diesel fuels &amp
Diesel Fuels ..........................................................................1
Common Diesel Fuel ......................................................... 2
Diesel Fuel Grades ........................................................ 2
Low Grade ............................................................... 2
High Grade............................................................... 2
American Society for Testing and Materials (ASTM)..... 2
Diesel Fuel Types.......................................................... 3
Crude Oil ................................................................. 3
Residual Oil or Blended Heavy Fuel Oil (HFO)................ 3
Distillate Fuel............................................................ 3
Marine Diesel Oil....................................................... 3
Aircraft Jet Fuels and Kerosene Type Fuels .................. 4
Biodiesel .................................................................. 4
Ultra Low Sulfur Diesel (ULSD) ................................... 4
Diesel Fuel Characteristics ............................................. 4
Diesel Fuel Selection ......................................................... 6
Diesel Fuel Systems ...............................................................7
Basic Fuel System ............................................................ 8
MUI™ Fuel System ........................................................ 8
MEUI™ Fuel System....................................................... 8
HEUI Fuel System ......................................................... 9
Common Rail Fuel System ............................................. 9
ACERT Technology ......................................................10
Diesel Fuel System Design Considerations ..........................12
Fuel Storage Systems...................................................12
Main Fuel Tank ........................................................12
Auxiliary Fuel Tanks .................................................13
Fuel Head Limiting Tank............................................16
Base Mounted Tanks ................................................16
Fuel Tank Design Considerations ...................................17
Fuel Tank Sizing ......................................................17
Fuel Tank Material ...................................................17
Fuel Tank Installation ...............................................17
Fuel Tank Drains ......................................................17
Fuel Tank Grounding ................................................17
Fuel Tank Maintenance .............................................18
Fuel Transfer Systems ..................................................18
Fuel Transfer Pumps.................................................19
Fuel Piping Design Considerations ..................................21
Fuel Supply Piping....................................................21
Fuel Return Piping ....................................................21
Purging ...................................................................22
Siphoning & Check Valves ........................................22
Material ..................................................................22
Sizing .....................................................................22
Fuel Filtration Systems .................................................23
Filter Micron Ratings ................................................24
Primary Fuel Filter Element Specification .....................24
Duplex Fuel Filters ...................................................25
Water Separation .....................................................25
Miscellaneous Fuel System Considerations..........................29
Fuel Temperature.........................................................29
Fuel Coolers ................................................................29
Fuel Heaters................................................................30
Partial Load Operation ..................................................31
Burning Used Crankcase Oil ..........................................31
Continuous Blending.................................................33
Fuel Conservation Practices ..............................................34
Appendix 1 .........................................................................35
Day Tank Sizing (When Day Tank Serves as a Heat Sink) .......35
Day Tank Calculations ..................................................35
Day Tank Thermal Capacity Calculation ......................36
Useful Fuel Formulas and Data ..................................44
Appendix 2 .........................................................................46
Crude Oil Fuel .................................................................46
Pretreatment of Crude Oils............................................46
Crude Oil Maintenance Intervals ....................................48
Crude Oil Settling Tanks ...............................................48
Reference Material ...............................................................51
This section of the Application and Installation Guide generally describes
Diesel Fuels and Diesel Fuel Systems for Cat® engines listed on the cover of
this section. Additional engine systems, components and dynamics are
addressed in other sections of this Application and Installation Guide.
Engine-specific information and data are available from a variety of
sources. Refer to the Introduction section of this guide for additional
Systems and components described in this guide may not be available or
applicable for every engine.
Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Diesel Fuels
Diesel fuel quality is an important factor in satisfactory engine life and
performance. Fuels must provide adequate combustion without producing
excess contaminates that can harm the engine. Additionally, fuel selection
involves economic and environmental considerations. The availability of
certain grades of diesel fuels may be cost prohibitive or inappropriate for
various applications. This Application and Installation Guide provides
information on the various diesel fuel oil types and how they relate to Cat
engine installations.
Common Diesel Fuel............. 2
 Diesel Fuel Grades
 Diesel Fuel Types
 Diesel Fuel Characteristics
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Diesel Fuel Selection .............6
Page 1
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Common Diesel Fuel
Diesel Fuel Grades
A variety of fuel oils, also known
as middle distillates, is marketed for
use in diesel engines. Their
properties and performance depend
upon the refining practices employed
and the nature of the crude oils from
which they are produced. Because
of constituents in the oil, some
crude oils are naturally suited for
refinement into high-grade fuels
while others are best used for lowergrade fuels. Similarly, high-grade
fuels, low-grade fuels and the
various grades between them
provide choices for the most suitable
fuel for any given installation.
Note: The use of very high-grade
or very low-grade fuel oils often
requires modification to the fuel
system and special consideration
of additional costs that may be
encountered. Contact your Cat
dealer for information regarding the
use of these fuel types.
Low Grade
Low-grade fuels produce a higher
heat value which translates into
more engine power, but they also
produce more contaminates that
could negatively impact engine-life.
Additionally, the use of low-grade
fuel oil in diesel engines often
produces darker exhaust and a more
pronounced odor. These attributes
may be objectionable in hospital,
office, commercial or urban settings
and require the use of a higher-grade
Page 2
The high sulfur content often
found in low-grade fuels causes
corrosion, wear and deposits in the
engine. Fuels that are not volatile
enough or don’t ignite rapidly may
leave harmful deposits in the engine
and may cause poor starting or
running under adverse operating
conditions. The use of low-grade
fuels may require the use of high
priced, higher detergent lubricating
oils and more frequent oil changes
to yield appropriate performance and
engine life.
High Grade
High-grade fuels burn cleaner,
but have a lower heat value, which
yields slightly less power. Aviation
jet fuels and kerosene are considered
high-grade fuels and seldom
contribute to the formation of
harmful engine deposits and
corrosion. Other attributes of highgrade fuels include the benefits of
faster engine starting and less
frequent overhauls, and the
drawback of reduced lubricity.
American Society for Testing
and Materials (ASTM)
Due to the different engine
applications, designs and sizes,
standards for the limits of fuel
properties have been set by the
American Society for Testing and
Materials (ASTM). Utilizing the
correct fuel for the engine will
minimize wear of the injection
system, allowing easier starting and
improve component service life.
Experience has proven that
distillate fuels meeting basic
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
specifications will result in optimum
engine performance and durability.
Depending on fuel costs and
availability, the proper use of alternative fuels such as crude oil, blended
oil or residual oil can also provide
cost competitive engine operation.
deposit formations which can cause
increased cylinder and ring wear.
Diesel Fuel Types
Cat 3600/C280 diesel engines, in
general EPG applications only, can be
modified to run on blended fuels, but
MUST BE TAKEN, including following
a thorough maintenance program and
use of high quality fuel treatment
equipment. For any other applications
including marine, petroleum, industrial,
etc. that require the burning of blended
fuels, MAK Engines should be
Crude Oil
The term crude oil is used to
describe petroleum-based oils/fuels
that are not yet refined. They are
essentially in the same state as when
they were pumped from the earth.
Certain types of crude oils can be
burned in Cat engines. In some
cases, crude oil is a practical and
economical fuel for diesel engines.
Crude oils are evaluated individually
and special equipment may be
needed to condition the fuel.
Minimum guidelines have been
established to determine the
suitability of crude oils as shown in
Appendix 2.
Residual Oil or Blended Heavy Fuel
Oil (HFO)
Residual fuel (which resembles tar
and contains abrasive and corrosive
substances) is composed of the
remaining elements from crude oil
after the crude has been refined into
diesel fuel, gasoline, or lubricating
After the more desirable products
have been refined, residual fuel can
be combined or diluted with a lighter
fuel to produce a mixture that can
flow. This mixture is called blended
or heavy fuel. Heavy fuels tend to
create more combustion chamber
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Blending may improve fuel density;
however, adding alcohol (ethanol,
methanol) or gasoline causes an
explosive atmosphere in the tank
and is not recommended.
Blended fuel can lower fuel cost,
but there are often significant tradeoffs. Fuel price must be weighed
against the following.
Fuel containment effects
Reduced engine component life
Higher maintenance and
personnel costs
Reduced warranty
Distillate Fuel
Distillate fuels are refined from
crude oil and are commonly referred
to as diesel fuel, furnace oil, gas oil,
or kerosene.
Marine Diesel Oil
Many different names are used for
marine diesel fuels, which can often
cause a misunderstanding. Four
types of marine diesel fuel are
generally recognized and available
at bunkering ports around the world.
However, not all of the types are
available at every station.
Page 3
Application and Installation Guide
Gas Oil
This is a light distillate fuel which
does not contain any residual fuel.
Gas oil is approximately ASTM No. 1
diesel fuel.
Marine Diesel
This is a distillate fuel that boils
at a higher temperature than gas oil.
The fuel varies from ASTM No. 2
diesel fuel to ASTM No. 4 diesel
fuel. The composition can vary
within the following range: ASTM
No. 2 diesel fuel, No. 2 that is
contaminated with heavier fuel in
the bottom of the tanker, and
No. 2 that is blended with as much
as 20 % residual fuel.
Blended Fuel Oil
This is a blend of distillate and
residual fuel. This fuel is blended to
the viscosity that is requested by the
operator or the engine manufacturer.
Blended fuel is not recommended for
use in Cat engines that are
configured to use distillate fuel.
Residual Fuel
This is residue from the distillation
of crude oil in a refinery. DO NOT
use residual fuel in Cat engines that
are configured to use distillate fuel.
Aircraft Jet Fuels and Kerosene Type
Aircraft jet fuels and kerosene type
fuels may be used as a diesel engine
fuel provided they meet acceptable
limits. Adequate viscosity,
particularly with kerosene type fuels
is a major concern. For Cat engine
fuel systems, a minimum viscosity
of 1.4 cSt at 38°C (100°F) is
required at the engine transfer pump
to properly lubricate fuel system
Page 4
Diesel Fuels & Diesel Fuel Systems
components. Kerosene type fuels
have lower energy content than
diesel fuels and therefore will
produce less peak power output
and/or will require more fuel volume
to do an equivalent amount of work.
Biodiesel is a fuel that can be made
from a variety of sources. Soybean
oil and rapeseed oil are the primary
sources, but alternate base stocks
may include animal tallow, waste
cooking oil, or a variety of other
In original forms, these oils are not
suitable for use as a fuel in compression engines; they must first be
esterified. Without esterification,
these oils will gel in the crankcase
and the fuel tank.
Ultra Low Sulfur Diesel (ULSD)
Ultra low sulfur diesel represents
distillate fuels with ≤15 ppm sulfur.
It has been developed to reduce
particulate engine emissions.
