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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Southern Hemisphere In Situ Observations of OH, HO2, CIO and BrO from the ER-2 Aircraft for the 1994 ASHOE Mission

A summary of the first order scientific conclusions that emerged from the research done under this grant are as follows: (1) For the first time, the concentration of the key hydrogen and halogen radicals OH, H02, ClO and BrO were determined on a global scale extending from the arctic circle to the antarctic circle, over the altitude domain of the ER-2. That domain extends from 15-20 km altitude, covering a critical part of the lower stratosphere; (2) Simultaneous, in situ measurements of the concentrations of OH, H02, ClO, BrO, NO and NO2 demonstrate the predominance of odd-hydrogen and halogen free radical catalysis in determining the rate of removal of ozone in the lower stratosphere over the complete ASHOE mission. This extends to the global scale the "first look" data obtained during the NASA Stratospheric Photochemistry and Dynamics Experiment (SPADE), executed out of Ames Research Center in June 1993. This represents a major rearrangement of our understanding with respect to the hierarchy of dominant catalytic cycles controlling ozone loss in the lower stratosphere. For the past twenty years, it has been assumed that nitrogen radicals dominate the destruction rate of ozone in the lower stratosphere; (3) Throughout the altitude and latitude range covered by ASHOE, it was determined that a single catalytic cycle, HO2 + O3 yields OH + 2O2, accounted for one half of the total O3 removal in this region of the atmosphere. Halogen radical catalytic cycles were found to account for one third of the ozone loss, and nitrogen radicals were found to account for 20% of the loss; (4) Simultaneous observations of the full complement of radicals, tracers, ozone, and water vapor during ASHOE demonstrated quantitatively the coupling that exists between the rate limiting radicals and other reactive species in the photochemical reaction network. Specifically, the concentrations of ClO and HO2 are inversely correlated with the concentration of NOx. This carries the implication that the NOx effluent from the proposed High Speed Civil Transport may be less destructive to stratospheric ozone than had previously been thought. ASHOE brought this conclusion forward for the first time on a global basis; and (5) The density of BrO was measured on a global scale during ASHOE in the lower stratosphere. It was found that bromine is responsible for 55-65% of the local rate of catalytic destruction of ozone by reactions involving bromine and chlorine. Normalizing calculated loss rates to total available inorganic bromine and chlorine explicitly demonstrates that bromine is 60-80 times more efficient than chlorine in removing ozone in the lower stratosphere. An inferred value of total inorganic bromine is in excellent agreement with measurements of their source species, organic bromine compounds in the troposphere.

Anderson, James G.↗
NASA NTRS1999

Observations of the Rotational Transitions of OH from the Orion Molecular Cold

The goal of the observations carried out under this grant was to use several transitions of OH to infer conditions within a 1-arcminute region centered on Orion-KL. OH was selected as a diagnostic because: (1) it was predicted to be sufficiently abundant to be detectable by the KAO spectrometers; (2) there exist a number of transitions in the far- infrared free from atmospheric interference at airplane altitudes; and (3) these transitions are sensitive to a range of collisional and radiative excitation conditions believed to apply toward Orion-KL These observations were carried out as a Guest Investigator in collaboration with the Townes and Houck spectrometer groups. Though not every flight series resulted in usable data -due to technical difficulties with instrumentation - sufficient data was obtained to yield a clear picture of the source of the OH emission in Orion-KL.

Melnick, Gray J.↗
NASA NTRS2000

The Reactions of Polycyclic Aromatic Hydrocarbons with OH

The OH radical adds to naphthalene and naphthalene cation without a barrier. For the neutrals, the most favorable path for this intermediate is the loss of the OH, and the next most favorable option is the loss of an H atom to form the alcohol. For the cation, the most favorable path appears to be a hydrogen migration followed by the loss of a hydrogen to form the alcohol. The OH at carbon atom 1 is energetically most favorable for both the initial complex and final product. This is true for both the neutrals and cations.

Ricca, Alessandra↗
NASA NTRS2005

SABER Observations of the OH Meinel Airglow Variability Near the Mesopause

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, one of four on board the TIMED satellite, observes the OH Meinel emission at 2.0 m that peaks near the mesopause. The emission results from reactions between members of the oxygen and hydrogen chemical families that can be significantly affected by mesopause dynamics. In this study we compare SABER measurements of OH Meinel emission rates and temperatures with predictions from a 3-dimensional chemical dynamical model. In general, the model is capable of reproducing both the observed diurnal and seasonal OH Meinel emission variability. The results indicate that the diurnal tide has a large effect on the overall magnitude and temporal variation of the emission in low latitudes. This tidal variability is so dominant that the seasonal cycle in the nighttime emission depends very strongly on the local time of the analysis. At higher latitudes, the emission has an annual cycle that is due mainly to transport of oxygen by the seasonally reversing mean circulation.

