Search NASA⌕ Search

SEARCH · Search NASA

Results for “GAS DISSOCIATION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

High-pressure CO 2 dissociation with nanosecond pulsed discharges

Herein we investigate the conversion of CO 2 into CO and O 2 with nanosecond repetitively pulsed (NRP) discharges in a high-pressure batch reactor. Stable discharges are obtained at up to 12 bar. By-products are measured with gas chromatography. The energy efficiency is determined for a range of processing times, pulse energy, and fill pressures. It is only weakly sensitive to the plasma operating parameters, i.e the extent of CO 2 conversion is almost linearly-dependent on the specific energy invested. A conversion rate as high as 14% is achieved with an energy efficiency of 23%. For long processing times, saturation in the yield and a drop in efficiency are observed, due to the increasing role of three-body recombination reactions, as described by zero-dimensional detailed kinetic modeling. The modeling reveals the presence of three-stage kinetics between NRP pulses, controlled by electron-impact CO 2 dissociation, vibrational relaxation, and neutral elementary kinetics. Transport effects are shown to be important for CO 2 conversion at high pressures. For fill pressures beyond 10 bar, CO 2 may locally transit into supercritical states. The supercritical plasma kinetics may bypass atomic oxygen pathways and directly convert CO 2 into O 2 . This work provides a detailed analysis of plasma-based high-pressure CO 2 conversion, which is of great relevance to future large-scale sustainable carbon capture, utilization, and storage.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

On the importance of phase saturation heterogeneity in the analysis of laboratory studies of hydrate dissociation

Methane hydrates (MHs) have been considered as the future source of energy because of its vast resource volume and high energy density. Energy recovery from MH-bearing sediments has attracted intensifying research activities. Fundamentally, heat transfer, fluid flow through porous media, and the kinetics of hydrate reaction are the three key processes controlling the behavior of MH dissociation and the associated fluid production. Earlier studies have suggested that heterogeneous spatial distribution of SH is inevitable in MH-bearing samples synthesized in laboratory. In this paper, we extend our study to analyze numerically the simulation results from the two realizations of the samples (homogeneous and heterogeneous) to identify differences in the fluid production and to determine if they are sufficiently different. Additionally, we conduct a sensitivity analysis and a statistical analysis on the key transport and kinetic rate parameters that could affect hydrate dissociation and fluid production in the context of a heterogeneous hydrate-bearing sample, in an effort to provide insights that could lead to improved designs for laboratory experiments and (possibly) field applications. Our results suggest that the approximation of an artificial hydrate-bearing core with heterogeneous phase saturations by an assumption of uniform phase saturation distributions results in practically similar fluid production profile except for the very early stage with maximum 20.0% deviation in the water production. From the sensitivity and statistical analysis, we determine that gas production depends strongly on the kinetic rate constant, K d 0 and the composite thermal conductivity of the hydrate-bearing sediments, λ θ ; while, water production is very sensitive to K d 0 and the absolute permeability of the sandy medium, k. Understanding the effect of phase heterogeneity and the relative importance of key parameters on the production behavior of hydrate-bearing sediments could provide basis for novel production technologies that lead to enhanced gas production and energy efficiency in the energy recovery process.

42 ENGINEERING↗
NASA NTRS2017

Development of a Molecular Tagging Velocimetry Technique for Non-Intrusive Velocity Measurements in Low-Speed Gas Flows

N2O molecular tagging velocimetry (N2O-MTV) is developed for use in very-high-temperature reactor environments. Tests were carried out to determine the optimum excitation wavelength, tracer concentration, and timing parameters for the laser system. Using NO tracers obtained from photo-dissociation of N2O, velocity profiles are successfully obtained in air, nitrogen, and helium for a large range of parameters: temperature from 295 to 781 K, pressure from 1 to 3 bars, with a velocity precision of 0.01 m/s. Furthermore, by using two read pulses at adjustable time delays, the velocity dynamic range can be increased. An unprecedented dynamic range of 5,000 has been obtained to successfully resolve the flow during a helium blowdown from 1000 m/s down to 0.2 m/s. This technique is also applied to the high-temperature test facility (HTTF) at Oregon State University (OSU) during a depressurized condition cooldown (DCC) event. Details of these measurements are presented in a companion paper. This technique shows a strong potential for fundamental understanding of gas flows in nuclear reactors and to provide benchmark experimental data to validate numerical simulations.

