Numerical simulation of nano-aluminum ignition in oxygen and steam environments

The ignition characteristics of nano-aluminum (nano-Al) in oxygen and steam environments were numerically studied in this work. A detailed kinetic mechanism of nano-Al combustion was developed, and the effects of initial reaction temperature, ignition pressure, the phase of reactant, and the ratio of O₂ and H₂O in the oxidizer on the oxidation performance of aluminum (Al) were analyzed in detail. Numerical results show that increasing the initial temperature promotes the ignition of liquid-phase Al, while the promotion is not significant for gas-phase Al ignition. The oxidation of liquid-phase Al is significantly slower than that of gas-phase Al, and the phase transition reaction of liquid-phase Al exhibits a typical endothermic process, which results in a temperature drop before ignition. The increase of initial reaction pressure can accelerate the consumption of both liquid-phase Al and gas-phase Al in the ignition process. The oxidizability of O₂ is much larger than that of H₂O, and the oxidation of Al becomes slower by adding H₂O in the oxidizer. The rate of production (ROP) was performed to deeply realize the reaction pathways of Al consumption and main products formation. The reaction Al + O₂ = AlO + O is the key reaction pathway in the Al-O₂ ignition process, while the reaction Al + H₂O = AlOH + O plays a more important role in the Al-H₂O ignition process. In the all ignition cases, Al₂O₂ is a key intermediate species since it is the main precursor of gaseous Al₂O₃, and liquid-phase Al₂O₃ formed by the phase transition reaction of gaseous Al₂O₃ is the dominant final product.