Diesel Exhaust Fluid Demystified

by Bronson Motor Speedway | Monday, Nov 16, 2015 | 1047 views

Fuel TankDiesel exhaust is a menace to people and for the environment because it contains poisonous chemicals that are slowly killing both. The biggest offenders are trucks that transport goods and commodities to groceries and warehouses. Trucks play an important role in the American way of life, so we cannot get rid of them. But, there are ways to manage toxic compounds like nitrous oxide that come out of the tailpipe. One of these is the use of diesel exhaust fluid, or DEF.

What is DEF?

Diesel Exhaust Fluid (DEF) is a mix of about one-third urea (actually 32.5%) and two-thirds deionized water. The purpose of DEF is to break down nitrous oxide, a byproduct of diesel engines, into harmless nitrogen gas and water. DEF has no effect on other contaminants such as silicates, but nitrous oxide makes up a large part of diesel exhaust, so breaking them down helps make the air much cleaner.

How does it work?

DEF plays a key part in an after-treatment method called selective catalytic reduction (SCR). In SCR, the diesel exhaust goes through a series of chambers that first filters the large stuff such as soot and silicates, and then breaks down nitrous oxide by spraying the stream in a small amount of DEF. The nitrous oxide, water, carbon dioxide, and smaller stuff that got through the filters then pass through the tail pipe. The final product is not completely free of toxic substances, but it is much cleaner than if it did not get the DEF treatment.

Is DEF toxic?

Most people associate urea with urine, which smells bad. While urea is present in urine, it does not have a smell, and it is only present in small amounts. Urine smells bad because of the bacteria that get in when it hits the air. The fact is humans need urea to help the kidney break down protein and assist in hydrating the body, so it is definitely not toxic. If you still feel a little queasy about DEF, you should know that the urea in DEF is synthetic. It did not actually come from humans.

DEF is a step in the right direction for environmental and human protection. You should support laws that require its use in trucks and machines that use diesel.

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