Diesel Fuel Characteristics
The following information
describes the basic fuel
characteristics and their relation to
engine performance.
Cetane Number: Index of
ignition quality determined by
comparing with fuels used as
standards for high and low
cetane numbers. The higher
the cetane number is the
shorter the ignition delay
period which affects warmup, combustion, cold start
and exhaust smoke density.
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Diesel Fuels & Diesel Fuel Systems
Sulfur: Sulfur is an element
that occurs naturally in all
crude oils, and when burned
in the combustion chamber,
can form oxides of sulfur.
These can react with water
vapor to create sulfuric acid,
which can cause severe
engine damage. High sulfur
content requires usage of high
Total Base Number (TBN) oils
or shortening of the oil change
Gravity: An index of weight of
a measured volume of fuel.
Lower American Petroleum
Institute (API) ratings indicate
heavier fuel containing greater
heat content.
Viscosity: A time measure
to resistance of flow. High
viscosities cause poor fuel
atomization thereby
decreasing combustion
efficiency. Low viscosity may
not provide adequate
lubrication to fuel system
Distillation: This involves
heating crude to relatively
high temperatures. Vapor
drawn at various temperatures
produce fuels of different
types. Lighter fuels, such as
gasoline, are drawn off first
and heavier fuels last. It has
an influence on viscosity of
the fuel and the BTU content,
which affects exhaust and
smoke, starting and power
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Application and Installation Guide
Flash Point: Lowest
temperature at which fuel will
give off sufficient vapor to
ignite when flame is applied.
Pour Point: Is the temperature
which is 3°C (5°F) above the
temperature where the fuel
just fails to flow or turns
Cloud Point: The temperature
at which a cloud or a haze
appears in the fuel. This will
happen when the temperature
falls below the melting point
of waxes or paraffins that
occur naturally in petroleum
Water and Sediment:
Percentage by volume of
water and foreign material
removed by centrifuging.
Carbon Residue: Percentage
by weight of dry carbon
remaining when fuel is burned
until no liquid remains.
Ash: Percentage by weight of
dirt, dust, sand, and other
foreign matter remaining after
Corrosion: A polished copper
strip is immersed in fuel for
three hours at 50°C (122°F).
Fuel imparting more than
slight discoloration is rejected.
Page 5
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Diesel Fuel Selection
Fuel should always be selected
based on the requirements set forth
in the Engine specific Operation
and Maintenance Manual. The
information and charts below are
for reference only. The fuels
recommended for use in Cat diesel
engines are normally No. 2-D diesel
fuel and No. 2 fuel oil, although
No. 1 grades are also acceptable.
Table 1 lists the worldwide fuel
standards which meet Caterpillar
Table 2 lists acceptable aircraft jet
fuels and kerosene type fuels.
Aviation Turbine Fuel
(JET A-1)
Aviation Turbine Fuel
(NATO Code No. F-44)
Aviation Turbine Fuel
(NATO Code No. F-34)
Table 2
No. 1-D & No. 2-D
Diesel Fuel Oils
No. 1 & No. 2 Fuel
ASTM No. 1-GT & No. 2-GT
Gas Turbine Fuels
Classes A1, A2 & B2
BS 2869
Engine Fuels
Classes C2 & D Burner
BS 2869
Diesel Fuel
Heating Oil El
Automotive Diesel
Types 1 (spl), 1, 2, 3,
& 3 (spl) Gas Oil
DF-1, DF-2 Conus &
W-FDF-20 Conus Diesel
W-FFS-1 & FS-2 Burner
Fuel Oil
MIL-LMarine Oil
Military 16884G
Table 1
Page 6
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Diesel Fuel Systems
The fuel system on a diesel engine is a highly specialized set of
components which must deliver the correct amount of fuel to the cylinder
at the precise moment it is needed. A well-designed fuel system enables the
engine to produce maximum power at maximum efficiency with a minimum
of exhaust emissions.
Today’s diesel injectors must develop very high injection pressures to
function with modern high compression ratio engine designs. They must also
control the start and duration of injection within milliseconds to perform at
the level demanded by engine customers. These precision injectors require an
adequate supply of clean, stable fuel for proper operation. This requirement
in turn demands careful attention to the fuel storage and handling systems
specified for each installation.
This section discusses the various fuel systems available on current Cat
diesel engines, details the numerous fuel storage and handling system
options available for diesel fuels, and outlines the advantages,
disadvantages, and special considerations which accompany each system.
Diesel Engine Fuel System Descriptions/Components
Cat diesel engines are all furnished with a fuel system based on a
conventional design, utilizing unit injectors, but with differing means of
injector actuation and control.
The following sections briefly describe the basic fuel system and the three
types of injector control systems currently in use.
Basic Fuel System................ 8
 MUI Fuel System
 MEUI Fuel System
 HEUI Fuel System
 Common Rail Fuel System
 ACERT™ Technology
Design Considerations .........12
 Fuel Storage Systems
 Fuel Tank Design
 Fuel Transfer Systems
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Fuel Piping Design
 Fuel Filtration Systems
Considerations ...................29
 Fuel Temperature
 Fuel Coolers
 Fuel Heaters
 Burning Used Crankcase Oil
Fuel Consumption
Practices ...........................34
Page 7
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Basic Fuel System
The basic fuel system, common
to all Cat diesel engines, includes
an engine driven fuel transfer pump,
a secondary fuel filter, unit fuel
injectors and a fuel pressure
regulator. Optional Caterpillar
supplied fuel system components
include flexible hoses, a manual fuel
priming pump, and a duplex primary
fuel strainer. A basic fuel system
schematic is shown in Figure 1.
The engine driven transfer pump
delivers fuel to the unit injectors via
the secondary fuel filter. The pump
is equipped with a pump-mounted
safety valve and the fuel flow at
rated rpm is listed in the technical
data and varies with engine speed.
The unit injector, either
mechanically or hydraulically
actuated, combines the functions of
pumping, metering and injecting into
a single unit. It is located near the
center of the combustion chamber in
each cylinder head, between the
rocker arms. External manifolds
supply fuel from the transfer pump
to the injectors, eliminating the need
for high pressure fuel lines. Fuel
continuously circulates through the
injectors, and the excess fuel that is
not used for combustion cools the
injectors and is returned to the fuel
tank via the pressure regulating
valve. This excess fuel also aids in
the purging of air from the system.
The fuel delivery pressure to the
injectors is controlled by a pressure
regulating valve. The pressure
regulator must be adjusted at the
installation site in order to provide
Page 8
the proper fuel pressure to the
The manual fuel priming pump is
recommended if no electrical priming
pump is available. The manual pump
helps to bleed air from the fuel
piping before initial engine operation
and following engine maintenance
such as filter element changes and
injector replacement.
Caterpillar also recommends the
use of a duplex primary fuel filter
prior to the engine driven fuel
transfer pump. This filter is available
from Caterpillar via custom quote.
When used, the duplex primary fuel
filter is installed, remotely from the
engine, in the fuel transfer pump
suction piping.
MUI Fuel System
The Mechanically actuated and
controlled Unit Injectors (MUI) use
the engine camshaft and push rods
to generate fuel injection pressure,
and a mechanical linkage system to
control the amount of fuel injected
into the cylinders. The mechanical
linkage system connects the
governor to the fuel rack, which
allows the fuel rate to the engine
to be controlled in relation to the
varying engine loads.
MEUI Fuel System
The Mechanically actuated
Electronically controlled Unit
Injectors (MEUI), formerly known as
Electronic Unit Injectors (EUI), also
use the engine camshaft and push
rods to generate fuel injection
pressure, but use an Electronic
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Diesel Fuels & Diesel Fuel Systems
Control Module (ECM) to control the
amount of fuel injected into the
cylinders. A solenoid on each
injector receives voltage signals from
the ECM to become energized. The
injectors will inject fuel only while
the injector solenoid is energized.
The ECM controls the amount of
fuel that is injected by varying the
signals that are sent to the injectors.
By controlling the timing and the
duration of the voltage signal, the
ECM can control injection timing and
the amount of fuel that is injected.
HEUI Fuel System
The Hydraulically actuated
Electronically controlled Unit
Injectors (HEUI) use a hydraulic
pump and engine oil to generate fuel
injection pressure, and an ECM to
control the pressure and amount of
fuel injected into the cylinders.
The operation of the HEUI fuel
system is completely different from
any other type of fuel system that is
actuated mechanically. The HEUI
fuel system is completely free of
adjustment. Changes in performance
are made by installing different
software in the ECM.
Common Rail Fuel System
Unlike the MEUI fuel system, in a
common rail fuel system injection
pressure is created external to the
unit injectors in a high-pressure fuel
pump which is driven off the engine.
The pump pressurizes a highpressure fuel manifold that runs
along both sides of the engine
feeding high pressure fuel to the
injectors. The electronic fuel
injectors at each cylinder control the
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Application and Installation Guide
delivery and timing of the fuel
injection(s). Similar to some other
systems, the common rail fuel
system has capability of multiple
injections for a given combustion
The main components of a
common rail system include the
high-pressure pump, the highpressure lines and rail system, and
the injectors. The low-pressure fuel
system utilizes similar components
to the unit injector fuel system. See
Figure 2 for a schematic of the
common rail fuel system.
The common rail fuel system does
not continually circulate fuel through
the entire system like the unit
injector fuel system. Instead, small
amounts of fuel are bypassed during
the injection event. Due to the very
high pressure in the fuel manifold,
more heat is put into the fuel than
on previous systems. Because of the
additional heat added to the fuel, it
is critical that the fuel inlet
temperature is maintained within
guidelines provided for the engine
model. Recommended, and
sometimes required, is the use
of a fuel cooler to maintain the
appropriate inlet fuel temperature.
Otherwise, the overheated fuel will
have very low viscosity and film
strength which makes the fuel
system components, especially the
injectors, more susceptible to
damage from fuel contaminants and
wear, hence the importance of
proper filtration practices on
common rail engines.
Page 9
Application and Installation Guide
ACERT Technology
Caterpillar ACERT Technology
improves diesel engine performance.
This technology provides precise
control over a range of combustion
variables, which can be regulated to
produce higher performance with
Diesel Fuels & Diesel Fuel Systems
fewer emissions. This new
technology works with the MEUI,
HEUI and Common Rail fuel
Fuel System Schematic
Figure 1
Page 10
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Common Rail System Schematic
Figure 2
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Page 11
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Diesel Fuel System Design Considerations
Diesel fuel supply systems must
ensure continuous and clean supply
of fuel to the engine’s fuel system.
The recommended diesel fuel supply
system typically has three major
components: a fuel storage system,
a fuel transfer system and a fuel
filtration system. The three
component systems provide clean
operating fuel to the engine.
