Mechanical and chemical contributions to the erosion rates of graphite throats in rocket motor nozzles

The paper presents an analytical approach, substantiated by experimental results, which predicts throat erosion in a rocket motor nozzle with fair accuracy over a wide range of graphite grades, pressures, and propellants. Both surface chemical reactions and mechanical removal are assumed to occur; the effectiveness of each depends on the composition of the reacting products in the combustion gases, the temperature, the pressure, the quality of the graphite, and the geometry of the nozzle. A simplified diffusion equation has been solved for the turbulent boundary layer close to the throat surface, and a suitable expression for the mass transfer coefficient that considers the geometry of the convergent portion of the nozzle has been employed to evaluate the chemical contribution. For the mechanical effect, a simple logarithmic function depending on porosity of the carbon and characteristic velocity of the propellant gases has been determined using dimensional analysis and experimental data. The results obtained under a nozzle material evaluation program, from both full-size and small-scale motors operating under different pressures and using various graphite grades and propellants, show a fairly close agreement with the theory. A new dimensionless number based on physical constants of the graphite throat has been defined for the graphical representation of results

The effect of acoustic field on the thermal conductivity of composite propellants

A study is conducted to determine the effect of acoustic field on the thermal conductivity of composite propellants based on poly- butadiene and polyurethane binders. The thermal conductivity of the propellant is determined by a specially designed equipment. The thermal conductivity measurements are made in steady state conditions and in an acoustic field of constant amplitude at various frequencies ranging from 1 kHz to 6 kHz and at different temperatures ranging from 30°C to 50°C. The results indicate that the thermal conductivities of the composite propellants increase when they are subjected to an acoustic field. The data obtained are presented in the paper. Since the burning behaviour of solid propellants is influenced also by its thermal conductivity, the present work may be of direct relevance in improving upon some of the existing burning rate and combustion models

A new prepolymer: lactone-terminated polybutadiene (LTPB) for high-energy solid propellants

The development of a new polybutadiene prepolymer with lactone terminals for use in solid propellants is reported. The data presented include those relating to the nature of reactions involved in synthesis, the spectroscopic and analytical studies to establish the nature of the functional terminals, and the mechanical and ballistic properties of the propellants based on the lactone-terminated polybutadiene (LTPB) prepolymer. Aging and low-temperature properties of the LTPB-based "Lactodiene" propellants are found to be comparable to the conventional carboxyl-terminated polybutadiene (CTPB)-based propellants. The studies on Lactodiene propellants bring out the experimental feasibility for a high-energy and high-density solid propellant system