Vapor-Phase Diffusion Flames in the Combustion of Magnesium, Calcium and Strontium

TLDR: In this article, an experimental investigation of the flame structure of metal vapor-phase diffusion flames, in particular the low-pressure flames of Mg, Ca, and Sr, is described.

Abstract: This paper describes an experimental investigation of the flame structure of metal vapor-phase diffusion flames, in particular the low-pressure flames of Mg, Ca, and Sr. Two types of experiments were employed. In the first type, metal wire samples were mounted between electrodes and heated electrically. In the second type, a two-dimensional diffusion flame burner was adapted to low-pressure metal combustion studies. Space-resolved spectroscopy was used to define the location of emitters in both experiments. A new model for the flame structure is presented. The model is characterized by a broad reaction zone in the inner region of the luminous envelope. The radiation is attributed mainly to a thermal excitation mechanism. As a result of the reaction (which is thought to be predominantly homogeneous), a large supersaturation of oxide vapor is generated in the inner zone leading to rapid nucleation of particles. Various possible kinetic steps for the reaction are compared. It is concluded that the t...