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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

CARS measurement of velocity in a supersonic jet

It is shown that CW CARS can be used to measure velocity in supersonic flows. The accuracy with which the Doppler shift can be measured is determined through the drift in the laser frequencies. In the experiment described here, it is found that a laser drift error of 10 MHz during the recording of a spectrum would limit the velocity resolution to 34 m/s. It is noted that improved frequency stabilization of the laser sources could lead to a velocity measurement accuracy of several m/s. In the experiment, a 4-W single axial mode argon ion laser is the pump source, and the Stokes-shifted frequency is generated by a 100-mW tunable dye laser.

Gustafson, E. K.↗
NASA NTRS1986

IUE observations of the dwarf novae OY Car in superoutburst

The May 1985 superoutburst of OY Car, an eclipsing member of the SU UMa subclass of dwarf novae, was observed extensively with IUE to obtain phase-resolved spectra throughout several orbital cycles, when the superhump was well developed and lay close in phase to the eclipse. The UV lines and continuum vary with orbital phase and show a strong UV eclipse coincident with the optical eclipse. This implies that the superhump source at eclipse is not a strong contributor in the ultraviolet. The UV emission line spectrum and lack of X-ray eclipse suggest the presence of an extended coronal region. The flux evolution observed is unusual in that gross changes occur during the decline from superoutburst. The later spectra actually appear hotter than spectra earlier in the decline, and suggest that, early on, the inner disk is obscured from view.

Hassall, B. J. M.↗
NASA NTRS1987

Application of CARS to scramjet combustion

A coherent anti-Stokes Raman spectroscopic (CARS) instrument has been developed for measuring simultaneously temperature and N2 - O2 species concentration in hostile flame environments. A folded BOXCARS arrangement was employed to obtain high spatial resolution. Polarization discrimination against the nonresonant background decreased the lower limits of O2 detectivity. The instrument has been primarily employed for validation of computational fluid-dynamics computer-model codes. Comparisons have been made to both the CHARNAL and TEACH codes on a hydrogen diffusion flame with good results.

Antcliff, R. R.↗
NASA NTRS1986

Picosecond coherent anti-Stokes Raman scattering (CARS) study of vibrational dephasing of carbon disulfide and benzene in solution

The vibrational dephasing of the 656/cm mode (nu1, a1g) of CS2 and the 991/cm mode (nu2, a1g) of benzene have been studied as a function of concentration in mixtures with a number of solvents using a ps time-resolved CARS technique. This technique employs two tunable synchronously-pumped mode-locked dye lasers in a stimulated Raman pump, coherent anti-Stokes Raman probe time-resolved experiment. Results are obtained for CS2 in carbon tetrachloride, benzene, nitrobenzene, and ethanol and for benzene nu2 in CS2. The dephasing rates of CS2 nu1 increase on dilution with the polar solvents and decrease or remain constant on dilution with the nonpolar solvents. The CS2/benzene solutions show a contrasting behavior, with the CS2 nu1 dephasing rate being nearly independent of concentration whereas the benzene nu2 dephasing rate decreases on dilution. These results are compared to theoretical models for vibrational dephasing of polyatomic molecules in solution.

Perry, Joseph W.↗
NASA NTRS1988

Measurement of detonation temperature of hydrogen-oxygen mixture by CARS (Coherent Anti-Stokes Raman Spectroscopy)

It was confirmed that CARS is very useful as a temperature measurement method of detonation. By revising the detecting system so that a lot of information can be handled simultaneously like an optical multi-channel analyzer, it is possible to obtain information concerning the detailed three dimensional structure of detonation which has never been obtained.

Tezaki, Atsumu↗
NASA NTRS1989

Opposed jet diffusion flames of nitrogen-diluted hydrogen vs air - Axial LDA and CARS surveys; fuel/air rates at extinction

An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF.

