Propellant Samples Research Articles

Kr^+ and Ar^+ laser-excited fluorescence of CN in a flame

Laser-excited fluorescence of the CN radical was obtained using various discrete prism selected lines of krypton and argon-ion lasers. The source of hot CN is a slightly rich atmospheric pressure CH4/N2O premixed flame diluted with N2. The flame is placed within the extended cavity of the ion lasers to take advantage of much higher light intensities. Both B2∑+ ← X2∑+ and B2∑+ ← A2Π transitions of CN have been pumped. The Kr+ laser lines, 6764, 6471, 5309, 4680, 4154, 4131, and 3564 A, all pump CN. The 4545-A line of the Ar+ laser also pumps CN. Vibrational and rotational assignments have been made. Detection of CN in a burning propellant sample has been accomplished by this technique.

Ignition of composite solid propellant at subatmospheric pressures

The ignition of composite solid propellants by CO 2 laser irradiation at low pressures has been investigated experimentally. Three ignition modes are found at subatmospheric pressures: self-sustaining ignition, non-self-sustaining ignition, and pulsating ignition. Here, the self-sustaining and the non-self-sustaining ignition modes have been studied. Samples of an ammonium perchlorate polybutadiene propellant were ignited. The incipient flame was detected with a phototransistor, and the temperatures at the surface and in the solid phase were measured by means of Type K thermocouples. Aspects of surface regression were recorded by photography. It is found that non-self-sustaining ignition occurs in the lower pressure range and with the higher incident heat flux from the laser. At ignition, the heat loss into the solid phase in the non-self-sustaining mode is much larger than that in the self-sustaining one. It is concluded that these ignition modes are determined independently of the exposure time after the flame's appearance.

Application of the impedance tube technique in the measurement of the driving provided by solid propellants during combustion instabilities

This paper describes the adaptation of the impedance tube technique for the measurement of solid propellant response functions. The experimental setup consists of a tube with a disc-shaped solid propellant sample placed at one end and an additional propellant sample at the side wall of the tube at some distance downstream of the end propellant sample. When the pressure coupled response function is measured only the disc-like sample of the propellant is needed while determination of the velocity coupled response function requires the use of both propellant samples. During an experiment, an acoustic driver located at the opposite end of the tube is utilized to establish a standing wave of a desired frequency within the impedance tube and an array of pressure transducers mounted at preselected locations along the impedance tube walls is utilized to measure the continuously varying wave structure within the tube throughout the course of the experiment. Upon the completion of the experiment, the measured data together with solutions of the impedance tube wave equations are utilized to determine the propellant response function. The paper discusses the different data reduction procedures that have been developed for the determination of both the pressure and velocity coupled response functions. Furthermore, the paper describes the results of pressure coupled response measurements for both aluminized and nonaluminized propellants and the results of a theoretical study that show that the impedance tube method could also be used in the measurement of the velocity coupled response function.

Determination of Solid Propellant Admittances by the Impedance Tube Method

The adaptation of the impedance tube technique for the measurement of solid propellant admittances and response functions is described. These quantities are needed for combustion stability analysis of solid rocket motors. The experimental set up consists of a tube with a disk of solid propellant sample placed at one end and a combination of an exhaust valve and an acoustic driver placed at the other end. Performing a test consists of turning on the acoustic driver to excite a standing wave of a predetermined frequency in the tube, ignition, and burnout of the solid propellant sample. During a test, acoustic pressure data is measured by fifteen pressure transducers distributed along a distance that includes, at least, two standing wave pressure minima. The data are transferred via a fast analog-to-digital converter to a minicomputer system for immediate storage and later analysis. The measured acoustic pressure amplitude and phase data are input into a newly developed data reduction procedure that is based upon the solution of the impedance tube wave equations, for the determination of the admittance and response function of the tested solid propellant sample and the acoustic energy losses in the gas phase. The paper presents results obtained in a series of tests conducted with an A-14 propellant. The paper demonstrates the capability of the developed experimental technique to determine simultaneously the acoustic characteristics of the flow inside the impedance tube and the admittance of the burning solid propellant for the duration of the experiment. Nomenclature A /y = defined in the Appendix C = constant defined in Eq. (8) c = velocity of sound, m/s cp - specific heat at constant pressure, kcal/kg K cv = specific heat at constant volume, kcal/kg K E = error function defined in Eq. (15),, (N/m 2)2 or Pa 2 F = losses due to viscosity and gas phase damping, kg/m2s2 G = gas phase bulk loss coefficient, kg/m3 s / = identity matrix M = Mach number m = mass flow rate per unit cross-sectional area, kg/m2 s p = pressure, N/m2 or Pa Q = volumetric heat source, kcal/m3 s mole R = gas constant, kcal/kg mole K r = burning rate, m/s s = entropy, kcal/kg K T = temperature, K; also transmission matrix defined in Eq. (10) TWQ = wall temperature at x = 0, K u = axial velocity, m/s Y = specific admittance, dimensionless Z = variable used to represent oscillatory quantities, defined by Eq. (6) ps = density of solid propellant, kg/m3 p = density, kg/m3 Superscripts (~) = variable describing a steady-state quantity ()' = variable describing a perturbation quantity

