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Indian Head, MD, United States

Darling K.,Syracuse University | Ouellette W.,Naval Surface Warfare Center Indian Head Division | Zubieta J.,Syracuse University
Inorganica Chimica Acta | Year: 2012

The hydrothermal reactions of various Cu(II) salts with 3- and 4-pyridinetetrazole and pyrazinetetrazole were exploited in the preparation of a series of Cu(II) and Cu(I) azolate materials. The parent copper/ pyridyltetrazole compositions are observed in the two-dimensional [Cu(3-pyrtet) 2] (1), the reduced three-dimensional [Cu(4-pyrtet)] (2) and reduced two-dimensional [Cu(4-pyrtet)]·0.5DMF (3·0.5DMF) (Hpyrtet = pyridyltetrazole). The consequences of introducing coordinating anions are revealed in the structures of the one-dimensional [CuCl 2(4-Hpyrtet)]·0.5H 2O (4·0.5H 2O) and the two-dimensional [Cu 2I 2(4-Hpyrtet)] (5) and [Cu(acac)(4-pyrtet)] (7) (acac = acetylacetonate; H 2en = ethylenediammonium cation). The pyrazinetetrazolate derivative [H 2en] 0.5[CuCl 2(prztet)] (Hprztet = pyrazinetetrazole) (6) is one-dimensional, but structurally distinct from the chain observed for 4. © 2012 Elsevier B.V. All rights reserved. Source

Johansson R.H.,Pennsylvania State University | Connell Jr. T.L.,Pennsylvania State University | Risha G.A.,Pennsylvania State University | Yetter R.A.,Pennsylvania State University | Young G.,Naval Surface Warfare Center Indian Head Division
International Journal of Energetic Materials and Chemical Propulsion | Year: 2012

Pressurized counterflow burner and static-fired motor studies were conducted to explore the possibility of a reverse hybrid system, having a solid oxidizer and gaseous fuel. Theoretical performance analysis indicates such a system may yield specific impulse and density specific impulse similar to composite solid propellants. Pressurized counterflow flame studies, conducted using pressed ammonium perchlorate (AP) pellets and gaseous ethylene, show three pressure dependent combustion regimes. AP decomposition, for pressures below 1 MPa, is controlled by heat transfer from the resulting diffusion flame, which forms between the fuel and decomposition products of AP. In this low pressure regime, the AP burning rate is found to increase with flame strain rate and pressure, yielding measured values between 0.1 to 0.5 mm/s. As pressure increases, the monopropellant flame moves closer to the oxidizer surface until the pressure reaches the self-decomposition limit, at which point the monopropellant flame becomes nearly independent of the diffusion flame. Further increasing the pressure yields burning rates between 0.4 to 0.7 cm/s, which are consistent with the literature. Variation of flame strain rate under these conditions has little or no influence on the AP burning rate for the range of flow conditions tested. Similar studies conducted with methane suggest burning rates are unaffected by fuel type. Lab-scale static motor firings were conducted to examine ignition, variation of fuel flow rate and initial motor pressure, and system performance. Results indicate that successful motor operation requires initial pressures capable of boosting the system into the higher burning rate regimes. © 2012 by Begell House, Inc. Source

Young G.,Naval Surface Warfare Center Indian Head Division | Risha G.A.,Pennsylvania State University | Miller A.G.,Pennsylvania State University | Glass R.A.,Pennsylvania State University | And 2 more authors.
International Journal of Energetic Materials and Chemical Propulsion | Year: 2010

In this study the combustion behavior of solid fuels loaded with micron-sized aluminum, nanoaluminum, and aluminum hydride with loadings of 10, 20, and 40 mass % are compared directly using pure oxygen as the oxidizer. An opposed flow burner was used to screen the various fuels at various oxidizer flow rates. Regression rates were gathered over oxidizer impingement velocities ranging from approximately 40 to 160 cm/s (strain rates of 80-320 s -1). Fuels loaded with aluminum hydride were found to have regression rates comparable to or better than that of the baseline hydroxyl terminated polybutadiene (HTPB) fuel. In addition, the regression rate increased with increasing aluminum hydride content. Conversely, the regression rates of fuels loaded with micron-sized aluminum were found to decrease with increasing aluminum content. Emission spectroscopy revealed that under most conditions the aluminum in the fuels loaded with micron-sized aluminum did not ignite within the immediate vicinity of the solid fuel sample. Temperature measurements determined from thermal emission support this conclusion as well. Finally, a lab-scale hybrid rocket motor was used to compare the combustion performance of the fuels relative to each other. It was found for the same oxidizer mass flow rate, pressure and thrust were highest for alanized fuels. Data included were thrust, pressure, regression rate, and mass burning rate. © 2010 by Begell House, Inc. Source

