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National Advisory Committee for Aeronautics, Technical Notes - Some Characteristics of Fuel Sprays from Open Nozzles

The penetration and cone-angle of fuel sprays from open
nozzles were recorded with the N.A.G.A. Spray Photography
Equipment. The results show that for injection systems in
which the rate of pressure rise at the discharge orifice is
high, open nozzles give spray—tip velocities and penetrations
which compare favorably with those of closed nozzles. The
spray cone—angle was the same for all tests, although open
nozzles having different orifice diameters were used, and one
nozzle was used both as an open and as a closed nozzle. In
designing a fuel system using open nozzles, particular care
must be taken to avoid air pockets. The check valve should
be placed close to the discharge orifice.

When Open nozzles are used in solidwinjection engines,
no injection valve is necessary. Instead, a check valve is
used to prevent the flowing of cylinder gases into the fuel
system during the part of the cycle when no fuel is being

injected. This arrangement simplifies the injection system.
The open nozzle is now used on the Packard and Junkers air—
craft Diesel engines, showing that its advantages are being
recognized. However, with pump injection systems such as are
on these engines, the open nozzle gives low sprayhtip veloci—
ties during the start of injection and also at low speeds be— .
1 cause the pressures forcing the fuel through the discharge i
orifice are necessarily low (Reference 1). The open nozzle (
will probably find more favor in a fuel injection system in
which the rate of pressure rise at the discharge orifice is
high at all engine speeds. Since the injection system of the
N.A.C.A. Spray Photography Equipment (Reference 2) gives a high
rate of pressure rise at the discharge orifice (Reference 3),
an investigation was undertaken with this equipment to deter-
mine the spray characteristics of open nozzles and to compare
these characteristics with those of closed noZzles. The tests
were conducted at the Langley Hemorial Aeronautical Laboratory.