Fuel Storage Systems
Bulk fuel is usually stored in large
main storage tanks and transferred
to smaller auxiliary tanks (service
tanks or day tanks) near engines by
electric motor-driven pumps as
shown in Figure 3.
If auxiliary tanks are not
necessary, the main fuel tank must
provide a ready fuel supply to the
engine-mounted transfer pump.
Main Fuel Tank
The main fuel tank represents
the primary fuel reservoir in all
applications, and must have
adequate capacity for the intended
Page 12
application. Rule of thumb for tank
size is to find the fuel consumption
rate at 100% load factor (depending
on application: Prime, stand-by etc.)
and multiply it with the number of
hours between refills. Fuel
consumption rates are shown on the
Engine Technical Data Sheets for the
specific engine. Additionally, 10%
should be added to the result; 5%
for expansion at the top of the tank,
and 5% for sediment settlements at
the bottom.
A power plant with one (1) 3516B
diesel generator set, rated for
1145 bkW (1560 bhp) at 100%
load. The fuel rate for the engine is
284 L/hr (75 G/hr) as found in TMI.
The time between tank refills is
based on weekly fuel tanker truck
deliveries, so refill time is 168 hours.
Tank vol. = 284 x 168 x 1.1 = 52,583 L
Tank vol. = 75 x 168 x 1.1 = 12,600 gal
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Installation Example with Main and Auxiliary Fuel Tanks
Figure 3
Auxiliary Fuel Tanks
Note: Additional clarification is
needed for C175. Reference TMI
and the special instructions
and operation. The purpose of an
auxiliary tank is to relieve the fuel
pressure “head” from the fuel
transfer pump and injection
equipment for efficient fuel flow.
Auxiliary fuel tanks, service tanks
and day tanks are secondary fuel
tanks located between the main fuel
tank and the engine. These tanks are
required in the following situations.
A manual fuel priming pump,
offered as an attachment, or an
electric motor-driver boost pump
may allow operation under
conditions more severe than those
previously described; but where
starting dependability is required,
Caterpillar recommends the use of
an auxiliary fuel tank.
The main fuel tank is located
on the same level but more
than 15 m (50 ft) away.
 The main fuel tank is located
3.7 m (12 ft) or more below
the engine.
 The main fuel tank is located
above the engine fuel
Any of the above conditions can
cause unsatisfactory engine starting
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Auxiliary tanks offer convenient
and ready fuel storage while
providing a settling reservoir for
water, sediment and sludge. An
example of an auxiliary fuel tank
is shown in Figure 4.
Page 13
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Typical Auxiliary Fuel Tank
Figure 4
Fuel Service Tank or Day Tank
Auxiliary tanks such as fuel service
tanks or day tanks can be quite
simple. It usually consists of a small
metal tank, either floor or wall
mounted, in the immediate vicinity
of the engine. The tank is usually
sized to hold approximately eight
hours of fuel, based on the engine’s
fuel consumption rate at full load.
Refilling can be accomplished by
gravity, a hand pump, or with a
motor-drive pump. Motor-drive
pumps can be either manually or
automatically controlled. For convenience and safety, automatic control is
Page 14
usually employed using a floatactuated, electric motor-drive pump.
The refilling pump can be positioned
either at the auxiliary tank or at the
main tank outlet. The performance
capability of the pump must be
considered during placement.
Features of the auxiliary tank, as
shown in Figure 5, should include
the following.
Fill line - Located above the
high fuel level, with outlet
baffled to prevent agitation of
sediment in the tank.
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Diesel Fuels & Diesel Fuel Systems
Delivery line - Located near
the bottom but not so low as
to pick up collected sediment
or condensation.
 Return line - To carry excess
fuel back to the auxiliary tank.
Should have its outlet baffled
for the reason described above.
 Overflow line - Allows excess
fuel to return to the main tank
in event of overfilling of the
auxiliary tank.
 Vent line - Allows air pressure
to equalize as tank is drained
or filled (vent cap should be
located away from open flame
or sparks).
 Drain valve - Allows removal
of condensate and sediment.
 Sight glass or float-type gauge
- Provides a positive check on
fuel level.
To prevent damage to the fuel
filter housings, the return line should
have no valves or restrictions to
allow dangerous pressure buildups.
Flexible rubber hoses, used as fuel
return lines, should be supported to
prevent closing off over time due to
weight of the hose and fuel. Hard
fuel lines prevent this problem, but a
flexible connection is still required to
isolate vibration between the line and
the tank.
A nonflammable tank mounting will
maximize fire protection.
The overflow line should be at least
two pipe sizes larger than the fill line.
To simplify engine maintenance, a
shut-off valve in the supply line is
The delivery line, carrying the fuel
to the engine-mounted fuel transfer
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Application and Installation Guide
pump, and the return line, carrying
excess fuel back to the tank, should
be no smaller in size than the
respective fittings on the engine.
Larger fuel supply and return lines
ensure adequate flow if the fuel tank
supplies multiple engines over 9 m
(30 ft.) away from the tank or when
temperatures are low. Consult
general dimension drawings for the
sizes for each model.
It is important that the fuel return
line is sloped down to the tank with
no traps or obstructions in the line.
If this is not done, the fuel system is
prone to air-lock with consequent
The auxiliary tank should be located
so that should be close enough the
level of the fuel when the tank is full
is no higher than the injection
valves. On electronic unit injector
fuel systems, static pressure on the
fuel system will cause fuel to leak
from the injectors leading to
excessive fuel dilution of the engine
oil. Static pressure would allow fuel
to leak into the combustion
chambers in the event of injection
valve leakage. The tank to the engine
so that the total suction lift to the
transfer pump with the fuel at low
level, plus the line loss of the supply
line, is less than the fuel pump’s
maximum suction lift capability. This
figure should be minimized for better
starting. A float valve or solenoid valve
in this type of day tank regulates the
fuel level to keep it below the level of
the injectors.
Note: For C175 installations that are
set up such that excess fuel from
the engine returns to the main tank
Page 15
Application and Installation Guide
and also require the fuel supply day
tank to be located higher than the
main tank, a check valve may be
Diesel Fuels & Diesel Fuel Systems
required to be installed in the return
line to prevent fuel drainage and loss
of prime. Reference REHS4726.
Typical Fuel Head Limiting Tank
Figure 5
Fuel Head Limiting Tank
If overhead mounting is
unavoidable, include an open/close
solenoid shut off valve in the supply
line and a 3.45 kPa (0.5psi) check
valve in the return line. Be sure
return restriction does not exceed
350kPa (51psi) at speed and load.
Base Mounted Tanks
Base mounted day tanks are sometimes used to provide a convenient
and close source of fuel with
Page 16
adequate capacity for four to eight
hours of operation. While minimizing
the floor space needed for fuel
storage, the height of the engine will
increase significantly with this option
designed to ease maintenance.
Fuel returning to the main tank
may, because of its volume, aid with
cooling, but returning to the day
tank is permissible.
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Fuel Tank Design
the danger of ground water
Fuel Tank Sizing
The fuel tank is typically one of the
least expensive items in an installation,
and it is wise to provide too much,
rather than too little, storage capacity.
However, while the minimum required
capacities of fuel tanks can be
estimated, as outlined in the previous
discussion of fuel tanks, some
applications may need to meet the
requirements of outside organizations,
such as the U.S. National Electrical
Code (NEC) or National Fire Protection
Association (NFPA).
Regulations governing the installation
and maintenance of both above and
below ground fuel tanks may apply.
Fuel Tank Material
Fuel tanks made from low carbon
rolled steel are best.
CAUTION: Zinc, either in the form
of plating or as a major alloying
component, should not be used with
diesel fuels. Zinc is unstable in the
presence of sulfur, particularly if
moisture is present in the fuel. The
sludge formed by chemical action is
extremely harmful to the engine’s
internal components.
Fuel Tank Installation
Large capacity storage tanks allow
bulk purchases and minimize dirt
contamination. Maintaining full tanks
reduces condensation, particularly if
fuel is seldom used.
Tanks may be above or below
ground level, but high fuel level
generally should not exceed the
engine injector’s height. This prevents
possible fuel leakage into cylinders.
Above ground tanks provide
accessibility, allowing for easy
draining of impurities and reducing
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Underground tanks allow the earth
to work as an insulator, limiting
radical temperature changes which
can cause flow restrictions,
condensation, and possible power
loss. Seasonal settlings are also
avoided when burying the tank
below frost line. In underground
tanks, the water must be removed
by pumping through a tube placed
down the fill pipe.
Locate storage tank fill tubes for
convenience and safety of filling
operations. Vents are necessary to
relieve air pressure created by filling
and prevent vacuum as fuel is
Fuel Tank Drains
All fuel tanks should have easily
accessible drain connections. Water
and sediment that collects in the
bottom of the tank must be
eliminated regularly. Provide cleanout openings for periodical removal
of sediment and trash that settles
out of fuel tanks.
Well-designed tanks have large
enough clean-out openings so the
lowest part of the fuel tank can be
accessed with cleaning equipment.
Fuel Tank Grounding
Fuel tanks, both bulk and auxiliary,
need to be grounded. This is to
improve personal safety and reduce
the fire hazard of sparks discharged
from static electricity build-up during
refueling operations.
Page 17
Application and Installation Guide
If the auxiliary tank is mounted to
the base of the engine, it will be
grounded at the same time as the
engine. If the fuel tank is placed
away from the engine, the tank
must be grounded separately.
Fuel Tank Maintenance
Fuel has a storage life of approximately one year. This period may
vary widely depending upon initial
fuel quality, contaminant levels and
storage conditions.
To remove water, scale and
bacteria growth, periodic exchange
of fuel and filtering/treating is
recommended to extend fuel life.
Water contamination of fuel during
long-term storage provides a medium
for bacterial growth, forming a dark
slime which:
Plugs filters
Deposits on tank walls and
 Swells rubber products that
it contacts
Sulfur compounds are natural
antioxidants, so low sulfur fuels
(0.05 percent by weight) degrade
quicker in storage.
Diesel fuels oxidize and form gums
and varnishes which can plug fuel
filters and injectors.
Because microorganism growth
occurs in the fuel/water layer, the
tank should be designed to minimize
this interface, and water bottoms
should be drained regularly.
Microbiocide additives, either
water or fuel soluble, can be added
to fresh fuel to inhibit microorganism
Page 18
Diesel Fuels & Diesel Fuel Systems
growth. Consult your local fuel
supplier for recommended additives.
In warm climates, large bulk storage
diesel fuel requires full filtering every
six months to one year.
Every two years the fuel should be
completely changed to remove water,
scale, bacteria growth, oxidized
gums/resins, and minimize filter
clogging due to fuel separation into
components such as asphaltenes.
