INTRODUCTION TO THE HMMWV - OD1615 - LESSON 1/TASK 2
2.
Fuel System
Ignition of the fuel in a diesel engine occurs because of heat developed in
the combustion chamber during the compression stroke. Thus, no spark plugs
or high voltage ignition is necessary for a diesel engine. However, fuel is
required for combustion; therefore, we will look first at the fuel system
and the travel of fuel from the fuel tank to the point of combustion.
Fuel is pulled from the fuel tank by a mechanical fuel pump located on the
right side of the engine. The primary fuel pump is driven, through a push
rod, by a lobe on the camshaft. The fuel, from the fuel pump, travels to
the fuel filter/water separator, located on the body bulkhead above the
engine. From the filter, the fuel travels to the fuel injection pump where
it is metered to the injectors.
The injectors open at approximately 1960
pounds per square inch (psi), injection pump pressure, and spray fuel into
the combustion chamber of the cylinder.
a. Components of the Fuel System. In the preceding paragraphs the flow
of fuel, from the fuel tank to the combustion chamber, was traced. In the
paragraphs that follow, the components that comprise the fuel system will be
discussed in a little more detail.
b. Fuel Tank. The first component of the fuel system is the fuel tank.
The fuel tank used on the HMMWV is made out of plastic (polypropylene).
This protects the fuel tank from small explosive charges.
Another reason
for the use of the plastic tank is that in a metal fuel tank, such as the
one found in an automobile, condensation (water) will form as the fuel level
in the tank decreases and the ambient or outside air temperature changes.
The tank can hold up to 25 gallons of either diesel fuel 1 (DF1), diesel
fuel 2 (DF2), or diesel fuel arctic (DFA). The fuel tank is located in the
rear of the vehicle, on the right side.
c. Fuel Pump.
Fuel injection pumps must be supplied with fuel under
pressure for the following reasons:
(1) The injection pump lacks the
suction capacity to draw the fuel from the tank by itself; (2) It is
necessary to supply the fuel to the injection pump in excess, so that the
fuel may be used to cool and lubricate the system before
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