Fuel
System
DIESEL FUEL
Diesel fuel, like gasoline and most gaseous fuels, is a
product of crude oil refining. Its heat content is
somewhat higher than that of gasoline.
In a diesel engine, fuel is sprayed into the combustion
chamber as the piston approaches the top of its com-
pression stroke. The fuel is ignited by the intense heat
that develops as the air within the engine cylinder is
compressed.
No
electrical ignition system is
necessary.
Diesel fuel requirements vary with engine size, speed
and load, and with ambient temperature. Factors
which must be considered include the fuel's cetane
number, pour point, viscosity, volatility, and the
amount of sediment, residues, and sulfur in the fuel.
The American Society for Testing Materials (ASTM)
has used these and other characteristics to define
three basic diesel fuel grades. Refer to the Service
and Maintenance section for the recommended grade
of fuel to use in the engine.
Cetane Rating
Cetane number is a measure of how quickly diesel
fuel will ignite under heat and pressure. For proper
engine operation, diesel fuel should ignite almost
immediately after entering the engine combustion
chamber. If ignition is delayed, too much fuel will
ignite at once, causing sudden explosions. These
explosions produce the familiar cackle heard when a
diesel engine is'cold or at idle. If the cackle does not
disappear as the engine is warmed or placed under
load,
it
is a sign that the cetane rating of the fuel may
be too low, which could cause serious engine
damage.
KEEP
FUEL
CLEAN!
0
DIRTY FUEL
IS
ONE OF THE MAJOR CAUSES OF
ENGINE FAILURE
0
REMEMBER- EVEN A TINY PARTICAL
OF
DIRT
IN
THE INJECTION SYSTEM MAY STOP YOUR ENGINE!
0
Pour
Poi
n
t
The temperature at which a diesel fuel will cease to
flow is known as its pour point. As diesel fuels
approach their pour point, waxes form and plug fuel
filters causing fuel starvation. For this reason, if low
ambient temperatures are possible, diesel fuel with a
pour point at least
10
degrees
F
(6°C) below the
lowest expected temperature should be specified.
Keeping Diesel Fuel Clean
and
Free From Water
It is essential that diesel fuel be kept clean and free
from water. Diesel injection pumps and nozzles are
precision-made units requiring extremely close tol-
erances. They are very sensitive to any abrasive
materials and are easily damaged by corrosion result-
ing from the introduction of water into the system.
To keep fuel contamination
to
a minimum, the fuel
storage and system maintenance procedures out-
lined below must be followed.
1.
Do not use zinc or galvanized storage tanks as
harmful compounds may form as a result of reac-
tions with diesel fuel impurities.
2.
Pitch fuel tanks away from the fuel outlet and
provide a drain cock to drain off water and sedi-
ment. The fuel outlet should be located several
inches above the bottom of the tank, Figure
8.
3.
Keep fuel tanks as near full as possible to minim-
ize condensation within the tank.
4.
Drain sediment traps and change fuel filters on a
regular basis as recommended by the engine
manufacturer.
FIGURE
8.
FUEL
STORAGE
22
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