Andre, M. A.↗
DOE OSTI2026

Spectroscopy and dynamics of the v = 1 levels derived from the OH(D) stretching modes in the I‾∙HDO complex using CW and time-resolved, resonant two-photon infrared excitation of the cryogenically cooled ions

The vibrational energy levels of the two isotopomers adopted by the I‾∙HDO ion-molecule complex occur such that the OH(D) stretching fundamentals span its dissociation energy, thus enabling a spectroscopic investigation of the dynamics displayed by a system prepared in the vicinity of the dissociation threshold. This regime is explored using infrared photoexcitation of the mass-selected complexes cooled in a cryogenic radiofrequency (Paul) ion trap. Survey spectra are obtained at modest resolution using two-color, IR-IR photodissociation with nanosecond lasers to establish the level structure and unimolecular decay dynamics of the v = 1 and 2 levels of the bound OH(D) oscillator. The v = 1 levels are prepared by fixed frequency excitation in the trap and the absorption spectra arising from this excited state are probed by photofragmentation of the complex with a second pulsed IR laser after a variable delay time (0 to 20 ms). The transitions to levels above the dissociation threshold for I‾ + HDO formation are observed to be sharp (~5 cm -1 FWHM). At low pressure, the bound OD (v = 1) population relaxes very slowly (~3 ms), consistent with resonant fluorescence in the IR. The collisional quenching rate constants of this level by the He buffer gas were estimated to be on the order 3 x 10 -12 cm 3 /s based on a crude Stern-Volmer analysis. Here, the rotational fine structure and linewidths (≲0.01 cm -1 FWHM) arising from transitions of the non-bonded OH stretch fundamental of the OD-bound isotopomer that lies just above the dissociation energy are determined using single photon photodissociation by excitation of the 10 K ions with a single-frequency, CW IR laser in the ion trap.

Cryogenic ion infrared spectroscopy↗
DOE OSTI2019

Hydroxylation of ZnO/Cu(1 1 1) inverse catalysts under ambient water vapor and the water–gas shift reaction

The interaction of water vapor with ZnO/CuO x /Cu(1 1 1) surfaces was explored using synchrotron-based ambient pressure x-ray photoelectron spectroscopy (AP-XPS) and density-functional theory (DFT) calculations. Cu(1 1 1) does not dissociate the water molecule. Cleavage of O–H bonds was seen with AP-XPS after depositing ZnO or preparing CuO x on the copper substrate. The findings of DFT calculations show unique behavior for ZnO/CuO x /Cu(1 1 1), not seen on Cu(1 1 1), CuO x /Cu(1 1 1) or ZnO(0 0 0). The ZnO/CuO x /Cu(1 1 1) system binds water quite well and exhibits the lowest energy barrier for O–H bond cleavage. The presence of unsaturated Zn cations in the islands of ZnO led to high chemical reactivity. In order to remove the OH from ZnO/CuO x /Cu(1 1 1) and ZnO/Cu(1 1 1) surfaces, heating to elevated temperatures was necessary. At 500–600 K, a significant coverage of OH groups was still present on the surfaces and did react with CO during the water–gas shift (WGS) process. The final state of the sample depended strongly on the amount of ZnO present on the catalyst surface. For surfaces with a ZnO coverage below 0.3 ML, the adsorption of water did not change the integrity of the ZnO islands. On the other hand, for surfaces with a ZnO coverage above 0.3 ML, a ZnO→Zn x OH transformation was observed. This transformation led to a decrease in the WGS catalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Effect of surface segregation on the oxidation resistance of Cu 3 Pt ( 100 )

