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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
NASA NTRS1973

High temperature lubricant screening and systems studies

Four candidate lubricants for next generation aircraft gas turbine application were tested under open atmosphere conditions in a rig simulating an advanced engine 125 mm bore mainshaft thrust bearing position. Testing was conducted at speeds to 24,000 rpm (3,000,000 bearing DN), bearing ring temperature of 500 F, and with 1200 F air and 100 psi differential pressure across the seals installed in a dual tandem arrangement. Test bearing was a 125 mm bore split inner ring, outer race riding angular contact ball bearing under a 3280 lb. thrust load. One lubricant, a type 2 ester, performed extremely well. The mainshaft seal limited the performance. Numerous design improvements for this seal were indicated.

Jones, D. A.↗
NASA NTRS1998

Computational Chemistry and Lubrication

Members of NASA Lewis Research Center's Tribology and Surface Science Branch are applying high-level computational chemistry techniques to the development of new lubrication systems for space applications and for future advanced aircraft engines. The next generation of gas turbine engines will require a liquid lubricant to function at temperatures in excess of 350 C in oxidizing environments. Conventional hydrocarbon-based lubricants are incapable of operating in these extreme environments, but a class of compounds known as the perfluoropolyether (PFAE) liquids (see the preceding illustration) shows promise for such applications. These commercially available products are already being used as lubricants in conditions where low vapor pressure and chemical stability are crucial, such as in satellite bearings and composite disk platters. At higher temperatures, however, these compounds undergo a decomposition process that is assisted (catalyzed) by metal and metal oxide bearing surfaces. This decomposition process severely limits the applicability of PFAE's at higher temperatures. A great deal of laboratory experimentation has revealed that the extent of fluid degradation depends on the chemical properties of the bearing surface materials. Lubrication engineers would like to understand the chemical breakdown mechanism to design a less vulnerable PFAE or to develop a chemical additive to block this degradation.

Zehe, Michael J.↗
NASA NTRS2006

Phosphate Reactions as Mechanisms of High-Temperature Lubrication

One of the major problems preventing the operation of advanced gas turbine engines at higher temperatures is the inability of currently used liquid lubricants to survive at these higher temperatures under friction and wear conditions. Current state-of-the-art organic liquid lubricants rapidly degrade at temperatures above 300 C; hence some other form of lubrication is necessary. Vapor-phase lubrication is a promising new technology for high-temperature lubrication. This lubrication method employs a liquid phosphate ester that is vaporized and delivered to bearings or gears; the vapor reacts with the metal surfaces, generating a solid lubricious film that has proven very stable at high temperatures. In this study, solid lubricious films were grown on cast-iron foils in order to obtain reaction and diffusion rate data to help characterize the growth mechanism. A phenomenological mathematical model of the film deposition process was derived incorporating transport and kinetic parameters that were coupled to the experimental data. This phenomenological model can now be reliably used as a predictive and scale-up tool for future vapor-phase lubrication studies.

Nagarajan, Anitha↗
NASA NTRS1984

Lubricity of well-characterized jet and broad-cut fuels by ball-on-cylinder machine

A ball-on-cylinder machine (BOCM) was used to measure the lubricity of fuels. The fuels tested were well-characterized fuels available from other programs at the NASA Lewis Research Center plus some in-house mildly hydroprocessed shale fuels from other programs included Jet-A, ERBS fuel, ERBS blends, and blend stock. The BOCM tests were made before and after clay treatment of some of these fuels with both humidified air and dry nitrogen as the preconditioning and cover gas. As expected, clay treatment always reduced fuel lubricity. Using nitrogen preconditioning and cover gas always resulted in a smaller wear scar diameter than when humidified air was used. Also observed was an indication of lower lubricity with lower boiling range fuels and lower aromatic fuels. Gas chromatographic analysis indicted changes in BOCM-stressed fuels.

