Numerical study of hydrogen addition effects on aluminum particle combustion

Aluminum particles have attracted attention as an energy carrier due to their high energy density and recyclability without carbon emissions. Despite their high combustibility leading to dust explosion, there have been some difficulties in fully controlling the aluminum particle flame. For the sake of enhancing usability and controllability, the addition of hydrogen to aluminum particle reaction systems is thought to be effective, while its effect has to be clarified thoroughly. Therefore, the present work aims to understand the effect of hydrogen addition on the aluminum particle combustion in numerical methods. Two ideal combustion modes sorely controlled by either kinetics or diffusion were assumed. In the kinetically-controlled mode, the particle was treated as a single molecule, and combustion characteristics of the homogeneous aluminum/hydrogen flame were evaluated with considering the detailed gas-phase reaction. In the diffusion-controlled mode, the burning properties of the single 200 μm-sized aluminum particle were investigated under hydrogen added atmospheres with additional consideration of the heterogeneous reaction occurring on the aluminum surface. Numerical results show that the addition of hydrogen generally reduces flame temperatures, and it can greatly shorten ignition delay times of the aluminum flame depending on initial temperatures. However, its effect on flame speeds may appear differently depending on the combustion mode, and the hydrogen addition can either promote or inhibit the combustion process of aluminum particle. Our attention was also paid to how the hydrogen reaction chemistry is coupled with the aluminum oxidation process especially in the aspect of hydrogen resynthesis from water.