Combustion of aluminized solid propellants exhibits phenomena associated with accumulation, agglomeration, ignition, and combustion of micro and nano-size aluminum particles. In general, agglomeration is an undesirable phenomenon, as it turns small particles into relatively large agglomerates, each containing many original particles, resulting in long combustion times which may lead to incomplete reaction, reduced jet momentum, and enhanced slag formation which adds parasite mass and may damage the motor insulation. This article presents a physical mechanism explaining the agglomeration process, revealing that small particles tend to agglomerate more than large particles. In addition, it suggests ways to reduce agglomeration of the aluminum particles via nano-coatings generating reactive heating and promoting ignition.
1. Introduction
Aluminum particles are commonly added to solid propellants (up to about 20% mass fraction) to increase their energy and energy density. However, during the propellant combustion, aluminum particles tend to form relatively large agglomerates which are ejected from the propellant surface into the hot gas fl ow fi eld. This situation may result in undesirable phenomena such as incomplete combustion, two-phase fl ow losses, and slag accumulation, particularly in motors having a submerged nozzle (e.g., in space motors such as the Space-Shuttle boosters). Besides demonstrating only partial oxidation which decreases the actual propellant energy, the existence of slag reduces the overall jet momentum, adds parasite mass, and may damage the motor insulation.
The objective of this research is to present a physical mechanism explaining the aluminum particle agglomeration process during the combustion of solid propellants and to show its dependence on particle size and operating parameters. In addition, it suggests ways to reduce agglomeration of the aluminum particles via nano-coatings generating reactive heating and promoting ignition.