Prok, G. M.↗
NASA NTRS2005

Analytic Modeling of the Hydrodynamic, Thermal, and Structural Behavior of Foil Thrust Bearings

A simulation and modeling effort is conducted on gas foil thrust bearings. A foil bearing is a self acting hydrodynamic device capable of separating stationary and rotating components of rotating machinery by a film of air or other gaseous lubricant. Although simple in appearance these bearings have proven to be complicated devices in analysis. They are sensitive to fluid structure interaction, use a compressible gas as a lubricant, may not be in the fully continuum range of fluid mechanics, and operate in the range where viscous heat generation is significant. These factors provide a challenge to the simulation and modeling task. The Reynolds equation with the addition of Knudsen number effects due to thin film thicknesses is used to simulate the hydrodynamics. The energy equation is manipulated to simulate the temperature field of the lubricant film and combined with the ideal gas relationship, provides density field input to the Reynolds equation. Heat transfer between the lubricant and the surroundings is also modeled. The structural deformations of the bearing are modeled with a single partial differential equation. The equation models the top foil as a thin, bending dominated membrane whose deflections are governed by the biharmonic equation. A linear superposition of hydrodynamic load and compliant foundation reaction is included. The stiffness of the compliant foundation is modeled as a distributed stiffness that supports the top foil. The system of governing equations is solved numerically by a computer program written in the Mathematica computing environment. Representative calculations and comparisons with experimental results are included for a generation I gas foil thrust bearing.

Bruckner, Robert J.↗
NASA NTRS1978

Fuel delivery system including heat exchanger means

A fuel delivery system is presented wherein first and second heat exchanger means are each adapted to provide the transfer of heat between the fuel and a second fluid such as lubricating oil associated with the gas turbine engine. Valve means are included which are operative in a first mode to provide for flow of the second fluid through both first and second heat exchange means and further operative in a second mode for bypassing the second fluid around the second heat exchanger means.

Coffinberry, G. A.↗
NASA NTRS1989

The nature of cometary materials

Because cometary surfaces are likely to be far colder and of a different composition than planetary surfaces, there are some new considerations that must be examined in regards to placing instrumented packages or sample return devices on their surfaces. The qualitative analysis of the problem of attaching hardware to a comet and not being ejected back into space can be divided into two parts. The first problem is to pierce the mantle and obtain access to the icy core. Drilling through the mantle requires that the drilling forces be reacted. Reacting such forces probably requires attachment to the icy core below. Therefore, some kinetic impact piercing device is likely to be required as the first act of attachment. The second problem for a piercing device to overcome is the force produced by the impact kinetic energy that tries to eject the piercing device back into space. The mantle and icy core can absorb some of the impact kinetic energy in the form of fracture formation and friction energy. The energy that is not absorbed in these two ways is stored by the core as elastic deformation of the mantle and icy core. It is concluded that because the cometary materials are almost certainly brittle and the icy core is likely to be self lubricating, the elastic rebound and gas pressure expulsion forces must be counteracted by forces greater than those that may be provided by a piercing device or its capture devices (barbs).

Stephens, James↗
NASA NTRS1993

Calculation of stiffness and damping coefficients for elastically supported gas foil bearings

The stiffness and damping coefficients of an elastically supported gas foil bearing are calculated. A perfect gas is used as the lubricant, and its behavior is described by the Reynolds equation. The structural model consists only of an elastic foundation. The fluid equations and the structural equations are coupled. A perturbation method is used to obtain the linearized dynamic coefficient equations. A finite difference formulation has been developed to solve for the four stiffness and the four damping coefficients. The effect of the bearing compliance on the dynamic coefficients is discussed in this paper.

Peng, J.-P.↗
NASA NTRS2007

Feasibility Study of Vapor-Mist Phase Reaction Lubrication Using a Thioether Liquid

A primary technology barrier preventing the operation of gas turbine engines and aircraft gearboxes at higher temperatures is the inability of currently used liquid lubricants to survive at the desired operating conditions over an extended time period. Current state-of-the-art organic liquid lubricants rapidly degrade at temperatures above 300 C; hence, another form of lubrication is necessary. Vapor or mist phase reaction lubrication is a unique, alternative technology for high temperature lubrication. The majority of past studies have employed a liquid phosphate ester that was vaporized or misted, and delivered to bearings or gears where the phosphate ester reacted with the metal surfaces generating a solid lubricious film. This method resulted in acceptable operating temperatures suggesting some good lubrication properties, but the continuous reaction between the phosphate ester and the iron surfaces led to wear rates unacceptable for gas turbine engine or aircraft gearbox applications. In this study, an alternative non-phosphate liquid was used to mist phase lubricate a spur gearbox rig operating at 10,000 rpm under highly loaded conditions. After 21 million shaft revolutions of operation the gears exhibited only minor wear.

