ИСТИНА

Boron-containing solid propellants with an oxidizer deficit and a high content of boron are considered as the promising propellants for the ducted rockets. Such solid propellants are capable to self-sustained combustion and their combustion occurs in a special gas generator. The design of the ducted rocket is directed to obtain a maximum efficiency of boron combustion. For theoretical estimation of the completeness of boron combustion in secondary combustor, the data obtained in the experiments on ignition and combustion of the single boron particles are usually used. However, there are direct and indirect data indicating that combustion of the boron-containing propellants is accompanied by an intense agglomeration of the boron particles near the burning surface. As a result, not the single boron particles leave the propellant burning surface but the large conglomerates containing a large number of the primary boron particles. This results in decrease in combustion efficiency in ducted rockets. There are different methods to increase the combustion efficiency but the their development depends on understanding the mechanisms of the agglomeration process and identification of the controlling factors, by changing of which one can control the intensity of the agglomeration. Moreover, for the correct calculation of the processes in the secondary combustor, it is necessary to know the combustion regularities exactly the conglomerates, rather than the single boron particles. In particular, for calculation of the ignition and combustion behavior of the conglomerate, one needs to know not only its size but also its structure and shape that can significantly affect these processes. The model and the common method of calculation of the boron particles agglomeration during combustion of the boron-containing solid propellants have been suggested. The process of the boron particles agglomeration is considered as a result of competition between two main processes: the formation of adhesive bonds between 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 mechanism of formation of the adhesive bonds between the boron particles and a dependence of the strength of these bonds on the residence time of boron particles in the heated layer of condensed phase of propellant have been suggested. The criterion of occurrence of intense boron particles agglomeration has been suggested, and it was shown that depending on the propellant burning rate law, two different types of propellants with different behavior of the agglomeration process at pressure change can exist. The model of formation of boron oxide, boron nitride and boron carbide near the burning surface is suggested. The calculations of the boron particles agglomeration which demonstrates the effect of the strength of adhesive bonds between boron particles on the intensity of agglomeration have been carried out. The criterion of solid residues formation and dependence of their relative mass on pressure are obtained and analyzed.