Ignition and Combustion of Levitated Magnesium and Aluminium Particles in Carbon Dioxide B. Legrand, M. Marion, C. Chauveau, I. Gökalp Laboratoire de Combustion et Systèmes Réactifs Centre National de la Recherche Scientifique 45071 Orléans cedex 2, France gokalp@cnrs-orleans.fr and E. Shafirovich Institute of Structural Macrokinetics and Material Science Russian Academy of Sciences Chernogolovka 142432, Russia shaf@cnrs-orleans.fr, shaf@ism.ac.ru Abstract This article considers ignition and combustion of single particles of magnesium and aluminium in carbon dioxide at pressures 0.1-2 MPa. An experimental set-up with an electrodynamic levitator inside a high- pressure chamber was employed. The CO 2 -laser was used for heating to ignition of the particles. The results show that ignition mechanisms of Mg and Al in CO 2 are different. Experiments with Mg indicate the existence of the critical partial pressure of CO 2 , whereas the ignition probability of Al particles in CO 2 is low but independent on pressure. Analysis of flame images and combustion parameters shows that the mechanism of Mg particle burning in CO 2 corresponds to conventional models of vapour-phase diffusion-controlled combustion, whereas in the case of Al exothermic processes on the particle surface or close to it play a leading part in the burning process. Introduction Combustion of aluminium and magnesium in gaseous carbon dioxide is of interest for rocket engine applications. Current solid propellants normally contain metals as high energetic fuel, and the gaseous CO 2 , along with H 2 O, is often the main oxidising component for metal particles in a solid rocket motor. Aluminium is characterised by a higher heat of combustion than magnesium, and for this reason it is aluminium that is used in most of solid rocket motors. However, magnesium offers an important advantage over aluminium, namely, its ignites much easier than aluminium, especially in CO 2 containing atmospheres. In some cases this advantage may be the deciding argument in favour of magnesium. One example of a propulsion system where magnesium might be advantageous is a rocket engine for Mars missions using Martian CO 2 as an oxidiser [1]. It is therefore important to compare combustion characteristics and mechanisms of these metals. In this paper we summarise and analyse the experimental results on ignition and combustion of single particles of magnesium and aluminium in carbon dioxide, which have been obtained with the metal particle burning facility of the LCSR. Experimental set-up The experimental set-up (Fig. 1) composes essentially of an electrodynamic levitator placed inside a high- pressure combustion chamber [2, 3]. Single charged particles are levitated inside the hermetic chamber and ignited with a CO 2 -laser. The laser is automatically switched off after ignition. Photomultipliers and high-speed cinematography are used to obtain information on the ignition and combustion processes. The experiments reported here were conducted with the oxidiser at room temperature over the range of pressures from 0.1 to 2 MPa.