Study on the mechanism of explosion flame propagation of aluminum powder coated with stearic acid

To investigate the explosion flame development and propagation mechanism of coated aluminum powder, a shell and core structure of stearic acid-coated aluminum powder (SA@Al) was prepared using the solvent evaporation method. The influence of dust concentration on the explosion flame propagation characteristics of SA@Al dust with coating concentrations of 5%, 10%, and 15% was experimentally studied using an improved Hartmann tube. Flame propagation behavior was observed through high-speed photography, and the flame propagation velocity was calculated. The kinetic characteristics of the gas-phase explosion reaction were analyzed using CHEMKIN-PRO software to reveal the mechanism of SA@Al dust explosion flame propagation. The results indicated that as the dust concentration increased, the fullness and continuity of the explosion flames for 5%, 10%, and 15% SA@Al dust first increased and then decreased, with the average flame propagation velocity showing a trend of first rising and then falling. The flame propagation velocity reached its maximum at a dust concentration of 500 g/m³. In contrast, the explosion flame propagation velocity of pure aluminum powder reached its maximum at 750 g/m³, suggesting that the stearic acid coating layer promotes the propagation of the aluminum powder explosion flame. Additionally, under each dust concentration, the explosion flame of 10% coating concentration SA@Al was the most intense, with the highest average flame propagation velocity. The temperature rise of the SA@Al explosion flame with different dust concentrations mainly consisted of two stages: a rapid heating stage and a slow heating stage. The rapid heating stage exhibited higher temperature sensitivity for reactions R2, R11, and R10, while the slow heating stage exhibited higher temperature sensitivity for reactions R5 and R11. The dust concentration significantly affected the rate of temperature rise in the slow heating stage, resulting in the highest explosion equilibrium temperature for SA@Al at 500 g/m³. The combustion of the stearic acid coating promoted the oxidation of the aluminum core, thereby strengthening the explosion reaction. However, high dust concentration led to limitations in O radicals, which weakened the reaction intensity to some extent.