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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Hydrogen-rich syngas production from the steam co-gasification of low-density polyethylene and coal refuse

Gasification provides a promising pathway for transforming waste materials into valuable products, such as fuels and chemicals. Here, this study investigates the steam co-gasification of low-density polyethylene (LDPE) and compressed thickener underflow, representative of coal refuse (CR), in a drop tube reactor. The effects of feed blend ratio (0–100 wt% LDPE) and temperature (800–1000 °C) on syngas composition, tar formation, and process efficiency are examined. The high volatility of LDPE makes it more reactive than CR but also promotes the formation of 2–7 ring aromatic tars. Increasing temperature improves carbon conversion efficiency (CCE), cold gas efficiency (CGE), and syngas yield, although the lower heating value (LHV) of syngas decreases. Hydrogen is the dominant gas product, reaching 59 vol% with the H 2 /CO molar ratio ranging from 2.27 to 4.74. Synergistic effects from alkali and alkali earth metals (AAEMs), particularly K and Ca, in CR ash enhance syngas yield by catalyzing char gasification and tar cracking. Hematite (Fe 2 O 3 ) and ash from sub-bituminous/bituminous coals are explored as tar reforming catalysts. Fe 2 O 3 achieves 100 % tar reforming efficiency, while coal ash, with a lower Fe 2 O 3 content (15 wt%), is less effective at cracking polycyclic aromatic hydrocarbons, particularly naphthalene. These findings demonstrate the flexibility of co-gasification, allowing precise tuning of syngas characteristics for specific downstream applications. Further optimization of waste-derived catalysts could enhance the economic viability of gasification in waste-to-energy processes.

01 COAL, LIGNITE, AND PEAT↗
NASA NTRS1988

Ply-level failure analysis of a graphite/epoxy laminate under bearing-bypass loading

A combined experimental and analytical study was conducted to investigate and predict the failure modes of a graphite/epoxy laminate subjected to combined bearing and bypass loading. Tests were conducted in a test machine that allowed the bearing-bypass load ratio to be controlled while a single-fastener coupon was loaded to failure in either tension or compression. Onset and ultimate failure modes and strengths were determined for each test case. The damage-onset modes were studied in detail by sectioning and micrographing the damaged specimens. A two-dimensional, finite-element analysis was conducted to determine lamina strains around the bolt hole. Damage onset consisted of matrix cracks, delamination, and fiber failures. Stiffness loss appeared to be caused by fiber failures rather than by matrix cracking and delamination. An unusual offset-compression mode was observed for compressive bearing-bypass laoding in which the specimen failed across its width along a line offset from the hole. The computed lamina strains in the fiber direction were used in a combined analytical and experimental approach to predict bearing-bypass diagrams for damage onset from a few simple tests.

Naik, R. A.↗
NASA NTRS1990

Ply-level failure analysis of a graphite/epoxy laminate under bearing-bypass loading

A combined experimental and analytical study was conducted to investigate and predict the failure modes of a graphite/epoxy laminate subjected to combined bearing and bypass loading. Tests were conducted in a test machine that allowed the bearing-bypass load ratio to be controlled while a single-fastener coupon was loaded to failure in either tension or compression. Onset and ultimate failure modes and strengths were determined for each test case. The damage-onset modes were studied in detail by sectioning and micrographing the damaged specimens. A two-dimensional, finite-element analysis was conducted to determine lamina strains around the bolt hole. Damage onset consisted of matrix cracks, delamination, and fiber failures. Stiffness loss appeared to be caused by fiber failures rather than by matrix cracking and delamination. An unusual offset-compression mode was observed for compressive bearing-bypass loading in which the specimen failed across its width along a line offset from the hole. The computed lamina strains in the fiber direction were used in a combined analytical and experimental approach to predict bearing-bypass diagrams for damage onset from a few simple tests.