Fuel Transfer Systems
Note: For C175 installations please
review REHS4726.
The diesel engine fuel supply,
delivery and governing systems are
designed to deliver clean fuel in the
precise quantity and time needed to
produce the required engine
All connection lines, valves and
tanks should be thoroughly cleaned
before making final connections to
the engine. The entire fuel system
external to the engine should be
flushed prior to connection to engine
and startup.
Caterpillar supplies the engine with
a transfer pump and the secondary
filter. The customer must provide the
primary filter and, if needed, an
auxiliary transfer pump. The auxiliary
transfer pump is required when the
distance, vertically or horizontally,
between the day tank and engine
exceeds the requirements discussed
in Auxiliary Fuel Tanks. An example
of a fuel transfer system is shown in
Figure 6.
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Typical Fuel Transfer System
(Distillate Fuel Supply System)
Figure 6
Fuel Transfer Pumps
Engine Driven
Cat engine-mounted transfer
pumps are positive displacement
gear-type or piston-type pumps, with
a limited prime and lift capability.
The pump lifts the fuel by
displacing air from the suction pipe
to the discharge pipe. Low pressure
(vacuum) develops in the suction
pipe and atmospheric pressure
[101 kPa (14.5 psi) at sea level]
moves the fuel into the vacuum.
However, a perfect vacuum cannot
be maintained, and the maximum
that a pump can lift is about
5 m (17 ft).
Cat fuel pumps’ prime and lift
capability is 3.7 m (12 ft), but pipe
size, routing, and ambient
temperature will impact this
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To determine if a pump can
perform the required lift, the
following items must be considered.
1. The vertical distance from the
tank to the pump. The distance
should be measured from the
inlet pump port of the pump to
the bottom of the tank.
2. Internal piping system losses
reduce the lifting capability. This
is based primarily on the size and
the total length of the pipes, but
also includes the various fittings
and valves. As the temperature
goes down the resistance goes
up. The internal losses can be
estimated using the Piping
System Basic Information section
of the Application & Installation
3. Elevation has a big impact on the
pump’s lifting capability. As
Page 19
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
described above the atmospheric
pressure is helping the fuel into
the vacuum, but as the elevation
gets greater, the atmospheric
pressure decreases and the
available lift will also decrease.
Refer to Table 3.
Note: This table does not apply to
C175. Reference instructions in
psi meters feet
Table 3
An auxiliary transfer pump is
required when the service tank or
day tank is located further away,
horizontally or vertically, than the
engine driven pump’s lift capability.
Special considerations must be
given to the auxiliary transfer pump
when dealing with electronic engines
and the 3500 engine family. Refer to
technical data for the engine's fuel
pump capacity to determine sizing
auxiliary fuel transfer pumps.
A primary filter must be installed
before the auxiliary pump and as
close as possible to the tank.
Page 20
Note: For C175, primary fuel filters
are standard.
In many cases, the auxiliary pump
will be driven by an electric motor
and therefore needs a regulator
valve so that the fuel flow can
match the engine speed.
A power plant with one (1) 3516B
diesel generator set, rated for
1145 bkW (1560 bhp) at 100%
load. The fuel rate for the engine is
284 L/hr (75 G/hr) as found in TMI.
The time between tank refills is
based on weekly fuel tanker truck
deliveries, so refill time is 168 hours.
The fuel tank for this genset is
located 22 m (72.2 ft) horizontally
and 2.5 m (8.2 ft) vertically (below)
from the engine. This situation
exceeds the fuel system
requirements discussed in Auxiliary
Fuel Tanks, therefore, an auxiliary
pump is needed.
TMI indicates that the fuel flow at
rated speed is 1260 L/hr (333 G/hr)
@ 1200 rpm.
The auxiliary transfer pump
required for this sample installation
must be able to deliver fuel at
1260 L/hr (333 G/hr) at a pressure
of 34.5 kPa (5 psi).
Many marine applications require
the capability to connect an
emergency fuel oil transfer pump
into the engine’s fuel oil system.
Cat engines can be provided with
these optional connections when
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Diesel Fuels & Diesel Fuel Systems
This is a specific requirement of
marine classification societies for
seagoing single propulsion engine
applications. The purpose is to
ensure fuel oil supply in the event of
an engine fuel oil pump failure. The
emergency fuel oil pump allows the
single propulsion engine to operate
and the ship to reach port for engine
Guidelines for emergency fuel oil
system operation:
1. Keep pressure drops to a
minimum by using short, lowrestriction lines.
2. Use a line size at least as large
as the engine connection point.
3. Install a low-restriction strainer in
front of the emergency oil pump.
4. Install a low-restriction check
valve between the emergency
pump discharge and the engine
inlet connection.
5. Use a pressure-limiting valve in
the emergency system set at the
maximum oil pressure limit of the
6. TMI contains flow rates and
pressure limits to fulfill minimum
engine requirements for full
power at rated speeds for Cat
Fuel Piping Design
Fuel Supply Piping
Using shutoff valves in the delivery
line may pull air into the system
during shutdown and cause hard
starting. The engine control system
provides adequate shutdown
options, but, if a shutdown solenoid
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Application and Installation Guide
is specified in the supply line, it
should be timed to close after the
engine stops rotating.
The pressure measured in the fuel
supply line should be kept below the
values shown in TMI.
Fuel Return Piping
Fuel return piping should normally
enter the tank at the top and extend
downward, exiting above the fuel
level. Inlet and return lines should be
separated in the tank as far apart as
possible to allow fuel warmed in the
engine to dissipate excess heat. Fuel
tanks can function as a radiator of
sorts, especially in engines that are
not equipped with a fuel cooler or
engines that use fuel to cool the
injectors. Placing return lines and
suction lines as far apart as possible
provides the most opportunity for
cooling. Return line placement is
particularly important on smaller
tanks and day tanks where the fuel
volume is allowed to run down.
The fuel return line is under
pressure, although not as high as the
supply line.
Note: Shut-off valves should not be
used in fuel return lines. Engine
operation with the valve closed will
cause damaging pressures.
Engine fuel pressure measured in
the fuel return line should be kept
below 27 kPa (4 psi), except for the
3300 engine family, which is 20 kPa
(3 psi), C175 engine family, which is
60 kPa (8.7 psi) and the 3600 or
C280 family, which is 350 kPa
(51psi). The location of the day tank
Page 21
Application and Installation Guide
and the design of the pipes should
accommodate these requirements.
Purging should take place both in
the supply and the return line.
Siphoning & Check Valves
Siphoning can occur in full fuel
pipes when the one end of the pipe
is placed in the fuel and the other
end is below the level of fuel.
Siphoning is a flow of fuel in the
pipe without the help of pumps. It
can occur in supply and return lines.
Siphoning is most likely to occur
after a fuel line failure, which can be
due to corrosion, fire or a cut from
foreign objects or collision force.
The consequences of fuel line
siphoning are fuel loss and the
creation of a fire hazard. If the fuel
ignites and the flow is not stopped,
the fire will be more difficult to
The fuel supply line has a fuel
transfer pump. To avoid siphoning,
the pump must be equipped with
a check valve. This is in case the
pump has been deactivated and the
fuel supply line is breeched. For
certain C175 installations, a check
valve may be necessary. Reference
page 15.
Black iron pipe is best suited for
diesel fuel lines. Steel or cast iron
valves and fittings are preffered.
CAUTION: Copper and Zinc, either in
the form of plating or as a major
alloying component, should not be
used with diesel fuels. Zinc is
unstable in the presence of sulfur,
particularly if moisture is present in
Page 22
Diesel Fuels & Diesel Fuel Systems
the fuel. The sludge formed by
chemical action is extremely harmful
to the engine’s internal components.
Pipes, hoses and fittings must be
mechanically strong and resistant to
deterioration due to age or
environmental conditions. They must
also be airtight to avoid entry of air
into the suction side of the fuel
system. A joint, which is leak-tight
to fuel, can sometimes allow air to
enter the fuel system, causing
erratic running and loss of power.
Sizing of pipes, hoses and fittings
must be adequate to minimize flow
Sizing for a particular application is
determined by the supply and return
line restrictions. This can be
estimated with help from the Piping
System Basic Information section of
the Application & Installation Guide.
The maximum allowable restrictions
are published in the TMI.
Generally, the supply line carrying
fuel to the fuel transfer pump and
the return line carrying excess fuel
back to the tank should be no
smaller in size than the connection
fittings on the engine. In addition,
the return line should be at least as
large as the supply line.
If the fuel tank supplies multiple
engines over 9.14 m (30 ft) from the
tank, or ambient temperatures are
low, larger fuel supply and return
lines should be considered to ensure
adequate flow. The overflow line
from the day tank (or, if no day tank
is used, the engine fuel return line)
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Diesel Fuels & Diesel Fuel Systems
should be one size larger than the
supply and return lines.
Fuel lines should be well routed
and clipped with flexible hose
connections where relative motion is
present. Lines should be routed
away from hot surfaces, like
manifolds and turbochargers, to
avoid fuel heating and potential
hazard if a fuel line should fail.
Fuel lines should be routed to avoid
formation of traps, which can catch
sediments, or pockets of water,
which will freeze in cold weather.
Whenever possible, route fuel lines
down low, so any potential leakage
will be confined to the fuel tank base
or floor space. Leaks from overhead
fuel system components may fall onto
hot machinery, increasing the
likelihood of fire danger.
Route fuel lines to avoid crossing
paths and walkways. Protect fuel
lines from abrasion and damage.
Whenever possible, route fuel lines
so they are visible for leak checking.
For electronic unit injector fuel
systems, supply line pressure must
decay to atmospheric pressure after
engine shut down. Any sustained
static pressure on the fuel system
when the engine is not operating will
cause excessive fuel to oil dilution.
Fuel Filtration Systems
Clean fuel that meets Caterpillar
fuel recommendations provides
outstanding engine service life and
performance. The use of lesser fuels
is a compromise and the risk is the
user’s responsibility. Fuels not
meeting Caterpillar's minimum
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Application and Installation Guide
specifications as described in
SEBU 6251 will adversely affect:
The perceived performance of
the combustion system and
fuel filters.
 The service life of the fuel
injection system, valves,
pistons, rings, liners and
Even when fuel is handled very
carefully, foreign particles will find
their way in during handling or
storage. Foreign particles could be
paint flakes, dust, sand, rust or
microbiologic particles.
Clean fuel is necessary for dependable engine performance. Engine
filters protect the fuel injection pumps
and nozzles and should never be
removed or bypassed. The compareison in Figure 7 demonstrates the very
tight clearance in the fuel system and
the size of visible particles.
