Which exhaust aftertreatment system uses diesel exhaust fluid (DEF) to reduce emissions?

Which exhaust aftertreatment system uses diesel exhaust fluid (DEF) to reduce emissions?

• A. Diesel Particulate Filter
• B. Selective Catalyst Reductant
• C. Exhaust Gas Recirculation
• D. Catalytic Converter

Answer: (B)

The concept being tested is which system uses a urea-based fluid to reduce NOx emissions from diesel exhaust. This is the Selective Catalytic Reduction (SCR) system. In an SCR setup, Diesel Exhaust Fluid (DEF)—a solution of urea in water—is injected into the exhaust. The urea hydrolyzes to ammonia, and the ammonia then reacts with NOx over a catalyst to form nitrogen and water. This targeted chemical reduction specifically lowers NOx, which is a major pollutant from diesel engines, especially at higher operating loads. Other systems do not rely on DEF. A diesel particulate filter focuses on trapping soot particles. Exhaust Gas Recirculation lowers NOx by recirculating exhaust back into the intake to lower combustion temperatures, not by using DEF. A catalytic converter broadly reduces pollutants but does not rely on DEF to convert NOx.

The concept being tested is which system uses a urea-based fluid to reduce NOx emissions from diesel exhaust. This is the Selective Catalytic Reduction (SCR) system. In an SCR setup, Diesel Exhaust Fluid (DEF)—a solution of urea in water—is injected into the exhaust. The urea hydrolyzes to ammonia, and the ammonia then reacts with NOx over a catalyst to form nitrogen and water. This targeted chemical reduction specifically lowers NOx, which is a major pollutant from diesel engines, especially at higher operating loads.

Other systems do not rely on DEF. A diesel particulate filter focuses on trapping soot particles. Exhaust Gas Recirculation lowers NOx by recirculating exhaust back into the intake to lower combustion temperatures, not by using DEF. A catalytic converter broadly reduces pollutants but does not rely on DEF to convert NOx.