Ignition kinetics and burn rates of Al particles

Document Type

Conference Proceeding

Publication Date

1-1-2009

Abstract

This talk will present recent results describing ignition and combustion of aluminum particles in different environments. Ignition is defined as a process in which external heat sources are required to bring the particle temperature up to the point when the exothermic reaction becomes self-sustaining. As a rule, only a small fraction of metal is consumed during this process. Combustion follows up and comprises a self-sustaining oxidation resulting in the major consumption of metal fuel. To model aluminum ignition, heterogeneous oxidation producing a growing alumina layer on the particle surface needs to be described. The rate of this reaction is controlled by diffusion through the alumina layer. It is of critical importance that its diffusion resistance changes as a result of polymorphic phase transformations occurring in alumina upon its growth and upon temperature increase. Presence of different oxidizers, such as CO2 and H2O affects these transformations and respectively affects the rates of oxidation processes controlling ignition. Ensuing combustion reactions involve a combination of the vapor-phase and heterogeneous oxidation processes. It is found that the purely vapor phase flame becomes unsustainable as the particle size decreases to single microns. While a detailed model of the particle combustion is not available, the rates of combustion are measured for the micron-sized particles in air, N2/CO2 and N2/H2O mixtures. The measured burn times exceed substantially the commonly used "d-power" law predictions used in many practical calculations and based upon experiments with much coarser particles.

Identifier

84946606633 (Scopus)

ISBN

[9781615676682]

Publication Title

Fall Meeting of the Eastern States Section of the Combustion Institute 2009

First Page

902

Last Page

914

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