Combustion Of Composite Solid Propellants Research Articles

Combustion of Nitramine Propellants

Abstract : The composite solid propellant combustion model of Beckstead, Derr and Price is modified to describe the combustion of Nitramine propellants. Modifications are based upon experimental observations of the combustion characteristics of hydrocarbon binder propellants containing cyclotetramethylenetetranitramine (HMX).

On the mechanism of the copper(II)-catalyzed low-temperature decomposition of ammonium perchlorate

Iron oxide and copper chromite are the known burn rate enhancers used in a composite solid propellant. Lot of research has been carried out to understand the mechanism or location of action of the burn rate modifiers so as to better tailor the burning rate of a composite propellant. The literature is still very confusing in affirming the mechanism. Here, a systematic study has been carried out, by undertaking experiments at varying levels of combinations of the individual components (ammonium perchlorate, which is oxidizer and hydroxyl terminated poly butadiene, which is both fuel and binder) of composite solid propellant. Firstly, thermal gravimetric analysis, differential scanning calorimetry and burning rate measurements on the individual components are carried out to study the effect of iron oxide and copper chromite on the components themselves. It has been noticed that though both iron oxide and copper chromite are effective on ammonium perchlorate, iron oxide is slightly more effective than copper chromite. Also, copper chromite enhanced the binder melt flow, while iron oxide reduced it. These are followed-up by experiments on sandwich propellants, which give greater insight and enables better understanding of the behavior of iron oxide and copper chromite in composite propellants, as these are simple two-dimensional analogue of the composite solid propellants. Finally, experiments are carried out on the composite solid propellants to obtain a holistic understanding of the behavior/location of action of iron oxide and copper chromite in them. These studies are used to explain certain unexplained but observed phenomena, at the same time elucidating the location of action of these burn rate modifiers in composite solid propellant combustion. Based on these observations, it has been proposed that both iron oxide and copper chromite are primarily acting on the condensed phase. These studies are further complimented with experiments to analyze the thermal conductivity measurements of various propellant samples. This is pursued to understand the reason for the differences in burn rate pressure index for the composite propellants with iron oxide and with copper chromite. It has been understood from these studies that the thermal conductivity of a composite propellant is a key parameter, which affects the burn rate pressure index. Literature has never addressed it from this perspective.

A model for the combustion and extinction of composite solid propellants during depressurization

In this paper are described some results of an investigation of the transient burning rate and critical pressure decay rate required to cause extinction of a steadily burning solid propellant subject to sudden depressurization. The analysis takes into account the finite times associated with the conduction process and the variation of condensed phase heat release in the solid during a transient. It is postulated that composition of the solid decomposition products,is oxidizer-rich immediately after the start of depressurization and fuel-rich afterwards. The theoretically calculated transient burning rates qualitatively agree with experimentally measured values, reported by Norton and Schultz [1]. Yin and Hermance [2], and Fletcher and Bunde [3]. A stability analysis under the linear approximation predicts the existence of a minimum burning, surface temperature below which stable combustion of the solid propellant is not possible. The analysis correctly predicts the critical depressurization rate required to extinguish a burning solid propellant by sudden preventing of the combustion chamber.

