Characteristics of Diesel Fuel
The fuel lubricity is important. You should consider the fuel's lubricity whenever you operate the equipment in arctic weather. Also, you should consider the fuel's lubricity whenever you use fuels that are lower in viscosity. There are many aftermarket additives that are available to treat fuel. If the fuel's lubricity is an issue, consult your fuel supplier for proper recommendations regarding fuel additives.
The viscosity of the fuel is significant because the fuel serves as a lubricant for fuel system components. Arctic fuels need to have sufficient viscosity. The fuel must lubricate the fuel system at a temperature of
The cetane number of the fuel has an effect on the ability of the engine to start. Also, the cetane number has an effect on the interval of time before the engine runs smoothly. Generally, an increase of ten in the cetane number will allow the engine to be started at a lower temperature. The starting temperature can be improved approximately
During average starting conditions, direct injection engines require a minimum cetane number of 40. A higher cetane value may be required for operation in high altitudes or for cold weather operation. The minimum fuel cetane number that is required for the precombustion engine is 35.
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 supplier can provide the information about the cetane number of a particular fuel.
Additives can also be used to improve the cetane number of a fuel. Additives are evaluated through testing in special engines. However, the fuel characteristics of additives are not identical to a natural product. While both fuels may be rated as having the same cetane number, starting may be different.
It is important to understand that the cloud point of a fuel is different from the pour point. There is no relationship between cloud point and the pour point. The cloud point is the temperature that allows some of the heavier components in the wax to solidify in the fuel. This wax is not a contaminant in the fuel. The wax is an important element of No. 2 diesel fuel. The wax has a high fuel energy content and the wax has a very high cetane value. Removal of the heavier wax lowers the cloud point of the fuel. Removal of the wax also increases the cost because less fuel can be made from the same amount of crude oil. Basically, a No. 1 diesel fuel is formulated by removing the wax from a No. 2 diesel fuel.
The cloud point of the fuel is important because the cloud point can limit the performance of the fuel filter. The wax can alter the fuel characteristics in cold weather. Solid wax can fill the fuel filters. The solidified wax will stop the flow of fuel. Fuel filters are necessary in order to remove dirt from the fuel. The filters block foreign material, and the filters protect the parts for the fuel injection system. Since fuel must flow through the filters, installing a fuel heater is the most practical way to prevent the problem. A fuel heater will keep the fuel above the cloud point as the fuel flows through the fuel system. The fuel heater will permit the wax to flow through the filters with the fuel.
You can lower the cloud point of a diesel fuel by mixing the diesel fuel with a different fuel that has a lower cloud point. No. 1 diesel fuel or kerosene may be used to lower the cloud point of a diesel fuel. 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 amount of fuel with low cloud point that is required makes the process less preferable to use.
The following illustration contains a table that can be used to find the necessary mixture for two fuels with different cloud points. In order to use the table, you must know the exact fuel cloud point of each fuel. This specification can change from one purchase of fuel to the next purchase of fuel. This specification is normally available from personnel at the source of the fuel supply. When fuels that have a lower cloud point are not available, this method cannot be used.
The manufacturer of the fuel can add cold flow improvers to the fuel. Cold flow improvers modify the wax crystals in the fuels. The cold flow improvers do not change the fuel's cloud point. However, the cold flow improvers keep the wax crystals small enough to pass through standard fuel filters. For mixing precautions, see the topic "Pour Point".
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| Illustration 1 | g00592741 |
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Cloud point of fuel mixtures Generally, the most practical method that is used to prevent problems that are caused by fuel cloud point at low temperatures is the use of fuel heaters. In most applications, fuel heaters can be used at a lower cost than fuel mixtures. | |
The fuel's pour point is a temperature below the fuel's cloud point. Fuel stops flowing below the pour point. 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
A fuel's pour point should be at least
You can lower the fuel's pour point by using additives. You can also lower the pour point of a diesel fuel by mixing the diesel fuel with a different fuel that has a lower pour point. No. 1 diesel fuel or kerosene may be used to lower the pour point of a diesel fuel. The amount of fuel with low pour point that is required makes the process less preferable to use.
