INTRODUCTION TO THE HMMWV - OD1615 - LESSON 1/TASK 2
g. Fuel Supply and Return Line(s).
The final two components of the
fuel system that will be discussed are the fuel supply and the fuel return
lines. The fuel supply line is the line through which the fuel travels on
its way from the fuel tank to the various other components of the fuel
system. The fuel return line is the line through which unused fuel travels
on its way back to the fuel tank from the injection pump.
3.
Engine Construction and Operation
a. 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.
b. In a diesel engine, the fuel and air mixture is ignited
by the heat
generated by the compression stroke, in contrast to 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.
c. The air is compressed to about one-twentieth of its original volume
in a diesel engine.
In contrast, the fuel and air mixture in a gasoline
engine is compressed to about one-eighth of its original volume. The diesel
engine must compress the air tightly to generate enough heat to ignite the
fuel when it is injected into the cylinder. The gasoline engine mixes the
fuel and air before it reaches the combustion chamber.
A diesel engine
takes in only air through the intake port. Fuel is then injected into the
combustion chamber just before completion of the compression stroke. As the
fuel is injected, it mixes with the air and ignites because of the heat.
d. The engine speed and power output of the diesel engine are
controlled by the quantity of the fuel admitted to the combustion chamber.
The amount of air remains constant. This contrasts with the gasoline engine
where the speed and power output are regulated by limiting the air entering
the engine.
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