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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Computation of Space Shuttle high-pressure cryogenic turbopump ball bearing two-phase coolant flow

A homogeneous two-phase fluid flow model, implemented in a three-dimensional Navier-Stokes solver using computational fluid dynamics methodology is described. The application of the model to the analysis of the pump-end bearing coolant flow of the high-pressure oxygen turbopump of the Space Shuttle main engine is studied. Results indicate large boiling zones and hot spots near the ball/race contact points. The extent of the phase change of the liquid oxygen coolant flow due to the frictional and viscous heat fluxes near the contact areas has been investigated for the given inlet conditions of the coolant.

Chen, Yen-Sen↗
NASA NTRS1941

Preignition Characteristics of Several Fuels Under Simulated Engine Conditions

The preignition characteristics of a number of fuels have been studied under conditions similar to those encountered in an engine. These conditions were simulated by suddenly compressing a fuel-air mixture in contact with an electrically heated hot spot in the cylinder head of the NACA combustion apparatus. Schlieren photographs and indicator cards were taken of the burning, and the hot-spot temperatures necessary to cause ignition under various conditions were determined.

Spencer, R C↗
DOE OSTI2021

Friction reduction for engine components

The present invention relates to techniques for lowering friction between moving surfaces of, for example, an internal combustion engine. Friction reduction is achieved by adding texture modifications to surfaces that come in contact with each other. Texture modifications that reduce friction in accordance with the present invention include dimples of varying geometries and depths ion the surfaces of components. The present invention also relates to the fabrication technique for applying the texture to the surfaces. In another embodiment, the patterned soft mask is applied onto a large surface (flat or curved including cylindrical rollers surfaces) to be followed by electrochemical etching to imprint the textures onto the component And, in another embodiment, a diamond-like-carbon (DLC) film may be applied to the turbine component to also reduce friction.

Hsu, Stephen M.↗
DOE OSTI2024

Fabrication and Performance Evaluation of Double-Sided Copper Nanowire Arrays as Thermal and Electrical Interfacial Layers

Reducing contact interface thermal and electrical resistances is in great demand across various industries, particularly in the semiconductor industry. This study introduces an approach using double-sided copper nanowire (Cu NW) arrays on copper sheets as both thermal and electrical interfacial layers, designed to effectively accommodate the topographical inconsistencies between contact surfaces. Further, experimental outcomes reveal a significant reduction in thermal contact resistance (TCR), with a value of 2.5 mm 2 K W –1 , thereby exceeding the efficiency of reported nanostructural thermal interface materials (TIMs). Additionally, when utilized as an electrical interfacial layer, these double-sided Cu NWs arrays dramatically reduced electrical contact resistance (ECR), outperforming traditional conductive grease in applications necessitating separable bonding, though showing comparable performance to costly silver-based conductive epoxies required for permanent, inseparable bonds. The promising results of the double-sided Cu NWs arrays in reducing both TCR and ECR, confirmed by finite element simulation, highlight their substantial potential in advancing TIMs and electrical interconnection applications across various sectors.

42 ENGINEERING↗
NASA NTRS2001

Pathfinder Technologies Specialist, X-37

The X-37 is a technology demonstrator sponsored by NASA. It includes a number of experiments both imbedded (i.e., essential aspects of the vehicle) and separate. The technologies demonstrated will be useful in future operational versions as well as having broad applications to other programs. Mr. James R. French, of JRF Engineering Services and as a consultant to SAIC, has provided technical support to the X-37 NASA Program office since the beginning of the program. In providing this service, Mr. French has maintained close contact with the Boeing Seal Beach and Rocketdyne technical teams via telephone, e-mail, and periodic visits. His interfaces were primarily with the working engineers in order to provide NASA sponsors with a different view than that achieved through management channels. Mr. French's periodic and highly detailed technical reports were submitted to NASA and SAIC (Science Applications International Corporation) on a weekly/monthly basis. These reports addressed a wide spectrum of programmatic and technical interests related to the X-37 Program including vehicle design, flight sciences, propulsion, thermal protection, Guidance Navigation & Control (GN&C), structures, and operations. This deliverable is presented as a consolidation of the twelve monthly reports submitted during the Contract's Option Year,

French, James R.↗
DOE OSTI2020

Measuring Transverse Displacements Using Unmanned Aerial Systems Laser Doppler Vibrometer (UAS-LDV): Development and Field Validation

