V. Babuk

Propellant Formulation Factors and Metal Agglomeration in Combustion of Aluminized Solid Rocket Propellant

Abstract An experimental study of aluminized solid rocket propellant combustion was conducted in order to determine the influence of various propellant formulation factors on metal agglomeration. The results allowed us to determine the dependencies of the agglomeration process characteristics on the physical and mechanical properties of the propellant binder, the particle size of the metal fuel, the type of film covering the original metal particles, and the type of oxidizer in the propellant. These results, combined with earlier data, were used to develop a physical picture of the agglomeration process, which may serve as the basis for conducting analysis of the influence of various propellant formulation factors on agglomeration.

Nanoaluminum as a Solid Propellant Fuel

Experimental studies on the burning of nanoaluminum-based solid rocket propellants are carried out. Data on the properties of condensed combustion products, mechanisms of their formation, and burning-rate law are obtained. Based on these data, a physical picture is developed of the considered burning-propellant classes. Mathematical modeling of burning nanoaluminum in composite solid rocket propellants is carried out. The influence of nanoaluminum on ignition temperature of the metal fuel and burning-rate law is shown. The results of this study allow carrying out the analysis and selection of good-quality propellants using nanoaluminum.

Microstructure Effects in Aluminized Solid Rocket Propellants

Experiments concerning the ballistic characterization of several nanoaluminum (nAl) powders are reported. Most studies were performed with laboratory composite solid rocket propellants based on ammonium perchlorate as oxidizer and hydroxyl-terminated polybutadiene as inert binder. The ultimate objective is to understand the flame structure of differently metallized formulations and improve their specific impulse efficiency by mitigating the two-phase losses. Ballistic results confirm, for increasing nAl mass fraction or decreasing nAl size, higher steady burning rates with essentially the same pressure sensitivity and reduced average size of condensed combustion products. However, aggregation and agglomeration phenomena near the burning surface appear noticeably different for microaluminum (μAl) and nAl powders. By contrasting the associated flame structures, a particle-laden flame zone with a sensibly reduced particle size is disclosed in the case of nAl. Propellant microstructure is considered the main controlling factor. A way to predict the incipient agglomerate size for μAl propellants is proposed and verified by testing several additional ammonium perchlorate/hydroxyl-terminated polybutadiene/aluminum formulations of industrial manufacture.

Simulation of Agglomerate Dispersion in Combustion of Aluminized Solid Propellants

The paper deals with mathematical simulation of dispersion of agglomerates formed in combustion of aluminized solid propellants. A substantial effect of the separation conditions of agglomerating metal particles from the surface of the burning propellant on the size of agglomerates is demonstrated. A mathematical model of agglomerate formation is constructed for propellants whose typical feature is active burning of the metallic fuel in the surface layer. Satisfactory quality of simulation is validated by the agreement of experimental and numerical data.

Modeling the structure of composite solid rocket fuel

Results are reported on the creation of a model for the structure of a composite solid rocket fuel in terms of such concepts as “pockets” and “interpocket bridges.” Appropriate model calculations and experimental data are presented, and the possibility of using the model for predicting the characteristics of the combustion process is pointed out.

Formulation Factors and Properties of Condensed Combustion Products

A review of state-of-the-art experimental results concerning the influence of various formulation factors on the properties of the condensed combustion products (agglomerates and smoke oxide particles) formed at the burning propellant surface is provided. The influence of the properties of binder, oxidizer, and metal fuel is investigated. Analysis is carried out with reference to the following components: active and inactive binder, ammonium perchlorate, ammonium nitrate (pure and phase stabilized), ammonium dinitramide, cyclotrimethylenetetranitramine, micro-sized and nano-sized aluminum, aluminum with a polymeric, and refractory covering. The proposed analysis is based on the formulated general physical picture of the formation of the condensed products. It is shown that the properties of the condensed products (in terms of size, chemical composition, and internal structure) depend on properties of the burning propellant surface layer, which in turn depend on the properties of the propellant components. The importance of formation of a surface layer and the properties of such structures as a skeleton layer is underlined. The results of these research activities open the possibility to take reasonable formulation decisions when creating new solid propellants.

Simulation of Characteristics of Condensed Products in a Combustion Chamber

The principles of computational determination of the characteristics of both coarse and fine fractions of condensed combustion products formed at the propellant surface and evolving as part of the multiphase flow in the combustion chamber. The characteristics of condensed products at the propellant surface are determined by modeling the processes involved in their formation using a decision-making system based on an expert system approach. An evolution model for non-one-dimensional flow with the mutual influence of the characteristics of condensed and gaseous combustion products is developed to determine the characteristics of condensed products in the multiphase flow of combustion products. The developed tools allow the characteristics of condensed products to be determined depending on the propellant composition, characteristics of the propellant grain, and combustion chamber parameters. Parametric analysis of the developed models was performed for combustion chamber conditions.