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At least 271 records · Page 15

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NASA NTRS1993

Simultaneous pressure measurement and high-speed photography study of cavitation in a dynamically loaded journal bearing

Cavitation of the oil film in a dynamically loaded journal bearing was studied using high-speed photography and pressure measurement simultaneously. Comparison of the visual and pressure data provided considerable insight into the occurence and non-occurrence of cavitation. It was found that (1), cavitation typically occurred in the form of one bubble with the pressure in the cavitation bubble close to the absolute zero; and (2), for cavitation-producing operating conditions, cavitation did not always occur; with the oil film then supporting a tensile stress.

Sun, D. C.↗

NASA NTRS1938

Fuel Consumption of a Carburetor Engine at Various Speeds and Torques

An investigation was conducted to obtain fuel-consumption curves for a single-cylinder engine with a Wright 1820-G and Pratt & Whitney 1340-H cylinder at varying speeds, manifold pressures, and air-fuel ratios. The 1340- H cylinder was tested at speeds from 1,200 to 2,400 r.p.m. and at manifold pressures from 21 to 38 inches of mercury absolute. Less than extensive tests were made of the 1820-G cylinder. The results of the tests showed that the minimum brake fuel consumption was obtained when the engines were operating at high torques and at speeds from 60 to 70 percent of the rated speed. The fuel consumption increased at an increasing rate as the torque was reduced; and, at 45 percent of maximum torque, the fuel consumption was 20 percent higher than at maximum torque when the engines were operating at 70 percent of rated speed. Minimum specific fuel consumption was obtained at the same air-fuel ratio regardless of compression ratio. No improvement in fuel consumption was obtained when mixtures leaner than an air-fuel ratio of 15.5 were used. The leanest mixture ratio on which the engine with the 1340-H cylinder would operate smoothly was 18.5 and the spark advance for maximum power with this mixture ratio was 50 degrees B.T.C. A method is discussed for reducing the amount of testing necessary to obtain curves for minimum brake fuel consumption.

Schey, Oscar W↗

NASA NTRS1955

Performance of a single fuel-vaporizing combustor with six injectors adapted for gaseous hydrogen

The combustor was operated over a range of inlet-air pressures from 5.3 to 24.0 inches of mercury absolute and inlet-air reference velocities from 60 to 100 feet per second. The combustion efficiencies obtained with the six configurations varied from about 65 to 95 percent for a combustor temperature-rise range of 200 degrees to 1400 degrees F. At a temperature rise of 1200 degrees F (near-rated engine conditions), the spread in efficiencies of the six configurations was about 5 percent. Efficiencies in the range of 65 to 85 percent were obtained at operating conditions beyond the burning range of conventional jet fuels. A fuel-injector configuration that fed only gaseous hydrogen fuel into the standard liquid-fuel-vaporizing tubes generally gave the highest efficiencies. This configuration minimizes the possibility of combustion in the fuel-vaporizing tubes and could be easily adapted to the full-scale engine combustor.

Wear, Jerrold D↗

NASA NTRS1957

Performance of an Experimental Annular Turbojet Combustor with Methane and Propane

Combustion efficiencies obtained with gaseous methane were compared with reported data obtained with gaseous propane for the same experimental combustor configuration. The combustion efficiencies obtained with methane were 98, 91, and 77 percent at simulated flight altitudes of 56,000, 70,000 and 80,000 feet, corresponding to combustor inlet-air pressures from 15 to 5 inches of mercury absolute. Combustion efficiencies with propane were equivalent to those with methane up to a simulated altitude of 70,000 feet. At the most severe conditions investigated propane operated with a higher efficiency and over a wider range of fuel-air ratio than methane.

Norgren, Carl T↗

NASA NTRS1943

Exhaust-stack nozzle area and shape for individual cylinder exhaust-gas jet-propulsion system

This report presents the results of an investigation conducted on the effect of exhaust-stack nozzle area, shape, and length on engine power, jet thrust, and gain in net thrust (engine propeller plus jet). Single-cylinder engine data were obtained using three straight stacks 25, 44, and 108 inches in length; an S-shaped stack, a 90 degree bend, a 180 degree bend, and a short straight stack having a closed branch faired into it. Each stack was fitted with nozzles varying in exit area from 0.91 square inch to the unrestricted area of the stack of 4.20 square inches. The engine was generally operated over a range of engine speeds from 1300 to 2100 r.p.m, inlet-manifold pressures from 22 to 30 inches of mercury absolute, and a fuel-air ratio of 0.08. The loss in engine power, the jet thrust, and the gain in net thrust are correlated in terms of several simple parameters. An example is given for determining the optimum nozzle area and the overall net thrust.