Measurement of bridge displacements is important for ensuring the safe operation of railway bridges. Traditionally, contact sensors such as Linear Variable Displacement Transducers (LVDT) and accelerometers have been used to measure the displacement of the railway bridges. However, these sensors need significant effort in installation and maintenance. Therefore, railroad management agencies are interested in new means to measure bridge displacements. This research focuses on mounting Laser Doppler Vibrometer (LDV) on an Unmanned Aerial System (UAS) to enable contact-free transverse dynamic displacement of railroad bridges. Researchers conducted three field tests by flying the Unmanned Aerial Systems Laser Doppler Vibrometer (UAS-LDV) 1.5 m away from the ground and measured the displacement of a moving target at various distances. The accuracy of the UAS-LDV measurements was compared to the Linear Variable Differential Transducer (LVDT) measurements. The results of the three field tests showed that the proposed system could measure non-contact, reference-free dynamic displacement with an average peak and root mean square (RMS) error for the three experiments of 10% and 8% compared to LVDT, respectively. Such errors are acceptable for field measurements in railroads, as the interest prior to bridge monitoring implementation of a new approach is to demonstrate similar success for different flights, as reported in the three results. This study also identified barriers for industrial adoption of this technology and proposed operational development practices for both technical and cost-effective implementation.

42 ENGINEERING↗
DOE OSTI2022

Novel and effective surface passivation for high efficiency n- and p-type Silicon solar cell

The project objective was to develop a novel Si surface passivation method using chalcogens, sulfur (S) and/or selenium (Se), as passivating elements, to withstand industry-standard high temperature contacting and metallization schemes for p-type Si based passivated emitter and rear contact (p-PERC) solar cells. The back surface passivation of PERC cells has been improved drastically with the invention and successful application of an Al 2 O 3 passivation layer. However, the front n + diffused junction surface is still poorly passivated by the standard amorphous silicon nitride (SiNx) anti-reflection coating (ARC) layer. This project sought to address the passivation challenges of both front n+ emitter and undiffused p-Si back surface. Improved p-PERC solar cell performance with open circuit voltage (V OC ) > 680 mV and efficiency of 22% were targeted to validate superior defect passivation properties as compared to standard SiO 2 / Al 2 O 3 passivation. During this project, we systematically investigated process-structure-properties-performance relationships of this novel advanced defect passivation approach. The S/Se passivation was carried out by reacting industrial Czochralski (Cz) Si wafers in H 2 S and H 2 Se gases in a chemical vapor deposition (CVD) reactor at temperatures up to 700°C. After an exhaustive optimization of the process parameters (temperature, time, and gas concentration), we established an optimized process and demonstrated extremely low surface recombination velocities (SRVs) of 1.5 cm/s and 8 cm/s on n-type and p-type Si, respectively, by S-passivation. In-depth surface and interface characterization were performed using soft x-ray and photoelectron spectroscopies (XPS, UPS, XES), combined with capacitance-voltage-frequency (C-V-f) measurements, to decipher the surface chemical/electronic structure and interface defect state densities. These measurements provided critical understanding of the defect passivation mechanism and elucidated the presence of surface S-Si bonds, a reduction of surface dipoles, and low interface state densities (D it ) < 10 11 cm -2 ev -1 . We also found that the Se-passivation is inferior to the S-passivation (by at least one order of magnitude in SRV). Application of the optimized S-passivation to the n+ diffused emitter surface led to a low surface recombination current density, J0 ≈ 40 fA/cm 2 (~ 1/4 of the industry-standard SiNx-passivation), and high implied V OC (686 mV) in p-PERC solar cell structures. The S-passivation process also was found to improve the bulk quality of the p-type Si, better than the SiO 2 or Al 2 O 3 passivation processes. After successful demonstration of efficient passivation of Si surface defects by S, we extensively studied the air, thermal, and illumination stability of the passivation structure. S-passivation itself degrades in air due to competing reactions with moisture and oxygen to form oxides, which can be eliminated by a SiNx capping layer (also acting as a anti-reflective coating). After SiNx process optimization, we demonstrated illumination and thermally stable S-passivation with SRV < 5 cm/s and J 0 < 80 fA/cm 2 . These enhancements in Si passivation, incorporated into p-PERC cells, achieved an efficiency of 19.93% with V OC = 649 mV, using manufacturing metallization and contacting schemes. The low cell performance (cell V OC is much less than the implied V OC = 686 mV, anticipated from surface passivation) was identified due to degradation of S-passivation during the metal firing step (out-diffusion of S from the Si interface to the SiNx surface). The S-passivation of Si surfaces shows significant promise with excellent passivation quality, essential for high performance (high V OC , high efficiency) solar cells. Integration of this innovative defect passivation into devices, however, demands further development of the capping layer, low temperature (<700°C) metallization process, and/or engineering of advanced device structures. Surface passivation-dominated advanced Si solar cells, such as tunnel oxide passivated contacts and Si heterojunctions, are increasingly of interest due to their high-performance potential and will have a growing photovoltaic market share in the near future.

