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Diesel Goes Blue

If cleanliness is next to godliness then the U.S. Environmental Protection Agency and the California Air Resources Board must have the golden keys to the pearly gates.

It was just a few years ago that bureaucrats on the left and right sides of the U.S. devised a way to potentially outlaw diesel engines. Who could blame them when you see the massive amounts of black smoke spewing out of some semis? The new regulations not only put pressure on the oil industry to devise a much cleaner diesel fuel, but forced automakers to deal with a dual set of emission regulations that required one level of cleanliness for national distribution and yet another more stringent standard to sell vehicles in the critical state of California, as well as several East Coast states that followed that state’s lead. Those tough emission laws and worries over whether the oil companies would meet cleaner diesel fuel standards caused some automakers-Volkswagen in particular-to throw their hands up in dismay, deciding to stop selling diesel passenger cars in the U.S. until the final standards go into effect in 2008. Engineers at DaimlerChrysler responded by developing an emissions aftertreatment module called BLUETEC that meets both current and future diesel emission standards via the use of an oxidation catalyst, particulate filter, NOx storage catalyst and the future addition of "Adblue" (AUS32), a urea-based solution.

 

Sitting Out Not an Option

Despite the regulations, DCX execs-based, in part, on the success of the E320 CDI diesel, which had surpassed initial sales projections-initiated the BLUETEC program. "It took us about three years between start of BLUETEC product development to start of production," said Joachim Schommers, head of passenger car diesel engine development for DCX. BLUETEC team members worked alongside engineering colleagues at Mercedes developing the new family of aluminum closed-deck OM 642 V6 CDI engines, to assure the systems would work cohesively, especially since the engines have to be tailored with specific system controls. "BLUETEC cannot be a retrofit on existing engines," Schommers said. "With the BLUETEC system, the engine and aftertreatment systems have to work more closely together than in any other emission system." 

 

Building Blocks

The biggest development challenge in meeting emissions requirements? Software. Schommers pointed to software application development as the single largest challenge in assuring BLUETEC would meet emission requirements. DCX engineers focused on optimizing the combustion process of the OM 642 engine to reduce harmful emissions as much as possible through the use of electronic engine controls, four-valve engine design, third-generate common-rail direct injection via piezo injectors, variable geometry turbochargers and exhaust gas recirculation. Along with utilizing existing particulate filter technology, BLUETEC uses a refined nitrogen oxide (NOx) storage catalytic converter to lower NOx emissions. The storage catalyst technology was done with the assistance of Umicore, which improved the substrate and catalytic coating to meet the rigorous durability cycles. The oxidation catalytic converter stores nitrous oxides until the engine is operated for a few seconds, with a rich air-to-fuel mixture, and converts the NOx to nitrogen and water and regenerates the NOx-storage catalyst. While the existing BLUETEC system used in the Mercedes-Benz E320 does not require an injection of the AdBlue solution, the feature will be added in select vehicles-Mercedes-Benz SUVs and Jeep Grand Cherokee-beginning in 2008. AdBlue will require the use of a Selective Catalytic Reduction (SCR) converter designed to reduce nitrogen oxide emissions by up to 80%, meeting U.S. BIN 5 standards that go into effect in 2009.

Adblue-a urea-based aqueous reduction solution in demineralized water-is injected into the hot exhaust gas and decomposes into ammonia, which subsequently transforms the NOx water and nitrogen. Plans call for AdBlue-which breaks down thermally and is consumed at a rate of 0.1 liters every 100 kilometers-to be stored in a separate, compact tank which will be replenished when the vehicle is taken in for routine maintenance. "The dosing of AdBlue follows a sophisticated strategy, based on numerical models in the engine controller and control strategies based on several aftertreatment sensors," Schommers said, adding DCX has come to an agreement with the E.P.A. on an effective warning system that will alert the driver before the vehicle runs out of AdBlue and result in a potential violation of emission rules. Developing a system where AdBlue could be mixed in with diesel fuel at the refinery was considered, but testing showed the solution began to decompose during the combustion process, degrading its capability to form ammonia for aftertreatment purposes.

 

Spreading the Wealth

DCX has plans to make the BLUETEC brand as well known as Kleenex via a partnership with Volkswagen and Audi. Expansion plans also encompass Chrysler Group vehicles, including future Jeep-brand vehicles. Since optimization of the BLUETEC system will require close assimilation with the various engines used, each automaker will have to tailor the aftertreatment system for their particular engines. Audi and Volkswagen will continue to use the "TDI" moniker for their diesel variants. Schommers expects the partnership to help reduce cost of the BLUETEC system, making it amenable to install on mass-market vehicles: "We feel we already have a good value proposition with our current product, the E320 BLUETEC. Nevertheless, we will continue our focus on optimizing system cost, both with regard to engine out emissions and aftertreatment."

According to a recent study by J.D. Power Automotive Forecasting, diesel light-vehicle sales are expected to increase from 3.2% in 2005 to more than 10% by the middle of the next decade. Volkswagen is expected to remain the largest global supplier of diesel-fueled light vehicles, with Ford ranking second.

Launched 70 years ago, the Mercedes-Benz 260D was the world’s first production diesel car. In 1997, Mercedes debuted its first CDI—Common-rail Direct Injection—engine. Audi brought Turbocharged Direct Injection (TDI) to production in 1989 in the Audi 100.