Alloying element segregation often occurs under a reactive environment but its interplay with the subsequent surface oxidation of the alloy remains unclear. Using synchrotron-based ambient-pressure x-ray photoelectron spectroscopy, we dynamically monitor the surface segregation in Cu 3 Pt(100) in response to temperature and oxygen gas. Vacuum annealing leads to surface segregation of Cu along with the enrichment of Pt in the subsurface region. Upon switching to the O 2 atmosphere, dissociative chemisorption of oxygen does not change the surface segregation profile from that under the vacuum annealing condition. A stepwise increase in the oxygen pressure results in the transformation pathway of Cu → Cu 2 O → CuO, in which the selective oxidation of Cu gives rise to further accumulation of Pt underneath the oxide/alloy interface that hinders the supply of Cu from the bulk to the oxide/alloy interface, thereby leading to the termination of the surface oxidation after the Cu 2 O → CuO conversion is completed. This differs from the transformation pathway of Cu → Cu 2 O → Cu 2 O/CuO for the oxidation of pure Cu and Cu-Au alloys, in which the oxidation of Cu continues and the Cu 2 O/CuO bilayer growth is constantly maintained. Furthermore, these key differences provide useful insight into alloy design for controlling the surface properties such as corrosion resistance and catalytic performance of Cu base alloys.

36 MATERIALS SCIENCE↗
NASA NTRS1974

An experimental and analytical study of slip and catalytic boundary conditions applied to spheres in low Reynolds number arc jet flows

Measurements of low-density dissociated arc-heated flows around low and high surface catalycity spheres are compared with numerical solutions to the full Navier-Stokes equations for reacting gas flow fields, taking into account slip and finite surface catalytic boundary conditions. A time-dependent finite difference solution technique developed by Li (1973, 1974) is used in the investigation and a simple transport model is employed for the flows considered. The correctness of the solution approach is demonstrated by the very good agreement obtained between experimental and computational data.

Scott, C. D.↗
DOE OSTI2021

Free Energies of Proton-Coupled Electron Transfer Reagents and Their Applications

Here, we present an update and revision to our 2010 review on the topic of proton- coupled electron transfer (PCET) reagent thermochemistry. Over the past decade, the data and thermochemical formalisms presented in that review have been of value to multiple fields. Concurrently, there have been advances in the thermochemical cycles and experimental methods used to measure these values. This Review (i) summarizes those advancements, (ii) corrects systematic errors in our prior review that shifted many of the absolute values in the tabulated data, (iii) provides updated tables of thermochemical values, and (iv) discusses new conclusions and opportunities from the assembled data and associated techniques. We advocate for updated thermochemical cycles that provide greater clarity and reduce experimental barriers to the calculation and measurement of Gibbs free energies for the conversion of X to XHn in PCET reactions. In particular, we demonstrate the utility and generality of reporting potentials of hydrogenation, E°(V vs H 2 ), in almost any solvent and how these values are connected to more widely reported bond dissociation free energies (BDFEs). The tabulated data demonstrate that E°(V vs H 2 ) and BDFEs are generally insensitive to the nature of the solvent and, in some cases, even to the phase (gas versus solution). This Review also presents introductions to several emerging fields in PCET thermochemistry to give readers windows into the diversity of research being performed. Some of the next frontiers in this rapidly growing field are coordination-induced bond weakening, PCET in novel solvent environments, and reactions at material interfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1994