Connell Jr. T.L.,Pennsylvania State University | Risha G.A.,Pennsylvania State University | Risha G.A.,Altoona College | Yetter R.A.,Pennsylvania State University | And 2 more authors.
49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference | Year: 2013

A composition comprised of 80% polytetrafluoroethylene and 20% boron (by weight) is considered as a potential high-density solid fuel mixture for mixed hybrid rocket propulsive applications. Constant pressure strand burner experiments were conducted over a pressure range from approximately 1.46 to 10.6 MPa (198 to 1,538 psia) under nearly constant pressure in nitrogen environment to determine the low-pressure self-deflagration limit and measure burning rates as a function of pressure in an optically accessible chamber. A burning rate correlation rb[cm/s] = 0.042(P[MPa])0.531 was determined for the given formulation. A low-pressure self deflagration limit of approximately 2.2 MPa (319 psia) was obtained. Pressurized counterflow burner experiments conducted using pure oxygen revealed formation of surface char which prevented measurement of solid regression rates below 2MPa indicating an additional resistance for heat and mass transfer. Static-fired rocket motor experiments were conducted to determine the pressure and flow dependencies of the system by variation of oxidizer flow rates and nozzle throat areas, and to evaluate propulsive performance parameters. Characteristic exhaust velocity efficiency (C*efficiency), which provides a measure of combustion efficiency, ranged from approximately 86 to 96% depending on motor operating conditions. While classical hybrids do not have a strong dependence of fuel regression rate on pressure, a pressure dependence was observed in this system below the self deflagration limit due to the pressure dependence of the decomposition and fluorination kinetics of the solid fuel mixture. Below the self-deflagration limit, the motor operated at a constant pressure, typical of a classical hybrid, while above the limit, a progressive burn was observed characteristic of a composite propellant. Systematic oxidizer dilution with nitrogen revealed a decrease in pressurization rate with decreasing oxygen content and an ignition limit was achieved for this system when the oxygen mass fraction was reduced from 0.65 to 0.6. C*efficiencies were not noticeably affected by oxidizer dilution with nitrogen over the range considered. Source

Young G.,Naval Surface Warfare Center Indian Head Division | Stoltz C.A.,Naval Surface Warfare Center Indian Head Division | Mason B.P.,Naval Surface Warfare Center Indian Head Division | Joshi V.S.,Naval Surface Warfare Center Indian Head Division | And 4 more authors.
International Journal of Energetic Materials and Chemical Propulsion | Year: 2012

An experimental study was conducted to evaluate the potential of solid fuels based on PTFE and boron mixtures for hybrid rocket motor applications. Specifically, a processing technique based on sintering was studied to determine the viability of these fuels. Sintering of the fuels provided reasonable mechanical properties to allow for exploration of these fuels without the addition of performancerobbing ingredients. Linear regression rates of sintered and unsintered fuels were collected in a diffusion flame setting with gaseous oxygen as the oxidizing component demonstrating that the sintering process had no effect. This family of fuels has shown that they will not combust at atmospheric pressure unless pure oxygen is present. However, sintered fuels with boron loadings greater than or equal to 25% by weight do self-propagate at atmospheric pressure once ignited in the presence of oxygen, whereas unsintered fuels do not self-propagate unless they have boron loadings greater than or equal to 30% by weight. At pressures up to 12 MPa, fuels containing 10% by weight boron would not self-propagate in a nitrogen atmosphere, whereas fuels containing 20% boron would self-propagate at pressures greater than about 5.7 MPa. Preliminary lab-scale rocket motor firings demonstrate the viability of a hybrid rocket based on PTFE and boron mixtures. In addition, they demonstrate that the regression rates of these fuels show dependencies on pressure and possibly oxidizer flow rate as well. Thermochemical analysis suggests that these fuels offer a significant performance benefit in terms of density impulse, while also presenting a significant technological challenge due to excessively high flame temperatures for some mixtures. © 2012 by Begell House, Inc. Source

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