SCR Technology

Selective catalytic reduction is an active emissions regulating technology system applied to diesel engines that converts NOx into safe, breathable molecules. This chemical conversion is initiated using a catalyst and a liquid-reductant agent. The most commonly used reductant source is automotive-grade urea, also referred to as diesel exhaust fluid (DEF).

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When directed onto an SCR catalyst, DEF is converted into ammonia, which reacts with NOx to create nitrogen, water, and small amounts of CO2. This chemical reaction is dependent on an SCR catalyst, which provides the required oxidizing atmosphere that permits nitrogen oxide reduction to take place.

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SCR is the most cost-effective, reliable, and fuel-efficient way to meet the very strict EPA 2010 emissions standards. The ability to meet strict requirements affordably without compromising vehicle performance, operating cost and uptime is essential. In commercial trucking, the ability to reduce emissions to near-zero levels while also delivering fuel savings and improved engine reliability distinguishes SCR as the preferred emissions control technology that is as good for business as it is for the environment. These considerations have led majority of diesel engine and truck manufacturers, to select SCR as the technology of choice to meet EPA 2010 emissions standards.

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How SCR Works

SCR works by injecting a very precise amount of an automotive grade urea/water solution (called Diesel Exhaust Fluid, or DEF) into the vehicle’s hot exhaust stream. Under the heat of the vehicle’s exhaust, the urea in the DEF is converted into ammonia gas and carbon dioxide. Once inside the SCR catalyst, this ammonia gas forms a chemical reaction with the oxides of nitrogen (NOx) emitted by the engine. As a result of this chemical reaction, SCR is able to reduce harmful oxides of nitrogen into harmless water vapor and nitrogen gas – natural elements common to the air we breathe.

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The SCR Performance Advantage

When EPA 2010 standards go into effect, no heavy duty on-highway engine can emit oxide of nitrogen (NOx) levels higher than 0.2 g/bhp-hr(grams per brake horsepower-hour). This is the most stringent emissions standard in the world. In Europe, where SCR technology has been in use for several years, SCR operators have demonstrated lower operating costs and increased truck resale values. It is the only technology that optimizes fuel efficiency while allowing the engine to run cleaner. SCR is reliable and reigns as the dominant emissions control technology in Europe where more than 600,000 SCR-equipped trucks are in operation today.

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Manufacturers are Adopting Urea SCR as a Worldwide Technology

More than 600,000 diesel trucks in Europe now use SCR and the fleet is growing by approximately 25,000 trucks per month. SCR technology is not limited to medium and heavy-duty trucks. Passenger car and light truck manufacturers around the world are adopting SCR technology as all industrialized countries adopt more stringent emissions requirements. According to one European Truck manufacturer, the engine efficiency achieved by using SCR technology has saved customers more than 280 million liters of diesel fuel and nearly half a billion dollars in fuel spending. At the same time, 800,000 metric tons of carbon dioxide have not entered the environment.