Automotive spark-ignited direct-injection gasoline engines

the design rail pressure during crank and start. It may also
permit a fuel system without an accumulator to be used. The
spray cone angle should ideally become smaller as the
required engine air utilization is reduced. This can be
achieved mechanically or electrically, or may occur due to
the inherent collapse of a swirling cone of droplets that are
injected into elevated air densities.
For the more stringent emissions and performance
requirements of future (2002–2008) GDI vehicles, the
fuel spray requirements of future GDI engines set
threshold performance limits for the fuel injectors and
for the fuel system as a whole. Some of the key requirements
for the next generation of injectors (2002–2008) are as
follows.
• SMD: 16 mm or less (main spray);
F. Zhao et al. / Progress in Energy and Combustion Science 25 (1999) 437–562 469
Fig. 30. Comparison of the spray characteristics of air-assisted and single-fluid swirl injectors [72]: (a) droplet size distribution; and (b) spray-tip
penetration rate.
• SMD: 21 mm or less (sac spray);
• DV90: 30 mm or less (main spray);
• DV90: 34 mm or less (sac spray);
• sac volume of less than 6% of idle fuel delivery;
• sufficient spray symmetry to permit injector rotation
or rail mounting tolerance without combustion degradation;
• narrower spray footprint (cone collapse) for injection
into higher ambient density;
• a design fuel pressure of 5.0–9.0 MPa;
• stable injection at 0.75 ms pulse width;
• 0.25 ms or less opening time;
• 0.40 ms or less closing time;
• no after injection;
• reduced power consumption;
• reduced noise level.