Pellett, G. L.↗
NASA NTRS1990

Fiber-Optic Coupler And Dynamic-Range Enhancer For CARS

Simpler equipment yields higher coupling efficiency with fewer adjustments. In improved scheme for coupling coherent anti-Stokes Raman spectroscopy (CARS) signal from measurement volume to monochromator, optical fiber and two lenses used in place of previous system. Cylindrical lenses focus light from optical fiber into beam of approximately rectangular cross section at input plane of monochromator. Optical wedge diverts part of beam in monochromator to produce less-intense secondary image.

Cutler, Andrew D.↗
NASA NTRS1991

A hardened CARS system utilized for temperature measurements in a supersonic combustor

A coherent anti-Stokes Raman scattering (CARS) system has been hardened for utilization in a NASA Langley supersonic combustion test cell that can obtain temperature cross sections of the flow at three locations. This system is remotely operated and environmentally protected. Measurements were obtained in a scramjet combustor model consisting of a rearward-facing step, followed by an expansion duct. The freestream conditions were Mach 2, with static pressure that ranged from 0.8 to 1.9 atm, and a static temperature of about 800 K. Data for two different flow conditions were obtained that provided a comparison between reacting and nonreacting mixing of injected hydrogen fuel with the combustion-heated supersonic stream.

Antcliff, Richard R.↗
NASA NTRS1992

The evaluation of partial binocular overlap on car maneuverability: A pilot study

An engineering approach to enlarge the helmet mounted display (HMD) field of view (FOV) and maintain resolution and weight by partially overlapping the binocular FOV has received renewed interest among human factors scientists. It is evident, based on the brief literature review, that any panoramic display with a binocular overlap, less than a minimum amount, annoys the viewer, degrades performance, and elicits undesirable behavior. The major finding is that across the 60 deg conditions, subjects moved their heads a greater distance (by about 5 degs on each side) than in the 180 deg condition, presumably to compensate for the lack of FOV. It is quite clear that the study, based on simple car maneuverability and two subjects, reveals differences in FOV, but nothing significant between binocular overlap levels and configurations. This tentatively indicates that some tradeoffs of binocular vision for a larger overall display FOV are acceptable.

Tsou, Brian H.↗
NASA NTRS1998

Development of Synchronously Scanned OPO CARS as a New Probe for Hostile Environments

During the second year of this project, we have focused on three new developments. The first has been the accidental discovery of a degenerate peak at the 0/cm position in the coherent Raman spectrum that is not due to incoherent Rayleigh scattering. The second is the incorporation of a second OPO to provide additional capability to the instrument. The third is the design of a new system that could perform single-shot CARS using a solid state broad-band OPO, The project continues to focus on student research training at the undergraduate level, and three students have worked on the project through this grant. The outcome of this work has been I publication published during this period, 2 publications submitted (by invitation), and 7 presentations given or invited, During this period, one additional grant was funded.

Chen, Peter C.↗
NASA NTRS2002

Cars Thermometry in a Supersonic Combustor for CFD Code Validation

An experiment has been conducted to acquire data for the validation of computational fluid dynamics (CFD) codes used in the design of supersonic combustors. The primary measurement technique is coherent anti-Stokes Raman spectroscopy (CARS), although surface pressures and temperatures have also been acquired. Modern- design- of-experiment techniques have been used to maximize the quality of the data set (for the given level of effort) and minimize systematic errors. The combustor consists of a diverging duct with single downstream- angled wall injector. Nominal entrance Mach number is 2 and enthalpy nominally corresponds to Mach 7 flight. Temperature maps are obtained at several planes in the flow for two cases: in one case the combustor is piloted by injecting fuel upstream of the main injector, the second is not. Boundary conditions and uncertainties are adequately characterized. Accurate CFD calculation of the flow will ultimately require accurate modeling of the chemical kinetics and turbulence-chemistry interactions as well as accurate modeling of the turbulent mixing

Cutler, A. D.↗
NASA NTRS2000

First XMM-Newton Observations of a Cataclysmic Variable II: Spectral Studies of OY Car

We present XMM-Newton X-ray spectra of the disc accreting cataclysmic variable OY Car, which were obtained during the performance verification phase of the mission. These data were taken 4 days after a short outburst. In the EPIC spectra we find strong Iron K(beta) emission with weaker Iron K(alpha) emission together with Silicon and Sulphur lines. The spectra are best fitted with a three temperature plasma model with a partial covering absorber. Multiple temperature emission is confirmed by the emission lines seen in the RGS spectrum and the H/He like intensity ratio for Iron and Sulphur which imply temperatures of approx. 7keV and approx. 3keV respectively.

