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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Jet formation in GRBs: a semi-analytic model of MHD flow in Kerr geometry with realistic plasma injection

We construct a semi-analytic model for magnetohydrodynamic (MHD) flows in Kerr geometry that incorporates energy loading via neutrino annihilation on magnetic field lines threading the horizon. We compute the structure of the double-flow established in the magnetisphere for a wide range of energy injection rates and identify the different operation regimes. At low injection rates, the outflow is powered by the spinning black hole via the Blandford-Znajek mechanism, whereas at high injection rates, it is driven by the pressure of the plasma deposited on magnetic field lines. In the intermediate regime, both processes contribute to the outflow formation. The parameter that quantifies the load is the ratio of the net power injected below the stagnation radius and the maximum power that can be extracted magnetically from the black hole.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Momentum injection by supernovae in the interstellar medium

Supernova (SN) explosions deposit prodigious energy and momentum in their environments, with the former regulating multiphase thermal structure and the latter regulating turbulence and star formation rates in the interstellar medium (ISM). However, systematic studies quantifying the impact of SNe in realistic inhomogeneous ISM conditions have been lacking. Using three-dimensional hydrodynamic simulations, we investigate the dependence of radial momentum injection on both physical conditions (considering a range of mean density n{sub 0} = 0.1–100 cm{sup −3}) and numerical parameters. Our inhomogeneous simulations adopt two-phase background states that result from thermal instability in atomic gas. Although the supernova remnant (SNR) morphology becomes highly complex for inhomogeneous backgrounds, the radial momentum injection is remarkably insensitive to environmental details. For our two-phase simulations, the final momentum produced by a single SN is given by 2.8×10{sup 5} M{sub ⊙} km s{sup −1}n{sub 0}{sup −0.17}. This is only 5% less than the momentum injection for a homogeneous environment with the same mean density, and only 30% greater than the momentum at the time of shell formation. The maximum mass in hot gas is also quite insensitive to environmental inhomogeneity. Strong magnetic fields alter the hot gas mass at very late times, but the momentum injection remains the same. Initial experiments with multiple spatially correlated SNe show a momentum per event nearly as large as single-SN cases. We also present a full numerical parameter study to assess convergence requirements. For convergence in the momentum and other quantities, we find that the numerical resolution Δ and the initial size of the SNR r{sub init} must satisfy Δ,r{sub init}<r{sub sf}/3, where the shell formation radius is given by r{sub sf}=30 pc n{sub 0}{sup −0.46} for two-phase models (or 30% smaller for a homogeneous medium).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Cosmological constraints on exotic injection of electromagnetic energy

We compute cosmic microwave background (CMB) anisotropy constraints on exotic forms of energy injection in electromagnetic (e.m.) channels over a large range of timescales. We show that these constraints are very powerful around or just after recombination, although CMB keeps some sensitivity e.g. to decaying species with lifetimes as long as 10{sup 25} s. These bounds are complementary to CMB spectral distortions and primordial nucleosynthesis ones, which dominate at earlier timescales, as we also review here. For the first time, we describe the effects of the e.m. energy injection on the CMB power spectra as a function of the injection epoch , using the lifetime of a decaying particle as proxy. We also identify a suitable on-the-spot approximation, that can be used to derive accurate constraints, and describe its differences with the most up-to-date treatment. Our results are of interest not only for early universe relics constituting (a fraction of) the dark matter, but also for other exotic injection of e.m. radiation. For illustration, we apply our formalism to: i) Primordial black holes of mass 10{sup 13.5} g ∼< M ∼< 10{sup 16.8} g, showing that the constraints are comparable to the ones obtained from gamma-ray background studies and even dominate below ∼ 10{sup 14} g. ii) To a peculiar mass-mixing range in the sterile neutrino parameter space, complementary to other astrophysical and laboratory probes. iii) Finally, we provide a first estimate of the room for improvement left for forthcoming 21 cm experiments, comparing it with the reach of proposed CMB spectral distortion (PiXiE) and CMB angular power spectrum (CORE) missions. We show that the best and most realistic opportunity to look for this signal (or to improve over current constraints) in the 21 cm probe is to focus on the Cosmic Dawn epoch, 15 ∼< z ∼< 30, where the qualitatively unambiguous signature of a spectrum in emission can be expected for models that evade all current constraints.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Simulation of DIII-D disruption with argon pellet injection and runaway electron beam

