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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Operating Conditions of a Main Bearing Contact in a Commercial Wind Turbine

This presentation described acoustic emissions and temperature characteristics of a commercial main bearing in a wind turbine drivetrain. These characteristics were measured on the outer ring of the bearing by SKF DVST nodes, which are mounted on both upwind and downwind rows of the main bearing at four equally spaced circumferential locations. The measurement started in early 2018 and ends in 2020 and five-month data in 2018 winter was analyzed in this study.

acoustic emission↗
DOE OSTI2021

Exploration of multifidelity UQ sampling strategies for computer network applications.

Network modeling is a powerful tool to enable rapid analysis of complex systems that can be challenging to study directly using physical testing. Here, two approaches are considered: emulation and simulation. The former runs real software on virtualized hardware, while the latter mimics the behavior of network components and their interactions in software. Although emulation provides an accurate representation of physical networks, this approach alone cannot guarantee the characterization of the system under realistic operative conditions. Operative conditions for physical networks are often characterized by intrinsic variability (payload size, packet latency, etc.) or a lack of precise knowledge regarding the network configuration (bandwidth, delays, etc.); therefore uncertainty quantification (UQ) strategies should be also employed. UQ strategies require multiple evaluations of the system with a number of evaluation instances that roughly increases with the problem dimensionality, i.e., the number of uncertain parameters. It follows that a typical UQ workflow for network modeling based on emulation can easily become unattainable due to its prohibitive computational cost. In this paper, a multifidelity sampling approach is discussed and applied to network modeling problems. The main idea is to optimally fuse information coming from simulations, which are a low-fidelity version of the emulation problem of interest, in order to decrease the estimator variance. By reducing the estimator variance in a sampling approach it is usually possible to obtain more reliable statistics and therefore a more reliable system characterization. Several network problems of increasing difficulty are presented. For each of them, the performance of the multifidelity estimator is compared with respect to the single fidelity counterpart, namely, Monte Carlo sampling. For all the test problems studied in this work, the multifidelity estimator demonstrated an increased efficiency with respect to MC.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Selection and Use Considerations for Laser Power Photovoltaic Receivers

III-V PV receivers provide high performance over wide range of application conditions. Operating conditions including irradiance and cell temperature must be accounted for. Very high efficiencies demonstrated for small GaAs devices. Potential for significant future advances in performance, especially for other wavelengths and for cost.

GaAs↗
DOE OSTI2022

Parametric Testing and Evaluation of a Novel Biphasic Absorption Process for Post-Combustion Carbon Capture

A novel biphasic CO2 absorption process (BiCAP) is being developed at the University of Illinois. BiCAP is enabled by using a new class of biphasic solvents developed based on multi-property criteria for postcombustion carbon capture. The process was previously demonstrated at the lab-scale, including in 10 kWe absorption and desorption column systems. In the current study, the process has been scaled up by building and testing a 40 kWe integrated capture skid at a power plant. Parametric tests for two biphasic solvents were conducted with the synthetic flue gas made of bottle CO2 gas and air to validate the performance and operational flexibility of the unit with respect to varying process or operating conditions. Operation of the phase separator, which is unique equipment to BiCAP, was verified to be stable and efficient. Two liquid phases could be separated via static settlement based on a density difference and >90% of the CO2 absorbed was concentrated in the separated CO2-rich phase. Results of parametric tests showed that the minimum heat duty appeared at the optimal stripping pressure. A higher stripping temperature was more favourable to improve overall energy performance. Introducing a secondary cold solvent feed stream to the top of the stripper via bypassing the cross heat exchanger helped reduce the heat loss carried with water vapour. Test results also revealed that the heat duty requirement was comparable when the CO2 concentration in flue gas decreased from ~11 to 4 vol.% as the phase separation decoupled the absorption and desorption steps in BiCAP. Under typical steady-state conditions, both biphasic solvents lowered the process heat duty by >40% compared with the reference 30 wt.% monoethanolamine solvent.

