SCR: An Advanced Technology for Diesel Vehicles that Protects the Environment
What is an SCR System?
The Selective Catalytic Reduction (SCR) technology in your units is a crucial component for protecting our planet.
This system, installed in diesel vehicles, reduces harmful nitrous oxide (NOx) emissions. It works by injecting automotive-grade urea, or Diesel Exhaust Fluid (DEF), into the exhaust flow through a specially designed catalyst.
With the assistance of DEF, such as Compass Blue®, the SCR system breaks down the nitrogen oxides (NOx) produced by the engine’s combustion into harmless nitrogen and water. This process allows vapors to pass through the Diesel Particulate Filter (DPF), removing harmful oxides. The DEF is injected directly onto the DPF’s emissions, triggering a chemical reaction in the catalyst that converts NOx into nitrogen, water, and trace amounts of carbon dioxide (CO2)—particles naturally present in the air we breathe.
SCR technology operates in an oxidizing environment, and its “selective” nature refers to its ability to reduce NOx levels using ammonia as a reducing agent inside the catalyst system. This reaction, known as “reduction,” occurs when DEF is broken down to produce ammonia, which then interacts with NOx in the exhaust, converting it into safer compounds.
FAQs
1. What is DEF?
DEF (Diesel Exhaust Fluid) is a fluid used in Selective Catalytic Reduction (SCR) systems to reduce NOx emissions from diesel engines.
2. What is Selective Catalitic Reduction (SCR)?
SCR is a technology that uses urea-based DEF and a catalytic converter to reduce nitrogen oxide (NOx) emissions from diesel engines. It is widely adopted by OEM manufacturers. SCR systems aim to lower NOx levels, which are harmful to both the environment and human health. The system injects small amounts of DEF into the exhaust gases, where it evaporates and breaks down into ammonia and carbon dioxide. The ammonia (NH3) then reacts with the SCR catalyst, converting NOx into harmless nitrogen (N2) and water (H2O).
3. What is urea?
Urea is a nitrogen compound whose aqueous solution produces ammonia when heated. It is used in various industries, including agriculture, where it serves as a fertilizer.
4. Why should you use 32.5% urea?
A 32.5% urea solution is recommended because it crystallizes and freezes at 12.2˚F (-11˚C). When frozen, DEF expands by about 7%, but the tank and packaging are designed to accommodate this expansion. Freezing does not affect the solution’s quality. SCR systems are equipped with heating elements for the DEF tank and supply lines, ensuring that DEF performs normally even after freezing. The system will quickly return DEF to its liquid state once it thaws, without impacting engine operation or ignition.