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TM 9-8000
regulated to a constant 20 psi regardless of engine
Multifuel Engine Authorized Fuels. Multifuel
speed and load range.
engines are four-stroke cycle diesel engines that will
operate satisfactorily on a wide variety of fuels.  The
b. The pressure regulated fuel then passes through
fuels are grouped accordingly:
a series of two orifices.  The two orifices, by offering
greatly different resistances to flow, form a system that is
a. Primary and Alternate I Fuels. These fuels will
sensitive to viscosity changes.
operate the multifuel engine with no additives.
(1)  The first orifice is annular, formed by the
b. Alternate II Fuels. These fuels generally require
clearance between the servo piston and its cylinder.
the addition of diesel fuel to operate the multifuel engine.
This orifice is sensitive to viscosity.
c.  Emergency Fuels. These fuels will operate the
(2)  The second orifice is formed by an
multifuel engine with the addition of diesel fuel.
adjustable needle valve, and, unlike the first, it is not
Extended use of fuels from this group will cause
viscosity sensitive.
eventual  fouling  of fuel Injection components. It
should be noted that there are no adjustments necessary
(3)  After the fuel passes through the two
to the engine when changing from one fuel to another.
orifices It leaves the compensator through an outlet port.
From here the fuel passes back to the pump.
Fuel Density Compensator (Fig. 5.1).  The
multifuel engine operates on a variety of fuels that have.
c.  The higher the viscosity of the fuel, the more
a broad range of viscosities and heat values.  These
trouble that It will have passing through the first orifice.
variations In the fuels affect engine output. Because it is
Because of this, the fuel pressure under the servo piston
unacceptable for the power output of the engine to vary
will rise proportionally with viscosity.
Because the
with fuel changes, the multifuel engine is fitted with a
second orifice is not viscosity sensitive, the pressure
device known as a fuel density compensator. The fuel
over the servo piston will remain fairly constant. This will
density compensator is a device that serves to vary the
quantity of fuel Injected to the engine by regulating the
proportionally with viscosity, that in turn will cause the
full load stop of the fuel pump (para 4-3).
piston to seek a position In Its bore that becomes higher
characteristics of the fuels show that their heat values
as viscosity increases.
decrease  almost  Inversely  proportional  to  their
viscosities. The fuel density compensator uses viscosity
d. The upward movement of the servo piston will
as the Indicator for regulating fuel flow. Its operation is
move a wedge-shaped moveable plate, which will
as follows:
decrease fuel delivery. A lower viscosity fuel will cause
the piston to move downward, causing the pump to
a. The fuel supply enters the compensator through
Increase fuel delivery.
the fuel pressure regulator, where the supply pressure is
Change 1 5-2


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