Diesel Progress North America

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the urea solutions as well as the ana- lytical test methods. ISO 22241-2 was developed to pro- vide test methods for ensuring the purity of the urea solution as well as the proper concentration of urea in the solution. The reactions that take place in SCR are very specific to urea, the ammonia formed from the urea and the NOx and other exhaust gas compounds. The presence of other impurities in the urea solution can interfere with the reactions, causing reduced NOx re- moval efficiency or undesirable side reactions.

While SCR is viewed primarily as an on-highway technology in the U.S., it is also used in many nonroad applications around the world. Early in 2009, AGCO became the first manu- facturer to take the leap off-highway with the introduction of its e3 SCR technology on three all-new high-horsepower row crop tractor series, encompassing 12 tractor models in all.

TECHNOLOGY OF CLEAN AIR

Some impurities may also harm the catalyst or simply cause residue buildup on the catalyst and injectors. Included in the standard for the analysis of the urea solutions are the following tests: Aldehyde — Aldehyde is an unde- sirable byproduct that is found in many urea sources, such as agricul- tural grade fertilizers and industrial urea formulations used in resin manu- facturing. Only very pure grades of urea can be used to ensure effective- ness of the SCR. Alkalinity — The alkalinity is measured as ammonia in the solution and may be present as a residual pro- duction component, as a urea break- down product or as both. The amount of ammonia present in the urea solu- tion needs to be controlled to prevent noxious odors from the solution and to minimize competing reactions with- in the SCR. Biuret — Biuret is a residual continued on page 28

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