Automotive spark-ignited direct-injection gasoline engines

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F. Zhao et al. / Progress in Energy and Combustion Science 25 (1999) 437–562
Fig. 8. Spray characteristics of the Mitsubishi GDI injector [20,50,51]: (a) injector design; (b) spray outlook; and (c) spray characteristics.
which is the opposite of what is generally obtained using
inwardly opening pintles. Since no nozzle holes are directly
exposed to the combustion chamber environment, this
outwardly opening design may prove to be more robust to
combustion product deposition. More development and
evaluation experience is required on this issue. According
to Xu and Markle [58], the outwardly opening injector is
able to produce a spray with an SMD of less than 15 mm as
measured by laser diffraction at 30 mm downstream from
the nozzle, a DV90 of less than 40 mm, and a maximum
limiting penetration of 70 mm into one atmosphere. With
regards to the relative advantages of inwardly opening
versus outwardly opening needles, the inwardly opening
needle generally provides better pulse-to-pulse repeatability
of the spray cone geometry, especially when a flow guide
bushing is present at the needle tip, and does provide
enhanced design flexibility in achieving angled sprays.
The outwardly opening geometry is, however, acknowledged
to have enhanced leakage resistance [64,65] due to
the fact that the combustion gas pressure assists in sealing
the injector positively. A comparison of the aforementioned
three typical GDI injector designs for four key criteria is
provided in Fig. 13. As may be noted, the inwardly opening
design has some significant advantages and has consequently
been widely utilized in GDI development.
In some applications having significant packaging
constraints, the GDI injector is required to deliver a spray
that is angled, or offset, from that of the injector axis. Both
the Toyota and Nissan production GDI engines use an
offset-spray injector [21,66]. This requirement makes the
GDI injector design much more complicated, as some of
the techniques for producing a symmetric and wellatomized
spray may no longer be as effective. For example,
swirling flow, as an effective technique to enhance the
atomization of a symmetric spray, may be significantly
less effective in an injector design having an offset spray.
As a result, a higher injection pressure may be required to
achieve the same degree of spray atomization for an on-axis
spray design. Also, achieving an offset-spray may not be
possible with an outwardly opening pintle.
Even with a symmetric fuel distribution, the conventional
cone-shaped spray tends to coat the piston surface