A - Fuel control rod
B - Fulcrum lever
C - Shaft spring plate
D - Operating shaft spring
E - Operating shaft
F - Operating lever
Figure 5-37.Governorsectional view.
Types of Nozzles
Bosch nozzles are inward opening with a multiple
orifice and hydraulically operated nozzle valve. The
two models of this nozzle in use are the American Bosch
and Robert Bosch. They may be easily identified by
either the length of the nozzle tip holding nut or the
nozzle drilling code on the smaller diameter of the
nozzle valve body. The American Bosch nozzle nut is 3
inches long, and the nozzle tip has a hand-printed
drilling code. The Robert Bosch nozzle nut is 2 inches
long, and the nozzle tip has a machined-etched drilling
code. Component parts, although similar, are not
interchangeable between the two nozzles.
The pressurized fuel from the injection pump enters
the top of the nozzle body and flows through a passage
in the body and nozzle spring retainer. An annular
groove in the top face of the nozzle valve body fills with
fuel, and two passages in the nozzle valve body direct
fuel around the nozzle valve. When the fuel in the
pressure chamber reaches a predetermined pressure, the
spring force (adjusted by shims) is overcome and
injection occurs. Atomized fuel sprays from the orifice
holes in the nozzle tip, as the nozzle valve is opened
inward by pressurized fuel. When injection ends,
spring pressure snaps the valve in its seat. During each
injection, a small quantity of high-pressurized fuel
passes between the nozzle valve stem and the nozzle
valve body to lubricate and to cool the nozzle valve. A
manifold that connects to all of the nozzles returns this
fuel to the tank.
Fuel Density Compensator
The multifuel engine operates on a variety of fuels
that have a broad range of viscosities and heat values.
These variations in the fuels affect engine output.
Because it is unacceptable for the power output of the
engine to vary with fuel changes, the multifuel engine is
fitted with a device known as a fuel density
compensator (fig. 5-38). The fuel density compensator
is a device that serves to vary the quantity of fuel
injected to the engine by regulating the full-load stop of
the fuel pump. The characteristics of the fuels show that
their heat values decrease almost inversely proportional
to their viscosities. The fuel density compensator uses
viscosity as the indicator for regulating fuel flow. Its
operation is as follows:
The fuel enters the compensator through the fuel
pressure regulator where the fuel pressure is
regulated to a constant 20 psi regardless of
engine speed and load range.
The pressure-regulated fuel then passes through
a series of two orifices. The two orifices, by
offering greatly different resistances to flow,
form a system that is sensitive to viscosity
changes. The first orifice is annular, formed by
the clearance between the servo piston and its
cylinder. This orifice is sensitive to viscosity.
The second orifice is formed by an adjustable
needle valve and is not viscosity sensitive.