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 on 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
teat 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.
Lighter fuels are frequently used in arctic
temperatures. These lighter fuels are the
following fuels: Jet A-1, JP-8, JP-5, and kerosene.
The fuel lubricity is not a requirement for these
fuels. Do not assume that a fuel meets the
minimum specification. Contact the fuel supplier
The viscosity of the fuel is significant because the fuel serves
as a lubricant for fuel system components. Arctic fuels should
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.
The cetane number of the fuel has an effect on the ability of
the engine to start. Also, the cetane number has an effect on
the interval of time before the engine runs smoothly.
Generally, an increase of ten in the cetane number will allow
the engine to be started at a lower temperature. The starting
temperature can be improved approximately 7 to 8°C (12 to
15°F) for every increase of ten in the cetane number. After the
engine reaches the normal operating temperature, a change in
the cetane from 40 to 50 will have a minimum effect on engine