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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

NASA Numerical and Experimental Evaluation of UTRC Low Emissions Injector

Computational and experimental analyses of a PICS-Pilot-In-Can-Swirler technology injector, developed by United Technologies Research Center (UTRC) are presented. NASA has defined technology targets for near term (called "N+1", circa 2015), midterm ("N+2", circa 2020) and far term ("N+3", circa 2030) that specify realistic emissions and fuel efficiency goals for commercial aircraft. This injector has potential for application in an engine to meet the Pratt & Whitney N+3 supersonic cycle goals, or the subsonic N+2 engine cycle goals. Experimental methods were employed to investigate supersonic cruise points as well as select points of the subsonic cycle engine; cruise, approach, and idle with a slightly elevated inlet pressure. Experiments at NASA employed gas analysis and a suite of laser-based measurement techniques to characterize the combustor flow downstream from the PICS dump plane. Optical diagnostics employed for this work included Planar Laser-Induced Fluorescence of fuel for injector spray pattern and Spontaneous Raman Spectroscopy for relative species concentration of fuel and CO2. The work reported here used unheated (liquid) Jet-A fuel for all fuel circuits and cycle conditions. The initial tests performed by UTRC used vaporized Jet-A to simulate the expected supersonic cruise condition, which anticipated using fuel as a heat sink. Using the National Combustion Code a PICS-based combustor was modeled with liquid fuel at the supersonic cruise condition. All CFD models used a cubic non-linear k-epsilon turbulence wall functions model, and a semi-detailed Jet-A kinetic mechanism based on a surrogate fuel mixture. Two initial spray droplet size distribution and spray cone conditions were used: 1) an initial condition (Lefebvre) with an assumed Rosin-Rammler distribution, and 7 degree Solid Spray Cone; and 2) the Boundary Layer Stripping (BLS) primary atomization model giving the spray size distribution and directional properties. Contour and line plots are shown in comparison with experimental data (where this data is available) for flow velocities, fuel, and temperature distribution. The CFD results are consistent with experimental observations for fuel distribution and vaporization. Analysis of gas sample results, using a previously-developed NASA NOx correlation, indicates that for sea-level takeoff, the PICS configuration is predicted to deliver an EINOx value of about 3 for the targeted supersonic aircraft. Emissions results at supersonic cruise conditions show potential for meeting the NASA goals with liquid fuel.

Hicks, Yolanda R.↗
NASA NTRS1993

Hybrid rocket combustion study

The objectives of this study of 'pure' or 'classic' hybrids are to (1) extend our understanding of the boundary layer combustion process and the critical engineering parameters that define this process, (2) develop an up-to-date hybrid fuel combustion model, and (3) apply the model to correlate the regression rate and scaling properties of potential fuel candidates. Tests were carried out with a hybrid slab window motor, using several diagnostic techniques, over a range of motor pressure and oxidizer mass flux conditions. The results basically confirmed turbulent boundary layer heat and mass transfer as the rate limiting process for hybrid fuel decomposition and combustion. The measured fuel regression rates showed good agreement with the analytical model predictions. The results of model scaling calculations to Shuttle SRM size conditions are presented.

Strand, L. D.↗
NASA NTRS1989

Analysis of rotary engine combustion processes based on unsteady, three-dimensional computations

A new computer code was developed for predicting the turbulent, and chemically reacting flows with sprays occurring inside of a stratified charge rotary engine. The solution procedure is based on an Eulerian Lagrangian approach where the unsteady, 3-D Navier-Stokes equations for a perfect gas mixture with variable properties are solved in generalized, Eulerian coordinates on a moving grid by making use of an implicit finite volume, Steger-Warming flux vector splitting scheme, and the liquid phase equations are solved in Lagrangian coordinates. Both the details of the numerical algorithm and the finite difference predictions of the combustor flow field during the opening of exhaust and/or intake, and also during fuel vaporization and combustion, are presented.

