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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Laminar Non-Premixed Flames of Gaseous Fuel Aboard the International Space Station

From late 2017 to early 2022, six independent studies with flames of gaseous fuels were conducted on the International Space Station (ISS) in the U.S. combustion research facility. An exploration of flames at the extremes of high sooting and high dilution was conducted with a coaxial coflow burner, where the fuel and oxidizer velocities were typically matched. An investigation of electric-field effects also used the same coflow burner as well as a simple gas-jet burner, with a circular electrode mesh, downstream of the burner, at voltages of either polarity up to 10 kV. A study focused on material flammability in a quiescent atmosphere emulated the burning of condensed-phased fuels using cylindrical burners with a flat perforated outlet instrumented to measure the heat flux to the burner, i.e., emulated fuel. Three studies of soot processes, flame dynamics, and low-temperature combustion used porous spherical burners, yielding a nominally one-dimensional flame structure. The objectives and selected findings of each investigation will be briefly discussed after a short review of the advantages of studying combustion in microgravity, earlier ISS research, and the experimental hardware and its operation.

flames↗
NASA NTRS2021

Dynamic fire and smoke detection and classification for flashover prediction

Flashover is a dangerous phenomenon caused by near-simultaneous ignition of exposed materials. It is one of the major causes of firefighter fatalities. Research has been done using CMOS vision cameras combined with thermal sensors to perform remote detection and dynamic classification of fire and smoke patterns. Tests and experiments have been done to detect fire and smoke remotely. The inexpensive visible and infrared sensors used in the tests corroborate and closely follow the detailed trends recorded by the more expensive (and less mobile) radiometers and thermocouples. Deep neural networks (DNN) have been used to detect, classify and track fire and smoke areas. Real-time segmentation is utilized to measure the fire and smoke boundaries. The segmentations are used to dynamically monitor fluctuations in temperature, fire size and smoke progression in the monitored areas. A fire and smoke progression curve has been drawn to predict the flashover point. In the paper, data analysis and preliminary results will be shown. Keywords: Flashover, fire, smoke, deep learning, visible and infrared vision

Chow, Edward↗
NASA NTRSDate not supplied

Laminar Non-Premixed Flames of Gaseous Fuel Aboard the International Space Station

From late 2017 to early 2022, six independent studies with flames of gaseous fuels were conducted on the International Space Station (ISS) in the U.S. combustion research facility. An exploration of flames at the extremes of high sooting and high dilution was conducted with a coaxial coflow burner, where the fuel and oxidizer velocities were typically matched. An investigation of electric-field effects also used the same coflow burner as well as a simple gas-jet burner, with a circular electrode mesh, downstream of the burner, at voltages of either polarity up to 10 kV. A study focused on material flammability in a quiescent atmosphere emulated the burning of condensed-phased fuels using cylindrical burners with a flat perforated outlet instrumented to measure the heat flux to the burner, i.e., emulated fuel. Three studies of soot processes, flame dynamics, and low-temperature combustion used porous spherical burners, yielding a nominally one-dimensional flame structure. The objectives and selected findings of each investigation will be briefly discussed after a short review of the advantages of studying combustion in microgravity, earlier ISS research, and the experimental hardware and its operation.

flames↗
NASA NTRSDate not supplied

ACME: Advanced Combustion via Microgravity Experiments

From Nov. 2017 to Feb. 2022, the ACME project’s six independent investigations of laminar, non-premixed flames of gaseous fuels were conducted on the International Space Station (ISS) in the Combustion Integrated Rack (CIR). An exploration of flames at the extremes of high sooting and high dilution was conducted with a coaxial coflow burner, where the fuel and oxidizer velocities were typically matched. An investigation of electric-field effects also used the same coflow burner as well as a simple gas-jet burner, with a circular electrode mesh downstream of the burner, at voltages of either polarity up to 10 kV. A study focused on material flammability in a quiescent atmosphere emulated the burning of condensed-phased fuels using cylindrical burners with a flat perforated outlet instrumented to measure the heat flux to the burner, i.e., emulated fuel. Three studies of soot processes, flame dynamics, and low-temperature combustion used porous spherical burners yielding a nominally one-dimensional flame structure. The ACME research will be represented through images and text.

