Formation of solid residues in combustion of boron-containing solid propellants

Abstract

Boron-containing solid propellants are promising propellants for ducted rockets. The experimental data show that combustion of boron-containing propellants is accompanied by an intense conglomeration of the boron particles near the burning surface. As a result, the boron particles conglomerates which are the branched coral structures composed of sintered boron particles are formed in combustion of boron-containing solid propellants. This results in decrease in combustion efficiency of ducted rockets. To calculate the ignition and combustion of a conglomerate in the secondary combustor of a ducted rocket, it is necessary to know the size, structure and shape of the boron particle conglomerates that can significantly affect these processes. In this paper, we consider a model and a method for calculating the boron particles conglomeration in combustion of the boron-containing solid propellants. The process of the boron particles conglomeration is considered as a result of competition between two main processes: the formation of adhesive bonds between the contacting boron particles and rupture of these bonds under the action of the aerodynamic detached force from the side the flow of gaseous combustion products of solid propellant. The criterion of formation of residues (slag) on the burning surface of boron-containing propellants is considered. It is shown that depending on the propellant burning rate law, two different types of propellants with different conglomeration behavior can exist. The results of calculations of the boron particles conglomeration which demonstrate the slag formation are shown.