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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

The effects of complex chemistry on triple flames

The structure, ignition, and stabilization mechanisms for a methanol (CH3OH)-air triple flame are studied using Direct Numerical Simulations (DNS). The methanol (CH3OH)-air triple flame is found to burn with an asymmetric shape due to the different chemical and transport processes characterizing the mixture. The excess fuel, methanol (CH3OH), on the rich premixed flame branch is replaced by more stable fuels CO and H2, which burn at the diffusion flame. On the lean premixed flame side, a higher concentration of O2 leaks through to the diffusion flame. The general structure of the triple point features the contribution of both differential diffusion of radicals and heat. A mixture fraction-temperature phase plane description of the triple flame structure is proposed to highlight some interesting features in partially premixed combustion. The effects of differential diffusion at the triple point add to the contribution of hydrodynamic effects in the stabilization of the triple flame. Differential diffusion effects are measured using two methods: a direct computation using diffusion velocities and an indirect computation based on the difference between the normalized mixture fractions of C and H. The mixture fraction approach does not clearly identify the effects of differential diffusion, in particular at the curved triple point, because of ambiguities in the contribution of carbon and hydrogen atoms' carrying species.

Echekki, T.↗
NASA NTRS1983

Destabilization of a 650 km chemical boundary layer and its bearing on the evolution of the continental crust

A mechanism for the production of a chemical change in the mantle, from primordial silicate compositions above the 650 km discontinuity to differentiated compositions below, is reviewed. Some consequences of this are the stabilization of two layer convection with a temperature contrast between the anhydrous mantle solidus and the geotherm which, at 650 km depth, is lower than any other location in the mantle. With thermal contributions from the concentration of the heat producing elements U, Th and K below the 650 km mantle boundary layer and the higher geotherms in the past, widespread or catastrophic melting may have taken place at this location. An episodic breach of this boundary layer by extensive heat and mass transport may have periodically destroyed any simple two-layer convection geometry in the mantle. Such episodic injections of mass and energy into the upper mantle from below may have been the mechanism responsible for episodes of enhanced surface tectonism and thermal activity which appear to be recorded in apparent polar wandering paths and radiometric ages of continental rocks.

Herzberg, C. T.↗
NASA NTRS1994

Thermochemistry of dense hydrous magnesium silicates

Recent experimental investigations under mantle conditions have identified a suite of dense hydrous magnesium silicate (DHMS) phases that could be conduits to transport water to at least the 660 km discontinuity via mature, relatively cold, subducting slabs. Water released from successive dehydration of these phases during subduction could be responsible for deep focus earthquakes, mantle metasomatism and a host of other physico-chemical processes central to our understanding of the earth's deep interior. In order to construct a thermodynamic data base that can delineate and predict the stability ranges for DHMS phases, reliable thermochemical and thermophysical data are required. One of the major obstacles in calorimetric studies of phases synthesized under high pressure conditions has been limitation due to the small (less than 5 mg) sample mass. Our refinement of calorimeter techniques now allow precise determination of enthalpies of solution of less than 5 mg samples of hydrous magnesium silicates. For example, high temperature solution calorimetry of natural talc (Mg(0.99) Fe(0.01)Si4O10(OH)2), periclase (MgO) and quartz (SiO2) yield enthalpies of drop solution at 1044 K to be 592.2 (2.2), 52.01 (0.12) and 45.76 (0.4) kJ/mol respectively. The corresponding enthalpy of formation from oxides at 298 K for talc is minus 5908.2 kJ/mol agreeing within 0.1 percent to literature values.