Morales, Wilfredo↗
NASA NTRS1978

Static evaluation of surface coatings for compliant gas bearings in an oxidizing atmosphere to 650 C

Hard wear-resistant coatings and soft low shear strength coatings were developed for an air-lubricated compliant journal bearing for a future automotive gas turbine engine. The coatings were expected to function in either 540 or 650 C ambient. Soft lubricant coatings were generally limited in temperature. Therefore emphasis was on the hard wear-resistant coatings. The coating materials covered were TiC, B4C, Cr3C2, WC, SiC, CrB2, TiB2, Cr2O3, Al2O3, Si3N4, Tribaloy 800, CaF2, CaF2-BaF2 eutectic, Ni-Co, silver, CdO-graphite and proprietary compounds. The coatings on test coupons were subjected to static oven screening tests. The test consisted of exposure of material samples in an oven for 300 h at the maximum temperature (540 or 650 C) and ten temperature cycles from room temperature to the maximum service temperature. On the basis of the specimen examinations the following coatings were recommended for future wear tests: TiC (sputtered), Cr2O3 (sputtered), Si3N4 (sputtered), CdO and graphite (fused), Kaman DES (a proprietary coating), CrB2 (plasma sprayed), Cr3C2 (detonation gun) and NASA PS-106 (plasma sprayed).

Bhushan, B.↗
NASA NTRS1995

The tribology of PS212 coatings and PM212 composites for the lubrication of titanium 6A1-4V components of a Stirling engine space power system

The Stirling space power machine incorporates a linear alternator to generate electrical power. The alternator is a reciprocating device that is driven by a solar or nuclear-powered Stirling engine. The power piston and cylinder are made of titanium 6A1-4V (Ti6-4) alloy, and are designed to be lubricated by a hydrodynamically-generated gas film. Rubbing occurs during starts and stops and there is a possibility of an occasional high speed rub. Since titanium is known to have a severe galling tendency in sliding contacts, a 'backup,' self-lubricating coating on the cylinder and/or the piston is needed. This report describes the results of a research program to study the lubrication of Ti6-4 with the following chromium carbide based materials: plasma-sprayed PS212 coatings and sintered PM212 counterfaces. Program objectives are to achieve adherent coatings on Ti6-4 and to measure the friction and wear characteristics of the following sliding combinations under conditions simulative of the Stirling-driven space power linear alternator: Ti6-4/Ti6-4 baseline, Ti6-4/PS212 coated Ti6-4, and Ps212 coated Ti6-4/PM212

Sliney, Harold E.↗
NASA NTRS1994

The tribology of PS212 coatings and PM212 composites for the lubrication of titanium 6Al-4V components of a Stirling engine space power system

The Stirling space power machine incorporates a linear alternator to generate electrical power. The alternator is a reciprocating device that is driven by a solar or nuclear-powered Stirling engine. The power piston and cylinder are made of titanium 6Al-4V (Ti6-4) alloy, and are designed to be lubricated by a hydrodynamically-generated gas film. Rubbing occurs during starts and stops and there is the possibility of an occasional high speed rub. Since titanium is known to have a severe galling tendency in sliding contacts, a 'back-up', self-lubricating coating on the cylinder and/or the piston is needed. This report describes the results of a research program to study the lubrication of Ti6-4 with the following chromium carbide based materials: plasma-sprayed PS212 coatings and sintered PM212 counterfaces. Program objectives are to achieve adherent coatings on Ti6-4 and to measure the friction and wear characteristics of the following sliding combinations under conditions simulative of the Stirling-driven space power linear alternator: Ti6-4/Ti6-4 baseline, Ti6-4/PS212-coated Ti6-4, and PS212-coated Ti6-4/PM212.

