Usage:
All Caterpillar Products
Because of current fuel distribution problems, the No. 1 Diesel Fuel needed for operation in cold atmospheric temperatures will be available only in limited quantities in many areas. For this reason, it will be necessary for many customers to use No. 2 Diesel Fuel during operation in cold temperatures. No. 2 Diesel Fuel is a heavier fuel than No. 1 and this can cause problems with fuel filters, and possibly with fuel lines, fuel tanks, and fuel storage. For assistance with these problems, this article gives some general information about fuel characteristics that have an effect on operation and performance in cold temperatures, and what can be done to keep fuel problems at a minimum. More information about fuels is available in Special Instruction "Fuels For Caterpillar Diesel Engines", Form SEHS7067. Also, an Operation, Lubrication & Maintenance Guide "Cold Weather Operation", Form SEBU5338-02 is available as a reference.
Diesel Fuel Characteristics
The primary characteristics of diesel fuel which have an effect on engine operation and performance in cold temperatures are: Cetane Number, Cloud Point, Pour Point, and Moisture Content (amount of water in the fuel).
CETANE NUMBER: The cetane number of the fuel has an effect on the ability of the engine to start, and the interval of time before it runs smoothly. Generally, an increase of ten in the cetane number will lower the temperature at which the engine can be started approximately 12° to 15°F (7° to 8°C). After the engine heats up to its normal temperature for operation, the difference between a 40 Cetane and a 50 Cetane (for example) has very little effect on engine performance. Most fuels that have a Cetane Number above 40 will permit acceptable engine starts in warmer atmospheric temperatures, or when the engine is kept warm, either in a heated room or with a coolant heater system.
CLOUD POINT: It is important to understand that the "cloud point" of a fuel is different from the "pour point", and has no relation to the temperature at which the fuel will not flow. The cloud point is the temperature at which some of the heavier paraffin components (wax) in the fuel become solid particles. This wax is not a contaminant (foreign material) in the fuel, but is an important element of No. 2 Diesel Fuel, and has a high energy content and a very high cetane value. Removal of the heavier wax lowers the cloud point of the fuel, but also increases the cost because less fuel can be made from the same amount of crude oil. Basically, No. 1 Diesel Fuel is a No. 2 Diesel Fuel with this wax removed.
The cloud point of the fuel is important because it can limit the performance of the fuel filter. Solid wax particles can fill the fuel filters and stop the flow of fuel. Since the fuel must flow through the filters to remove dirt and foreign material which can damage fuel injection components, the most practical way to prevent the problem is to keep the fuel above cloud point temperature in the filters. This can be done by using a fuel heater. A fuel heater will keep the wax fluid and permit it to flow through the filters with the fuel.
In conditions where the atmospheric temperature is near the cloud point of the fuel, and the filters are in a location where air flow causes a cooling action during operation, this cooling action can cause the same problems. In these conditions, installation of a cover or some type of protection to keep the cold air away from the filters will probably permit normal engine heat to keep the fuel above cloud point temperature in the filters.
POUR POINT: The pour point of a fuel is a temperature below the cloud point at which the fuel will no longer flow. The pour point is the temperature which limits movement of the fuel with pumps.
To measure the pour point, the fuel temperature is lowered below the cloud point in steps of 5°F (3°C) at a time until the fuel will no longer flow. The pour point is the last temperature shown before the flow stops. At the pour point temperature, the amount of wax particles has increased to a point where they connect together. This makes the fuel more solid than it is liquid. The pour point of a fuel can be improved without removal of important elements as in cloud point improvement. See the topic "Modification of Fuel Characteristics".
MOISTURE CONTENT: Moisture (water) in fuel can cause filter problems at any time, but at low temperatures, moisture causes special problems. There are three types of moisture in fuel: "Dissolved" (in solution), "free and dispersed" (mixed), and "free and settled" (at the bottom of the tank).
