Search for Diesel Exhaust Fluid, or Selective Catalytic Recuction It's what they are calling urea.
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Facts About Scr Site
Diesel Exhaust Fluid is subject to freezing at the lowest temperatures. For example, Diesel Exhaust Fluid (made up of a 32.5% urea solution) may freeze at temperatures at or below 12° F. Although this temperature is encountered in colder climates during the winter season, it has not proven to be a problem for SCR-equipped trucks. Freezing does not impact its functionality and Diesel Exhaust Fluid is easily thawed within moments by the warmth of the engine.
Some automotive-grade urea producers are working on non-freezing additives and technologies. In the meantime, equipment systems are being developed and will be used to ensure that Diesel Exhaust Fluid thaws quickly. In fact, the EPA sees no problem in allowing it to reheat in the morning using the warmth of the engine when the truck is started.
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