Showing papers on "Burn rate (chemistry) published in 1984"

Constant pressure end burning gas generator

Abstract: End burning gas generators for use either as propulsion systems or means for generating large volume of gases for various purposes such as the generation of the fuel for a ducted rocket engine, the rapid inflation of air bags for personal protection or recovery of submersed items or the expulsion of projectiles from subsurface launch tubes are currently widely utilized. End burning gas generator grains are ignited at one end of a generally cylindrical charge mounted within a combustion chamber which is fixed with a suitable exhaust means. For many of the applications described above, it is desirable that the gas generator burn in a uniform manner such that a constant volume of gas is generated per unit of time so that the chamber pressure and the mass flow rate of gas remain constant. It has been observed, however, that rather than regressing at a uniform rate, the propellant grain burns in a manner which produces a convex cone, the angle of which increases with time thereby causing the burning surface to increase with time and to result in a progressive pressure trace within the combustion chamber and a corresponding continually increasing mass flow rate through the nozzle. According to this invention, it has been found that an end burning propellant grain can be caused to produce a substantially uniform pressure trace throughout its burn time if the interface between the grain and its container has a length greater than the axial length of the grain. The relationship between the length of the interface and the length of the grain is selected to compensate for the increased burning rate which is observed to occur at the interface and which produces the coning effect. The increased interfacial length can be easily obtained by the use of the corrugated member between the propellant grain and the case, the length across the corrugations providing the increase over the axial length of the grain. For typical gas generator propellant compositions, it has been found that if the interface is between 1.4 and 1.6 times the axial length of the grain that a substantially uniform pressure trace can be obtained. The corrugated interface also acts to improve the bond strength between the grain and the case.

Solid rocket motor with nozzle containing aromatic amide fibers

Abstract: A solid rocket motor is provided which comprises a rocket case and a centrally ported propellant grain comprising a main portion and a nozzle portion, wherein the main portion is a shaped and cured first propellant and wherein the nozzle portion comprises a shaped and cured second propellant composition having a lower burn rate than the first composition and having a plurality of aromatic amide fibers dispersed therethrough.

Method for burning rate characterization of solid propellants

Abstract: A method for determining the burning rate of a propellant. The method involves the single firing of a subscale, propellant motor that has been modified so that the propellant motor has a tapered cylindrical port that produces a non-neutral pressure-time trace when burned. The pressure-time trace is initially progressive (pressure increases with time), and then regressive (pressure decreases with time). Unlike conventional motors, this motor operates over a range of burning rates; therefore, the burning rate behavior of the propellant can be characterized with a single motor firing. The burning rate of the propellant is extracted from the motor pressure-time history by a computer analysis package. The analysis package employs an optimization program which uses an internal ballistics model of the motor. The ballistics model is used to generate a theoretical pressure-time trace which can be compared with the digitized output signal from the actual motor. The optimization routine of the computer determines the propellant burning rate behavior by selecting the burning rate law which, when employed in the internal ballistics model of the motor, produces the best match between the computer generated and the actual motor pressure-time traces. Thus by using the tapered port motor and by reducing the data, the burning rate of a propellant can be characterized with a single motor firing.

Low Burning Rate Aluminized Propellants in Acceleration Fields

Abstract: To reduce slag formation and burning rate increases, the effects of radial acceleration (up to 20 g) and low pressure (2-7 MPa) on the combustion of low-burning rate aluminized propellants (87 formulations) were investigated. Experiments were performed to obtain agglomerate size distribution, slag formation, and burning rate data. Data sources included photographs under cross flow and acceleration conditions, scanning electron probe (Cl and Al) images, particle collection combustors, and rocket motors. The tendency to form slag increases as the agglomeration size at the burning surface increases. A lower burning rate increases acceleration effects. However, residue formation is more sensitive to formulation than is burning rate; for example, bimodal vs trimodal AP can cause significant changes in residue in the absence of burn rate changes; RDX produces larger agglomerates than HMX. Through understanding obtained from this research, reduction in agglomeration, slag formation, and burning rate augmentation are directly attributable to systematic changes in formulation ingredient levels and sizes.

Hydraulic power supply system utilizing a solid propellant gas generator

Abstract: A hydraulic power supply system utilizing a turbine-driven pump in a hydraulic circuit and a solid propellant gas generator providing gas for driving the turbine. A gas pressure relief valve is operable to maintain the gas generator at constant pressure and has a range of pressure settings to vary the burn rate of gas generator and, thus, the power delivered to the turbine dependent upon the flow demands on the pump. There is a relatively low pressure setting when there is a reduced flow demand on the pump. The control provided by the settable hot gas relief valve reduces the size and weight of a number of components of the hydraulic supply system.

Low Pressure Combustion of Composite Propellant

Abstract: The combustion behaviour of two batches of a new type of composite propellant was investigated in the pressure range between 5 kPa and 915 kPa absolute. A newly developed technique to determine simultaneously the burning rate, combustion efficiency, and the propellant's sensitivity for combustion instability is described together with a specially developed data reduction code. Notwithstanding the low pressure during the experiments no lower deflagration limit could be traced but a Vieille type burning rate law appeared to be applicable for the whole pressure range of interest. A large difference found in the combustion behaviour could be attributed to the fact that the two batches had been manufactured with AP from different suppliers. Combustion efficiency was poor while combustion instability occurred in the whole pressure range.

