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The intermittent spray characteristics of a multi-hole and a single-hole diesel nozzle were
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experimentally investigated. The hole number of the multi-hole nozzle was 5, and the hole
diameter of the 5-hole and the single-hole nozzle was the same as dn=0.32 mm with the constant
hole length to diameter ratio (In/dn=2.81). The droplet diameters of the spray, including the
time-resolved droplet diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean
diameter), injected intermittently from the two nozzles into the still ambient were measured by
using a 2-D PDPA (phase Doppler particle analyzer). Through the time-resolved evolutions of
the droplet diameter, it was found that the structure of the multi-hole and the single-hole nozzle
spray consisted of the three main parts : (a) the leading edge affected by surrounding air and
composed of small droplets; (b) the central part surrounded by the leading edge and mixing
flow region and scarcely affected by the resistance of air; (c) the trailing edge formed by the
passage of the central part. The SMD decreases gradually with the increase in the radial distance,
and the constant value is obtained at the outer region of the radial distance (normalized by hole
diameter) of 7-8 and 6 for the 5-hole and single-hole nozzle, respectively. The SMD along the
centerline of the spray decrease shapely with the increase in the axial distance after showing the
maximum value near the nozzle tip. The SMD remains the constant value near the axial distance
(normalized by hole diameter) of 150 and 180 for the 5-hole and the single-hole nozzle,
respectively.4475
Key Words:Atomization Characteristics, Intermittent Diesel Spray, SMD (Sauter Mean Di-
ameter), PDPA (Phase Doppler Particle Analyzer)
1. Introduction
Recently, multi-hole nozzles are widely used in
direct injection (D. I.) diesel engines, owing to its
potentiality in the reduction of exhaust emissions.
However, the spray characteristics of the multi-
* Corresponding Author,
E-mail : j klee @ mec.hiroshima-u.ac.jp
TEL: +81-824 24 7566; FAX : +81-824-22-7034
Department of Mechanical System Engineering, Uni-
versity of Hiroshima, Hi&ashi-Hiroshima 739-8527,
Japan. (Manuscript Received July 3, 2001;Revised
September 30, 2002)
hole nozzle are not clear until now due to the
sophisticated geometry and the flow structure
inside the nozzle tip, contrary to the cases of
single-hole nozzles. Moreover, many experimen-
tal studies on the spray characteristics deal with