A major responsibility shared by commercial and industrial vehicle manufacturers is to be aware of and help reduce the environmental impact of emissions, as well as stay up to date on any current standards and technologies. Increased awareness of this issue has led to strict emissions regulations worldwide to curb pollutants that contribute to air quality degradation and climate change. Among the technologies developed to meet these rigorous standards, Selective Catalytic Reduction (SCR) systems stand out as an important innovation.
SCR systems are essential in reducing the output of harmful emissions from a variety of sources, including commercial vehicles and industrial equipment. They have become integral components in achieving cleaner air, representing a significant leap forward in environmental technology.
The SCR System Explained
SCR systems represent a convergence of chemistry and engineering, providing a pathway to cleaner air and a healthier environment. The following will help to outline and define what SCR means, the system’s role in emissions reductions, and how it works to mitigate pollutants.
What Does SCR Stand For?
Selective Catalytic Reduction (SCR) is a means of converting nitrogen oxides, also known as NOx emissions, into harmless nitrogen (N2) and water (H2O) through the use of a catalyst system. This process is crucial because NOx is a primary component of smog and acid rain and is a significant contributor to the greenhouse effect. It essentially helps to turn the application into a cleaner burning vehicle, while still maintaining easy and common fuel options.
The Significance of SCR in Emissions Reduction
SCR technology is vital for regulatory compliance and protecting public health and the environment. By significantly reducing NOx emissions, SCR systems help prevent the formation of ground-level ozone and fine particulates, which are hazardous to respiratory health.
SCR Aftertreatment Systems and Common Emissions
Major components in the SCR exhaust aftertreatment system include a DEF supply module or injector, a DEF tank assembly, and an SCR catalyst. These components work together to reduce harmful emissions that would otherwise be expelled from the vehicle, including:
- Particulate Matter (PM). These tiny particles can penetrate deep into the lungs and are a serious health risk. SCR systems help to trap and burn off these particles.
- Hydrocarbons (HCs). Unburned fuels that form toxic compounds. An SCR system, in conjunction with other treatments like Diesel Particulate Filters (DPFs), can reduce the release of HCs.
- Nitrogen Oxides (NOx). NO and NO2 emissions contribute to the formation of smog and acid rain. The core function of SCR systems is to reduce these NOx emissions.
SCR systems are widely used across sectors, including in commercial on-road and off-road vehicles, and in industrial applications. The aftertreatment process varies according to the system and its application but generally involves injecting a urea solution (commonly known as Diesel Exhaust Fluid (DEF), or AdBlue®) into the exhaust stream, which then reacts with the NOx over a catalyst.
How Does the SCR System Work?
An SCR system begins its work where the combustion process ends. Exhaust gasses containing high levels of NOx enter the SCR catalyst. Here, a dosing valve injects DEF into the exhaust, which decomposes into ammonia (NH3). This ammonia then reacts with NOx on the catalyst’s surface to form harmless nitrogen and water vapor output.
Active SCR Systems vs. Passive Catalytic Converters
SCR systems in diesel engines represent a more active approach to emissions control compared to the passive catalytic converters found in gasoline vehicles. While catalytic converters act like a filter that traps harmful emissions, SCR systems actively inject Diesel Exhaust Fluid (DEF) into the exhaust, which chemically reacts with nitrogen oxides (NOx) to form harmless nitrogen and water. This active process is continuously adjusted based on real-time engine data, ensuring efficient NOx reduction across various operating conditions.
The advantage of SCR systems lies in their precision and adaptability, unlike the passive nature of catalytic converters. SCR systems dynamically manage emissions, resulting in more effective pollution reduction, making SCR an essential technology for meeting modern environmental standards and advancing eco-friendly automotive technologies.
