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

In order to investigate the coated aluminum powder explosion flame development and propagation mechanism, a shell and core structure of stearic acid coated aluminum powder(SA@Al) was prepared by solvent evaporation method; the improved Hartmann tube was applied to experimentally study the influence of dust cloud concentration on the explosion flame propagation characteristics of SA@Al dust with 5%, 10%, and 15% coating concentration, observing the flame propagation behavior through high-speed photography and calculate flame propagation speed; and the CHEMKIN-PRO software was applied to analyze the kinetic characteristics of gas-phase explosion reaction, thereby revealing the mechanism of SA@Al dust explosion flame propagation. The results indicated that with the increase of dust cloud concentration, the fullness and continuity of 5%, 10%, and 15% SA@Al dust explosion flames were enhanced firstly and then weakened, and the average flame propagation speed showed a trend of first increasing and then decreasing. The flame propagation speed reached its maximum when the dust cloud concentration was 500 g/m3. In comparison, the pure aluminum powder explosion flame propagation velocity reached a maximum at 750 g/m3, indicating that the stearic acid coating layer promotes the propagation of the aluminum powder explosion flame. In addition, under each dust cloud concentration, 10% coating concentration SA@Al explosion flame were the most intense, and the average flame propagation velocity was maximized. The temperature rise of the SA@Al explosion flame with different dust cloud concentrations mainly consisted of two stages: rapid heating stage and slow heating stage. The rapid heating stage had higher temperature sensitivity for R2, R11, and R10, while the slow heating stage had higher temperature sensitivity for R5 and R11. The dust cloud concentration has a significant effect on 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 stearic acid coating promotes the oxidation of the aluminum core, which strengthens the explosion reaction, but high dust cloud concentration leads to the limitation of O radicals, which weakens the reaction intensity to some extent.