DEF Explained

Apr - 06
2017
Def chemical chart

DEF Explained

What is DEF?

DEF or Diesel Exhaust Fluid is a mixture of automotive grade urea and water.  Expressed chemically  (NH2)2CO. It is a clear fluid, that is non-toxic, non-flammable and safe to handle.  To be exact diesel exhaust fluid is a 32.5% solution of urea, and 67.5% distilled water.  These ratios need to be very close to this for the mixture to work in the SCR systems on modern diesel trucks.

What is SCR? and Why DEF?

To meet EPA 2010 and Tier 4 final for off road, all diesel trucks and equipment are required to have SCR systems installed.  Modern diesels can burn lean to keep soot emissions down.  The only problem is, this raises NOX emission levels. NOX or nitrogen oxides is a gas that is harmful to our atmosphere.  Because of EPA allowable emission levels, manufactures have developed systems that require DEF to reduce NOX output.  This is done within a complicated exhaust system including an SCR catalyst.  DEF is “dosed” or injected into the exhaust stream.  A combination of the chemical makeup of diesel exhaust fluid and extreme heat, turn NOX into nitrogen. Nitrogen of course being a safe and inert gas.

So when you are filling up, you are also cleaning the air we breathe. Thank you!

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