The formation of carbon in a magnesium/ethylene/oxygen flame

Carbon dioxide breathing propulsion systems have been proposed for magnesium fueled ramjet engines operating in the Martian atmosphere. The formation of solid carbon in the exhaust of such a system is of interest because of the effects of solid carbon on performance and operating characteristics as well as radiative heat transfer from the exhaust gases. Previous investigators are in disagreement over the formation of carbon in magnesium/carbon dioxide combustion. In the current investigation magnesium ribbon was burned in the exhaust of a fuel-rich ethylene/oxygen rocket motor. The UV spectra obtained during this oxygen-poor combustion confirmed that the magnesium was oxidized to form MgO. Sufficient quantities of soot were formed to coat the test apparatus. X-rау dispersive microscopic examination indicated the presence of micron-size magnesium oxide spheres coated with solid carbon. The formation of soot is shown to be consistent with equilibrium chemistry calculations which take into account the stoichiometry of the mixing region which forms over the magnesium surface. Equilibrium calculations for a typical aluminized solid propellant formulation are also presented. These calculations show that the equilibrium behavior of aluminum is expected to be very similar to magnesium. The disagreements between previous investigators are resolved through the experimental and theoretical results of the current study.