Figure 1-29.—Diesel fuel system.
mixture in the cylinders for the harder job of starting at
low temperature.
DIESEL FUEL SYSTEM
The primary job of the diesel fuel system is to inject
a precise amount of atomized and pressurized fuel into
each engine cylinder at the precise time. The major parts
of the diesel system are the fuel tank, fuel transfer pump,
fuel filters, injection pump, and injection nozzles
(fig. 1-29).
Fuel Transfer Pump
The fuel transfer pump is normally used on modern
high-speed diesel engines. It can be driven by either
engine or battery voltage. The fuel transfer pump can be
located on the outside of the fuel tank in the supply line,
submerged within the fuel tank, or mounted on the
backside of the injection pump. The fuel pump pushes
or draws the fuel through the filters where the fuel is
cleaned.
Injection Pump
Several types of injection pumps are used on diesel
engines. Each has its own unique operating principles.
The primary function of the injection pump is to supply
high-pressure fuel for injection.
Injection Nozzles
A wide variety of injector nozzles are in use today.
All are designed to perform the same basic function
which is to spray the fuel in atomized form into the
combustion chamber of each cylinder.
Cold Weather Starting Aids
Diesel fuel evaporates much slower than gasoline
and requires more heat to cause combustion in the
cylinders of the engine. For this reason, preheater and
starting aids, called glow plugs, are installed on
equipment equipped with diesel engines.
PREHEATERS.— Preheaters are normally
installed in the intake manifold; however, in a
two-stroke cycle engine, they are placed in the air
passages surrounding the cylinders. The preheater burns
a small quantity of diesel fuel in the air before the air is
drawn into the cylinders. This burning process is
accomplished by the use of either a glow plug or an
ignition coil that produces a spark to ignite a fine spray
of diesel fuel. The resulting heat warms the remaining
air before it is drawn into the cylinders.
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