Raju, M. S.↗
NASA NTRS1990

Analysis of rotary engine combustion processes based on unsteady, three-dimensional computations

A new computer code was developed for predicting the turbulent and chemically reacting flows with sprays occurring inside of a stratified charge rotary engine. The solution procedure is based on an Eulerian Lagrangian approach where the unsteady, three-dimensional Navier-Stokes equations for a perfect gas mixture with variable properties are solved in generalized, Eulerian coordinates on a moving grid by making use of an implicit finite volume, Steger-Warming flux vector splitting scheme, and the liquid phase equations are solved in Lagrangian coordinates. Both the details of the numerical algorithm and the finite difference predictions of the combustor flow field during the opening of exhaust and/or intake, and also during fuel vaporization and combustion, are presented.

Raju, M. S.↗
NASA NTRSDate not supplied

The Influence of Chemical Descriptors on the Reactivity of Potential Hypergolic Fuels With Hydrogen Peroxide

The state-of-the-art for storable hypergolic bipropellant systems is monomethylhydrazine (MMH) and mixed oxides of nitrogen (MON). While MMH and MON provide fast and highly reliable hypergolic ignition with excellent propulsive performance, they suffer from safety concerns impacting their production, cost, and supply to various test and launch facilities. In contrast, identifying and demonstrating low-toxicity fuels hypergolic with rocket grade hydrogen peroxide (H2O2) has been challenging with long ignition delay (IDT) and low propulsive performance affecting their deployment in flight systems. This work describes a preliminary observational study to assess the effects of molecular descriptors suspected to predict the reactivity and hypergolicity of compounds within the same chemical class (i.e., thioamide). The approach centered on evaluating functional groups, electrostatic potential, number of carbons, dipole moment, and adiabatic ionization energy. Thiourea is hypergolic with 89.2 wt.% H2O2 (minimum IDT of 21.9 ms) and was selected as a core fuel to study the reactivity of derived fuels with different functionalities. Additionally, the chemical properties were calculated with the Gaussian16 suite. The results showed that group substitution and generally increased number of carbons on thiourea increases IDT. It was observed that a more positively charged sulfur atom in the thioamide does not increase the reactivity towards H2O2. The dipole moment analysis revealed an overall trend of decreasing IDT due to increasing dipole moment. Finally, a lower adiabatic ionization energy related to increased IDTs for most cases. Additional chemical classes comprising a wider range of functionalities and electrophilic attributes are being investigated in on-going work.

Propellant↗
NASA NTRS2018

Tuning Process for the Modified Magnussen Combustion Model

In the application of CFD to turbulent reacting flows, one of the main limitations to predictive accuracy is the chemistry model. Using a full or skeletal kinetics model may provide good predictive ability, however, at considerable computational cost. Adding the ability to account for the interaction between turbulence and chemistry improves the overall fidelity of a simulation but adds to this cost. An alternative is the use of simple models, such as the Magnussen model, which has negligible computational overhead, but lacks general predictive ability except for cases that can be tuned to the flow being solved. In this paper, a technique will be described that allows the tuning of the Magnussen model for an arbitrary fuel and flow geometry without the need to have experimental data for a particular case. The tuning is based on comparing the results of the Magnussen model and full finite-rate chemistry when applied to perfectly and partially stirred reactor sim- ulations. In addition, a modification to the Magnussen model is proposed that allows the upper kinetic limit for the reaction rate to be set, giving better physical agreement with full kinetic mechanisms. In order to improve the agreement with flame temperatures, the thermal properties of the product species is adjusted to better match the mixture proper- ties of the full mechanism. The combustion model is then applied to the simulation of a representative scramjet flowpath, and the results compared to experimental data and other kinetic models. This procedure allows a simple reacting model to be used in a predictive manner, and affords significant savings in computational costs for CFD simulations.

Norris, A. T.↗
NASA NTRS2001

Modeling and Prediction of Wildfire Hazard in Southern California, Integration of Models with Imaging Spectrometry