Abstract The next generation of large tokamaks, including ITER, will be equipped with a disruption mitigation system (DMS) that can be activated if a disruption is deemed to be imminent. Introducing impurities by pellet (large or shattered) or massive gas injection has been shown to be an effective mitigation mechanism on many tokamaks. The goal of the mitigation is to lessen the thermal and electromagnetic loads from the disruption without generating enough high-energy (runaway) electrons to damage the device. Variations of this mitigation process with impurity injection are presently being tested on many experiments. We have modeled one such impurity injection experiment on DIII-D using the M3D-C1 nonlinear 3D extended MHD code (Jardin et al 2012 Comput. Sci. Discovery 6 014002), The model includes an argon large pellet injection and ablation model, impurity ionization, recombination, and radiation, and runaway electron formation and subsequent evolution, including both Dreicer and avalanche sources. We obtain reasonable agreement with the experimental results for the timescale of the thermal and current quench and for the magnitude of the runaway electron plateau formed during the mitigation. This is the first 3D full MHD simulation with pellets and REs to simulate the disruption process and it also provides a partial validation of the M3D-C1 DMS model.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

X-Ray Characterization of Real Fuel Sprays for Gasoline Direct Injection

Here, the effects of fuel blend properties on spray and injector performance has been investigated in a side-mount injector for gasoline direct injection (GDI) using two certification fuel blends: Euro 5 and Euro 6. Several X-ray diagnostic techniques were conducted to characterize the injector and spray morphology. Detailed internal geometry of the GDI injector was resolved to 1.8 μm, through the use of hard X-ray tomography. The geometry characterization of this six-hole GDI, side mount injector, quantifies relevant hole and counterbore dimensions and reveals the intricate details within the flow passages, including surface roughness and micron-sized features. Internal valve motion was measured with a temporal resolution of 20 μs and a spatial resolution of 2.0 μs, for three injection pressures and several injector energizing strategies. The needle motion for both fuels exhibits similar lift profiles for common energizing commands. A combination of X-ray radiography and ultra-small-angle X-ray scattering (USAXS) was used to characterize the fuel mass distribution and the droplet sizing, respectively. Tomographic spray radiography revealed the near-nozzle distribution of fuel mass for each of the fuels and the asymmetry produced by the angled nozzles. Under evaporative conditions, the two fuels show minor differences in peak fuel mass distribution during steady injection, though both exhibit fluctuations in injection during the early, transient phase. USAXS measurements of the path-specific surface area of the spray indicated lower peak values for the more evaporative conditions in the near nozzle region.

09 BIOMASS FUELS↗
DOE OSTI2017

Injection-induced terahertz electroluminescence from silicon p–n structures

Injection-induced terahertz electroluminescence from silicon p{sup +}–n structures is observed at helium temperatures. Structures fabricated by the diffusion of boron into a phosphorus-doped n-Si substrate are studied. Relatively narrow luminescence lines are observed in the luminescence spectra against a broad smooth background. The spectral position of a number of emission lines corresponds to optical transitions between excited donor states and the ground state of phosphorus donors. The intracenter optical transitions of electrons at phosphorus donors are excited as a result of recombination processes occurring in the n-type region of the structure under the injection of nonequilibrium holes. A number of other lines in the terahertz emission spectra are associated with intracenter transitions at acceptor centers, which are also excited as a result of injection. The structureless background in the electroluminescence spectra may be due to terahertz emission upon the intraband energy relaxation of “hot” carriers having an effective temperature exceeding the lattice temperature. These “hot” carriers appear in the structure under injection conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Initial Results from Boron Powder Injection Experiments in WEST Lower Single Null L-mode Plasmas