Naik, R. A.↗
DOE OSTI2019

Using cylindrical implosions to investigate hydrodynamic instabilities in convergent geometry

Hydrodynamic instabilities such as the Rayleigh–Taylor (RT) and Richtmyer–Meshkov instabilities disrupt inertial confinement fusion (ICF) implosions through the growth of 3D perturbations. Growth of these 3D imperfections at the interfaces of an ICF capsule during implosion lead to mixing between materials that is detrimental to performance. These instabilities have been studied extensively in planar geometry, but such experiments lack the effects of convergence in spherical implosions. While several studies have been performed in spherical geometry, these often lack a direct means to measure perturbation growth. Experiments in cylindrical geometry include convergence effects while maintaining direct diagnostic access. Although cylinders have less compression than spheres, they do provide an excellent platform to validate modeling for convergent geometries. The problem with previous cylindrical implosion experiments was that the convergence ratios were limited to ~4. With the National Ignition Facility (NIF), larger cylindrical targets can be driven to convergences of 10–15 while maintaining a large enough final diameter to measure perturbation growth. This paper reviews the design process used to both benchmark radiation hydrodynamics codes and enable 1D post-processed simulations to explore design space to separate compression effects from acceleration/deceleration RT instability. Results from 1D simulations suggest that cylindrical implosions on the NIF can produce high-convergence experiments to validate RT instability growth for ICF implosions.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Polar symmetric flow of a viscous compressible atmosphere; an application to Mars

The atmosphere is assumed to be driven by a polar symmetric temperature field and the equations of motion in pressure ratio coordinates are linearized by considering the zero order in terms of a thermal Rossby number R delta I/(2a omega) sq where delta T is a measure of the latitudinal temperature gradient. When the eddy viscosity is greater than 1 million sq cm/sec, the boundary layer extends far up into the atmosphere, making the geostrophic approximation invalid for the bulk of the atmosphere. A temperature model for Mars was used which was based on Mariner 9 infrared spectral data with a 30% increase in the depth averaged temperature from the winter pole to the subsolar point. The results obtained for the increase in surface pressure from the subsolar point to the winter pole, as a function of eddy viscosity and with no-slip conditions imposed at the surface, are given.

Pirraglia, J. A.↗
NASA NTRS1981

A compressed cloud in the Vela supernova remnant

Strong interstellar absorption lines of C I, arising from the two excited fine-structure levels, are found in IUE observations of HD 72350 (type B4 III). An analysis of the excited-level populations of C I gives local temperature and pressure limits, and auxiliary data on the limit of column density for excited O I and the carbon ionization help to establish that (1) the local temperature is within the limits of 25-100 K, and (2) the pressure/Boltzmann's constant ratio is at least 10 to the 4.3/cu cm K, despite its small size. This high-pressure cloud is discussed in terms of shock compression by the Vela supernova blast wave, along with the relationship of this kind of cloud compression to star formation and to the origin of the characteristic filamentary emission arcs seen in Vela and other supernova remnants

Jenkins, E. B.↗
NASA NTRS1989

Geometric transformations for video compression and human teleoperator display

A method for bandwidth-efficient processing of video imagery to be viewed by the teleoperator of a remotely-operated vehicle on which the camera is mounted is described. The method comprises image coding, transmission, and reconstruction. It is assumed that the transmission bandpass is the limiting factor rather than encoding/decoding schemata; that image coding and reconstruction will be done within the general abilities of the NASA/TI Programmable Remapper; and that the ratio of retained local detail to the operator's visual resolution is held constant throughout the large-field image that is seen. Novel features include that the compression and reconstruction address certain characteristics of the human visual system, that two-way communication controls a moving 'fovea' in the transformation, and that resolution varies over the image. Conventional motivations accommodated include the Cartesian raster-scan nature of available imagers and display devices and a need for low bandwidth in the image transmission. Unique image processing hardware, NASA's Programmable Remapper, allows demonstration of the method. Once refined, the technology could be adapted to special purpose imagers and display devices, or otherwise to dedicated image processing hardware.

Juday, Richard D.↗
NASA NTRS1944

The "limiting line" in mixed subsonic and supersonic flow of compressible fluids

It is well known that the vorticity for any fluid element is constant if the fluid is non-viscous and the change of state of the fluid is isentropic. When a solid body is placed in a uniform stream, the flow far ahead of the body is irrotational. Then if the flow is further assumed to be isentropic, the vorticity will be zero over the whole filed of flow. In other words, the flow is irrotational. For such flow over a solid body, it is shown by Theodorsen that the solid body experiences no resistance. If the fluid has a small viscosity, its effect will be limited in the boundary layer over the solid body and the body will have a drag due to the skin friction. This type of essentially isentropic irrotational flow is generally observed for a streamlined body placed in a uniform stream, if the velocity of the stream is kept below the so-called "critical speed." At the critical speed or rather at a certain value of the ratio of the velocity of the undisturbed flow and the corresponding velocity of sound, shock waves appear. This phenomenon is called the "compressibility bubble." Along a shock wave, the change of state of the fluid is no longer isentropic, although still adiabatic. This results in an increase in entropy of the fluid and generally introduces vorticity in an originally irrotational flow. The increase in entropy of the fluid is, of course, the consequence of changing part of the mechanical energy into heat energy. In other words, the part of fluid affected by the shock wave has a reduced mechanical energy. Therefore, with the appearance of shock waves, the wake of the streamline body is very much widened, and the drag increases drastically. Furthermore, the accompanying change in the pressure distribution over the body changes the aerodynamic moment acting on it and in the case of an airfoil decreases the lift force. All these consequences of the breakdown of isentropic irrotational flow are generally undesirable in applied aerodynamics. Its occurrence should be delayed as much as possible by modifying the shape or contour of the body. However, such endeavor will be very much facilitated if the cause or the criterion for the breakdown can be found first.