Most diesel fuels have some dissolved moisture. Just like the moisture in air, the fuel can hold only a specific maximum amount of moisture at any one temperature, and this amount becomes less as the temperature is lowered. For example, a fuel with 100 ppm (parts per million) (0.010%) of water in solution at 65°F (17°C), can possibly hold only 30 ppm (0.003%) at 40°F (4°C). Any moisture in the fuel which is more than the maximum amount that can be dissolved, becomes "free and dispersed" as very small drops of water mixed in the fuel. Since the water is heavier than the fuel, it will slowly become "free and settled" at the bottom of the tank. In the above example, when the fuel temperature was lowered from 65°F (17°C) to 40°F (4°C), 70 ppm of water became "free and dispersed" in the fuel. The small drops of water cause a "cloudy" look in the fuel and, if the change in temperature is slow, the water can settle (go down) to the bottom of the tank. When the fuel temperature is lowered rapidly to a temperature below freezing, the moisture that comes out of solution changes to very fine particles of ice (like snowflakes) instead of small drops of water. These ice particles are lighter than the fuel, and will not settle to the bottom of the tank. When this type of moisture is mixed in the fuel, it will fill the filters in the same way as wax particles do when the fuel is below the cloud point. If a filter is filled, and fuel flow stops, the only way to find the cause is to remove the filter, cut it open, and inspect it before it becomes warm. This inspection will show the filter is filled with particles of either ice or wax.
The moisture which is "free and settled" at the bottom of the tank can become mixed with the fuel by the force of pump action when fuel is put into, or taken out of the tank. This becomes "free and dispersed" water, and can cause ice in the filters, but it can cause other filter problems at any temperature. Generally, the same force that mixes the water into the fuel will also mix dirt and rust from the bottom of the tank with the water. The result is a dirty mixture of fuel and water which can also fill the filters and stop fuel flow.
Modification Of Fuel Characteristics
CETANE NUMBER: The cetane number of a fuel can be changed if the fuel is mixed with a fuel that has a different cetane number. Generally, the cetane number of the mixture will be in direct relation to the ratio of the fuels that were mixed. Your fuel dealer is the best source of cetane information.
A different method to improve the cetane number of a fuel is with the use of additives. While additives will increase the cetane number of a fuel as measured in a cetane test engine, the fuel characteristics when an engine is started in real conditions are not necessarily the same as those of a natural product with the same cetane number.
CLOUD POINT: Additives have little or no effect on the cloud point of a fuel. One method to lower the cloud point of a diesel fuel is to mix it with a different fuel that has a lower cloud point, like No. 1 Diesel Fuel or Kerosene. The efficiency of this method is not good, because the ratio of the mixture does not have a direct relation to the improvement in cloud point. The percent of low cloud point fuel that must be used increases more than the cloud point is lowered. The illustration shows a chart that can be used to find the necessary mixture for two fuels with different cloud points. To use the chart in the illustration, it is necessary to know the exact cloud point specification of each fuel to be mixed. This specification can change from one purchase of fuel to the next, and is normally available from personnel at the source of the fuel supply. This method can not be used to prevent cloud point problems when lower cloud point fuels are not available.
Generally, the most practical method to prevent problems caused by fuel cloud point at low temperatures is the use of fuel heaters. In most applications, these can be used at lower cost than fuel mixtures.
POUR POINT: The pour point of a fuel can be lowered either by the use of additives or by a mixture with a lower pour point fuel, as given in the paragraphs for "Cloud Point". As with the cloud point, use of a mixture does not give good efficiency or low cost. The same chart shown in the illustration for cloud points can be used for an estimate of pour points, if the fuels do not have additives which change the pour point.
Chart to find approximate cloud point of fuel mixtures.
Additives are a good method to lower the pour point of a fuel. These additives are known as "pour depressants", "cold flow improvers", or "wax modifiers", and will permit fuels to flow through pumps, lines and hoses when used at very low levels of concentration. It is important that these additives be completely and thoroughly mixed into the fuel at temperatures above the cloud point of the fuel if they are to have an effect. They will have no effect if the fuel temperature is below the cloud point when the additive is mixed with the fuel.