The sensitivity of tropospheric chemistry to cloud interactions

Clouds, although only occupying a relatively small fraction of the troposphere volume, can have a substantial impact on the chemistry of the troposphere. In newly formed clouds, or in clouds with air rapidly flowing through, the chemistry is expected to be far more active than in aged clouds with stagnant air. Thus, frequent cycling of air through shortlived clouds, i.e. cumulus clouds, is likely to be a much more efficient media for altering the composition of the atmosphere than an extensive cloud cover i.e. frontal cloud systems. The impact of clouds is tested out in a 2-D channel model encircling the globe in a latitudinal belt from 30 to 60 deg N. The model contains a detailed gas phase chemistry. In addition physiochemical interactions between the gas and aqueous phases are included. For species as H2O2, CH2O, O3, and SO2, Henry's law equilibria are assumed, whereas HNO3 and H2SO4 are regarded as completed dissolved in the aqueous phase. Absorption of HO2 and OH is assumed to be mass-transport limited. The chemistry of the aqueous phase is characterized by rapid cycling of odd hydrogen, (H2O2, HO2, and OH). O2(-) (produced through dissociation of HO2) reacting with dissolved O3 is a major source of OH in the aqueous phase. This reaction can be a significant sink for O3 in the troposphere. In the interstitial cloud air, odd hydrogen is depleted, whereas NO(x) remains in the gas phase, thus reducing ozone production due to the reaction between NO and HO2. Our calculations give markedly lower ozone levels when cloud interactions are included. This may in part explain the overpredictions of ozone levels often experienced in models neglecting cloud chemical interactions. In the present study, the existence of clouds, cloud types, and their lifetimes are modeled as pseudo random variables. Such pseudo random sequences are in reality deterministic and may, given the same starting values, be reproduced. The effects of cloud interactions on the overall chemistry of the troposphere are discussed. In particular, tests are performed to determine the sensitivity of cloud frequencies and cloud types.

Jonson, Jan E.↗
DOE OSTI2019

Activation of Water by Pentavalent Actinide Dioxide Cations: Characteristic Curium Revealed by a Reactivity Turn after Americium

Swapping of an oxygen atom of water with that of a pentavalent actinide dioxide cation, AnO 2 + also called an “actinyl”, requires activation of an An–O bond. It was previously found that such oxo exchange in the gas phase occurs for the first two actinyls, PaO 2 + and UO 2 + , but not the next two, NpO 2 + and PuO 2 + . The An–O bond dissociation energies (BDEs) decrease from PaO 2 + to PuO 2 + , such that the observation of a parallel decrease in the An–O bond reactivity is intriguing. To elucidate oxo exchange, we here extend experimental studies to AmO 2 + , americyl(V), and CmO 2 + , curyl(V), which were produced in remarkable abundance by electrospray ionization of Am 3+ and Cm 3+ solutions. Like other AnO 2 + , americyl(V) and curyl(V) adsorb up to four H 2 O molecules to form tetrahydrates AnO 2 (H 2 O) 4 + with the actinide hexacoordinated by oxygen atoms. It was found that AmO 2 + does not oxo-exchange, whereas CmO 2 + does, establishing a “turn” to increasing the reactivity from americyl to curyl, which validates computational predictions. Because oxo exchange occurs via conversion of an actinyl(V) hydrate, AnO 2 (H 2 O) + , to an actinide(V) hydroxide, AnO(OH) 2 + , it reflects the propensity for actinyl(V) hydrolysis: PaO 2 + hydrolyzes and oxo-exchanges most easily, despite the fact that it has the highest BDE of all AnO 2 + . We note a reexamination of the computational results for actinyl(V) oxo exchange reveals distinctive properties and chemistry of curyl(V) species, particularly CmO(OH) 2 + .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Prediction challenge: First principles simulation of the ultrafast electron diffraction spectrum of cyclobutanone

Computer simulation has long been an essential partner of ultrafast experiments, allowing the assignment of microscopic mechanistic detail to low-dimensional spectroscopic data. However, the ability of theory to make a priori predictions of ultrafast experimental results is relatively untested. Herein, as a part of a community challenge, we attempt to predict the signal of an upcoming ultrafast photochemical experiment using state-of-the-art theory in the context of preexisting experimental data. Specifically, we employ ab initio Ehrenfest with collapse to a block mixed quantum–classical simulations to describe the real-time evolution of the electrons and nuclei of cyclobutanone following excitation to the 3s Rydberg state. The gas-phase ultrafast electron diffraction (GUED) signal is simulated for direct comparison to an upcoming experiment at the Stanford Linear Accelerator Laboratory. Following initial ring-opening, dissociation via two distinct channels is observed: the C3 dissociation channel, producing cyclopropane and CO, and the C2 channel, producing CH2CO and C2H4. Direct calculations of the GUED signal indicate how the ring-opened intermediate, the C2 products, and the C3 products can be discriminated in the GUED signal. We also report an a priori analysis of anticipated errors in our predictions: without knowledge of the experimental result, which features of the spectrum do we feel confident we have predicted correctly, and which might we have wrong?