MACH NUMBER↗
DOE OSTI2018

Bright, Mechanosensitive Upconversion with Cubic-Phase Heteroepitaxial Core–Shell Nanoparticles

Lanthanide-doped nanoparticles are an emerging class of optical sensors, exhibiting sharp emission peaks, high signal-to-noise ratio, photostability, and a ratiometric color response to stress. The same centrosymmetric crystal field environment that allows for high mechanosensitivity in the cubic-phase (α), however, contributes to low upconversion quantum yield (UCQY). In this work, we engineer brighter mechanosensitive upconverters using a core–shell geometry. Sub-25 nm α-NaYF 4 :Yb,Er cores are shelled with an optically inert surface passivation layer of ~4.5 nm thickness. Using different shell materials, including NaGdF 4 , NaYF 4 , and NaLuF 4 , we study how compressive to tensile strain influences the nanoparticles’ imaging and sensing properties. All core–shell nanoparticles exhibit enhanced UCQY, up to 0.14% at 150 W/cm 2 , which rivals the efficiency of unshelled hexagonal-phase (β) nanoparticles. Additionally, strain at the core–shell interface can tune mechanosensitivity. In particular, the compressive Gd shell results in the largest color response from yellow-green to orange or, quantitatively, a change in the red to green ratio of 12.2 ± 1.2% per GPa. For all samples, the ratiometric readouts are consistent over three pressure cycles from ambient to 5 GPa. Furthermore, heteroepitaxial shelling significantly improves signal brightness without compromising the core’s mechano-sensing capabilities and further, promotes core–shell cubic-phase nanoparticles as upcoming in vivo and in situ optical sensors.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1993

Compressibility effects on rotor forces in the leakage path between a shrouded pump impeller and its housing

A modified approach to Childs' previous work on fluid-structure interaction forces in the leakage path between an impeller shroud and its housing is presented in this paper. Three governing equations consisting of continuity, path-momentum, and circumferential-momentum equations were developed to describe the leakage path inside a pump impeller. Radial displacement perturbations were used to solve for radial and circumferential force coefficients. In addition, impeller-discharge pressure disturbances were used to obtain pressure oscillation responses due to precessing impeller pressure wave pattern. Childs' model was modified from an incompressible model to a compressible barotropic-fluid model (the density of the working fluid is a function of the pressure and a constant temperature only). Results obtained from this model yielded interaction forces for radial and circumferential force coefficients. Radial and circumferential forces define reaction forces within the impeller leakage path. An acoustic model for the same leakage path was also developed. The convective, Coriolis, and centrifugal acceleration terms are removed from the compressible model to obtain the acoustics model. A solution due to impeller discharge pressure disturbances model was also developed for the compressible and acoustics models. The results from these modifications are used to determine what effects additional perturbation terms in the compressible model have on the acoustic model. The results show that the additional fluid mechanics terms in the compressible model cause resonances (peaks) in the force coefficient response curves. However, these peaks only occurred at high values of inlet circumferential velocity ratios greater than 0.7. The peak pressure oscillation was shown to occur at the wearing ring seal. Introduction of impeller discharge disturbances with n = 11 diametral nodes showed that maximum peak pressure oscillations occurred at nondimensional precession frequencies of f = 6.4 and f = 7.8 for this particular pump. Bolleter's results suggest that for peak pressure oscillations to occur at the wearing ring seal, the nondimensional excitation frequency should be on the order of f = 2.182 for n = 11. The resonances found in this research do not match the excitation frequencies predicted by Bolleter. At the predicted peak excitation frequencies given by Bolleter, the compressible model shows an attenuation of the pressure oscillations at the seal exit. The compressibility of the fluid does not have a significant influence on the model at low values of nondimensional excitation frequency. At high values of nondimensional frequency, the effects of compressibility become more significant. For the acoustic analysis, the convective, Coriolis, and centrifugal acceleration terms do affect the results to a limited extent for precession excitation and to a large extent for a pressure excitation when the fluid operates at relatively high Mach numbers.

