TROUBLESHOOTING THE HMMWV - OD1616 - LESSON 1/TASK 1
(5) Fuel Injectors. For proper engine performance, the fuel must
be injected into the combustion space in a definite spray pattern.
This is accomplished by the fuel injector.
The fuel enters the nozzle holder body through the high-pressure
inlet. It then passes down to the pressure chamber above the valve
seat. When the pressure developed by the injection pump exceeds the
force exerted by the pressure adjusting spring, the nozzle valve will
be lifted off of its seat, resulting in the injection of fuel into
the cylinder. The valve on the HMMWV will open at approximately 1960
psi.
A controlled seepage exists between the lapped surfaces of the nozzle
valve and its body to provide for lubrication. This leakage/overflow
passes around the spindle and into the pressure adjusting spring
chamber.
From here, the fuel leaves the injector through the
overflow outlet and finally to the overflow lines, which lead back to
the low-pressure fuel supply.
(6) Fuel Supply and Return Line(s). The final two components of
the fuel system are the fuel supply and the fuel return lines. The
fuel supply line is the line that the fuel travels through on its way
from the fuel tank to the various other components of the fuel
system.
The fuel return line is the line that the unused fuel
travels through on its way back to the fuel tank from the injection
pump.
c.
Engine Construction and Operation.
In many respects, the four-
stroke cycle gasoline engine and the four-stroke cycle diesel engine
are very similar. They both follow an operating cycle that consists
of intake, compression, power, and exhaust strokes. They also share
the same system for intake and exhaust valves. The major differences
between gasoline and diesel engines will be discussed in the
paragraphs that follow.
(1) The fuel and air mixture is ignited by the heat generated by
the compression stroke in a diesel engine versus the use of a spark
ignition system on a gasoline engine.
The diesel engine needs no
ignition system. For this reason, the gasoline engine is referred to
as a spark ignition engine, while the diesel engine is referred to as
a compression ignition engine.
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