Direct Identification of Two Regimes of Metal Particle Combustion using Condense-luminescence

Abstract

Experiments were designed to investigate two regimes of metal particle combustion: fast and slow burning regimes. Stress-altering aluminum particles had been shown to produce a distinctly faster burning rate compared to untreated aluminum particles. The root cause for the differences in burning rate had been unclear. In this study, stress-altered and untreated aluminum particles were reacted as dispersed powder in a closed bomb calorimeter designed to monitor the transient temperature changes resulting from energy release upon combustion. The product residue was analyzed for size and species concentration. Results showed metastable γ-alumina that is associated with nano-oxide formation was in substantially higher concentration for stress-altered particle reactions that produced greater energy transfer rates. The increased energy transfer rate corresponded to higher radiant energy emission owing to condensation of nano-oxide particles. This study justifies condense-luminescence as a means for increasing the energy release rate of aluminum particles. By strategically altering metal fuels to control a formation of nano-oxide particles upon combustion, appreciable increases in the radiant energy flux can transform energy release rates.