SCR system
The SCR system (Selective Catalytic Reduction) is an advanced emissions control technology used in diesel engines to reduce NOx (nitrogen oxides) emissions. It works by injecting a diesel exhaust fluid (DEF, also called AdBlue) into the exhaust stream, which reacts with NOx to convert it into harmless nitrogen (Nâ‚‚) and water (Hâ‚‚O).
How the SCR System Works:
1. Exhaust Gases Enter the SCR System – The engine produces exhaust gases containing NOx.
2. DEF Injection – A precise amount of Diesel Exhaust Fluid (DEF) is sprayed into the exhaust before reaching the SCR catalyst.
3. Chemical Reaction – DEF (a mixture of urea and deionized water) reacts with NOx inside the SCR catalyst, breaking it down into nitrogen and water vapor.
4. Clean Emissions Exit – The final exhaust is mostly nitrogen and water, reducing air pollution significantly.
Key Components of the SCR System:
– DEF Tank – Stores the Diesel Exhaust Fluid (AdBlue).
– DEF Injector – Sprays DEF into the exhaust stream.
– SCR Catalyst – Where the chemical reaction takes place.
– NOx Sensors – Monitor emissions to ensure proper operation.
– Control Module (ECU) – Manages DEF injection and monitors system performance.
SCR System Benefits:
1) Reduces NOx emissions by up to 90%
2) Improves fuel efficiency (compared to older emission control methods)
3) Helps meet stringent emission regulations (like Euro 6, EPA standards)
Common SCR System Issues:
(1) Low DEF Warning – Running out of DEF can limit engine performance or prevent the engine from starting.
(2) DEF Crystalization – DEF can crystallize in cold temperatures or due to improper handling.
(3) Faulty NOx Sensors – Can trigger warning lights or reduce efficiency.
(4) Blocked SCR Catalyst – May cause higher emissions and performance issues.
SCR System Maintenance Tips:
– Keep the DEF tank filled – Most vehicles warn when fluid is low.
– Use high-quality DEF (AdBlue) – Contaminated fluid can damage the system.
– Drive the vehicle regularly – Long idle times or short trips can affect system efficiency.
