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Effect of Orifice Length Diameter Ratio on Spray Characteristics

The effect of variations of orifice length to diameter
ratio on spray characteristics was determined for a 0.014—inch
and a 0.040—inch orifice for ratios of 0.5 to 4.0. The nozzles
containing the orifices were mounted in an injection valve and_”
tested with a plain stem and with a helically grooved stem.

The injection pressure Was varied from 4000 to 8000 pounds per
square inch. The air density into which the fuel was sprayed
Was varied from the density obtained with a pressure of 60
pounds per square inch to the density obtained with a pressure
of 350 pounds per sQuare inch at room_temperature. The tests
showed that increasing the orifice length to diameter ratio with
a plain stem in the injection valve causes the spray tip pene—
tration first to decrease, reaching a minimum between a ratio
of 1.5 and 2.5, and then to increase, reaching a maximum at a
ratio greater than 3.5. The spray cone—angle showed little
change with variation of the ratio. With a helically grooved
stem and a small ratio of orifice area to groove area, the pene—
tration at first shows little tendency towards a minimum; but,
as the time of injection is increased to 0.004 second, the pene—
tration becomes a minimum at a ratio between 0.5 and 2.0. As
the ratio of orifice to groove area is increased, there is less
tendency for a minimum penetration to occur between the ratios
of orifice length to diameter of 0.5 and 4.0 up to 0.004 second
after the start of injection.

One of the important factors influencing the penetration
and the distribution of the fuel spray in the combustion chamber
of a fuel—injection engine is the ratio of the length to the di—
ameter of the discharge orifice. The results published on re—
searches to determine the effect of the orifice length—diameter
ratio on the fuel spray are meager. Joachim and Beardsley (Ref—
erence 1) found that, with an injection valve employing a heli—
cally grooved stem, a ratio of 1.5 gave the greatest spray tip
penetration during the time available for injection in compres—
sion—ignition engines. They also found that the Spray cone—angle
increased slightly with an increase in the ratio. McKechnie,
as quoted by Buchner (Reference 8), concluded that to obtain
the greatest ultimate penetration, the length-of the orifice
should be made as long as possible, and to obtain the great—
est fineness of atomization the length should be made as short
as possible.