The following illustration contains a table that can be used to find the necessary mixture for two fuels with different pour points. This is true only if the fuels do not have additives which change the pour point. In order to use the table, you must know the exact pour point of each fuel. This specification can change from one purchase of fuel to the next purchase of fuel. This specification is normally available from personnel at the source of the fuel supply. When fuels that have a lower pour point are not available, this method cannot be used.
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| Illustration 2 | g01034833 |
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Pour point of fuel mixtures | |
In order to calculate the amount of lighter fuel that is required to be blended with the heavier fuel, perform the following steps:
- Obtain the specification for the cloud point or the pour point of both fuels from your fuel supplier.
- Locate the cloud point or the pour point of the heavier fuel on the left side of the table. Mark the point on the table.
- Locate the cloud point or the pour point of the lighter fuel on the right side of the table. Mark the point on the table.
- Draw a line between the two points that were established. Label this line "A".
- Determine the lowest outside temperature for machine operation. Find this point on the left side of the table. Mark this point. Draw a horizontal line from this point. Stop the line at the intersection of line "A". Label this new line "C".
- Line "C" and line "A" intersect. Mark this point. Draw a vertical line from this point. Stop the line at the bottom of the table. Label this line "B". The point at the bottom of line "B" reveals the percentage of lighter fuel that is required to modify the cloud point or the pour point.
The above example shows that the blending will require a thirty percent mixture of lighter fuel.
Additives are a good method to use in order to lower the pour point of a fuel. These additives are known by the following names: pour point depressants, cold flow improvers and wax modifiers. When the additives are used in a low concentration, the fuel will flow through pumps, lines, and hoses. These additives must be thoroughly mixed into the fuel at temperatures that are above the cloud point. The fuel supplier should be contacted in order to blend the fuel with the additives. The blended fuel can be delivered to your fuel tanks.
Problems with fuel filters can occur at any time. The cause of the problem can be water in the fuel or moisture in the fuel. At low temperatures, moisture causes special problems. There are three types of moisture in fuel: dissolved moisture (moisture in solution), free and dispersed moisture in the fuel and free and settled at the bottom of the tank.
Most diesel fuels have some dissolved moisture. Just as the moisture in air, the fuel can only contain a specific maximum amount of moisture at any one temperature. The amount of moisture decreases as the temperature is lowered. For example, a fuel could contain
After the fuel has absorbed the maximum possible amount of water, the additional water will be free and dispersed. Free and dispersed moisture is fine droplets of water that is suspended in the fuel. Since the water is heavier than the fuel, the water will slowly become free and settled at the bottom of the tank. In the above example, when the fuel temperature was lowered from
The small drops of water cause a cloudy appearance in the fuel. If the change in temperature is slow, the small drops of water can settle to the bottom of the tank. When the fuel temperature is lowered rapidly to freezing temperature, the moisture that comes out-of-solution changes to very fine particles of ice instead of small drops of water.
The particles of ice are lighter than the fuel, and the particles of ice will not settle to the bottom of the tank. When this type of moisture is mixed in the fuel, this moisture will fill the fuel filters. The ice crystals will plug the fuel filters in the same way as wax plugs the fuel filters.
If a filter is plugged and fuel flow is stopped, perform the following procedure to determine the cause:
- Remove the fuel filters.
- Cut the fuel filters open.
- Inspect the fuel filter before the filter warms. This inspection will show that 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. The force of any pumping action will mix the moisture with the fuel whenever fuel is transferred. This moisture then becomes free and dispersed water. This moisture can cause ice in the filters. This moisture can cause other problems with filters 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.
The two main types of diesel fuel that are available for your truck engine are typically low sulfur No. 1 diesel fuel and low sulfur No. 2 diesel fuel. Although No. 2 diesel fuels are the most commonly used fuel, No. 1 diesel fuels or a blend of No. 1 diesel fuel and No. 2 diesel fuel is best suited for cold weather operation.
There are three major differences between No. 1 diesel fuel and No. 2 diesel fuel.
