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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Field Effects of Buoyancy on a Premixed Turbulent Flame Studied by Particle Image Velocimetry

Typical laboratory flames for the scientific investigation of flame/turbulence interactions are prone to buoyancy effects. Buoyancy acts on these open flame systems and provides upstream feedbacks that control the global flame properties as well as local turbulence/flame interactions. Consequently the flame structures, stabilization limits, and turbulent reaction rates are directly or indirectly coupled with buoyancy. The objective of this study is to characterize the differences between premixed turbulent flames pointing upwards (1g), pointing downwards (-1g), and in microgravity (mg). The configuration is an inverted conical flame stabilized by a small cone-shaped bluff body that we call CLEAN Flames (Cone-Stabilized Lean Flames). We use two laser diagnostics to capture the velocity and scalar fields. Particle image velocimetry (PIV) measures the mean and root mean square velocities and planar imaging by the flame fronts method outlines the flame wrinkle topology. The results were obtained under typical conditions of small domestic heating systems such as water heaters, ovens, and furnaces. Significant differences between the 1g and -1g flames point to the need for including buoyancy contributions in theoretical and numerical calculations. In Earth gravity, there is a complex coupling of buoyancy with the turbulent flow and heat release in the flame. An investigation of buoyancy-free flames in microgravity will provide the key to discern gravity contributions. Data obtained in microgravity flames will provide the benchmark for interpreting and analyzing 1g and -1g flame results.

Cheng, Robert K.↗
NASA NTRS1996

Morphology and Surface Areas of Thin Ice Films

Thin ice films formed by deposition from the vapor phase in a fast flow-tube reactor have been used to simulate polar stratospheric cloud surfaces in order to obtain laboratory data on uptake and heterogeneous reaction rates.

ice ozone depletion ice films polar stratopsheric ↗
NASA NTRS1995

Deuterium Exchange in the Systems of H2O+/H2O and H3O+/H2O

Using tandem mass spectrometry various water ion interactions were observed. These reactions consisted of a series of charge transfer, proton transfer, and isotopic exchange steps. The experimental data sets consist of variations of ion abundances over a neutral pressure range. An expected sequence of isotopic exchange reactions is given along with differential equation solutions & reaction rate data.

Spectroscopy Deuterium Proton Ion Atmospheric Scie↗
NASA NTRS1993

Advances in Studies of Electrode Kinetics and Mass Transport in AMTEC Cells (abstract)

Previous work reported from JPL has included characterization of electrode kinetics and alkali atom transport from electrodes including Mo, W, WRh(sub x), WPt(sub x)(Mn), in sodium AMTEC cells and vapor exposure cells, and Mo in potassium vapor exposure cells. These studies were generally performed in cells with small area electrodes (about 1 to 5 cm(sup 2)), and device geometry had little effect on transport. Alkali diffusion coefficients through these electrodes have been characterized, and approximate surface diffusion coefficients derived in cases of activated transport. A basic model of electrode kinetic at the alkali metal vapor/porous metal electrode/alkali beta'-alumina solid electrolyte three phase boundary has been proposed which accounts for electrochemical reaction rates with a collision frequency near the three phase boundary and tunneling from the porous electrode partially covered with adsorbed alkali metal atoms. The small electrode effect in AMTEC cells has been discussed in several papers, but quantitative investigations have described only the overall effect and the important contribution of electrolyte resistance. The quantitative characterization of transport losses in cells with large area electrodes has been limited to simulations of large area electrode effects, or characterization of transport losses from large area electrodes with significant longitudinal temperature gradients. This paper describes new investigations of electrochemical kinetics and transport, particularily with WPt(sub 3.5) electrodes, including the influence of electrode size on the mass transport loss in the AMTEC cell. These electrodes possess excellent sodium transport properties making verification of device limitations on transport much more readily attained.

electrode kinetics alkali atom transport transport↗
NASA NTRS2004

Measured and modeled HOCl profiles in the mid-latitude stratosphere : implication for ozone loss