Sizes of Particles
Figure 7
Primary filters will extend engine
filter and transfer pump life. Water
and sediment traps can be included
upstream of the transfer pump, but
pump flow must not be restricted.
Page 23
Application and Installation Guide
Filter Micron Ratings
Caterpillar specifies actual filter
capability, rupture strength, the
capacity for holding dirt, flow
resistance, filter area, etc.
Caterpillar does not specify filter or
filter paper by micron rating. Micron
ratings are easily confused for the
following reasons:
The test for micron ratings is
not repeatable at different
labs. One manufacturer may
give a rating of 10 microns
(0.00039 in.), another at
2 microns (0.000079 in.) and
a third may rate a particular
filter media (paper) at
15 microns (0.00059 in.).
 There is no consistent
relationship between micron
rating and actual filtration
efficiency. The entire filter
needs to be tested, not just
the media (paper).
 The micron rating does not
show what happens to a filter
over time. The test provides
no information about how a
filter will stand up under
continual use.
Micron ratings are overemphasized;
a 10-micron filter will not always stop
a 10-micron particle. Many reputable
filter manufacturing firms are drifting
away from micron ratings to more
conclusive tests. Smaller micron
ratings are not necessarily better.
If all other factors (area) were
equal, a smaller micron number
media (paper) has a severe drawback: it has less capacity before
plugging and needs to be replaced
more often. The size of the pores in
Page 24
Diesel Fuels & Diesel Fuel Systems
the paper needs to be balanced
against the costs of the filter
Common questions are:
What is the maximum particle
size which can pass through
Cat filters?
 What is the difference
between nominal size and
absolute size filters?
For example: A nominal 10 micron
filter media (paper) will pass some
particles up to about 50 microns in
size. Theoretically, an absolute rating
of 10 microns will stop all particles
larger than 10 microns. In fact, filters
with absolute micron ratings of 10
will pass some particles larger than
10 microns due to the irregularity of
the paper weave. New filters may
pass larger particles than they will
after only a few hours of use.
As a rule, Caterpillar fuel filter media
(paper) is about 3 microns nominal,
20 microns absolute. Oil filter media
(paper) is about 10 microns nominal,
50 microns absolute. These are
approximate values only.
Filters are not effectively compared
on the basis of micron rating alone.
Evaluate filters on the basis of their
ability to collect foreign material as
a whole.
Primary Fuel Filter Element
The specs for primary fuel system
elements are as below:
10 Micron Nominal Filtration
For additional information see
SENR9620 Fuel Systems Improving Component
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Duplex Fuel Filters
Many Cat engines can be equipped
with duplex fuel filters as shown in
Figure 8.
Figure 8
These filters may be serviced
(change elements), without shutting
off the engine. There are two types:
the symmetrical type, which has
two identical filter sets and the
main-auxiliary type, which has a
main filter set and a smaller capacity
auxiliary filter set. A special valve
connects the two sets of filters in
each type. The valve routes the fuel
to be filtered through either or both
sets of filters.
Both filter sets can be used
simultaneously to extend running
time in an emergency.
Duplex filters for fuel and
lubricating oil allow extended
operation without interruption.
The main and auxiliary filter
systems allow changing either
the main or auxiliary filter
elements with the engine
running under load.
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Generally, the same elements
are used in both systems, and
are capable of providing
adequate filtration for at least
100 hours full load running
time with reasonably clean
fuel and oil.
Use pressure gauges to
determine when filters must
be changed.
Avoid mounting filters near
the radiator fan, because
a fuel or oil leak during
replacement could create
a fire hazard. (As either
substance passes through the
fan it can be atomized, and
therefore easier to ignite.)
Plus, coated radiator fins trap
dirt which can diminish
cooling capability.
Water Separation
Water in the diesel fuel is absolutely
unwanted as it will cause damage to
the engine and its components. Water
appears in the fuel because of condensation, handling and environmental
conditions. Environmental conditions
relate to the humidity of some
climates. Water in the fuel will be
more prevalent in humid climates.
Water can impact the fuel system
in the following ways.
If water appears in the injection
system, the fuel will not be able
to lubricate as it is supposed to
and it will lead to early wear.
Water together with diesel fuel
will form microbiological growth
which will build up sludge.
Sludge will cause wear of the
filter system and influence the
injection performance.
Page 25
Application and Installation Guide
Iron will oxidize when in
contact with water and can
infiltrate the fuel. The iron
oxide will cause injector wear.
Engines using high injection
pressure fuel pumps must be
protected from water and sediment
in the fuel. It is extremely important
to maintain water and sediment
levels at or below 0.1%.
Note: Water and sediment collecting
in fuel tanks may give the appearance that poor quality fuel was
delivered to the site.
Several methods can be used to
remove excess water and sediment
from the fuel system:
A water and sediment
separator can be installed in
the supply line ahead of the
transfer pump. The separator
must be sized to the handle
the fuel being consumed by
the engine as well as fuel
being returned to the tank.
Coalescing filter systems work
effectively to remove sediment
and water. If the level in the
day tank is not maintained at a
consistent level, install them
between the main tank and the
day tank. If proper day tank
levels are maintained, a smaller
system can be used between
the main tank and the day tank
to clean only the fuel being
burned. These filters can plug
and careful attention must be
given to fuel pressure levels at
the injectors to guard against
Page 26
Diesel Fuels & Diesel Fuel Systems
A centrifuge system can be
used, particularly if the fuel
quality consistently falls
below the defined limits
discussed in this guide.
The centrifuge represents the most
expensive and complex method of
water separation, but it is the most
effective. It is used extensively in
marine, offshore and power
generation applications where a
continuous power supply is essential,
and the continuous supply of clean
fuel cannot be left to chance. A
typical distillate fuel centrifuge
schematic is shown in Figure 9.
A centrifuge manufacturer should
be consulted to determine the proper
centrifuge type, size and flow
requirements for a specific
While Figure 9 shows a single
centrifuge schematic, many
applications will require the use of
two (2) centrifuges, with one of the
centrifuges acting as a standby.
The required flow rate of a
centrifuge can be approximated as
P x b x 24 x 1.15
Q= Flow required, L/hr
P= Total Engine Output, kW
b= Fuel Consumption, g/kW-hr
R= Density of fuel, kg/m3
T= Daily separating time in
automatic operation: 23 hr
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Diesel Fuels & Diesel Fuel Systems
f x be x 24 x 1.15
Application and Installation Guide
T= Daily separating time in
automatic operation: 23 hr
Note the following considerations
for configuring a centrifuge.
Q= Flow required, gal/hr
P= Total engine output, bhp
Be= Specific fuel consumption,
R= Density of fuel, lb/gal
The centrifuge manufacturer
should assist in the final
centrifuge selection.
The centrifuge flow has been
increased by 15% as a safety
factor for operational
Typical Distillate Fuel Centrifuge
Figure 9
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Page 27
Application and Installation Guide
Centrifuge seal water and control
air requirements must be specified
by the centrifuge manufacturer.
Sample Points
The centrifuge operating efficiency
is checked by drawing samples from
both sides of the centrifuge.
Suction Strainer
Install a simplex strainer ahead of
the centrifuge supply pump and use
a stainless steel basket with
perforations sized nominally at
0.8 mm (0.03125 in) to protect the
pump. The strainer body is normally
manufactured from cast iron or
Centrifuge Supply Pump
Mount an electric motor driven
supply pump separately from the
centrifuge and size it appropriately
for the centrifuge flow. The
Page 28
Diesel Fuels & Diesel Fuel Systems
following pump characteristics are
provided for guidance:
Operating pressure - to suit
conditions of piping system
Operating fluid temperature 38°C (100°F)
Viscosity for sizing pump
motor - 500 cSt
Centrifuge Fuel Heater
The heater is sized using the pump
capacity and the temperature rise
required between the settling tank
and the final centrifuge. The heater
should be thermostatically controlled
and set to maintain fuel temperature
to the centrifuge within ± 2°C
(± 4°F). The maximum preheating
temperature for distillate fuel is 40°
to 50°C (104° to 122°F).
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Miscellaneous Fuel System Considerations
Fuel Temperature
The fuel temperature supplied to
the engine can affect unit injector
life and maximum power capability.
Reduced lubrication capability due to
high temperature/low viscosity fuel
may result in component scuffing.
The minimum allowable viscosity at
the injectors is 1.4 cSt. A maximum
fuel temperature limit of 66°C
(150°F) to the unit injectors,
regardless of fuel viscosity, prevents
coking or gumming of the injectors.
The maximum fuel viscosity to the
unit injectors of 20 cSt prevents
overpressure damage to the
Maximum fuel temperature limits
to the low-pressure fuel transfer
pump for Common Rail Fuel systems
vary with engine model. Values are
listed below in Table 4.
Maximum Allowable Inlet Fuel
Temperature to the Low Pressure Fuel
Transfer Pump for Common Rail
70°C (158°F)
C7, C9, C15, C18
80°C (176°F)
Table 4
The engines are power set at the
factory, and higher fuel
temperatures will reduce maximum
power capability. The fuel stop
power reduction is 1% for each
6°C (10°F) fuel supply temperature
increase above the maximum fuel
temperature limit. If the engine is
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operating below the fuel stop limit,
the governor will add fuel as
required to maintain the required
engine speed and power.
Fuel Coolers
As mentioned earlier in the Basic
Fuel System description, Cat diesel
engine fuel delivery systems are
designed to deliver more fuel to the
engine than is required for
combustion, with the excess being
returned to the fuel tanks. This
excess fuel, on many engines, is
used for cooling and lubricating of
the pumps and injection systems
and in doing so picks up engine heat
and can raise the temperature of the
fuel in the tanks.
As previously specified, engine
power will be reduced if the fuel
temperature exceeds the maximum
limit because of the expansion of the
fuel (low viscosity). With very low
viscosity, the oil loses the capability
to lubricate and damage to the
injection components will occur.
Proper considerations regarding
fuel tank location and size will help
temperature control. If the tank is
properly located and sized so the
accumulated heat will not be
objectionable when temperature
stabilizes, then nothing more needs
to be done. If the stabilized fuel tank
temperature is high, the returning
fuel should be cooled.
The following factors affect the
need for fuel cooling equipment.
Page 29
Application and Installation Guide
Length of periods of
continuous operation; If the
operating periods are short,
the amount of heat returned
to the fuel tanks will be
relatively small. Fuel coolers
are not generally required for
engines used in applications
requiring intermittent
 Length of time between
periods of operation; if the
time between periods of
operation is long, the heat will
have an opportunity to
 Volume of the fuel tank; If the
volume of the fuel tank is
large (larger than 11 000 L
[3,000 gal]), it will accept a
great deal of heat before the
temperature of the fuel
leaving the tank increases
Note: Day tank sizing is critical to
maintain the desired fuel supply
temperature. Fuel coolers may be
required. For a more detailed
discussion of required fuel tank
volume, see the Day Tank Sizing
(When Serving as a Heat Sink)
section in Appendix 1.
