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At least 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Ignition and combustion characteristics of metallized propellants

Over the past six months, experimental investigations were continued and theoretical work on the secondary atomization process was begun. Final shakedown of the sizing/velocity measuring system was completed and the aluminum combustion detection system was modified and tested. Atomizer operation was improved to allow steady state operation over long periods of time for several slurries. To validate the theoretical modeling, work involving carbon slurry atomization and combustion was begun and qualitative observations were made. Simultaneous measurements of aluminum slurry droplet size distributions and detection of burning aluminum particles were performed at several axial locations above the burner. The principle theoretical effort was the application of a rigid shell formation model to aluminum slurries and an investigation of the effects of various parameters on the shell formation process. This shell formation model was extended to include the process leading up to droplet disruption, and previously developed analytical models were applied to yield theoretical aluminum agglomerate ignition and combustion times. The several theoretical times were compared with the experimental results.

Mueller, D. C.↗
NASA NTRS1993

ASRM propellant and igniter propellant development and process scale-up

A program of formulation and process development for ANB-3652 motor propellant was conducted to validate design concepts and screen critical propellant composition and process parameters. Design experiments resulted in the selection of a less active grade of ferric oxide to provide better burning rate control, the establishment of AP fluidization conditions that minimized the adverse effects of particle attrition, and the selection of a higher mix temperature to improve mechanical properties. It is shown that the propellant can be formulated with AP and aluminum powder from various producers. An extended duration pilot plant run demonstrated stable equipment operation and excellent reproducibility of propellant properties. A similar program of formulation and process optimization culminating in large batch scaleup was conducted for ANB-3672 igniter propellant. The results for both ANB-3652 and ANB 37672 confirmed that their processing characteristics are compatible with full-scale production.

Landers, L. C.↗
NASA NTRS1993

2D axisymmetric analysis of SRM ignition transient

To analyze ignition transient of Space Shuttle solid rocket motor, a transient two-dimensional numerical model based on turbulent compressible Navier-Stokes equations in a generalized coordinate system was developed. One-dimensional numerical models (Peretz et al., 1973; Han, 1992; Pardue and Han, 1992) with empirical correlations data obtained from steady turbulent boundary layer flows agrees reasonably well with test rocket data by adjusting a few parameters. However, a 1D model can not provide a physical insight into the complex multidimensional thermal fields and flowfields in the chamber and the converging-diverging rocket nozzle. As an interim step, a 2D model was developed and compared with test data. A modified version of SIMPLE algorithm was used for the numerical model, and the standard k-epsilon model with a wall function was used for turbulence closure. Transient flowfields and thermal fields in the combustion chamber and the attached nozzle were obtained for a selected rocket geometry and propellant. Transient behaviors of the flow and thermal fields were analyzed, and were found to be in good agreement with physical expectations.

Bai, S. D.↗
NASA NTRS1921

Causes of Cracking of Ignition Cable

The experiments described here show that the cracking at sharp bends, observed in the insulation of internal combustion engine high tension ignition wires after service, is due to a chemical attack upon the rubber by the ozone produced by the electric discharge that takes place at the surface of the cable. This cracking does not occur if the insulating material is not under tension, or if the cable is surrounded by some medium other than air. But it does occur even if the insulation is not subjected to electric stress, provided that the atmosphere near the cable contains ozone. The extent of this cracking varies greatly with the insulating material used. The cracking can be materially reduced by using braided cable and by avoiding sharp bends.

Silsbee, F B↗
NASA NTRS1930

Performance of a High-Speed Compression-Ignition Engine Using Multiple Orifice Fuel Injection Nozzles

This report presents test results obtained at the Langley Memorial Aeronautical Laboratory of the National Advisory Committee for Aeronautics during an investigation to determine the relative performance of a single-cylinder, high-speed, compression-ignition engine when using fuel injection valve nozzles with different numbers, sizes, and directions of round orifices. A spring-loaded, automatic injection valve was used, centrally located at the top of a vertical disk-type combustion chamber formed between horizontally opposed inlet and exhaust valves of a 5 inch by 7 inch engine.

Spanogle, J A↗
NASA NTRS1931

The effectiveness of a double-stem injection valve in controlling combustion in a compression-ignition engine

An investigation was made to determine to what extent the rates of combustion in a compression-ignition engine can be controlled by varying the rates of fuel injection. The tests showed that the double-stem valve operated satisfactorily under all normal injection conditions; the rate of injection has a definite effect on the rate of combustion; the engine performance with the double-stem valve was inferior to that obtained with a single-stem valve; and the control of injection rates permitted by an injection valve of two stages of discharge is not sufficient to effect the desired rates of combustion.

