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selected to represent the time-dependent inter-
mittent characteristics as well as the mean droplet
sizes of the spray.
Through the time-resolved evolutions of the
droplet size, information on the internal structure
of the spray injected intermittently would be
found. That is, the fuel was injected with the
relatively short injection durations of 1.1 and
0.8 ms for the 5-hole and the single-hole nozzle.
Moreover, the droplet sizes were measured at the
centerline of the spray. Therefore, the time-re-
solved evolutions of the droplet diameter with
time from the start of injection (SOI) could well
show the time-dependent development process of
the internal structure of the spray.
There is a certain period, usually called the
spray tip arrival time, in which droplets are not
detected before the leading edge of the spray
reaches the measurement point. Just after the
leading edge of the spray arrived at the measure-
ment point, comparatively small-sized droplets,
which can be distinguished from the floating dro-
plets around the measurement point, are detected.
After the leading edge of the spray passed, there is
a certain period in which the detecting frequency
of the droplets is remarkably decreased. This
duration is a period in which the central part
enclosing the leading edge and the mixing flow
region of the spray, as shown in Fig. 3, passes
through the measurement point. This result,
showing the low detecting frequency, indicates
that the shape of the droplets passing through the
measurement point during this period is not
spherical at least. However, the boundary between
the leading edge and the central part of the spray
is not clear. It is also difficult to make clear
definition of the end part of central part of the
spray.
The low detecting frequency of the droplets in
the central part of the spray does not mean there
are no droplets but there are a t~w spherical
droplets. The PDPA system, which was used to
measure the droplet size, evaluates the droplet size
based on the phase difference of the scattered Intermittent Atomization Characteristics of Multi- Hole and Single- Hole Diesel Nozzle 1697
lights produced when the spherical droplets pass
through the measurement volume. In this study,