3Com Caterpillar Commercial Diesel Engine SEBU6251-06 - Manual (Page 20)

20
Maintenance Section
Fuel Specifications
i01111650
Characteristics of Diesel Fuel
SMCS Code: 1250; 1280
The primary characteristics that affect engine
operation and performance in cold temperatures
are the following characteristics: Lubricity, Viscosity,
Cetane Number, Cloud Point, Pour Point, and
Moisture Content.
Refer to Special Publication, SEBD0717, “Diesel
Fuels and Your Engine” for information about the
following fuel properties: ignition quality, gravity
(density), viscosity, cloud point, pour point, and
sulfur content.
Lubricity and Low Sulfur Fuel
Note: The fuel lubricity is important. You should
consider the fuel’s lubricity whenever you operate
the equipment in arctic weather. Also, you should
consider the fuel’s lubricity whenever you use
fuels that are lower in viscosity. There are many
aftermarket additives that are available to treat fuel.
If the fuel’s lubricity is an issue, consult your fuel
supplier for proper recommendations regarding fuel
additives.
In the USA, a 0.05 percent limit on the amount of
fuel sulfur in diesel fuel was mandated in January
of 1994 for on-highway trucks. The removal of
sulfur from diesel fuel helps to reduce particulate
emissions from diesel engines. While limits for
fuel sulfur have not generally been mandated for
off-highway use, some local governments have
regulations that include off-highway use. There
is frequently no difference in the fuel that is
sold for different applications. The same fuel is
often used for both on-highway applications and
off-highway applications. Other areas of the world
are mandating similar limits. Regulations continue to
become more stringent. Lower sulfur limits can be
expected in the future.
The fluid’s lubricity describes the ability of the fluid
to reduce the friction between surfaces that are
under load. This ability reduces the damage that
is caused by friction. Fuel injection systems rely
on the lubricating properties of the fuel. Until fuel
sulfur limits were mandated, the fuel’s lubricity was
generally believed to be a function of fuel viscosity.
The process that is most commonly used to remove
sulfur from fuel is called hydro-treatment. This
process is also the most economical process. Each
source of crude oil contains different amounts
of sulfur. Crude oils with low sulfur require little
hydro-treatment to obtain the 0.05 percent limit.
Crude oils with high sulfur require a more severe
treatment.
The Hydro-treatment removes the fuel’s sulfur as
well as other components. The treatment removes
nitrogen compounds, polar materials, bicyclic
aromatics, polycyclic aromatics, and oxygen
compounds. While the removal of sulfur has shown
no detrimental effects to the engine, the removal of
other compounds have lowered the lubricity of the
fuel. As a result of the lowered lubricity, the fuel is
less tolerant of contamination by water and dirt. The
lower fuel lubricity can be seen as abrasive wear
of fuel system components. Fuels that have a low
lubricity may not provide adequate lubrication to
plungers, to barrels, and to injectors. This problem
may be compounded in areas that require winter
blends of fuel. The lighter winter fuel blend has
the following characteristics: lower viscosity, lower
cloud point, and lower pour point.
All low sulfur fuels do not have a low lubricity. The
fuel’s lubricity may be enhanced with additives.
Many fuel suppliers treat the fuel with these
additives. Do not use a fuel lubricity additive before
you consult the fuel’s supplier. Some aftermarket
additives may not be compatible with the additives
that are already in the fuel. Some additive packages
that are supplied by the aftermarket manufacturer
may not be compatible with the seals that are used
in fuel systems of some diesel engines. Other
additive packages that are supplied by aftermarket
manufacturers cannot provide proper performance
in high temperature conditions. These additives may
leave deposits because of the high temperatures
that exist in the fuel systems of diesel engines.
Maximum life of the fuel system can be achieved by
performing the following tasks: using a reliable fuel
supplier, performing proper maintenance of the fuel
system, and installing Caterpillar high efficiency fuel
filters in the fuel system.
Note: Lighter fuels are frequently used in arctic
temperatures. Lighter fuels may include the following
fuels: Jet A-1, JP-8, JP-5, and kerosene. The fuel
lubricity is not a requirement of the specifications
for these fuels. Do not assume that a fuel meets
the minimum Caterpillar specification. Contact the
fuel supplier for proper recommendations on fuel
lubricity additives.
Viscosity
The viscosity of the fuel is significant because
the fuel serves as a lubricant for fuel system
components. Arctic fuels need to have sufficient
viscosity. The fuel must lubricate the fuel system at
a temperature of 0

C (32

F) or below freezing. If the
kinematic viscosity of the fuel is lower than 1.4 cSt
as supplied to the fuel injection pump or to the unit
injectors, excessive scuffing and seizure can occur.