AdBlue works as part of the Selective Catalytic Reduction (SCR) system in diesel engines to reduce harmful nitrogen oxide (NOx) emissions, a major contributor to air pollution and smog. Here’s how it works step by step:
- Injection into Exhaust: AdBlue is injected into the exhaust gases after combustion but before the gases pass through the catalytic converter. The injection is controlled by the engine management system, ensuring the right amount is used based on the engine load and conditions.
- Thermal Decomposition: In the hot exhaust gases (around 200-300°C), AdBlue decomposes into ammonia (NH₃) and carbon dioxide (CO₂). This process happens before the gases reach the SCR catalyst.
- NOx Reduction: The ammonia (NH₃) generated reacts with the nitrogen oxides (NOx) in the SCR catalyst. This reaction converts the NOx gases into two harmless byproducts:
- Nitrogen (N₂), which makes up about 78% of the Earth’s atmosphere.
- Water vapor (H₂O), which is also harmless.
- Emission of Cleaned Gases: After passing through the SCR system, the cleaned exhaust gases—now containing mostly nitrogen, water vapor, and CO₂—are emitted from the vehicle’s tailpipe.
Summary of the Reaction
- Before the SCR: Exhaust contains NOx gases (nitrogen oxides) which are harmful to the environment.
- After the SCR: NOx is converted into nitrogen and water vapor.
By reducing NOx emissions, AdBlue helps diesel vehicles meet strict emissions regulations, such as Euro 6 in Europe or Tier 2 in the U.S. The system requires periodic refilling of AdBlue (usually a separate tank) but doesn’t affect engine performance.