74 SEBU8605-01
Maintenance Section
Refill Capacities
Diesel Fuel Characteristics
Cetane Number
Fuel that has a high cetane number will give a
shorter ignition delay. A high cetane number will
produce a better ignition quality. Cetane numbers are
derived for fuels against proportions of cetane and
heptamethylnonane in the standard CFR engine.
Refer to “ISO 5165” for the test method.
Cetane numbers in excess of 45 are normally
expected from current diesel fuel. However, a cetane
number of 40 may be experienced in some territories.
The United States of America is one of the territories
that can have a low cetane value. A minimum cetane
value of 40 is required during average starting
conditions. A fuel with higher cetane number is
recommended for operations at high altitudes or in
cold-weather operations.
Fuel with a low cetane number can be the root cause
of problems during a cold start.
Viscosity
Viscosity is the property of a liquid of offering
resistance to shear or flow. Viscosity decreases
with increasing temperature. This decrease in
viscosity follows a logarithmic relationship for normal
fossil fuel. The common reference is to kinematic
viscosity. Kinematic viscosity is the quotient of the
dynamic viscosity that is divided by the density. The
determination of kinematic viscosity is normally by
readings from gravity flow viscometers at standard
temperatures. Refer to “ISO 3104” for the test
method.
The viscosity of the fuel is significant because fuel
serves as a lubricant for the fuel system components.
Fuel must have sufficient viscosity in order to lubricate
the fuel system in both extremely cold temperatures
and extremely hot temperatures. If the kinematic
viscosity of the fuel is lower than “1.4 cSt” at the fuel
injection pump, damage to the fuel injection pump
can occur. This damage can be excessive scuffing
and seizure. Low viscosity may lead to difficult hot
restarting, stalling, and loss of performance. High
viscosity may result in seizure of the pump.
Perkins recommends kinematic viscosities of 1.4 and
4.5 mm2/sec that is delivered to the fuel injection
pump. If a fuel with a low viscosity is used, cooling of
the fuel may be required to maintain 1.4 cSt or greater
viscosity at the fuel injection pump. Fuels with a high
viscosity might require fuel heaters in order to lower
the viscosity to 4.5 cSt at the fuel injection pump.
Density
Density is the mass of the fuel per unit volume
at a specificte
mperature. This parameter has a
direct influence on engine performance and a direct
influence on emissions. This influence determines
from a heat ou
tput given injected volume of fuel. This
parameter is quoted in the following kg/m
3
at 15 °C
(59 °F).
Perkins recommends a density of 841 kg/m
3
in order
to obtain the correct power output. Lighter fuels are
acceptable
but these fuels will not produce the rated
power.
Sulfur
The level of sulfur is governed by emissions
legislati
ons. Regional regulation, national regulations,
or international regulations can require a fuel with
aspecific sulfur limit. The sulfur content of the fuel
and the fu
el quality must comply with all existing local
regulations for emissions.
Perkins
1200 series diesel engines have been
designed to operate only with ULSD. By using the
test methods “ASTM D5453, ASTM D2622, or ISO
20846 IS
O 20884”, the content of sulfur in ULSD fuel
must be below 15 PPM (mg/kg) or 0.0015% mass.
NOTICE
Use of d
iesel fuel with higher than 15 PPM sulphur lim-
it in these engines will harm or permanently damage
emissions control systems and/or shorten their ser-
vice i
nterval.
Lubricity
Lubr
icity is the capability of the fuel to prevent pump
wear. The fluids lubricity describes the ability of the
fluid to reduce the friction between surfaces that are
unde
r 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
wer
e mandated, the fuels lubricity was generally
believed to be a function of fuel viscosity.
The
lubricity has particular significance to the current
ultra low sulfur fuel, and low aromatic fossil fuels.
These fuels are made in order to meet stringent
ex
haust emissions.
The lubricity of these fuels must not exceed wear scar
di
ameter of 0.52 mm (0.0205 inch). The fuel lubricity
test must be performed on an HFRR, operated at
60 °C (140 °F). Refer to “ISO 12156-1 ”.
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