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holes were located with same intervals in a plain
met at right angles. The diameter of a hole, length
to diameter ratio ([n/dn) of the nozzle and nozzle
hole total area were 0.32 mm, 2.81 and 0.412 mm 2,
respectively. The diameter and [n/dn of the single
-hole were 0.32 mm and 2.81, which are the same
as those of the multi-hole nozzle. The rotating
speed of the pump in this experiment was set up
to 500 rpm with constant total injection quantity
of 30 mm3/st. The injection quantity of a tested
hole was 7.31 mm3/st, and that of the single-hole
nozzle was the same. The injection duration was
1.l.and 0.8 ms for the 5-hole and the single-hole
nozzle, respectively.
2.3 PDPA system
The droplet size measurements of the fuel spray
were carried out by a 2-dimensional PDPA (Dan-
tec Co.) system. The PDPA system consists of a
transmitter optics with a 750 mW air cooled Ar-
ion laser as a light source, receiver optics as a
scattered light collection system, a signal pro-
cessing electronics (Dantec Co., 58N50), a three
I
III Tradm, g e~'k:je
Outer
regqon
',., "\ /
a,r ~, '\..
/
/ ¢
",... "..,..,~. J ./
$'fl
Fig. 3
~1 Central part
MnXd~:.g
flow region
~- I. Lead~n9 edge
Illustration of typical structure of spray
formed by diesel nozzle and definitions of
coordinate system in spray flow field
dimensional traverse and data acquisition system
including a computer. Two laser beams, repres-
enting the wavelengths of 514.5 (green) and 488
(blue) nm, from transmitting optics cross at one
point and form a measurement volume. Receiving
optics detects the scattered lights, which is pro-
duced when droplets pass through the
measurement volume, and then transmits them to
the signal processor. Therefore, the droplet size is
measured by the frequency and relative phase
difference of the Doppler signal.
The measurement of the droplet size was con-
ducted in the two dimensions at axis because the
sprays would be considered as an axi-symmetric
structure in the spray flow field. Figure 3 shows
the schematic diagram of the typical structure of