Burning Of Composite Solid Propellants Research Articles

Burning Rate Studies: Potassium-Doped Ammonium Perchlorate with Other Burn-Rate Modifiers

Iron oxide and copper chromite have been used as burn-rate modifiers of composite solid propellants. In recent times, studies have been reported on potassium-doped ammonium perchlorate and on dry activated charcoal. These have shown an increase in composite solid propellant burning rates. The studies on composite solid propellants using dry activated charcoal have also shown a reduction in the burn-rate pressure index for a composite solid propellant. With this knowledge, experiments are conducted to develop compositions that result in both high burning rates and low burn-rate pressure index of the propellant. In addition to these, the study also reports propellants with dual burn-rate pressure index. The change in the burn-rate pressure index is from 0.2 to 0.65 in one of the propellants. These could be very useful in that the same grain can act as boost and sustain grain depending on the combustion chamber pressure. With the addition of different burn-rate modifiers, the pressure at which the change in burn-rate pressure index is observed shifts. This could be a very useful tool for propellant designers. It was observed that, with the use of activated charcoal along with potassium-doped ammonium perchlorate, the burn-rate pressure index was brought down from around 0.65 to 0.38, whereas the burn rates were still higher (60%) than the base propellant.

Activated charcoal: as burn rate modifier and its mechanism of action in non-metalized composite solid propellants

Modification of composite solid propellant burning rates becomes a requirement based on the necessities of a mission. Literature discusses about various burn rate modifiers which can modify the burning rates effectively. This paper attempts to understand the behavior and mechanism of (dry) activated charcoal (a recently reported burn rate modifier) in composite solid propellant combustion. Extensive experimental studies are performed to achieve this objective. Effects of activated charcoal are studied on the individual components (fuel and oxidizer) of a composite solid propellant. Its behavior when present at various locations in a sandwich propellant and the quenched surface structures these sandwich propellants is also studied. These studies are further extended to composite propellants as well. From these studies, it is concluded that activated charcoal acts on the primary diffusion flame and enhances the binder melt flow over the surface. The unique features observed with activated charcoal (enhancement in burning the rates is observed only at low pressures and burn rate pressure index reduced) are justified with the proposed mechanism and site of its action. Understanding the mechanism of activated charcoal provided an opportunity to tailor a propellant composition, with activated charcoal coated on ammonium perchlorate, which exhibited very high burning rates (17.34 mm/s at 70 bar) and a near plateau burning (n ~0.08) in the pressure range of 20–70 bar. Also, this paper proposes a mechanism, as to what causes a propellant to have a relatively larger binder melt flow and consequently lower n has been answered.

Enhancing Composite Solid Propellant Burning Rates with Potassium Doped Ammonium Perchlorate—Part 2

This paper reports the development of a nonaluminized composite solid-propellant formulation with high burning rates. To achieve high burning rates, potassium (described in the literature as an impurity) has been doped into ammonium perchlorate. It is seen that beyond a potassium content of 0.19% the increase in the burning rates of a composite propellant is not significant. A high-burn-rate pressure index at high pressures and the dual slope has been observed with the potassium doped ammonium perchlorate in a composite solid propellant even with the use of only fine sized ammonium perchlorate particles. These features have been explained through surface scanning electron microscope pictures of quenched propellant samples.

Enhancing Composite Solid Propellant Burning Rates with Potassium Doped Ammonium Perchlorate-Part I

The objective of this paper is to understand the observed changes in behavior of ammonium perchlorate deflagration characteristics reported in literature, when it is doped with potassium. Successive recrystallization is employed to dope potassium into ammonium perchlorate. This paper, through various recrystallization techniques, conclusively puts an end to doubts regarding the actual process of acquisition of potassium by ammonium perchlorate. It is concluded that the increase in the potassium content in ammonium perchlorate is due to the filter used during recrystallization process. From the experiments conducted to obtain the deflagration rates of ammonium perchlorate, it is observed that potassium doped ammonium perchlorate has higher burning rates and also a higher low-pressure deflagration limit. As potassium doped is within the ammonium perchlorate crystal, thermal conductivity and specific heat values for ammonium perchlorate with various percentages of potassium are obtained. These values are incorporated into the computational studies on ammonium perchlorate. The computational studies performed in this paper are not intended to reproduce the experimental results but to illustrate the various features of the potassium doped ammonium perchlorate deflagration. With these computational studies, the observed burning rate increase and low-pressure deflagration limit increase of ammonium perchlorate with doped potassium are explained.

