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Diesel Exhaust Fluid

What is DEF?
What is an SCR?
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What is an SCR?

Selective Catalytic Reduction

Diesel engines power many of today’s mechanical wonders, the workhorses of several different industries including fleet, marine and rail. In 2010, after more than 2 decades of emissions reductions, the EPA through the Clean Air Act demanded even more. Manufacturers were tasked to come up with a technology that would cut NOx emissions by at least 90 percent.

The leading solution is Selective Catalytic Reduction (SCR), an emissions-reduction technology with the ability to deliver near-zero emissions of nitrogen oxides (NOx), a smog-causing pollutant and greenhouse gas. SCR remains the only proven catalyst technology capable of reducing diesel NOx emissions to levels required by a number of future emission standards. SCR is a reliable, cost-effective technology designed to control nitrogen oxides (NOx) emissions from medium and heavy-duty diesel engines in on-road, non road and stationary applications.

Catalysts perform by lowering the temperature required to allow a chemical reaction to occur. In this case, a reduced nitrogen compound (ammonia or urea) is introduced into the air. The "oxidized" chemical (NO or NO2 or both) then reacts with the other nitrogen compound forming elemental nitrogen and water. The two common sources of neutralizing chemical are either ammonia, which is a gas at room temperature or urea, which is normally used as a solution DEF and must be atomized into the air.