DETROIT DIESEL 53
F u e l Injector 2.1.1
through the lower port until the, port is closed off by
Operation
the lower end of the plunger. A portion of the fuel
trapped below the plunger is then forced up through a
Fuel, under pressure, enters the injector at the inlet
central passage in the plunger into the fuel metering
side through a filter cap and filter (Fig. 2). From the
recess and into the supply chamber through the upper
tiller. the fuel passes through a drilled passage into the
port until that port is closed off by the upper helix of
supply chamber, that area between the plunger
the plunger. With the upper and lower ports both
bushing and the spill deflector, in addition to that ares
closed off. the remaining fuel under the plunger is
under the injector plunger within the bushing. The
subjected to increased pressure by the continued
plunger operates up and down in the bushing, the bore
downward movement of the plunger.
of which is open to the fuel supply in the annular
chamber by two funnel-shaped ports in the plunger
When sufficient pressure is built up. it opens the flat,
bushing.
non-return check valve. The fuel in the check valve
cage, spring cage, tip passages and tip fuel cavity is
The motion of the injector rocker arm is transmitted
compressed until the pressure force acting upward on
to the plunger by the follower which bears against the
the needle valve is sufficient to open the valve against
follower spring (Fig. 6). In addition to the reciprocat-
the downward force of the valve spring. As soon as the
ing motion, the plunger can be rotated, during
needle valve lifts off of its seat. the fuel is forced
operation, around its axis by the gear which meshes
through the small orifices in the spray tip and
with the control rack. For metering the fuel, an upper
atomized into the combustion chamber.
helix and a lower helix are machined in the lower part
of the plunger. The relation of the helices to the two
When the lower land of the plunger uncovers the
ports changes with the rotation of the plunger.
lower port in the bushing, the fuel pressure below the
plunger is relieved and the valve spring closes the
As the plunger moves downward, under pressure of
needle valve, ending injection.
the injector rocker arm, a portion of that fuel trapped
under the plunger is displaced into the supply chamber
A pressure relief passage has been provided+ in the
spring cage to permit bleed-off of fuel leaking past the
needle pilot in the tip assembly.
A check valve, directly below the bushing, prevents
leakage from the combustion chamber into the fuel
Fig. 6 - Fuel Injector Mounting
Fig. 7- Removing Injector from Cylinder Head
SEC. 2.1.1 Page 3
March, 1973
