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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Impact of anion-exchange membrane degradation on long-term CO 2 electrolysis to ethylene

Electrochemical CO 2 reduction (eCO2R) to ethylene offers a unique opportunity to diversify domestic supply chains for chemical manufacturing. Large-scale deployment of eCO2R to ethylene reactors is currently limited by low energy efficiencies and poor durability. Herein, we demonstrate >100 h of continuous electrolysis at an industrially relevant current density of 200 mA cm −2 in a 25 cm 2 geometric area zero-gap reactor with a full-cell voltage <3.1 V and ethylene Faradaic efficiency >30%. Incorporating expanded polytetrafluoroethylene (PTFE)-supported electrodes into zero-gap reactors allows for durable electrode catalysts that are resistant to flooding, and this enables wider ranges of operating parameters not typically accessible in CO 2 electrolysis. Finally, we identify membrane degradation, evidenced by a loss of membrane ion-exchange capacity, as the leading cause of performance loss over 144 h of electrolysis.

Energy - Conversion↗
NASA NTRS1971

A closely regulated TWT converter.

The design concept for the TWT amplifier converter for possible use in the Thermoelectric Outer Planet Spacecraft (TOPS) is presented. An unusual combination of semiconductors and magnetics was utilized to achieve very stable voltage regulation on a number of separate outputs to satisfy the requirements of a high-power TWT, and at the same time operate at an efficiency of better than 90% from a 30-V source. The circuitry consists of an output filter, an auxiliary Jensen oscillator driving a high-reactance transformer to provide current limiting to the heater, a variable time delay, a main Jensen oscillator driving the power transformer with a maximum step-up ratio of 120 to 1, and series transistorized post regulators to provide precise voltage adjustment and low output impedance. This paper discusses the design of the high-reactance transformer and the high step-up ratio transformer, as well as the high-voltage series regulators that are limited in range and operate at the top of the unregulated output voltage. Test data are presented, and details of current transients caused by charging the filter circuits, input current ripple, and output voltage ripples are considered.

Hopper, D. J.↗
NASA NTRS1990

Low noise and conductively cooled microchannel plates

Microchannel plate (MCP) dynamic range has recently been enhanced for both very low and very high input flux conditions. Improvements in MCP manufacturing technology reported earlier have led to MCPs with substantially reduced radioisotope levels, giving dramatically lower internal background-counting rates. An update is given on the Galileo low noise MCP. Also, new results in increasing the MCP linear counting range for high input flux densities are presented. By bonding the active face of a very low resistance MCP (less than 1 megaohm) to a substrate providing a conductive path for heat transport, the bias current limit (hence, MCP output count rate limit) can be increased up to two orders of magnitude. Normal pulse-counting MCP operation was observed at bias currents of several mA when a curved-channel MCP (80:1) was bonded to a ceramic multianode substrate; the MCP temperature rise above ambient was less than 40 C.

Feller, W. B.↗
NASA NTRS1992

Current collection through the transport of electrons across magnetic field lines

Numerical simulations are used to investigate the collection of electrons by a long conducting cylinder in a flowing plasma. The plasma flow simulates the relative motion between a spacecraft and the plasma. The sheath structures and the levels of electron current collections for the cases with and without an ambient magnetic field are examined. It is found that for the flow perpendicular to the magnetic field, the current is considerably enhanced depending on the relative drift velocity. In the case of a nonzero magnetic field perpendicular to the cylinder axis, the potential structure is a 2D double layer with dimensions L-perpendicular much less than L-parallel. L-perpendicular is found to be the current limiting radius given by the Parker-Murphy model (1967). For the flow along the ambient magnetic field, the electron current is found to be smaller than that for the flow perpendicular to this field. This is explained in terms of the potential structures.

Singh, N.↗
NASA NTRS2001

Feasibility of Actively Cooled Silicon Nitride Airfoil for Turbine Applications Demonstrated