Effects of HMX Addition on the Combustion of Energetic Binders

Abstract: : This paper presents a simplified model for the effects of HMX on the combustion of energetic binders. It has been found that an exothermic condensed phase is an important feature of energetic binder combustion. The effects of HMX addition can be summarized by a reduction in the overall exothermicity of the condensed phase together with an increase in the heat feedback from the gas phase. Consequences include an increase in pressure exponent along with a reduction in temperature sensitivity. Effects on burn rate magnitude depend upon binder composition and pressure, but the energy tradeoffs keep the burning rates within a narrow range at a given pressure. HMX addition is also shown to thin the combustion zone, with possible implications for the effectiveness of ballistic modifiers.

Closed Vessel Combustion of Stick Propellant.

Abstract: : Combustion of slotted single-perforated stick, triple base, M31-type propellant was studied in a closed vessel environment. The primary objective of these studies was to provide information for the characterization of stick propellants. Burning rates were determined as a function of propellant stick lengths, igniter configurations, and closed bombs with different length-to- diameter ratios. Low pressure burning rates were obtained from strand burner tests to eliminate possible variability in the extrapolation from the burning rate curve obtained from closed bombs. Studies of changes in the effective burning surface area of the propellant were performed in terms of vivacity. Orientation of the propellant sticks appeared to change the initial vivacity values and thereby, the effective burning surface area. With random orientation of the propellant sticks, burning rates obtained were higher than those obtained from the stacked orientation. This may be due to change in the ignition gas flow patterns over the propellant bed.

HMX Combustion Modification

Abstract: : Studies were conducted during this 3-year program to better understand the HMX decomposition mechanism by focusing upon the later stages of the multistep, complex decomposition process utilizing both isotopically labeled (N to the 15th power) and unlabeled HMX under low (approximately 300 C) and high (approximately 800 C) temperatures and at high heating rates. A novel experimental technique was developed, which utilized mass spectrometry and gas chromatography to identify quantitatively the amounts of gaseous species generated on pyrolysis of the substrates. This permitted detection of any chemical and/or thermal interactions between various energetic materials and an understanding of those interactions that contributed or deterred the burn rate of HMX or RDX. Compounds that yielded NH3, were oxygen free, and decomposed exothermically, had a significant effect upon the decomposition of HMX via an exothermic gas-phase reduction of NO (a decomposition product of HMX). This effect was caused by the formation of amidogen (NH2) radicals from the generated NH3. Pyrolysis studies performed on various azide compounds showed that the azide moiety increased the burn rate of HMX. Close matching of the decomposition temperatures of HMX and the additive was required to enhance the chemical and/or thermal interactions between the gaseous decomposition products. Attempts to incorporate the azide group into the HMX structure were successful. Its incorporation in propellants containing HMX did not result in an enhanced burn rate.

Study of deflagration-to-detonation transition (DDT) in the granular explosive, CP

Abstract: In this report, we present an experimental and theoretical study of the combustion processes associated with deflagration-to-detonation transition in the granular explosive, CP. Image-enhanced, high-speed streak photography recorded the various stages of flame spread within heavily confined charges as viewed through a lexan window in a thick wall, stainless steel tube. To describe these observations we apply a multiphase reactive flow model based on the theory of mixtures. This nonequilibium model treats each phase as fully compressible and incorporates a compaction model for the granular reactant. Formulation of the constitutive models includes a pressure-dependent burn rate and experimentally-determined porous bed permeability. Predictions of this model agree well with experimental observations.

The direct effects of strain on burning rates of composite solid propellants

Abstract: A mathematical model is developed to predict burn rate augmentation due to strain in a composite solid propellant. The model assumes the effect is due to the ability of the flame to penetrate the small fissures and voids that form when a propellant is strained. The number and size of these fissures is obtained by applying a flaw propagation analysis to randomly distributed flaws that form when the binder-oxidizer particle bonds break under stress. A flame height is calculated with Summerfield's burn rate equation and is used to compute the burn rate augmentation based upon the additional burn area created when the flame penetrates the fissures. Comparisons are made with data obtained from published sources. The existence of threshold pressure and strains, above which augmentation occurs, is verified although the model predicts a lower threshold pressure and higher threshold strain than expected. Further results and applications of the model are discussed.

Mechanisms and models of solid propellant burn rate-temperature sensitivity - A review

Abstract: Passage en revue des mecanismes qui affectent la sensibilite a la temperature: les mecanismes directs traites dans les modeles analytiques, les aspects non ideaux du processus de combustion, la derive des mecanismes de controle

Thrust Characterization of Very High Burning Rate Propellants

Abstract: : A series of closed bomb combustion tests were conducted on several very high burning rate (VHBR) propellants in which, in addition to the standard pressure measurements, the thrust produced by a burning propellant column was measured using a dynamic force gage located at the end of the propellant column. The results indicate that in several instances the total force imparted to the force gage substantially exceeded that due to the gas pressure alone. The difference is ascribed to the thrust or impulse resulting from very high apparent burning rates. In fact, an analysis of the data for two VHBR propellants indicates that effective burning rates from 100 to 300 m/s are required to produce the observed thrust levels. Such burning rates are not yet explainable by conventional combustion models. Additional physical processes such as convective flamespread or stress-induced surface fracture must be invoked to explain such high apparent burning rates.