Urea Tank May Soon Be Required For Diesel-Powered Vehicles

They have been talking about this for a few years and it applies to diesel owners Diesels are very big NOx generators as one diesel SUV makes as much or more NOx as about 10 gas powered ones. When the urea solution is injected into exhaust flow it converts to ammonia (NH3) and then via a SCR "CAT" it breaks down the NOx into water vapor and plain nitrogen (Nx) There are few other methods out there but this seems to be most popular. You are only becoming aware of this problem now because diesel have had a free "lead" in this area for many years and now are being brought into compliance. Gas motors have been complying for over 30 years now.

----------------- TheSnoMan.com

SCR for NOx control is currently used on stationary diesel engines, and has been proposed for mobile applications. SCR uses ammonia as a NOx reducing agent. The ammonia is typically supplied by introducing a urea/water mixture into the exhaust upstream of the catalyst. The urea/water mixture is stored in a separate tank that must be periodically replenished. These systems can be very effective, with NOx reductions of 70 to 90%, and appear to be tolerant of current U.S. on-highway diesel fuel sulfur levels. However, there is concern that applying current SCR technology to highway vehicles will require use of catalyst formulations that are sensitive to sulfur, such as those employing platinum, to deal with the broad range of operating temperatures typical of highway diesel engines in use. There is also potential for formation of ammonia sulfate, which is undesirable because it is a component of fine PM28

In addition, SCR systems bring some unique concerns. First, precise control of the quantity of urea injection into the exhaust, particularly during transient operation, is very critical. Injection of too large of a quantity of urea leads to a condition of ``ammonia slip'', whereby excess ammonia formation can lead to both direct ammonia emissions (with accompanying health and odor concerns) and oxidation of ammonia to produce (rather than reduce) NOx. Second, there are potential hurdles to overcome with respect to the need for frequent replenishment of the urea supply. This raises issues related to supply infrastructure, tampering, and the possibility of operating with the urea tank dry.

Third, there may be modes of engine operation with substantial NOX generation in which SCR does not function well. Finally, there is concern that SCR systems may produce N2O, a gas that has been associated with greenhouse-effect emissions.

Anyone know the NOX issues of biodiesel fuel compared to petroleum diesel?

Bill