Engineering topics

Spencer, R C

Publications and source records attributed to Spencer, R C.

6 records

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↗

NASA NTRS1941

Preignition Characteristics of Several Fuels Under Simulated Engine Conditions

The preignition characteristics of a number of fuels have been studied under conditions similar to those encountered in an engine. These conditions were simulated by suddenly compressing a fuel-air mixture in contact with an electrically heated hot spot in the cylinder head of the NACA combustion apparatus. Schlieren photographs and indicator cards were taken of the burning, and the hot-spot temperatures necessary to cause ignition under various conditions were determined.

Spencer, R C↗

NASA NTRS1939

The Influence of Directed Air Flow on Combustion in Spark-Ignition Engine

The air movement within the cylinder of the NACA combustion apparatus was regulated by using shrouded inlet valves and by fairing the inlet passage. Rates of combustion were determined at different inlet-air velocities with the engine speed maintained constant and at different engine speeds with the inlet-air velocity maintained approximately constant. The rate of combustion increased when the engine speed was doubled without changing the inlet-air velocity; the observed increase was about the same as the increase in the rate of combustion obtained by doubling the inlet-air velocity without changing the engine speed. Certain types of directed air movement gave great improvement in the reproducibility of the explosions from cycle to cycle, provided that other variables were controlled. Directing the inlet air past the injection valve during injection increased the rate of burning.

Rothrock, A M↗

NASA NTRS1938

A Photographic Study of Combustion and Knock in a Spark-Ignition Engine

Report presents the results of a photographic study of the combustion in a spark-ignition engine using both Schlieren and flame photographs taken at high rates of speed. Although shock waves are present after knock occurs, there was no evidence of any type of sonic or supersonic compression waves existing in the combustion gases prior to the occurrence of knock. Artificially induced shock waves in the engine did not in themselves cause knock. The photographs also indicate that, although auto-ignition ahead of the flame front may occur in conjunction with knock, it is not necessary for the occurrence of knock. There is also evidence that the reaction is not completed in the flame front but continues for some time after the flame front has passed through the charge.

Rothrock, A M↗

NASA NTRS1937

A Preliminary Study of Flame Propagation in a Spark-ignition Engine

The N.A.C.A. combustion apparatus was altered to operate as a fuel-injection, spark-ignition engine, and a preliminary study was made of the combustion of gasoline-air mixtures at various air-fuel ratios. Air-fuel ratios ranging from 10 to 21.6 were investigated. Records from an optical indicator and films from a high-speed motion-picture camera were the chief sources of data. Schlieren photography was used for an additional study. The results show that the altered combustion apparatus has characteristics similar to those of a conventional spark-ignition engine and should be useful in studying phenomena in spark-ignition engines. The photographs show the flame front to be irregularly shaped rather than uniformly curved. With a theoretically correct mixture the reaction, as indicated by the photographs, is not completed in the flame front but continues for some time after the combustion front has traversed the mixture.

Rothrock, A M↗

NASA NTRS1935

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↗