Pinkel, Benjamin↗

NASA NTRS1994

Simultaneous pressure measurement and high-speed photography study of cavitation in a dynamically loaded journal bearing

Cavitation of the oil film in a dynamically loaded journal bearing was studied using high-speed photography and pressure measurement simultaneously. Comparison of the visual and pressure data provided considerable insight into the occurrence and nonoccurrence of cavitation. It was found that (1) for the submerged journal bearing, cavitation typically occurred in the form of one bubble with the pressure in the cavitation bubble close to the absolute zero; and (2) for cavitation-producing operating conditions, cavitation did not always occur; with the oil film then supporting a tensile stress.

Sun, D. C.↗

NASA NTRS1999

Undercooling, Rapid Solidification, and Relations to Processing in Low Earth Orbit (A Review of the Works of Bingbo Wei)

This is a survey of the published works of Prof. Bingbo Wei of the Department of Applied Physics at Northwestern Polytechnical University, Xian P.R. China. Transformations among solid - liquid - and vapor are fundamental to the foundations of life and culture on Earth. The development and understanding of materials has lead the evolution and advancement of the human race since antiquity. Materials and fluids research is continuing today, with us standing on the shoulders of those that have gone before us. Technological and scientific breakthroughs continue due to studies of greater and greater complexity, that include for example, research done at high pressures, in high magnetic fields, at temperatures near absolute zero, and in the low gravity environment of low Earth orbit. Of particular technological importance is the liquid to solid transformation of metals and alloys. Solidification processing is generally the most important factor in the final properties of objects made of metal; and undercooling is the fundamental driving force for all solidification. The interest and resources dedicated to the study of solidification and undercooling are great and World wide. For many years B. Wei and his coworkers have been studying undercooling and rapid solidification and have amassed a significant body of published research in this important field, contributing to the leading edge of the state-of-the-art. It is the goal of this memorandum to provide a review of the research of B. Wei et al.; publications in Chinese are included in the reference list but are not discussed. The bulk of Wei's work has been in the area of undercooling and rapid solidification [1-11, 13-16, 24-36] with papers dating back to 1989, the same year he earned his Ph.D. Below, discussions of Wei's undercooling and rapid solidification research have been grouped together mostly on the basis of alloy type, such as eutectic, intermetallic, or monotectic.

deGroh, Henry C., III↗

NASA NTRS1947

Investigation of X24C-2 10-Stage Axial-Flow Compressor: Effect of Inlet-Air Pressure and Temperature of Performance - 2

Effect of inlet-air pressure and temperature on the performance of the X24-2 10-Stage Axial-Flow Compressor from the X24C-2 turbojet engine was evaluated. Speeds of 80, 89, and 100 percent of equivalent design speed with inlet-air pressures of 6 and 12 inches of mercury absolute and inlet-air temperaures of approximately 538 degrees, 459 degrees,and 419 degrees R ( 79 degrees, 0 degrees, and minus 40 degrees F). Results were compared with prior investigations.

Finger, Harold B.↗

NASA NTRSDate not supplied

Numerical Simulation of No-Vent Chill and Fill of a Large Liquid Hydrogen Tank

To enable the design of future in-space cryogenic propellant transfer vehicles, high accuracy models of the cryogenic propellant transfer process are desired. For in-space refueling applications, accurate simulations are desired of the propellant tank chilldown and no-vent fill (NVF) process in order to estimate the amount of propellant required, to determine the maximum sustainable flow rate to fill the tank, and to establish a timeline for the filling process. NVF is a complex process that involves numerous two-phase heat and mass transfer phenomena, such as boiling at the wall and evaporation and condensation at the liquid/vapor interface. In recent years, progress has been made in developing a numerical modeling technique using the Generalized Fluid System Simulation Program (GFSSP) that has been validated against several small-scale liquid nitrogen NVF tests. This paper presents GFSSP numerical model validation against three liquid hydrogen NVF tests on a large-scale propellant tank. Comparing the GFSSP model to the data for pressure, fill level, and wall temperature, the mean absolute percentage error is below 20% across the range of simulated conditions, indicating very good predictive agreement for this large-scale hydrogen NVF test series.