The HOCl catalytic cycle is an efficient ozone loss mechanism in the lower mid-latitude stratosphere. We use a diurnal steady-state photochemical model to calculate profiles of HOCl for conditions encountered by a number of high-altitude balloon flights. To assess how well this model represents ozone loss by the HOCl cycle, we compare our calculations of HOCl and its precursors Cl0 and HO2 with measurements obtained by an FTIR solar absorption spectrometer (MkIV), a far-infrared emission spectrometer (FIRS-2), and a submillimetenvave limb sounder (SLS). We then evaluate these comparisons in light of a number of recent laboratory studies of the main formation mechanism of HOCl, the reaction of Cl0 + HO2. Those studies measured both the reaction rate constant and the quantum yield for a second product pathway, formation of HCl.

stratosphere↗
NASA NTRS2007

Low-Emission Hydrogen Combustors for Gas Turbines Using Lean Direct Injection

One of the key technology challenges for the use of hydrogen in gas turbine engines is the performance of the combustion system, in particular the fuel injectors. To investigate the combustion performance of gaseous hydrogen fuel injectors flame tube combustor experiments were performed. Tests were conducted to measure the nitrogen oxide (NO(x)) emissions and combustion performance at inlet conditions of 588 to 811 K, 0.4 to 1.4 MPa, and equivalence ratios up to 0.48. All the injectors were based on Lean Direct Injection (LDI) technology with multiple injection points and quick mixing. One challenge to hydrogen-based premixing combustion systems is flashback since hydrogen has a reaction rate over 7 times that of Jet-A. To reduce the risk, design mixing times were kept short and velocities high to minimize flashback. Five fuel injector designs were tested in 6.35- and 8.9-cm-diameter flame tubes with non-vitiated heated air and gaseous hydrogen. Data is presented on measurements of NO(x) emissions and combustion efficiency for the hydrogen injectors at 2.540, 7.937, and 13.652 cm from the injector face. Results show that for some configurations, NO(x) emissions are comparable to that of state of the art Jet-A LDI combustor concepts.

Marek, C. John↗
NASA NTRS2005

Low Emission Hydrogen Combustors for Gas Turbines Using Lean Direct Injection

One of the key technology challenges for the use of hydrogen in gas turbine engines is the performance of the combustion system, in particular the fuel injectors. To investigate the combustion performance of gaseous hydrogen fuel injectors flame tube combustor experiments were performed. Tests were conducted to measure the nitrogen oxide (NOx) emissions and combustion performance at inlet conditions of 600 to 1000 deg F, 60 to 200 pounds per square inch absolute (psia), and equivalence ratios up to 0.48. All the injectors were based on Lean Direct Injection (LDI) technology with multiple injection points and quick mixing. One challenge to hydrogen based premixing combustion systems is flashback since hydrogen has a reaction rate over seven times that of Jet-A. To reduce the risk, design mixing times were kept short and velocities high to minimize flashback. Five fuel injector designs were tested in 2.5 and 3.5-in. diameter flame tubes with non-vitiated heated air and gaseous hydrogen. Data is presented on measurements of NOx emissions and combustion efficiency for the hydrogen injectors at 1.0, 3.125, and 5.375 in. from the injector face. Results show that for some configurations, NOx emissions are comparable to that of state of the art Jet-A LDI combustor concepts.

Marek, C. John↗
NASA NTRS2005

Ion Temperature Control of the Io Plasma Torus

We report on observational and theoretical studies of ion temperature in the Io plasma torus. Ion temperature is a critical factor for two reasons. First, ions are a major supplier of energy to the torus electrons which power the intense EUV emissions. Second, ion temperature determines the vertical extent of plasma along field lines. Higher temperatures spread plasma out, lowers the density and slows reaction rates. The combined effects can play a controlling role in torus energetics and chemistry. An unexpected tool for the study of ion temperature is the longitudinal structure in the plasma torus which often manifests itself as periodic brightness variations. Opposite sides of the torus (especially magnetic longitudes 20 and 200 degrees) have been observed on numerous occasions to have dramatically different brightness, density, composition, ionization state, electron temperature and ion temperature. These asymmetries must ultimately be driven by different energy flows on the opposite sides, presenting an opportunity to observe key torus processes operating under different conditions. The most comprehensive dataset for the study of longitudinal variations was obtained by the Cassini UVIS instrument during its Jupiter flyby. Steffl (Ph.D. thesis, 2005) identified longitudinal variations in all the quantities listed above wit the exception of ion temperature. We extend his work by undertaking the first search for such variation in the UVIS dataset. We also report on a 'square centimeter' model of the torus which extend the traditional 'cubic centimeter' models by including the controlling effects of ion temperature more completely.