Nickel-base superalloys currently limit gas turbine engine performance. Active cooling has extended the temperature range of service of nickel-base superalloys in current gas turbine engines, but the margin for further improvement appears modest. Therefore, significant advancements in materials technology are needed to raise turbine inlet temperatures above 2400 F to increase engine specific thrust and operating efficiency. Because of their low density and high-temperature strength and thermal conductivity, in situ toughened silicon nitride ceramics have received a great deal of attention for cooled structures. However, the high processing costs and low impact resistance of silicon nitride ceramics have proven to be major obstacles for widespread applications. Advanced rapid prototyping technology in combination with conventional gel casting and sintering can reduce high processing costs and may offer an affordable manufacturing approach. Researchers at the NASA Glenn Research Center, in cooperation with a local university and an aerospace company, are developing actively cooled and functionally graded ceramic structures. The objective of this program is to develop cost-effective manufacturing technology and experimental and analytical capabilities for environmentally stable, aerodynamically efficient, foreign-object-damage-resistant, in situ toughened silicon nitride turbine nozzle vanes, and to test these vanes under simulated engine conditions. Starting with computer aided design (CAD) files of an airfoil and a flat plate with internal cooling passages, the permanent and removable mold components for gel casting ceramic slips were made by stereolithography and Sanders machines, respectively. The gel-cast part was dried and sintered to final shape. Several in situ toughened silicon nitride generic airfoils with internal cooling passages have been fabricated. The uncoated and thermal barrier coated airfoils and flat plates were burner rig tested for 30 min without and with air cooling. Without cooling, the surface temperature of the flat plate reached approximately 2350 F. Starting with computer aided design (CAD) files of an airfoil and a flat plate with internal cooling passages, the permanent and removable mold components for gel casting ceramic slips were made by stereolithography and Sanders machines, respectively. The gel-cast part was dried and sintered to final shape. Several in situ toughened silicon nitride generic airfoils with internal cooling passages have been fabricated. The uncoated and thermal barrier coated airfoils and flat plates were burner rig tested for 30 min without and with air cooling. Without cooling, the surface temperature of the flat plate reached approximately 2350 F. With cooling, the surface temperature decreased to approximately 1910 F--a drop of approximately 440 F. This preliminary study demonstrates that a near-net-shape silicon nitride airfoil can be fabricated and that silicon nitride can sustain severe thermal shock and the thermal gradients induced by cooling and, thus, is a viable candidate for cooled components.

Bhatt, Ramakrishna T.↗
NASA NTRS2011

Can CO2 Turbulent Flux Be Measured by Lidar? A Preliminary Study

The vertical profiling ofCO2 turbulent fluxes in the atmospheric boundary layer (ABL) is investigated using a coherent differential absorption lidar (CDIAL) operated nearby a tall tower in Wisconsin during June 2007. A CDIAL can perform simultaneous range-resolved CO2 DIAL and velocity measurements. The lidar eddy covariance technique is presented. The aims of the study are (i) an assessment of performance and current limitation of available CDIAL for CO2 turbulent fluxes and (ii) the derivation of instrument specifications to build a future CDIAL to perform accurate range-resolved CO2 fluxes. Experimental lidar CO2 mixing ratio and vertical velocity profiles are successfully compared with in situ sensors measurements. Time and space integral scales of turbulence in the ABL are addressed that result in limitation for time averaging and range accumulation. A first attempt to infer CO2 fluxes using an eddy covariance technique with currently available 2-mm CDIAL dataset is reported.

Gilbert, Fabien↗
NASA NTRS2016

Wire Rope Failure on the Guppy Winch

On January 6, 2016 at El Paso, the Guppy winch motor was changed. After completion of the operational checks, the load bar was being reinstalled on the cargo pallet when the motor control FORWARD relay failed in the energized position. The pallet was pinned at all locations (each pin has a load capacity of 16,000 lbs.) while the winch was running. The wire rope snapped before aircraft power could be removed. After disassembly, the fractured wire rope was shipped to ES4 lab for further characterization of the wire rope portion of the failure. The system was being operated without a clear understanding of the system capability and function. The proximate cause was the failure of the K48 -Forward Winch Control Relay in the energized position, which allowed the motor to continuously run without command from the hand controller, and operation of the winch system with both controllers connected to the system. This prevented the emergency stop feature on the hand controller from functioning as designed. An electrical checkout engineering work instruction was completed and identified the failed relay and confirmed the emergency stop only paused the system when the STOP button on both connected hand controllers were depressed simultaneously. The winch system incorporates a torque limiting clutch. It is suspected that the clutch did not slip and the motor did not stall or overload the current limiter. Aircraft Engineering is looking at how to change the procedures to provide a checkout of the clutch and set to a slip torque limit appropriate to support operations.