Spanogle, J A↗
NASA NTRS1931

Performance of a Compression-ignition Engine with a Precombustion Chamber Having High-Velocity Air Flow

Presented here are the results of performance tests made with a single-cylinder, four stroke cycle, compression-ignition engine. These tests were made on a precombustion chamber type of cylinder head designed to have air velocity and tangential air flow in both the chamber and cylinder. The performance was investigated for variable load and engine speed, type of fuel spray, valve opening pressure, injection period and, for the spherical chamber, position of the injection spray relative to the air flow. The pressure variations between the pear-shaped precombustion chamber and the cylinder for motoring and full load conditions were determined with a Farnboro electric indicator. The combustion chamber designs tested gave good mixing of a single compact fuel spray with the air, but did not control the ensuing combustion sufficiently. Relative to each other, the velocity of air flow was too high, the spray dispersion by injection too great, and the metering effect of the cylinder head passage insufficient. The correct relation of these factors is of the utmost importance for engine performance.

Spanogle, J A↗
NASA NTRS1935

Performance tests of a single-cylinder compression-ignition engine with a displacer piston

Engine performance was investigated using a rectangular displacer on the piston crown to cause a forced air flow in a vertical-disk combustion chamber of a single-cylinder, 4-stroke-cycle compression-ignition engine. The optimum air-flow area was determined first with the area concentrated at one end of the displacer and then with the area equally divided between two passages, one at each end of the displacer. Best performance was obtained with the two-passage air flow arranged to give a calculated maximum air-flow speed of 8 times the linear crank-pin speed. With the same fuel-spray formation as used without the air flow, the maximum clear exhaust brake mean effective pressure at 1,500 r.p.m. was increased from 90 to 115 pounds per square inch and the corresponding fuel consumption reduced from 0.46 to 0.43 pound per brake horsepower-hour. At 1,200 r.p.m., a maximum clear exhaust brake mean effective pressure of 120 pounds per square inch was obtained at a fuel consumption of 0.42 pound per brake horsepower-hour. At higher specific fuel consumption the brake mean effective pressure was still increasing rapidly.

Moore, C S↗
NASA NTRS1936

Boosted performance of a compression-ignition engine with a displaced piston

Performance tests were made using a rectangular displacer arranged so that the combustion air was forced through equal passages at either end of the displacer into the vertical-disk combustion chamber of a single-cylinder, four-stroke-cycle compression-ignition test engine. After making tests to determine optimum displacer height, shape, and fuel-spray arrangement, engine-performance tests were made at 1,500 and 2,000 r.p.m. for a range of boost pressures from 0 to 20 inches of mercury and for maximum cylinder pressures up to 1,150 pounds per square inch. The engine operation for boosted conditions was very smooth, there being no combustion shock even at the highest maximum cylinder pressures. Indicated mean effective pressures of 240 pounds per square inch for fuel consumptions of 0.39 pound per horsepower-hour have been readily reproduced during routine testing at 2,000 r.p.m. at a boost pressure of 20 inches of mercury.

Moore, Charles S↗
NASA NTRS1934

Effect of Combustion-chamber Shape on the Performance of a Prechamber Compression-ignition Engine

The effect on engine performance of variations in the shape of the prechamber, the shape and direction of the connecting passage, the chamber volume using a tangential passage, the injection system, and the direction od the fuel spray in the chamber was investigated using a 5 by 7 inch single-cylinder compression-ignition engine. The results show that the performance of this engine can be considerably improved by selecting the best combination of variables and incorporating them in a single design. The best combination as determined from these tests consisted of a disk-shaped chamber connected to the cylinder by means of a flared tangential passage. The fuel was injected through a single-orifice nozzle directed normal to the air swirl and in the same plane. At an engine speed of 1,500 r.p.m. and with the theoretical fuel quantity for no excess air, the engine developed a brake mean effective pressure of 115 pounds per square inch with a fuel consumption of 0.49 pound per brake horsepower-hour and an explosion pressure of 820 pounds per square inch. A brake mean effective pressure of 100 pounds per square inch with a brake-fuel consumption of 0.44 pound per horsepower-hour at 1,500 r.p.m. was obtained.

Moore, C S↗
NASA NTRS1937

Effect of air-entry angle on performance of a 2-stroke-cycle compression-ignition engine

An investigation was made to determine the effect of variations in the horizontal and vertical air-entry angles on the performance characteristics of a single-cylinder 2-stroke-cycle compression-ignition test engine. Performance data were obtained over a wide range of engine speed, scavenging pressure, fuel quantity, and injection advance angle with the optimum guide vanes. Friction and blower-power curves are included for calculating the indicated and net performances. The optimum horizontal air-entry angle was found to be 60 degrees from the radial and the optimum vertical angle to be zero, under which conditions a maximum power output of 77 gross brake horsepower for a specific fuel consumption of 0.52 pound per brake horsepower-hour was obtained at 1,800 r.p.m. and 16-1/2 inches of Hg scavenging pressure. The corresponding specific output was 0.65 gross brake horsepower per cubic inch of piston displacement. Tests revealed that the optimum scavenging pressure increased linearly with engine speed. The brake mean effective pressure increased uniformly with air quantity per cycle for any given vane angle and was independent of engine speed and scavenging pressure.

