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.
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 problems unless applied to the entire fuel storage volume.
Consider the following suggestions when applying fuel heaters to Cat engines.
- 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 page.
- 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.
Maintenance responsibility of this type of heater must be clearly defined.
- 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.
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.
- 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 operation.
- Length of time between periods of operation; if the time between periods of operation is long, the heat will
have an opportunity to dissipate.
- 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 significantly.
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 temperature.
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.
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 injectors.
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.
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 operating below the fuel stop limit, the governor will add fuel as required to maintain the required engine speed and power.
Centrifuge seal water and control air requirements must be specified by the centrifuge manufacturer.
The centrifuge operating efficiency is checked by drawing samples from both sides of the centrifuge.
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 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).
The specs for primary fuel system elements are as below:
- 10 Micron Nominal Filtration
- For additional information see SENR9620 Fuel Systems – Improving Component Durability
Duplex Fuel Filters
Many Cat engines can be equipped with duplex fuel filters as shown in 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.
- 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 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.
- 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 misfiring.
- 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 application.
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 follows:
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
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 draw-back: it has less capacity before plugging and needs to be replaced more often. The size of the pores in the paper needs to be balanced
against the costs of the filter replacements.
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.
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 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 bearings.
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.
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.
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 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 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 extinguish.
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.
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 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 loss.
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) 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.
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 performance.
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.
Fuel Transfer Pumps
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 capability.
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 Guide.
3. Elevation has a big impact on the pump’s lifting capability. As 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.
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.
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 necessary.
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 repairs.
Guidelines for emergency fuel oil system operation:
1. Keep pressure drops to a minimum by using short, low-restriction 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 engine.
6. TMI contains flow rates and pressure limits to fulfill minimum engine requirements for full power at rated speeds for Cat engines.