Cao, Nhai The↗
NASA NTRS1975

Numerical calculation of unsteady transonic potential flow over helicopter rotor blades

The small-disturbance potential equation appropriate to a helicopter in forward flight is derived. This equation is then solved for the flow over a nonlifting transonic rotor blade, using a completely implicit scheme that is an extension of the Murman-Cole mixed-difference technique. The flow in the tip region is most unsteady in the decelerating flow region, after the blade passes the psi = 90 deg azimuthal station. The unsteadiness appears to be caused by expansion and compression waves that move slowly upstream of the blade as the relative incident flow decelerates. The influence of aspect ratio, advance ratio, and Mach number on this process is discussed.

Caradonna, F. X.↗
NASA NTRS1976

Notched and Unnotched Fatigue Behavior of Angle-Ply Graphite/Epoxy Composites

The axial fatigue behavior of both notched and unnotched graphite/epoxy composites was studied. In unnotched studies, conducted on a 0/+ or - 30 3S AS/3501 laminate, S-N curves were determined for various stress ratios R using simply supported test specimens. Apparent fatigue limits in tension-tension (T-T) and compression-compression (C-C) cycling occurred at about 60% of the respective static strengths. The overall results were expressed in the form of a constant life diagram showing the relationship between mean stress and stress amplitude. The diagram illustrates a skew-symmetry in fatigue life caused by the relatively low compressive strength of the unrestrained test specimens used. In effect, a maximum in fatigue properties occurs at a positive value of mean stress. Results are of significance in situations where structural members are buckling or crippling critical in design.

Ramani, S. V.↗
NASA NTRS1978

Compressible flow across narrow passages: Comparison of theory and experiment for face seals

Computer calculation for determining compressible flow across radial face seals were compared with measured results obtained in a seal simulator rig at pressure ratios to 0.9 (ambient pressure/sealed pressure). In general, the measured and calculated leakages across the seal dam agreed within 3 percent. The resultant loss coefficient, dependent upon the pressure ratio, ranged from 0.47 to 0.68. The calculated pressures were within 2.5 N/cu um of the measured values.

Allen, G. P.↗
NASA NTRS1979

On the stability of the boundary layer on a transonic swept wing

Both incompressible and compressible linear stability theory are applied to the three-dimensional compressible boundary layer on a particular transonic sweptback wing of infinite span. A spatial stability theory is used which identifies the growth direction with the real part of the complex angle of the group velocity. It is found that in the forward, but not the rear, crossflow instability region, the maximum amplification rates of the steady disturbances may be calculated to within about 10% by the incompressible stability theory. There is little difference between the sixth and eighth-order compressible theories. The maximum amplification rate of the steady disturbances at any chordwise station is closely related to the maximum crossflow at that station independent of the Reynolds number. For other than crossflow instability, there can be large differences between the incompressible and compressible theories, both as to the amplification rate and the angle of the wavenumber vector for maximum instability. Amplitude ratios of individual wave components are obtained by integrating the spatial amplification rate along the growth direction subject to the constraint that the wavenumber vector is irrotational. This procedure yields steady disturbances aligned with the local potential flow direction whose wavelengths are nearly independent of downstream distance.

Mack, L. M.↗
NASA NTRS1992

Numerical investigation of performance degradation of wings and rotors due to icing

The aerodynamic load characteristics and the performance degradation of moderate aspect ratio wings and rotors with simulated glaze leading-edge ice have been studied using a three-dimensional, compressible Navier-Stokes solver. The effect of a splitter plate at the wing root on both clean and iced wing configurations has been studied and the results are compared with the experiment. A significant difference has been observed with and without splitter plates in the magnitude of flow separation and aerodynamic loading at the inboard stations for the iced wing at 8-deg angle of attack. Inviscid calculations were performed and compared with viscous calculations to investigate whether the performance of iced swept wings can be inexpensively predicted using Euler methods. It is shown that inviscid calculations predict higher aerodynamic loading than viscous calculations, and cannot model separation effects. A typical nonlifting helicopter rotor in forward flight condition is also studied, and the penalty due to the leading-edge ice formation on the required torque is numerically demonstrated.