Large urban wildfires throughout southern California have caused billions of dollars of damage and significant loss of life over the last few decades. Rapid urban growth along the wildland interface, high fuel loads and a potential increase in the frequency of large fires due to climatic change suggest that the problem will worsen in the future. Improved fire spread prediction and reduced uncertainty in assessing fire hazard would be significant, both economically and socially. Current problems in the modeling of fire spread include the role of plant community differences, spatial heterogeneity in fuels and spatio-temporal changes in fuels. In this research, we evaluated the potential of Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and Airborne Synthetic Aperture Radar (AIRSAR) data for providing improved maps of wildfire fuel properties. Analysis concentrated in two areas of Southern California, the Santa Monica Mountains and Santa Barbara Front Range. Wildfire fuel information can be divided into four basic categories: fuel type, fuel load (live green and woody biomass), fuel moisture and fuel condition (live vs senesced fuels). To map fuel type, AVIRIS data were used to map vegetation species using Multiple Endmember Spectral Mixture Analysis (MESMA) and Binary Decision Trees. Green live biomass and canopy moisture were mapped using AVIRIS through analysis of the 980 nm liquid water absorption feature and compared to alternate measures of moisture and field measurements. Woody biomass was mapped using L and P band cross polarimetric data acquired in 1998 and 1999. Fuel condition was mapped using spectral mixture analysis to map green vegetation (green leaves), nonphotosynthetic vegetation (NPV; stems, wood and litter), shade and soil. Summaries describing the potential of hyperspectral and SAR data for fuel mapping are provided by Roberts et al. and Dennison et al. To utilize remotely sensed data to assess fire hazard, fuel-type maps were translated into standard fuel models accessible to the FARSITE fire spread simulator. The FARSITE model and BEHAVE are considered industry standards for fire behavior analysis. Anderson level fuels map, generated using a binary decision tree classifier are available for multiple dates in the Santa Monica Mountains and at least one date for Santa Barbara. Fuel maps that will fill in the areas between Santa Barbara and the Santa Monica Mountains study sites are in progress, as part of a NASA Regional Earth Science Application Center, the Southern California Wildfire Hazard Center. Species-level maps, were supplied to fire managing agencies (Los Angeles County Fire, California Department of Forestry). Research results were published extensively in the refereed and non-refereed literature. Educational outreach included funding of several graduate students, undergraduate intern training and an article featured in the California Alliance for Minorities Program (CAMP) Quarterly Journal.

Roberts, Dar A.↗
NASA NTRS1993

Small rocket research and technology

Small chemical rockets are used on nearly all space missions. The small rocket program provides propulsion technology for civil and government space systems. Small rocket concepts are developed for systems which encompass reaction control for launch and orbit transfer systems, as well as on-board propulsion for large space systems and earth orbit and planetary spacecraft. Major roles for on-board propulsion include apogee kick, delta-V, de-orbit, drag makeup, final insertions, north-south stationkeeping, orbit change/trim, perigee kick, and reboost. The program encompasses efforts on earth-storable, space storable, and cryogenic propellants. The earth-storable propellants include nitrogen tetroxide (NTO) as an oxidizer with monomethylhydrazine (MMH) or anhydrous hydrazine (AH) as fuels. The space storable propellants include liquid oxygen (LOX) as an oxidizer with hydrazine or hydrocarbons such as liquid methane, ethane, and ethanol as fuels. Cryogenic propellants are LOX or gaseous oxygen (GOX) as oxidizers and liquid or gaseous hydrogen as fuels. Improved performance and lifetime for small chemical rockets are sought through the development of new predictive tools to understand the combustion and flow physics, the introduction of high temperature materials to eliminate fuel film cooling and its associated combustion inefficiency, and improved component designs to optimize performance. Improved predictive technology is sought through the comparison of both local and global predictions with experimental data. Results indicate that modeling of the injector and combustion process in small rockets needs improvement. High temperature materials require the development of fabrication processes, a durability data base in both laboratory and rocket environments, and basic engineering property data such as strength, creep, fatigue, and work hardening properties at both room and elevated temperature. Promising materials under development include iridium-coated rhenium and a ceramic composite of mixed hafnium carbide and tantalum carbide reinforced with graphite fibers.

Schneider, Steven↗
NASA NTRS1987

Heat Shields for Aerobrakes

Performances of three types of heat protectors predicted. Estimates of expected performances of heat shields for conical drag brake presented in paper. Drag brakes, or aerobrakes, being considered as devices for slowing space vehicles when they return to Space Shuttle altitudes from higher satellite altitudes after supply missions. Aerobrakes add less weight than do retro-rockets for same purpose and consume no fuel. Paper provides general information on sensitivity of performance to thermal and physical properties of materials used in aerobrakes. Information useful to both designers of brakes and developers of materials for brake fabrication on aerospace structures.