Absorption↗
NASA NTRSDate not supplied

Going beyond reliability to achieve robustness

Reliability is the ability to perform well and consistently. More formally, reliability is defined as the mathematical probability that a system does not fail during a specified time period under its specified operating conditions. The specified operating conditions often go beyond the nominal environment to include variations and challenges encountered in operational use. The difficulty is that systems are often operated outside of their specified operating conditions and, if they fail, the designers are in theory blameless. Unanticipated damaging events include internal failures, external disruptions in supporting systems, accidents, and repurposing. The most common explanation of a system failure is human error, which is usually the first assumption of the system designers. Robustness is the capability to perform without failure under a wide range of conditions that go beyond the specified operating conditions. The first step towards improving robustness would be to expand the system’s specified operating conditions to include a wider range of anticipated challenges, especially human error. Beyond this, there is a need for general approach to reduce the impact of unanticipated future events, the unknown unknowns, by improving the system’s general ability to cope. Robustness can be improved by providing additional processing capacity, larger flow control buffers, increased backup storage, more online redundancy, and more capable supervisory monitoring and control.

Harry W Jones↗
NASA NTRS2010

Thermal and Evolved Gas Analysis of Calcite Under Reduced Operating Pressures: Implications for the 2011 MSL Sample Analysis at Mars (SAM) Instrument

The Mars Science Laboratory (MSL) is scheduled for launch in 2011. The science objectives for MSL are to assess the past or present biological potential, to characterize the geology, and to investigate other planetary processes that influence habitability at the landing site. The Sample Analysis at Mars (SAM) is a key instrument on the MSL payload that will explore the potential habitability at the landing site [1]. In addition to searching for organic compounds, SAM will have the capability to characterized evolved gases as a function of increasing temperature and provide information on the mineralogy of volatile-bearing phases such as carbonates, sulfates, phyllosilicates, and Fe-oxyhydroxides. The operating conditions in SAM ovens will be maintained at 30 mb pressure with a He carrier gas flowing at 1 sccm. We have previously characterized the thermal and evolved gas behaviors of volatile-bearing species under reduced pressure conditions that simulated operating conditions of the Thermal and Evolved Gas Analyzer (TEGA) that was onboard the 2007 Mars Phoenix Scout Mission [e.g., 2-8]. TEGA ovens operated at 12 mb pressure with a N2 carrier gas flowing at 0.04 sccm. Another key difference between SAM and TEGA is that TEGA was able to perform differential scanning calorimetry whereas SAM only has a pyrolysis oven. The operating conditions for TEGA and SAM have several key parameter differences including operating pressure (12 vs 30 mb), carrier gas (N2 vs. He), and carrier gas flow rate (0.04 vs 1 sccm). The objectives of this study are to characterize the thermal and evolved gas analysis of calcite under SAM operating conditions and then compare it to calcite thermal and evolved gas analysis under TEGA operating conditions.

Lauer, H. V. Jr.↗
DOE OSTI2022

A Fast and Accurate Transient Stability Assessment Method Based on Deep Learning: WECC Case Study

Transient stability is one of the critical aspects of power system stability assessment. The increasing integration of inverter-based resources and the retirement of conventional synchronous generators result in the decreasing system inertia and growing complexity of system operating conditions. Using a few selected typical operating conditions cannot guarantee system transient stability in all operating conditions, and the time-domain simulation of all operating conditions requires tremendous time and is often infeasible. This paper proposes a more efficient transient stability assessment method based on deep learning. The binary search method is used to determine the critical clearing time (CCT) in creating training databased by time-domain simulation. This method is fast and accurate with 1 ms resolution. The buses whose CCTs are lower than 200 ms are considered critical buses. Buses close to each other are grouped based on their mutual admittance matrix to reduce the search space of the critical buses. This paper also proposes the generator feature normalization based on the physical model. Case study on the reduced 240-bus WECC system model demonstrates that the proposed method can predict CCT accurately and efficiently.

critical clearing time↗
DOE OSTI2022

Deep Learning Based Frequency Stability Assessment in Power Grid with High Renewables

