Cetane improvers: The (not so) good, the bad and the ugly

Updated Feb 17, 2023
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[This article was originally published in 2021 by Trucks, Parts, Service. It has been updated to include more timely information.]

With diesel fuel additives becoming more important for fuel systems, many questions and misconceptions surround fuel additives containing cetane boosters.

The most common question? “Does the performance of a cetane booster outweigh the potential damage cetane could cause in the fuel system?” The answer may surprise you.

Some people are convinced that cetane improvers will promote larger gains in engine performance and reduce engine knock. Unfortunately, that’s not true. Big companies promoting cetane additives add to this misconception by stating claims which are not, in fact, backed by science. Higher cetane numbers actually have very limited benefits with modern diesel engines and could cause more harm than good.

The (not so) good

One of the very few benefits of cetane is its ability to speed up the ignition process in the cylinder, helping with cold-weather engine starting. However, the benefit of the cetane ends there. Once the engine gets to normal operating temperature, there is no added gain in engine performance.

Engine manufacturers recommend using a 42 cetane rating number in the summer and 46 cetane rating number in the winter. The higher winter number is what provides the aid in cold-weather starting. What you may not know is the cetane rating number directly from the diesel pump is normally between 45-46.

Additionally, if the diesel fuel contains a biodiesel blend, it will increase the cetane number even higher. As such, a cetane improver is not needed because the fuel itself already contains an adequate amount of cetane. If you increase the cetane number too high (55 and beyond), it can deteriorate the fuel and actually cause a reduction in overall engine performance.

The bad

The truth is the negative effects of cetane boosters far outweigh the benefits. The majority of engine manufacturers do not recommend using a cetane boosting additive at all. But for those who choose to regardless, there are warnings.

For example, an OEM releases service bulletins to the public when there are problems in the field. One such service bulletin warns, “If such [cetane boosting] additives are to be used, it must not contain any metal-based additives, alcohol, or other water emulsifiers.” 

Yet, most cetane improver additives on the market do contain alcohol or harmful solvents (2-exthylhexyl nitrate), which can be detrimental to a fuel system. Alcohol and harmful solvents in diesel fuels are a fuel system’s worst enemy. Adding a cetane booster, especially one containing alcohol, can put an engine on the fast track for disaster.

The ugly

Why is alcohol so harmful to the fuel system? Alcohol and harmful solvents can cause preignition, which is likely to damage fuel injectors.

When water molecules are present in diesel, alcohol causes the water to emulsify, or mix into the fuel. It then travels through the injection system at extremely high pressure and temperatures. The abrasiveness of the water can score your injectors and get vaporized, turning into steam. This will eventually damage the tip of the injector, resulting in uneven spray patterns and wasted fuel. Over time, the alcohol and harmful solvents will also cause the swelling and breakdown of gaskets, as well as dry out the entire fuel system.

The solution

If your customer is looking to safely gain overall performance in their diesel vehicle’s engine and get preventive maintenance for the fuel system, suggest products that do not contain any alcohol or harmful solvents.

Products made from petroleum distillates are always safe to use, so it’s important to check the ingredients of the additives you are putting into your system. Many products with alcohol and harmful solvents emulsify water, blending it into the fuel to be sent through the system. But diesel engine manufacturers’ preferred method of water removal is demulsification, the practice of separating water molecules and pushing them down and out of the fuel.

Quality products that enhance engine performance, increase fuel economy and naturally improve the combustion quality of diesel fuel, can eliminate the need for potentially harmful cetane boosters.

Not all additives are created equally. When your customer asks, be sure to recommend one that will benefit their engine instead of causing harm. You’ll be glad you did.

Robert B. Howes II is the executive vice president and chief testing officer at Howes Products. A fifth- generation leader of Howes, Rob works closely on the development, business planning and marketing of all Howes efforts and products. Tapping his experience in chemical engineering and his MBA in Business, Rob is working to drive Howes Products into the next evolution of the brand and its products.

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