Combustion characteristics of well-dispersed aluminum nanoparticle streams in post flame environment

The combustion characteristics of well-dispersed aluminum nanoparticles (nano-Al) are investigated in the post flame region of a non-premixed flat flame burner. The dispersion and feeding of nanoparticles are fulfilled by a self-developed jet Collison nebulizer connected to a diffusion dryer. The mean mobility diameter of the fed nano-Al is 173 nm, which is only almost twice as that of the primary particle (92 nm) statistically calculated from TEM images. The flame of well-dispersed nano-Al is red and mild, different from that of aluminum microparticles. Temperature of the flame is found to be several hundred degrees higher than the ambient. Characteristic burning time of nano-Al derived from the flame images increases from 2.46 ms to 6.35 ms as the ambient temperature decreases from 1290 K to 987 K, which obeys well with an Arrhenius-type exponential formula. Combustion products thermophoretically sampled along the different height above the burner are observed to exhibit the crystallized and hollow structure. It indicates the crystallization of oxide shell and the outward diffusion of aluminum across the oxide shell during combustion. A single-particle combustion model based on the ionic diffusive mechanism is developed to predict the burning time after the validation by both Al/O ratio and oxide shell thickness. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.