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At least 397 records · Page 22

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NASA NTRS1979

The erosion of planetary and satellite atmospheres by energetic atomic particles

Analytic expressions are presented which may be used to compute the sputter-erosion yield from any unimolecular gravitationally bound gas by any atomic charged particle of any energy. A calculation of solar wind proton and alpha particle induced erosion of the CO2 atmosphere of Mars predicts molecular sputtering yields. An expression for the emission yield of energetic molecular fragments produced in primary knock-on events is given in closed form; such fragment emission is of secondary importance for mass loss compared to the molecular yield itself. Erosion by radiation belt protons of a hypothetical thin O2 atmosphere associated with the Jovian satellite Ganymede is considered, and molecular sputtering yields for proton energies are determined.

Haff, P. K.↗

NASA NTRS1980

Implications of cyclotron features in the X-ray spectrum of Hercules X-1

The modification of physical processes due to an intense magnetic field is investigated in order to uncover implications for X-ray spectra from binary pulsars. It is found that for large enough fields, the quantum nature of electron orbits must be taken into account, and for densities typical of binary X-ray pulsars it is found that electrons spend most of their time in the ground state. For this case, the production of cyclotron line photons following collisional excitation is estimated and the effects of the transfer of line photons through the hot plasma are considered. A line feature as narrow as reported by Truemper et al. appears unlikely. However, more recent observations allow a much broader line; in addition, a consistent absorption feature due to knock-on electrons may explain the spectral steepening at about 20 keV.

Bussard, R. W.↗

NASA NTRS1983

Lightweight aircraft engines, the potential and problems for use of automotive fuels

A comprehensive data research and analysis for evaluating the use of automotive fuels as a substitute for aviation grade fuel by piston-type general aviation aircraft engines is presented. Historically known problems and potential problems with fuels were reviewed for possible impact relative to application to an aircraft operational environment. This report reviews areas such as: fuel specification requirements, combustion knock, preignition, vapor lock, spark plug fouling, additives for fuel and oil, and storage stability.

Patterson, D. J.↗

NASA NTRS1984

Asteroids and meteorites - Origin of stony-iron meteorites at mantle-core boundaries

Stony-iron meteorites formed at the core/mantle interfaces of small asteroidal parents. The mesosiderites formed when the thick crust of a largely molten parent body (100-200 km in diameter) foundered and sank through the mantle to the core. Pallasites formed in smaller parent bodies (50-100 km) in which olivine crystals from the partially molten mantle sank to the core/mantle interface and rafted there. Subsequent collisions stripped away the rocky mantles of both kinds of parent bodies, exposing the stony-iron surfaces of their cores to direct impacts, which continue to knock off meteorite fragments.

Greenberg, R.↗

NASA NTRS1983

On the generation of delta-rays in detectors for high-energy cosmic-ray nuclei

A common problem in detectors for cosmic-ray nuclei is the generation of energetic knock-on electrons by an incident nucleus. These electrons may produce additional signals which can obscure the true nature of the signal from the nucleus itself. In this paper, Monte Carlo simulations of these effects are discussed in the University of Chicago CRNE instrument for Spacelab-2, and show that they do not impair the performance of the transition radiation detector as designed. Some qualitative properties of delta-ray effects are identified, which are of use to other experimenters in this field.

Swordy, S. P.↗

NASA NTRS1989

A guide to structural factors for advanced composites used on spacecraft

The use of composite materials in spacecraft systems is constantly increasing. Although the areas of composite design and fabrication are maturing, they remain distinct from the same activities performed using conventional materials and processes. This has led to some confusion regarding the precise meaning of the term 'factor of safety' as it applies to these structures. In addition, composite engineering introduces terms such as 'knock-down factors' to further modify material properties for design purposes. This guide is intended to clarify these terms as well as their use in the design of composite structures for spacecraft. It is particularly intended to be used by the engineering community not involved in the day-to-day composites design process. An attempt is also made to explain the wide range of factors of safety encountered in composite designs as well as their relationship to the 1.4 factor of safety conventionally applied to metallic structures.

