An experimental study on the ignition temperature of iron particles in an electrically-heated drop-tube furnace
Di Chang, Echo St. Germain, Randall M. Erb, XiaoCheng Mi, Jeffrey M. Bergthorson, Yiannis A. Levendis
Abstract
This manuscript reports on experimental research addressing the ignition temperature of iron particles in hot furnace gases and compares this experimental data to previous experiments and theoretical models. Iron particles of different sizes were injected into an electrically heated drop tube furnace in oxygen-containing gases with different mole fractions of nitrogen diluent (including air). Experiments were also conducted using other diluents (helium, argon and carbon dioxide) at a fixed mole fraction of oxygen. Though the ignition temperature of a combustible material is an extrinsic property influenced by structural and operating parameters, useful approximations can still be derived from experiments and theory. This investigation corroborated the onset and probability of ignition by three independent techniques: (a) visual observation of the luminosity of particles, (b) physical examination of the particle size and shape characteristics of the collected products of combustion and (c) assessment of the chemical composition of the collected particles. Results revealed that particle size, shape and particle concentration appeared to be influential, as 28–32 µm spherical particles started to ignite at temperatures above 1037 K, 45–53 µm spherical particles at temperatures above 1022 K, and irregular 49–62 µm particles at temperatures above 968 K. Ignition temperatures increased with decreasing particle concentrations. Tuning the oxygen mole fraction (in the range of 15–100 %) in nitrogen had no discernible effect on ignition temperature. Replacing nitrogen with helium increased the ignition temperature significantly. Replacing nitrogen with argon or carbon dioxide slightly influenced the ignition temperature.