14 SOLAR ENERGY↗
NASA NTRS1984

Ceramic-coated metals can survive contact with hot working fluid

Thermal barrier coatings (TBCs) have been developed as a means of protecting turbine blades and other engine hot section components whose surfaces are exposed to the most extreme operating conditions. By adding a thin, insulating ceramic oxide layer to an air-cooled turbine blade, the difference between the gas temperature and the metal temperature is further increased as a function of ceramic coating thickness, heat flux, and oxide thermal conductivity. An 0.04-cm thick ceramic layer can typically yield a 100-300 C temperature drop. Of the various techniques available for the deposition of thermal barrier coatings, the most common is that of plasma spraying. Significant improvements have been made in TBC durability through the use of bond coat compositions with increased oxidation resistance.

Levine, S. R.↗
NASA NTRS1987

An expert system for scheduling requests for communications links between TDRSS and ERBS

An ERBS-TDRSS Contact Planning System (ERBS-TDRSS CPS) is described which uses a graphics interface and the NASA Transportable Inference Engine. The procedure involves transfer of the ERBS-TDRSS Ground Track Orbit Prediction data to the ERBS flight operations area, where the ERBS-TDRSS CPS automatically generates requests for TDRSS service. As requested events are rejected, alternative context sensitive strategies are employed to generate new requested events until a schedule is completed. A report generator builds schedule requests for separate ERBS-TDRSS contacts.

Mclean, David R.↗
NASA NTRS1987

An expert system for scheduling requests for communications Links between TDRSS and ERBS

An ERBS-TDRSS Contact Planning System (ERBS-TDRSS CPS) is described which uses a graphics interface and the NASA Transportable Interference Engine. The procedure involves transfer of the ERBS-TDRSS Ground Track Orbit Prediction data to the ERBS flight operations area, where the ERBS-TDRSS CPS automatically generates requests for TDRSS service. As requested events are rejected, alternative context sensitive strategies are employed to generate new requested events until a schedule is completed. A report generator builds schedule requests for separate ERBS-TDRSS contacts.

Mclean, David R.↗
NASA NTRS1972

Advanced airbreathing engine lubricants study with a tetraester fluid and a synthetic paraffinic oil at 492 K (425 F)

Groups of 120-mm-bore angular-contact ball bearings made from AISI M-50 steel were fatigue tested with a tetraester and a synthetic paraffinic oil at a bearing temperature of 492 K (425 F) in an air environment. Bearing life exceeded AFBMA-predicted (catalog) life by factors in excess of 4 and 10 for the tetraester and synthetic paraffinic fluids, respectively. The final viscosities after 500 hours of operation were 14 and 6 times the initial values, respectively. During the same time period, when the test oil is replaced at a rate approximating the replenishment rate in actual commerical engine usage, no significant increase in lubricant viscosity with time was observed.

Zaretsky, E. V.↗
DOE OSTI2021

Engineered Thin Diffusion Layers for Anion-Exchange Membrane Electrolyzer Cells with Outstanding Performance

Anion-exchange membrane electrolyzer cells (AEMECs) are one of the most promising technologies for carbon-neutral hydrogen production. Over the past few years, the performance and durability of AEMECs have substantially improved. Herein, we report an engineered liquid/gas diffusion layer (LGDL) with tunable pore morphologies that enables the high performance of AEMECs. The comparison with a commercial titanium foam in the electrolyzer indicated that the engineered LGDL with thin-flat and straight-pore structures significantly improved the interfacial contacts, mass transport, and activation of more reaction sites, leading to outstanding performance. We obtained a current density of 2.0 A/cm 2 at 1.80 V with an efficiency of up to 81.9% at 60 °C under 0.1 M NaOH-fed conditions. The as-achieved high performance in this study provides insight to design advanced LGDLs for the production of low-cost and high-efficiency AEMECs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

A High-Speed Rotational Diamond Anvil Cell for In Situ Analysis of Hierarchical Microstructural Evolution of Metallic Alloys during Extreme Shear Deformation