Compensation For Heavier Fuels
Heavier fuels, like No. 2 Diesel Fuel, can be used in diesel engines during cold temperatures, with a minimum amount of "pour depressant" additive. There are several possible methods of compensation for these fuels, as follows:
STARTING AIDS: The use of starting aids is a common method of assistance for cold starts in low temperature conditions. Ether starting aids are available, and can be used for Caterpillar products equipped with direct injection fuel systems. Glow plug starting aids are used for products equipped with precombustion chamber type fuel injection systems. Be sure to follow recommendations for the correct use of either type of starting aid. Information about the use of starting aids is given in the operation guide sent with the product, and in the Operation, Lubrication & Maintenance Guide for Cold Weather Operation.
ENGINE COOLANT HEATERS: These units heat the engine coolant, which flows through the cylinder block and keeps the engine warm. This permits easy starts in the coldest temperature conditions. Most coolant heaters use electrical power, and a source of electricity is necessary for this type. Other heaters are available, which burn fuel as a source of heat, and can be used where electrical power is not available. With either type heater, starting aids and/or fuels with high cetane numbers are less important because the engine is warm. Remember, engine coolant heaters do not prevent possible filter problems caused by fuel cloud point, especially on engines in vehicles where the filter can be cooled by air flow during vehicle operation.
FUEL HEATERS: When the relation of cloud point to filter problems is understood, it can be seen that the addition of a small amount of heat to the fuel before it flows through the filter can prevent wax problems. Remember that the fuel will flow through pumps and lines at temperatures below the cloud point, down to the pour point temperature.
In some engine installations, small modifications can prevent cloud point filter problems. For example, a change in the location of fuel filters and/or supply lines, or the addition of a cover or some type of protection to prevent the cooling effect of air flow, can prevent filter problems in many conditions. In other conditions, where more heat is needed, fuel heaters can be used to keep the fuel above cloud point temperature in the filters. There are several different fuel heaters available for this purpose, which use either engine coolant or exhaust gas as a heat source. Most of these systems will prevent all filter problems without the use of de-icers (anti-freeze additives), except where the fuel has large amounts of dirt and water.
FUEL LINE INSULATION: In an installation with long fuel lines, the movement of air can lower the fuel temperature rapidly. This can be prevented with a cover of insulation around the lines.
DE-ICERS: De-icers (anti-freeze additives) lower the freezing point of moisture in the fuel. These are not generally needed when fuel heaters are used.
Items To Remember
Some important items to remember about operation of diesel engines in cold temperatures are:
... No. 2 Diesel Fuels with a high cloud point and without a mixture of other fuel can be used in a diesel engine in any temperature conditions with correct preparation of the engine.
... The cloud point of a fuel will limit its ability to flow through a filter at low temperatures, unless the fuel is heated.
... Cloud point does not limit the ability of a fuel to flow through pumps and lines; the pour point limits ability to flow.
... Cloud point can not be controlled with good efficiency by additives.
... Pour point can be controlled with additives.
... No. 2 Diesel Fuel not mixed with lighter fuel has a lower cost and more energy per gallon or liter.
... Diesel engines that have correct preparation and are equipped with fuel heaters can be operated without de-icer additives.
Explanation:
1. Make a straight line (A) between the cloud point of the heavier fuel and the cloud point of the lighter fuel (to be mixed with the heavier fuel).
2. Make a straight vertical line (B) between the percent of the lighter fuel in the mixture and line (A).
3. Make a straight horizontal line (C) from the point where lines (A) and (B) connect to the left side of the chart. This will show the approximate cloud point of the fuel mixture.
EXAMPLE: The lines on the chart are for a mixture of two fuels where the heavier fuel has a cloud point of +30°F (-1°C), and the lighter fuel has a cloud point -30°F (-34°C). When 30% of the mixture content is the lighter fuel (with 70% basic fuel), the cloud point of the mixture will be approximately +20°F (-7°C).