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SOLUTION of the problem of igniting and burning the fuel in the high-speed Diesel engine profoundly affects its development, according to the authors. This paper describes the photo-electric set-up selected to indicate the behavior of the fuel in the combustion-chamber because of its high speed, its intensity, its zero time lag, and its freedom from inertia effects. A magnetic-type oscillograph for recording the impulses, a cantilever-spring indicator for picking up the pressure impulse, and an amplifier between the photo-cell and the oscillograph, comprise the principal parts of this instrumentation, as applied to a single-cylinder test engine. Results of tests with a three-beam vibrator-type oscillograph are given with oscillograms for different fuels, loads, and injection angles. Other tests are described using a cathode-ray oscillograph and a high-speed camera.

NOT only does a high-cetane diesel fuel start to burn earlier in the cycle due to its shorter ignition-lag period, but it continues to burn longer during the expansion stroke than does a low-cetane fuel, the authors announce. This and other findings, they explain, are the results of an investigation of the effect of fuel quality and injection advance angle on ignition lag and combustion duration in a 4-cycle high-turbulence diesel engine. The same photo-electric combustion indicator, developed at the University of Wisconsin, was used, they point out, as was described previously before the Society, with the exception of several improvements. Combustion characteristics of 27 different fuels were determined by studying the oscillograms for more than 5000 engine cycles obtained at a film speed of 60 fps. From dynamometer tests run both on 1-cyl and 6-cyl 4-cycle diesel engines, fuel rates were obtained from six different fuels varying in cetane number from 25 to 87.

THIS paper is a sequel of the paper, “Photo-Electric Combustion Analysis,” presented at the 1936 Semi-Annual Meeting of the Society. The indicator described in that paper has been used to study combustion of 28 fuels and chemicals. A complete table of information of the materials used as fuels is included. The results obtained from over 1000 oscillograms show a different shape of ignition-lag curve versus injection advance angle than it is ordinarily thought to have. Even though the cetane values for these 28 fuels varied from 24 to 100, they all had nearly the same ignition lag when injected near the dead-center position. This minimum value is shown to be about 1/1000 sec. The fuels of higher-cetane value reach this minimum at an earlier injection angle than do those of low-cetane value. The paper shows how a high-cetane fuel can be just as rough as a low-cetane fuel if the injection timing is too early.