Experimental Investigation and Numerical Modeling of the Condensed Combustion Products of Micro and Nano-Aluminized Solid Propellants

Nano-aluminized propellants are investigated and compared with micro-aluminized propellants in order to evaluate the use of aluminum nano-powders for solid rocket applications. Special attention is devoted to the condensed combustion products (CCPs) which significantly affect the solid rocket motor behavior. The experimental investigation performed in this work aims to study the effects of the propellant composition on the formation and evolution of the CCPs; in particular, the influence of oxidizer (AP and AN), particles size distribution (monomodal or multi-modal AP oxidizer), binder nature (HTPB or isoprene rubber) and the aluminum powder size (micro or nano powders) are considered in a compared evaluation. A detailed characterization of the original metal powder is performed in order to investigate the influence on the general behavior of CCPs. A high-speed video recording system is used to visualize the agglomeration formation at the burning surface and their evolution in the gas phase. A chemical analysis (mainly performed with X-ray Photoelectron Spectroscopy technique) is developed in order to measure the aluminum and aluminum oxide content in the quench-collected agglomerates, and to evaluate the combustion efficiency. A X-ray Diffraction technique allows to investigate the CCPs crystalline structure. Under the explored operating conditions, the results confirm that nano-aluminized propellants show larger steady burning rate, without significant change in pressure sensitivity, and lower aggregation / agglomeration phenomena in combustion products. Combustion efficiency is in turn favored by those factors reducing the importance of aggregation / agglomeration phenomena in the combustion process.