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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Considerations for the temperature stratification in a pre-burn constant-volume combustion chamber

In recent years, the Engine Combustion Network (ECN) has developed as a worldwide reference for understanding and describing engine combustion processes, successfully bringing together experimental and numerical efforts. Since experiments and numerical simulations both target the same boundary conditions, an accurate characterization of the stratified environment that is inevitably present in experimental facilities is required. The difference between the core-, and pressure-derived bulk-temperature of pre-burn combustion vessels has been addressed in various previous publications. Additionally, thermocouple measurements have provided initial data on the boundary layer close to the injector nozzle, showing a transition to reduced ambient temperatures. The conditions at the start of fuel injection influence physicochemical properties of a fuel spray, including near nozzle mixing, heat release computations, and combustion parameters. To address the temperature stratification in more detail, thermocouple measurements at larger distances from the spray axis have been conducted. Both the temperature field prior to the pre-combustion event that preconditions the high-temperature, high-pressure ambient, as well as the stratification at the moment of fuel injection were studied. To reveal the cold boundary layer near the injector with a better spatial resolution, Rayleigh scattering experiments and thermocouple measurements at various distances close to the nozzle have been carried out. The impact of the boundary layers and temperature stratification are illustrated and quantified using numerical simulations at Spray A conditions. Next to a reference simulation with a uniform temperature field, six different stratified temperature distributions have been generated. These distributions were based on the mean experimental temperature superimposed by a randomized variance, again derived from the experiments. The results showed that an asymmetric flame structure arises in the computed results when the temperature stratification input is used. In these predictions, first-stage ignition is advanced by 24 $\mu$s , while second-stage ignition is delayed by 11 $\mu$s. At the same time a lift-off length difference between the top and the bottom of up to 1.1 mm is observed. Furthermore, the lift-off length is less stable over time. Given the shown dependency, the temperature data is made available along with the vessel geometry data as a recommended basis for future numerical simulations.

42 ENGINEERING↗
DOE OSTI2021

Flow visualisation in real-size optical injectors of conventional, additised, and renewable gasoline blends

Research on renewable and alternative fuels is crucial for improving the energy and environmental efficiency of modern gasoline internal combustion engines. To highlight the influence of fuel rheological and thermodynamic properties on phase change and atomisation processes, three types of gasoline blends were tested. More specifically, the campaign comprised a reference gasoline, an ethanol/gasoline blend (10% v/v) representative of renewable fuels, and an additised gasoline sample treated with viscoelasticity-inducing agents. High-speed imaging of the transient two-phase flow field arising in the internal geometry and the near-nozzle spray region of gasoline injectors was performed employing Diffuse Backlight Illumination. The metallic body of a commercial injector was modified to fit transparent tips realising two nozzle layouts, namely a two-hole real size model resembling the Engine Combustion Network spray G injector and an enraged replica with an offset hole. Experiments were conducted at realistic operating conditions comprising an injection pressure of 100 bar and ambient pressures in the range of 0.1–6.0 bar to cover the entire range of chamber pressures prevailing in Gasoline Direct Injection engines. The action of viscoelastic additives was verified to have a suppressive effect on in-nozzle cavitation (6% reduction in cavitation extent) , while also enhancing spray atomisation at flash-boing conditions, in a manner resembling the more volatile gasoline/ethanol blends. Finally, persisting liquid ligaments were found to form after the end of injection for the additised sample, owing to the surfactant nature of the additives.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Spectral induced polarization signatures of smoldering remediation enhanced with colloidal activated carbon: An experimental study

