Atomic insights into the combustion behavior of Al nano-droplets with H2O vapor at high temperature

Y Zhao and DX Ma and FQ Zhao and SY Xu and XH Ju, APPLIED SURFACE SCIENCE, 586, 152777 (2022).

DOI: 10.1016/j.apsusc.2022.152777

Al/H2O based fuel has been a hot research area in energy field. But the combustion behavior of molten Al nano-droplets (ANDP) and H2O vapor at high temperatures is unclear. Reactive molecular dynamic was used to reveal the reaction mechanism of molten ANDP and H2O vapor at high temperature from an atomic perspective. The effects of temperature, ANDP particle size and H2O vapor concentration on ANDP combustion were considered. In general, the combustion of ANDP particle is accompanied with the outward extending growth of the oxidized phase in shapes of withe, bough and micro-explosion. The reactions of ANDP and H2O can be divided into: (1) H2O + Al & RARR; O-Al + H-2; (2) 2H(2)O + 2Al & RARR; 2OH-Al + H-2; (3) H2O + Al & RARR; OH-Al + H or (H-Al); and (4) H2O + H Al & RARR; OH-Al + H-2. The branched oxidation of ANDP is mainly a heterogeneous reaction in which active Al converts into O-Al phase. The micro-explosion of ANDP leads to the gas phase combustion of Al, which can rapidly catapult the active Al into the H2O environment. The micro- explosion makes the H2O molecules to decompose in pathway (1). The micro-explosion of ANDP increases the consumption of H2O and the production of H-2. Increasing the temperature, decreasing the particle size or increasing H2O vapor concentration can promote the micro- explosion of ANDP. The charge and temperature distributions indicate that ANDP micro explosion brings about the rapid formation of hot spots, voids and large electrostatic potential differences. The uncovered details in the reaction process of molten nano-Al with H2O vapor are expected to guide the application of Al/H2O fuel and Al/H2O hydrogen production technology.

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