The combustion characteristics of 10-micron aluminum particles at elevated temperature and pressure

Aluminum particles are often added to solid prope llants to increase performance. This work presents experimental evidence that flame structure deviates from the vapor -phase diffusion flame observed in larger particles as the particles size decreases below 20 microns. As this transition occurs, the emis sion temperature measured via AlO emission spectroscopy, which is close to the peak temperature in the flame, decreases significantly and approaches the particle surface temperature . T he reaction zone moves closer to the particle surface. The combustion time s of 10 micron particles are found to differ from larger particles. Measurement s in different oxidizing environments indicate that combustion time decreases as percent oxidizer increases, with oxygen being the strongest oxidizer followed by CO 2 and H2O, respectively. The burn time in oxygen decreases dramatically with increasing pressure, while the burn time in water vapor and carbon dioxide increases slightly when pressure increased. At the particle sizes investigated here, there is some evidence th at surface processes could be playing an important role in overall rate of aluminum combustion.