Pitts, W. C.↗
NASA NTRS1999

Combustion of Metals in Reduced-Gravity and Extra Terrestrial Environments

The combustion of metals is a field with important practical applications in rocket propellants, high-temperature flames, and material synthesis. Also, the safe operation of metal containers in high-pressure oxygen systems and with cryogenic fuels and oxidizers remains an important concern in industry. The increasing use of metallic components in spacecraft and space structures has also raised concerns about their flammability properties and fire suppression mechanisms. In addition, recent efforts to embark on unmanned and manned planetary exploration, such as on Mars, have also renewed the interest in metal/carbon-dioxide combustion as an effective in situ resource utilization technology. In spite of these practical applications, the understanding of the combustion properties of metals remains far behind that of the most commonly used fuels such as hydrocarbons. The lack of understanding is due to the many problems unique to metal- oxidizer reactions such as: low-temperature surface oxidation prior to ignition, heterogeneous reactions, very high combustion temperatures, product condensation, high emissivity of products, and multi-phase interactions. Very few analytical models (all neglecting the influence of gravity) have been developed to predict the burning characteristics and the flame structure details. Several experimental studies attempting to validate these models have used small metal particles to recreate gravity-free conditions. The high emissivity of the flames, rapid reaction, and intermittent explosions experienced by these particles have made the gathering of any useful information on burning rates and flame structure very difficult. The use of a reduced gravity environment is needed to clarify some of the complex interactions among the phenomena described above. First, the elimination of the intrusive buoyant flows that plague all combustion phenomena is of paramount importance in metal reactions due to the much higher temperatures reached during combustion. Second, a low-gravity environment is absolutely essential to remove the destructive effect of gravity on the shape of a molten metal droplet in order to study a spherically symmetric condition with large bulk samples. The larger size of the spherical metal droplet and the longer burning times available in reduced gravity extend the spatial and temporal dimensions to permit careful probing of the flame structure and dynamics. Third, the influence of the radiative heat transfer from the solid oxides can be studied more carefully by generating a stagnant spherical shell of condensed products undisturbed by buoyancy.

Branch, M.C.↗
NASA NTRS2001

Solid Inflammability Boundary at Low-Speed (SIBAL)

This research program is concerned with the effect of low-speed, concurrent flow on the spreading and extinction processes of flames over solid fuels. The primary objective is to verify the theoretically predicted extinction boundary, using oxygen percentage and flow velocity as coordinates. Of particular interest are the low-speed quenching limits and the existence of the critical oxygen flammability limit. Detailed flame spread characteristics, including flame spread rate, flame size, and flame structure are sought. Since the predicted flame behavior depends on the inclusion of flame and surface radiation, the measured results will also be used to assess the importance of radiative heat transfer by direct comparison to a comprehensive numerical model. The solid fuel used in this experiment is a custom-made fabric consisting of a 1:1 blend of cotton and fiberglass. This choice was made following an extensive search to yield a material with favorable properties, namely, rollability, non-cracking behavior during combustion, strength after combustion, and flammability in a range of oxygen limits permissible within the Combustion Integrated Rack (CIR) on the International Space Station. At the present time, an effort is being made to characterize both the radiative properties of the fuel and the flame spreading behavior in normal gravity at reduced pressure. These will provide a basis for comparison with the microgravity results as well as aid in bracketing the anticipated flammability boundary for the flight experiment. An overview of recent work, with emphasis on theoretical results, is presented.

T'ien, James↗
NASA NTRS1997

An Investigation of SiC/SiC Woven Composite Under Monotonic and Cyclic Loading

The desirable properties in ceramic matrix composites (CMCs), such as high temperature strength, corrosion resistance, high toughness, low density, or good creep resistance have led to increased use of CMCs in high-speed engine structural components and structures that operate in extreme temperature and hostile aero-thermo-chemical environments. Ceramic matrix composites have been chosen for turbine material in the design of 21 st-century civil propulsion systems to achieve high fuel economy, improved reliability, extended life, and reduced cost. Most commercial CMCs are manufactured using a chemical vapor infiltration (CVI) process. However, a lower cost fabrication known as melt-infiltration process is also providing CMCs marked for use in hot sections of high-speed civil transports. The scope of this paper is to report on the material and mechanical characterization of the CMCs subjected to this process and to predict the behavior through an analytical model. An investigation of the SiC/SiC 8-harness woven composite is ongoing and its tensile strength and fatigue behavior is being characterized for room and elevated temperatures. The investigation is being conducted at below and above the matrix cracking stress once these parameters are identified. Fractography and light microscopy results are being studied to characterize the failure modes resulting from pure uniaxial loading. A numerical model is also being developed to predict the laminate properties by using the constituent material properties and tow undulation.