Effect of Specific Surface Area of Aluminum on Composite Solid Propellant Burning

This paper proposes the use of micron-sized aluminum (pyral, average particle size ) with a higher specific surface area as a good candidate to enhance the burn rate of the composite propellant. Experiments were performed in the pressure range of 10 to 70 bar in a window bomb for measuring the burn rate. Comparison of these burn rate results with those obtained using micron- and nanosized aluminum found that the performance of pyral was in between that of micron- and nanosized aluminum. The reason for the high burn rates observed with pyral is due to the flake like appearance of pyral with a large specific surface area. It is argued that, if the specific surface area is large, then the thickness becomes the characteristic length scale. This ensures the heat release from the aluminum combustion to occur closer to the propellant surface as the thickness of pyral is in nanometers. Both the x-ray diffraction and heat of formation analyses indicated that pyral had higher purity than nanoaluminum, which has an implication to the specific impulse of the propellant. In addition to this, it shows that the micron-sized catalyst is effective with pyral, whereas it is ineffective with nanoaluminum. This study also reports the mechanical properties of the propellant containing pyral.

Mechanism of steady-state burning of composite solid propellants including those with negative pressure-exponents

The mechanism of steady-state burning of AP-based composite solid propellants has been studied by means of single-frame microphotography with self-illumination or laser-shadow for the observation of the burning samples and scanning electron microscope for the examination of extinguished combustion strands. It has been found that covering of the molten binder over the oxidizer surface is not a particular phenomenon of PU propellants in the mesa-burning region, but a general phenomenon taking place under quite extensive circumstances. The experimental results also indicated that the local covering may not result in local extinction and features of the propellant combustion in the mesa-region are quite analogous to those of pure AP crystal deflagrating in the Regime III. A new theoretical model has been further developed, in which the existence of the covering of molten binder over oxidizer surface has been taken into consideration. And in analysing the part of AP surface covered with molten binder, the condensed-phase reaction and opposed gasification of covered AP are considered. The model developed for AP-based composite solid propellants can be used to explain plateau, mesa and normal burning features and to analyse the effects of initial temperature and AP particle size on burning behaviors.

Solid propellant combustion zone structure from analysis of hydroxylradical chemiluminescence

Hydroxyl radical Chemiluminescence spectra have been obtained in the combustion zone above ammonium perchlorate composite solid propellant burning at multiatmospheric pressures in a laboratory scale strand burner. These semiresolved (.13 nm) spectra were analyzed by constructing OH synthetic spectra and employing a best-fit technique to determine the rotational temperature and vibrational population distribution in the A!, electronic state of OH in the flame. Values for rotational temperature and vibrational population distribution were obtained for pressures from 0.2 to 7.0 MPa at three positions above the propellant surface. Quantitative comparison of results over a range of pressures for a given spatial position is mitigated by the potentially significant effects of self absorption on the measured spectra. Comparisons at a given pressure for various positions above the propellant surface should not be affected by self-absorption, and show a fairly constant rotational temperature and vibrational population distribution from near the surface out to the maximum position investigated (12 mm). These results indicate that a chemical combustion environment involving short lived radical species exists at distances very far from the propellant surface even at elevated pressures. Interpretation of the spectral characteristics of the emission data also indicates highly nonequilibrium vibrational populations and possible non-Boltzmann rotational distributions which increasingly diverge from equilibrated distributions with increasing pressure.

