Evolution of condensed oxide at early and late stages of an aluminum particle combustion

This work provides new insights into the dynamics of the initial oxide lobe that forms from the native alumina layer covering an aluminum particle. This lobe is a distinctive hallmark of aluminum particle combustion — absent in hydrocarbon droplet combustion — and is commonly considered the origin of micrometric oxide residues. While it is generally accounted for in numerical simulations, this study challenges the prevailing assumption of its persistence. Instead, it demonstrates that the initial alumina lobe progressively regresses over time. The rate of this regression is closely linked to the availability of gaseous aluminum near the droplet surface and is notably delayed in nitrogen-containing environments. Moreover, this research offers a novel perspective on the final phase of the particle’s combustion, which is initiated by the formation of a surface layer composed of alumina and/or oxynitrides. The presence of nitrogen plays a key role in triggering this covering process, which subsequently induces spinning and jetting phenomena. The study elucidates the mechanisms behind these dynamics — particularly jetting — and provides quantitative data on their effects in more complex configurations involving particle suspensions.