In Situ high spatiotemporal imaging of Al-Li microparticles in levitated combustion

The ability to observe micron-sized particle combustion with high temporal and spatial resolution is essential for advancing fundamental combustion models and understanding critical processes in extreme environments, such as those required for in-situ resource utilization on Mars. However, achieving high resolution through non-intrusive methods remains a significant challenge. We demonstrated a high temporal (∼10 µs) and spatial (∼700 nm/px) resolution, non-contact combustion setup for observing Al-Li particle combustion. The presence of 5 % lithium in Al-Li particles leads to enhanced ignition and combustion rates. This improvement is attributed to lithium’s low melting and boiling points, which significantly reduce combustion time compared to pure aluminum particles. Additionally, a power law relationship between particle size and combustion time is maintained. The initial alumina cap forms through molten alumina surface convection, leading to asymmetric flames and rapid particle rotation. During steady combustion, high-precision observations reveal that the alumina cap covers 30 % of the surface with a contact angle of approximately 35.9°. Under high-pressure conditions, the condensed-phase products agglomerating around the aluminum droplet collide with the rapidly rotating alumina cap. This impact causes the molten alumina cap to fracture and splash, reducing its coverage of the aluminum droplet and thereby accelerating the combustion process of the particle.