Erosive Burning of Composite Solid Propellants: Mechanism, Correlation, and Grain Design Applications

With increasing interest evidenced in the developrrient of nozzleless and high-performance solid rocket motors, an understanding of Ifie errrsivz-bsrning charwrter:;iics of sollid propellants in high-velocity cross flows is important in establishment of grain design procedures. A theo~etical model based on a turbulent reacting boundary-layer analysis, validated with experimentnl data, was used to conduct parametric studies under broad ranges of Mach number, pressure, surface roughness, pressure gradient, port diameter, and propellant initial temperature. Using nonlinear regression analysis, an erosive-burning rate correlation was developed in terms of the cited parameters. The results for two motor grain contours were used to demonstrate the applicability of this correlation to grain design.

Erosive Burning Study of Composite Solid Propellants by Turbulent Boundary-Layer Approach

Erosive burning of composite solid propellants is investigated by analyzing a steady, two-dimensional, chemically reacting, turbulent boundary layer over a propellant surface. Predicted erosive burning rates agree closely with experimental data. The erosive burning rate augmentation is found to be caused by the increase in heat feedback introduced by the increase in transport coefficients, and the turbulence enhanced mixing and reaction of the oxidizer and fuel gases. The increase in freestream gas velocity brings the location of the peak turbulence intensity and the heat release zone closer to the propellant surface, thereby increasing the burning rate of a propellant.

Some statistical considerations in the burning of composite solid propellants

Propagation of a deflagration wave through a nearly ordered composite propellant is considered. The intent is to see some effects of the particle packing statistics on the propagation rate. A highly oversimplified model of the deflagration physics is considered, and only the statistics are emphasized. It is found that, for propellants of usual packing density, the least-time path of burning to a given point depends primarily on the packing statistics in a line parallel to the burn rate vector; there is little effect of particles only a few particle diameters to the side of this line. In a simplified model that may be solved analytically, there are clearly seen particle-size, pressure, and packing density effects on burn rate which are due to the statistics alone and not the deflagration physics.

Role of Binders in Solid Propellant Combustion

Abstract : The objective of this program was to investigate and define the effects of inert binder properties on composite solid propellant burning rate. Experimental pyrolysis data were obtained for many binders of practical interest over a wide range of heating rates and pressures, in several environmental gases, with and without 10-percent ammonium perchlorate (AP) contained in the sample, and in some cases with catalysts. These data were used to extract kinetics constants from Arrhenius plots, and heat of decomposition. In addition, motion pictures were taken of the pyrolyzing surface and gas samples were extracted for analysis. Pyrolysis kinetics varied between binders, but were found to be independent of pressure, the presence of AP, and the presence of burn rate catalysts; however, a chlorine gas environment had a material effect upon the results. All of the binders exhibited molten, boiling surfaces mingled with char, to varying degrees; the amount of char increased with AP present, and in chlorine. Relevant data were input to the Derr-Beckstead-Price combustion model in order to associate binder properties with known binder effects on burning rate. Although the effects were predictable, they stemmed from properties other than pyrolysis kinetics; however, the binder data as applied to the model revealed possible deficiencies in the model, which are discussed. It appears that the approach of combustion tailoring by binder modification would have to involve the gas phase combustion processes rather than surface pyrolysis. Therefore, future work concerning the role of binder should be directed toward the gas phase.

Particulate matter in the exhaust of a boron- loaded solid propellant

2 Sturm, E. J. and Reichenbach, R. E., Aluminized Composite Solid-Propellant Burning Rates in Acceleration Fields, AIAA Journal, Vol. 7, No. 11, Nov. 1969, pp. 2087-2093. 3 Manda, L. J., Compilation of Rocket Spin Data, Vol. II: Literature Survey, Rept. 3001-2, CR-66641, 1968, NASA. 4 Anderson, J. B. and Reichenbach, R. E., '76-Inch Diameter Centrifuge Facility, TN 66T-4, Sept. 1966, Dept. of Aeronautics, Naval Postgraduate School, Monterey, Calif. 5 Sturm, E. J., A Study of the Burning Rates of Composite Solid Propellants in Acceleration Fields, Ph.D. thesis, AD832206, March 1968, Naval Postgraduate School, Monterey, Calif. 6 Green, L., Jr., Burning of Some Composite Solid Propellants, Jet Propulsion, Vol. 24, No. 1, Jan-Feb. 1954 DD 9-15. ' 7 Wimpress, R. N., Internal Ballistics of Solid Fuel Rockets, 1st ed., McGraw-Hill, New York, 1950. 8 Lawrence, W. J. and Deverall, L. L, The Erosive Burning Behavior of Selected Composite Propellants, Proceedings from the 4th ICRPG Combustion Conference, Stanford Research Inst., Menlo Park, Calif., Oct. 1967, pp. 459-466. 9 Crump, J., Aluminum Combustion in Composite Propellants, Proceedings of the Second ICRPG Combustion Conference, Aerospace Corp., El Segundo, Calif., 1965.