Lang, J.↗
NASA NTRS2000

Thermophysics Characterization of Kerosene Combustion

A one-formula surrogate fuel formulation and its quasi-global combustion kinetics model are developed to support the design of injectors and thrust chambers of kerosene-fueled rocket engines. This surrogate fuel model depicts a fuel blend that properly represents the general physical and chemical properties of kerosene. The accompanying gaseous-phase thermodynamics of the surrogate fuel is anchored with the heat of formation of kerosene and verified by comparing a series of one-dimensional rocket thrust chamber calculations. The quasi-global combustion kinetics model consists of several global steps for parent fuel decomposition, soot formation, and soot oxidation, and a detailed wet-CO mechanism. The final thermophysics formulations are incorporated with a computational fluid dynamics model for prediction of the combustor efficiency of an uni-element, tri-propellant combustor and the radiation of a kerosene-fueled thruster plume. The model predictions agreed reasonably well with those of the tests.

Wang, Ten-See↗
NASA NTRS2001

Thermophysics Characterization of Kerosene Combustion

A one-formula surrogate fuel formulation and its quasi-global combustion kinetics model are developed to support the design of injectors and thrust chambers of kerosene-fueled rocket engines. This surrogate fuel model depicts a fuel blend that properly represents the general physical and chemical properties of kerosene. The accompanying gaseous-phase thermodynamics of the surrogate fuel is anchored with the heat of formation of kerosene and verified by comparing a series of one-dimensional rocket thrust chamber calculations. The quasi-global combustion kinetics model consists of several global steps for parent fuel decomposition, soot formation, and soot oxidation and a detailed wet-CO mechanism to complete the combustion process. The final thermophysics formulations are incorporated with a computational fluid dynamics model for prediction of the combustion efficiency of an unielement, tripropellant combustor and the radiation of a kerosene-fueled thruster plume. The model predictions agreed reasonably well with those of the tests.

Wang, Ten-See↗
NASA NTRS1995

Combustion Module 1: Spacelab Racks Integrated at the Lewis Research Center for the First Time

The Combustion Module-1 (CM-1), NASA's largest (over 1800 lb) and one of the most sophisticated combustion experiments ever to fly on the Spacelab, will be carried on the first Microgravity Science Laboratory (MSL-1) mission aboard the space shuttle flight STS-84 in April 1997. The CM-1 project is a stepping stone to the space station era, because the hardware can support multiple investigators on the same mission and can be integrated at user locations and shipped to the launch site. CM-1 is being developed to accommodate microgravity combustion experiments that are designed to help explain and predict the behavior of combustion processes. Although the two principal investigators for CM-1 are both studying combustion processes, their investigations are quite different. Professor Paul D. Ronney of the University of Southern California will examine the Structures of Flame Balls at Low Lewis Numbers (SOFBALL), in which a variety of fuel-lean gaseous mixtures fill the combustion chamber and are ignited. Professor Gerard M. Faeth of the University of Michigan will investigate Laminar Soot Processes (LSP) by studying the key properties of burning gas jets of fuel, employing different fuels and nozzle sizes.

Source record↗
NASA NTRS1986

On the Theory of Type 1 X-Ray Bursts: The Energetics of Bursts and the Nuclear Fuel Reservoir in the Envelope

The observed properties of type 1 X-ray bursts from 4U/MXB 1636-53 and those of models of thermonuclear flashes on accreting neutron stars are compared. Ways to explain variations in the burst recurrence properties without an apparent correlation with the accretion rate, including the rapid succession of bursts at intervals 10 min are discussed. The strongest X-ray bursts, which occur after a very long interval, are well described by thermonuclear flash models with simple accumulation of accreted fuel, and a spherically symmetric structure in the burning shell. The majority of observed bursts, however, occur after much shorter intervals, and radiate much smaller amounts of energy, by a factor of up to 10 times that predicted by the spherical models. An ignition mechanism of the bursts is proposed in terms of elemental mixing and dissipative heating associated with hydrodynamical instabilities in the neutron star envelope caused by angular momentum carried inward by accreted gas.

