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At least 253 records · Page 14

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NASA NTRS1993

Effect of vaporization on cryogenic spray dropsize measurement

The fluid mechanics of multi-phase flow breakup of liquid nitrogen, LN2, jets injected into sonic velocity nitrogen gasflow, was experimentally investigated. A scattered-light scanning instrument was used to measure the characteristic dropsize, D(sub v.5), of LN2 sprays and to determine the effect of droplet vaporization on experimental dropsize measurements. Under sonic gas-velocity conditions, liquid-jet breakup occurred in the regime of aerodynamic stripping. As a result, the following correlation of volume-median drop diameter, D(sub v.5), with atomizing gas flowrate, W(sub g), was derived for two-fluid atomizers: (D(sub v.5)) (exp -1) = k(sub c) (W(sub g)) (sup n), where proportionally constant k(sub c) and exponent n are functions of droplet vaporization rate. Partially vaporized sprays were investigated and it was found that n = 1.11, which is considerably less than the value of 1.33 that is predicted by atomization theory. This was attributed to the evaporative loss of very small droplets. As a result, the following expression was obtained experimentally: (D(sub v.5e)) (exp -1) = 301 (W(sub g)) (sub 1.11). Values of D(sub v.5), that existed prior to partial vaporization of the LN2 sprays, were calculated and the following expression was derived for originally unvaporized LN2 sprays: (D(sub v.5)) (exp -1) = 285 (W(sub g)) (sub 1.33). This expression agrees well with atomization theory that predicts n = 1.33, for liquid jet breakup in high-velocity gasflow.

Ingebo, Robert D.↗

NASA NTRS1993

The characteristics of sprays produced by coaxial airblast atomisers

Measurements of droplet size, velocity, liquid flux and concentration were made in sprays produced by a coaxial airblast atomizer using a phase Doppler anemometer. The atomizer comprised a liquid jet with exit diameter varied between 1.1 and 2.3 mm positioned in the center of a gaseous annular stream. The characteristics of the preburner sprays of the main engine of the space shuttle were simulated by using water and air respectively replacing liquid oxygen and hydrogen. Reduction of the diameter of the liquid tube was found to improve the atomization and reduce the rate of spread of sprays with similar gas-to-liquid velocity ratio. The presence of a converging nozzle at the exit of the gaseous jet improved the atomization and increased the rate of spread of sprays with gas-to-liquid velocity ratio up to around 45, but had no effect for higher velocity ratios.

Hardalupas, Y.↗

NASA NTRS1993

Thermal spray forming of refractory sample ampoule cartridges for single crystal growth space furnaces

A thermal spray process is being used to build up refractory metals and ceramics into a containment cartridge for high temperature, single crystal semiconductor growth experiments. This process uses high energy plasma inside a low pressure (100-200 torr) inert environment to apply layers of material onto a removable mandrel. A variety of materials are being characterized and evaluated against a demanding set of requirements, including high service temperature (1700 C), oxidation resistance, and resistance to liquid metal attack. Techniques to spray form refractory metals (tungsten, molybdenum, niobium, tantalum) and ceramics (alumina, boron nitride) are being developed in the Plasma Spray Cell at Marshall Space Flight Center. These plasma spray formed materials have been evaluated for mechanical properties, density, microstructure, and resistance to liquid metal attack. Forming techniques and the resultant mechanical and metallurgical properties will be presented.

Zimmerman, Frank↗

NASA NTRS1993

Computations of spray, fuel-air mixing, and combustion in a lean-premixed-prevaporized combustor

A code was developed for computing the multidimensional flow, spray, combustion, and pollutant formation inside gas turbine combustors. The code developed is based on a Lagrangian-Eulerian formulation and utilizes an implicit finite-volume method. The focus of this paper is on the spray part of the code (both formulation and algorithm), and a number of issues related to the computation of sprays and fuel-air mixing in a lean-premixed-prevaporized combustor. The issues addressed include: (1) how grid spacings affect the diffusion of evaporated fuel, and (2) how spurious modes can arise through modelling of the spray in the Lagrangian computations. An upwind interpolation scheme is proposed to account for some effects of grid spacing on the artificial diffusion of the evaporated fuel. Also, some guidelines are presented to minimize errors associated with the spurious modes.

Dasgupta, A.↗

NASA NTRS1930

Effect of Orifice Length-Diameter Ratio on Spray Characteristics

The effect of variations of orifice length to diameter ratio on spray characteristics was determined for a 0.014-inch and a 0.040-inch orifice for ratio of 0.5 to 4.0. The nozzles containing the orifices were mounted in an injection valve and tested with a plan stem and with a helically grooved stem. The injection pressure was varied from 4000 to 8000 pounds per square inch. The air density into which the fuel was sprayed was varied from the density obtained with a pressure of 60 pounds per square inch to the density obtained with a pressure of 250 pounds per square inch at room temperature. The tests showed that increasing the orifice length to diameter ratio with a plain stem in the injection valve causes the spray tip penetration first to decrease, reaching a minimum between a ratio of 1.5 and 2.5, and then to increase, reaching a maximum at a ratio greater than 3.5. The spray cone angle showed little change with variation of the ratio. With a helically grooved stem and small ratio of orifice area to groove area, the penetration at first shows little tendency towards a minimum; but as the time of injection is increased to 0.004 second, the penetration becomes a minimum at a ratio between 0.5 and 2.0.

