Combustion and trajectory of dispersed micro-sized aluminum particles in a non-premixed methane-air flame

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Combustion behaviors of micro-sized aluminum particles were experimentally investigated in a laminar, non-premixed methane-air flame, to understand how the localized flame conditions influence particle ignition, oxidation and transportation. Advanced optical diagnostics, including high-speed imaging and two-color pyrometry, were utilized to measure the particle trajectory, velocity and temperature. A thin filament pyrometry setup, validated by the numerical simulations, was used to characterize the flame environment. Experimental results revealed a clear and distinct performance of individual aluminum particles' combustion, which has been highlighted by the appearances of transient temperature spikes, abrupt trajectory deviation, molten aluminum ejection, and fragmentation. It was found that the particle trajectories and heating rates were strongly correlated to local flame conditions, such as temperature gradients and oxygen availability. Individual particle temperatures were frequently above the local gas temperature, indicating the non-equilibrium effects between the particle-level exothermic processes and the convective and radiative transfer with the surrounding flame. Chemiluminescence imaging further confirmed active oxidation reactions involving AlO radicals at the particle surface. These results demonstrated the critical roles of the local flame structure in controlling the particle-level combustion dynamics and provided insights for the development of metal-fueled combustion systems.