Bose, Kunal↗
NASA NTRS2001

Chemical Aging of Environmentally Friendly Cleaners

Use of cleaners in the manufacturing area demands bottles that will hold a sufficient amount of material and allow for easy and controlled dispensing by the operator without contamination or material leaching from the bottle. The manufacturing storage conditions are also a factor that may affect cleaner chemical integrity and its potential to leave a residue on the part. A variety of squeeze bottles stored in mild (72 F, 10% R.H., dark) and harsh (105 F, 50% R.H., fluorescent lighting) conditions were evaluated to determine the effect of environment and bottle exposure on ozone depleting chemicals (ODC) cleaners chemical composition. Low Density Polyethylene (LDPE) bottles were found to be quite permeable to all the cleaners evaluated in this study indicating this bottle type should not be used in the manufacturing area. Fluorinated Polyethylene (FLPE) bottles showed little cleaner loss and change in cleaner chemical composition over time suggesting these bottles would be acceptable for use. Chemical analysis indicates limonene containing cleaners show increased non-volatile residue (NVR) content with storage under harsh conditions. Some cleaners use BHT (butylated hydroxytoluene) as stabilizer and to protect against limonene oxidation. Under harsh conditions, BHT was quickly depleted resulting in higher NVR levels.

Biegert, L. L.↗
NASA NTRS2008

Reversible Chemochromic Hydrogen Detectors

The Florida Solar Energy Center (FSEC), affiliated with the University of Central Florida, has invented a reversible pigment that changes from light beige to blue when exposed to hydrogen and back to light beige when exposed to atmospheric oxygen. In laboratory and environmental studies, the FSEC pigment in its tape form failed to change color adequately when exposed to hydrogen after one day of exposure at Kennedy Space Center's Beach Corrosion Test Facility. The reversible hydrogen-detecting tape also lost its ability to change color after being placed in an environmental chamber at 45 C for one day. The first attempts at extruding the reversible pigment into various polymers were unsuccessful because of the pigment's poor thermal stability. The goal of this project was to formulate a pigment with improved thermal and environmental stability for extrusion into a variety of appropriate polymer matrices. The formulation of the reversible hydrogen-detecting pigment was modified by removing one reagent and chemically modifying the hydrogen sensitive ingredient. This was intended to improve the hydrophobicity of the pigment and alter the thermal degradation mechanism.

Source record↗
NASA NTRS2013

Three Decades of Global Methane Sources and Sinks

Methane is an important greenhouse gas, responsible for about 20 of the warming induced by long-lived greenhouse gases since pre-industrial times. By reacting with hydroxyl radicals, methane reduces the oxidizing capacity of the atmosphere and generates ozone in the troposphere. Although most sources and sinks of methane have been identified, their relative contributions to atmospheric methane levels are highly uncertain. As such, the factors responsible for the observed stabilization of atmospheric methane levels in the early 2000s, and the renewed rise after 2006, remain unclear. Here, we construct decadal budgets for methane sources and sinks between 1980 and 2010, using a combination of atmospheric measurements and results from chemical transport models, ecosystem models, climate chemistry models and inventories of anthropogenic emissions. The resultant budgets suggest that data-driven approaches and ecosystem models overestimate total natural emissions. We build three contrasting emission scenarios which differ in fossil fuel and microbial emissions to explain the decadal variability in atmospheric methane levels detected, here and in previous studies, since 1985. Although uncertainties in emission trends do not allow definitive conclusions to be drawn, we show that the observed stabilization of methane levels between 1999 and 2006 can potentially be explained by decreasing-to-stable fossil fuel emissions, combined with stable-to-increasing microbial emissions. We show that a rise in natural wetland emissions and fossil fuel emissions probably accounts for the renewed increase in global methane levels after 2006, although the relative contribution of these two sources remains uncertain.

periodic variations↗
NASA NTRS1983

Research on aviation fuel instability

The underlying causes of fuel thermal degradation are discussed. Topics covered include: nature of fuel instability and its temperature dependence, methods of measuring the instability, chemical mechanisms involved in deposit formation, and instrumental methods for characterizing fuel deposits. Finally, some preliminary thoughts on design approaches for minimizing the effects of lowered thermal stability are briefly discussed.