Vanwagenen, Robert↗

NASA NTRS1991

Radio frequency interference effect on PN code sequence lock detector

The authors find the probabilities of detection and false alarm of the pseudonoise (PN) sequence code lock detector when strong radio frequency interference (RFI) hits the communications link. Both a linear model and a soft-limiter nonlinear model for a transponder receiver are considered. In addition, both continuous wave (CW) RFI and pulse RFI are analyzed, and a discussion is included of how strong CW RFI can knock out the PN code lock detector in a linear or a soft-limiter transponder. As an example, the Space Station Freedom forward S-band PN system is evaluated. It is shown that a soft-limiter transponder can protect the PN code lock detector against a typical pulse RFI, but it can degrade the PN code lock detector performance more than a linear transponder if CW RFI hits the link.

Kwon, Hyuck M.↗

NASA NTRS1993

Autonomous Deicing System For Airplane Wing

Prototype autonomous deicing system for airplane includes network of electronic and electromechanical modules at various locations in wings and connected to central data-processing unit. Small, integrated solid-state device, using long coils installed under leading edge, exciting small vibrations to detect ice and larger vibrations to knock ice off. In extension of concept, outputs of vibration sensors and other sensors used to detect rivet-line fractures, fatigue cracks, and other potentially dangerous defects.

Hickman, G. A.↗

NASA NTRS1932

Compression-ignition engine tests of several fuels

The tests reported in this paper were made to devise simple engine tests which would rate fuels as to their comparative value and their suitability for the operating conditions of the individual engine on which the tests are made. Three commercial fuels were used in two test engines having combustion chambers with and without effective air flow. Strictly comparative performance tests gave almost identical results for the three fuels. Analysis of indicator cards allowed a differentiation between fuels on a basis of rates of combustion. The same comparative ratings were obtained by determining the consistent operating range of injection advance angle for the three fuels. The difference in fuels is more pronounced in a quiescent combustion chamber than in one with high-velocity air flow. A fuel is considered suitable for the operating conditions of an engine with a quiescent combustion chamber if it permits the injection of the fuel to be advanced beyond the optimum without exceeding allowable knock or allowable maximum cylinder pressures.

Spanogle, J A↗

NASA NTRS1950

Antiknock evaluation of hydrocarbons and ethers as aviation fuel components

The results of a NACA investigation conducted over a period of several years to evaluate the anti-knock characteristics of organic compounds are summarized. Included are data for 18 branched paraffins and olefins, 27 aromatics, and 22 ethers. The factors of performance investigated were blending characteristics, temperature sensitivity, lead response, and relation between molecular structure and antiknock ratings. Four engines were used.

Barnett, Henry C↗

NASA NTRS1921

Comparison of alcogas aviation fuel with export aviation gasoline

Mixtures of gasoline and alcohol when used in internal combustion engines designed for gasoline have been found to possess the advantage of alcohol in withstanding high compression without "knock" while retaining advantages of gasoline with regard to starting characteristics. Test of such fuels for maximum power-producing ability and fuel economy at various rates of consumption are thus of practical importance, with especial reference to high-compression engine development. This report discusses the results of tests which compares the performance of alcogas with x gasoline (export grade) as a standard.

Gage, V R↗

NASA NTRS1935

Infrared radiation from explosions in a spark-ignition engine

This report presents the results of an investigation to determine the variations in intensity and spectral distribution of the radiant energy emitted by the flames during normal and knocking explosions in an engine. Radiation extending into the infrared was transmitted by a window of fluorite, placed either near the spark plug or over the detonation zone at opposite ends of the combustion chamber. Concave, surface-silvered mirrors focused the beam, first at the slit of a stroboscope which opened for about 2 degrees of crank angle at any desired point in the engine cycle, and then upon the target of a sensitive thermocouple for measuring radiation intensity. Spectral distribution of the radiant energy was determined by placing over the window, one at a time, a series of five filters selected with a view to identifying, as far as possible without the use of a spectrograph, the characteristic emissions of water vapor, carbon dioxide, and incandescent carbon.

Marvin, Charles F , Jr↗

NASA NTRS1946

The NACA High-Speed Motion-Picture Camera Optical Compensation at 40,000 Photographs Per Second

The principle of operation of the NACA high-speed camera is completely explained. This camera, operating at the rate of 40,000 photographs per second, took the photographs presented in numerous NACA reports concerning combustion, preignition, and knock in the spark-ignition engine. Many design details are presented and discussed, details of an entirely conventional nature are omitted. The inherent aberrations of the camera are discussed and partly evaluated. The focal-plane-shutter effect of the camera is explained. Photographs of the camera are presented. Some high-speed motion pictures of familiar objects -- photoflash bulb, firecrackers, camera shutter -- are reproduced as an illustration of the quality of the photographs taken by the camera.