Gellales, A G↗

NASA NTRS1930

Some Characteristics of Fuel Sprays from Open Nozzles

The penetration and cone-angle of fuel sprays from open nozzles were recorded with the NACA Spray Photography Equipment. The results show that for injection systems in which the rate of pressure rise at the discharge orifice is high, open nozzles give spray-tip velocities and penetrations which compare favorably with those of closed nozzles. The spray cone-angle was the same for all tests, although open nozzles having different orifice diameters were used, and one nozzle was used both as an open and as a closed nozzle. In designing a fuel system using open nozzles, particular care must be taken to avoid air pockets. The check valve should be placed close to the discharge orifice.

Rothrock, A M↗

NASA NTRS1931

Some Characteristics of Fuel Sprays at Low-injection Pressures

This report presents the results of tests conducted at the Langley Memorial Aeronautical Laboratory, Langley Field, Va., to determine some of the characteristics of the fuel sprays obtained from an 0.008-inch and a 0.020-inch open nozzle when injection pressures from 100 to 500 pounds per square inch were used. Fuel oil and gasoline were injected into air at densities of atmospheric land 0.325 pound per cubic foot. It was found that the penetration rate at these low pressures was about the same as the rate obtained with higher pressures. Spray cone-angles were small and individual oil drops were visible in all the sprays. Gasoline and fuel oil sprays had similar characteristics.

Rothrock, A M↗

NASA NTRS1931

Effect of High Air Velocities on the Distribution and Penetration of a Fuel Spray

By means of the NACA Spray Photography Equipment high speed moving pictures were taken of the formation and development of fuel sprays from an automatic injection valve. The sprays were injected normal to and counter to air at velocities from 0 to 800 feet per second. The air was at atmosphere temperature and pressure. The results show that high air velocities are an effective means of mixing the fuel spray with the air during injection.

Rothrock, A M↗

NASA NTRS1933

The Effect of Spray Strips on a Model of the P3M-1 Flying Boat Hull

This note presents the results of a series of tests made in the N.A.C.A. tank on a one-sixth full-size model of the hull and side floats of the Navy P3M-1 flying boat for the purpose of finding a method of reducing the amount of spray thrown into the propellers of this craft when taking off and landing. The model was tested without spray strips and with five different spray-strip arrangements. The best arrangement was an improvement over the bare hull with no spray strips, but the improvement was not sufficient to be satisfactory with the propellers in the designed position.

Dawson, John R↗

NASA NTRS1926

Spray Penetration with a Simple Fuel Injection Nozzle

The purpose of the tests covered by this report was to obtain specific information on the rate of penetration of the spray from a simple injection nozzle, having a single orifice with a diameter of 0.015 inch when injecting into compressed gases. The results have shown that the effects of both chamber and fuel pressures on penetration are so marked that the study of sprays by means of high-speed photography or its equivalent is necessary if the effects are to be appreciated sufficiently to enable rational analysis. It was found for these tests that the negative acceleration of the spray tip is approximately proportional to the 1.5 power of the instantaneous velocity of the spray tip.

Miller, Harold E↗

NASA NTRS1928

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↗

NASA NTRS1933

The NACA Apparatus for Studying the Formation and Combustion of Fuel Sprays and the Results from Preliminary Tests

This report describes the apparatus as designed and constructed at the Langley Memorial Aeronautical Laboratory, for studying the formation and combustion of fuel sprays under conditions closely simulating those occurring in a high-speed compression-ignition engine. The apparatus consists of a single-cylinder modified test engine, a fuel-injection system so designed that a single charge of fuel can be injected into the combustion chamber of the engine, an electric driving motor, and a high-speed photographic apparatus. The cylinder head of the engine has a vertical-disk form of combustion chamber whose sides are glass windows. When the fuel is injected into the combustion chamber, motion pictures at the rate of 2,000 per second are taken of the spray formation by means of spark discharges. When combustion takes place the light of the combustion is recorded on the same photographic film as the spray photographs. The report includes the results of some tests to determine the effect of air temperature, air flow, and nozzle design on the spray formation.