Ability of the fuel tanks to
dissipate heat. In marine
applications for instance, fuel
in contact with the shell
plating, where at least 10% of
the inside surface area of the
tank is shell plating, the heat
will be easily dissipated and
the stored fuel temperature
will remain within a few
degrees of the ambient water
Page 30
Diesel Fuels & Diesel Fuel Systems
A plate type heat exchanger may
be used with titanium plates for
seawater cooling or stainless steel
plates for fresh water cooling.
Refer to Sea Water Systems in
the Cooling Systems Application
and Installation Guide for proper
installation and maintenance
procedures of fuel cooler in sea
water applications.
Fuel Heaters
Just as the ability to remove
excess heat from fuel is an
important design consideration in
some applications, so is the ability
to add heat to fuel in applications
involving cold environments. Diesel
fuel must not be too warm or too
cool. Both cases will reduce life.
With mid-distillate No. 1 or No. 2
diesel fuel, cold weather can cause
wax crystals to form in the fuel
systems, partially or completely
blocking fuel flow. The addition of
a small amount of heat to the fuel
before it flows through the filter(s)
can prevent wax problems. The fuel
will flow through pumps and lines
but not through filters at
temperature below the cloud point
(where a cloud or haze appears in
the fuel).
At temperatures below the pour
point (the lowest temperature that
fuel will flow or pour), fuel will not
flow in lines or pumps. The use of
fuel with a pour point above the
minimum expected ambient
temperature is not recommended.
Fuel heaters will often solve cloud
point problems but not pour point
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Diesel Fuels & Diesel Fuel Systems
problems unless applied to the entire
fuel storage volume.
Consider the following suggestions
when applying fuel heaters to Cat
Application and Installation Guide
Maintenance responsibility of this
type of heater must be clearly
Fuel heaters should be used
when the ambient
temperature is below the fuel
cloud point. Many types of
heaters can be used;
however, the fuel should be
heated before the first filter in
the fuel system. Fuel heaters
should not be used when the
ambient temperature exceeds
15°C (60°F). Under no
condition should the maximum
fuel temperature at the outlet
of the fuel heater exceed the
limit specified on the previous
 Heaters used should be
capable of handling the
maximum fuel flow of the
engine. The restriction created
should not exceed published
levels of the engine (published
values for fuel flow and
allowable restriction can be
found in the TMI).
 Coolant may be taken from
taps on the engine when
using the engine as a heat
source. Care must be taken to
assure that coolant shunting
to one system does not
adversely affect another
system, and that both have
adequate flow.
CAUTION: Failed water sourced fuel
heaters can introduce excessive
water into the engine fuel system
and cause injector failure.
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Fuel heaters offered by
Caterpillar use engine coolant
to heat the fuel and prevent
the development of solid wax
When any fuel heater is used
and ambient temperatures are
below approximately 0°C
(32°F), the engine should be
started and run at low idle
until the engine temperature
rises slightly. This allows heat
transfer to the fuel before
high fuel flow rates at high
power output are experienced
by the system. This will
reduce the possibility of wax
plugging the fuel filter shortly
after a cold start.
Partial Load Operation
Extended operation at low idle or
at reduced load may cause increased
oil consumption and carbon buildup
in the cylinders. Carbon buildup
results in a loss of power and/or
poor performance. When possible,
apply a full load at least on an hourly
basis. This will burn excess carbon
from the cylinders.
Burning Used Crankcase Oil
With legislation and ecological
pressures, it is becoming
increasingly difficult to dispose of
used oil. The burning of used
crankcase oil in 3600/C280 engines
is not recommended due to the
detrimental effects on exhaust
emissions. However, if ancillary
methods of reducing exhaust
Page 31
Application and Installation Guide
emissions to acceptable limits are
used, or if emissions are not a
problem, burning crankcase oil in
3600/C280 engines is possible with
the following guidelines.
It is necessary to collect,
store, and dispose of used
crankcase oil from engines
correctly. It is not acceptable
to dump used crankcase oil
into the oceans, rivers, and
harbors from vessels or
offshore drilling and
production platform
installations. It may be
necessary for engine
operators to consider burning
crankcase oil in their Cat
engines. This can be done,
providing the precautions
below are carefully followed:
Only diesel engine crankcase
oils can be mixed with the
diesel engine fuel supply. The
ratio of used oil to fuel must
not exceed 5%. Premature
filter plugging will occur at
higher ratios. Under no
circumstances should gasoline
engine crankcase oil,
transmission oils, special
hydraulic oils not covered by
Caterpillar recommendations,
grease, cleaning solvents,
etc., be mixed with the diesel
fuel. Do not use crankcase
oils containing water or
antifreeze from engine coolant
leaks or poor storage
Page 32
Diesel Fuels & Diesel Fuel Systems
Adequate mixing is essential.
Lube oil and fuel oil, once mixed,
will combine and not separate.
Mix used filtered crankcase oil
with an equal amount of fuel,
then add the 50-50 blend to the
supply tank before new fuel is
added (maintaining the 5% used
oil-to-fuel ratio). This procedure
should normally provide
sufficient mixing. Failure to
achieve adequate mixing will
result in premature filter plugging
by slugs of undiluted oil.
Note: Review SEBU6251for fuel
Filter or centrifuge used oil
before putting it in the fuel
tanks to prevent premature
fuel filter plugging,
accelerated wear, or plugging
of fuel system parts. Soot,
dirt, metal, and residue
particles larger than 5 microns
(0.000197 in.) should be
removed by this process. If
filtering or centrifuging is not
used before adding the oil to
the fuel, primary filters with
5 microns (0.000197 in.)
capability must be located
between the fuel supply and
engine. These will require
frequent servicing.
Clean handling techniques
of the used crankcase oils
are essential to prevent
introducing contaminants from
outside sources into the diesel
fuel supply. Care must be
taken in collecting, storing
and transporting the used
crankcase oil to the diesel fuel
tanks. Diesel fuel day tank
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Diesel Fuels & Diesel Fuel Systems
sight glasses may become
blackened in time due to the
carbon content in the
crankcase oil. Ash content of
the lube oil added to the fuel
may also cause accumulation
of turbocharger and valve
deposits more rapidly than
Continuous Blending
If the installation warrants, used
lubricating oil can be blended and
used in the engine in a continuous
manner. The normal method uses a
centrifuge module similar to Figure
9. The following information
describes this system.
Centrifuge No. 1
Engine crankcase oil is
continuously centrifuged except
when the clean waste oil tank is
low, at which time the dirty waste
Application and Installation Guide
oil is centrifuged and directed to the
clean waste oil tank.
Centrifuge No. 2
Distillate fuel/oil mixture daytank
is continually centrifuged.
Metering Pump
Adds up to 5% clean waste oil
to the distillate fuel (from the main
supply tank) when the daytank low
level switch calls for more fuel.
Static Mixer
Runs when the metering pump is
on to insure a proper homogeneous
mixture of the fuel and clean waste
The centrifuge module is
electronically controlled and includes
the components within the dotted
line as shown in Figure 10. Size the
system for appropriate fuel delivery.
Figure 10
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Page 33
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Fuel Conservation Practices
Fuel costs typically represent the
single highest operating cost
associated with any diesel engine
application. This has promoted
various fuel conservation practices
that can usually be applied to all
Avoid fuel spillage. Do not
overfill the fuel tank. Fuel
expands when warm and may
overflow, especially when
tank is not designed correctly.
Operate the engine with a
good electrical system. One
bad cell in a battery will
overwork the alternator,
consuming more engine
horsepower and fuel. A poor
electrical system can also lead
to hard starting, which
encourages excessive idling.
Size the engine or generator
set to the job. Engines operate
more efficiently at relatively
high load factors.
Page 34
Do not increase fuel settings
to obtain more power.
Make sure all air hoses and
connections do not leak.
Leaks keep the compressor
working unnecessarily.
Make sure the turbocharger
is turning freely so that proper
air-fuel ratio is maintained.
A clean burning exhaust
should indicate these items
are functioning correctly.
Operate the engine with
a thermostat all year; cold
engines consume more fuel
and wear out more quickly.
Keep air cleaners clean. Use
an air cleaner restriction
indicator to avoid guessing
at air cleaner condition.
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Appendix 1
Day Tank Sizing (When Day
Tank Serves as a Heat Sink)
The fuel supply temperature must
be within specified limits for
optimum injector life and maximum
power capability.
Fuel systems without fuel coolers
rely on the day tank to dissipate the
heat of fuel returning from the
engine. Day tank temperatures are
affected by the following conditions.
Day tank wetted surface area
(including tank bottom)
 Engine(s) fuel consumption
 Day tank replenishing level
 Storage tank fuel temperature
 Ambient temperature
 Spaces contiguous to the day
tank (void tanks, cofferdams,
vessel shell plating, etc.)
 Return fuel temperature
Tank temperature calculation are
performed in five [5] steps. The first
determines the fuel mass in the tank
at each time interval. The second
step is based on a fuel mix
temperature resulting from the
engine driven transfer pump flow
rate to the engine and the return
flow rate to the day tank. The third
step determines the day tank fuel
height for each incremental time
element. Typically, the calculations
will be based upon a 30-60 minute
iterative time function. The end
point for the calculation is assumed
to be when the day tank is refilled.
The fourth step approximates the
heat transfer from the tank to the
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surrounding environment due to the
temperature difference between the
fuel mix temperature and the
ambient temperature. This
convective heat transfer then
determines the resultant tank
temperature. The fifth step evaluates
the impact of the final fuel supply
temperature on the engine’s
maximum power capability.
The included example calculations
should only be used to provide
general guidance. If the day tank
size is marginal, use a fuel cooler.
To simplify the following
calculations, it is assumed the day
tank walls are surrounded by free
moving air. If the tank walls are
contiguous to the shell plating, heat
transfer from the day tank will be
enhanced. Conversely, if the day
tank is bounded by void spaces and
cofferdams, heat rejection from the
day tank will be retarded. Typically,
most day tanks are located with
various combinations of the
preceding boundary elements. The
individual performing the evaluation
must be familiar with the installation
as well as the fundamental
engineering concepts of the formulas
used in the calculations.
