“Tortoise and Hare” in combustion dynamics of titanium microwires

Metal fuels attract significant research attention due to their high energy density, carbon-neutral combustion characteristics, and safe storage and transportation properties. The current study primarily focuses on the metal powder or cloud, with the combustion dynamics of the wire configuration remaining unexplored. Here, we report a unique “Tortoise-and-Hare” paradigm in titanium (Ti) microwire combustion: the burning Ti droplet acts as the “Hare”, periodically overtakes the slowly propagating combustion wave, which acts as the “Tortoise”. We reveal that this unique dynamic stems from a thermal imbalance between the combustion heat release and the latent heat of downstream wire melting, which is inherent to the heterogeneous combustion nature of metals. Furthermore, we demonstrate that a dimension effect amplifies this imbalance: with wire diameter increases, the outcome of the “Tortoise-and-Hare” race shifts—the once swift “Hare” can no longer catch up with the “Tortoise”, leading to a persistent separation. This study provides fundamental insight into the one-dimensional combustion propagation behaviour in Ti microwire, showcasing their promising potential in micro-combustors or micro power generators. <br/>© 2026 The Author(s). Published by Elsevier Inc. on behalf of The Combustion Institute.