High speed shear deformation is ubiquitous in engineering applications, ranging from material processing methods such as friction stir processing/extrusion and in tribological contacts. However, analyzing the microstructural evolution of materials while they are undergoing high speed shear deformation have been a long-standing challenge. This led to predominant reliance on ex situ microscopy before and after shear deformation. But ex situ microscopy lacks the ability to analyze dynamic and transient hierarchical microstructural evolution mechanisms that could occur during shear deformation of materials. Therefore, to better understand the dynamic mechanisms of mass and energy transfer in materials under shear deformation, we developed a first of its kind high-speed rotational diamond anvil cell (HS-RDAC) for synchrotron-based in situ high-energy x-ray diffraction (XRD). We studied the time resolved lattice strain evolution, XRD peak broadening and changes in spatial variation of shear deformation induced alloying in pure metal and metal alloy sheets and powder mixture using the HS-RDAC. These in situ results were combined with detailed ex situ microstructural characterization before and after the shear deformation using transmission electron microscopy and atom probe tomography, which revealed the different stages of evolution of a shear deformation induced hierarchical nanostructure. Multiscale computational simulations including computational fluid dynamics, crystal plasticity, molecular dynamic simulation and density functional theory uncovered the mechanisms behind morphological changes, evolution of defect structures and changes in driving force for shear deformation induced intermixing. In conclusion, this in situ HS-RDAC capability, in combination with ex situ microstructural characterization and computational simulations, can provide new insights into the hierarchical microstructural evolution pathway during shear deformation.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Liquid phase products and solid deposit formation from thermally stressed model jet fuels

The relationship between solid deposit formation and liquid degradation product concentration was studied for the high temperature (400 C) stressing of three hydrocarbon model fuels. A Jet Fuel Thermal Oxidation Tester was used to simulate actual engine fuel system conditions. The effects of fuel type, dissolved oxygen concentration, and hot surface contact time (reaction time) were studied. Effects of reaction time and removal of dissolved oxygen on deposit formation were found to be different for n-dodecane and for 2-ethylnaphthalene. When ten percent tetralin is added to n-dodecane to give a simpler model of an actual jet fuel, the tetralin inhibits both the deposit formation and the degradation of n-dodecane. For 2-ethylnaphthalene primary product analyses indicate a possible self-inhibition at long reaction times of the secondary reactions which form the deposit precursors. The mechanism of the primary breakdown of these fuels is suggested and the primary products which participate in these precursor-forming reactions are identified. Some implications of the results to the thermal degradation of real jet fuels are given.

Kim, W. S.↗
NASA NTRS1989

Simulation of flexible structures with impact: Experimental validation

The simulation of the dynamic behavior of flexible structures with impact, is experimentally and numerically investigated. A radially rotating flexible beam attached to a rigid shaft is considered. Both experimental and numerical studies are undertaken. Experimental studies how excellent agreement with simulation studies using both the momentum balance (coefficient of friction), and spring-dashpot (impact pair) models. The simulation studies are even capable of predicting the high-speed multiple impacts which occur due to structural flexibility and which are experimentally observed using high-speed video photography. The results of the studies show that a simple momentum balance (coefficient of restitution) method for simulating the impact is sufficiently accurate in predicting the dynamic behavior of the system for most engineering applications. The momentum balance method cannot simulate the impact force which develops during the contact duration, but is computationally very efficient. The spring-dashpot model is more difficult to develop and requires significantly larger computation time, but can simulate impact forces and stresses due to impact. The momentum balance (coefficient of restitution) method, although strictly not applicable to flexible bodies, has been shown to provide an accurate and computationally efficient method for simulating the dynamic behavior of flexible structures with impact when contact stresses are not needed.

Ulsoy, A. Galip↗
NASA NTRS1993

"Starfish" Heater Head For Stirling Engine

Proposed "starfish" heater head for Stirling engine enables safe use of liquid sodium as heat-transfer fluid. Sodium makes direct contact with heater head but does not come in contact with any structural welds. Design concept minimizes number of, and simplifies nonstructural thermal welds and facilitates inspection of such welds.

Vitale, N.↗
NASA NTRS1993

The development of hydrogen sensor technology at NASA Lewis Research Center

The detection of hydrogen leaks in aerospace applications, especially those involving hydrogen fuel propulsion systems, is of extreme importance for reasons of reliability, safety, and economy. Motivated by leaks occurring in liquid hydrogen lines supplying the main engine of the Space Shuttle, NASA Lewis has initiated a program to develop point-contact hydrogen sensors which address the needs of aerospace applications. Several different approaches are being explored. They include the fabrication of PdAg Schottky diode structures, the characterization of PdCr as a hydrogen sensitive alloy, and the use of SiC as a semiconductor for hydrogen sensors. This paper discusses the motivation behind and present status of each of the major components of the NASA LeRC hydrogen sensor program.

Hunter, Gary W.↗
NASA NTRS1940

Measurement of Knock Characteristics in Spark-ignition Engines

This paper presents a discussion of three potential sources of error in recording engine knocking which are: the natural oscillation of the membrane, the shock process between test contacts, and the danger of burned contacts. Following this discussion, the paper calls attention to various results which make the bouncing-pin indicator appear fundamentally unsuitable for recording knock phenomena.

Schutz, R↗