Burn time and combustion regime of laser-ignited single iron particle

An improved particle generator based on electrodynamic powder fluidization is proposed and constructed for investigating single metal particle's combustion. The designed setup is able to generate a single metal particle moving upward with a well controlled velocity and trajectory and ignite it at near-uniform conditions by an infrared laser beam with flattened elliptical beam profile. Mechanically sieved narrow fractions of spherical iron particles with mean sizes in the range of around 26–54 μm were used in experiments. Particles burned in O 2/N 2 mixtures with oxygen content varying from 21% to 36%. Particle's trajectories, velocities, and arbitrary radiant intensities were measured by taking images with a high-speed camera and processing them with an in-house developed data processing program. Two characteristic times associated with particle combustion were measured: 1) total duration of high-temperature phase (t tot) and 2) time to the maximum brightness (t max). The results show that t tot and t max can be described by a d n-law with 1.57≲n≲1.72 and 1.46≲n≲1.60, respectively. The effect of oxygen concentration on t tot, t max, and t dec=t tot−t max was analyzed for selected particle sizes of 30, 40, and 50 μm. It was found that t max∝(1/X O2) n with 1.04≲n≲1.18 is almost linearly proportional to 1/X O2, while t dec shows a very weak dependency on the oxygen concentration at 26%–36%. This can be explained by the idea that the overall combustion process of iron is controlled by first external and then internal diffusion of oxygen owing to the saturation of oxygen on the particle surface.