Figure 11C-4. Fuel Metering from
Figure 11C-5. Phases of Injector
No-Load to Full-load
Operation
NOTE
er which bears against the follower
sprin
Figure 11C-7 on
(see
page
Do not intermix the needle valve
11C-4).
In addition to the reciprocating
injector with other type of injec-
motion, the plunger can be rotated, dur-
tors in an engine.
ing operation, a r o u n d i t s a x i s b y t h e
gear which meshes with the control rack.
For metering the fuel, an upper helix
Each fuel injector has a circular disc
and a lower helix are machined in the
pressed into a recess at the front side of
lower part of the plunger. The relation
the injector body for identification pur-
of the helices to the two ports changes
poses (see Figure 11C-6 on page 11C-4).
with the rotation of the plunger.
The identification tag indicates the nomi-
nal
output of the injector in cubic
As the plunger moves downward, under
millimeters.
pressure of the injector rocker arm, a
portion of that fuel trapped under the
Each injector control rack (Figure 11C-3
plunger is displaced into the supply
on page 11C-2) is actuated by a lever on
chamber through the lower port until the
the injector control tube which, in turn,
port is closed off by the lower end of the
is connected to the governor by means of
plunger.
A portion of the fuel trapped
a fuel rod. These levers can be adjusted
below the plunger is then forced up
independently on the control tube, thus
through a central passage in the plunger
permitting a uniform setting of all injec-
into the fuel metering recess and into the
tor racks.
supply chamber through the upper port
until that port is closed off by the upper
The fuel injector combines in a single
helix of the plunger. With the upper
unit all of the parts necessary to provide
and lower ports both closed off, the re-
complete and independent fuel injection
maining
fuel
under
is
the plunger
at each cylinder.
subjected to increased pressure by the
continued downward movement of the
plunger.
Operation
When sufficient pressure is built up, it
Fuel, u n d e r p r e s s u r e , e n t e r s t h e i n j e c -
opens the flat, non-return check valve.
tor at the inlet side through a filter cap
The fuel in the check valve cage, spring
and filter (see Figure 11C-3 on page
cage, tip passages and tip fuel cavity is
11C-2).
compressed until the pressure force act-
From the filter, the fuel passes
through a drilled passage into the supply
upward on the needle valve is
ing
chamber, that area between the plunger
sufficient to open the valve against the
bushing and the spill deflector, in addi-
downward force of the valve spring. As
tion to that area under the injector
soon as the needle valve lifts off of its
plunger within the bushing, the bore of
seat, the fuel is forced through the small
which is open to the fuel supply in the
orifices in the spray tip and atomized in-
annular chamber by two funnel-shaped
to the combustion chamber.
ports in the plunger bushing.
When the lower land of the plunger un-
covers the lower port in the bushing,
The motion of the injector rocker arm is
the fuel pressure below the plunger is
transmitted to the plunger by the follow-
Fuel System and Governor