Diesel Exhaust After Treatment
Understanding the Components and Functions
Modern diesel engines are cleaner and more efficient than ever before. Thanks to sophisticated exhaust after-treatment systems, harmful emissions such as nitrogen oxides (NOx) and particulate matter are dramatically reduced. Understanding these systems is key to maintaining peak engine performance and ensuring compliance with environmental regulations.
Here’s a straightforward explanation of the major components and how they work together to keep diesel engines running clean.
1. Diesel Oxidation Catalyst (DOC)
The first major component in an after-treatment system is the Diesel Oxidation Catalyst. The DOC’s primary job is to convert harmful carbon monoxide (CO) and unburned hydrocarbons (HC) into less harmful substances like carbon dioxide (CO₂) and water vapor (H₂O).
It works much like the catalytic converter in a gasoline vehicle but is tuned for the specific needs of diesel combustion. The DOC also generates heat, which is crucial for the performance of downstream components.
2. Diesel Particulate Filter (DPF)
After exhaust passes through the DOC, it enters the Diesel Particulate Filter. The DPF captures and stores soot particles (unburned carbon) from the exhaust gas to prevent them from being released into the atmosphere.
Over time, the trapped soot must be burned off — a process called regeneration. Regeneration happens either passively (with the heat from normal engine operation) or actively (by injecting extra fuel to raise the exhaust temperature). Proper maintenance and monitoring of the DPF are vital to prevent costly downtime.
3. Selective Catalytic Reduction (SCR)
Next in line is the Selective Catalytic Reduction system. SCR tackles nitrogen oxides (NOx), a major contributor to smog and acid rain.
In SCR, a fluid called Diesel Exhaust Fluid (DEF) — a mixture of urea and deionized water — is sprayed into the exhaust stream. When heated, DEF breaks down into ammonia, which reacts with NOx over a catalyst to produce harmless nitrogen and water vapor.
SCR systems are highly effective, reducing NOx emissions by up to 90%.
4. Ammonia Slip Catalyst (ASC)
Some systems include an Ammonia Slip Catalyst after the SCR unit. Its role is to capture and neutralize any excess ammonia that might escape the reaction, ensuring that only clean gases exit the tailpipe.
Key Takeaways
DOC: Reduces CO and HC; generates heat.
DPF: Captures soot; requires regeneration.
SCR: Converts NOx into nitrogen and water using DEF.
ASC: Removes excess ammonia.
Each component is essential. A failure in one part can lead to increased emissions, reduced performance, costly repairs, or regulatory non-compliance.
At DSG Power Systems, we specialize in diagnosing, repairing, and maintaining diesel after-treatment systems to keep your fleet compliant and on the move.
If you’re experiencing warning lights, poor engine performance, or increased fuel consumption, contact us for a professional inspection and service.
Contact us at (800) 667-6879 or Visit our website to learn more.
