Combustion of Magnesium with Carbon Dioxide and Carbon Monoxide at Low Gravity

Abstract

The burning behavior and  ame structure of magnesium in pure carbon dioxide and pure carbon monoxide atmospheres in low-gravity conditions are investigated. Cylindrical specimens are suspended by a thermocouple wire and are radiatively ignited. Spherical  ames are obtained during steady-state burning of the metal sample with increasing metal-oxide accumulation in an outer shell. Burning times twice as long as in normal gravity are observed, revealing a diffusion-controlled reaction. The burning time is proportional to the square of the metal sample diameter. Combustion of magnesium with carbon monoxide is not possible without constant heating of the sample. A one-dimensional, quasi-steady numerical model of the spherically symmetric diffusion  ame using elementary gas-phase reactions and detailed transport property calculations shows qualitative agreement with the observed structure of the  ames. It predicts a maximumtemperature close to the vaporization–decomposition point of themetal oxide, as well as the coexistence of the gaseous and condensed phases of the oxideproduct. It also predicts a diffusion-controlledreaction formagnesiumburning in oxygen, air, and carbon dioxide and provides an accurate comparison of the burning rates of these systems. The discrepancies between the numerical simulation and the experimental observations may be attributed to the absence of accurate condensation, radiation, and surface-reaction models.