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Half -Million Stationary Images per Second With Refocused Revolving Beams*
BY C. D. MILLER
BATTELLE MEMORIAL INSTITUTE, COLUMBUS 1, OHIO
Summary — A motion picture camera is described, developed in the laboratories of the National Advisory Committee for Aeronautics, which has made photographs of combustion phenomena in an engine cylinder at 500,000 frames per second. Illustrations and references are included. Sample photographs are reproduced.
THE TIME INVOLVED in the normal nonknocking combustion process in an engine cylinder varies about inversely as engine speed, other things being equal. Even with a speed of only 500 revolutions per minute the normal combustion process in a single cycle of engine operation is completed in less than 10 ~2 second. And with.-knocking combustion things happen much faster.
Recent studies in laboratories of the National Advisory Committee for Aeronautics1 have shown that knocking combustion in an engine often involves detonation waves traveling more than a mile a second. In an engine of 5-inch bore such a wave would move entirely across the cylinder in less than 10 ~4 second. As this wave usually traverses only part of the chamber, it must be "seen" in an interval of only 2 X 10~5 to 4 X 10~5 second, if at all. If we want this wave to occupy an interval of, say, one second on the projection screen, at 16 frames per second, we must photograph at 4 X 105 to 8 X 106 frames per second.
In response to the demonstrated need in the study of knock, two different types of high-speed camera have been developed. The first2 has been operated over a period of years at 40,000 frames per second in the NACA laboratories, and a slightly modified form of that camera now under construction at Battelle Memorial Institute is expected to operate at rates up to 100,000 frames per second.
* Presented April 6, 1949, at the SMPE Convention in New York.
NOVEMBER, 1949 JOURNAL OF THE SMPE VOLUME 53 479