Delamere, P. A.↗
NASA NTRS2009

Fischer-Tropsch-Type Production of Organic Materials in the Solar Nebula: Studies Using Graphite Catalysts and Measuring the Trapping of Noble Gases

The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Graphite is not a particularly good FTT catalyst, especially compared to iron powder or to amorphous iron silicate. However, like other silicates that we have studied, it gets better with exposure to CO. N2 and H2 over time: e.g., after formation of a macromolecular carbonaceous layer on the surfaces of the underlying gains. While amorphous iron silicates required only 1 or 2 experimental runs to achieve steady state reaction rates, graphite only achieved steady state after 6 or more experiments. We will present results showing the catalytic action of graphite grains increasing with increasing number of experiments and will also discuss the nature of the final "graphite" grains aster completion of our experiments.

Nuth, Joseph A., III↗
NASA NTRS2009

Old Faithful Model for Radiolytic Gas-Driven Cryovolcanism at Enceladus

A new model is presented on how chemically driven cryovolcanism might contribute to episodic outgassing at the icy moon Enceladus and potentially elsewhere including Europa and Kuiper Belt Objects. Exposed water ices can become oxidized from radiolytic chemical alteration of near-surface water ice by space environment irradiation. In contact with primordially abundant reductants such as NH3, CH4, and other hydrocarbons, the product oxidants can react exothermically to produce volatile gases driving cryovolcanism via gas-piston forces on any subsurface liquid reservoirs. Radiolytic oxidants such as H2O2 and O2 can continuously accumulate deep in icy regoliths and be conveyed by rheological flows to subsurface chemical reaction zones over million-year time scales indicated by cratering ages for active regions of Enceladus and Europa. Surface blanketing with cryovolcanic plume ejecta would further accelerate regolith burial of radiolytic oxidants. Episodic heating from transient gravitational tides, radioisotope decay, impacts, or other geologic events might occasionally accelerate chemical reaction rates and ignite the exothermic release of cumulative radiolytic oxidant energy. The time history for the suggested "Old Faithful" model of radiolytic gas-driven cryovolcanism at Enceladus and elsewhere therefore consists of long periods of chemical energy accumulation punctuated by much briefer episodes of cryovolcanic activity. The most probable sequence for detection of activity in the current epoch is a long evolutionary phase of slow but continuous oxidant accumulation over billions of years followed by continuous but variable high activity over the past 10(exp 7)-10(exp 8) years. Detectable cryovolcanic activity could then later decline due to near-total oxidation of the rheologically accessible ice crust and depletion the accessible reductant abundances, as may have already occurred for Europa in the more intense radiation environment of Jupiter's magnetosphere. Astrobiological potential of Enceladus could correspondingly be higher than at Europa due to a less extreme state of oxidation and greater residual abundance of organics.

Cooper, John F.↗
NASA NTRS2010

Producing Hydrogen by Plasma Pyrolysis of Methane

Plasma pyrolysis of methane has been investigated for utility as a process for producing hydrogen. This process was conceived as a means of recovering hydrogen from methane produced as a byproduct of operation of a life-support system aboard a spacecraft. On Earth, this process, when fully developed, could be a means of producing hydrogen (for use as a fuel) from methane in natural gas. The most closely related prior competing process - catalytic pyrolysis of methane - has several disadvantages: a) The reactor used in the process is highly susceptible to fouling and deactivation of the catalyst by carbon deposits, necessitating frequent regeneration or replacement of the catalyst. b) The reactor is highly susceptible to plugging by deposition of carbon within fixed beds, with consequent channeling of flow, high pressure drops, and severe limitations on mass transfer, all contributing to reductions in reactor efficiency. c) Reaction rates are intrinsically low. d) The energy demand of the process is high.