Marsh, Daniel R.↗
NASA NTRS2017

High-Spatial-Resolution OH PLIF Visualization in a Cavity-Stabilized Ethylene-Air Turbulent Flame

High-spatial-resolution OH planar laser-induced fluorescence was measured for a premixed ethylene-air turbulent flame in an electrically-heated Mach 2 continuous-flow facility (University of Virginia Supersonic Combustion Facility, Configuration E.) The facility comprised a Mach 2 nozzle, an isolator with flush-wall fuel injectors, a combustor with optical access, and an extender. The flame was anchored at a cavity flameholder with a backward-facing step of height 9 mm. The temperature-insensitive Q1(8) transition of OH was excited using laser light of wavelength 283.55 nm. A spatial filter was used to create a laser sheet approximately 25 microns thick based on full-width at half maximum (FWHM). Extension tubes increased the magnification of an intensified camera system, achieving in-plane resolution of 40 microns based on a 50% modulation transfer function (MTF). The facility was tested with total temperature 1200 K, total pressure 300 kPa, local fuel/air equivalence ratios of approximately 0.4, and local Mach number of approximately 0.73 in the combustor. A test case with reduced total temperature and another with reduced equivalence ratio were also tested. PLIF images were acquired along a streamwise plane bisecting the cavity flameholder, from the backward facing step to 120 mm downstream of the step. The smallest observed features in the flow had width of approximately 110 microns. Flame surface density was calculated for OH PLIF images.

Geipel, Clayton M.↗
NASA NTRSDate not supplied

Modeling and Observations of OH UV-emissions in the Lunar Exosphere

The discovery of water on the Moon has led to several questions about lunar water’s origin, evolution, and total amount. One of the technique used to better understand the origin of the water, notably by the NASA LADEE/UVS instrument, is the observation of OH fluorescence. However, to better interpret the data, it is important to understand the processes leading to that emission. We present an application of the Aeroplanets model to the simulation of the OH emissions from the solar fluorescence and the dissociation of H2O from photon and electron impact in function of the solar activity. We applied the model to several cases of Lunar exosphere affected or not by meteor impacts that are known to release water in the exosphere.We show how we can retrieve the amount of OH and H2O on the line of sight of the different instruments and how the solar activity can affect that retrieval.

Guillaume Gronoff↗
NASA NTRSDate not supplied

Airborne observations in support of a satellite observation-based OH product

This presentation outlines work to date analyzing airborne observations to improve a satellite observation-based hydroxyl radical (OH) column product by interrogating model chemistry processes. Anderson et al., 2023, established a machine learning method to combine satellite observations of O3, CO, NO2, HCHO, H2O, and aerosol optical depth, along with analyzed sea surface temperatures, for the prediction of tropospheric column OH (TCOH). Since the TCOH machine learning model was trained on output from the MERRA-2 GMI model simulation, we seek to identify if any model deficiencies may yield errors in the TCOH prediction. By evaluating F0AM box model simulations and neural networks trained to reproduce in situ OH concentrations, together with output reaction rates and interpretability metrics, respectively, we validate the Anderson et al. TCOH model and assess the largest contributors to uncertainties.

Hydroxyl, oxidizing capacity, troposphere, airborn↗
NASA NTRSDate not supplied

Time-Resolved OH-PLIF Assessment of Deflagrations Levels in a CH4-O2 Rotating Detonation Rocket Combustor

The parasitic loss incurred by deflagrative pre-burning is considered to be one of the key challenges to the effective implementation of rotating detonation engine (RDE) systems. Thus far, there have been relatively limited high fidelity, spatio-temporally resolved measurements of the pre-burning process as a function of the reactant conditions and composition within an RDE. In this work, simultaneous high-repetition-rate broadband OH* chemiluminescence and OH planar laser-induced fluorescence (PLIF) imaging are employed to investigate deflagrative burning dynamics in a fully optically accessible CH4-O2 RDE as compared to a H2-air systems under the same conditions. A custom-built optical parametric oscillator (OPO) is coupled with a high-repetition-rate burst-mode laser to generate the 284 nm source for the excitation of the Q1(9) transition of the OH radical. Significant deflagrative burning is observed throughout the chamber as a consequence of the oxygen-rich environment. Trailing wave systems that consume unburned reactants in the region immediately following the primary detonation wave are observed. The formation of a product gas recirculation zone that entrains and combusts incoming reactants is observed, and quantitative analysis is performed to gain valuable insight into deflagration characteristics. At an oxidizer mass flux of Gox ≈ 350kg/m2/s, it is found that the levels of pre-wave burning in CH4-O2 are a factor of ∼2-3 times higher than in H2-air in the region directly ahead of the detonation wave at a global equivalence ratio Φ ≈ 1.0. This study highlights the key roles of ignition delay and turbulent mixing of the combustion product and reactant fields on the levels of pre-burning and establishes a methodology for further investigation, such as for the effects of various RDE inlet configurations.

