Diesel Fuel And Its Additives: A Primer

This following is an article from the February 1996 issue of the AMSOIL Dealer Magazine. However, since a new article (Preserving Diesel Performance) which deals with diesel fuel additives was posted yesterday in AMSOIL Product Articles on the main site, I thought it appropriate to post this one which explains in more detail, some of the factors diesel fuel additives address.

Fuel is one of the largest expense items diesel operators face. AMSOIL diesel fuel additives help diesel operators get maximum benefit from their fuel dollars.

Compression-ignition engines, also known as diesel engines, run on crude-oil-based fuels with volatilities falling between those of gasoline and lubricating oil.

U.S. specifications for automotive diesel fuel include parameters for volatility, viscosity, ignition quality, low temperature flow, copper corrosivity (which affects storage stability), water and sediment content, ash content, tendency to leave carbon residue (all of which affect component compatibility), and sulfur content. Heating value, while not included as a tested parameter in the U.S. specification, is also important to diesel fuel performance.

AMSOIL diesel fuel additives improve ignition quality, low temperature flow, storage stability, component compatibility and the wear characteristics of low sulfur fuel.

(Shown in specification as: Distillation Temperature, range; Flash Point, min. temp.)

Diesel fuels are classified as nonflammable liquids for freight purposes, so they must meet strict safety criteria, including a flash point minimum and a range of temperatures at which 90 percent of the fuel reaches the point of distillation. Flash point and 90 percent distillation temperature both relate to the fuel’s volatility.

(Unspecified characteristic)

Heating value denotes the amount of energy a diesel fuel contains. The higher a fuel’s heating value, the more energy it provides. The more energy a fuel provides, the better the fuel economy it provides. No. 2 diesel fuel has more heating value than No. 1 does.

While no U.S. specification for the heating value of diesel fuel is in place, the higher distillation temperature range of No. 2 fuel as compared to No. 1 indicates the greater heating value of No. 2 fuel.

(Kinematic Viscosity and Saybolt Viscosity, ranges)

Viscosity affects injector spray pattern, smoke output and injector wear. High viscosity fuels form a coarse spray pattern, which causes excessive smoking in high speed road-transport engines. Light viscosity fuels allow more injector wear and are not appropriate for use in large marine diesels.

(Cetane Number, minimum)

Ignition delay is the period between fuel injection and combustion of the fuel-air mixture. Fuels with shorter ignition delay have better ignition quality than fuels with longer ignition delays have. Ignition quality affects the ease of starting, the duration of white smoke after starting, prewarm-up drivability and the intensity of diesel knock at idle.

Ignition quality is measured by the fuel’s cetane number. The higher the cetane number, the better the fuel’s ignition quality.

Diesel engines are designed to use fuels with ignition qualities falling within a range of cetane numbers. Most truck manufacturers call for fuels with cetane numbers between 40 and 45. However, North American diesel fuels tend to have low cetane numbers, some as low as 37.1

AMSOIL Cetane Boost increases cetane three to seven numbers.

Makes Cold Starting Easier
• Helps engines run smoother and quieter
• Increases available power
• Reduces post startup white smoke
• Controls diesel knock at idle

(Cloud Point, max. temp.)

The wax in diesel fuel gels at temperatures commonly found in the northern tier states and Canada during winter months.

As diesel fuel gels, it passes through the cloud point, the point at which wax crystals may first be seen; the cold filter plugging point, the point at which the fuel will not pass through the fuel filter; and the pour point, the point at which the fuel no longer flows. Gelling or gelled fuel may cause an engine to fail to start or it may cause a running engine to stall.

AMSOIL Diesel Fuel Additive Concentrate and AMSOIL Diesel Fuel Modifier suppress the formation of wax crystals in cold temperatures. They reduce the temperature at which wax crystals appear as compared to the temperature at which they would appear in untreated fuel. They also suppress ice formation in water contaminated fuels.

Allows engines to start and run at colder temperatures than they could with untreated fuel

(Copper Strip Corrosion, max.)

As storage tanks undergo _ changes in temperature, they accumulate and condense water which washes into the stored fuel. Bacteria live at the water/fuel interface and consume fuel. Bacterial colonies and their waste materials may plug fuel filters and lines.

Water also damages metal surfaces by promoting rust.

AMSOIL Diesel Fuel Additive Concentrate and AMSOIL Diesel Fuel Modifier inhibit fuel oxidation, inhibit water agglomeration by keeping water suspended as tiny droplets, help reduce the potential for biological growth and inhibit rust.

• Keeps stored fuel fresh
• Keeps storage tanks, engine fuel tanks and engine components clean
• Preserves metal surface integrity

(Water and Sediment, max. vol.; Carbon Residue, percent on 10 residuum; Ash, max. vol.)

Water, sediment and high boiling point components damage delicate fuel system components with rust, abrasion, carbon residues and deposits.

Carbon and deposits impede the free movement of components and the free flow of fuel through injectors, both of which reduce fuel efficiency, reduce injector life and increase emissions, including black smoke.

AMSOIL Diesel Fuel Additive Concentrate and AMSOIL Diesel Fuel Modifier remove carbon residue, varnish and sludge deposits caused by high boiling point fuels and fuel oxidation. Continued use of ADC or ADM inhibits the formation of new residues.

• Improves fuel mileage
• Reduces emissions
• Reduces smoke opacity
• Increases injector life

(Sulfur, max.  weight)

On October 1, 1993, the United States adopted low sulfur diesel fuel as a means of reducing particulate sulfate emissions. On-highway diesel vehicles were mandated to use fuels with no more than 0.05 percent sulfur by weight.

Sulfur, and the aromatic compounds which are removed with sulfur, have anti-wear characteristics. Use of low sulfur diesel fuel sometimes increases the rate of injector pump wear.

Sulfur also has anti-oxidant characteristics. Use of low sulfur diesel fuels can lead to increased fuel injector deposits over the rate experienced with high sulfur fuel.

AMSOIL Diesel Fuel Additive Concentrate inhibits injector wear.

AMSOIL Diesel Fuel Additive Concentrate and AMSOIL Diesel Fuel Modifier inhibit fuel oxidation.

• Increases injector pump life
• Keeps fuel fresh
• Keeps storage tanks, engine fuel tanks and engine components clean

1 SLS Note: While at the time this article was written most diesel engines would run on diesel fuel with a cetane rating in the lower to mid 40’s, if you own a Ford 6.0 or 6.4 diesel (and probably many of the newer diesels, not just Ford’s), it requires a minimum 45 cetane and preferably a 50 cetane fuel. If you have one of these (or any diesel) that is running rough, especially at idle, add some Cetane Boost the next time you add fuel. If you have a cetane problem you should see an improvement in just 2 or 3 minutes.

*All trademarked names and images are the property of their respective owners and may be registered marks in some countries. No affiliation or endorsement claim, express or implied, is made by their use. All products advertised here are developed by AMSOIL for the use in the application shown.

Reproduced With The Permission Of AMSOIL INC. All Rights Reserved.

AMSOIL Cetane Boost (ACB) – An updated version is still available.

AMSOIL Diesel Fuel Additive Concentrate (ADC) and AMSOIL Diesel Modifier (ADM)- Have been reformulated and renamed. It is now AMSOIL Diesel Injector Clean (ADF) and one product is available for both applications.

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