Kwon, Oh J.↗
NASA NTRS1992

Leading edge sweep effects in generic three-dimensional sidewall compression scramjet inlets

A computational and experimental study of generic 3D sidewall compression inlets is conducted to examine the effects of fore and aft leading edge sweep on the internal shock structure. Inlets with leading edge sweeps of +30 deg and -30 deg with sidewall compression angles of 6 deg were tested in the NASA Langley Mach 4 air tunnel at a geometric contraction ratio of 1.87. The principal difference in performance was determined to be in the mass capture. Spillage was identified as having two components: a pressure induced component and a sweep induced component. It was found that while the direction of the leading edge sweep had a large influence on the spillage, the pressure effects were more important.

Cozart, Aaron B.↗
NASA NTRS1993

Production of Lunar Concrete Using Molten Sulfur

The United States has made a commitment to go back to the moon to stay in the early part of the next century. In order to achieve this objective it became evident to NASA that a Lunar Outpost will be needed to house scientists and astronauts who will be living on the moon for extended periods of time. A study has been undertaken by the authors and supported by NASA to study the feasibility of using lunar regolith with different binders such as molten sulfur, epoxy or hydraulic cement as a construction material for different lunar structures. The basic premise of this study is that it will be more logical and cost effective to manufacture lunar construction materials utilizing indigenous resources rather than transporting needed materials from earth. Lunar concrete (made from Hydraulic Cement and lunar soil) has been studied and suggested as the construction material of choice for some of the lunar projects. Unfortunately, its hydration requires water which is going to be a precious commodity on the moon. Therefore this study explores the feasibility of using binders other than hydraulic cement such as sulfur or epoxy with lunar regolith as a construction material. This report describes findings of this study which deals specifically with using molten sulfur as a binder for Lunar concrete. It describes laboratory experiments in which the sulfur to lunar soil simulant ratios by weight were varied to study the minimum amount of sulfur required to produce a particular strength. The compressive and tensile strengths of these mixes were evaluated. Metal and fiber glass fibers were added to some of the mixes to study their effects on the compressive and tensile strengths. This report also describes experiments where the sulfur is melted and mixed with the lunar regolith in a specially designed vacuum chamber. The properties of the produced concrete were compared to those of concrete produced under normal pressure.

Omar, Husam A.↗
DOE OSTI2020

An experimental and kinetic modeling study of cyclopentane and dimethyl ether blends

Cyclopentane is a suitable naphthene, or cycloalkane, in a palette for multi-component gasoline surrogate fuels due to its presence in market fuels and its relevance to alkyl substituted cyclopentanes also present. However, the previous oxidation studies of cyclopentane have primarily focused on neat mixtures. Blending cyclopentane with dimethyl ether in this work therefore serves to inform our understanding of, and improve predictive models for, multi-component mixtures. Here, the auto-ignition of cyclopentane/dimethyl ether blends was studied in a high-pressure shock tube and in a rapid compression machine. A wide range of temperatures (650 – 1350 K) and elevated pressures of 20 and 40 bar were studied at equivalence ratios of 0.5, 1.0 and 2.0 in air for two blending ratios (30/70 and 70/30 mole% cyclopentane/di-methyl ether mixtures). A detailed kinetic model for cyclopentane was revised to capture the measured ignition delay times and apparent heat release rates in this study. Literature ignition delay time, jet-stirred reactor, and laminar burning velocity measurements of neat cyclopentane were used as additional validation. Improvements to the kinetic model were based on recent literature studies related to sub-models including cyclopentene and cyclopentadiene which allowed the removal of previous local rate-constant optimizations. Low temperature reactivity of cyclopentane was found to be controlled by the branching ratio between concerted elimination of HO͘ 2 and the strained formation of Q&#775OOH radicals in agreement with previous studies. In this study, the low branching ratio of Q&#775OOH formation increases the influence of a competing consumption pathway for cyclopentyl-peroxy (CPTO͘ 2 J) radicals. The sensitivity of the simulated ignition delay times to the formation of cyclopentyl hydroperoxide (CPTO 2 H), from CPTO͘ 2 J and HO͘ 2 , is discussed. The current model is used to analyze the influence of dimethyl ether on the reactivity of cyclopentane in the context of previous literature studies of dimethyl ether binary blends with ethanol and toluene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