Rothrock, A M↗

NASA NTRS1934

Photomicrographic Studies of Fuel Sprays

A large number of photomicrographs of fuel sprays were taken for the purpose of studying the spray structure and the process of spray formation. They were taken at magnifying powers of 2.5, 3.25, and 10, using a spark discharge of very short duration for illumination. Several types and sizes of nozzles were investigated, different liquids were used, and a wide range of injection pressures was employed. The sprays were photographed as they were injected into a glass-walled chamber in which the air density was varied from 14 atmospheres to 0.0013 atmosphere.

Lee, Dana W↗

NASA NTRS1937

Fuel Spray and Flame Formation in a Compression-Ignition Engine Employing Air Flow

The effects of air flow on fuel spray and flame formation in a high-speed compression-ignition engine have been investigated by means of the NACA combustion apparatus. The process was studied by examining high-speed motion pictures taken at the rate of 2,200 frames a second. The combustion chamber was of the flat-disk type used in previous experiments with this apparatus. The air flow was produced by a rectangular displacer mounted on top of the engine piston. Three fuel-injection nozzles were tested: a 0.020-inch single-orifice nozzle, a 6-orifice nozzle, and a slit nozzle. The air velocity within the combustion chamber was estimated to reach a value of 425 feet a second. The results show that in no case was the form of the fuel spray completely destroyed by the air jet although in some cases the direction of the spray was changed and the spray envelope was carried away by the moving air. The distribution of the fuel in the combustion chamber of a compression-ignition engine can be regulated to some extent by the design of the combustion chamber, by the design of the fuel-injection nozzle, and by the use of air flow.

Rothrock, A M↗

NASA NTRS1993

Thermal spray forming of refractory sample ampoule cartridges for single crystal growth space furnaces

Zimmerman, Frank↗

NASA NTRS1993

Spray combustion experiments and numerical predictions

The next generation of commercial aircraft will include turbofan engines with performance levels significantly better than those in the current fleet. Control of particulate and gaseous emissions will also be an integral part of the engine design criteria. These performance and emission requirements present a technical challenge for the combustor: control of the fuel and air mixing and control of the local stoichiometry will have to be maintained much more rigorously than with combustors in current production. A better understanding of the flow physics of liquid fuel spray combustion is necessary. This paper describes recent experiments on spray combustion where detailed measurements of the spray characteristics were made, including local drop-size distributions and velocities. Also, an advanced combustor CFD code has been under development and predictions from this code are compared with experimental results. Studies such as these will provide information to the advanced combustor designer on fuel spray quality and mixing effectiveness. Validation of new fast, robust, and efficient CFD codes will also enable the combustor designer to use than as valuable additional design tools for optimization of combustor concepts for the next generation of aircraft engines.

Mularz, Edward J.↗

NASA NTRS1994

Quality optimization of thermally sprayed coatings produced by the JP-5000 (HVOF) gun using mathematical modeling

Currently, thermal barrier coatings (TBC) of gas-turbine blades and similar applications have centered around the use of zirconia as a protective coating for high thermal applications. The advantages of zirconia include low thermal conductivity and good thermal shock resistance. Thermally sprayed tungsten carbide hardface coatings are used for a wide range of applications spanning both the aerospace and other industrial markets. Major aircraft engine manufacturers and repair facilities use hardface coatings for original engine manufacture (OEM), as well as in the overhaul of critical engine components. The principle function of these coatings is to resist severe wear environments for such wear mechanisms as abrasion, adhesion, fretting, and erosion. The (JP-5000) thermal spray gun is the most advanced in the High Velocity Oxygen Fuel (HVOF) systems. Recently, it has received considerable attention because of its relative low cost and its production of quality coatings that challenge the very successful but yet very expensive Vacuum Plasma Spraying (VPS) system. The quality of thermal spray coatings is enhanced as porosity, oxidation, residual stress, and surface roughness are reduced or minimized. Higher densification, interfacial bonding strength, hardness and wear resistance of coating are desirable features for quality improvement.

Tawfik, Hazem↗

NASA NTRS1993

Spray Combustion Experiments and Numerical Predictions

The next generation of commercial aircraft will include turbofan engines with performances significantly better than those in the current fleet. Control of particulate and gaseous emissions will also be an integral part of the engine design criteria. These performance and emission requirements present a technical challenge for the combustor: control of the fuel and air mixing and control of the local stoichiometry will have to be maintained much more rigorously than combustors in current production. A better understanding of the flow physics of liquid fuel spray combustion is necessary. This presentation describes recent experiments on spray combustion where detailed measurements of the spray characteristics were made, including local drop-size distributions and velocities. In addition, an advanced combustor CFD code has been under development and predictions from this code are presented and compared with measurements. Studies such as these will provide information to the advanced combustor designer on fuel spray quality and mixing effectiveness. Validation of new fast, robust, and efficient CFD codes will also enable the combustor designer to use them as valuable design tools for optimization of combustor concepts for the next generation of aircraft engines.

Mularz, Edward J.↗