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National Advisory Committee for Aeronautics, Report - Some Factors Affecting the Reproducibility of Penetration and the Cutoff of Oil Sprays for Fuel Injection Engines

This incestigation was undertaken at the Langley Memorial Aeronautical Laboratory at Lang-
ley Field, Virginia, in connection with a general research on fuel-injection engines for aircraft. The
purpose of the investigation was to determine the factors controlling the reproducibility of spray
penetration and secondary discharges after cut-cf.

The derelopment of single sprays from automatic injection calves was recorded by means of
special high-speed photographic apparatus capable of taleing 25 consecutive pictures of the moving
spray at a rate of 4,000 per second. The efiects of two types of injection values, injection-calm tube
length, initial pressure in the injection-valve tube, speed of the injection control mechanism, and
time of spray cut-of, on the reproducibility of spray penetration, and on secondary discharges were
incestigated.

It was found that neither type of injection value materially afected spray reproducibility.
The initial pressure in the injection-colic tube controlled the reproducibility of spray penetrations.
An increase in the initial pressure or in the length of the injection-calm tube slightly increased the
spray penetration within the limits of this investigation. The speed of the injection-control mech-
anism did not afiect the penetration.

Analysis of the results indicates that secondary discharges were caused in this apparatus
by pressure waves initiated by the rapid opening of the cut-of valve. The secondary discharges
were eliminated in this investigation by increasing the length of the injection-calm tube.

During an investigation of the characteristics and development of the sprays from several
types of automatic fuel injection valves, designed for use in high-speed fuel-injection engines,
considerable difficulty was experienced in obtaining the same spray penetrations, when using
the same injection valve under seemingly similar conditions. Also spray discharges, of much
smaller mass and at lower pressure than the main sprays, took place after cut-off.