Ramsay, Gavin↗
NASA NTRS2003

N2/O2/H2 Dual-Pump Cars: Validation Experiments

The dual-pump coherent anti-Stokes Raman spectroscopy (CARS) method is used to measure temperature and the relative species densities of N2, O2 and H2 in two experiments. Average values and root-mean-square (RMS) deviations are determined. Mean temperature measurements in a furnace containing air between 300 and 1800 K agreed with thermocouple measurements within 26 K on average, while mean mole fractions agree to within 1.6 % of the expected value. The temperature measurement standard deviation averaged 64 K while the standard deviation of the species mole fractions averaged 7.8% for O2 and 3.8% for N2, based on 200 single-shot measurements. Preliminary measurements have also been performed in a flat-flame burner for fuel-lean and fuel-rich flames. Temperature standard deviations of 77 K were measured, and the ratios of H2 to N2 and O2 to N2 respectively had standard deviations from the mean value of 12.3% and 10% of the measured ratio.

OByrne, S.↗
NASA NTRS2004

Health Monitoring System for Car Seat

A health monitoring system for use with a child car seat has sensors mounted in the seat to monitor one or more health conditions of the seat's occupant. A processor monitors the sensor's signals and generates status signals related to the monitored conditions. A transmitter wireless transmits the status signals to a remotely located receiver. A signaling device coupled to the receiver produces at least one sensory (e.g., visual, audible, tactile) output based on the status signals.

Susan Vinz Elrod↗
NASA NTRS2006

Targeting Inaccurate Atomic Data in the Eta Car Ejecta Absorption

The input from the laboratory spectroscopist community has on many occasions helped the analysis of the eta Car spectrum. Our analysis has targeted spectra where improved wavelengths and oscillator strengths are needed. We will demonstrate how experimentally derived atomic data have improved our spectral analysis, and illuminate where more work still is needed.

Nielsen, K. E.↗
NASA NTRS2007

Characterization of a Combined CARS and Interferometric Rayleigh Scattering System

This paper describes the characterization of a combined Coherent anti-Stokes Raman Spectroscopy and Interferometric Rayleigh Scattering (CARS-IRS) system by reporting the accuracy and precision of the measurements of temperature, species mole fraction of N2, O2, and H2, and two-components of velocity. A near-adiabatic H2-air Hencken burner flame was used to provide known properties for measurements made with the system. The measurement system is also demonstrated in a small-scale Mach 1.6 H2-air combustion-heated supersonic jet with a co-flow of H2. The system is found to have a precision that is sufficient to resolve fluctuations of flow properties in the mixing layer of the jet.

Tedder, Sarah A.↗
NASA NTRS2009

CARS Temperature Measurements in a Combustion-Heated Supersonic Jet

Measurements were made in a combustion-heated supersonic axi-symmetric free jet from a nozzle with a diameter of 6.35 cm using dual-pump Coherent Anti-Stokes Raman Spectroscopy (CARS). The resulting mean and standard deviation temperature maps are presented. The temperature results show that the gas temperature on the centerline remains constant for approximately 5 nozzle diameters. As the heated gas mixes with the ambient air further downstream the mean temperature decreases. The standard deviation map shows evidence of the increase of turbulence in the shear layer as the jet proceeds downstream and mixes with the ambient air. The challenges of collecting data in a harsh environment are discussed along with influences to the data. The yield of the data collected is presented and possible improvements to the yield is presented are discussed.

Tedder, S. A.↗