flames↗
NASA NTRS1991

Dynamics of the 4-day wave in the Southern Hemisphere polar stratosphere

Horizontal wind and temperature data are employed to investigate the dynamics of the 4-day wave in the Southern Hemisphere polar stratosphere. They were derived from synoptic maps of satellite-measured brightness temperatures, which were generated using the fast Fourier synoptic mapping technique of Salby (1982). Circulation statistics from these data are compared to those from the NMC operational stratospheric analyses, demonstrating improvements afforded by detailed treatment of asynoptic sampling effects. The 40-day wave is isolated using temporally filtered data. Several events of wave growth and decay are observed in the upper stratosphere during August 1980. Derived zonal-mean and eddy statistics suggest that the 4-day wave results from an instability of the zonal-mean flow near 55-60S, at and above 1 mb. It is inferred from climatological data that the source of the instability is the 'double-jet' structure in the upper stratosphere and mesosphere.

Randel, William J.↗
NASA NTRS1974

Low-temperature relaxations in amorphous polyolefins

The dynamic mechanical relaxation behavior of two series of amorphous polyolefins, was investigated from 4.2 K to the glass transition. Most of the polymers show a damping maximum or plateau in the 40 to 50 K region. Various mechanisms which have been suggested for cryogenic relaxations in amorphous polymers are considered as they might relate to the polyolefins. Two secondary relaxation processes above 80 K are distinguished. A relaxation at about 160 K (beta) in the second and third member of each series is associated with restricted blackbone motion. This process requires a certain degree of chain flexibility since it is not observed in the first member of each series. A lower temperature process (gamma) is observed in each member of the second series and is attributed to motion of the ethyl side group.

Hiltner, A.↗
NASA NTRS2011

Simulated Seasonal Spatio-Temporal Patterns of Soil Moisture, Temperature, and Net Radiation in a Deciduous Forest

The temperature and moisture regimes in a forest are key components in the forest ecosystem dynamics. Observations and studies indicate that the internal temperature distribution and moisture content of the tree influence not only growth and development, but onset and cessation of cambial activity [1], resistance to insect predation[2], and even affect the population dynamics of the insects [3]. Moreover, temperature directly affects the uptake and metabolism of population from the soil into the tree tissue [4]. Additional studies show that soil and atmospheric temperatures are significant parameters that limit the growth of trees and impose treeline elevation limitation [5]. Directional thermal infrared radiance effects have long been observed in natural backgrounds [6]. In earlier work, we illustrated the use of physically-based models to simulate directional effects in thermal imaging [7-8]. In this paper, we illustrated the use of physically-based models to simulate directional effects in thermal, and net radiation in a adeciduous forest using our recently developed three-dimensional, macro-scale computational tool that simulates the heat and mass transfer interaction in a soil-root-stem systems (SRSS). The SRSS model includes the coupling of existing heat and mass transport tools to stimulate the diurnal internal and external temperatures, internal fluid flow and moisture distribution, and heat flow in the system.

Ballard, Jerrell R., Jr.↗
NASA NTRS1977

Output feedback regulator design for jet engine control systems

A multivariable control design procedure based on the output feedback regulator formulation is described and applied to turbofan engine model. Full order model dynamics, were incorporated in the example design. The effect of actuator dynamics on closed loop performance was investigaged. Also, the importance of turbine inlet temperature as an element of the dynamic feedback was studied. Step responses were given to indicate the improvement in system performance with this control. Calculation times for all experiments are given in CPU seconds for comparison purposes.

Merrill, W. C.↗
NASA NTRS1977

Output feedback regulator design for jet engine control systems

A multivariable control design procedure based on the output feedback regulator formulation is described and applied to an F100 turbofan engine model. Full order model dynamics, are incorporated in the example design. The effect of actuator dynamics on closed loop performance is investigated. Also, the importance of turbine inlet temperature as an element of the dynamic feedback is studied. Step responses are given to indicate the improvement in system performance with this control. Calculation times for all experiments are given in CPU seconds for comparison purposes.