Chemistry↗
DOE OSTI2024

Partially cracked ammonia mixture combustion in gas turbine combustors

Ammonia is gaining popularity for single fuel use in existing gas turbines, as it is carbonless, has higher hydrogen content per unit volume than liquid hydrogen, and facilitates easy storage and handling. However, the low flame speed of ammonia makes it prone to flame blow off and remains the chief concern for its use in power generation. Following previous studies that have shown improved combustion performance by partially cracking the fuel, in this computational study, efficacy of partially cracked ammonia as a replacement fuel for natural gas is evaluated. A high-pressure optically accessible combustor operated at ~10 bar pressure with non-vitiated heated air was used as the test platform. This combustor was equipped with a novel multifuel multi-tube micromixing injector (M3 injector). High resolution simulations of the flow fields both in the injector as well as the combustor were performed to understand the fuel mixing in the injector and in the inlet region of the combustor. These modeling results showed that the injector was highly effective for achieving mixture homogeneity at the entrance of the combustor for ammonia and natural gas injection, whereas, for hydrogen an earlier injection facilitating longer residence time would be beneficial. Also, these simulations show that while harnessing waste heat the ideal fuel dissociation fraction is between 0.4 and 0.55 for optimal operation.

Ammonia↗
NASA NTRS1974

Shock-tube study of carbon monoxide dissociation kinetics

Carbon monoxide dissociation-rate data were obtained over the temperature range 5600-12,000 K. The experiments were conducted with undiluted CO to emphasize rate constants applicable to molecular gas systems. Data were obtained as time-resolved pressure measurements on the end wall of a shock tube and, in some cases, as emission histories of the C2 Swan system (0-0 band) behind incident shock waves. Results confirm the presence of C2 as an intermediate species in CO decomposition.

Hanson, R. K.↗
NASA NTRS1981

The molecular cloud associated with NGC 7538

CO maps and preliminary H2S and H2CO data for the molecular cloud associated with NGC 7538 are used to compare the molecular distributions with those of ionized, neutral, and molecular hydrogen and dust. South of the H II regions is a ridge of high (C-13)O column density with cold, self-absorbed H I just beyond it. A dense clump within the ridge is found adjacent to the H II region in the southeast, and a lower density region of expanding gas is seen next to the H II region in the southwest. NGC 7538 is the first region which appears to show observational evidence for a molecular dissociation wave.

Dickel, H. R.↗
NASA NTRS1995

Observations and analysis of O(1D) and NH2 line profiles for the coma of comet P/Halley

A set of high-resolution Fabry-Perot measurements of the coma of comet P/Halley was acquired in the (O I) 6300 A and NH2 6298.62 A emission lines. These high-resolution measurements provide the first optical observations capable of studying directly the photochemical kinetics and dynamic outflow of the coma. The observations were analyzed by a Monte Carlo Particle Trajectory Model. The agreement of the model and observed line profiles was excellent and verified the underlying dynamics, exothermic photodissociative chemistry, and collisional thermalization in the coma. The somewhat wider intrinsic line profile width for the O(1D) emission in 1986 January compared to 1986 May, is, for example, produced by the larger outflow speeds and gas temperatures nearer perihelion in January. The January O(1D) profile, which is wider than the January NH2 profile, is indicative of the photochemical kinetics in the dissociation of the parent molecules H2O and OH in the coma. The absolute calibration of the observations in 1986 January allowed the production rates for H2O and the NH2-parent molecules to be determined. The average daily water production rates derived from the O(1D) emission data for January 16 and 17 are presented. These very large water production rates are consistent with the extrapolated (and 7.6 day time variable) water production rates determined from the analysis of lower spectral resolution observations for O(1D) and H-alpha emissions that covered the time period up to January 13. The large production rates on January 16 and 17 establish that the maximum water production rate for comet Halley accurred pre-perihelion in January. Implications drawn from comparison with 18 cm radio emission data in January suggest that the peak water production rate was even larger. The average production rate for NH3 determined from the NH2 emission data for January 17 was (1.48 +/- 0.10) x 10(exp 28) molecules/s, yielding an NH3/H2O production rate ratio of 0.55%.