Alok Majumdar↗

NASA NTRSDate not supplied

Numerical Simulation of No-Vent Chill and Fill of a Large Liquid Hydrogen Tank

Alok Majumdar↗

DOE OSTI2020

Spatially resolved density measurements of singlet delta oxygen in a non-equilibrium atmospheric pressure plasma jet by molecular beam mass spectrometry

Singlet delta oxygen (O 2 (a 1 Δ g )), the first electronically excited state of O 2 , plays an important role in many applications. We report the first measurements of absolute densities of O 2 (a 1 Δ g ) in an atmospheric pressure plasma jet (APPJ) by molecular beam mass spectrometry (MBMS). The ability to measure axial and radial profiles of O 2 (a 1 Δ g ) impinging on a substrate in the effluent of the APPJ is a key advantage of the MBMS diagnostic method over previously reported optical methods. Here, the measured large O 2 (a 1 Δ g ) densities in the APPJ effluent, up to one order of magnitude higher than the O density, underline the potential importance of O 2 (a 1 Δ g ) in many applications using APPJs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

Spatial profile of argon (1s 5 ) metastables in an electron beam generated plasma

Electron beams with an applied magnetic field generate a secondary cold plasma with a selective chemical composition, featuring low-energy ions and metastable species in the discharge periphery, ideal for low-damage plasma treatment of material substrates. In this work, we studied the plasma generated by an e-beam using a 4 kV voltage in a pure argon gas environment under a magnetic field of 150 G and in the pressure range of 25–90 mTorr. We measured the absolute spatial density profile of argon (1 s 5 ) metastables in an electron beam generated plasma by laser-induced fluorescence and found it to be of the order of 10 16 m −3 . The electron temperature and the electron density measured by a Langmuir probe were of the order of 10 16 m −3 and less than an eV respectively. Electron-impact quenching was identified as a significant loss mechanism for the Ar(1s 5 ) state, leading to the saturation of the metastable density at higher pressures. Outside the primary ionization region, the spatial distribution of argon metastables followed a linear diffusion profile, indicating negligible additional production in those regions.

EEDF↗

NASA NTRS1991

Range optimization for a supersonic aircraft

Range optimal trajectories for an aircraft flying in the vertical plane are obtained from Pontryagin's Minimum Principle. Control variables are load factor n which appears nonlinearly in the equations of motion and throttle setting eta, which appears only linearly. Both controls are subject to fixed bounds, namely eta between values of 0 and 1 and absolute value of n not greater than n(max). Additionally, a dynamic pressure limit is imposed, which represents a first-order state-inequality constraint. For fixed flight time, fixed initial coordinates, and partially fixed final coordinates, the effect of the load factor limit absolute value of n not greater than n(max) is studied. Upon varying n(max), six different switching structures are obtained. All trajectories involve singular control along arcs with active dynamic pressure limit.

Seywald, Hans↗

NASA NTRS1956

Component Performance Investigation of J71 Experimental Turbine I : Over-all Performance with 97-percent-design Stator Areas

The over-all component performance characteristics of a J71 experimental three-stage turbine with 97 percent design stator areas were determined over a range of speed and pressure ratio at inlet-air conditions of approximately 35 inches of mercury absolute and 700 degrees R. The turbine break internal efficiency at design operating conditions was 0.877; the maximum efficiency of 0.886 occurred at a pressure ratio of 4.0 at 120 percent of design equivalent rotor speed. In general, the turbine yielded a wide range of efficient operation, permitting flexibility in the choice of different modes of engine operation. Limiting blade loading of the third rotor was approached but not obtained over the range of conditions investigated herein. At the design operating point, the turbine equivalent weight flow was approximately 105 percent of design. Choking of the third-rotor blades occurred at design speed and an over-all pressure ratio of 4.2.