Atwater, James↗
NASA NTRS2010

A Computer Model for Analyzing Volatile Removal Assembly

A computer model simulates reactional gas/liquid two-phase flow processes in porous media. A typical process is the oxygen/wastewater flow in the Volatile Removal Assembly (VRA) in the Closed Environment Life Support System (CELSS) installed in the International Space Station (ISS). The volatile organics in the wastewater are combusted by oxygen gas to form clean water and carbon dioxide, which is solved in the water phase. The model predicts the oxygen gas concentration profile in the reactor, which is an indicator of reactor performance. In this innovation, a mathematical model is included in the computer model for calculating the mass transfer from the gas phase to the liquid phase. The amount of mass transfer depends on several factors, including gas-phase concentration, distribution, and reaction rate. For a given reactor dimension, these factors depend on pressure and temperature in the reactor and composition and flow rate of the influent.

Guo, Boyun↗
NASA NTRS2010

Kinetic Re-Evaluation of Fuel Neutralization by AKGA

Baseline characterization testing previously identified alpha-ketoglutaric acid (AKGA) cis a potential alternative to the current standard hydrazine (HZ) family fuel neutralization techniques in use at Kennedy Space Center (KSC). Thus far, the reagent shows promise for use in hardware decontamination operations and as a drop-in replacement for the scrubber liquor currently used in KSC four tower vapor scrubbers. Implementation of AKGA could improve process safety and reduce or eliminate generation of hydrazine-Iaden waste streams. This paper focuses on evaluation of the kinetics of these decontamination reactions in solution. Pseudo first order reaction rate constants with respect to the pyridazine products (6-oxo-4,5-dihydro-1H-pyridazine-3-carboxylic acid, (PCA) and 1-methyl-6-oxo-4,5-dihydro-pyridazine-3-carboxylic acid (mPCA)) in the presence of excess AKGA were determined by monitoring product formation using a ultra-violet visible absorption spectroscopy method. The results are presented here in comparison to previous data obtained by monitoring reactant depletion by gas chromatography with nitrogen phosphorus detector (GC-NPD).

Oropeza Cristina↗
NASA NTRS2009

Data Parallel Line Relaxation (DPLR) Code User Manual: Acadia - Version 4.01.1

Data-Parallel Line Relaxation (DPLR) code is a computational fluid dynamic (CFD) solver that was developed at NASA Ames Research Center to help mission support teams generate high-value predictive solutions for hypersonic flow field problems. The DPLR Code Package is an MPI-based, parallel, full three-dimensional Navier-Stokes CFD solver with generalized models for finite-rate reaction kinetics, thermal and chemical non-equilibrium, accurate high-temperature transport coefficients, and ionized flow physics incorporated into the code. DPLR also includes a large selection of generalized realistic surface boundary conditions and links to enable loose coupling with external thermal protection system (TPS) material response and shock layer radiation codes.

Wright, Michael J.↗
NASA NTRS2010

A Powerful Toolkit for Synthetic Biology: Over 3.8 Billion Years of Evolution

The combination of evolutionary with engineering principles will enhance synthetic biology. Conversely, synthetic biology has the potential to enrich evolutionary biology by explaining why some adaptive space is empty, on Earth or elsewhere. Synthetic biology, the design and construction of artificial biological systems, substitutes bio-engineering for evolution, which is seen as an obstacle. But because evolution has produced the complexity and diversity of life, it provides a proven toolkit of genetic materials and principles available to synthetic biology. Evolution operates on the population level, with the populations composed of unique individuals that are historical entities. The source of genetic novelty includes mutation, gene regulation, sex, symbiosis, and interspecies gene transfer. At a phenotypic level, variation derives from regulatory control, replication and diversification of components, compartmentalization, sexual selection and speciation, among others. Variation is limited by physical constraints such as diffusion, and chemical constraints such as reaction rates and membrane fluidity. While some of these tools of evolution are currently in use in synthetic biology, all ought to be examined for utility. A hybrid approach of synthetic biology coupled with fine-tuning through evolution is suggested