Ultrasonic assessment of cumulative internal damage in filled polymers (II)

An ultrasonic technique previously developed for studying dewetting and cumulative internal damage in filled polymers, such as solid rocket propellents, has been improved. The previous theoretical treatment is here expanded to include internal vacuoles of general spheroidal (rather than spherical) shape. Experimental measurements of sound speed and attenuation in a solid propellant material are utilized together with the modified theoretical model to calculate the internal damage parameters of effective vacuole size and number density as functions of applied uniaxial tensile strain. Results obtained from the model near the point of material failure are in excellent agreement with those provided by independent microscopic observations made on several rupture surfaces of propellant samples stressed to failure.

Measurements and Model Validation for Composite Propellants Burning under Cross Flow of Gases

Erosive burning rates of three types of ammonium perchlorate-based composite propellant formulations were measured by using the high-speed motion picture method. Experiments were conducted in a test rig designed to develop a well-defined, turbulent boundary layer with a distinct leading edge by the flow of combustion gases over two-dimensional propellant samples. Erosive burning rate correlations which relate the burning rate to freestream velocity and pressure were developed. The comparison of experimental data and theoretical results obtained from the erosive burning model, based upon the turblilent boundary-layer approach developed by the authors, showed a close agreement.

Indirect determination of nitroglycerine by biamperometric titrimetry

A procedure is described for the determination of nitroglycerine in propellant samples by biamperometric titrimetry. The method is simple, avoids the use of expensive instruments, and is free from interferences other than those occurring in the classical techniques. The accuracy and precision are equal to those of existing methods. The reduction and titration steps are performed in the specially designed flask.

Combustion of Highly Loaded Composite Propellants: Study of Pressure Exponents

Abstract Experimental results are given on the burning rate characteristics of highly loaded composite propellants. The binder used.is CTEB,. the concentration of which is fixed at 12 percent by weight with the remaining materials being oxidizers (ammonium perchlorate, potassium perchlorate) and aluminium. The propellant samples are burnt in a moderate pressure range (10 to l00 atm) and the influences of oxidants particle size and of the mixture ratio on the pressure exponent are determined. Frames from high-speed movies of the combustion of AP, AP+KP propellants showing the structure of the burning propellant surfaces at.high and low pressures help to clarify the combustion mechanism.

Determination of lead in propellant samples by atomic-absorption spectrophotometry

A procedure is described for the determination of lead in different types of propellant samples by atomic-absorption spectrophotometry. The method is simple, rapid and avoids the use of strong acids and prior sample digestion. Complete lead extraction is achieved with 10% acetic acid. The results obtained by the proposed method are compared with those obtained by the gravimetric chromate method. The variation of the efficiency of lead extraction with sample type is discussed.

Energy balances and uniaxial damage of highly filled elastomers

AbstractA propellant sample undergoes internal damage while it is tested at finite deformation. The damage consists of broken molecular chains and void spaces which form around the filler particles and contribute to failure of the propellant. Attempts were made to determine the amount of this damage from the viewpoint of energy dissipations. Mechanical energy losses, called damage energy, were computed from energy changes during tension cycling experiments carried out at different temperatures and straining rates. Shift procedures were applied to the experimental results, and a double‐reduced master curve for damage energies was obtained by using time–temperature and strain shift factors. The reduced master curve can be used to predict the extent of damage accumulated in a propellant sample during tensile tests at different straining rates and temperatures.

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.

Solid propellant acoustic admittance corrections

The acoustic behavior of solid rocket propellants is conveniently expressed in terms ofthe specific acoustic admittance of the burning surface. Numerous measurements of the admittance have been made in T-burners, and it is generally assumed that the data can be used directly in estimates of rocket motor acoustic stability. However, as this paper shows, the propellant response to incident acoustic waves is influenced by the orientation of the propellant surface to the waves. If there is a tangential component of acoustic velocity, then viscous effects give rise to the generation of a traveling shear wave which modifies the apparent propellant response. This wave is out of phase with the velocity fluctuations and obviously represent an energy loss to the system. It is demonstrated that the shear wave is strongly influenced by the mean flow due to propellant combustion; for larger values of burning surface Mach number, the speed of propagation approaches that of the combustion gases. Thus admittance data from T-burners with the propellant samples arranged with normal wave incidence must be corrected for the shear effects if they are to be used in motor calculations wherein acoustic modes with grazing incidence are of interest. For the same reason it is essential to interpret carefully T-burner data secured in devices employing extended or cup-shaped grains, since part of the propellant produces shear waves and thus exhibits a different effective admittance. The corrections are shown to be of the order of the mean flow Mach number; that is, they are of the same order as the real part of the admittance and must not be ignored in motor calculations. It is demonstrated that inclusion of the corrections brings about a marked improvement in agreement between the classical linearized theory of acoustic combustion instability and experimental observations of the phenomenon.

