Got Urea?
That is the question that the EPA wants asked by truck operators beginning in 2010 when the latest diesel truck emissions rules go into effect. Further, they want the truck engine OEMs to assure that Urea – an organic commercial chemical compound of carbon, nitrogen, oxygen and hydrogen with many uses that is also found in the urine of mammals, fish, etc. either as urea or uric acid – is widely available so the answer is "Yes!" Urea is the reactant in the emissions reduction system known as SCR – Selective Catalytic Reduction. Unlike current emissions reductions systems that depend only on a catalyst – a material that must be present for a reaction to occur but is not consumed in the reaction – to reduce NOx, CO, and Hydrocarbons, urea in SCR will be consumed. Fortunately the consumption rate is low relative to the amount of fuel burned. A few gallons will be enough to handle quite a few tank fulls. Europeans have been partial to the system for several years.

The EPA wants a distribution system established so urea can be obtained whenever needed. If not, the engine control system will note that it is not available. The emissions system will then not be effective so EPA wants engines downrated or otherwise restricted until the urea is obtained. Truck stops seem like the most logical place to make urea available. Another possibility is to make the on-board urea quantity large enough so that it lasts between regularly scheduled service periods. Urea will become another required fluid to operate an engine like oil or antifreeze or brake fluid or windshield washer. This seems a small price to pay in order to keep air quality reasonable.

Previously on AutoblogGreen:
[Source: Light and Medium Truck magazine, May 2007]

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