Using a recently installed impurity powder dropper (IPD), boron powder (< 150 μm) was injected into lower single null (LSN) L-mode discharges in WEST. IPDs possibly enable real-time wall conditioning of the plasma-facing components and may help to facilitate H-mode access in the full-tungsten environment of WEST. The discharges in this experiment featured Ip = 0.5 MA, BT = 3.7 T, q95 = 4.3, tpulse = 12–30 s, ne,0 ~ 4×1019 m-2, and PLHCD ~ 4.5 MW. Estimates of the deuterium and impurity particle fluxes, derived from a combination of visible spectroscopy measurements and their corresponding S/XB coefficients, showed decreases of ~ 50% in O+, N+, and C+ populations during powder injection and a moderate reduction of these low-Z impurities (~ 50%) and W (~ 10%) in the discharges that followed powder injection. Along with the improved wall conditions, WEST discharges with B powder injection observed improved confinement, as the stored energy WMHD, neutron rate, and electron temperature Te increased significantly (10–25% for WMHD and 60–200% for the neutron rate) at constant input power. These increases in confinement scale up with the powder drop rate and are likely due to the suppression of ion temperature gradient (ITG) turbulence from changes in Zeff and/or modifications to the electron density profile.

Boronization↗
DOE OSTI2018

Correlation of nanoparticle size distribution features to spatiotemporal flame luminosity in gasoline direct injection engines

Particle size distribution measured by mobility instruments is a common diagnostic used to characterize ultrafine and nanoparticle emissions in engine exhaust; however, some features of particle size distribution data are poorly correlated to in-cylinder combustion phenomena. In this work, in-cylinder spatiotemporal flame luminosity is quantitatively correlated to features in the solid particle size distribution measured in the exhaust of a gasoline direct injection engine operating in lean and stoichiometric combustion modes. A multi-channel optical sensor was used to measure diffusion flame light intensity in different areas of the combustion chamber. Furthermore, total solid particle number and particle size distribution in the exhaust were measured using a scanning mobility particle sizer after a catalytic stripper that removed semi-volatile compounds. Results of the experiments showed that different flame phenomenon resulted in distinct particle size distribution characteristics. A large accumulation mode (particles with diameter of 50–100 nm) in the particle size distribution from stoichiometric engine operation with early injection resulted from anomalous diffusion flames like piston-top pool fires. In lean operation incorporating a secondary fuel injection, particle emissions were dominated by flame propagation through fuel-rich regions of the combustion chamber resulting in a comparatively broad particle size distribution. More generally, this work illustrates how particle size distribution data can be more accurately used to diagnose soot formation in gasoline direct injection engines.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2020

Injection Overmolding of Continuous Carbon Fiber Preforms

This project explored and developed a process to injection overmold continuous carbon fiber preforms fabricated with tailored fiber placement. Much early work was focused on the ability to infuse dry carbon fiber tow, fully wetting out the fibers, in an injection molding process. Various approaches were explored, including using commingled fiber and pre-consolidated flexible preforms. The commingled fiber was a blend of carbon fiber and polymer fiber matching the injecting polymer. This approach showed some merit but required an extremely high quality homogeneous mixing of the polymer fibers with the carbon fibers to wet out the carbon fiber tow. Therefore, the project focused on pre-consolidated preforms. The pre-consolidated preform manufacturing method was first developed using compression molded flat plates that were cut into tensile specimen for testing. Work then progressed to an injection molded simplified corner fitting bracket. It was shown that a viable manufacturing method for overmolding continuous carbon fiber preforms could be developed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ducted Fuel Injection versus Conventional Diesel Combustion: An Operating-Parameter Sensitivity Study Conducted in an Optical Engine with a Four-Orifice Fuel Injector

