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Mercedes-Benz Introduces a New Clean Diesel System

Bluetec: Has Mercedes Developed a Global Clean Diesel System?
There were several Bluetec-equipped vehicles on DaimlerChrysler company stands at the 2006 North American International Auto Show this January, including a Jeep Grand Cherokee Bluetec, the E320 Bluetec, and the concept Vision GL320 Bluetec. AutoPacific explains a bit about this system and where U.S. consumers might see it in real applications.
The Bluetec system is the result of Mercedes search for a diesel emission-control system that can be applied worldwide, meeting federal and market conditions that vary from country to country. The overall difficulty with diesel is the amount of aftertreatment required to lower emissions to levels required by various governments, and how expensive these processes can be.

Two Primary Emissions Created by Burning Diesel
Emissions from diesels fall into two categories, particulates and nitrogen oxides (NOx). By 2008, EPA requirements are that NOx emissions be reduced to 0.14 and particulates to 0.02 grams per mile. California’s CARB is even more strict, requiring reductions to 0.07 g/mi for NOx (it was 1.0 in 1998) and 0.01 g/mi for particulates (0.08 in 1998). Clean diesel is possible from a technological standpoint, but the cost can be prohibitive to most consumers at worst and high enough to be unappealing at the least. Particulate filters are standard on most European diesel engines, but drive the cost of replacement muffler and system up spectacularly.
Bluetec Employs Several Techologies
Bluetec uses a particulate filter for particulates and two solutions for nitrogen oxides, though the system starts with engine technology for minimizing untreated emissions. These include electronic engine management, four valves per cylinder, third-generation common-rail direct injection with piezoelectric injectors, a turbocharger with variable nozzle turbine and exhaust gas recirculation. Logic indicates that if you start with cleaner exhaust, you have less work to do before it exits the vehicle. Also used are an oxidizing catalytic converter to reduce carbon monoxide emissions and unburned hydrocarbons. A particulate filter meets or exceeds requirements for reduction of particulate emissions.
Then there is the reduction of oxides of nitrogen (NOx), and Bluetec shows two solutions. Both systems use a Selective Catalytic Reduction system that optimizes the cleaning of emissions based on the engine operation and the required emissions levels. One system uses an advanced De NOx storage catalytic converter, and was applied to the E320 Bluetec. Another solution is injecting an aqueous urea solution into pre-cleaned exhaust gas in a downstream catalytic converter, which releases ammonia and causes the nitrogen oxides to be converted to harmless nitrogen and water. Mercedes version of this is called AdBlue; this system was displayed on the Vision MLG320 Bluetec.
Though the E320 Bluetec De NOx storage catalytic converter method is not as efficient or effective, the urea solution is not approved for use in many markets, including the United States, because the solution itself has to be stored in a separate container that the owner needs to refill at intervals different from normal refuelling. There is concern that people would simply not bother to refill and therefore the emissions would be above regulations.
Real-World Application. Mercedes Bluetec with the AdBlue system will be used in European-market vehicles this fall. North America gets the Bluetec system as seen on the E320 Bluetec this fall, followed shortly by use in the M-Class and R-Class. Though there was a Jeep Grand Cherokee Bluetec on display, production intent for North America was not indicated. The Bluetec approach allows Mercedes to tailor its diesels to a given set of market conditions, a critical issue for any increase in diesel availability in the States in the future. Not only are emissions requirements more and more strict, each market has different legislation that affects what solutions a company can apply. And whether particulate filter, urea injection, or more catalysts, the solutions are all expensive and could price diesel engines out of the market.

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