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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Simulations of NOx Emissions from Low Emissions Discrete Jet Injector Combustor Tests

An experimental and computational study was conducted to evaluate the performance and emissions characteristics of a candidate Lean Direct Injection (LDI) combustor configuration with a mix of simplex and airblast injectors. The National Combustion Code (NCC) was used to predict the experimentally measured EINOx emissions for test conditions representing low power, medium power, and high-power engine cycle conditions. Of the six cases modeled with the NCC using a reduced-kinetics finite-rate mechanism and lagrangian spray modeling, reasonable predictions of combustor exit temperature and EINOx were obtained at two high-power cycle conditions.

Ajmani, Kumud↗
NASA NTRSDate not supplied

Nanoflare Heating of an X-Ray Bright Point

Nanoflares are thought to be one of the prime candidates that can keep the solar corona to its multimillion kelvin temperature. Individual nanoflares are difficult to detect with the present generation instruments, however their presence can be inferred by comparing the nanoflare heated simulated plasma emissions with the observed emission. Here, we present a simulation of emission from an X-ray Bright Point (XBP) that was observed by the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS), along with concurrent observations from SDO/AIA and Hinode/XRT. We use EBTEL hydrodynamic code to simulate the XBP loops. Length and magnetic field strength of these loops are derived from the potential field extrapolation of the observed photospheric magnetogram by HMI/SDO. Each loop is assumed to be heated by random nanoflares, whose magnitude and frequency are determined by the looplength and magnetic field strength. The simulated outputs are used to predict the intensity of spectrally pure map of Fe-18, Fe-17, Ne-9 ,O-8, O-9, Ne-9 etc, which are then compared with the derived intensity from MaGIXS observation. Further we have predicted the intensity map as observed by AIA and XRT and compared them with the observation. We also estimated the temperature distribution of the XBP from the simulation and found a good agreement with the derived distribution from MaGIXS observation.

coronal heating↗
NASA NTRS2013

Simulation of the Microwave Emission of Multi-layered Snowpacks Using the Dense Media Radiative Transfer Theory: the DMRT-ML Model

DMRT-ML is a physically based numerical model designed to compute the thermal microwave emission of a given snowpack. Its main application is the simulation of brightness temperatures at frequencies in the range 1-200 GHz similar to those acquired routinely by spacebased microwave radiometers. The model is based on the Dense Media Radiative Transfer (DMRT) theory for the computation of the snow scattering and extinction coefficients and on the Discrete Ordinate Method (DISORT) to numerically solve the radiative transfer equation. The snowpack is modeled as a stack of multiple horizontal snow layers and an optional underlying interface representing the soil or the bottom ice. The model handles both dry and wet snow conditions. Such a general design allows the model to account for a wide range of snow conditions. Hitherto, the model has been used to simulate the thermal emission of the deep firn on ice sheets, shallow snowpacks overlying soil in Arctic and Alpine regions, and overlying ice on the large icesheet margins and glaciers. DMRT-ML has thus been validated in three very different conditions: Antarctica, Barnes Ice Cap (Canada) and Canadian tundra. It has been recently used in conjunction with inverse methods to retrieve snow grain size from remote sensing data. The model is written in Fortran90 and available to the snow remote sensing community as an open-source software. A convenient user interface is provided in Python.

snowpacks↗
NASA NTRS1974

Measurement of gaseous emissions from a turbofan engine at simulated altitude conditions

Gaseous emission from a TFE 731-2 turbofan engine were measured over a range of fuel-air ratios from idle to full power at simulated from near sea level to 13,200 m. Carbon monoxide and unburned hydrocarbon emissions were highest at idle and lowest at high power settings; oxides of nitrogen exhibited the reverse trend. Carbon monoxide and unburned hydrocarbon levels decreased with increasing altitude. Oxides of nitrogen emissions were successfully correlated by a parametric group of combustor operating variables.