Ducted fuel injection (DFI) has been shown to attenuate engine-out soot emissions from diesel engines. The concept is to inject fuel through a small tube within the combustion chamber to enable lower equivalence ratios at the autoignition zone, relative to conventional diesel combustion. Previous experiments have demonstrated that DFI enables significant soot attenuation relative to conventional diesel combustion for a small set of operating conditions at relatively low engine loads. This is the first study to compare DFI to conventional diesel combustion over a wide range of operating conditions and at higher loads (up to 8.5 bar gross indicated mean effective pressure) with a four-orifice fuel injector. This study compares DFI to conventional diesel combustion through sweeps of intakeoxygen mole fraction (XO 2 ), injection duration, intake pressure, start of combustion (SOC) timing, fuel-injection pressure, and intake temperature. DFI is shown to curtail engine-out soot emissions at all tested conditions. Under certain conditions, DFI can attenuate engine-out soot by over a factor of 100. In addition to producing significantly lower engine-out soot emissions, DFI enables the engine to be operated at low-NO x conditions that are not feasible with conventional diesel combustion due to high soot emissions.

42 ENGINEERING↗
DOE OSTI2020

Combined Experimental/Numerical Study of the Soot Formation Process in a Gasoline Direct-Injection Spray in the Presence of Laser-Induced Plasma Ignition

Here, combustion issued from an eight-hole, direct-injection spray was experimentally studied in a constant-volume pre-burn combustion vessel using simultaneous high-speed diffused back-illumination extinction imaging (DBIEI) and OH* chemiluminescence. DBIEI has been employed to observe the liquid-phase of the spray and to quantitatively investigate the soot formation and oxidation taking place during combustion. The fuel-air mixture was ignited with a plasma induced by a single-shot Nd:YAG laser, permitting precise control of the ignition location in space and time. OH* chemiluminescence was used to track the high-temperature ignition and flame. The study showed that increasing the delay between the end of injection and ignition drastically reduces soot formation without necessarily compromising combustion efficiency. For long delays between the end of injection and ignition (1.9 ms) soot formation was eliminated in the main downstream charge of the fuel spray. However, poorly atomized and large droplets formed at the end of injection (dribble) eventually do form soot near the injector even when none is formed in the main charge. The quantitative soot measurements for these spray and ignition scenarios, resolved in time and space, represents a significant new achievement. Reynolds-averaged Navier-Stokes (RANS) simulations were performed to assess spray mixing and combustion. An analysis of the predicted fuel-air mixture in key regions, defined based upon experimental observations, was used to explain different flame propagation speeds and soot production tendencies when varying ignition timing. The mixture analysis indicates that soot production can be avoided if the flame propagates into regions where the equivalence ratio (Φ) is already below 2. Reactive RANS simulations have also been performed, but with a poor match against the experiment, as the flame speed and heat-release rate are largely over estimated. This modeling weakness appears related to a very high level of turbulent viscosity predicted for the high-momentum spray in the RANS simulations, which is an important consideration for modeling ignition and flame propagation in mixtures immediately created by the spray.

42 ENGINEERING↗
NASA NTRS1999

Myogenic expression of an injectable protease-resistant growth hormone-releasing hormone augments long-term growth in pigs

Ectopic expression of a new serum protease-resistant porcine growth hormone-releasing hormone, directed by an injectable muscle-specific synthetic promoter plasmid vector (pSP-HV-GHRH), elicits growth in pigs. A single 10 mg intramuscular injection of pSP-HV-GHRH DNA followed by electroporation in three-week-old piglets elevated serum GHRH levels by twofold to fourfold, enhanced growth hormone secretion, and increased serum insulin-like growth factor-I by threefold to sixfold over control pigs. After 65 days the average body weight of the pigs injected with pSP-HV-GHRH was approximately 37% greater than the placebo-injected controls and resulted in a significant reduction in serum urea concentration, indicating a decrease in amino acid catabolism. Evaluation of body composition indicated a uniform increase in mass, with no organomegaly or associated pathology.

