(632b) Effect of Flow Conditions on Burn Rates of Magnesium and Magnesium-Containing Reactive Material Particles

In practical applications, such as propellants, explosives, and pyrotechnics, powders of metals and metal-based reactive materials burn in turbulent flows. However, in most experiments aimed to determine the particle burn rates, metal particles are burning in quiescent gases. Recently, it was shown that the burn rates of aluminum, titanium, boron, and several metal-based reactive materials are affected by flow conditions; higher burn rates are observed in turbulent flows compared to those in quiescent gas or laminar flow. The effect is different for different materials. In this work, the effect of flow conditions on combustion of magnesium and magnesium-containing reactive materials is studied. Magnesium commonly burns with a vapor phase flame forming away from the particle surface, so that the effect of flow conditions is expected to be particularly strong. The materials used in this project are a fine spherical Mg powder and mechanically prepared Al-Mg alloys and Mg-S composite powders. All the powders are fed into a focused beam of a CO2 laser, where they are ignited and burned in air. Different flow patterns are produced using a circular flow air knife, through which the particles are passing. The light emission pulses produced by burning particles are recorded using two photomultipliers equipped with interference filters at 700 and 800 nm. In addition, the emission pulses are recorded using a 32-channel spectrometer covering visible part of the spectrum. Finally, time-integrated spectra are measured from multiple burning particles. The optical measurements are interpreted to recover the flame temperature as a function of the particle size and time-dependent temperature traces for individual particles. Combustion products are also captured and examined using electron microscopy.

This paper will present results of experiments and discuss them in terms of mechanistic understanding of combustion of magnesium and magnesium containing reactive materials. This understanding is expected to serve as a foundation for a model describing combustion of different reactive material particles in different flow configurations.