Effect of Agglomeration on Combustion of Metallized Propellants for Air-Breathing Propulsion System.

Combustion phenomena of metallized propellants containing the metals viz. Mg, Zr, Al and B with NaND3 as oxidizer have been studied in order to find out burning rate variations at different oxidizer levels and at different particle sizes of the ingredients. It is found that the burning rate of Mg-NaND3 and Zr-NaND3 compositions with finer size NaND3 shows higher values at lower oxidizer content and decreases with increasing concentration of the oxidizer. In contrast AI-NaND3 and B-NaND3 formulations show continuous increase in burning rate with the increase in oxidizer content. Further, the burning rate of all the formulations with NaND3 of coarser size is found to increase on increasing the oxidizer content. Thermal decomposition results indicate that in the case of Mg and Zr formulations, decomposition products of finer size NaND3 formed before reacting to ignition temperature of the metal, react with the metal particles leading to condensed phase heat release causing higher burning rate. An increase of oxidizer content leads to a thicker oxide coating on the metal particles resulting in the formation of metal agglomerates which burn inefficiently in the vapour phase causing lower burning rate. With coarser size NaND3, due to its decomposition occurring beyond the ignition temperature of the metal particles, reactions shift to the vapour phase diffusion zone causing increase in the burning rate as the concentration of NaND3 increases. Combustion of Al and B particles with NaND3 occurs beyond the melting/ignition temperatureof the metal at all the concentrations and particle sizes of oxidizer, causing increase of burningrate with increasing oxidizer content