Monitoring the remediation of soil and groundwater contaminated by organic compounds remains highly challenging. The spectral induced polarization (SIP) method exhibits significant promise for monitoring changes to the electrical properties of soils that are undergoing remediation. Thermal treatments, such as smoldering combustion, have become established remediation techniques for destroying contaminants. Smoldering combustion is now being supported by colloidal activated carbon (CAC), with CAC able to adsorb contaminants and supplement the fuel source for destroying contaminants. The objective of this study is to investigate the potential of SIP for tracking the smoldering remediation of imitated field soils supplemented with CAC. SIP column experiments were first conducted to assess the response of SIP to varying concentrations of CAC in field soils that contain, or do not contain, organic material (OM). Here these results demonstrate that increasing OM and CAC contents increase both the real and imaginary components of the complex conductivity, with the imaginary conductivity also showing frequency dependence. Next, a suite of smoldering and SIP column experiments was conducted to investigate if SIP can detect changes in imitated field soils of varying OM and CAC contents that have been remediated by smoldering combustion. The SIP results on the examined soils both before and after smoldering show that SIP can detect changes in the real conductivity, and particularly the imaginary conductivity, between different soil compositions and different stages of the remediation process. High resolution scanning electron microscopy (SEM) imaging was performed on all samples to validate the SIP and smoldering experiments, confirming significant reductions in carbon after smoldering. Overall, this study suggests that SIP has potential to detect changes in the electrical properties of field soils due to the addition of remedial fluids like CAC and contaminant destruction by smoldering remediation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Synthesis and Characterization of Sol–Gel Auto Combustion-Derived Ce/Zr-Substituted Strontium Hexaferrite Nanoparticles

In this work, Ce/Zr-substituted strontium hexaferrite (SrFe{sub 12}O{sub 19}) nanoparticles have been synthesized by the sol–gel auto combustion method and the synthesized samples were annealed at 900 {sup ∘}C for 3 h. The powder XRD pattern revealed that all the diffraction peaks match the hexagonal phase of strontium hexaferrite and the lattice parameters are determined. The VSM study revealed that the values of saturation magnetization, coercivity and remanent magnetization are decreased for the Ce/Zr-substituted strontium hexaferrite sample. Thermal analysis reveals the formation of a hexagonal phase above 670 {sup ∘}C. The specific vibration band of hexagonal ferrite was observed in the range 400–600 cm{sup −1}. The FE-SEM image shows that the particles are spherical shaped and particle size varied from 37 to 44 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Electronic structure, magnetic and structural properties of Ni doped ZnO nanoparticles

Highlights: • XRD, and HR-TEM results show the single phase nature of Ni doped ZnO nanoparticles. • dc magnetization results indicate the RT-FM in Ni doped ZnO nanoparticles. • Ni L{sub 3,2} edge NEXAFS spectra infer that Ni ions are in +2 valence state. • O K edge NEXAFS spectra show that O vacancy increases with Ni doping in ZnO. - Abstract: We report structural, magnetic and electronic structural properties of Ni doped ZnO nanoparticles prepared by auto-combustion method. The prepared nanoparticles were characterized by using X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and dc magnetization measurements. The XRD and HR-TEM results indicate that Ni doped ZnO nanoparticles have single phase nature with wurtzite lattice and exclude the presence of secondary phase. NEXAFS measurements performed at Ni L{sub 3,2}-edges indicates that Ni ions are in +2 valence state and exclude the presence of Ni metal clusters. O K-edge NEXAFS spectra indicate an increase in oxygen vacancies with Ni-doping, while Zn L{sub 3,2}-edge show the absence of Zn-vacancies. The magnetization measurements performed at room temperature shows that pure and Ni doped ZnO exhibits ferromagnetic behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Absorption spectroscopy based high-speed oxygen concentration measurements at elevated gas temperatures

