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.