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National Advisory Committee for Aeronautics, Report - Experiments on the Distribution of Fuel in Fuel Sprays

The distribution of the fuel in sprays for compression
ignition engines was investigated by taking highrspeed
spark photographs of fuel sprays produced under a wide
variety of conditions, and also by injecting them against
pieces of Plastieine. A photographic study was made of
sprays injected into evacuated chambers, into the atmos-
phere, into compressed air, and into transparent
liquids. Pairs of identical sprays were injected counter
to each other and their behavior analyzed. Small high
velocity air jets were directed normally to the axes of
fuel sprays, with the result that the envelope of spray
which usually obscures the core was blown aside, leaving
the core exposed on one side.
The results showed that the dishiquimz, of the fuel
within the sprays was very uneven. Under engine-
operating conditions the fuel was subdivided into many
small particles by the time it had penetrated 0. 75 inch.
In the cores of the sprays, these particles had a high
velocity relative to the air in their immediate vicinity,
but as their velocity was reduced, they were forced out of
the core andde the spray envelope. The shape of
the central core varied with the density of the chamber
air, becoming shorter and thicker with increasing air
density.
Because of the great importance of fuel distribution
in the development of light-weight compression-
tion engines, this series of experiments was under-
taken for the purpose of obtaining more information
on the distribution of the fuel within fuel sprays for
this type of engine. There are two general methods
available for such an investigation: The separation
of the sprays into parts, followed by-a determination
of the amounts of fuel in each part, and the high-
speed photography of sprays produced under con-
ditions especially arranged to reveal the desired infor—
mation. The first method has been successfully used
at the Pennsylvania State College with sprays from
plain cylindrical nozzles (references 1 and 2), and the
results show that the fuel concentration was greatest
in the center of the spray. Many early spark photo—
graphs made by the National Advisory Committee
for Aeronautics also show a core of concentrated fuel
but the density of the spray cloud was so great that
little could be learned of the internal structure of the
sprays.