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NASA NTRS1982

Extended near infrared emission from visual reflection nebulae

Extended near infrared (2 to 5 microns) emission was observed from three visual reflection nebulae, NGC 7023, 2023, and 2068. The emission from each nebula consists of a smooth continuum, which can be described by a greybody with a color temperature of 1000 K, and emission features at 3.3 and 3.4 microns. The continuum emission cannot be explained by free-free emission, reflected light, or field stars, or by thermal emission from grains, with commonly accepted ratios of infrared to ultraviolet emissivities, which are in equilibrium with the stellar radiation field. A possible explanation is thermal emission from grains with extremely low ratios of infrared to ultraviolet emissivities, or from grains with a temperature determined by mechanisms other than equilibrium radiative heating. Another possibility is continuum fluorescence.

Sellgren, K.↗

NASA NTRS1983

Extended near-infrared emission from visual reflection nebulae

Sellgren, K.↗

NASA NTRS1990

A plasma radiation model for the prompt radio emission of supernova 1987 A

It is proposed that the prompt radio emission of supernova 1987a a few days after the explosion is the result of a plasma interaction between the ejecta and the presupernova circumstellar matter. The emission frequency then is determined by the electron density in the front of the ejecta, and the radio flux density mainly depends on the velocity of the ejecta and the circumstellar electron density. Free-free absorptions in the interaction region and by the circumstellar medium limit the emission on the high, respectively low, frequency side and inhibit observable emission in the first two days.

Benz, A. O.↗

NASA NTRS2011

Global Precipitation Measurement, Validation, and Applications Integrated Hydrologic Validation to Improve Physical Precipitation Retrievals for GPM

Land surface modeling and data assimilation can provide dynamic land surface state variables necessary to support physical precipitation retrieval algorithms over land. It is well-known that surface emission, particularly over the range of frequencies to be included in the Global Precipitation Measurement Mission (GPM), is sensitive to land surface states, including soil properties, vegetation type and greenness, soil moisture, surface temperature, and snow cover, density, and grain size. In order to investigate the robustness of both the land surface model states and the microwave emissivity and forward radiative transfer models, we have undertaken a multi-site investigation as part of the NASA Precipitation Measurement Missions (PMM) Land Surface Characterization Working Group. Specifically, we will demonstrate the performance of the Land Information System (LIS; http://lis.gsfc.nasa.gov; Peters-Lidard et aI., 2007; Kumar et al., 2006) coupled to the Joint Center for Satellite Data Assimilation (JCSDA's) Community Radiative Transfer Model (CRTM; Weng, 2007; van Deist, 2009). The land surface is characterized by complex physical/chemical constituents and creates temporally and spatially heterogeneous surface properties in response to microwave radiation scattering. The uncertainties in surface microwave emission (both surface radiative temperature and emissivity) and very low polarization ratio are linked to difficulties in rainfall detection using low-frequency passive microwave sensors (e.g.,Kummerow et al. 2001). Therefore, addressing these issues is of utmost importance for the GPM mission. There are many approaches to parameterizing land surface emission and radiative transfer, some of which have been customized for snow (e.g., the Helsinki University of Technology or HUT radiative transfer model;) and soil moisture (e.g., the Land Surface Microwave Emission Model or LSMEM).

Peters-Lidar, Christa D.↗

NASA NTRS2017

Global Wetland Contribution to 2000-2012 Atmospheric Methane Growth Rate Dynamics

Increasing atmospheric methane (CH4) concentrations have contributed to approximately 20% of anthropogenic climate change. Despite the importance of CH4 as a greenhouse gas, its atmospheric growth rate and dynamics over the past two decades, which include a stabilization period (1999-2006), followed by renewed growth starting in 2007, remain poorly understood. We provide an updated estimate of CH4 emissions from wetlands, the largest natural global CH4 source, for 2000-2012 using an ensemble of biogeochemical models constrained with remote sensing surface inundation and inventory-based wetland area data. Between 2000-2012, boreal wetland CH4 emissions increased by 1.2 Tg yr(sup -1) (-0.2-3.5 Tg yr(sup -1), tropical emissions decreased by 0.9 Tg yr(sup -1) (-3.2-1.1 Tg yr(sup -1), yet globally, emissions remained unchanged at 184 +/- 22 Tg yr(sup -1). Changing air temperature was responsible for increasing high-latitude emissions whereas declines in low-latitude wetland area decreased tropical emissions; both dynamics are consistent with features of predicted centennial-scale climate change impacts on wetland CH4 emissions. Despite uncertainties in wetland area mapping, our study shows that global wetland CH4 emissions have not contributed significantly to the period of renewed atmospheric CH4 growth, and is consistent with findings from studies that indicate some combination of increasing fossil fuel and agriculture-related CH4 emissions, and a decrease in the atmospheric oxidative sink.

