Combustion of a single iron-based impure particle: numerical analysis of four non-volatile oxide impurities using a parametric approach

Iron powder has been proposed as a high energy-dense, sustainable, safe and abundant energy carrier. However, despite a rising number of studies related to pure iron combustion, the influence of impurities on the combustion is still unclear. The objective of the current study is to understand how the presence of a non-volatile oxide impurity at a varying concentrations impacts the peak temperature and combustion time. To this end, we developed a single-particle combustion model containing up to 20 wt.% of Al₂O₃, SiO₂, MnO or CaO. The combustion regime is assumed to be fully external-diffusion-limited and the oxidation is limited to stoichiometric FeO ( X O = 0.5 in the liquid phase). The model predicts a decrease in peak temperature (up to 146 K with 20 wt.% of MnO), in liquid combustion time (up to 11.5 % with 20 wt.% of SiO₂) and in the time to peak temperature (up to 23 % with 20 wt.% of SiO₂). Both phenomena limit nanoparticle formation and micro-explosion event frequency, two of the main issues currently faced in pure Fe combustion. Iron combustion is already a low NO emissions process, which can also be further reduced with the addition of non-volatile impurities. The possibility of creating a complex ternary oxide phase is investigated and the challenges of incomplete oxidation or reduction are discussed. The assumptions made in the numerical model are questioned and the effect of impurities on them is discussed. This work highlights the promising potential of the presence of non-volatile impurities in Fe powders for their use as high-energy dense carriers. Most promising compositions will be selected based on this model and experimentally tested to validate the numerical results and improve the single-particle model in a future work.