Everything You Wanted to Know About Urea But Were Afraid to Ask


Come 2010, all new diesel-powered pickups will have to meet tougher federal diesel emission standards that will reduce allowable nitrogen oxide levels by 90 percent from today and 98 percent from 1988. NOx is a major air pollutant that contributes to smog, asthma, and respiratory and heart diseases. It's a byproduct of high combustion temperatures.

There are two primary ways to lower NOx emissions in diesels: The first method is exhaust gas recirculation. EGR recirculates a portion of the engine's exhaust back into the engine at a lower temperature. The cooled gases have a higher heat capacity and contain less oxygen than air, lowering combustion temperatures and reducing the formation of NOx. The second, newer approach is selective catalytic reduction using urea. A urea solution is held in a separate storage tank and injected as a fine mist into the hot exhaust gases. The heat breaks the urea down into ammonia that, when combined with a special catalytic converter, breaks the NOx down into harmless nitrogen gas and water vapor.

While EGR has been around for years, selective catalytic reduction is a newer technology that will require periodic maintenance — refilling the urea storage tank — plus extra upfront costs at purchase time. It also has that funny name.

To get the word out, more than 200 companies have created a coalition called the North American SCR Stakeholders Group. It's just unveiled a new website, FactsAboutSCR.com, where you can learn everything you wanted to know about urea SCR but were afraid to ask.


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