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Everything You Need to Know About Diesel Exhaust Fluid

If you are running diesel equipment anywhere in North America, Europe, and many other places in the world, you are probably required by local laws to utilize Diesel Exhaust Fluid (DEF) to make your emissions less harmful.¬† DEF is also known as “AdBlue” in some areas, but whatever the name used, it is a necessary additive which allows diesel engines to operate in an ecologically friendly manner.

Since regulations mandating the use of DEF are relatively new, many still misunderstand aspects of this fluid.  This article will hopefully address those concerns, explaining what DEF is, how it works, and providing other useful information on its storage and handling.

  1. What is Diesel Exhaust Fluid?

DEF is an environmentally friendly substance made primarily of 67.5% de-ionized water, mixed with 32.5% urea.  Urea, also known as carbamide, is a naturally-occurring substance most frequently found in mammal urine.  It is effectively non-toxic, as well as being pH-neutral.  Urea is known for its ability to bind to certain chemicals, most notably nitrogen.  This makes it an excellent choice for capturing nitrogen compounds in diesel exhaust.

  1. How does DEF improve diesel engine exhaust?

Diesel engines had numerous issues preventing them from burning cleanly, and often attempts to improve the cleanliness of diesel ended up creating new problems.  For example, old-style diesel engines tended to be inefficient, releasing soot and unburnt fuel into the atmosphere.

Changing the engines to use a lean burn fuel-to-air ratio would allow them to fully burn their fuel but doing so caused the release of nitrogen oxides instead Рand NOx emissions were at least as harmful to the environment, if not more so.   This is when urea began to enter the picture.  Given its affinity for nitrogen, it could theoretically bind to the exhaust and prevent the nitrogen release.

So, Diesel Emission Fluid was developed, using de-ionized water as a transportation method for the urea.  DEF is injected into the hot exhaust gas stream, causing the water to immediately boil and release the urea.

From there, a complex series of chemical changes occur.  The super-heated urea degrades into isocyanic acid and ammonia, then the isocyanic acid hydrolyses into carbon dioxide and more ammonia.  From there, the ammonia strips the oxygen from the NOx, which then combines with the CO2 to create water.

So, in the end, almost nothing is emitted except water and carbon dioxide.

III.  How should DEF be handled?

Given that DEF is non-toxic, it is relatively easy to work with.  However, it is also vulnerable to contamination, and any contamination will cause it to fail Рand possibly damage your engine in the process.

Here are some tips for handling and using DEF for your fleet.

1 – DEF should be kept in cool conditions

DEF has a shelf life, before the urea degrades and becomes useless.¬† This is heavily influenced by heat!¬† The hotter the place it’s stored, the more quickly it will break down.¬† In particular, try to avoid ever allowing it to go above 70¬įF, and storing it at¬†860¬įF will allow it to last even longer – potentially between 2-3 years.

Never store DEF outdoors, as it is damaged by both high heat and UV rays.

2 РDEF is not harmed by freezing and thawing

Conversely, cold does nothing to DEF.¬† It will freeze at 12 ¬įF (-11¬įC), and can be safely thawed with no adverse effects as long as the temperature is still kept well below 70¬įF.¬† In cold-weather environments, DEF might potentially freeze within a vehicle not in operation.¬† This should not cause any issues, as DEF containment systems contain heaters that will thaw it after the engine is started.

However, do be aware that DEF expands by approximately 7% when frozen, due to the high-water content.  If you will be storing it in cold conditions, take this into account when selecting a container.

3 – DEF reacts with many storage container types

The only materials which should be used to store DEF are titanium, stainless steel, rubber, or plastic.  Fortunately, these are relatively easy to obtain.   On the other hand, DEF should absolutely not be stored in copper, brass, or nickle containers due to its corrosive effects, and the corresponding chemical contamination.

4 РNever repurpose existing storage vessels for DEF storage 

Due to how easily it can be contaminated, DEF should only be stored in new vessels which have not held any other materials or chemicals.  Any existing chemical residue will likely contaminate the DEF.  In particular, anything which has stored any petroleum products will instantly ruin the batch.

5 – DEF usually changes colors when contaminated

While batch testing is needed to be absolutely sure DEF has not been contaminated, one clear sign is a change in color.  When properly stored, and uncontaminated, it will remain the same color throughout its life Рeven if frozen and thawed.  Should you ever notice DEF in storage has developed an unusual color, it is contaminated and must be discarded.

6 – White crystals around the storage vessel are not a sign of contamination

Small amounts of DEF may creep or leach out of its container while being transported, or in storage.  This exposed DEF will turn into white crystals upon exposure to the air.  By itself, this is not a problem, although it can be unsightly.

As with DEF itself, the crystals are non-toxic and safe to clean off the exterior of the vessel.  Just be careful not to contaminate the contents within.

6 – Contaminated DEF cannot be purified

There is no known filtration process which can restore DEF which has been contaminated.  It will have to be disposed of.  Likewise, any container which has held contaminated DEF should, itself, be considered contaminated and disposed of.

7 – DEF should not be used as a fuel additive

DEF is never added to fuel directly.  It is kept in a separate tank within an engine compartment and added to the combustive process as it occurs.  Putting DEF into fuel directly will ruin both, and very possibly harm the engine if that mixture is run.

  1. Cleanup and disposal of diesel emissions fluid 

Because DEF is relatively clean and non-toxic, spills are not a cause for alarm.  For relatively minor spills, simply cover the liquid with an absorptive material such as sand, to soak up the liquid.  Then the sand can be scooped up and shoveled into a container for disposal via your standard disposal service.

DEF should not be sent down drains or into public water supplies, but small amounts will do no harm either – after all, it’s just water mixed with a¬†urine byproduct.¬† The main danger from sending DEF down a drain is the possibility of it corroding copper pipes along the line.¬† If DEF is flushed down a drain, it should be followed by plenty of water.

For large quantities of DEF, or in cases where the DEF has been contaminated, you should contact your local environmental regulatory board for advice.

  1. Obtaining DEF in Ontario

If you need Diesel Exhaust Fluid for your Ontario business, turn to Bird Fuels. Our delivery service can ensure you have all the DEF you need, delivered in clean containers for maximum shelf life.  Contact us directly to learn more.


This Post Has 2 Comments

  1. Lillian Demoski

    What color does contaminated DEF change to versus the clear uncontaminated DEF.

  2. Tammy

    Hi Lillian, thank you for reaching out to us! A member of our Bird Fuels Team will be in touch with you. Thank you

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