Poulter, Benjamin↗

NASA NTRS1971

Visible and near-ultraviolet spectra of low-pressure rare-gas microwave discharges

The spectral emission characteristics of three commercial low pressure rare gas discharge lamps wire obtained in the near ultraviolet and visible wavelength range. All three lamps show a definite continuum over the entire wavelength range from 0.185 to 0.6 micrometers. Considerable line emission is superimposed on much of the continuum for wavelengths greater than 0.35 micrometers. These sources were used to make transmittance measurements on quartz samples in the near ultraviolet wavelength range.

Campbell, J. P.↗

DOE OSTI2022

Ducted fuel injection with Low-Net-Carbon fuels as a solution for meeting future emissions regulations

Several studies have proven how ducted fuel injection (DFI) reduces soot emissions for compression-ignition engines. Nevertheless, no comprehensive study has investigated how DFI performs over a load range in combination with low-net-carbon fuels. In this study, optical-engine experiments were performed with four different fuels—conventional diesel and three low-net-carbon fuels—at low and moderate load, to measure emissions levels and performance. The 1.7-liter single-cylinder optical engine was equipped with a high-speed camera to capture natural luminosity images of the combustion event. Conventional diesel and DFI combustion were investigated at four different dilution levels (to simulate exhaust-gas recirculation effects), from 14 to 21 mol% oxygen in the intake. At a given dilution level, with commercial diesel fuel, DFI reduced soot by 82% at medium load, and 75% at low load without increasing NO x . The results further show how DFI with dilution reduces soot and NO x without compromising engine performance or other emission types, especially when combined with low-net-carbon fuels. DFI with the oxygenated low-net-carbon blend HEA67 simultaneously reduced soot and NO x by as much as 93 % and 82 %, respectively, relative to conventional diesel combustion with commercial diesel fuel. These soot and NO x reductions occurred while lifecycle CO 2 was reduced by at least 70 % when using low-net-carbon fuels instead of conventional diesel. All emissions changes were compared with future emissions regulations for different vehicle sectors to investigate how DFI can be used to facilitate achievement of the regulations. Finally, the results show how the DFI cases fall below several future emissions regulation levels, rendering less need for aftertreatment systems and giving a possible lower cost of ownership.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2022

First all-flavor search for transient neutrino emission using 3-years of IceCube DeepCore data

Since the discovery of a flux of high-energy astrophysical neutrinos, searches for their origins have focused primarily at TeV-PeV energies. Compared to sub-TeV searches, high-energy searches benefit from an increase in the neutrino cross section, improved angular resolution on the neutrino direction, and a reduced background from atmospheric neutrinos and muons. However, the focus on high energy does not preclude the existence of sub-TeV neutrino emission where IceCube retains sensitivity. Here we present the first all-flavor search from IceCube for transient emission of low-energy neutrinos, focusing on the energy region of 5.6-100 GeV using three years of data obtained with the IceCube-DeepCore detector. We find no evidence of transient neutrino emission in the data, thus leading to a constraint on the volumetric rate of astrophysical transient sources in the range of ~ 705-2301 Gpc -3 yr -1 for sources following a subphotospheric energy spectrum with a mean energy of 100 GeV and a bolometric energy of 1 052 erg.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1977

Nonthermal galactic emission below 10 MHz

The Radio Astronomy Explorer-2 (RAE-2) satellite has provided new measurements of the nonthermal galactic radio emission at frequencies below 10 MHz. Measurements of the emission spectra are presented for the center, anticenter, north polar, and south polar directions at 22 frequencies between 0.25 and 9.18 MHz. Survey maps of the spatial distribution of the observed low frequency galactic emission at 1.31, 2.20, 3.93, 4.70, 6.55, and 9.18 MHz are presented. The observations were obtained with the 229-meter traveling-wave V-antenna on this lunar orbiting spacecraft. The improved frequency coverage offers additional insights into structure of the local galactic neighborhood.

Novaco, J. C.↗

NASA NTRS2004

Adaptive Controls Method Demonstrated for the Active Suppression of Instabilities in Engine Combustors

An adaptive feedback control method was demonstrated that suppresses thermoacoustic instabilities in a liquid-fueled combustor of a type used in aircraft engines. Extensive research has been done to develop lean-burning (low fuel-to-air ratio) combustors that can reduce emissions throughout the mission cycle to reduce the environmental impact of aerospace propulsion systems. However, these lean-burning combustors are susceptible to thermoacoustic instabilities (high-frequency pressure waves), which can fatigue combustor components and even the downstream turbine blades. This can significantly decrease the safe operating lives of the combustor and turbine. Thus, suppressing the thermoacoustic combustor instabilities is an enabling technology for lean, low-emissions combustors under NASA's Propulsion and Power Program. This control methodology has been developed and tested in a partnership of the NASA Glenn Research Center, Pratt & Whitney, United Technologies Research Center, and the Georgia Institute of Technology. Initial combustor rig testing of the controls algorithm was completed during 2002. Subsequently, the test results were analyzed and improvements to the method were incorporated in 2003, which culminated in the final status of this controls algorithm. This control methodology is based on adaptive phase shifting. The combustor pressure oscillations are sensed and phase shifted, and a high-frequency fuel valve is actuated to put pressure oscillations into the combustor to cancel pressure oscillations produced by the instability.