Diehl, L. A.↗
NASA NTRS1990

Simulated and observed 37 GHz emission over Africa

A model for simulating polarized 37-GHz microwave emissions from vegetated surfaces is proposed. An equation expressing the radiative transfer is solved using a two-point Gauss quadrature method. Surface temperature, reflectance, normalized difference, and polarized brightness temperatures are obtained from processed multispectral satellite data. The model simulations are evaluated against satellite data collected between January 1982 and December 1983 along a transect going from rain forest to hot desert over Africa (0 deg to 20 deg N, 11 deg E). It is found that the temporal variation of the average brightness temperature matches closely the surface temperature. The seasonal variation of the polarization difference is confined within the latitude band of 8 deg to 18 deg N, but the normalized difference continues to show seasonal variation south of 8 deg N. The relations between the polarization difference and the normal difference and between the polarization difference and the reflectance are considered to be nonlinear and almost linear, respectively.

Choudhury, B. J.↗
NASA NTRS1992

Numerical simulations of bursty radio emissions from planetary magnetospheres

One-dimensional electromagnetic particle simulations are used to investigate the characteristics of radiation from electron beams with a large temperature anisotropy, in order to identify the origin of the smooth and bursty radio emissions from Uranus and Neptune observed by the Voyager spacecraft. It is shown that these electron beams, which would typically originate from the sporadic or impulsive injections of energetic electrons, can generate electromagnetic radiation which should be able to escape into the solar wind despite the growth of the electrostatic instability. The amount of radiation with frequencies above the local x mode cutoff increases with the beam speed. It is also proposed that some of the radiation generated below the local x mode cutoff may also be able to escape the plasma and be detected remotely via mode conversion between regions where field-aligned currents produce local perturbations in the magnetic field.

Winglee, R. M.↗
NASA NTRS1996

Virtual Anodes in Ion Beam Emissions in Space: Numerical Simulations

From introduction: Many space experiments and applications involve plasma beam emissions. For instance, electron and ion beam experiments have been conducted to study beam-plasma interactions, neutralization processes, spacecraft charging and discharge, etc. This paper is concerned with the physics of ion beam emissions from spacecraft to aq low density space plasma. The emphasis is on space charge effects.

plasma↗
NASA NTRS2018

Estimating CO2 Emissions Using Real and Simulated Total Column Observations

Total column measurements of CO2 (XCO2) have been proposed as a possible way to estimate emissions from large urban regions. Using calculations from the Weather Research and Forecasting (WRF) model with a 1km emissions field, we investigate the viability of both real and proposed observing systems consisting of surface and/or column measurements for constraining emission sources of various types and sizes in the San Francisco Bay Area. We find that column observations are best suited for assessing enhancements downwind of very large emissions sources. For smaller sources (such as highways), in situ surface monitors are required to provide sufficient sensitivity. We explore methods for estimating emissions from the real and simulated observations.

Raheja, Garima↗
NASA NTRS1992

An SSM/I radiometer simulator for studies of microwave emission from soil

A ground-based simulator of the defense meterological satellite program special sensor microwave/imager (DMSP SSM/I) is described, and its integration with micrometeorological instrumentation for an investigation of microwave emission from moist and frozen soils is discussed. The simulator consists of three single polarization radiometers which are capable of both Dicke radiometer and total power radiometer modes of operation. The radiometers are designed for untended operation through a local computer and a daily telephone link to a laboratory. The functional characteristics of the radiometers are described, together with their field deployment configuration and an example of performance parameters.

Galantowicz, J. F.↗
NASA NTRS1972

Light-emission measurements of iron at simulated meteor conditions.

Ionization and spectral emission (3500-4200 A) cross-sections have been measured for FE + N2, O2 reactions between 350 and 2000 eV. Meteor luminous efficiencies from 3500 to 5400 A were calculated from these measurements. These results are thought to be accurate within plus or minus 40% for meteor velocities greater than 35 km/sec and at conditions where free molecular flow prevails. A general tendency is exhibited for a decrease in the luminous efficiency with increasing velocity. The present results compare favorably with previous meteor simulation experiments.

Boitnott, C. A.↗
NASA NTRS2006

3-D RPIC Simulations of Relativistic Jets: Particle Acceleration, Magnetic Field Generation, and Emission

Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets into ambient plasmas show that acceleration occurs in relativistic shocks. The Weibel instability created in shocks is responsible for particle acceleration, and generation and amplification of highly inhomogeneous, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection in relativistic jets. The "jitter" radiation from deflected electrons has different properties than the synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understand the complex time evolution and spectral structure in relativistic jets and gamma-ray bursts. We will present recent PIC simulations which show particle acceleration and magnetic field generation. We will also calculate associated self-consistent emission from relativistic shocks.