Effects of copper chromite and iron oxide catalystson AP/CTPB sandwiches

Results are presented of an experimental motion-picture study designed to provide observations of catalyzed composite solid-propellant combustion. Various methods of catalyst addition were incorporated into two-dimensional sandwiches, composed of pressed ammonium perchlorate (AP) oxidizer sections laminated together with a thin layer of carboxy terminated polybutadiene (CTPB) binder. Catalysts investigated were harshaw Catalyst Cu 0202 (copper chromite—CC) and Fe 2 O 3 (iron II oxide—IO). The sandwiches were burned in a window bomb at pressures of 600 and 2000 psig. Cinephotomacrography, at a frame rate of 1600 pictures per second and magnification of 2:1, was used. Copper chromite was found to be a more effective catalyst than IO for AP/CTPB sandwich systems. Copper chromite appeared to: augment the AP-deflagration process; possibly catalyze gas-phase reactions; possibly promote gas-phase reactions in crevices between the solid fuel and solid AP (at the interface); not promote heterogeneous reactions of gases with the solid-fuel binder; not modify the pyrolysis mechanism of the solid-fuel binder. Iron oxide was found to have effects qualitatively similar to CC, with the exception that it inhibited the AP-deflagration process at 600 psig. With the exception of IO at low pressures (600 psig), the addition of CC and IO in the AP was found to be the most effective method of increasing sandwich burn rate; their addition at the AP/binder interface was less effective; and their addition in the binder did not appear to be very effective at all, at least in the sandwich configuration. These findings, concerning CC and IO catalysts, indicate that some of the theories concerning the catalytic mechanisms of CC and IO with AP/binder composite propellants are justified, whereas others are not.

A model of composite solid-propellant combustion based on multiple flames

A model describing the combustion of AP composite propellants has been developed. The model is based on a flame structure surrounding individual oxidizer crystals; the relationship between crystals and the binder matrix being evaluated statistically. Three separate flame zones are considered: 1) a primary flame between the decomposition products of the binder and the oxidizer, 2) a premixed oxidizer flame, and 3) a final diffusion flame between the products of the other two flames. Simple global kinetics are assumed for gas-phase reactions, and the surface decomposition of the propellant ingredients is assumed to be adequately described by simple Arrhenius expressions. The oxidizer decomposition is taken as being the over-all controlling factor in the combustion process. The results obtained show that the calculated surface temperature and the effect of oxidizer concentration predicted by the model are in agreement with observed experimental trends. The predicted effect of particle size is somewhat greater than observed experimentally while the temperature sensitivity is in excellent agreement with experimental data. The results of the calculations indicate a relatively strong exothermic reaction taking place at the propellant surface. Apparently the ammonium perchlorate (AP) partially decomposes exothermically in the thin surface melt previously reported in AP deflagration studies.

A phalanx flame model for the combustion of composite solid propellants

A new model for the combustion of composite solid propellants is developed. The flame is represented as burning at the interfacial region between streams of fuel and oxidant which are generated by vaporization of each solid component. The interface between the two solid phases receives the greatest heat flux from the reaction zone and vaporization occurs most rapidly near the interface. The reaction zone is a ‘phalanx’ which spearheads the attack of hot reaction gases on the solid. The model provides a rational physical explanation for many qualitative observations of solid propellant combustion and successfully correlates the pressure dependence of burning rates.

Comments on "Alumina Size Distributions from High-pressure Composite Solid-Propellant Combustion"

Comments on "Alumina Size Distributions from High-pressure Composite Solid-Propellant Combustion"

Alumina size distributions from high-pressure composite solid-propellant combustion

Alumina size distributions were obtained for both a coarse and a fine oxidizer composite propellant burning in a nitrogen atmosphere over the pressure range from atmospheric to 500 pounds per square inch. The amount of additive agglomeration was found to be significantly higher for the coarse oxidizer propellant and decreased with increasing pressure to the 0.3 power over the range from atmospheric pressure to 250 pounds per square inch. High-speed photographs of the burning propellant surface revealed that the additives moved on the surface with the average particle velocity decreasing with pressure to approximately the 0.3 power over the pressure range from atmospheric to 50 pounds per square inch. The empirical relation between particle velocity and pressure was used to modify an agglomeration criterion presented previously. Evaluation of the critical aluminum diameter required for agglomeration indicated that both propellant types used in this study should experience some agglomeration over the pressure range studied. The aluminum size required for agglomeration was found to increase with increasing pressure. The experimental findings of the critical aluminum diameter required for agglomeration were in reasonable agreement with the calculated data. The volume mean diameter of the alumina was found to decrease with increasing pressure.