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National Advisory Committee for Aeronautics, Technical Notes - Some Effects of Air and Fuel Oil Temperatures on Spray Penetration and Dispersion

This note presents experimental results obtained from a
brief investigation of the appearance, penetration, and disPer—
sion of oil sprays injected into a chamber of highly heated air
at atmospheric pressure.

The development of single sprays injected into a chamber
containing air at room temperature and at high temperature was
recorded by means of the N.A.G.A. Spray photography equipment.

A comparison of the spray records showed that with the air
at the higher temperature the spray assumed the appearance of
a thin, transparent cloud, the greatest part of which rapidly
disappeared from View. With the chamber air at room temperature
a compact Spray with an opaque core was obtained. Measurements
of the records showed a decrease in penetration and increase in
dispersion of the Spray injected into the heated air. No igni—
tion of the fuel injected was observed or recorded until the
spray particles came in contact with the much hotter walls of
the chamber about 0.3 second after the start of injection.

Most of the research work carried out thus far on the var—
ious factors affecting the characteristics of fuel sprays for
compressioneignition engines has been conducted at room temper—
atures. The design of an engine with favorable ignition lag
and efficient burning of the fuel injected, however, requires
among other things a knowledge of the effect on the Spray of
the factors involved under the temperature and pressure condi—
tions in actual engine operation. The investigations that have
been made on sprays injected into air and other gases at vary—
ing pressures and temperatures indicate that the temperatures
of the fuel and air considerably influence Spray penetration
and dispersion. An outstanding investigation on oil Sprays in—
jected into heated air was presented in a paper by Bird (Refer—
ence 1). He found that increasing the temperature of the fuel
decreased penetration and increased dispersion of the spray.
Increasing the viscosity of the air alone by increasing its
temperature had no appreciable effect on penetrations As the
sprav advanced through the heated air in the chamber, however,
a large part of the fuel was vaporized.