Flame structures and particle-combustion mechanisms in nano and micron titanium dust explosions

Abstract

Explosion processes of 50 nm, 5.3 μm, 23.5 μm and 39.5 μm titanium dust in the open space were recorded by a high-speed camera. A colorimetric thermometry was used to characterize temperature distribution of the dust flame, and the flame propagation characteristics, flame structures and particle combustion mechanisms of titanium dust were also discussed. Experimental results indicated that nano titanium dust explosion formed a smooth continuous flame front during the burning process, while micron titanium dust explosions presented clusters flame fronts. The heat transfers of nano and micron titanium dust explosions were mainly controlled by the external heat transfer, and the pulsating flame propagation velocity increased with the decreasing particle size. The flames of titanium particles of 50 nm and 5.3 μm presented a spherical shape, while those in 23.5 and 39.5 μm titanium dust clouds propagated downward obviously for their higher falling velocities. Furthermore, micro-explosions of titanium particles were observed in a very short combustion time of 2–4 ms, during which titanium particles in the molten state rapidly burned and oxidized in air to form irregularly shaped oxide particles. The colorimetric temperature distribution images showed that the temperature of titanium particles rose rapidly in a very short time after the micro-explosion.