Frequency stability assessment is one critical aspect of power system security assessment. Traditional N-1 screening method is based on the simulations of a few typical daily and seasonal operation scenarios. However, the increasing integration of inverter-based renewables and the retirement of conventional synchronous generators result in decreasing system inertia and growing complexity of system operating conditions. Selecting a few typical operation scenarios cannot cover all operating conditions, and the time-domain simulation of all operation conditions requires tremendous time. This paper proposes a more efficient frequency stability assessment method based on deep learning. The affinity propagation clustering algorithm is used to divide the dataset into different clusters, so the selected dataset for training can cover the diversified operating conditions as much as possible. Also, feature normalization is applied to both the training dataset and testing dataset in order to remove any unnecessary bias. Especially, trained model based on full dataset normalization has bounded error in the prediction. The case study on the reduced 240-bus WECC system demonstrates that the proposed method can predict accurate frequency nadir with limited training dataset. The deep learning model using the revised feature normalization can predict more accurate frequency nadir than that using the traditional feature normalization and has very small maximum prediction error.

affinity propagation↗
DOE OSTI2023

Voltage-Based Strategies for Preventing Battery Degradation under Diverse Fast-Charging Conditions

Maintaining safe operating conditions is a key challenge for high-performance lithium-ion battery applications. The lithium-plating reaction remains a risk during charging, but limited studies consider the highly variable charging conditions possible in commercial cells. Here we combine pseudo-2D electrochemical modeling with data visualization methods to reveal important relationships between the measurable cell voltage and difficult-to-predict Li-plating onset criteria. An extensively validated model is used to compute Li plating for thousands of multistep charging conditions spanning diverse rates, temperatures, states-of-charge, and cell aging. Here we observe an empirical cell operating voltage limit below which plating does not occur across all conditions, and this limit varies with the battery state-of-charge and aging. A model sensitivity analysis also indicates that, when comparing two charging voltage profiles, the capacity difference at 4.0 V correlates well with the difference in the plating onset capacity. These results encourage simple strategies for Li-plating prevention that are complementary to existing battery controls.

25 ENERGY STORAGE↗
DOE OSTI2020

Multi-mode advanced combustion engine with supervisory control

An engine system uses data associated with at least one operating condition of an engine to set the engine system to an AI mode when the engine is in an SI mode 1) within first operating condition limits, and 2) when a rate of change of a first operating condition is within rate of change limits, maintain the engine system in the SI mode when the engine is outside of first operating condition limits or when the rate of change of the first operating condition is not within rate of change limits, set the engine system to the SI mode when the engine is in the AI mode outside second operating condition limits, and maintain the engine system in the AI mode when the engine is within second operating condition limits, wherein the second operating condition limits are different from the first operating condition limits.

42 ENGINEERING↗
NASA NTRS1985

Evaluation of fuel preparation systems for lean premixing-prevaporizing combustors

A series of experiments was carried out in order to produce design data for a premixing prevaporizing fuel-air mixture preparation system for aircraft gas turbine engine combustors. The fuel-air mixture uniformity of four different system design concepts was evaluated over a range of conditions representing the cruise operation of a modern commercial turbofan engine. Operating conditions including pressure, temperature, fuel-to-air ratio, and velocity, exhibited no clear effect on mixture uniformity of systems using pressure-atomizing fuel nozzles and large-scale mixing devices. However, the performance of systems using atomizing fuel nozzles and large-scale mixing devices was found to be sensitive to operating conditions. Variations in system design variables were also evaluated and correlated. Mixing uniformity was found to improve with system length, pressure drop, and the number of fuel injection points per unit area. A premixing system capable of providing mixing uniformity to within 15 percent over a typical range of cruise operating conditions is demonstrated.

Dodds, W. J.↗
DOE OSTI2024

Adjustable primary and supplemental power units

A propulsion system for an aircraft includes a core flow path in communication with a compressor section, combustor section and a turbine section. A first bottoming cycle system includes a bottoming working fluid flow in thermal communication with a high energy exhaust gas flow that is generated by the core engine. The first bottoming cycle is configured to recover power from the high energy exhaust gas flow in a first engine operating condition and in a second engine operating condition. A second bottoming cycle system is configured to recover power from the high energy exhaust gas flow in the first engine operating condition and not to recover power in a second engine operating condition.

MacDonald, Malcolm P.↗
NASA NTRS1994

Aircraft maneuver envelope warning system

A maneuver envelope warning system for an aircraft having operating limits, operating condition sensors and an indicator driver. The indicator driver has a plurality of visual indicators. The indicator driver determines a relationship between sensed operating conditions and the operating limits; such as, a ratio therebetween. The indicator driver illuminates a number of the indicators in proportion to the determined relationship. The position of the indicators illuminated represents to a pilot in an easily ascertainable manner whether the operational conditions are approaching operational limits of the aircraft, and the degree to which operational conditions lie within or exceed operational limits.