Earle, Sherod L↗
NASA NTRS1946

Improving the performance of a compression ignition engine by directing flow of inlet air

The object of this report is to present the results of tests performed by the National Advisory Committee for Aeronautics to determine the effect on engine performance of directing the flow of the inlet air to a 5-inch by 7-inch cylinder, solid injection, compression ignition engine, After a few preliminary tests, comparative runs were made at a speed of 1500 r.p.m. with and without directed air flow. It was found that directing the flow of the inlet air toward the fuel injection valve gave steadier engine operation, and an appreciable increase in power, and decreased fuel consumption. The results indicate the possibility of improving the performance of a given type of combustion chamber without changing its shape and with no change in valve timing. They would also seem to prove that directional turbulence, set up before the inlet valve of a four-stroke cycle engine, continues in the engine cylinder throughout the compression stroke.

Kemper, Carlton↗
NASA NTRS1920

The subsidiary gap as a means for improving ignition

This report was prepared at the Bureau of Standards for the National Advisory Committee for Aeronautics. Additional or subsidiary gaps have frequently been used in jump-spark ignition systems, in order to cause the resumption of sparking in fouled spark plugs. The series gap, to which the greater part of this report is devoted, is a subsidiary gap in the connection between the high tension terminal of the plug and that of the magneto or coil. A brief account is given of the use of this gap up to the present time and also of the statements concerning it which have gained some currency, most of which are shown to be erroneous. The simple theory of the action of the series gap is discussed and a detailed account given of the effect upon the sparking ability of the plug produced by changes in the values of the electrical resistance of the fouling and of the capacities in parallel with the plug and with the magneto or coil. This report presents the results of an investigation into the utility, action, and design of the auxiliary spark gap as a means for insuring freedom from spark plug failure due to fouling, and also to enable the restarting of fouled plugs.

Gorton, W S↗
NASA NTRS1927

Electrical characteristics of spark generators for automotive ignition

This paper reports the results of an extensive program of measurements on 11 ignition systems differing widely in type. The results serve primarily to give representative data on the electric and magnetic constants of such systems, and on the secondary voltage produced by them under various conditions of speed, timing, shunting resistance, etc. They also serve to confirm certain of the theoretical formulas which have been proposed to connect the performance of such systems with their electrical constants, and to indicate the extent to which certain simplified model circuits duplicate the performance of the actual apparatus.

Brode, R B↗
NASA NTRS1934

Increasing the Air Charge and Scavenging the Clearance Volume of a Compression-Ignition Engine

The object of the investigation presented in this report was to determine the effects of increasing the air charge and scavenging the clearance volume of a 4-stroke-cycle compression-ignition engine having a vertical-disk form combustion chamber. Boosting the inlet-air pressure with normal valve timing increased the indicated engine power in proportion to the additional air inducted and resulted in smoother engine operation with less combustion shock. Scavenging the clearance volume by using a valve overlap of 145 degrees and an inlet-air boost pressure of approximately 2 1/2 inches of mercury produced a net increase in performance for clear exhaust operation of 33 percent over that obtained with normal valve timing and the same boost pressure. The improved combustion characteristics result in lower specific fuel consumption, and a clearer exhaust.

Spanogle, J A↗
NASA NTRS1937

The Quiescent-Chamber Type Compression-Ignition Engine

Report presents the results of performance tests of a single-cylinder 4-stroke-cycle compression-ignition engine having a vertical disk form of combustion chamber without air flow. The number, size, and direction of the orifices of the fuel-injection nozzles used were independently varied. A table and graphs are presented showing the performance of the engine with different nozzles; results of tests at different compression ratios, boost pressures, and coolant temperatures are also included.

Foster, H H↗
NASA NTRS1938

Prechamber Compression-Ignition Engine Performance

Single-cylinder compression-ignition engine tests were made to investigate the performance characteristics of prechamber type of cylinder head. Certain fundamental variables influencing engine performance -- clearance distribution, size, shape, and direction of the passage connecting the cylinder and prechamber, shape of prechamber, cylinder clearance, compression ratio, and boosting -- were independently tested. Results of motoring and of power tests, including several typical indicator cards, are presented.

Moore, Charles S↗
NASA NTRS1941

A High-Speed Motion-Picture Study of Normal Combustion, Knock and Preignition in a Spark-Ignition Engines

Combustion in a spark-ignition engine was investigated by means of the NACA high-speed motion-picture cameras. This camera is operated at a speed of 40,000 photographs a second and therefore makes possible the study of changes that take place in the intervals as short as 0.000025 second. When the motion pictures are projected at the normal speed of 16 frames a second, any rate of movement shown is slowed down 2500 times. Photographs are presented of normal combustion, of combustion from preignitions, and of knock both with and without preignition. The photographs of combustion show that knock may be preceded by a period of exothermic reaction in the end zone that persists for a time interval of as much as 0.0006 second. The knock takes place in 0.00005 second or less.

Rothrock, A M↗