(457c) Combustion Dynamics of Aluminum in Turbulent Flows

 A.L. Corcoran, V.K. Hoffmann, E.L. Dreizin

 New Jersey Institute of Technology

Predictive mechanisms for particle ignition and combustion rates are required in order to develop optimized propellant and energetic formulations using micron-sized metal powders, such as aluminum. Most current descriptions are based on laboratory experiments performed in stationary or laminar combustion configurations. However, turbulent environments exist in most applications and validity of the present descriptions for such environments has not been established. This experimental study is aimed to measure burn times versus size of fine aluminum powders burning in environments with different levels of turbulence. An initial laminar oxygen-acetylene flame is produced, and auxiliary tangential jets of air with adjustable flow rates are used to achieve different controlled levels of turbulence. Aluminum powder is forced into the center of the flame using a flow of nitrogen. A spherical powder with nominal particle size of 6.5 µm is used. Metal mass feed rate is adjusted using a custom-made powder feeder. The flame with burning aluminum is photographed using a Sony DSC-H50 camera. A spinning disk with multiple holes is used to interrupt the photo-exposure with a pre-set frequency. In the obtained images, the streaks of luminous burning particles appear dashed, and the particle burn times are determined by counting the dashes for each streak. Image processing produced statistical information on particle burn times. The particle burn times are correlated with the particle size distributions to obtain the burn times as a function of the particle size for flows with different turbulence levels. The data are compared with similar correlations available in the literature. Additional spectroscopic flame measurements will be performed to further characterize aluminum combustion at different flow conditions.