Day Tank Calculations
The following information is
required to perform the calculations:
Engine model
Engine developed power
(MCR or CSR)
Engine speed
Brake specific fuel
consumption (bsfc)
Page 35
Application and Installation Guide
Initial day tank fuel
Storage tank fuel temperature
Ambient air temperature
Day tank length, width, and
Typical full day tank fuel
height (assume 95% of tank
Engine fuel transfer pump
flow rate (see TMI)
Fuel heat rejection from the
engine (see TMI)
Incremental time element
Day Tank Thermal Capacity
 Application: Single main
 Engine Model: 3612
 Rated Power: 4640 bhp (CSR)
 Rated Speed: 900 rpm
 bsfc: 0.326 lb/bhp-hr
 Initial Day Tank Fuel
Temperature = 85°F
 Storage Tank Temperature =
 Ambient Air Temperature =
 Day Tank Dimensions:
o Length (L) = 12 ft.
o Width (W) = 8 ft.
o Height (H) = 8.42 ft.
 Fuel Height (@ 95% of total
Capacity) (H) = 8 ft.
 Engine Fuel Oil Transfer Pump
Flow Rate: qxfer = 19.0 gpm
 Heat rejection from engine to
fuel oil: Q = 1252 Btu/min
 Incremental time element: t =
60 min.
Page 36
Diesel Fuels & Diesel Fuel Systems
Assume that the day tank will be
replenished from the fuel storage
tanks when the day tank level falls
to approximately 50-55% of normal
operating capacity.
Some of the data above must be
converted to other units prior to
beginning calculations. The following
formulas can be used:
1. Engine Driven Transfer Pump
Mass Flow Rate = Mxfer (lb/min)
Assume: #2 DO with an API
gravity of 35 (7.1 lb/gal)
Mxfer = qxfer x 7.1 lb/gal =
19.0 gpm x 7.1 lb/gal =
134.9 lb/min
2. Engine burn rate under full load
a. Burn rate (gpm)
bsfc x bhp x 1 Hr.
Fuel density x 60 min.
0.326 lb/bhp-hr x 4640 bhp x 1 hr.
7.1 lb/gal. x 60 min.
= 3.55 gpm
b. Fuel mass flow burn rate
= MBR (lb/min)
= 3.55 gpm x 7.1 lb/gal
= 25.21 lb/min
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Diesel Fuels & Diesel Fuel Systems
3. Engine fuel return rate under full
load conditions:
a. Fuel return flow rate
= qrtn (gal/min)
= Supply rate - burn rate
= 19.0 gpm - 3.55 gpm
= 15.45 gpm
Application and Installation Guide
Step 1
Calculate the fuel mass in the day
tank at specific time intervals:
Day Tank Fuel Quantity = MDT (MBR x t)
MDT = Day tank contents at a
specific time step (lbs)
MBR = Engine fuel consumption
t = Incremental time step (min)
b. Fuel return mass flow rate
= Mrtn (lb/min)
= 15.45 gpm x 7.1 lb/gal
Assume the day tank is replenished
at 55% of initial quantity of fuel.
Prepare a table of volumes as shown
below for this example. Refer to
Table 5.
= 109.70 lb/min
4. ∆TENG of fuel = (Tsupply - Trtn)
Mrtn x Cp
1252 Btu/min
(109.70 lb/min x
0.5 Btu/lb-°F)
5. 95% Capacity of Diesel Oil Day
Tank, (lb)
Weight density (p) for #2 diesel
oil = 52.42 lb/ft3
Time (Min)
Tank Fuel
Quantity (lb)
Table 5
MDT = L x W x H x pDO = 12 ft x
8 ft x 8 ft x 52.42 lb/ft3 =
40258.6 lb.
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Page 37
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Step 2
Calculate the fuel oil mix temperature (Tmix):
MDT(t -1) - [(Mxfer x t)] TDT(t -1) + (MRTN x t) x (TDT(t -1)+ ∆ TENG)
MDT(t -1) - (MBR x t)
Values for the example calculation:
= Day tank contents at a
specific time step (lb)
MDT(t -1)
= Day tank contents from
previous time step (lb)
= Engine transfer pump
mass flow rate (lb/min)
= 134.9 lb/min
= 60 min.
= Incremental time step
TDT(t -1)
=Initial day tank
temperature is used for
first iteration, 85°F
= 109.70 lb/min
= 22.83°F
= 25.21 lb/min
TDT(t -1) =Day tank temperature for
previous time step or
starting temperature (°F)
=Engine return mass flow
rate (lb/min)
∆T ENG= Fuel temperature rise
across the engine (°F)
Tmix =
= Engine fuel consumption
[(40258.6 - (134.9)(60))(85)] + [(109.70)(60)(85 + 22.83)]
[40258.6 -(25.21)(60)]
Tmix = 88.9°F @ t = 60 min.
Page 38
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
This calculation is repeated for
each increment (t).
Prepare a summary table as shown
in Table 6 for each increment (t).
Step 3
Calculate the height of fuel
contained in the day tank at t =
incremental time step. Prepare a
summary table for each time
increment (t) as shown in Table 7.
Time (Min)
Temperature (°F)
= Height of fuel in the tank
= Fuel contained in the day
tank at each incremental time
= Weight density of #2 DO
(52.42 lb/ft3)
= Length of day tank (12 ft)
= Width of day tank (8 ft)
Table 6
Incremental Time
Height (ft)
Table 7
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Page 39
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Step 4
Calculate the heat transferred between the fuel in the day tank and the
atmosphere, the ∆T of the fuel in the day tank due to the heat transfer, and
the resulting fuel day tank temperature.
a. Heat transferred between the day tank and the atmosphere:
QTK = U x [ (H x (2L + 2W) + (L x W) ] x
=Heat transfer to/from
atmosphere (Btu)
This considers 6mm (0.25
in.) steel plate forming the
tank boundaries, and the
film coefficient for air and
oil. The air side film
coefficient is predominant
when compared to the oil
side film. The tank thickness
has a negligible effect.
= Coefficient of heat
transfer, (0.0424 Btu/min
= Day tank length (ft)
= Day tank width (ft)
= Ambient temperature (°F)
= Mix temperature of return
fuel and fuel in tank (°F)
= Day tank temperature
resulting from heat transfer
to/from day tank (°F)
b. Temperature change in the day
tank resulting from heat to/from
day tank:
∆ TDT =
MDT x Cp
= Temperature change of
fuel in the day tank (°F)
= Heat transfer to/from
atmosphere (Btu)
= Mass of fuel in day tank
= Specific heat of #2 MDO
= 0.5 Btu/lb •°F
c. Day tank temperature resulting
from heat transfer to/from day
= Incremental time step
= Day tank temperature
= Fuel height for specific
time step (ft)
= Mix temperature of return
fuel and tank fuel (°F)
= Temperature change of
day tank (°F)
Page 40
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Diesel Fuels & Diesel Fuel Systems
These three calculations are
interdependent in nature. First, QTK is
determined for the first incremental
time step. The resulting value for QTK
is then used to compute the ∆ TDT.
Application and Installation Guide
∆TDT is then used to determine TTK.
This process is then repeated for
each incremental time step.
Example a.:
QTK = U x [ (H x (2L + 2W) + (L x W) ] x
QTK =0.0424 x [7.7 (40) + 96] x
95 -
(88.9 + 85)
] x 60
QTK = 8283.6 Btu
Example b.:
MDT x Cp
∆ TDT =
∆ TDT =
8283.6 Btu
(38746.0 lb) (0.5 Btu/lb °F)
∆ TDT =
0.43 °F (From atmosphere to day tank)
Example c.:
TDT = 88.9 °F + 0.43°F
TDT = 89.3 °F
This series of calculations is then repeated
for the subsequent incremental time steps.
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Page 41
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Prepare a summary table for each time increment (t) as shown in Table 8.
Incremental Time
Heat Rejection to/from
Day Tank (Btu)
Temperature Chg. in Day Tank Temperature
Day Tank (°F)
Table 8
The last part in Step 4 determines the day tank temperature after refilling
(TDT refill):
TDT refill
[ (MDT full - MDT tn ) x TMUF] + (MDT tn x TTK n )
MDT full
MDT full
= Capacity of day tank, (lb)
MDT tn
= Fuel in day tank prior to refilling, (lb)
= Temperature of make-up fuel, (°F)
= Temperature of tank fuel prior to refilling, (°F)
TDT refill =
[(40258.6 - 22107.4) x 85] + (22107.4 x 143.1)
40258.6 lb
TDT refill = 116.9°F
Page 42
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Step 5
The last step calculates the
maximum power capability of the
engine at the resultant day tank
temperature for each time interval.
A summary table for each increment
(t) is also prepared and shown in
Table 9:
Note: The engines are power set at
the factory with 30 ±3°C (86
±5°F) fuel to the engine transfer
pump. Higher fuel temperatures
reduce maximum power capability.
The fuel stop power reduction is 1%
for each 5.6°C (10° F) fuel supply
temperature increase above 30°C.
If the engine is operating below the
fuel stop limit, the governor will add
fuel as required to maintain the
required engine speed and power.
Pcorr = Prated x
[1 -
(TDT - Tref )
= Corrected Engine Power,
= Rated bhp
= 86° (Power setting)
= Actual day tank fuel
temperature, °F
For t = 60, the corrected power of
the engine is:
Pcorr = 4640 bhp x
Pcorr = 4625 bhp
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(89.3°F - 86°F)
Time (min)
Day Tank
Temp. (°F)
Engine Power
Table 9
The previous calculations indicate
day tank fuel temperatures can have
an effect on the maximum power
capability of the engine. The example
was based upon a fixed pitch propeller
application. Typically, a fixed pitch
propeller is selected and sized to
absorb 85-90% of the engine's name
plate rating. In this example, this
would equate to 3950-4175 bhp. The
lowest calculated corrected power
was determined to be 4375 bhp. This
would leave a 5-10% power margin
and vessel performance would not be
While vessel performance may not
be affected in this example, the maximum fuel temperature of 143.1°F
will put the fuel viscosity near or
below the minimum allowable
viscosity of 1.4 cSt at the injectors
Page 43
Application and Installation Guide
depending on the type of distillate fuel
being used. In addition, the temperature of the fuel in the tank after
refill is now 116.9°F instead of 85°F
as used at the beginning of the
iteration. Therefore, continued
operation at full load on this fuel tank
would cause the fuel temperature to
rise even higher than the maximum
temperature shown in this iteration.
To protect the fuel injectors a fuel
cooler should be used in this
application, despite the fact that
available engine power is still
Diesel Fuels & Diesel Fuel Systems
Aside from the impact on engine
performance, maximum fuel tank
temperatures are also established
by various marine classification
societies and regulatory bodies.
Their interest is based upon the
increased risks of fire that results
from elevated fuel temperatures.