Kopasakis, George↗

NASA NTRS2005

Innovative Adaptive Control Method Demonstrated for Active Suppression of Instabilities in Engine Combustors

This year, an improved adaptive-feedback control method was demonstrated that suppresses thermoacoustic instabilities in a liquid-fueled combustor of a type used in aircraft engines. Extensive research has been done to develop lean-burning (low fuel-to-air ratio) combustors that can reduce emissions throughout the mission cycle to reduce the environmental impact of aerospace propulsion systems. However, these lean-burning combustors are susceptible to thermoacoustic instabilities (high-frequency pressure waves), which can fatigue combustor components and even downstream turbine blades. This can significantly decrease the safe operating life of the combustor and turbine. Thus, suppressing the thermoacoustic combustor instabilities is an enabling technology for meeting the low-emission goals of the NASA Ultra-Efficient Engine Technology (UEET) Project.

Kopasakis, George↗

NASA NTRS1978

Nonthermal galactic emission below 10 megahertz

The Radio Astronomy Explorer 2 (RAE 2) lunar-orbiting satellite has provided measurements of the nonthermal galactic radio emission at frequencies below 10 MHz. Measurements of the emission spectra are presented for the center, anticenter, north polar, and south polar directions at 22 frequencies between 0.25 and 9.18 MHz. Survey maps of the spatial distribution of the observed low-frequency Galactic emission at 1.31, 2.20, 3.93, 4.70, 6.55, and 9.18 MHz are presented. The observations were obtained with the 229-m traveling-wave V antenna on this lunar-orbiting spacecraft. The improved frequency coverage offers additional insights into the structure of the local Galactic neighborhood.

Milky Way↗

NASA NTRS2004

An Off-Axis Model for GRB 031203

The low luminosity radio emission of the unusually faint GRB 031203 has been argued to support the idea of a class of intrinsically sub-energetic gamma-ray bursts (GRBs), currently comprising two members. While low energy GRBs probably exist, we show that the collective prompt and multiwavelength observations of the afterglow of GRB 031203, do not necessarily require a sub-energetic nature for that event. In fact, the data are more consistent with a typical, powerful GRB seen at an angle of about twice the opening angle of the central jet. The (redshift corrected) peak energy, E(sub p), of GRB 031203 then becomes approximately 2 MeV, similar to many other GRBs.

Ramirez-Ruiz, Enrico↗

DOE OSTI2025

Techno-economic evaluation of emission control configurations for AMP/PZ-based post-combustion CO 2 capture

Minimizing the environmental impacts of amine-based post-combustion carbon capture technologies is essential for regulatory compliance and public acceptance. Experimental campaigns at RWE's CO 2 capture pilot plant in Niederaussem using CESAR1 demonstrated that combining existing emission abatement technologies can substantially reduce the concentration of amines and degradation products in the CO 2 -depleted flue gas to below the detection limit of an infrared spectrometer. The campaign confirmed that a proprietary dry bed technology (OEASE aerozone™) or a second water wash can reduce AMP and PZ emissions to below 1 mg/Nm 3 . However, an acid or chemically active wash downstream of the water wash is necessary to reduce NH 3 emissions to very low levels (<2 mg/Nm 3 ). Combining a dry bed with an acid wash significantly reduces both the required acid solution and the resulting acid waste. The techno-economic analysis indicates that implementing emission mitigation technologies provides substantial environmental benefits for the CESAR1 process, with only a marginal increase (<1 €/tCO 2 ) in both the carbon capture cost (CCC) and CO 2 avoidance cost (CAC). The additional capital cost associated with extra column packing is offset by operational cost savings from reduced solvent losses. For stringent emission permits targeting NH 3 , a configuration combining a dry bed upstream of the water wash followed by an acid wash achieves the best balance between emission control and cost efficiency. This configuration results in a Levelized Cost of Electricity (LCOE) of 143 €/MWh, a CCC of 45.4 €/tCO 2 , and a CAC of 88.4 €/tCO 2 .