Smyth, William H.↗
NASA NTRS1997

Method for Trace Oxygen Detection

Trace levels of molecular oxygen are measured by introducing a gas containing the molecular oxygen into a target zone, and impacting the molecular oxygen in the target zone with electrons at the O(-) resonant energy level for dissociative electron attachment to produce O(-) ions. Preferably, the electrons have an energy of about 4 to about 10 eV. The amount of O(-) ions produced is measured, and is correlated with the molecular oxygen content in the target zone. The technique is effective for measuring levels of oxygen below 50 ppb. and even less than 1 ppb. The amount of O(-) can be measured in a quadrupole mass analyzer. Best results are obtained when the electrons have an energy of about 6 to about 8 eV. and preferably about 6.8 eV. The method can be used for other species by selecting the appropriate electron energy level.

Man, Kim Fung↗
NASA NTRS2007

A Comparison of Major and Minor Species in Io's Exosphere

The atmosphere of the volcanically active moon Io is continuously stripped away through interactions with Jupiter's magnetic field and replenished by volcanically supplied gas. Io's exosphere, the low density region consisting of bound and escaping, non-interacting neutrals, is dominated by oxygen and sulfur atoms formed from the dissociation of SO2. The radial distributions of oxygen and sulfur emissions exhibit an asymmetry between the intensity over Io's leading and trailing hemispheres (Wolven et al. 2001). Sodium, a minor but well studied exospheric component, shows a different asymmetry: the sub-Jupiter exosphere is denser than the anti-Jupiter exosphere (Burger et al. 2001). In addition, the sodium density decreases much faster with distance than the intensities of the oxygen and sulfur emissions. We explore possible sources for these. One possibility is the dependence of the observed emissions lines on plasma flowing through the exosphere. Variations in the electrons affect the excitation rates of the transitions, while leaving the resonantly scattered sodium emission unaffected. The observations may also point to differences in the loss mechanisms from Io's atmosphere: sodium is believed to be sputtered from the atmosphere and surface by high energy ions in the magnetosphere (reviewed Johnson et al 2004; Thomas et al. 2004). It is unclear whether oxygen and sulfur are lost in the same manner, or instead by the dissociation of SO2 near or above the exobase, which would produce a significantly different energy distribution than sputtering, producing the observed differences.

Burger, M. H.↗
NASA NTRS1988

Numerical simulation of hypersonic inlet flows with equilibrium or finite rate chemistry

An efficient numerical program incorporated with comprehensive high temperature gas property models has been developed to simulate hypersonic inlet flows. The computer program employs an implicit lower-upper time marching scheme to solve the two-dimensional Navier-Stokes equations with variable thermodynamic and transport properties. Both finite-rate and local-equilibrium approaches are adopted in the chemical reaction model for dissociation and ionization of the inlet air. In the finite rate approach, eleven species equations coupled with fluid dynamic equations are solved simultaneously. In the local-equilibrium approach, instead of solving species equations, an efficient chemical equilibrium package has been developed and incorporated into the flow code to obtain chemical compositions directly. Gas properties for the reaction products species are calculated by methods of statistical mechanics and fit to a polynomial form for C(p). In the present study, since the chemical reaction time is comparable to the flow residence time, the local-equilibrium model underpredicts the temperature in the shock layer. Significant differences of predicted chemical compositions in shock layer between finite rate and local-equilibrium approaches have been observed.

Yu, Sheng-Tao↗