Bivens, Courtland C.↗
NASA NTRS1956

Effect of Engine Operating Variables on Combustor-inlet Parameters

Studies of the fundamental processes of combustion are usually concerned with wide ranges of investigation of individual processes. In general, each fundamental combustion process may be studied in an environment that is most suited to its evaluation and possibly unrelated basically to any practical application. The majority of the data presented in volume I of this series concern the fundamental aspects of combustion as functions of the individual occurrence of various contributing processes. In a jet engine, however, the various fundamental combustion processes may occur simultaneously and may interact. Furthermore, the engine environment usually does not permit independent variation of single combustion parameters, since specified operating conditions impose specific values on the parameters. In volume II, data are presented to show the effect of operating conditions on the over-all combustion process in different combustion components. To show the effect of operating conditions, it is necessary to specify the range of these conditions within which combustion components may operate. Therefore, this chapter presents only the operating conditions that might be required in the primary combustors and afterburners of typical current turbojet engines. (Corresponding information on ram-jet engines is presented in ch. xisi.) This chapter is not intended to serve as an explanation of engine operation. The operating conditions of the combustion components are presented in terms of total pressures and temperatures at the primary-combustor and afterburner inlets, reference velocities and outlet total temperatures of the primary combustors, and velocities at the plane of the flameholder in the afterburners. The data are presented to relate the operating regions of typical current turbojet combustion components to flight altitudes, Mach numbers, and modes of engine operation. Specifically, data are presented for the combustion parameters of the primary combustor and afterburner of three turbojet engines having rated compressor total-pressure ratios of 5, 8, and 12 under full-throttle conditions. Operational data for the primary combustor also include part-throttle operation at 70, 80, and 90 percent of rated engine speed and windmifling operation. The range of flight conditions includes altitudes from sea level to 65,000 feet and flight Mach numbers from zero to 1.6.

Jones, A. W.↗
NASA NTRS1986

Atomization and combustion characteristics of antimisting fuels using JT8D and air-boost injectors

The atomization levels of antimisting fuels are presently determined for a JT8D fuel injector, a low emission airblast JT8D injector, and an air-boost injector, at operating conditions simulating engine operating conditions. The effects of the use of antimisting kerosene (AMK) on component performance are also studied in the case of an in-service JT8D engine. The use of the AMK fuel causes a decline in the quality of the spray, most notably as a large increase in the Sauter mean diameter for all three injector types. In addition, the idle patternation data obtained indicate that the low emission injector fuel distribution changed from a hollow cone Jet A spray having no fuel at its center to a semihollow spray cone in the case of AMK; this change could disrupt the combustor primary zone recirculation pattern.

Kennedy, J. B.↗
NASA NTRS1999

Development of an Empirical Methods for Predicting Jet Mixing Noise of Cold Flow Rectangular Jets

This report presents an empirical method for predicting the jet mixing noise levels of cold flow rectangular jets. The report presents a detailed analysis of the methodology used in development of the prediction method. The empirical correlations used are based on narrow band acoustic data for cold flow rectangular model nozzle tests conducted in the NASA Langley Jet Noise Laboratory. There were 20 separate nozzle test operating conditions. For each operating condition 60 Hz bandwidth microphone measurements were made over a frequency range from 0 to 60,000 Hz. Measurements were performed at 16 polar directivity angles ranging from 45 degrees to 157.5 degrees. At each polar directivity angle, measurements were made at 9 azimuth directivity angles. The report shows the methods employed to remove screech tones and shock noise from the data in order to obtain the jet mixing noise component. The jet mixing noise was defined in terms of one third octave band spectral content, polar and azimuth directivity, and overall power level. Empirical correlations were performed over the range of test conditions to define each of these jet mixing noise parameters as a function of aspect ratio, jet velocity, and polar and azimuth directivity angles. The report presents the method for predicting the overall power level, the average polar directivity, the azimuth directivity and the location and shape of the spectra for jet mixing noise of cold flow rectangular jets.

Russell, James W.↗