Miller, Cearcy D↗

NASA NTRS1945

Effect of Maximum Cruise-power Operation at Ultra-lean Mixture and Increased Spark Advance on the Mechanical Condition of Cylinder Components

A continuous 50-hour test was conducted to determine the effect of maximum cruise-power operation at ultra-lean fuel-air mixture and increased spark advance on the mechanical conditions of cylinder components. The test was conducted on a nine-cylinder air-cooled radial engine at the following conditions:brake horsepower, 750; engine speed, 1900 rpm; brake mean effective pressure, 172 pounds per square inch; fuel-air ratio, 0.052; spark advance, 30 deg B.T.C.; and maximum rear-spark-plug-bushing temperature, 400 F. In addition to the data on corrosion and wear, data are presented and briefly discussed on the effect of engine operation at the conditions of this test on economy, knock, preignition, and mixture distribution. Cylinder, piston, and piston-ring wear was small and all cylinder component were in good condition at the conclusion of the 50-hour test except that all exhaust-valve guides were bellmouthed beyond the Army's specified limit and one exhaust-valve face was lightly burned. It is improbable that the light burning in one spot of the valve face would have progressed further because the burn was filled with a hard deposit so that the valve face formed an unbroken seal and the mating seat showed no evidence of burning. The bellmouthing of the exhaust-valve guides is believed to have been a result of the heavy carbon and lead-oxide deposits, which were present on the head end of the guided length of the exhaust-valve stem. Engine operational the conditions of this test was shown to result In a fuel saving of 16.8 percent on a cooled-power basis as compared with operation at the conditions recommended for this engine by the Army Air Forces for the same power.

ENGINE CYLINDERS-WEAR↗

NASA NTRS1944

Use of Internal Coolant as a Means of Permitting Increase in Engine Take-Off Power

Engine tests, together with estimates made at Langley Memorial Aeronautical Laboratory, indicate that a 25-percent increase in take-off power can be obtained with present-day aircraft engines without increasing either the knock limit of the fuel or the external cooling requirements of the engine. This increase in power with present fuels and present external cooling is made possible through the use of an internal coolant inducted through the inlet manifold. Estimates on aircraft indicate that this 25-percent increase in power will permit an approximate usable increase of 8.5 percent in the take-off load of existing military airplanes. This increase in load is equivalent to an increase in the weight of gasoline normally carried of between 30 and 65 percent.

FUELS, ANTIKNOCK↗

NASA NTRS1947

The effect of preignition on cylinder temperatures, pressures, power output, and piston failures

An investigation was conducted using a cylinder of a V-type liquid-cooled engine to observe the behavior of the cylinder when operated under preignition conditions. Data were recorded that showed cylinder-head temperatures, time of ignition, engine speed, power output, and change in maximum cylinder pressure as a function of time as the engine entered preignition and was allowed to operate under preignition conditions for a short time. The effects of the following variables on the engine behavior during preignition were investigated: fuel-air ratio, power level, aromatic content of fuel, engine speed, mixture temperature, and preignition source. The power levels at which preignition would cause complete piston failure for the selected engine operating conditions and the types of failure encountered when using various values of clearance between the piston and cylinder barrel were determined. The fuels used had performance numbers high enough to preclude any possibility of knock throughout the test program.

Corrington, Lester C↗

NASA NTRS1940

The lead susceptibility of fuels and its dependence on the chemical composition

The fact that by the use of tetraethyl lead a number of otherwise unsuitable fuels could be made to meet engine requirements was not sufficiently appreciated. While use of tetraethyl lead is limited, the addition of special leaded fuels that increase the octane number is a requirement for many fuels. In this connection, the extent to which the action of tetraethyl lead through the addition of knock-resistant hydrocarbons to the base gasoline is influenced, is quite important. To the elucidation of this problem and of the storage stability of leaded fuels, the present report is dedicated.

Widmaier, O↗

NASA NTRS1940

Testing of high-octane fuels in the single-cylinder airplane engine

One of the most important properties of aviation fuels for spark-ignition engines is their knock rating. The CFR engine tests of fuels of 87 octane and above does not always correspond entirely to the actual behavior of these fuels in the airplane engine. A method is therefore developed which, in contrast to the octane number determination, permits a testing of the fuel under various temperatures and fuel mixture conditions. The following reference fuels were employed: 1) Primary fuels; isooctane and n-heptane; 2) Secondary fuels; pure benzene and synthetic benzine.

Seeber, Fritz↗