Figert, John↗
NASA NTRS1984

Interstellar scintillation and ultra-low-frequency gravitational wave observations

High precision pulsar timing measurements have been used to set upper limits on the flux of ultralong period (T greater than 3 years) stochastic gravitational waves. The data used to produce the current limits appear to be limited by timing noise that is intrinsic to the pulsars. Recently, however, there have been very low noise timing observations of the 1.5-millisecond pulsar. This suggests that significant sensitivity improvements in searches for ultralow frequency (ULF) gravitational waves may be possible. Here, the effects of the heretofore secondary noise source of phase scintillations caused by interstellar electron density fluctuations are calculated, and the prospects for improved ULF gravitational wave measurements using pulsar timing are discussed.

Armstrong, J. W.↗
DOE OSTI2025

Phenomenology of electroweak portal dark showers: high energy direct probes and low energy complementarity

We investigate the phenomenology of a dark QCD sector interacting with the Standard Model (SM) via the electroweak (EW) portals. The portal interactions allow SM bosons, such as Z and h, or additional bosons that mix with them, to decay into dark quarks, producing dark showers. The light dark mesons are expected to be long-lived particles (LLPs), as their decays back to the SM states through the EW-portal interactions typically have macroscopic decay lengths. We focus on dark shower events initiated by various bosons at the Large Hadron Collider (LHC). The most prominent signal is the displaced decay of GeV-scale dark pions as LLPs. Current limits on dark shower signals at LHC detectors are recast from public data to provide simplified limits insensitive to UV physics details. Future limits in the high-luminosity phase and proposed auxiliary detectors are also projected. Additionally, we study the flavor-changing neutral current (FCNC) B decays into dark pions, obtaining both current and projected constraints at the LHC and other facilities. These constraints can be combined for specific models, which are illustrated in two EW-portal benchmarks: one with the heavy doublet fermion mediation and another with the Z′ mediator including a mass mixing. The collider reach shows significant potential to probe the parameter space unconstrained by EW precision tests, highlighting the necessity of dedicated LLP search strategies and facilities.

Dark Matter at Colliders↗
DOE OSTI2026

Enabling Grid-Forming Control with Fault Ride-Through in Unbalanced Distribution Networks

Distribution networks are often unbalanced, causing oscillatory responses in inverter control designed for balanced conditions. Here, to address this problem, this paper proposes a novel time-domain transformation appropriate for inverter control and enables the decomposition of three-phase unbalanced signals into constant positive and negative components. Relations useful for calculating unbalanced active and reactive power are derived from first principle, providing insight into vector products of unbalanced three-phase signals. Furthermore, a grid-forming control effective under unbalanced conditions is developed, which delivers superior performance while meeting UNIFI1 specifications for grid-forming control under unbalanced conditions. specifications applicable to category 4 inverter-based resource, like setting and regulating frequency/voltage, providing voltage support, sharing active power, injecting negative sequence current, and riding through faults. A current limiter is proposed for safe fault ride-through and integrates with the grid-forming control featuring frequency/voltage droop controllers and current and voltage control loops. The transformation of interconnected inverters is formulated and stability of the proposed control analyzed to support robust parameter selections. The effectiveness of the proposed transformation and grid-forming control is demonstrated through analytical results and real-time simulation of a IEEE 123 distribution network on the Real-Time Digital Simulator. Comparison with existing methods shows that the proposed strategy satisfies the UNIFI specifications with a much better performance.

24 - POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1986

High efficiency crystalline silicon solar cells

The factors which may limit current crystalline silicon solar cells to less than 20 percent efficiency at AM 1 are investigated together with the factors which may limit the ultimate efficiency achievable. It was found that base recombination at residual defect and impurity recombination centers was the likely cause of the 20-percent efficiency barrier. Suggestions for design changes that would cut the losses due to recombinations are presented.

Sah, C. T.↗
NASA NTRS1998

Study of Bulk and Elementary Screw Dislocation Assisted Reverse Breakdown in Low-Voltage (less than 250 V) 4H-SiC p(+)n Junction diodes: DC Properties - Part 1

Given the high density (approx. 10(exp 4)/sq cm) of elementary screw dislocations (Burgers vector = 1c with no hollow core) in commercial SiC wafers and epilayers, all appreciable current (greater than 1 A) SiC power devices will likely contain elementary screw dislocations for the foreseeable future. It is therefore important to ascertain the electrical impact of these defects, particularly in high-field vertical power device topologies where SiC is expected to enable large performance improvements in solid-state high-power systems. This paper compares the DC-measured reverse-breakdown characteristics of low-voltage (less than 250 V) small-area (less than 5 x 10(exp -4)/sq cm) 4H-SiC p(+)n diodes with and without elementary screw dislocations. Compared to screw dislocation-free devices, diodes containing elementary screw dislocations exhibited higher pre-breakdown reverse leakage currents, softer reverse breakdown I-V knees, and highly localized microplasmic breakdown current filaments. The observed localized 4H-SiC breakdown parallels microplasmic breakdowns observed in silicon and other semiconductors, in which space-charge effects limit current conduction through the local microplasma as reverse bias is increased.

