Exhaust Treatment:
A clean career for diesel engines with BLUETEC
A clean career for diesel engines with BLUETEC
Diesel drives with BLUETEC have embarked on a clean career
"The Blue(Tec) Brothers": Researcher Bernd Krutzsch (left) and developer Bernd Lindemann played a major role in bringing BLUETEC to the series production stage.
Bernd Lindemann doesn’t need to reflect long before answering the question: "BLUETEC can best be compared with the three-way catalytic converter used with gasoline engines both in terms of its complexity and emissions reduction capability." Few people are as familiar with these two aspects of BLUETEC diesel exhaust gas treatment as the Daimler engineer. As the manager of the division-wide BLUETEC 1 project at Mercedes-Benz Cars Series Development from the very beginning, Lindemann has experienced just how many technical barriers the engineers had to overcome — and just how much potential the technology they developed harbors.
The BLUETEC 1 project team’s mission was to bring a new BLUETEC diesel vehicle to the series production stage in just two-and-a-half years. To this end, they were to utilize the results of research projects carried out by a department headed by Bernd Krutzsch. In fact, Krutzsch’s team and two colleagues from Passenger Car Development had received the Daimler Research Award in 2006 for their efforts. The vehicle the BLUETEC team eventually built was able to do something that many experts equate with squaring the circle. It made the diesel drive as clean as a gasoline engine in terms of pollutant emissions, without sacrificing two hallmarks of the diesel engine: its efficiency and its fuel economy. | ||||||||
The technological key to solving the puzzle was a package of engine-internal optimization measures combined with a modular exhaust treatment system consisting of four elements and held together by a sophisticated operating strategy (see box on p. 44). The crucial factor for the team’s success was its ability to optimally match the exhaust treatment system, engine, and
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The highly complex technology operates quietly and invisibly — but also with impressive effectiveness. This is most apparent with regard to nitrogen oxide emissions, the last remaining weak point of the diesel engine compared to gasoline systems. BLUETEC enabled the developers to make a great leap forward here — a fact best demonstrated by their latest coup, the E 300 BLUETEC, which premiered in Europe in September 2007. Nitrogen oxide emissions in the E 300 BLUETEC have been significantly reduced compared to those of the E 320 CDI, which has similar output and fuel consumption values. The vehicle is also exemplary when it comes to other pollutant emissions and CO2, and generally achieves values lower than those of the E 320 CDI.
The E 300 BLUETEC is therefore the first diesel production car available in Europe that meets the EURO 5 emission standard, which won’t even go into effect for new vehicles until the fall of 2009. Incidentally, the early introduction of the E 300 BLUETEC put the engineers from Mercedes-Benz Cars a step ahead of European lawmakers, as the EU bill governing EURO 5 and the more stringent EURO 6 standard for the fall of 2014 hasn’t even been signed into law yet.
Rudolf Thom, who is responsible for Vehicle Certification at Passenger Car Development, explains the significance of this head start on the legislation: "It means no agency in Europe can certify our vehicle in accordance with the EURO 5 standard until the law has gone into effect." More specifically, all registration and title papers for the E 300 BLUETEC will officially designate the car as a EURO 4 vehicle. However, Mercedes-Benz will guarantee the conversion to EURO 5 status by means of a certificate issued by the manufacturer as soon as the lawmakers have done their job. | ||||||||
The E 320 BLUETEC has been available in 45 U.S. states since October 2006, and in all 50 states since October 2007. The reason why the E 300 BLUETEC and the E 320 BLUETEC are not identical twins has to do with different levels of diesel fuel quality and average drive train stress loads on the two sides of the Atlantic.
Sales of the E 320 BLUETEC in the U.S. have turned out to be remarkable: 20 percent of all those who purchase an E-Class sedan with a six-cylinder engine (without a four-wheel drive variant) opt for BLUETEC. That might not seem so spectacular from a European point of view, but a 20 percent diesel share for any passenger car model in the U.S. is an earth-shattering event.
