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FUELS: QUESTION & ANSWER

Posted: August 1, 2014

The diesel fuel I bought recently has a darker color than I am used to seeing. Does this mean the fuel has gone bad?

The color of a diesel fuel is not related to its performance. As long as the fuel meets the specifications, it will perform well in your engine.

Diesel fuel can range from colorless to an amber or light brown color, depending
on the crude oil and the refinery processing used to produce it. Diesel fuel may
darken after months of storage, due to oxidation of trace components, but this will not affect its performance. However, if the darkening is accompanied by the formation of sediment, the fuel could plug filters.

If diesel fuel is stored for use in an emergency, it should be used within one year and replaced with fresh fuel, unless special precautions are taken.

What special precautions need to be taken with diesel fuel that must be stored for a long period of time?

While storage stability should not be a concern for the majority of diesel fuel users, those who store diesel fuel for a prolonged period, i.e., one year or longer, can
take steps to maintain fuel integrity. The actions listed below provide increasing
levels of protection:

1. Purchase clean, dry fuel from a reputable supplier. Keep the stored fuel cool
and dry. The presence of free water encourages corrosion of metal storage tanks and provides the medium for microbiological growth.

2. Add an appropriate stabilizer that contains an antioxidant, biocide, and
corrosion inhibitor.

3. Use a fuel quality management service to regularly test the fuel, and as necessary, polish it – by filtration through portable filters – and add fresh stabilizer. This is common practice for nuclear power plants with back-up diesel powered generators.

4. Install a dedicated fuel-quality management system that automatically tests and
purifies the fuel and injects fresh stabilizer.

Does low-sulfur diesel fuel have enough lubricity?

Yes. Even though the process used to lower the sulfur in diesel can also remove
some of the components that give the fuel its lubricity, reputable refiners monitor
this property and use an additive, as needed, to raise the lubricity to an
acceptable level.Will low-sulfur diesel or low aromatics diesel cause fuel system
leaks?

The introduction of low-sulfur diesel for on-road use in the U.S. was accompanied
by fuel-system leaks in a very small percentage of vehicles. Investigations into the cause of these leaks suggest that the problem was linked to the change in the
aromatics content of the fuel and to seal material and age.

Diesel fuel systems contain “O-rings” and other parts made of elastomeric
materials. These elastomers swell slightly when they contact diesel fuel, because
they absorb aromatic compounds from the fuel. Exposure to a fuel with a lower aromatics content will result in some of the absorbed aromatics being leached out, causing the elastomer to shrink towards its original size. If the elastomer is still pliable, this shrinkage will not cause a leak. However, if age or service at higher-than-normal temperatures has caused the elastomer to loose its elasticity, a leak could occur.

Vehicle owners should be aware that elastomeric parts have finite lives and should be replaced as necessary.

By itself, low-sulfur or low-aromatics diesel fuel does not cause fuel-system leaks.
They are caused by the combination of a change from higher to lower aromatics
fuel and aged O-rings and elastomeric parts that have lost their elasticity.

I accidentally mixed gasoline with my diesel. What can I
do?

One percent or less gasoline will lower the flash point of a gasoline/diesel fuel blend below the specification minimum for diesel fuel. This will not affect the fuel’s
engine performance, but it will make the fuel more hazardous to handle. Larger
amounts of gasoline will lower the viscosity and/or cetane number of the blend
below the specification minimums for diesel fuel. These changes can degrade
combustion and increase wear.

The best course of action is to recycle gasoline-contaminated diesel fuel back to your supplier. People ask if they can correct the problem by adding more diesel
fuel to the blend. Usually the answer is no; the amount of additional diesel fuel
needed to bring the flash point on test is impractically large. Those who try dilution should have the blend checked by a laboratory before use to be sure it meets specifications.

Does diesel fuel plug filters?

There can be several causes of a plugged filter. For example, low temperature
can cause wax crystallization, which can lead to filter plugging if summer diesel is used during cold weather. Dirt in the fuel or excessive microbial growth can also cause filter plugging. The latter are “housekeeping” issues and are not directly related to the fuel itself.

Under some circumstances, a fuel with poor thermal stability can plug a filter.

When the fuel is exposed to the hot surfaces of the injectors, it forms particulates.

If the fuel system is designed to return a significant proportion of the fuel to the fuel tank, the particulates are returned too. When the fuel is recycled, the fuel filter
collects some of the particulates. Over time, particulate build up plugs the filter.

This problem has been observed for engines that were operating at high load
and, therefore, engines that were operating at higher than average temperatures.

What is the Btu content of diesel fuel?

The heating value or energy content is not a product specification for diesel fuel, so it is not measured for each batch. However, the specifications effectively limit the heating value to a relatively narrow range. A typical net heating value for low sulfur No. 2-D fuel is 130,000 Btu per gallon.

How much No. 1-D diesel fuel must I add to No. 2-D diesel fuel to lower the cloud point for winter weather?

The cloud point of No. 2-D is lowered by about 3°F for every 10% volume of No. 1-D in the blend. Lowering the cloud point by 10°F requires the addition of more than 30% volume No. 1-D.

What is the difference between No. 1-D diesel fuel and No. 2-D
diesel fuel and can they be used interchangeably?

Always check with the manufacturer about the fuel requirements of your engine.

However, both No. 1-D and No. 2-D are intended for use in compression-ignition engines. In fact, in cold weather, No. 1-D is blended into No. 2-D or used by itself.

Three of the biggest differences between the two fuels are cetane number, heat
content, and viscosity. The cetane number of No. 1-D may be one to two numbers below that of No. 2-D, but still above 40, the required minimum.

Since No. 1-D is less dense then No. 2-D, its heat content, measured in
Btu/gallon, will be a few percent lower, leading to a similar reduction in fuel
economy.

The lubricity of No. 1-D is likely to be slightly lower than that of No. 2-D because of its lower viscosity. Its lubricity is unlikely to be low enough to cause catastrophic failure. However, a steady diet of No. 1-D in equipment designed for No. 2-D may result in greater long term wear in the fuel delivery system.

Can I get rid of my used engine oil by adding it to diesel fuel?

Adding used engine oil to diesel fuel used to be a common practice. However, it
almost certainly results in a blend that does not meet diesel fuel specifications.
One or more of these properties may be too high: 90% boiling point, sulfur
content, ash, water and sediment, viscosity, and carbon residue. A diesel
fuel/used oil blend may not be sold as diesel fuel, and we recommend against using it as a diesel fuel.

In California, addition of used engine oil to diesel fuel is a violation of hazardous waste regulations. Diesel fuel users in other areas who may consider this practice should check for any applicable regulations.

FOR MORE INFORMATION

Contact Chevron Fuels Technical Service at 510-242-5357. Or e-mail to
fueltek@chevron.com

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