Merrill, W.↗
NASA NTRS1972

Thermal dynamic modeling study

Some thermal dynamic requirements associated with the space shuttle vehicle are reviewed. Pertinent scaling laws are discussed and recommendations are offered regarding the need for conducting reduced-scale dynamic tests of major components at elevated temperatures. Items considered are the development and interpretation of thermal dynamic structural scaling laws, the identification of major related problem areas and a presentation of viable model fabrication, instrumentation, and test procedures.

Ojalvo, I. U.↗
NASA NTRS1986

Molecular dissociation and shock-induced cooling in fluid nitrogen at high densities and temperatures

Radiative temperatures and electrical conductivities were measured for fluid nitrogen compressed dynamically to pressures of 18-90 GPa, temperatures of 4000-14,000 K, and densities of 2-3 g/cu cm. The data show a continuous phase transition above 30 GPa shock pressure and confirm that (delta-P/delta-T)v is less than 0, as indicated previously by Hugoniot equation-of-state experiments. The first observation of shock-induced cooling is also reported. The data are interpreted in terms of molecular dissociation, and the concentration of dissociated molecules is calculated as a function of density and temperature.

Radousky, H. B.↗
NASA NTRS1973

Blade dynamics analysis using NASTRAN

The complexities of turbine engine blade vibration are compounded by blade geometry, temperature gradients, and rotational speeds. Experience indicates that dynamics analysis using the finite element approach provides an effective means for predicting vibration characteristics of compressor and turbine blades whose geometry may be irregular, have curved boundaries, and be subjected to high temperatures and speeds. The NASTRAN program was chosen to help analyze the dynamics of normal modes, rotational stiffening and thermal effects on the normal modes, and forced responses. The program has produced reasonable success. This paper presents the analytical procedures and the NASTRAN results, in comparison with a conventional beam element program and laboratory data.

Kuo, P. S.↗
NASA NTRS2002

A Study of Standing Pressure Waves Within Open and Closed Acoustic Resonators

The first section of the results presented herein was conducted on an axisymmetric resonator configured with open ventilation ports on either end of the resonator, but otherwise closed and free from obstruction. The remaining section presents the results of a similar resonator shape that was closed, but contained an axisymmetric blockage centrally located through the axis of the resonator. Ambient air was used as the working fluid. In each of the studies, the resonator was oscillated at the resonant frequency of the fluid contained within the cavity while the dynamic pressure, static pressure, and temperature of the fluid were recorded at both ends of the resonator. The baseline results showed a marked reduction in the amplitude of the dynamic pressure waveforms over previous studies due to the use of air instead of refrigerant as the working fluid. A sharp reduction in the amplitude of the acoustic pressure waves was expected and recorded when the configuration of the resonators was modified from closed to open. A change in the resonant frequency was recorded when blockages of differing geometries were used in the closed resonator, while acoustic pressure amplitudes varied little from baseline measurements.

Daniels, C.↗
NASA NTRS2006

Computing Isentropic Flow Properties of Air/R-134a Mixtures

MACHRK is a computer program that calculates isentropic flow properties of mixtures of air and refrigerant R-134a (tetrafluoroethane), which are used in transonic aerodynamic testing in a wind tunnel at Langley Research Center. Given the total temperature, total pressure, static pressure, and mole fraction of R-134a in a mixture, MACHRK calculates the Mach number and the following associated flow properties: dynamic pressure, velocity, density, static temperature, speed of sound, viscosity, ratio of specific heats, Reynolds number, and Prandtl number. Real-gas effects are taken into account by treating the gases comprising the mixture as both thermally and calorically imperfect. The Redlich-Kwong equation of state for mixtures and the constant-pressure ideal heat-capacity equation for the mixture are used in combination with the departure- function approach of thermodynamics to obtain the equations for computing the flow properties. In addition to the aforementioned calculations for air/R-134a mixtures, a research version of MACHRK can perform the corresponding calculations for mixtures of air and R-12 (dichlorodifluoromethane) and for air/SF6 mixtures. [R-12 was replaced by R-134a because of environmental concerns. SF6 has been considered for use in increasing the Reynolds-number range.]

Kvaternik, Ray↗