Influence of initial carbon and hydrogen content on micro-explosion of burning iron particles

Details

Supervisors

Contino, Francesco

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en génie de l'énergie , à finalité spécialisée

Abstract

enIron is a promising recyclable and zero-carbon fuel. However, burning iron particles often undergo micro-explosions: they fragment near their peak temperature and produce nanometric oxides that are harder to collect and to recycle. The event is driven by an internal gas, but its origin is debated. Carbon and hydrogen are the two plausible sources. Hydrogen is carried within a native hydroxide layer and therefore scales with the specific surface area; in the available feedstocks of previous studies, powders of high specific surface area also tended to have a high carbon content, so the effect of carbon and the effect of hydrogen could not be distinguished. This work decouples the two effects. Five iron powders were studied, in which the carbon content and the surface area vary more independently. For each powder, the occurrence, the timing and the strength of the inflation were measured, using a laser-ignited electrodynamic levitator with synchronized luminance and high-speed video diagnostics. The two species act at different stages. The occurrence of the inflation is set by the specific surface area, and therefore by hydrogen: a powder of lower surface area inflates less often than one of higher specific surface area. The timing is set by the two-phase structure of the molten particle, and not by its composition. The inflation occurs at a fixed fraction of the time to peak for every powder, which is consistent with the saturation of the shrinking metallic phase in dissolved gas. The strength of the ejection, in contrast, follows the carbon content. Hydrogen therefore sets whether and when a particle inflates, and carbon sets how violently it fragments. Both act through a threshold rather than scaling with content. This separation reconciles the surface-area and carbon hypotheses of earlier studies as two complementary stages of one mechanism. It also shows that the micro-explosion behavior of iron fuel is not fixed at production, but evolves with storage, and can be controlled through the surface chemistry of the powder.