What the meanig of «SCR (Selective Catalytic Reduction)»?
Selective Catalytic Reduction (SCR) is a part of a diesel engine exhaust system designed to reduce (up to 90%) nitrogen oxide NOx emissions in the engine exhaust gases.
The purpose of installing SCR systems in the engines of commercial vehicles and passenger cars is primarily to meet the strict environmental standards EURO V and VI.
SCR uses active NOx reduction technology which works as follows:
• A liquid, a nitric oxide reducing agent, is injected through a special catalyst into the exhaust gas stream of the diesel engine.
• The reducing agent triggers a chemical reaction that converts the nitrogen oxides into nitrogen (N), water (H2O) and carbon dioxide (CO2), which are the natural components of air.
• These components are then discharged through the vehicle’s exhaust pipe.
The SCR system requires a liquid nitric oxide reducing agent to function. In cars, it is an aqueous urea solution made from 32.5% highly purified urea and 67.5% deionized water. In Europe the reducing agent is known as AUS 32 (Aqueous Urea Solution), in the United States as DEF (Diesel Exhaust Fluid). German automobile industry association (VDA) has registered the trademark AdBlue for the automobile liquid for SCR systems, and under this name the reducing agent was widely used.
In modern diesel engines, selective catalytic reduction is often combined with a diesel particulate filter system (DPF) or exhaust gas recirculation (ERG) or both, as all gaseous and particulate emissions can then be reduced. Therefore, when selecting engine oil for a diesel engine with SCR, it is important to consider the requirements of the other engine systems regarding engine oil quality levels. Usually, car manufacturers indicate their recommendations for engine oil selection in the car’s instruction manuals. These recommendations consider requirements of all engine systems, and are based on international classifications, such as API, ACEA and JASO.