A sensor built upon tunable diode laser absorption spectroscopy (TDLAS) has been developed for concentration measurements in high-temperature (up to 800 K) gas streams; while the sensor measures gas oxygen and water concentration, temperature and pressure, this work focuses on the challenges and solutions to transient oxygen measurement. A 760-nm diode laser was used to probe a pair of oxygen absorption transitions, and a Herriott cell based multi-pass arrangement was utilized to compensate for the extremely weak oxygen absorption as well as the high gas temperature. This multi-pass arrangement provides a 4297.4-mm absorption path length across a 76.2-mm diameter duct, and an O 2 detection limit ([O 2 ] where SNR=1) of ca. 0.1%. Laboratory validation of the HITRAN spectral parameters of the chosen absorption transitions was performed over a range of high temperatures and oxygen concentrations relevant to engine-exhaust applications. The insensitivity of the Herriott cell arrangement to vibrations and spatial temperature gradients was demonstrated. Conclusions from applications to single- and multi-cylinder engine exhaust are presented and demonstrate the new sensor’s ability to measure fast intra-cycle gas-property transients, and provide insights relevant to advancing internal-combustion-engine technology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1986

Effects on optical systems from interactions with oxygen atoms in low earth orbits

Modifications of material surface properties due to interactions with ambient atomic oxygen have been observed on surfaces facing the orbital direction in low earth orbits. Some effects are very damaging to surface optical properties while some are more subtle and even beneficial. Most combustible materials are heavily etched, and some coatings, such as silver and osmium, are seriously degraded or removed as volatile oxides. The growth of oxide films on metals and semiconductors considered stable in dry air was measured. Material removal, surface roughness, reflectance, and optical densities are reported. Effects of temperature, contamination, and overcoatings are noted.

Peters, P. N.↗
NASA NTRS1949

Altitude performance of AN-F-58 fuels in J35-C-3 single combustor

Three fuel blends conforming to AN-F-58 specifications were tested in order to determine the influence of boiling temperatures and aromatic content on altitude performance in single combustor of 4000-pound-thrust turbojet engine. At simulated engine conditions from an altitude of 30,000 to an altitude of 60,000 feet and 85-percent rated engine speed, the three AN-F-58 fuels showed little difference in performance.

COMBUSTION - EFFECT OF ENGINE OPERATING CONDITIONS↗
NASA NTRS1951

Correlation of physical properties with molecular structure for some dicyclic hydrocarbons having high thermal-energy release per unit volume

As part of a program to study the correlation between molecular structure and physical properties of high-density hydrocarbons, the net heats of combustion, melting points, boiling points, densities, and kinematic viscosities of some hydrocarbons in the 2-n-alkylbiphenyl, 1,1-diphenylalkane, diphenylalkane, 1,1-dicyclohexylalkane, and dicyclohexylalkane series are presented.

Wise, P H↗
NASA NTRS1958

Effect of Fuel Variables on Carbon Formation in Turbojet-Engine Combustors

Report presents the results of an investigation of the effects of fuel properties and of a number of fuel additives on combustion-chamber carbon deposition and exhaust-gas smoke formation in a single tubular turbojet-engine combustor. Limited tests were conducted with a number of the fuels in several full-scale turbojet engines to verify single-combustor data.

Jonash, Edmund R↗
NASA NTRS1998

Development of Tripropellant CFD Design Code

A tripropellant, such as GO2/H2/RP-1, CFD design code has been developed to predict the local mixing of multiple propellant streams as they are injected into a rocket motor. The code utilizes real fluid properties to account for the mixing and finite-rate combustion processes which occur near an injector faceplate, thus the analysis serves as a multi-phase homogeneous spray combustion model. Proper accounting of the combustion allows accurate gas-side temperature predictions which are essential for accurate wall heating analyses. The complex secondary flows which are predicted to occur near a faceplate cannot be quantitatively predicted by less accurate methodology. Test cases have been simulated to describe an axisymmetric tripropellant coaxial injector and a 3-dimensional RP-1/LO2 impinger injector system. The analysis has been shown to realistically describe such injector combustion flowfields. The code is also valuable to design meaningful future experiments by determining the critical location and type of measurements needed.

