Date of Award

Fall 2014

Document Type

Thesis

Degree Name

Master of Science in Chemical Engineering - (M.S.)

Department

Chemical, Biological and Pharmaceutical Engineering

First Advisor

Edward L. Dreyzin

Second Advisor

Robert Benedict Barat

Third Advisor

Mirko Schoenitz

Abstract

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 and magnesium. Most current descriptions are based on laboratory experiments performed in stationary or laminar combustion configurations using pure metals burned in single oxidizers. However, practical configurations take into account different metals, including alloys, that burn in various oxidizing environments and various flow conditions. Validity of the present descriptions for such environments has not been established. This experimental study is aimed to measure burn times for aluminum, magnesium, and mechanically alloyed Al-Mg particles burning in different oxidizing environments; for aluminum and the mechanically alloyed Al-Mg alloys, turbulence is varied. The first environment consists of a laminar air-acetylene flame; auxiliary tangential jets of air with adjustable flow rates are used to achieve different controlled levels of turbulence. The second environment consists of a hydrogen/oxygen diffusion flame. In both cases, metal powder is injected in the flame axially using a flow of nitrogen. Aluminum powder is studied in both environments while magnesium is purely studied in the hydrogen/oxygen diffusion flame and the mechanically alloyed powders are studied in the combustion products of an air/acetylene flame. For the initial experimental data collection, aluminum streaks of burning particles are photographed using a camera placed behind a mechanical chopper interrupting the photo-exposure with a pre-set frequency. The obtained dashed streaks are used to measure the particle burn times for different flow conditions. The second experimental data collection includes filtered photomultiplier tubes which capture particle emission durations that represent the particle burn times. The particle burn times are correlated with the particle size distribution to obtain the burn time as a function of the particle size assuming larger particles burn longer. It is expected that these results will serve to develop a mechanistic model for burn rates of Al, Mg, and Al-Mg alloys in various gas environments.

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