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What is AdBlue? Q&A on DEF Confusion

AdBlue, or DEF, on a diesel vehicle

“What is AdBlue?” “Is AdBlue the same as DEF?” These are two of the first questions new diesel fleet vehicle owners and operators ask. If you’re confused about AdBlue and diesel exhaust fluid (DEF), you’re not alone.

This Q&A will help clear up confusion.

Q: What is AdBlue?

A: It’s a marketing term for diesel exhaust fluid. It’s a registered trademark of the German Association of the Automotive Industry, so you’ll see and hear the term more in Europe. In the U.S., you’ll see and hear DEF more.

Chemically and functionally, AdBlue and DEF are the same. Like prescription drugs whose patents expire and there is no legally protected exclusivity on the formula, DEF has a specific formula that can be manufactured and marketed by different companies. If we were to explain AdBlue and DEF using a drug store analogy, DEF is to acetaminophen (or paracetamol in some countries) as AdBlue is to the brand Tylenol. The difference is the name.

In this Q&A, we’ll stick to calling the fluid AdBlue for simplicity. (Calling it DEF or diesel exhaust fluid, however, would be equally correct.)

Q: What is AdBlue fluid?

A: The fluid is a clear, nontoxic fluid typically made of 32.5% synthetic, vehicle-grade urea (ammonia) and 67.5% deionized water. AdBlue must meet a purity standard set by the International Standards Organization (ISO).

“The ISO 22241 series provides the specifications for quality characteristics, for handling, transportation and storage and for the refilling interface as well as the test methods, needed by the manufacturers of motor vehicles and their engines, by converter manufacturers, by producers and distributors of the urea solution and by fleet operators,” the foreward on ISO 22241-1:2019 states.

“The urea solution (AUS 32) as specified in this document is commercially available and may exist under various trade names.”

AdBlue is one of those trade names.

Q: What does AdBlue do?

AdBlue gauge in diesel vehicleA: First, let’s clarify something: AdBlue is not a fuel, and it was not created to mix with fuel. It’s not a fuel additive. But it is transported, stored and dispensed like fuel. It requires its own separate, dedicated, clearly marked tanks in vehicles and for bulk storage. You can purchase it at gas station fuel dispensers near diesel. This wide availability of AdBlue at the pump and in volumes small enough to carry by hand provides convenience — and confusion.

Now that you know what AdBlue is not, you can make sense of how it works. AdBlue reduces harmful nitrogen oxide (NOX) emissions from heavy-duty diesel vehicles. These emissions contribute to air pollution and smog, according to the Environmental Protection Agency (EPA).

To protect human health and the environment, the EPA requires most diesel engine heavy-duty trucks manufactured after 2010 to come equipped with a technology called selective catalytic reduction (CSR). AdBlue works with CSR systems to reduce NOX emissions and meet EPA requirements. (Europe has its own regulations for diesel engine vehicles registered after 2015.)

When a CSR-equipped engine is running, the CSR system injects a small amount of AdBlue into the vehicle exhaust produced by normal diesel combustion. There, AdBlue mixes with the heated exhaust gases and breaks down into carbon dioxide and ammonia. Then, the NOX in the SCR catalyst reacts with the ammonia and breaks down into safe nitrogen gas and water vapor.

Beyond contributing to cleaner air, AdBlue boosts engine performance and fuel economy. And because injection occurs outside the engine, diesel engine manufacturers have boosted power output and achieved a cleaner burn and more efficient combustion.

Q: Where to Buy AdBlue?

A: You may buy small amounts of AdBlue at gas stations, auto parts stores and big box stores. It’s widely available. You also may buy it in bulk. This is the better option for owners of diesel fleet vehicles and gas stations. Ask your reputable bulk fuel supplier about the best bulk options for your needs.

Diesel fleets can benefit from AdBlue bulk storage

Q: Is AdBlue more of a consumer product?

A: It’s for any diesel vehicle with CSR technology. Joe Farmer can buy it for use in his one heavy-duty diesel farm vehicle. Large trucking companies can use AdBlue across their entire national fleets. The common requirement among all vehicles that use AdBlue is they have a tank for diesel fuel and another tank for AdBlue. (Never mix diesel fuel and AdBlue. Remember, injection of happens outside the engine after diesel combustion.) Two-tank systems ensure the proper diesel-to-AdBlue ratio, which is about 50-to-1 for most diesel vehicle manufacturers.

Q: Can I Store AdBlue in Bulk?

A: Yes. Small, medium and large businesses store AdBlue in bulk for use in their commercial diesel vehicles. The benefits of bulk storage include:

  • Price breaks for purchasing in bulk.
  • Convenience and immediate availability at specific, known locations.
  • Reduced risk of running out during critical operations.
  • Reduced contamination risk with AdBlue quality control and testing oversight.
  • Storage capacity flexibility.
  • Faster transfers.

Whether you call it AdBlue, DEF or diesel exhaust fluid, now you know what it means, how it works and why it’s required.

More Resources

Need Help? Ask the Experts

For help in choosing the right AdBlue storage tank or transfer tank, it makes sense to ask the experts. Unity Fuel Solutions is North America’s leader in double walled storage tanks. For advice on the tank and system that’s right for you, call the Unity team at 800-234-1689.

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