Product Description
Multec 3.5 Fuel Injector Application Manual
3-22
Delphi Energy and Chassis Systems
Revision: 11/05-1
Positioning of the injector must take into account the amount of time
required to vaporize the fuel (tra residence time), the impact of
wall wetting and the impact on the tip temperature of the injector. Shorter
distances will reduce fuel transport delays and aid in calibrating optimum
injection timing. Longer distances allow the injector fuel spray to spread
out, contacting the walls around the intake valve. Typical injector to valve
distances for MPFI systems are 70 to 120 mm.
Note
: The placement of the injector in the head versus the intake
manifold or too close to the intake valve can significantly increase the
injector tip temperatures (especially during hot soaks) and lead to hot
start and driveability problems. Maximum allowed injector tip
temperatures are dependent on fuel system pressure and test fuel
volatility. See section 8.4.1.
3.8.2 Cone
Angle
The injector spray cone angle is a measure of the included angle
containing a specified percentage of the fuel. At Delphi spray cone angles
are measured using a spray patternator consisting of a grid of hex shaped
cells that collect the fuel spray and measure the volume distribution.
•
Single spray injectors
: The spray patternator is located 100 to 143
mm
from the injector tip. N-Heptane at system pressure is supplied to
the injector, which is pulsed at 5 ms PW, and 40 ms period. The
included angle which contains 90% of the spray volume is calculated
as the single spray cone angle.
•
Dual spray injectors:
The spray patternator is located 100 mm from
the injector tip. The spray centroids are located from the volume
distribution of each spray cone. The included angle which contains
90% of the spray volume is calculated for each spray cone and
reported as the dual spray cone angle. The location of he spray
centroids is used to calculate the dual spray separation angle and
orientation angle (see Figure 3-11.) Examples of spray patternator
data for single and dual spray injectors are shown in Figure 3-12.
Actual injector fuel delivery rates and engine operating conditions
(MAP and port air flow rates) also affect the injector cone angle.
•
Placement of the injector within the manifold or head area must
comply with the interface requirements found in section 4 and should
minimize the potential for fuel from previous injection events puddling
at the interface. Puddled fuel will eventually dislocate from the
interface, causing an excess fuel condition. This will effectively lead
to a less stable combustion event or in the extreme case, a cylinder
misfire.