- No. 1 diesel fuel has a lower cloud point. The fuel cloud point is the temperature when a haze appears in the fuel. When the temperature falls below the melting point of the paraffins a haze results. Paraffins are a wax that naturally occurs in petroleum products. The wax can alter the fuel characteristics in cold weather. Solid wax can fill the fuel filters. The solidified wax will stop the flow of fuel. The cloud point must not exceed the lowest expected ambient temperature or other precautions must be taken. Installing a fuel heater is the most practical way to address problems with the cloud point.
- No. 1 diesel fuel has a lower pour point. The pour point of the fuel is the temperature that is
3 °C (5 °F) above the temperature that is required for fuel to flow. Fuel stops flowing below the pour point. A fuel's pour point should be at least6°C (10°F) below the lowest ambient temperature that is required for engine start-up and for engine operation. - No. 1 diesel fuel has a lower rating for kJ or Btu per unit volume of fuel than the average No. 2 diesel fuel.
| Fuel Recommendations for Ambient Temperatures | |
|---|---|
| Fuel Type | Temperature Range(1) |
| No. 2 | Above |
| No. 1 | |
| (1) | Contact your Caterpillar dealer for information regarding the acceptable fuels and/or the acceptable blends, if there is potential for colder operating temperatures. |
No. 2 diesel fuel may be blended with No. 1 diesel fuel or blended with kerosene in the following proportions in order to achieve the capability to flow at lower temperatures.
| Modification of No. 2 Fuel | ||
| Ambient Temperature | No. 2 Diesel Fuel (%)(1) | No. 1 Diesel Fuel(1) |
| Above |
90 | 10 |
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70 | 30 |
| Temperatures below |
50 | 50 |
| (1) | Never blend the fuel with gasoline under any circumstances. |
No. 1 diesel fuel does not have the same energy per unit volume as No. 2 diesel fuel. No. 1 diesel fuel has less energy per unit volume. A reduction in power and fuel efficiency may be noticed with No. 1 diesel fuel or a blend of No. 1 diesel fuel and No. 2 diesel fuel but other operating effects should not be experienced.
Check the type of fuel or the fuel blend that is being used before troubleshooting for poor performance during the winter. Be aware of these values when you purchase diesel fuel. Anticipate the average outside temperature for the area for operation of the engine. Engines that are fueled in a warm climate may not operate satisfactorily if the engine is moved to a cold climate because of problems that result from cold weather.
The use of distillate fuels with temperatures between
| Permissible Distillate Fuels at |
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| Specification | Grade |
| MIL-DTL-5624T | JP-5 |
| ASTM D1655 | Jet-A-1 |
| MIL-T-83133E | JP-8 |
| (1) | The fuel that is selected must meet the requirements that are specified in Special Publication, SEBU6385, "Caterpillar On-Highway Diesel Truck Engine Fluiids Recommendations", "Fuel Specifications". Follow the recommendations that are specified in Special Publication, SEBU6385, "Caterpillar On-Highway Diesel Truck Engine Fluids Recommendations", "Aftermarket Fuel Additives". |
| (2) | Contact the Fuel Supplier for the recommended additives in order to maintain the proper fuel lubricity. |
| (3) | Fuel cooling may be required in order to maintain the minimum viscosity of 1.4 cSt at the fuel injection pump. |
Additives for lubricity may be required in order to maintain the proper fuel lubricity. Cetane improvers may be used in order to obtain the minimum requirement of 40 for direct injection engines. Cetane improvers should be added by the fuel supplier. A higher cetane value may be required for high altitude operation or extreme cold weather starting. Biocides may be needed to eliminate microorganism growth in storage tanks. It may be necessary to use flow improvers and/or a treatment for entrained water. This will prevent the formation of ice during cold conditions.
Note: Fuel additives need to be used with caution. The additive may not be compatible with the fuel. Some additives may precipitate. This action causes deposits in the fuel system. The deposits may cause seizure. Contact your fuel supplier for those circumstances when fuel additives are required. Your fuel supplier can make recommendations for additives to use and for proper level of treatment. For best results, your fuel supplier should treat the fuel when additives are needed.