Experimental and theoretical study of single iron particle combustion under low-oxygen dilution conditions

Abstract

In the present study, a novel in situ particle sizing approach is proposed and used to measure the characteristic timescales of micron-sized iron particle combustion under low-oxygen (10–17vol%) dilution conditions. The particle size is determined by probing the light emission intensity of a burning particle during melting, which is proportional to the cross-section area of the particle projected to the camera. Detailed descriptions of the calibration, validation, and characterization of the experimental method are elaborated. With systematic measurements, we obtain one-to-one correlations between combustion timescales and single particle diameters at various diluted oxygen concentrations. Furthermore, we formally derive a theoretical model for heterogeneous combustion of growing (iron) particles in the diffusion-limited regime. The model suggests that the diffusion-limited burn time scales with the initial particle diameter squared (i.e., a new, generalized d2-law). Owing to accounting for the particle growth, the newly derived model suggests a significantly (1.66 times) shorter combustion duration compared to the conventional d2-law for shrinking particle combustion. It turns out that the new model agrees well with the experiment. This agreement also suggests that under low-oxygen dilution conditions, the combustion regime of iron particles during the intensive burning stage (i.e., from ignition to the peak particle temperature) is limited by external oxygen diffusion.