Accession Number:

ADA571672

Title:

Mechanistic Models for Ignition and Combustion of Metallic Powders in Different Environments

Descriptive Note:

Final rept. Oct 2006 - Aug 2010

Corporate Author:

NEW JERSEY INST OF TECH NEWARK DEPT OF CHEMICAL BIOLOGICAL AND PHARMACEUTICAL ENGINEERING

Personal Author(s):

Report Date:

2010-09-17

Pagination or Media Count:

138.0

Abstract:

This effort addressed ignition and combustion of aluminum particles in different environments. The focus was on identifying quantifiable characteristics of aluminum ignition and combustion that are useful for development and validation of the respective reaction models. It was shown that aluminum ignition in any oxidizing environment is governed by changes in the diffusion resistance of the protective surface layer of alumina and that these changes occur rapidly when the alumina film undergoes polymorphic phase changes. It was also shown that presence of water as an oxidizer dramatically affects alumina properties, in particular resulting in the disruption of the film continuity upon aluminum melting. It was further shown that the effect is amplified in mixed H2OCO2 environments. Finally, the model of aluminum oxidation is expanded and validated in high-heating rate thermo-analytical measurements. This model is directly applicable for describing thermally activated ignition of aluminum powders. A new experimental technique is developed to investigate combustion dynamics of individual metal particles in the size range of 2 15 microns. The technique is applied to study combustion of Al in different oxidizers. It is observed that stages reported earlier to be distinguished in combustion of coarse Al particles can also be observed for fine particles. A transition from the vapor phase to surface combustion regime was observed when the Al particle sizes decreased. The change in the combustion regime was explained by analyzing the heat transfer for a single Al particle combusting in room temperature air, and accounting for a transition heat transfer regime in vicinity of the micron-sized particles with dimensions comparable to the mean free path of the gas molecules. Burn times for Al particles were measured as a function of particle size for different oxidizers.

Subject Categories:

  • Inorganic Chemistry
  • Metallurgy and Metallography
  • Combustion and Ignition

Distribution Statement:

APPROVED FOR PUBLIC RELEASE