Nishikawa, K.-I.↗
NASA NTRS1973

Measurement of gaseous emissions from an afterburning turbojet engine at simulated altitude conditions

Gaseous emissions from a J85-GE-13 turbojet engine were measured over a range of fuel-air ratios from idle to full afterburning and simulated altitudes from near sea-level to 12,800 meters (42,000 ft). Without afterburning, carbon monoxide and unburned hydrocarbon emissions were highest at idle and lowest at takeoff; oxides of nitrogen exhibited the reverse trend. With afterburning, carbon monoxide and unburned hydrocarbon emissions were greater than for military power. Carbon monoxide emissions were altitude dependent. Oxides of nitrogen emissions were less at minimum afterburning than at military power. For power levels above minimum afterburning, the oxides of nitrogen emissions were both power level and altitude dependent.

Diehl, L. A.↗
NASA NTRS1974

Gaseous exhaust emissions from a J-58 engine at simulated supersonic flight conditions

Emissions of total oxides of nitrogen, unburned hydrocarbons, carbon monoxide, and carbon dioxide from a J-58 engine at simulated flight conditions of Mach 2.0, 2.4, and 2.8 at 19.8 km altitude are reported. For each flight condition, measurements were made for four engine power levels from maximum power without afterburning through maximum afterburning. These measurements were made 7 cm downstream of the engine primary nozzle using a single point traversing gas sample probe. Results show that emissions vary with flight speed, engine power level, and with radial position across the exhaust.

Holdeman, J. D.↗
NASA NTRS2012

A Tropospheric Emission Spectrometer HDO/H2O Retrieval Simulator for Climate Models

Retrievals of the isotopic composition of water vapor from the Aura Tropospheric Emission Spectrometer (TES) have unique value in constraining moist processes in climate models. Accurate comparison between simulated and retrieved values requires that model profiles that would be poorly retrieved are excluded, and that an instrument operator be applied to the remaining profiles. Typically, this is done by sampling model output at satellite measurement points and using the quality flags and averaging kernels from individual retrievals at specific places and times. This approach is not reliable when the model meteorological conditions influencing retrieval sensitivity are different from those observed by the instrument at short time scales, which will be the case for free-running climate simulations. In this study, we describe an alternative, categorical approach to applying the instrument operator, implemented within the NASA GISS ModelE general circulation model. Retrieval quality and averaging kernel structure are predicted empirically from model conditions, rather than obtained from collocated satellite observations. This approach can be used for arbitrary model configurations, and requires no agreement between satellite-retrieved and model meteorology at short time scales. To test this approach, nudged simUlations were conducted using both the retrieval-based and categorical operators. Cloud cover, surface temperature and free-tropospheric moisture content were the most important predictors of retrieval quality and averaging kernel structure. There was good agreement between the D fields after applying the retrieval-based and more detailed categorical operators, with increases of up to 30 over the ocean and decreases of up to 40 over land relative to the raw model fields. The categorical operator performed better over the ocean than over land, and requires further refinement for use outside of the tropics. After applying the TES operator, ModelE had D biases of 8 over ocean and 34 over land compared to TES D, which were less than the biases using raw model D fields.

Field, R. D.↗
NASA NTRS2003

Dust Emissions, Transport, and Deposition Simulated with the NASA Finite-Volume General Circulation Model

Mineral dust aerosols have radiative impacts on Earth's atmosphere, have been implicated in local and regional air quality issues, and have been identified as vectors for transporting disease pathogens and bringing mineral nutrients to terrestrial and oceanic ecosystems. We present for the first time dust simulations using online transport and meteorological analysis in the NASA Finite-Volume General Circulation Model (FVGCM). Our dust formulation follows the formulation in the offline Georgia Institute of Technology-Goddard Global Ozone Chemistry Aerosol Radiation and Transport Model (GOCART) using a topographical source for dust emissions. We compare results of the FVGCM simulations with GOCART, as well as with in situ and remotely sensed observations. Additionally, we estimate budgets of dust emission and transport into various regions.

Colarco, Peter↗