Combustion of bulk magnesium in carbon dioxide under reduced-gravity conditions

Abstract

The burning behavior and flame structure of magnesium in a carbon dioxide atmosphere are studied to assess the feasibility of using metal-carbon dioxide reactions as an in situ resource utilization technology for rocket propulsion and energy generation on other planets. Cylindrical specimens of 2, 3, and 4-mm diameter and length are suspended in a thermocouple wire and radiatively ignited after melting in a pure carbon dioxide environment at 1 atm under reducedgravity conditions. This novel experimental technique allows the study of free-floating bulk metal samples exhibiting a spherically symmetric flame. Spherical flames are obtained during steady-state burning of the metal sample with increasing metal-oxide accumulation in an outer shell. Only intermittent explosions and residual accelerations in the airplane distort the spherical flame shape. Burning times twice as long as in normal gravity and five times longer than in magnesium-oxygen flames are observed. The burning time is proportional to the square of the metal sample diameter. Combustion of magnesium with pure carbon monoxide is not possible without a constant heating of the sample. A numerical model combining gas-phase chemical kinetics and transport mechanisms simulates the one-dimensional, spherically symmetric combustion process by using opposed flows of fuel and oxidizer in a diffusion flame contiguration. The resulting concentration and temperature fields calculated with the model reveal a reaction zone thickness similar to that observed experimentally and a temperature profile close to the measured value. * Research Associate, Member AlAA t Graduate Student $ Graduate Student 5 Professor, Member AIAA Copyright