Rothschild, Lynn J.↗
NASA NTRS2011

A Model of Reduced Kinetics for Alkane Oxidation Using Constituents and Species for N-Heptane

The reduction of elementary or skeletal oxidation kinetics to a subgroup of tractable reactions for inclusion in turbulent combustion codes has been the subject of numerous studies. The skeletal mechanism is obtained from the elementary mechanism by removing from it reactions that are considered negligible for the intent of the specific study considered. As of now, there are many chemical reduction methodologies. A methodology for deriving a reduced kinetic mechanism for alkane oxidation is described and applied to n-heptane. The model is based on partitioning the species of the skeletal kinetic mechanism into lights, defined as those having a carbon number smaller than 3, and heavies, which are the complement of the species ensemble. For modeling purposes, the heavy species are mathematically decomposed into constituents, which are similar but not identical to groups in the group additivity theory. From analysis of the LLNL (Lawrence Livermore National Laboratory) skeletal mechanism in conjunction with CHEMKIN II, it is shown that a similarity variable can be formed such that the appropriately non-dimensionalized global constituent molar density exhibits a self-similar behavior over a very wide range of equivalence ratios, initial pressures and initial temperatures that is of interest for predicting n-heptane oxidation. Furthermore, the oxygen and water molar densities are shown to display a quasi-linear behavior with respect to the similarity variable. The light species ensemble is partitioned into quasi-steady and unsteady species. The reduced model is based on concepts consistent with those of Large Eddy Simulation (LES) in which functional forms are used to replace the small scales eliminated through filtering of the governing equations; in LES, these small scales are unimportant as far as the overwhelming part of dynamic energy is concerned. Here, the scales thought unimportant for recovering the thermodynamic energy are removed. The concept is tested by using tabular information from the LLNL skeletal mechanism in conjunction with CHEMKIN II utilized as surrogate ideal functions replacing the necessary functional forms. The test reveals that the similarity concept is indeed justified and that the combustion temperature is well predicted, but that the ignition time is over-predicted, a fact traced to neglecting a detailed description of the processes leading to the heavies chemical decomposition. To palliate this deficiency, functional modeling is incorporated into this conceptual reduction in addition to the modeling the evolution of the global constituent molar density, the enthalpy evolution of the heavies, the contribution to the reaction rate of the unsteady lights from other light species and from the heavies, the molar density evolution of oxygen and water, and the mole fractions of the quasisteady light species. The model is compact in that there are only nine species-related progress variables. Results are presented showing the performance of the model for predicting the temperature and species evolution. The model reproduces the ignition time over a wide range of equivalence ratios, initial pressure, and initial temperature.

Harstad, Kenneth G.↗
NASA NTRS2011

Radiolytic Cryovolcanism Revisited

Location of Enceladus within the inner magnetosphere of Saturn makes it likely that energetic electron irradiation, ion-neutral chemistry of the emergent cryovolcanic plume gas, and resultant radiolytic modification of surface ice composition could impact long-term evolution of molecular composition in the global ice crust. Thermally-driven convection of ice in the south polar terrain would bring radiolytic oxidant products into contact with subsurface reservoirs of primordial organics on million-year time scales. The chemical reactions leading to CO2 gas production as a primary gas-piston driver of cryovolcanic activity would be exponentially elevated in the warm-ice margins of a heated fluid. The fluid temperature is typically assumed to be below 273 K but could be much higher in a gas-pressurized deep subsurface environment. The Perrier Ocean model has demonstrated how a CO2-loaded fluid could account for the observed jets, while the heat content of the fluid arising from the moon's deeper interior could support high levels of chemical reactivity in the thermal margins. Since mass loss and tidal dissipation arguments do not support continuous activity over billions of years, the activity is likely very episodic so that even low-level energy sources including irradiation-driven radiolysis of surface ices could substantially contribute to the chemical dynamics of the activity apparently now in high phase. A multi-phase thermochemical model, and supporting laboratory measurements of temperature-dependent reaction rates, are needed to investigate these potentially complex processes.

Cooper, John F.↗