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Diesel Fuel Explained

"Rudolph Diesel’s First Engine Was Designed To Run On Peanut Oil"


Diesel fuel is principally a blend of petroleum-derived compounds called middle distillates (heavier than gasoline but lighter than lube oil) and may or may not contain additional additives. Other middle distillates include kerosene and No. 2 Heating Oil. Diesel fuel is designed to operate in a diesel engine where it is injected into the compressed, high-temperature air in the combustion chamber and ignites spontaneously. This differs from gasoline, which is ignited in a gasoline engine by the spark plugs.

Why Are Diesel Engines So Popular?

Diesel engines deliver 20% to 40% better fuel economy than gasoline engines. Diesel fuel does not require as much refining. Diesel engines are simple and easy to maintain. Diesel engines do not use spark plug, ignition cables, carburetors, and complicated fuel control devices. There are fewer harmful emissions from diesel fuel than gasoline. With new ultra-low sulfur diesel fuel, the benefits to the environment are huge.

Winter Vs Summer Diesel Fuel

To keep diesel fuels low temperature flow characteristics, fuel suppliers adjust the fuel properties through the year according to historical temperature data and where the fuel is sold. Generator owners may have fuel sitting in their tanks or storage for long periods. In cold weather, it would be advisable to add a fuel anti-gel additive. Anti-Gel treatment may be conveniently poured into the fuel tank before filling. It is inexpensive and worth spending the time to do it.

Diesel Smoke

When a cold diesel engine is started, the walls of the combustion chamber are still cold. The low temperature in the combustion chamber results in incomplete combustion and creates the white smoke you see.

Even after the engine has started, the temperatures in the combustion chamber may still be too low to induce complete combustion of the injected fuel. The resulting unburned and partially burned fuel is exhausted as a mist of small droplets that are seen as white smoke (cold smoke). This situation typically lasts for less than a minute, but the exhaust is irritating to the eyes. A fuel with a higher cetane number will shorten the time during which unburned fuel is emitted to the atmosphere.


Cetane is to diesel engines as octane is to gasoline engines. The Cetane number is a measure of how readily the fuel starts to burn (auto-ignites) under diesel engine conditions. A fuel with a high cetane number starts to burn shortly after it is injected into the cylinder; it has a short ignition delay period. Conversely, a fuel with a low cetane number resists auto-ignition and has a longer ignition delay period.

What Makes A Diesel Engine Noisy?

The noise produced by a diesel engine is a combination of combustion noise and mechanical noise. Fuel properties can affect only combustion noise. Some combustion noise is reduced in generators by using direct injection. A good muffler system can reduce a great deal of noise. Increasing the cetane number of the fuel can decrease the amount of knock also.

Low-Sulfur Diesel Fuel

Modern, clean diesel engines today are designed to use ultra-low sulfur fuel. They do not suffer from the issues older engines did when this fuel was introduced.

Ultra-low sulfur diesel (ULSD) began replacing conventional diesel fuel in 2006. The new fuel contains 97% less sulfur than what was considered traditional diesel in the past. The sulfur content was reduced from 500 parts per million (ppm) to 15 ppm.

There are many ways of removing the sulfur content. The cheapest of these involves hydrotreating, a process that removes sulfur by treating it with hydrogen. Unfortunately, hydrogen is highly reactive and also reduces the lubricity or lubrication properties of the end-product diesel.

With older engines, the removal of sulfur resulted in a lack of lubrication. Some of those engines would suffer from fuel injectors, and fuel pump failure since they were not lubricated like they were before. To help, some fuel companies had their additives in the fuel to bring back the lubrication properties.

Leading diesel manufactures recommend using a fuel additive such as Stantadyne with every fill up to restore the lost properties.

Additives are cheap and easy to use. Check your gas station or automotive parts dealers. They are as common as windshield washer fluid where diesel products are sold.

In your Diesel Generator the only lubrication your fuel valve, fuel pump and fuel injector receives is from the fuel itself. Since failure of these components are not covered by any warranty, it is important to take care of them. Taking care of them is easy if you use a fuel additive that restores or improves lubrication and antioxidant properties to your fuel.


Most diesel engine problems are related to the fuel system. The fuel injectors and fuel pumps must be lubricated and kept deposit free. Since sulfur has been removed from fuels, a fuel system additive that helps clean and lubricate the fuel system is required. You should use the additive with every fill up. Failure to use it will result in unusual wear and tear that will not be covered under warranty. (Modern engines today do not require any additives but it may sure help)

How the fuel is delivered is the most common reason for engine failure. Often looking at the color of the smoke will tell you a lot about what is going on.


Excessive diesel smoke is due to incomplete combustion, a rich air-fuel mixture. This may be the result of problems with the fuel injector pump or its timing. It may be a clue that the air cleaner is choked. Worn or damaged fuel injectors and adulterated diesel fuel can also cause this.

Sometimes when a fuel injector fails, it can leak fuel and drip. The excess fuel does not burn off and is pushed out into the exhaust where it can collect, burn and overheat the system. Often deposits left there will also glow cherry red and burn off. Black smoke is an indication that fuel is not burning properly.


White smoke occurs mainly during cold starts, when the fuel tends to condense into liquid and does not burn due to cold engine parts. The most common reason for white smoke are in-operative glow plugs, low engine compression, a bad injector spray pattern, late injection timing or injection pump problems.


Excessive blue smoke indicates problems from low engine compression and/or worn piston rings, scored cylinder walls or leaking valve stem seals The blue smoke is caused by crankcase oil entering the combustion chamber and being emitted after partial combustion through the exhaust

Diesel Fuel In Cold Weather

Below 15 degrees F, wax crystals begin to form in diesel fuel. These will clog the fuel filter and stop the engine as the temperature drops toward 0 F. Any good “winter fuel conditioner” for diesel fuel will keep the fuel moving to at least -20 degrees. Follow the instructions on the bottle.

Here is an example of oil waxing in cold weather. On the right is oil treated with an anti gelling additive.

Deposits And Corrosion

Residual carbon deposits from combustion can build up in nozzles and around the orifices and can obstruct the atomization of the fuel into the air preventing complete combustion. Deposit modifiers and detergents soften the hard deposits allowing for their removal. The detergent will clean the soft deposits and prevent additional deposit build-up. Also, they incorporate an anti-oxidant, which helps fuel maintain its potency and a corrosion inhibitor to help protect fuel injection parts from rust.

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Unknown member
Jan 16, 2021