Sliney, Harold E.↗
NASA NTRS2014

The MillSOT-A Spiral Orbit Tribometer on a Milling Machine

A spiral orbit tribometer (SOT) intended to characterize friction and wear phenomena has been constructed on a milling machine. The instrument, essentially a retainerless thrust bearing with one ball and flat races, is exceedingly simple and inexpensive to construct. The capabilities of the tribometer to measure both the coefficient of friction and contact electrical resistance are demonstrated with clean specimens as well as with well known lubricants such as molybdenum disulphide and Krytox oil. Operation in a purged environment of inert gas is also demonstrated. The results with these lubricants are quite close to what is obtained by other methods. Suggestions for extending the capabilities of the tribometer are given. This arrangement may find use in university mechanical engineering laboratories to introduce and study rolling contact motion as well as for research in contact mechanics and tribology.

Pepper, Stephen V.↗
NASA NTRS2004

Future Issues and Approaches to Health Monitoring and Failure Prevention for Oil-Free Gas Turbines

Recent technology advances in foil air bearings, high temperature solid lubricants and computer based modeling has enabled the development of small Oil-Free gas turbines. These turbomachines are currently commercialized as small (<100 kW) microturbine generators and larger machines are being developed. Based upon these successes and the high potential payoffs offered by Oil-Free systems, NASA, industry, and other government entities are anticipating Oil-Free gas turbine propulsion systems to proliferate future markets. Since an Oil-Free engine has no oil system, traditional approaches to health monitoring and diagnostics, such as chip detection, oil analysis, and possibly vibration signature analyses (e.g., ball pass frequency) will be unavailable. As such, new approaches will need to be considered. These could include shaft orbit analyses, foil bearing temperature measurements, embedded wear sensors and start-up/coast down speed analysis. In addition, novel, as yet undeveloped techniques may emerge based upon concurrent developments in MEMS technology. This paper introduces Oil-Free technology, reviews the current state of the art and potential for future turbomachinery applications and discusses possible approaches to health monitoring, diagnostics and failure prevention.

DellaCorte, Christopher↗
NASA NTRS1981

Development of CdO-graphite-Ag coatings for gas bearings to 427 C

Graphite is one of the most commonly known lubricants. Its effectiveness in a range between room temperature (RT) and 540 C is reportedly improved by adding cadmium oxide. CdO-graphite powder in a gas carrier has been used in numerous applications that rely on dry lubrication. A coating of this composition was developed and successfully tested in foil air bearings for long periods up to a temperature of 427 C and at a normal contacting load (during starting and stopping) of 14 kPa based on bearing projected area. The addition of ultra-fine silver to the CdO-graphite has improved the coating endurance. At 427 C, the CdO-graphite-Ag coating performed better than CdO-graphite without silver, both for extended periods at 14 kPa loading and for limited periods at 35 kPa. At 288 C, the coating was tested for an extended period up to 28 kPa and has also successfully completed high-speed shock tests to an acceleration level of 100g.

Bhushan, B.↗
NASA NTRS1960

Halogen Containing Gases as Lubricants for Crystallized Glass Ceramic Metal Combinations at Temperatures to 1500 F

Pyroceram 9608 (a crystallized glass ceramic) has been considered for use in high-temperature bearing and seal applications. One of the problems encountered with Pyroceram is the lack of availability of lubricants for the temperature range in which this material becomes practical. Experiments were conducted with Pyroceram sliding on various nickel- and cobalt-base alloys using reactive halogen-containing gases as lubricants. Friction and wear data were obtained as a function of sliding velocity and temperature. Studies were made with a hemispherical rider (3/16-in. rad., Pyroceram 9608) sliding in a circumferential path on the flat surface of a rotating disk (2(1/2) in. diam., nickel- or cobalt-base alloys). The specimens were run in an atmosphere of the various gases with a load of 1200 grams, a sliding velocity of 3200 feet per minute, and temperatures from 75 to 1500 F. The gas CF2Br-CF2Br was found to be an effective lubricant for Pyroceram 9608 sliding on Hastelloy R-235 and Inconel X up to 1400 F. The gas CF2Cl-CF2Cl provided effective lubrication for Pyroceram sliding on various cobalt-base alloys at 1000 F.

Buckley, Donald H.↗