Farmer, Richard C.↗
DOE OSTI2016

FUEL PERFORMANCE MODELING OF FECRAL CLADDING FAILURE DURING LOSS OF COOLANT CONDITIONS

Accident tolerant materials are defined as those that provide significantly increased response time in the event of an accident while providing similar or improved performance as the conventional UO2/Zircaloy-4 fuel rods during normal operation. One avenue for materials to demonstrate enhanced accident tolerance is to have improved reaction (e.g., oxidation) kinetics with steam, resulting in slower hydrogen (or other combustible gases) generation rate, while maintaining acceptable thermo-mechanical properties, fuel-clad interactions, and fission product behavior. Due to their improved reaction kinetics with steam compared to Zircaloy-4, iron-chromium-aluminum (FeCrAl) alloys are being considered as an accident tolerant cladding material. In order to determine whether FeCrAl alloys are indeed accident tolerant materials, comparisons between conventional zirconium-based claddings under accident conditions is required. To this end, we have developed a burst (failure) criterion for FeCrAl using existing experimental data for first-generation alloys. This model was incorporated into the BISON fuel performance code to perform comparative studies with Zircaloy-4 cladding tubes under non-oxidizing and oxidizing LOCA conditions. The separate effects LOCA conditions considered were adopted from the PUZRY and REBEKA test series. Due to the fact that FeCrAl alloys have a larger thermal absorption cross-section and higher stiffness than Zircaloy-4, cladding thickness will be smaller for FeCrAl than for Zircaloy-4. Three different cladding thicknesses were analyzed in this work. The results indicate that for both non-oxidizing (PUZRY) and oxidizing (REBEKA) LOCA conditions, FeCrAl has similar burst behavior (i.e., time to burst and pressure at burst) as Zircaloy-4. It should be noticed that this study used data for first-generation FeCrAl alloys to develop the burst criterion. Although no burst data?currently exists for C35M (a second-generation FeCrAl alloy under development at Oak Ridge National Laboratory), improved burst behavior is anticipated. As burst data for C35M becomes available the burst criterion will be updated and the simulations revisited to determine the accident tolerance of second-generation FeCrAl alloys.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Fuel performance modeling of FeCrAl cladding failure during loss of coolant conditions

Accident tolerant materials are defined as those that provide significantly increased response time in the event of an accident while providing similar or improved performance as the conventional UO2/Zircaloy-4 fuel rods during normal operation. One avenue for materials to demonstrate enhanced accident tolerance is to have improved reaction (e.g., oxidation) kinetics with steam, resulting in slower hydrogen (or other combustible gases) generation rate, while maintaining acceptable thermo-mechanical properties, fuel-clad interactions, and fission product behavior. Due to their improved reaction kinetics with steam compared to Zircaloy-4, iron-chromium-aluminum (FeCrAl) alloys are being considered as an accident tolerant cladding material. In order to determine whether FeCrAl alloys are indeed accident tolerant materials, comparisons between conventional zirconium-based claddings under accident conditions is required. To this end, we have developed a burst (failure) criterion for FeCrAl using existing experimental data for first-generation alloys. This model was incorporated into the BISON fuel performance code to perform comparative studies with Zircaloy-4 cladding tubes under non-oxidizing and oxidizing LOCA conditions. The separate effects LOCA conditions considered were adopted from the PUZRY and REBEKA test series. Due to the fact that FeCrAl alloys have a larger thermal absorption cross-section and higher stiffness than Zircaloy-4, cladding thickness will be smaller for FeCrAl than for Zircaloy-4. Three different cladding thicknesses were analyzed in this work. The results indicate that for both non-oxidizing (PUZRY) and oxidizing (REBEKA) LOCA conditions, FeCrAl has similar burst behavior (i.e., time to burst and pressure at burst) as Zircaloy-4. It should be noticed that this study used data for first-generation FeCrAl alloys to develop the burst criterion. Although no burst data?currently exists for C35M (a second-generation FeCrAl alloy under development at Oak Ridge National Laboratory), improved burst behavior is anticipated. As burst data for C35M becomes available the burst criterion will be updated and the simulations revisited to determine the accident tolerance of second-generation FeCrAl alloys.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Improvements to Modeling Capabilities of ATF Concepts in the BISON Fuel Performance Code

