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National Advisory Committee for Aeronautics, Technical Notes - Effect of High Air Velocities on the Distribution and Penetration of a Fuel Spray

By means of the N.A.C.A._Spray Photography Equipment high~
speed moving pictures were-taken’df'the formation and develop—
ment of fuel sprays from an automatic injection valve. The
sprays were injected.normal to and counter to.air at velocities
from O to 800 feet per second.. The air was at atmospheric tem-
perature and presSure. The results show that high air veloci-
ties are an effective-means of mixTng the fuel .spray with the
air during injection.

A year ago, Beardsley and the authOr'(Reference l) pub-
lished information on the effect of 16w air velocities (60 feet
per second) on the penetration and dispersion of fuel sprays for
compression—ignition engines. The results showed that although
during injection the moving air had little effect on the main
body of the spray, the fuel on the edge of the spray was blown
away from the main body when the air was directed Counter to the
spray. It was shown, in addition, that the air distributed the
fuel throughout the spray chamber at the end of injection. The
air velocity used in these experiments was much lower than that
in engines employing a small orifice-through which the piston
forces the air. In combustion chambers othhe shape employed by
the National Advisory Committee for Aeronautics in its research
on precombustion chambers (Reference-2) and in_chambers of the
type employed with the Acre—Bosch system (Reference 3), air ve-
locities of several hundred feet per second may be obtained.
Under these conditions the velocities are equal to or greater
than the velocity of the fuel spray after it has traversed an
inch or so of the combustion chamber. Consequently, we may ex—
pect that these air velacities will have a marked effect on the
fuel spray.

To determine the effect of air velocities of several hun-
dred feet per second on fuel—spray formation, a series of tests
has been conducted at the Langley Memorial Aeronautical Labora—
tory, Langley Field. Va., in which air velocities were calculat—
ed to be as high as 800 feet per second.__All tests were_made
with the fuel injected into air at atmospheric pressure and tem—
perature. From the results showing the effect of air density on
spray formation obtained by Joachim and Beardsley (Reference 4)
and from the results showing some effects of air temperatures on
spray formation obtained by Gelalles (Reference 5), it can be
concluded that any effects observed in the present tests will be
magnified under engine—operating conditions.