Schum, Harold J↗

NASA NTRS1956

Ram-jet Performance

The ram jet is basically one of the most dimple types of aircraft engine. It consists only of an inlet diffuser, a combustion system, and an exit nozzle. A typical ram-jet configuration is shown in figure 128. The engine operates on the Brayton cycle, and ideal cycle efficiency depends only on the ratio of engine to ambient pressure. The increased, engine pressures are obtained by ram action alone, and for this reason the ram jet has zero thrust at zero speed. Therefore, ram-jet-powered aircraft must be boosted to flight speeds close to a Mach number of 1.0 before appreciable thrust is generated by the engine. Since pressure increases are obtained by ram action alone, combustor-inlet pressures and temperatures are controlled by the flight speed, the ambient atmospheric condition, and by the efficiency of the inlet diffuser. These pressures and temperatures, as functions of flight speed and altitude, are shown in figure 129 for the NACA standard atmosphere and for practical values of diffuser efficiency. It can be seen that very wide ranges of combustor-inlet temperatures and pressures may be encountered over the ranges of flight velocity and altitude at which ram jets may be operated. Combustor-inlet temperatures from 500 degrees to 1500 degrees R and inlet pressures from 5 to 100 pounds per square inch absolute represent the approximate ranges of interest in current combustor development work. Since the ram jet has no moving parts in the combustor outlet, higher exhaust-gas temperatures than those used in current turbojets are permissible. Therefore, fuel-air ratios equivalent to maximum rates of air specific impulse or heat release can be used, and, for hydrocarbon fuels, this weight ratio is about 0.070. Lower fuel-air ratios down to about 0.015 may also be required to permit efficient cruise operation. This fuel-air-ratio range of 0.015 to 0.070 used in ram jets can be compared with the fuel-air ratios up to 0.025 encountered in current turbojets. Ram-jet combustor-inlet velocities range from 150 to 400 feet per second. These high linear velocities combined with the relatively low pressure ratios obtainable in ram jets require that the pressure drop through the combustor be kept low to avoid excessive losses in cycle efficiency. It has been estimated that, for a long-range ram-jet engine, an increase in pressure loss of one dynamic head would require a compensating 1-percent increase in combustion efficiency. Therefore, combustor pressure-loss coefficients (pressure drop/impact pressure) of the order of 1 to 4 are found in most current engines. The operating conditions described impose major problems in the design of stable and efficient ram-jet combustion systems. This chapter presents a survey of ram-jet combustor research and, where possible, points out criteria that may be useful in the design of ram-jet combustion systems.

Cervenko, A. J.↗

NASA NTRS1976

Absolute integrated intensity for the nu-1 sulfur dioxide band

The absolute integrated intensity of the IR vibration-rotation nu-1 SO2 band was measured using the linear portion of the curve of growth. Infrared spectroscopic-absorption cell measurements were performed on sulfur dioxide at partial pressures less than 0.15 torr with nitrogen added to give a total pressure of 705 torr, the path length being 4 mm. The absolute integrated intensity was determined to be 112.0 plus or minus 2.6/cm/sq (atm cm) at 296 K at the 95% confidence level.

Pilon, P. J.↗

NASA NTRS2007

Pressure and Temperature Dependence of the Reaction of Vinyl Radical with Ethylene

This work reports measurements of absolute rate coefficients and Rice-Ramsperger-Kassel-Marcus (RRKM) master equation simulations of the C2H3 + C2H4 reaction. Direct kinetic studies were performed over a temperature range of 300-700 K and pressures of 20 and 133 mbar. Vinyl radicals (H2C=CH) were generated by laser photolysis of vinyl iodide (C2H31) at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals through absorption at 423.2 nm. Measurements at 20 mbar are in good agreement with previous determinations at higher temperature. A weighted three-parameter Arrhenius fit to the experimental rate constant at 133 mbar, with the temperature exponent fixed, gives k = (7 +/- 1) x 10(exp -l4) cu cm/molecule/s (T/298 K)(exp 2) exp[-(1430 +/- 70) K/T]. RRKM master equation simulations, based on G3 calculations of stationary points on the C4H7 potential energy surface, were carried out to predict rate coefficients and product branching fractions. The predicted branching to 1-methylallyl product is relatively small under the conditions of the present experiments but increases as the pressure is lowered. Analysis of end products of 248 nm photolysis of vinyl iodide/ethylene mixtures at total pressures between 27 and 933 mbar provides no direct evidence for participation of I -methylallyl.

Ismail, Huzeifa↗

NASA NTRS1974

Absolute photon-flux measurements in the vacuum ultraviolet

Absolute photon-flux measurements in the vacuum ultraviolet have extended to short wavelengths by use of rare-gas ionization chambers. The technique involves the measurement of the ion current as a function of the gas pressure in the ion chamber. The true value of the ion current, and hence the absolute photon flux, is obtained by extrapolating the ion current to zero gas pressure. Examples are given at 162 and 266 A. The short-wavelength limit is determined only by the sensitivity of the current-measuring apparatus and by present knowledge of the photoionization processes that occur in the rate gases.

Samson, J. A. R.↗