Errata: GLInitial Temperature and Pressure Effects on Composite Solid Propellant Burning Rates: Comparisons with Theory"

Pressure vs burning rate data are presented for an ammonium perchlorate composite solid propellant at four levels of initial temperature. For each level of initial temperature the data are fitted by least squares to the equation P/r = a + bPN. Three values of N are considered at each temperature level, N — 1, N = f and N = value for best fit to the data. These fits are then used to evaluate the relative merits of two burning rate laws, N = 1.00 corresponding to a law that includes the axisymmetric jet diffusion flame theory and N = f corresponding to the Summerfield granular diffusion flame theory. The relative variation of the parameters a and b with temperature is compared with the expectation of the Summerfield theory. It is concluded that although N = f gives a superior fit to N = 1.00, no law of the type P/r = a + bPN fits the data without systematic error and that the variation of best fit N with initial temperature casts doubt upon the physical model underlying both burning rate laws. The burning rate law suggested by Fenn, P/r = a + brPN also is tested. Its best fit is superior to that for N = 1 in the previous equation but it is inferior to the fit of that law for N = or N taken as the best fit value.

Initial temperature and pressure effects on composite solid-propellant burning rates - Comparisons with theory

Initial temperature and pressure effects on composite solid-propellant burning rates - Comparisons with theory

Aluminized composite solid-propellant burning rates in acceleration fields

The average burning rates of a parametric series of propellants were determined in acceleration fields up to 1000 g using a combustion bomb mounted on a centrifuge. The propellant strands were burned at 500, 1000, and 1500 psia with the acceleration field directed normal and into the burning surface. Acceleration caused a time-dependent increase of as much as 100% in the burning rate of relatively slow-burning aluminized propellants. The relative amount of burning-rate increase for the various propellants was strongly dependent on the amount of aluminum retained on the propellant surface during burning. The burning rates of two very fast-burning propellants were found to be essentially accelerationindependent. OLID-PROPELLANT rocket motors are currently being used in applications which subject the metallized propellant grains to acceleration fields. The propellant burning rates increase appreciably when the acceleration field is imposed normal and into the burning surface.1'2 Postfire inspections of motors containing metallized propellants have revealed the presence of metal and/or metal oxide residue in the motor cases. The propellant burning-rate increase and the retention of residue appear to be interrelated. The review and abstracting of the literature on the effects of acceleration on solid-propell ant performance are presented in Refs. 3 and 4. Although progress has been made toward an understanding of some aspects of burning-rate augmentation in acceleration fields, it was believed that additional experimental studies with well-controlled propellant parameters would yield valuable insight. A parametric series of aluminized propellants was formulated to establish the importance of some of the propellant parameters that could be controlled to minimize the effects of acceleration. The objectives of this investigation were twofold. The first objective was to obtain the quantitative effect of acceleration on the burning rate of the propellants as a function of propellant composition, acceleration level, and time. The second objective was to obtain quantitative information on the amount of aluminum and/or aluminum oxide residue retained in the inhibitor case as a function of propellant -composition, acceleration level, pressure level, and propellant burning rate.

Some Effects of Oxidizer Concentration and Particle Size on Resonance Burning of Composite Solid Propellants

Some Effects of Oxidizer Concentration and Particle Size on Resonance Burning of Composite Solid Propellants