Neudeck, Philip G.↗
NASA NTRS1999

Study of Bulk and Elementary Screw Dislocation Assisted Reverse Breakdown in Low-Voltage (<250 V) 4H-SiC p+n Junction Diodes - Part 1: DC Properties

Given the high density (approx. 10(exp 4)/sq cm) of elementary screw dislocations (Burgers vector = lc with no hollow core) in commercial SiC wafers and epilayers, all appreciable current (greater than 1 A) SiC power devices will likely contain elementary screw dislocations for the foreseeable future. It is therefore important to ascertain the electrical impact of these defects, particularly in high-field vertical power device topologies where SiC is expected to enable large performance improvements in solid-state high-power systems. This paper compares the DC-measured reverse-breakdown characteristics of low-voltage (less than 250 V) small-area (less than 5 x 10(exp -4) sq cm) 4H-SiC p(+)n diodes with and without elementary screw dislocations. Compared to screw dislocation-free devices, diodes containing elementary screw dislocations exhibited higher pre-breakdown reverse leakage currents, softer reverse breakdown I-V knees, and highly localized microplasmic breakdown current filaments. The observed localized 4H-SiC breakdown parallels microplasmic breakdowns observed in silicon and other semiconductors, in which space-charge effects limit current conduction through the local microplasma as reverse bias is increased.

Neudeck, Philip G.↗
NASA NTRS1987

Power-processing unit

Power-processing unit uses AC buses (30, 32) to supply all current dependent needs such as connections (54, 56) to an ion thruster through an inductor (88) and the primary of a transformer (90), to assure limited currents to such loads. Where temperature control is also required, such as to the main discharge vaporizer heater connection (36, 38), switches (100, 102) are serially connected with inductor (96) and the primary of transformer (98). Temperature sensor (104) controls the switches (100, 102) for temperature regulation.

Wessel, Frank J.↗
NASA NTRS1972

Human responses to electricity: A literature review

An extensive review of literature on research concerning biomedical sensors is presented for establishing standards for current limiting devices. The physiological and pathological responses of the human, when exposed to electricity are reported including the thresholds: for perception of electricity, pain by electric current, induction of muscular contraction by electric shock, and ventricular fibrillation. The passive electrical properties of cells and tissues are also reported.

Turner, H. S.↗
NASA NTRS1980

Electronic system for high power load control

Parallel current paths are divided into two groups, with control devices in the current paths of one group each having a current limiting resistor, and the control devices in the other group each having no limiting resistor, so that when the control devices of the second group are turned fully on, a short circuit is achieved by the arrangement of parallel current paths. Separate but coordinated control signals are provided to turn on the control devices of the first group and increase their conduction toward saturation as a function of control input, and when fully on, or shortly before, to turn on the control devices of the second group and increase their conduction toward saturation as a function of the control input as that input continues to increase. Electronic means may be used to generate signals. The system may be used for 1-V characteristic measurements of solar arrays as well as for other load control purposes.

Miller, E. L.↗
NASA NTRS1990

White dwarf stars and the age of the Galactic disk

The history of the Galaxy is written in its oldest stars, the white dwarf (WD) stars. Significant limits can be placed on both the Galactic age and star formation history. A wide range of input WD model sequences is used to derive the current limits to the age estimates suggested by fitting to the observed falloff in the WD luminosity function. The results suggest that the star formation rate over the history of the Galaxy has been relatively constant, and that the disk age lies in the range 6-12 billion years, depending upon the assumed structure of WD stars, and in particular on the core composition and surface helium layer mass. Using plausible mixed C/O core input models, the estimates for the disk age range from 8-10.5 Gyr, i.e.,sustantially younger than most age estimates for the halo globular clusters. After speculating on the significance of the results, expected observational and theoretical refinements which will further enhance the reliability of the method are discussed.

Wood, M. A.↗