Estimating Metal Particle Combustion Kinetics
PHILCO NEWPORT BEACH CA AERONUTRONIC DIV
Pagination or Media Count:
A combustion model for metal particles is derived and compared with experimental results for a few metals with high combustion enthalpies. It is concluded that aluminum and beryllium oxidize slowly because of formation of solid oxide films which impede the transport of reactants at temperatures below their oxide melting points. Diffusion through the liquid oxides is several decades faster, causing ignition to occur at the oxide melting point. After ignition, the temperature rises rapidly. When the metal boiling point is reached, metal evaporation expands the liquid oxide shell until the evaporation rate and rate of diffusion of reactant through the oxide shell are equal. The oxidation reaction occurs at the oxide shell rather than the metal interface and proceeds by this mechanism until the particle is consumed. Expansion of this shell accounts for the prevalence of hollow oxide spheres observed in the quenched combustion products. Calculations of the elapsed times for each stage in the combustion sequence were machine computed. Inadequate knowledge about diffusion coefficients in liquid oxides is the principal uncertainty involved. The diffusion flame theory adequately accounts for the combustion of magnesium.
- Combustion and Ignition