structures and enhancing wave intensity. Specifically, with coal particle diameters of 1 μm, 3 μm, 7 μm, and 10 μm, respectively, three typical hybrid detonation structures were observed: single-front detonation (SFD), double-front detonation (DFD), and pseudo-gas detonation (PGD). Moreover, hybrid detonation with mixed particle diameters demonstrated that only smaller particles can support the DW, while larger particles have a negligible effect on it. These findings provide a theoretical foundation for successful initiation, powder selection, and performance improvement in powder detonation engines. • The mechanism for the difficulties in coal powder detonation onset was revealed. • The role of detonation-supporting gases in coal detonation onset was clarified. • The link between particle diameters and detonation wave structures was indicated. • SFD, DFD, and PGD with different coal particle diameters were studied. • Gas-solid hybrid detonation with mixed coal particle diameters was explored.