SCR

 FAQ

1. What is Selective Catalytic Reduction (SCR)?

SCR is a diesel exhaust aftertreatment technology that converts nitrogen oxides (NOx) into nitrogen and water using ammonia over a catalyst.

2. How does an SCR system work?

DEF is injected into the exhaust stream, decomposes into ammonia, and reacts with NOx over the SCR catalyst to form nitrogen and water.

3. What catalysts are used in SCR systems?

Common SCR catalysts include copper-exchanged zeolite (Cu-SCR) and iron-exchanged zeolite (Fe-SCR) on ceramic or metallic honeycomb substrates.

4. Why does SCR require DEF?

DEF decomposes into ammonia, which serves as the reducing agent required for the SCR reaction.

5. What is the difference between SCR and DPF?

SCR reduces NOx emissions, while DPF captures particulate matter (PM). They perform different functions within the exhaust aftertreatment system.

6. How does SCR work with a DOC?

A DOC oxidizes CO and HC and can generate NO₂, which supports the performance of downstream aftertreatment components.

7. What is the difference between Cu-SCR and Fe-SCR?

Cu-SCR uses copper-based zeolite catalysts, while Fe-SCR uses iron-based zeolite catalysts. Each offers different operating temperature characteristics.

8. Why is an ASC installed after an SCR?

An ASC converts excess ammonia that remains after the SCR reaction, helping minimize ammonia slip.

9. Which vehicles commonly use SCR systems?

SCR systems are widely used in trucks, buses, construction equipment, agricultural machinery, marine engines, generators, and other diesel-powered equipment.

10. Does an SCR catalyst require maintenance?

Routine inspection of the DEF system, injector, sensors, and catalyst is recommended according to the vehicle or equipment manufacturer's maintenance schedule.