Useful Fuel Formulas and Data
The following information can be useful in sizing fuel coolers and heaters:
Specific Gravity (SG) and Density
API Gravity = (141.5/SG) - 131.5
SG = 141.5/(API Gravity + 131.5)
SG =
998 kg/m3
Density (kg/m3) = SG x 998 kg/m3
Density (lbm/gal)= SG x 998 kg/m3 x
Mass Flow Rate
M (kg/sec) = Density (kg/m3) x
1 lbm/ft3
16.02 kg/m3
1000 L
1 ft3
7.48 gal
Flow Rate (L/min)
60 (sec/min)
M (lbm/min) = Density (lbm/gal) x Flow Rate (gal/min)
Page 44
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Specific Heat (cp)
Table 10 shows typical specific heat values for two different API gravity
fuels in Btu/lbm-°F:
API Gravity
Table 10
0.5461 Btu/lbm-°F = 4.186 kJ/kg-°C
Heat Rejection
Q (kW) = M (kg/sec) x cp (kJ/kg-°C) x ∆T (°C)
Q (Btu/min) = M (lbm/min) x cp (Btu/lbm-°F) x ∆T (°F)
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Page 45
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
Appendix 2
Crude Oil Fuel
Note: Crude oils are not suitable for
use as fuel in all engine applications.
The suitability of these fuels for use
is determined on a case-by-case
basis. A complete fuel analysis is
NOTICE: Use of permissible crude
oil fuels can result in higher
maintenance costs and in reduced
engine service life.
NOTICE: Caterpillar does not
recommend using any of the heavier
fractions such as residuals or
bottoms in engines that are
configured to use distillate diesel
fuel. Failure to follow this
recommendation will result in severe
wear of components and engine
Residual fuels or blended fuels
with residuals are unsuitable
because they have a high viscosity
range, low ignition quality and high
vanadium and sodium contents that
shorten engine life. Such fuels may
cause high wear rates in the fuel
system, on the piston rings, cylinder
liners, and exhaust valves. Also,
filter problems and deposits in the
piston ring belt may be evidenced.
Special crude oil fuel pretreatment
equipment may be required and is
available from suppliers of fuel
treatment equipment. Also, it may
be essential to start and stop the
engine on a better quality, ASTM
No. 2-D type fuel to prevent
plugging and sticking fuel system
Page 46
components and to permit
satisfactory starting capability.
The same diesel power ratings may
not always apply for Cat engines
burning crude oil. Reasonable engine
service life can be achieved when
proper procedures are followed.
However, the greater risks involved
make it good practice to include
slightly higher than normal
maintenance costs when figuring the
overall economics to be gained.
A fuel analysis should be
performed. Include a distillation
curve. Operation at light load is not
recommended. On occasion,
operation at 50% load has
reportedly caused smoking.
Engines for crude oil fuel operation
should be equipped with higher
temperature thermostats, bypass
centrifugal oil filter, and fuel injector
pushrod keepers.
Pretreatment of Crude Oils
1. The crude may contain excessive
amounts of sediment and water
that will require removal before
they get to the engine. This can
usually be accomplished with a
settling tank, Figure 11, a
centrifuge or special filtering
equipment or a combination of
these methods. The crude may
also contain solid particles of
wax at ambient temperature that
would plug the filters rapidly. It is
impractical to try to remove the
wax, but the crude can be heated
sufficiently to dissolve it. The
amount of heat needed will vary
from one crude to another and
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Diesel Fuels & Diesel Fuel Systems
each situation requires an
assessment. Jacket-water heated
fuel filters, available from fuel
equipment suppliers, are often
suitable for heating the crude.
If this is not appropriate for you
application, an external heating
system will be necessary.
2. The crude oil must not have too
high a viscosity. For maximum life
and minimum maintenance of the
fuel pumping and injection
systems, the viscosity of the crude
oil in these systems should be
within 1.4 to 20 cSt at 104°F
(40°C). If the crude’s natural
viscosity is higher than this, it may
be heated or diluted to reduce it.
The degree of heating required will
vary from one crude oil to another
and will have to be established in
each case. Another method of
reducing viscosity is to blend the
original crude with a sufficient
amount of lighter distillate
material. Again, the blending
proportions would have to be
determined for each crude oil.
3. The crude must have a cetane
number of at least 40. This
brings its distillation characteristics into the picture. The cetane
number should be determined by
actual engine test because
calculated numbers of crude oils
are unreliable. The cetane number
of a crude oil is a function of its
composition. Crude is generally
subdivided into fractions by
boiling temperatures. The
combination of the gasoline and
naphtha fractions, which have
low cetane numbers, should not
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Application and Installation Guide
exceed 30% of the total crude.
The kerosene, distillate and gas
oil fractions combined should
make up at least 30% of the
total because they have high
cetane numbers.
4. Another problem created by highly
volatile crude oils (low initial
boiling points) is vapor locking of
the fuel system. This situation can
be handled by an “air eliminator.”
This, in some cases, can be an
ordinary float-type steam trap
inverted, but it should be made of
corrosion-resistant materials. It
should be located after the
auxiliary filters. If the engine is
stopped occasionally and allowed
to cool, coagulation may build up
in this vapor trap and cause it to
be inoperative.
5. The proper oil change
recommendation must be made
in each case. Many crude oils
contain large amounts of material
that accelerate lube oil
deterioration. For this reason,
the standard change period with
recommended oils should be
reduced by one-half. From this
point, the length of change period
with crude is determined by sulfur
content the same as with distillate
fuels. With 0.4-1.0% sulfur, the
change period should again be
reduced by one-half. When sulfur
content exceeds 1.0%, still further
reduction is recommended. In
many cases, it may be desirable to
install a larger capacity lube oil
system to avoid short oil changes.
The use of Cat S•O•SSM, is
strongly recommended.
Page 47
Application and Installation Guide
Crude Oil Maintenance
Engine inspection intervals should
be reduced by 50% when using
crude oil as fuel, and maintenance
routines should be modified based
on the results of these increased
Crude Oil Settling Tanks
A great deal of sludge can be
removed from crude oil by proper
settling. A recommended settling
system consists of two conebottomed tanks, Figure 11, each
holding a little more than four days
usable supply of fuel.
Diesel Fuels & Diesel Fuel Systems
inside the settling tank building
should be maintained above 70°F
(21°C), and the tanks must be
vented outside the building.
A two-day supply of diesel fuel
should be maintained for emergency
use. This supply can also be used to
start and stop engine when the
crude oil fuel is highly viscous or
heavy with paraffins.
Sludge in the bottom third is
discarded before refilling. The tanks
must be housed in a heated building,
and each fitted with heating coils.
Immediately after filling, hot water
is circulated through the heating coil
until the tank is heated to 100°F
(38°C). The heat is then shut off
and the fuel allowed to settle
undisturbed for four days.
Figure 11
During this time, fuel is being used
from a second tank. Temperature
Page 48
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Crude Oil Specification
Specification and ASTM Test Method
Cetane number (ASTM D613)
(DI Engines)
Water and sediment % volume (ASTM
Pour point (ASTM D97)
10°F (6°C) below ambient temperature
Cloud point (ASTM D97)
Not higher than lowest expected ambient
Sulfur (ASTM D3605 or D1552)
3% - See pages 131 & 132 to adjust oil TBN for
sulfur content that is above 1%
1.4 cSt
20 cSt (as delivered to rotary fuel injection pumps)
20 cSt (as delivered to other fuel injection pumps)
API gravity (ASTM D287)
Specific gravity (via Standards tables) (3)
Distillation - 10%
- 90%
- cracking
- residue (ASTM D86)
540°F (282°C)
716°F (380°C)
Reid vapor pressure (ASTM D323)
20 psi (138 kPa)
Salt (ASTM D3230)
100 lb per 1,000 barrels (220 kg per 200 kL)
Kinematic Viscosity
Gasoline and naphtha fraction
(fractions boiled off below 392°F
Kerosene and distillate fraction (fractions
boiled off
392°F (200°C) d
Carbon residue (on 10% bottoms)
(ASTM D524)
Gums and Resins
5.8 grains per gallon (10 mg per 100 mL)
Copper strip corrosion (ASTM D130)
(ASTM D381)
No. 3
Flashpoint °F °C (ASTM D93)
legal limit
Ash % weight (ASTM D482)
Aromatics % (ASTM D1319)
Vanadium PPM (ASTM D3605)
Sodium PPM (ASTM D3605)
10 PPM
Nickel PPM (ASTM D3605)
Aluminum PPM (ASTM D3605)
Silicon PPM (ASTM D3605)
PPM = Parts Per Million
(1) The cetane number should be determined by actual engine test because calculated numbers of crude oils are
unreliable. A higher cetane number fuel may be required for operation at high altitude or in cold weather.
(2) The values of the fuel viscosity are the values as the fuel is delivered to the fuel injection pumps. For ease of
comparison, fuels should also meet the minimum and maximum viscosity requirements at 40°C (104°F) that are
stated by the use of either the “ASTM D445” test method of the “ISO 3104” test method. If a fuel with a low
©2013 Caterpillar
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Page 49
Application and Installation Guide
Diesel Fuels & Diesel Fuel Systems
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 bring down the viscosity to either 4.5 cSt or
less for rotary fuel injection pumps or 20 cSt viscosity or less for other fuel injection pumps.
(3) Via Standards tables, the equivalent specific gravity using the “ASTM D287” test method temperature of
15.56°C (60°F) for the minimum API gravity of 30 is 0.8762, and for the maximum API gravity of 45 is 0.8017.
The equivalent kg/m3 (kilograms per cubic meter) using the “ASTM D287” test method temperature of 15.56°C
(60°F) for the minimum API gravity of 30 is 875.7 kg.m3, and for the maximum API gravity of 45 is 801.3 kg/m3.
(4) Follow the test conditions and procedures for gasoline (motor).
NOTICE: These recommendations are subject to change without notice.
Contact your local Cat dealer for the most up-to-date fluids
Page 50
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Diesel Fuels & Diesel Fuel Systems
Application and Installation Guide
Reference Material
The following information is
provided as an additional reference
to subjects discussed in this manual.
Special Instruction
Diesel Fuels and Your Engine
Cat Commercial Diesel Engine
Fluids Recommendations
3600/C280 Diesel Engine Fluids
Recommendations for Lubricants,
Fuels, and Coolants
Guidelines for 3600/C280 Heavy
Fuel Oil (HFO) Engines
Improving Component Durability:
Fuel Systems
Web Engineering Cataloging and
Procuring website
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Page 51
CAT, CATERPILLAR, their respective logos, “Caterpillar Yellow,” the
“Power Edge” trade dress as well as corporate and product identity used herein,
are trademarks of Caterpillar and may not be used without permission.
©2013 Caterpillar
Printed in U.S.A.
All rights reserved.
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