Combustion of aluminum powder with steam entrained in a helium plasma using a 2.45 GHz microwave plasma torch

Ignition and combustion of ∼20 µm diameter aluminum powder was achieved with a helium-steam-based 2.45 GHz microwave plasma torch as a proof of concept due to interest in utilizing aluminum powder as a fuel source for power generation given the material's high energy density. Optical emission spectroscopy of the plasma in air, with steam-entrainment, and with aluminum particle injection was obtained in order to observe the radical species present. The combustion products were analyzed with x-ray diffraction (XRD) to determine the post-combustion composition and compared with published XRD data involving aluminum-water combustion. The results revealed that a microwave plasma torch in a steam environment is capable of igniting aluminum particles and sustains combustion between aluminum powder and radicals from water molecules. The torch design results in a mixing delay between the aluminum and steam radical reactants prior to sustained combustion. Enhanced mixing will be pursued with an improved injector design.