Fujimoto, Masayuki Y.↗
NASA NTRS1998

The NASA Low-Pressure Turbine Flow Physics Program

An overview of the NASA Lewis Low-Pressure Turbine (LPT) Flow Physics Program will be presented. The program was established in response to the aero-engine industry's need for improved LPT efficiency and designs. Modern jet engines have four to seven LPT stages, significantly contributing to engine weight. In addition, there is a significant efficiency degradation between takeoff and cruise conditions, of up to 2 points. Reducing the weight and part count of the LPT and minimizing the efficiency degradation will translate into fuel savings. Accurate prediction methods of LPT flows and losses are needed to accomplish those improvements. The flow in LPT passages is at low Reynolds number, and is dominated by interplay of three basic mechanisms: transition, separation and wake interaction. The affecting parameters traditionally considered are Reynolds number, freestream turbulence intensity, wake frequency parameter, and the pressure distribution (loading). Three-dimensional effects and additional parameters, particularly turbulence characteristics like length scales, spectra and other statistics, as well as wake turbulence intensity and properties also play a role. The flow of most interest is on the suction surface, where large losses are generated as the flow tends to separate at the low Reynolds numbers. Ignoring wakes, a common flow scenario, there is laminar separation, followed by transition on the separation bubble and turbulent reattachment. If transition starts earlier the separation will be eliminated and the boundary layer will be attached leading to the well known bypass transition issues. In contrast, transition over a separation bubble is closer to free shear layer transition and was not investigated as well, particularly in the turbine environment. Unsteadiness created by wakes complicates the picture. Wakes induce earlier transition, and the calmed regions trailing the induced turbulent spots can delay or eliminate separation via shear stress modification. Three-dimensional flow physics and geometry will have strong effects. Altogether a very complex and challenging problem emerges. The objective of the program is to provide improved models and physical understanding of the complex flow, which are essential for accurate prediction of flow and losses in the LPT. Experimental, computational and analytical work as complementing and augmenting approaches are used. The program involves industry, universities and research institutes, and other government laboratories. It is characterized by strong interaction among participants, quick dissemination of results, and responsiveness to industry's needs. The presentation will describe the work elements. Highlighting some activities in progress are experiments on simulated blade suction surface in low-speed wind tunnels, on curved wall, and on a flat-plate, both with pressure gradient. In the area of computation, assessment of existing models is performed using RANS (Reynolds Averaged Navier Stokes) simulations. Laminar flow DNS was completed. Analytical studies of instability and receptivity in attached and separated flows were started. In the near future the program is moving to include wake effects and development of improved modeling. Experimental work in preparation stages are: (1) Addition of wakes to the curved tunnel experiment; (2) Low-speed rotating rig experiment on GE90 engine LPT; and (3) Transonic cascade. In the area of computation, it is expected to move from model assessment towards development of improved models. In addition, a new project of Large Eddy Simulation (LES) of LPT is to begin and will provide numerical data bases. It is planned to implement the emerging improved models in a multistage turbomachinery code and to validate against the GE90 engine LPT.

Ashpis, David E.↗
NASA NTRS1992

Calculation of installation effects within performance computer programs

Gasturbine engine components as compressors, burners and turbines are usually tested on rigs prior to installation into an engine. In the engine, the component behaviour is different due to a variety of reasons. The installation effects are caused by small geometrical differences due to nonrepresentative rig operating temperatures and pressures, by different gas properties and Reynolds numbers and by radial as well as circumferential temperature and pressure profiles at the inlet to the component. For highly accurate performance predictions these rig-to-engine effects have to be taken into account. Traditionally the term "installation" is also used for describing all the differences in engine operation and behaviour between toothed and aircraft. Intake and afterbody drag, power offtake and bleed as well as intake pressure losses and inlet flow distortion have significant impact on airflow, thrust, specific fuel consumption and compressor stability. Using modem performance synthesis programs all these effects can be simulated reasonably well.

J Kurzke↗