Low-frequency cutoffs in synchrotron spectra
Synchrotron source spectra natural frequency cut- off in absence of self absorption and electron energy cut-offs, discussing pulsar NP 0532
Odell, S. L.↗
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Whistler duct properties deduced from vlf observations made with the OGO 3 satellite near the magnetic equator
Whistler ducts as enhanced ionization from OGO 3 satellite observations near magnetic equator, noting magnetospheric ionization hydrostatic model and predicted cut-off
Angerami, J. J.↗
Numerical analysis of wave propagation on a periodic linear array
Numerical solution of current distribution, wave propagation constant and propagation mode cut-off frequencies on periodic linear array
Shen, L.-C.↗
Stellar ultraviolet observations made from a stratospheric nacelle. II
Stellar UV cut-off by statospheric nacelle recorded on photographic film by Schmidt telescope fitted with objective prism, widening spectrum by scanning
Lehmann, M.↗
A procedure for predicting internal and external noise fields of blowdown wind tunnels
The noise generated during the operation of large blowdown wind tunnels is considered. Noise calculation procedures are given to predict the test-section overall and spectrum level noise caused by both the tunnel burner and turbulent boundary layer. External tunnel noise levels due to the tunnel burner and circular jet exhaust flow are also calculated along with their respective cut-off frequency and spectrum peaks. The predicted values are compared with measured data, and the ability of the prediction procedure to estimate blowdown-wind-tunnel noise levels is shown.
Hosier, R. N.↗
Lava tubes and channels in the Lunar Marius Hills.
The Marius Hills region, a volcanic plateau in Oceanus Procellarum, contains numerous rilles, rille-like structures, and chains of elongate craters. Most of these structures characteristically: (1) originate on or near irregular shaped craters associated with features previously interpreted as volcanic domes, (2) trend downslope onto Plateau Plains, (3) generally taper in width and become shallower, (4) are often discontinuous, (5) occupy the center, or apparent crest of a broad ridge, (6) may contain cut-off branches and distributary structures, and (7) may have local reversals in longitudinal slope. Structures having these characteristics are interpreted to be lava channels or partly collapsed lava tubes. Terrestrial lava tubes form exclusively, and commonly, in fluid basalt flows. Recent evidence indicates that viscosities of lunar mare 'basalt' lava flows were conducive for lava tube formation. Terrestrial analogs are offered for structures described in the Marius Hills.
Greeley, R.↗
The energy balance of wind waves and the remote sensing problem
Measurements of wave growth indicate an energy balance of the wave spectrum governed primarily by input from the atmosphere, nonlinear transfer to shorter and longer waves, and advection. The pronounced spectral peak and sharp low frequency cut-off characteristic of fetch-limited spectra are explained as a self-stabilizing feature of the nonlinear wave-wave interactions. The momentum transferred from the atmosphere to the wind waves accounts for a large part of the wind drag. These findings are relevant for remote microwave sensing of the sea surface by backscatter and passive radiometry methods.
Hasselmann, K.↗
A new solution to the accretion problem.
The Bondi-Hoyle theory of line-accretion is briefly reviewed, and it is shown that there are an infinity of steady-state solutions satisfying the requirements originally imposed as boundary conditions. Questions are raised as to the applicability of these solutions to physical reality. The existence of an entirely different type of steady-state solution that implies slow velocity in the accretion stream beyond the neutral point is demonstrated. Accurate numerical values of this solution are obtained for a number of cases. The braking action given by this solution, for any selected cut-off distance, is far stronger than in the Bondi-Hoyle solution. Consideration of the physical state in the accretion stream shows that for this slow solution the appropriate cutoff range would be only of the order of 100 AU rather than of interstellar-distance order.
Lyttleton, R. A.↗
The Determination of Several Spray Characteristics of a High-Speed Oil Engine Injection System with an Oscilloscope
An investigation was conducted to determine the injection lag, duration of injection, and spray start and cut-off characteristics of a fuel injection system operated on an engine and injecting fuel into the atmosphere.
Hicks, Chester W↗
Some Effects of Air Flow on the Penetration and Distribution of Oil Sprays
Tests were made to determine the effects of air flow on the characteristics of fuel sprays from fuel injection valves. Curves and photographs are presented showing the airflow throughout the chamber and the effects of the air flow on the fuel spray characteristics. It was found that the moving air had little effect on the spray penetration except with the 0.006 inch orifice. The moving air did, however, affect the oil particles on the outside of the spray cone. After spray cut-off, the air flow rapidly distributed the atomized fuel throughout the spray chamber.
Rothrock, A M↗
Influence of several factors on ignition lag in a compression-ignition engine
This investigation was made to determine the influence of fuel quality, injection advance angle, injection valve-opening pressure, inlet-air pressure, compression ratio, and engine speed on the time lag of auto-ignition of a Diesel fuel oil in a single-cylinder compression-ignition engine as obtained from an analysis of indicator diagrams. Three cam-operated fuel-injection pumps, two pumps cams, and an automatic injection valve with two different nozzles were used. Ignition lag was considered to be the interval between the start of injection of the fuel as determined with a Stroborama and the start of effective combustion as determined from the indicator diagram, the latter being the point where 4.0 x 10(exp-6) pound of fuel had been effectively burned. For this particular engine and fuel it was found that: (1) for a constant start and the same rate of fuel injection up the point of cut-off, a variation in fuel quantity from 1.2 x 10(exp-4) to 4.1 x 10(exp-4) pound per cycle has no appreciable effect on the ignition lag; (2) injection advance angle increases or decreases the lag according to whether density, temperature, or turbulence has the controlling influence; (3) increase in valve-opening pressure slightly increases the lag; and (4) increase of inlet-air pressure, compression ratio, and engine speed reduces the lag.