AMP↗

NASA NTRS2003

Active Control of High-Frequency Combustor Instability Demonstrated

To reduce the environmental impact of aerospace propulsion systems, extensive research is being done in the development of lean-burning (low fuel-to-air ratio) combustors that can reduce emissions throughout the mission cycle. However, these lean-burning combustors have an increased susceptibility to thermoacoustic instabilities-high-pressure oscillations much like sound waves that can cause severe high-frequency vibrations in the combustor. These pressure waves can fatigue the combustor components and even the downstream turbine blades. This can significantly decrease the combustor and turbine safe operating life. Thus, suppression of the thermoacoustic combustor instabilities is an enabling technology for lean, low-emissions combustors. Under the Propulsion and Power Program, the NASA Glenn Research Center in partnership with Pratt & Whitney, United Technologies Research Center, and Georgia Institute of Technology is developing technologies for the active control of combustion instabilities.

DeLaat, John C.↗

DOE OSTI2020

Ducted Fuel Injection vs. Free-Spray Injection: A Study of Mixing and Entrainment Effects Using Numerical Modeling

Diesel engines are an important technology for transportation of both people and goods. However, historically they have suffered a significant downside of high soot and nitrogen oxides (NO x ) emissions. Recently, ducted fuel injection (DFI) has been demonstrated to attenuate soot formation in compression-ignition engines and combustion vessels by 50% to 100%. This allows for diesel engines to be run at low-NO x emissions that would have otherwise produced significantly more soot due to the soot/NO x tradeoff. Currently the root causes of this soot attenuation are not well understood. To be able to better optimize DFI for use across a variety of engines and conditions, it is important to understand clearly how it works. This study expands on the current understanding of DFI by using numerical modeling under nonreacting conditions to provide insights about the roles of entrainment and mixing that would have been much more challenging to obtain experimentally. We report this study found that DFI enhances charge gas entrainment upstream of the duct and blocks entrainment inside of the duct. Mixing is enhanced by the duct, which results in lower peak equivalence ratios at the exit of the duct.

42 ENGINEERING↗

NASA NTRS2005

Angular Distribution of Elastically Scattered Electrons Determined and Its Effect on Collector Performance Computed

It has been demonstrated that the suppression of secondary electron emission significantly improves the performance of electron beam collectors (ref. 1). However, a complete analysis of the effects of secondary electron emission with respect to collector performance has not been possible because of the lack of quantitative data on angular distributions of secondary electrons. Secondary electrons are emitted with energies ranging from near zero to the energy of the incident primary. For our purposes, we define elastically scattered electrons as secondary electrons within 20 percent of the incident energy. Elastically scattered electrons are of great concern because their energy allows them to follow trajectories that can carry them almost anywhere within the vacuum envelope. If these secondaries leave the collector and reenter the slow wave circuit, they can produce undesired signal distortion and oscillation.This apparatus, which was built by Krainsky (ref. 2), was used at the NASA Lewis Research Center to obtain detailed measurements of the angular distributions of elastically scattered secondaries. Data were obtained for three surfaces of significant interest to collector applications: highly polished copper, copper roughened by ion sputtering, and isotropic graphite. Lewis researchers discovered that elastically scattered electrons have a complex angular distribution that is strongly dependent on the atomic number and surface morphology of the target material, as well as the energy and angle of incidence of the primary beam. At low energies, secondary emission from polished copper in the chosen energy range is primarily directed back to the source of primary electrons (backscattering). Forward scattering increases with primary energy until, at high energies, forward scattering dominates the angular distribution. Although back-scattered secondaries dominate the distributions of the textured copper surface, the yield is substantially lower. From the standpoint of secondary emission, isotropic graphite is the most attractive material because it exhibits low yield and little back scattering.

Krainsky, Isay L.↗

DOE OSTI2020

Arp 70: an interacting galaxy with extreme outflows

ABSTRACT We analysed a Fabry–Pérot (FP) cube of the interacting pair of galaxies Arp 70, which was obtained from the CeSAM public repository of FP data. On the larger galaxy Arp 70b, we detected the spectral signature of two different outflows, one located in the centre and the other associated with a giant H ii region in the arm region. The central outflow is especially prominent, with the flux of the secondary peaks in the emission-line profiles due to the outflowing gas being similar to that of the main peak. We used an archive fibre spectrum from SDSS to confirm this detection in H α as well as in the [N ii] line and, in addition, to perform diagnostics on the nature of the ionization. The emission at the centre is consistent with a low-ionization nuclear emission-line region and a weak active galactic nucleus. Using the spatial distribution of the profiles in the FP cube, we estimated the shape of the outflow which is consistent with two cones of expanding material, one approaching and the other receding from us, and used this to estimate the physical parameters of the outflow, finding energies of order 1057 erg and masses of order 108 M⊙. On the giant H ii region, we found a very large expanding superbubble with a diameter of ∼5 kpc. The bubble has an energy of order 1054 erg and a mass of about 4 × 107 M⊙. We discuss the possible origins for both of these features and whether they could be associated with the interaction between the galaxies.

Camps-Fariña, A.↗