DETROIT DIESEL 53
Fuel Injector 2.1.1
through the lower port until the port is closed off by the
Operation
lower end of the plunger. A portion of the fuel trapped
Fuel, under pressure, enters the injector at the inlet side
below the plunger is then forced up through a central
through a filter cap and filter (Fig. 1.). From the filter,
passage in the plunger into the fuel metering recess and
the fuel passes through a drilled passage into the supply
into the supply chamber through the upper port until that
chamber, that area between the plunger bushing and
port is closed off by the upper helix of the plunger. With
the spill deflector, in addition to that area under the
the upper and lower ports both closed off, the remaining
injector plunger within the bushing.
The plunger
fuel under the plunger is subjected to increased
operates up and down in the bushing, the bore of which
pressure by the continued downward movement of the
is open to the fuel supply in the annular chamber by two
plunger.
funnel-shaped ports in the plunger bushing.
When sufficient pressure is built up, it opens the flat,
The motion of the injector rocker arm is transmitted to
non-return check valve. The fuel in the check valve
the plunger by the follower which bears against the
cage, spring cage, tip passages and tip fuel cavity is
follower spring (Fig. 6.) In addition to the reciprocating
compressed until the pressure force acting upward on
motion. the plunger can be rotated, during operation.
the needle valve is sufficient to open the valve against
around its axis by the gear which meshes with the
the downward force of the valve spring. As soon as the
control rack. For metering the fuel, an upper helix and a
needle valve lifts off of its seat, the fuel is forced
lower helix are machined in the lower part of the
through the small orifices in the spray tip and atomized
plunger. The relation of the helices to the two ports
into the combustion chamber.
changes with the rotation of the plunger.
When the lower land of the plunger uncovers the lower
As the plunger moves downward, under pressure of the
port in the bushing, the fuel pressure below the plunger
injector rocker arm, a portion of that fuel trapped under
is relieved and the valve spring closes the needle valve,
the plunger is displaced into the supply chamber
ending injection.
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
1972 General Motors Corp.
July, 1972
SEC. 2.1.1 Page 3
