Combustion behaviors and residues characteristics in hydrogen/aluminum dust hybrid explosions

•The micro-diffusion flame and asymmetric flame appeared simultaneously.•The flame propagation velocities of hydrogen/aluminum dust mixtures were studied.•Pored oxide layers and small incompletely oxidized aluminum spheres were found.•A combustion model of hydrogen/aluminum dust hybrid explosion was established. Hybrid explosion experiments of hydrogen/aluminum dust in open space were performed. Aluminum dust with a median diameter of 56.18μm was mixed with hydrogen at different volume concentrations (0 %, 5 % and 10 %). Flame propagation was recorded by a high-speed camera. The explosion residues were observed by a scanning electron microscope, and their compositions were analyzed by X-ray photoelectron spectroscopy. The flame propagation velocities and structures, explosion residues and the combustion reaction mechanisms of hydrogen/aluminum dust mixtures were elucidated. The results show that the addition of hydrogen can increase the flame brightness and improve the continuity of the flame front. In the flame propagation process of a hydrogen/aluminum dust hybrid explosion, a micro-diffusion flame and asymmetric flame appeared simultaneously. Compared with pure aluminum dust combustion in air, when 5 % hydrogen-air mixtures were used to disperse the dust, the flame propagation velocities decreased by 0.11-0.15m/s. Attributable to a variety of intermediate products competing for oxygen and absorbing heat, the hybrid explosion residues cooled faster, porous oxide layers and incompletely oxidized aluminum spheres with small particle sizes were formed. The XPS showed that Al2O3, Al(OH)3, AlO(OH) and other complex products appeared in the combustion reactions. On this basis, a combustion model of hydrogen/aluminum dust hybrid explosion was established.