Gerrish, Harold C↗
Discharge characteristics of a simulated unit injection system
Rate-of-discharge curves that show the discharge characteristics of an injection system having a very short fuel passage are presented. The rate of discharge closely follows the rate of displacement of the injection-pump plunger for open nozzles in which the maximum calculated pressures at the orifice do not exceed a certain value, which is dependent on the particular injection pump. With small orifices and high pump speeds, the rate of discharge does not follow the rate of plunger displacement because the higher discharge pressure results in increased leakage with corresponding decrease in discharge rate. The rate of discharge is not directly related to the rate of plunger displacement with automatic injection valves having closed nozzles. The types of pump check valve tested did not control the rate of cut-off or the discharge rate but they did affect the injection lag. Use of the short fuel passage eliminated the formation of secondary discharges.
Marsh, Edred T↗
A Preliminary Motion-picture Study of Combustion in a Compression-ignition Engine
Motion pictures were taken at 1,850 frames per second of the spray penetration and combustion occurring in the N.A.C.A. combustion apparatus arranged to operate as a compression-ignition engine. Indicator cards were taken simultaneously with the motion pictures by means of the N.A.C.A. optical indicator. The motion pictures showed that when ignition occurred during injection it started in the spray envelope. If ignition occurred after injection cut-off, however, and after considerable mixing had taken place, it was impossible to predict where the ignition would start. The pictures also showed that ignition usually started at several points in the combustion chamber. With this apparatus, as the injection advance angle increased from 0 degrees to 40 degrees before top center, the rate of flame spread increased and the duration of the burning decreased.
Buckley, E C↗
The N.A.C.A. Photographic Apparatus for Studying Fuel Sprays from Oil Engine Injection Valves and Test Results from Several Researches
Apparatus for recording photographically the start, growth, and cut-off of oil sprays from injection valves has been developed at the Langley Memorial Aeronautical Laboratory. The apparatus consists of a high-tension transformer by means of which a bank of condensers is charged to a high voltage. The controlled discharge of these condensers in sequence, at a rate of several thousand per second, produces electric sparks of sufficient intensity to illuminate the moving spray for photographing. The sprays are injected from various types of valves into a chamber containing gases at pressures up to 600 pounds per square inch. Several series of pictures are shown. The results give the effects of injection pressure, chamber pressure, specific gravity of the fuel oil used, and injection-valve design, upon spray characteristics.
Beardsley, Edward G↗
The Effects of Fuel and Cylinder Gas Densities on the Characteristics of Fuel Sprays for Oil Engines
This investigation was conducted as a part of a general research on fuel-injection engines for aircraft. The purpose of the investigation was to determine the effects of fuel and cylinder gas densities with several characteristics of fuel sprays for oil engines. The start, growth, and cut-off of single fuel sprays produced by automatic injection valves were recorded on photographic film by means of special high-speed motion-picture apparatus. This equipment, which has been described in previous reports, is capable of taking twenty-five consecutive pictures of the moving spray at the rate of 4,000 per second. The penetrations of the fuel sprays increased and the cone angles and relative distributions decreased with increase in the specific gravity of the fuel. The density of the gas into which the fuel sprays were injected controlled their penetration. This was the only characteristic of the chamber gas that had a measurable effect upon the fuel sprays. Application of fuel-spray penetration data to the case of an engine, in which the pressure is rising during injection, indicated that fuel sprays may penetrate considerably farther than when injected into a gas at a density equal to that of the gas in an engine cylinder at top center.
Joachim, W F↗
Pressure Fluctuations in a Common-Rail Fuel Injection System
This report presents the results of an investigation to determine experimentally the instantaneous pressures at the discharge orifice of a common-rail fuel injection system in which the timing valve and cut-off valve were at some distance from the automatic fuel injection valve, and also to determine the methods by which the pressure fluctuations could be controlled. The results show that pressure wave phenomena occur between the high-pressure reservoir and the discharge orifice, but that these pressure waves can be controlled so as to be advantageous to the injection of the fuel. The results also give data applicable to the design of such an injection system for a high-speed compression-ignition engine.
Rothrock, A M↗
Effect of Moderate Air Flow on the Distribution of Fuel Sprays After Injection Cut-0ff
High-speed motion pictures were taken of fuel sprays with the NACA spray-photographic apparatus to study the distribution of the liquid fuel from the instant of injection cut-off until about 0.05 second later. The fuel was injected into a glass-walled chamber in which the air density was varied from 1 to 13 times atmospheric air density (0.0765 to 0.99 pound per cubic foot) and in which the air was at room temperature. The air in the chamber was set in motion by means of a fan, and was directed counter to the spray at velocities up to 27 feet per second. The injection pressure was varied from 2,000 to 6,000 pounds per square inch. A 0.20-inch single-orifice nozzle, an 0.008-inch single-orifice nozzle, a multiorifice nozzle, and an impinging-jets nozzle were used. The best distribution was obtained by the use of air and a high-dispersion nozzle.
Rothrock, A M↗
Details of the Construction and Production of Fuel Pumps and Fuel Nozzles for the Airplane Diesel Engine
This report presents investigations into the design and construction of fuel pumps for diesel engines. The results of the pump tests on the engines showed that, with a good cut-off, accurate injection, assured by the proper adjustment of the pump elements, there is a decrease in the consumption of fuel and hence an increase in the rated power of the engine. Some of the aspects investigated include: cam profile, coefficient of discharge, and characteristics of the injection system.
Lubenetsky, W S↗