Non-NASA Center↗
NASA NTRS1999

Continuum Modeling of the Dynamics of Externally Injection-locked Coupled Oscillator Arrays

Mutually injection-locked arrays of electronic oscillators provide a novel means of controlling the aperture phase of a phased-array antenna, thus achieving the advantages of spatial power combining while retaining the ability to steer the radiated beam. In a number of design concepts, one or more of the oscillators are injection locked to a signal from an external master-oscillator. The behavior of such a system has been analyzed by numerical solution of a system of nonlinear differential equations which, due to its complexity, yields limited insight into the relationship between the injection signals and the aperture phase. In this paper, we develop a continuum model, which results in a single partial differential equation for the aperture phase as a function of time. Solution of the equation is effected by means of the Laplace transformation and yields detailed information concerning the dynamics of the array under the influence of the external injection signals.

injection locked↗
NASA NTRS2014

Constraints on Smoke Injection Height, Source Strength, and Transports from MISR and MODIS

The AeroCom BB (Biomass Burning) Experiment AOD (Aerosol Optical Depth) motivation: We have a substantial set of satellite wildfire plume AOD snapshots and injection heights to help calibrate model/inventory performance; We are 1) adding more fire source-strength cases 2) using MISR to improve the AOD constrains and 3) adding 2008 global injection heights; We selected GFED3-daily due to good overall source strength performance, but any inventory can be tested; Joint effort to test multiple, global models, to draw robust BB injection height and emission strength conclusions. We provide satellite-based injection height and smoke plume AOD climatologies.

smoke injection height↗
NASA NTRS2017

Kepler Planet Detection Metrics: Pixel-Level Transit Injection Tests of Pipeline Detection Efficiency for Data Release 25

This document describes the results of the fourth pixel-level transit injection experiment, which was designed to measure the detection efficiency of both the Kepler pipeline (Jenkins 2002, 2010; Jenkins et al. 2017) and the Robovetter (Coughlin 2017). Previous transit injection experiments are described in Christiansen et al. (2013, 2015a,b, 2016).In order to calculate planet occurrence rates using a given Kepler planet catalogue, produced with a given version of the Kepler pipeline, we need to know the detection efficiency of that pipeline. This can be empirically determined by injecting a suite of simulated transit signals into the Kepler data, processing the data through the pipeline, and examining the distribution of successfully recovered transits. This document describes the results for the pixel-level transit injection experiment performed to accompany the final Q1-Q17 Data Release 25 (DR25) catalogue (Thompson et al. 2017)of the Kepler Objects of Interest. The catalogue was generated using the SOC pipeline version 9.3 and the DR25 Robovetter acting on the uniformly processed Q1-Q17 DR25 light curves (Thompson et al. 2016a) and assuming the Q1-Q17 DR25 Kepler stellar properties (Mathur et al. 2017).

Pixel-Level Transit Injection↗
DOE OSTI2016

Thermal-hydraulic validation tests using the SMART-ITL facility with a single train passive safety injection system for the smart design

A test program was launched using a large-scale thermal-hydraulic integral effect test facility of SMART-ITL (or FESTA) to validate the performance of the SMART passive safety system. In this paper thermal-hydraulic validation tests using the SMART-ITL facility equipped with a single train of a passive safety injection system were performed and their major results were summarized. The effect of the flow distributor, break size and different types of Core Makeup Tank (CMT) and Safety Injection Tank (SIT) on the thermal-hydraulic behavior during a Small-Break Loss of Coolant Accident (SBLOCA) scenario was investigated for the SMART passive safety system development. During the SBLOCA scenario, the water layer was well stratified thermally in the core makeup tank, and the safety injection water was injected efficiently into the reactor pressure vessel from the initial period. Eventually, the reactor coolant system was cooled down properly. From the test results, it was estimated that the SMART passive safety system has sufficient cooling capability to deal with the SBLOCA scenario of SMART. The acquired data will be used to validate the safety analysis code and its related models, to evaluate the performance of SMART PSS, and to provide the base data during the application phase of the revision of standard design approval and construction licensing. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Operator Action Time Evaluation of Emergency Water Injection Strategy for Extreme SGTR Accidents