Propulsion↗
NASA NTRS1972

Spectrocopic measurements of water vapor plasmas at high resolution: The optical transition probabilities for OH (A 2 Sigma - X 2 Pi)

Emission and absorption spectra of water vapor plasmas generated in a wall-stabilized arc at atmospheric pressure and 4 current, and at 0.03 atm and 15 to 50 A, were measured at high spatial and spectral resolution. The gas temperature was determined from the shape of Doppler-broadened rotational lines of OH. The observed nonequilibrium population distributions over the energy levels of atoms are interpreted in terms of a theoretical state model for diffusion-controlled arc plasmas. Excellent correlation is achieved between measured and predicted occupation of hydrogen energy levels. It is shown that the population distribution over the nonpredissociating rotational-vibrational levels of the A 2 Sigma state of OH is close to an equilibrium distribution at the gas temperature, although the total density of this state is much higher than its equilibrium density. The reduced intensities of the rotational lines originating in these levels yielded Boltzmann plots that were strictly linear.

Klein, L.↗
NASA NTRS1971

Formation of OH through inverse predissociation.

The formation of OH by inverse predissociation from continuum levels to the v = 1, k = 1 vibrational level of a repulsive molecular state originating from an asymptotic atomic ground state is discussed. A rate constant of (1 to 3) x 10 to the minus twentieth power cu cm/sec is calculated for temperatures greater than 20 K. Predicted OH densities are found to be consistent with observations in dense heavily obscured clouds, but appear to be somewhat low for H I clouds.

Julienne, P. S.↗
NASA NTRS1972

The reaction of O(1 D) with H2O and the reaction of OH with C3H6

The N2O was photolyzed at 2139 A to produce O(1 D) atoms in the presence of H2O and CO. The O(1 D) atoms react with H2O to produce HO radicals, as measured by CO2 production from the reaction of OH with CO. The relative rate constant for O(1 D) removal by H2O compared to that by N2O is 2.1. In the presence of C3H6, the OH can be removed by reaction with either CO or C3H6.

Simonaitis, R.↗
NASA NTRS1973

Structure and fluctuations in the OH airglow at 1.65 micron.

The OH airglow has been observed in the infrared with a 0.14-micron bandpass filter centered at 1.65 micron. Spatial fluctuations of 2-11% and temporal fluctuations of 1-7% are found about the mean nightly level. These fluctuations are compared with similar variations observed previously at 2.2 micron, also attributed to OH airglow. Sky maps at 1.65 micron as a function of altitude, azimuth and time are presented.

Kieffaber, L. M.↗
NASA NTRS1974

Photoelectric spectrophotometry of OQ 172 and OH 471

Absolute spectral energy distributions for the large redshift quasars OQ 172 and OH 471 are discussed along with similar data for two other quasars 4C05.34 and PHL 957. Assuming cosmological redshifts, OQ 172 and OH 471 are not as luminous as PHL 957. If these quasars are basically similar and if radiative processes dominate, the strength of Ly alpha and the behavior of the continuum at the Lyman limit strongly suggest that these objects consist of a central ionizing source surrounded by discrete clouds, filaments or a gaseous structure such as a disk. This gaseous matter does not cover the whole solid angle surrounding the source.

Oke, J. B.↗
NASA NTRS1974

Photoelectric spectrophotometry of OQ 172 and OH 471

Absolute spectral energy distributions for the large-redshift quasars OQ 172 and OH 471 are discussed along with similar data for two other quasars: 4C 05.34 and PHL 957. If the redshift are assumed to be cosmological, OQ 172 and OH 471 are not as luminous as PHL 957. If these quasars are basically similar and if radiative processes dominate, the strength of alpha and the behavior of the continuum at the Lyman limit strongly suggest that these objects consist of a central ionizing source surrounded by discrete clouds, filaments, or a gaseous structure such as a disk. This gaseous matter does not cover the whole solid angle surrounding the source.

Oke, J. B.↗