Research into accident tolerant materials for the fuel and cladding in Light Water Reactors has been at the forefront of the nuclear fuel research community since the events that occurred at the Fukushima Daiichi nuclear power plant in March 2011. Accident tolerant materials are defined as those that provide significantly increased response time in the event of an accident while providing similar or improved performance as the conventional UO{sub 2}/zirconium-based cladding fuel rods during normal operation. In particular, qualitative attributes for materials with enhanced accident tolerance include improved reaction (e.g., oxidation) kinetics with steam, resulting in lower hydrogen (or other combustible gases) generation rate, while maintaining acceptable thermo-mechanical properties, fuel-clad interactions, and fission-product behavior. Through it's Office of Nuclear Energy, the United States Department of Energy (U.S. DOE) has accelerated research in this area through the Fuel Cycle Research and Development (FCRD) Advanced Fuels Campaign (AFC). The goal of the AFC Accident Tolerant Fuel (ATF) program is to guide selection of promising concepts for insertion into a commercial reactor as part of a lead test rod or assembly in 2022. Given the aggressive development schedule, it is impossible to perform a comprehensive set of experiments to provide material characterization data. Therefore, the AFC is utilizing computational analysis tools in an effort to understand the proposed accident tolerant materials. The two materials of interest in this work are iron-chromium-aluminum (FeCrAl) cladding and U{sub 3}Si{sub 2}. From a fuel performance standpoint, the correlations available to describe the behavior of these two materials is limited. Therefore, as additional experimental data becomes available and correlations are updated, the fuel performance models must be updated as well to assure that the material models reflect the latest experimental findings. In this paper we demonstrate the importance of utilizing the latest state-of-the-art models for fuel performance simulations by comparing the change in the updated thermal conductivity model for U{sub 3}Si{sub 2} fuel and oxidation model for FeCrAl cladding alloys using the BISON fuel performance code under normal operating conditions. The results indicate that the latest thermal conductivity model for U{sub 3}Si{sub 2} results in fuel centerline temperatures that are on average approximately 3% higher than the previous model. For the oxidation behavior of FeCrAl alloys the new model predicts observable but small oxide thickness (6 μm) compared to the previous model which predicted essentially zero oxide scale formation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Palladium oxidation leads to methane combustion activity: Effects of particle size and alloying with platinum

Pd- and Pt-based catalysts are highly studied materials due to their widespread use in emissions control catalysis. However, claims continue to vary regarding the active phase and oxidation state of the metals. Different conclusions have likely been reached due to the heterogeneous nature of such materials containing various metal nanoparticle sizes and compositions, which may each possess unique redox features. In this work, using uniform nanocrystal catalysts, we study the effect of particle size and alloying on redox properties of Pd-based catalysts and show their contribution to methane combustion activity using operando quick extended x-ray absorption fine structure measurements. Results demonstrate that for all studied Pd sizes (3 nm–16 nm), Pd oxidation directly precedes CH 4 combustion to CO 2 , suggesting Pd oxidation as a prerequisite step to methane combustion, and an oxidation pretreatment shows equal or better catalysis than a reduction pretreatment. Results are then extended herein to uniform alloyed Pt x Pd 1–x nanoparticles, where oxidative pretreatments are shown to enhance low-temperature combustion. In these uniform alloys, we observe a composition-dependent effect with Pt-rich alloys showing the maximum difference between oxidative and reductive pretreatments. In Pt-rich alloys, we initially observe that the presence of Pt maintains Pd in a lower-activity reduced state. However, with time on stream, PdO eventually segregates under oxidizing combustion conditions, leading to a slowly increasing activity. Overall, across particle sizes and alloy compositions, we relate increased catalytic activity to Pd oxidation, thus shedding light on previous contrasting results related to the methane combustion activity of these catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