Baker, C. E.↗
NASA NTRS1990

Transverse liquid fuel jet breakup, burning, and ignition

An analytical study of the breakup, burning, and ignition of liquid fuels injected transversely into a hot air stream is conducted. The non-reacting liquid jet breakup location is determined by the local sonic point criterion. Two models, one employing analysis of an elliptical jet cross-section and the other employing a two-dimensional blunt body to represent the transverse jet, were used for sonic point calculations. An auxiliary criterion based on surface tension stability is used as a separate means of determining the breakup location. For the reacting liquid jet problem, a diffusion flame supported by a one-step chemical reaction within the gaseous boundary layer is solved along the ellipse surface in subsonic cross flow. Typical flame structures and concentration profiles were calculated for various locations along the jet cross-section as a function of upstream Mach numbers. The integration reaction rate along the jet cross-section is used to predict ignition position, which is found to be situated near the stagnation point. While a multi-step reaction is needed to represent the ignition process more accurately, the present calculation does yield reasonable predictions concerning ignition along a curved surface.

Li, Hsi-Shang↗
NASA NTRS1994

Development of processing techniques for advanced thermal protection materials

The effort, which was focused on the research and development of advanced materials for use in Thermal Protection Systems (TPS), has involved chemical and physical testing of refractory ceramic tiles, fabrics, threads and fibers. This testing has included determination of the optical properties, thermal shock resistance, high temperature dimensional stability, and tolerance to environmental stresses. Materials have also been tested in the Arc Jet 2 x 9 Turbulent Duct Facility (TDF), the 1 atmosphere Radiant Heat Cycler, and the Mini-Wind Tunnel Facility (MWTF). A significant part of the effort hitherto has gone towards modifying and upgrading the test facilities so that meaningful tests can be carried out. Another important effort during this period has been the creation of a materials database. Computer systems administration and support have also been provided. These are described in greater detail below.

Selvaduray, Guna S.↗
NASA NTRS2001

Chemical Aging of Environmentally Friendly Cleaners

Use of cleaners in the manufacturing area demands bottles that will hold a sufficient amount of material and allow for easy and controlled dispensing by the operator without contamination or material leaching from the bottle. The manufacturing storage conditions are also a factor that may affect cleaner chemical integrity and its potential to leave a residue on the part. A variety of squeeze bottles stored in mild (72 F, 10 % R.H., dark) and harsh (105 F, 50 % R.H., fluorescent lighting) conditions were evaluated to determine the effect of environment and bottle exposure on the chemical composition of TCA (1,1,1 trichloroethane) replacement solvents. Low Density Polyethylene (LDPE) bottles were found to be quite permeable to all the cleaners evaluated in this study indicating this bottle type should not be used in the manufacturing area. Fluorinated Polyethylene (FLPE) bottles showed little cleaner loss and change in cleaner chemical composition over time suggesting these bottles would be acceptable for use. Chemical analysis indicates limonene-containing cleaners show increased non-volatile residue (NVR) content with storage under harsh conditions. Some cleaners use BHT (butylated hydroxytoluene) as stabilizer and to protect against limonene oxidation. Under harsh conditions, BHT was quickly depleted resulting in higher NVR levels.

Evans, K.↗
NASA NTRS2001

Preliminary Results of Field Emission Cathode Tests

Preliminary screening tests of field emission cathodes such as chemical vapor deposited (CVD) diamond, textured pyrolytic graphite, and textured copper were conducted at background pressures typical of electric thruster test facilities to assess cathode performance and stability. Very low power electric thrusters which provide tens to hundreds micronewtons of thrust may need field emission neutralizers that have a capability of tens to hundreds of microamperes. From current voltage characteristics, it was found that the CVD diamond and textured metals cathodes clearly satisfied the Fowler-Nordheim emission relation. The CVD diamond and a textured copper cathode had average current densities of 270 and 380 mA/sq cm, respectively, at the beginning-of-life. After a few hours of operation the cathode emission currents degraded by 40 to 75% at background pressures in the 10(exp -5) Pa to 10(exp -4) Pa range. The textured pyrolytic graphite had a modest current density at beginning-of-life of 84 mA/sq cm, but this cathode was the most stable of all. Extended testing of the most promising cathodes is warranted to determine if current degradation is a burn-in effect or whether it is a long-term degradation process. Preliminary experiments with ferroelectric emission cathodes, which are ceramics with spontaneous electric polarization, were conducted. Peak current densities of 30 to 120 mA/sq cm were obtained for pulse durations of about 500 ns in the 10(exp -4) Pa pressure range.