Dynamic mechanical behavior of highly filled polymers: Energy balances and damage

Dynamic tests using the Naval Weapons Center torsion–tension tester and end-bonded cylindrical propellant specimen were carried out to evaluate the effects of internal damage on propellants by subjecting samples to small tensile oscillations during low constantstrain rate tests. It is shown that microstructural damage in a propellant causes significant changes in mechanical properties. The mechanical property curves demonstrate that the response is markedly strain sensitive. So long as the maximum strain experienced by the sample during a test is not exceeded, the response of the propellant to small tensile oscillation during repeated strains below that maximum value remains relatively unchanged after the first initial dramatic change. The differences between mechanical energy balances of “undamaged” and “damaged” propellant samples were used to demonstrate microstructural damage and to estimate the extent of damage. For any one propellant, the total lost energy caused by microscopic failure of the propellant seems to be additive, constant, and independent of the mechanical path to failure.

Dynamic mechanical behavior of highly filled polymers: Dewetting effect

AbstractThis paper describes the results of simultaneous dynamic measurements in tension and torsion made on propellant samples. The complex dynamic moduli E′, E″, G′, and G″ at low frequencies were determined within a temperature range from room temperature to −90°C. Time temperature shift factors and reduced master curves for both tension and shear properties are discussed. The effect of dewetting on the dynamic properties in tension and shear was also investigated. A preliminary attempt is made to compute the degree of dewetting in a propellant by applying Beer‐Lambert's law.

A Replica Technique to Facilitate the Investigation of Quenched Solid Propellant Samples

A Replica Technique to Facilitate the Investigation of Quenched Solid Propellant Samples

Capsule for Irradiation of Explosives

An aluminum capsule 2⅛ in. in diameter and 9 in. long completely contains the high-order detonation of 3.6 g of explosive. This was approved for insertion in the General Electric Test Reactor and successfully used to irradiate a series of explosive and propellant samples. Modifications were also made to permit continuous measurement of pressure and temperature of the sample during irradiation when desired. Methods used to measure gamma flux, neutron dosages, and temperature limits are also described.

Contaminants on the Moon

Contaminants on the Moon

Torsional Pendulum for Plastic Materials under Tensile Strain

This paper describes a torsional coupled pendulum combined with a tensile tester to measure simultaneously static tensile properties and dynamic and static shear properties of viscoelastic materials at constant temperature. The thermal environment of the sample is a liquid, permitting more efficient heat transfer and control in the sample itself. Several representative data are presented on carbon black filled rubber and highly filled rubber propellant samples.

Ignition of ammonium perchlorate composite propellants by convectiveheating.

A comprehensive experimental study was made of the ignition of ammonium perchlorate propellants in a shock-tube apparatus. Test variables were: 1) heat flux, 2) test-gas temperature, 3) test-gas velocity, and 4) pressure. Convective heat fluxes at the propellant surface were varied over the range of about 20 to 160 cal/cm sec. The experimental results showed that, in the range of conditions used, ignition characteristics of ammonium perchlorate propellants are in agreement with those predicted by thermal ignition theory. However, for propellant samples with surface irregularities, the thermal ignition process is accelerated at low test-gas velocities by external-flux-augmenting exothermic reactions among decomposition products at the surface. These decomposition products are produced at local hot spots resulting from two-dimensional Convective heating of protrusions and other surface imperfections. The experimental data indicate that the key reaction in the ignition process is the low-temperature thermal decomposition of ammonium perchlorate.

Continuous Measurement of Solid Propellant Burning Rates

An experimental system is presented for the direct and continuous measurement of the burning rates of solid rocket propellants under conditions closely approximating those of a solid rocket motor. The system involves a positioning type servomechanism which moves a sample of solid propellant within a two dimensional rocket motor such that the receding burning surface of the sample is maintained at a fixed position with respect to the motor. Since the burning surface remains fixed, the direct measurement of the velocity of the propellant feed mechanism for adjusting the position of the propellant sample yields the burning rate. The servomechanism incorporated a 50 m Ci 137Cs source of gamma rays coupled with a scintillation probe for detecting the position of the burning propellant surface. The output of the probe was converted into a voltage by a ratemeter. It was then amplified and compared to a standard voltage which was proportional to a desired propellant surface position. The resulting difference was amplified for the purpose of driving a 0.6 hp servomotor which positioned the burning surface of the propellant sample. The size of the sample was approximately 2.5 cm square by 10 cm long. The experimental data were obtained with the above servomechanism for two composite propellant formulations. The data were obtained for a range of pressures from 8.8 to 35.5 kg/cm2, and for burning rates ranging from 0.40 to 0.8 cm/sec. The data correlated well with previously published data. A theoretical analysis of the servomechanism was performed to determine system stability and performance. An optimization analysis of the servomechanism system yielded optimum operating parameters.