Experimental investigation on the ignition and combustion characteristics of moving micron-sized Mg particles in CO₂

Few databases exist for the research on the ignition or combustion of moving micron-sized Mg particles in CO₂. In this study, the ignition and combustion characteristics of moving micron-sized Mg particles in CO₂ were examined with a closed high-temperature furnace and a pneumatic ejection device. The ignition and combustion processes were captured and recorded with a high-speed camera. The condensed products were collected with a water-cooled probe and analyzed with a transmission electron microscope (TEM) or scanning electron microscope (SEM). The results showed that an uneven protective shell forms around a particle because of the heterogeneous reaction during the ignition stage. Ignition occurs when the weakest point of the shell ruptures because of the large pressure difference. The partial ejection of Mg vapor on the particle surface leads to a skewed distribution of the flame around the burning Mg particle in CO₂. During the combustion process, the particle may spin at speeds of 0.4–1.5 rotations per millisecond. Empirical formulas were derived for the ignition delay and burning time. No bright flame was observed around the particles when the ambient pressure dropped below 0.025 MPa, which was concluded to be the ignition pressure limit of Mg in CO₂. These results should be useful for the structural design and optimization of Mg/CO₂ powder rocket engines intended for Mars exploration.