The growing focus on reducing polluting emissions has led to the development of advanced technologies in diesel engines. Among these, the SCR (Selective Catalytic Reduction) system plays a crucial role in reducing nitrogen oxides (NOx), contributing to compliance with the most stringent environmental regulations.
What is the SCR System?
SCR is an exhaust gas aftertreatment technology designed to significantly reduce NOx emissions from diesel engines. These nitrogen oxides are among the main contributors to air pollution and can cause respiratory and environmental problems. SCR converts NOx into harmless substances such as nitrogen (N₂) and water vapor (H₂O) through a chemical reaction.
How Does the SCR System Work?
The SCR system works by injecting a reducing agent, commonly known as AdBlue, into the exhaust gas. AdBlue is a solution of 32.5% technical urea and 67.5% demineralised water. When AdBlue is injected into the hot exhaust gas, it decomposes into ammonia (NH₃). This reacts with the nitrogen oxides in the SCR catalyst, converting them into nitrogen and water vapour.
The main chemical reactions are:
- SCR standard : 4 NO + 4 NH₃ + O₂ → 4 N₂ + 6 H₂O
- NO₂ SCR : 6 NO₂ + 8 NH₃ → 7 N₂ + 12 H₂O
These reactions occur in the presence of a catalyst, often consisting of materials such as vanadium oxides supported on titanium.
SCR System Components
A typical SCR system includes:
- AdBlue tank : contains the urea solution.
- Dosing pump : regulates the injection of AdBlue into the exhaust gases.
- Injector : introduces AdBlue into the exhaust gas flow.
- SCR catalyst : where the chemical reaction to reduce NOx takes place.
- NOx sensors : monitor emissions to ensure system effectiveness.
Advantages of the SCR System
The adoption of the SCR system offers numerous benefits:
- Emissions Reduction : reduces up to 90% of nitrogen oxides, contributing to cleaner air.
- Regulatory Compliance : allows vehicles to comply with Euro 6 and later regulations.
- Engine Efficiency : Allows for more efficient combustion, as NOx reduction occurs in the exhaust system.
AdBlue Considerations
AdBlue is a non-toxic and non-flammable solution, but it is corrosive to some metals. It is essential to use only certified AdBlue to ensure the correct operation of the SCR system. AdBlue consumption varies according to the type of vehicle and driving conditions, generally between 3% and 5% of fuel consumption.
Maintenance and Refueling
It is essential to monitor the AdBlue level in your tank, as running low can limit the performance of your vehicle or prevent it from starting. Most vehicles have indicators that warn you when the level is low. AdBlue is available at most petrol stations and can be refilled easily.
The SCR system is an effective solution for reducing nitrogen oxide emissions in diesel vehicles, contributing to a cleaner environment and compliance with current regulations. Understanding how it works and the importance of AdBlue is essential to ensure the efficiency and longevity of the vehicle.