Sovey, James S.↗
NASA NTRS2005

Modeling Chemical and Isotopic Variations in Lab Formed Hydrothermal Carbonates

Chemical and mineralogical data (e.g. [1]) from Mars suggest that the history of liquid water on the planet was more sporadic in nature than long-lived. The non-equilibrium chemical and isotopic compositions of the carbonates preserved in the martian meteorite ALH84001 are direct evidence of ancient secondary minerals that have not undergone significant diagenesis or stabilization processes typical of long-lived aqueous systems on Earth. Thus secondary minerals and sediments on Mars may primarily record the characteristics of the aqueous environment in which they formed without being significantly overprinted by subsequent diagenetic processes during burial.

Niles, P. B.↗
NASA NTRS1993

Component Selection, Accelerated Testing, and Improved Modeling of AMTEC Systems for Space Power (abstract)

Alkali metal thermal to electric converter (AMTEC) designs for space power are numerous, but selection of materials for construction of long-lived AMTEC devices has been limited to electrodes, current collectors, and the solid electrolyte. AMTEC devices with lifetimes greater than 5 years require careful selection and life testing of all hot-side components. The likely selection of a remote condensed design for initial flight test and probable use with a GPHS in AMTEC powered outer planet probes requires the device to be constructed to tolerate T greater than 1150K, as well as exposure to Na(sub (g)), and Na(sub (liq)) on the high pressure side. The temperatures involved make critical high strength and chemical resistance to Na containing Na(sub 2)O. Selection among materials which can be worked should not be driven by ease of fabricability, as high temperature stability is the critical issue. These concepts drive the selection of Mo alloys for Na(sub (liq)) containment in AMTEC cells for T to 1150K operation, as they are significantly stronger than comparable NB or Ta alloys, are less soluble in Na(sub (liq)) containing dissolved Na(sub 2)O, are workable compared to W alloys (which might be used for certain components), and are ductile at the T greater than 500K of proposed AMTEC modules in space applications.

AMTEC thermal to electric conversion↗
NASA NTRS1998

On the Stability and Evolution of Isolated Molecular Clouds

We present the results of three dimensional hydrodynamic models of evolving, isolated, low mass, quiescent clouds and Bok gobules, where the interstellar radiation field plays an important role in the thermal and chemical evolution, and thermal pressure provides dominant support against gravitational collapse.

pressure chemical evolution interstellar radiation↗
NASA NTRS2012

Preparation and Evaluation of Multi-Layer Anodes of Solid Oxide Fuel Cell

The development of an energy device with abundant energy generation, ultra-high specific power density, high stability and long life is critical for enabling longer missions and for reducing mission costs. Of all different types of fuel cells, the solid oxide fuel cells (SOFC) is a promising high temperature device that can generate electricity as a byproduct of a chemical reaction in a clean way and produce high quality heat that can be used for other purposes. For aerospace applications, a power-to-weight of (is) greater than 1.0 kW/kg is required. NASA has a patented fuel cell technology under development, capable of achieving the 1.0 kW/kg figure of merit. The first step toward achieving these goals is increasing anode durability. The catalyst plays an important role in the fuel cells for power generation, stability, efficiency and long life. Not only the anode composition, but its preparation and reduction are key to achieving better cell performance. In this research, multi-layer anodes were prepared varying the chemistry of each layer to optimize the performance of the cells. Microstructure analyses were done to the new anodes before and after fuel cell operation. The cells' durability and performance were evaluated in 200 hrs life tests in hydrogen at 850 C. The chemistry of the standard nickel anode was modified successfully reducing the anode degradation from 40% to 8.4% in 1000 hrs and retaining its microstructure.

