Combustion behavior of single iron particles-part I: An experimental study in a drop-tube furnace under high heating rates and high temperatures

• Published in: Applications in energy and combustion science Vol. 13; p. 100097
• Main Authors: Panahi, Aidin, Chang, Di, Schiemann, Martin, Fujinawa, Aki, Mi, Xiaocheng, Bergthorson, Jeffrey M., Levendis, Yiannis A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2023; Elsevier
• Subjects: Burn-out time; Combustion; Iron; Metal fuel; Temperature; Burn-out time; Temperature; Iron; Combustion; Metal fuel
• ISSN: 2666-352X; 2666-352X
• DOI: 10.1016/j.jaecs.2022.100097

•Particle temperatures were measured by means of three-wavelength optical pyrometry.•High-speed cinematography was used to visualize the combustion process.•Iron particles ignited and burned brightly as generating micro-flames of nanometric particles.•Increasing the oxygen mole fraction was found to increase the peak particle temperature.•Particle size increase did not significantly affect the peak particle temperature. Micrometric spherical particles of iron in two narrow size ranges of (38–45) µm and (45–53) µm were injected in a bench scale, transparent drop-tube furnace (DTF), electrically heated to 1400 K. Upon experiencing high heating rates (104–105 K/s) the iron particles ignited and burned. Their combustion behavior was monitored pyrometrically and cinematographically at three different oxygen mole fractions (21%, 50% and 100%) in nitrogen. The results revealed that iron particles ignited readily and exhibited a bright stage of combustion followed by a dimmer stage. There was evidence of formation of envelope micro-flames around iron particles (nanometric particle mantles) during the bright stage of combustion. As the burning iron particles fell by gravity in the DTF, contrails of these fine particles formed in their wakes. Peak temperatures of the envelope flames were in the range of 2500 K in air, climbing to 2800 K in either 50% or 100% O2. Total luminous combustion durations of particles, in the aforesaid size ranges, were in the range of 40–65 ms. Combustion products were bimodal in size distribution, consisting of micrometric black magnetite particles (Fe3O4), of sizes similar to the iron particle precursors, and reddish nanometric iron oxide particles consisting mostly of hematite (Fe2O3).