In terms of severe accidents caused by earthquakes or tsunamis that are beyond expectation, a special safety inspection for operating plants, following the Fukushima accident, has been conducted by the government of Korea to verify that nation's nuclear power plants have been adequately designed to respond to extreme accidents. The inspection results show that Korean nuclear power plants in operation have no imminent risk for an expected maximum potential earthquake or coastal flooding based on the up-to-date investigation. However, there is a need to implement long- and short-term safety improvements in order to secure the level of safety for natural beyond-design-basis events. One of the measures to increase the mitigation capability during extreme accidents is installing the injection flow paths to provide emergency cooling water of extemal sources using fire engines to the steam generators (SGs) or reactor cooling system (RCS). An emergency cooling water system consists of a fixed pipe connected from the RCS or SGs to the outside of the containment. A standby valve is installed on the pipe. Following the occurrence of an extreme accident, movable equipment (for example, a fire truck hose) can be connected to the pipe hole at the opening of the isolation valve. The emergency cooling water injection strategy was not taken into account for the steam generator tube rupture (SGTR) accident management strategy of the OPR-1000. Therefore, it is necessary to develop some guidelines or strategies to cope with an extreme SGTR scenarios using the newly installed injection flow paths and fire engines. As long as the fission products released from the core during severe accidents are kept inside the containment, there may be several ways to reduce the radionuclide release into the environment, for example, by using plant safety features. The containment bypass sequences, however, allow the fission products to be released into the environment or directly to the auxiliary building. The SGTR accidents, which are one of the containment bypass sequences, have shown during various probabilistic safety assessments (PSAs) to be contributors to plant risk, mainly because of their potential for causing a release outside containment. This paper is intended to be an investigation of the characteristics of accident progressions and assessments for the mitigative effectiveness of the external cooling water injection strategies during extreme SGTR accidents in a typical OPR-1000 plant. Analyses were performed using a MAAP computer code version 5.03. The MAAP code is a system-level computer code capable of conducting integral analyses of potential severe accident progressions in nuclear power plants, whose main purpose is to support a level 2 PSA or severe accident management strategy developments.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Systematic Evaluation of Low-Frequency Hiss and Energetic Electron Injections

Here, the excitation of low-frequency (LF) plasmaspheric hiss, over the frequency range from 20 Hz to 100 Hz, is systematically investigated by comparing the hiss wave properties with electron injections at energies from tens of keV to several hundreds of keV. Both particle and wave data from the Van Allen Probes during the period from September 2012 to June 2016 are used in the present study. Our results demonstrate that the intensity of LF hiss has a clear day-night asymmetry, and increases with increasing geomagnetic activity, similar to the behavior of normal hiss (approximately hundred of hertz to several kilohertz). The occurrence rate of LF hiss in association with electron injections is up to 80% in the outer plasmasphere ( L > 4) on the dayside, and the strong correlation extends to lower L shells for more active times. In contrast, at lower L shells ( L < 3.5), LF hiss is seldom associated with electron injections. The LF hiss with Poynting flux directed away from the equator is dominant at higher magnetic latitudes and higher L shells, suggesting a local amplification of LF hiss in the outer plasmasphere. The averaged electron fluxes are larger at higher L shells, where significant LF hiss wave events are observed. Our study suggests the importance of electron injections and their drift trajectories toward the dayside plasmasphere in locally amplifying the LF hiss waves detected by the Van Allen Probes.

58 GEOSCIENCES↗