Rick's Free Auto Repair Advice

Selective Catalytic Reduction — What is it?

What is Selective Catalytic Reduction (SCR)?

SCR is a new and advanced technology for reducing emissions in diesel vehicles. SCR reduces nitrogen oxides (NOx) to near-zero levels.

How does Selective Catalytic Reduction work?

An SCR equipped vehicle routes hot exhaust gases into the SCR system where aqueous urea (Diesel Exhaust Fluid, or DEF) is sprayed onto a special catalyst. The application of the DEF starts a chemical reaction on the catalyst. The process converts nitrogen oxides into nitrogen, water, and small tiny amounts of carbon dioxide (CO2). The exhaust then passes  through a particulate filter before exiting the tailpipe.

The process is called “selective” because it reduces NOx using a reduction method with ammonia as the reductant.

SCR technology is the most cost-effective and fuel-efficient way to date to eliminate NOx and particulate emissions from diesel engines.

Selective Catalytic Reduction is capable of reducing NOx emissions by 90% while also reducing HC and CO emissions by 50-90%, and particulate matter (PM) emissions by 30-50%.

SCR allows diesel engine designers to balance performance to maximize fuel economy while still achieving near zero emissions. In fact, some SCR heavy-duty commercial truck operators report fuel economy gains of more than 4%.


Posted on by Rick Muscoplat


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