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Accueil du site > Thèmes de recherche > Combustion & systèmes réactifs > 1.7 Multiphase gasification and combustion phenomena > 1.7.2 Combustion of aluminum particles

1.7.2 Combustion of aluminum particles

Studies on the combustion of metallic particles such as aluminium and magnesium are motivated by their use, actual or potential, in solid rocket propulsion applications. In the continuation of our past work on this topic, a study was conducted in cooperation with SME/SNPE (2006-2008) concerning the combustion properties of nanosized aluminium particle clouds. A new experimental set-up was developed which allows determining the flame propagation velocities in a cloud of aluminium nanoparticles. Emission spectroscopy measurements also permitted to estimate gas and condensed phase temperatures. Experiments were conducted parametrically in terms of particles nature and concentrations and the behaviour of clouds of nanoparticles versus micron sized particles were determined. An associated numerical modeling and simulation study permitted to estimate the particle burning time versus the particle size and showed that the agglomeration of nanoparticles may hinder their beneficial size effect (TH11 ; AFF60 ; ACTI36-39 ; AFF65 ; ACTI68 ; ACLN6, ACL132).

A prospective study on the development of “frozen propellants based on passivated aluminium nanoparticles and water” was conducted in cooperation with CNES and SME. When initiated by a hot wire, this novel propellant exhibits a stable and autonomous combustion even in an inert atmosphere. Its burning rate was determined under various conditions for the propellant composition, nature and size distribution of the particles and the initial pressure, using the high pressure droplet combustion facility of ICARE. This “Cold Solid Propellant” was also successfully tested at the CRB/SNPE test facilities under real fire conditions (ACTI40 ; ACLN7).

The previous study has clearly shown the feasibility of the (2Al + 3H2O -> Al2O3 + 3H2) reactions under low temperature conditions. We capitalized on this information to study low temperature (40°C2 generation process. We have examined the effects of water temperature, chlorine content and pH and the particles nature on the hydrogen yield. We have shown that the reaction (Al + 2H2O -> AlO(OH) + 3/2 H2) starts after an induction period corresponding to the hydration-dissolution-precipitation time of the alumina layer covering the aluminium particle and the generation of H2 occurs steadily until complete conversion of the metal. The induction period and the maximum H2 yield were determined for all explored conditions (ACTI48). This study is presently ongoing by investigating alternative ways of de-passivating (or activating) the low temperature reactions of nano and microsized aluminium particles in water.