Santiago, Diana↗
NASA NTRS2002

Development of Microfabricated Chemical Gas Sensors and Sensor Arrays for Aerospace Applications

Aerospace applications require the development of chemical sensors with capabilities beyond those of commercially available sensors. In particular, factors such as minimal sensor size, weight, and power consumption are particularly important. Development areas which have potential aerospace applications include launch vehicle leak detection, engine health monitoring, fire detection, and environmental monitoring. Sensor development for these applications is based on progress in three types of technology: 1) Micromachining and microfabrication (Microsystem) technology to fabricate miniaturized sensors. 2) The use of nanocrystalline materials to develop sensors with improved stability combined with higher sensitivity. 3) The development of high temperature semiconductors, especially silicon carbide. However, due to issues of selectivity and cross-sensitivity, individual sensors are limited in the amount of information that they can provide in environments that contain multiple chemical species. Thus, sensor arrays are being developed to address detection needs in such multi-species environments. This paper discusses the needs of space applications as well as the point-contact sensor technology and sensor arrays being developed to address these needs. Sensors to measure hydrogen, hydrocarbons, hydrazine, nitrogen oxides (NO,), carbon monoxide, oxygen, and carbon dioxide are being developed as well as arrays for leak, fire, and emissions detection. Demonstrations of the technology will also be discussed. It is concluded that microfabricated sensor technology has significant potential for use in a range of aerospace applications.

Hunter, G. W.↗
NASA NTRS1982

Long-term thermal degradation and alloying constituent effects on five boron/aluminum composites

Thermal exposure effects on the properties of five boron/aluminum composite systems were experimentally investigated. The composite systems were 49 volume percent boron fibers (203 micron diameter) in aluminum-alloy matrices 1100 Al, 2024 Al, 3003 Al, 5052 Al, and 6061 Al. Specimens were thermally exposed up to 10,000 hours at 500 K and 590 K, up to 500 hours at 730 K, and up to 10,000 hours at 500 K and 590 K, up to 500 hours at 730 K, and up to 2000 thermal cycles between 200 K and 590 K. Composite longitudinal and transverse tensile strengths, longitudinal compression strength, and in-plane shear strength were determined. None of the systems was severely degraded by exposure at 590 K. The best performing system was B-2024 Al. Effects of matrix alloys on degradation mechanisms were experimentally investigated. Composite specimens and individual fibers were metallurgically analyzed with a scanning electron microscope and an electron microprobe to determine failure characteristics, chemical element distribution, and reaction layer morphology. Alloying constituents were found to be affect the composite degradation mechanisms as follows: alloys containing iron, but without manganese as a stabilizer, caused increased low-temperature degradation; alloys containing magnesium, iron, or manganese caused increased degradation; and alloys containing copper caused increased fiber strength.

Olsen, G. C.↗
NASA NTRS1982

The prebiological paleoatmosphere - Stability and composition

In the past, it was generally assumed that the early atmosphere of the earth contained appreciable quantities of methane (CH4) and ammonia (NH3). This was the type of atmosphere believed to be the most suitable environment for chemical evolution, the nonbiological formation of complex organic molecules, the precursors of living systems. Photochemical considerations suggest that a CH4-NH3 dominated early atmosphere was probably very short-lived, if it ever existed at all. Instead, an early atmosphere of carbon dioxide (CO2) and nitrogen (N2) is favored by photochemical as well as geological and geochemical considerations. Photochemical calculations also indicate that the total oxygen column density of the prebiological paleoatmosphere did not exceed 10 to the -7th of the present atmospheric level.

Levine, J. S.↗