In Europe, where no one is surprised by the agility and sportiness of diesel models, 80 percent of all purchasers of midsized sedans like the E-Class choose a diesel variant — mainly for reasons of economy. In contrast, the proportion of diesel cars and SUVs on the U.S. market is just three percent, which makes such models exotic there. Moreover, the diesel’s reputation in the U.S. is plagued by bad experiences from the distant past. While a lot of people in the country may remember their great fuel economy, most still associate diesel engines with large, loud, knocking vehicles that spew out foul-smelling exhaust behind them. Tremendous advances in diesel technology (common-rail diesel direct injection, emission reductions through oxidizing catalytic converters, and particulate filters) have led to the broad acceptance and great popularity of diesels in Europe. However, most people in the U.S. know nothing about these achievements. Against this backdrop, the fact that the E 320 BLUETEC variant has managed to capture 20 percent of the market right from the outset is nothing less than a smashing success. | ||||||||
family Inspired by this sign of widespread acceptance by customers, Mercedes-Benz Cars is now preparing a second "blue wave" of vehicles, according to Thom. Next year, the E 320 BLUETEC sedan will be joined by three big BLUETEC brothers in the ML, GL, and R-Class, thereby bringing the cleanest concept for exhaust treatment to the SUV segment as well. And the Mercedes-Benz developers have achieved a significant milestone with this vehicle trio. Whereas the E 320 BLUETEC meets the BIN 8 and LEV2 emission standards currently in effect in the U.S., the BLUETEC diesels in the ML, R, and GL-Class will go a step further by conforming to the most stringent emission limits for heavy vehicle models.
The required additional reduction of NOx emissions in the three new BLUETEC models was achieved through an active SCR catalytic converter system. With the help of the AdBlue additive, this system eliminates even more nitrogen oxide in the exhaust line than ever before (see box on p. 47). Here, the developers employed a concept that had already proved successful in Mercedes-Benz commercial vehicles. Conversion to the SCR treatment system with AdBlue, which is the more effective solution in the long run, was made possible by the fact that the additive will be available throughout North America when the new BLUETEC models are introduced to the market, says Thom. | ||||||||
Stepping up the BLUETEC offensive to include additional markets, model series, and engine variants is the top priority and challenge for developers at Mercedes-Benz Cars, according to Lindemann: "We’re working full steam to ensure that both NSK Advanced and SCR can be effectively incorporated into our entire product portfolio — and not just in the segment for six-cylinder engines." That’s why the development team’s agenda also includes a four-cylinder BLUETEC model in the form of the C 250 BLUETEC. Such expansion requires more than simply adapting the technology to new models; it also involves determining and developing the most suitable treatment technologies for vehicles that vary in terms of weight, engines, and equipment packages. In other words, the BLUETEC modules have to be integrated differently into each variant, the sizes of the catalytic converters must be optimized, and even the algorithms for engine control systems have to be customized for each model. Last but certainly not least, the additional costs invariably generated by each BLUETEC system must be acceptable to customers.
The second challenge Lindemann and his team are working on is to refine the self-diagnostic capability of BLUETEC systems. "Emission legislation itself requires onboard monitoring of the systems," he points out. "And the demands placed on us in this regard will increase significantly in both the U.S. and the
Simplification is the key
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The third challenge involves the BLUETEC modules themselves. While Lindemann considers NOX reduction with SCR plus AdBlue to be a stable technology, it does have an Achilles heel: the high complexity of the overall system. The engineers are therefore working to simplify the SCR module by reducing the number of components used, which will also lower costs. Work on the nitrogen storage catalytic converter (NSK) is focusing on its long-term stability.
When it’s new, an NSK (see box on p. 48) can achieve nitrogen oxide conversion rates that are on a par with those of an active SCR system. However, as a vehicle’s mileage increases, the conversion rate slowly declines and eventually settles at a low level. That’s why the developers at Mercedes-Benz are searching for more suitable types of materials and catalytic converters. Visitors who looked at the 19 Mercedes-Benz vehicles on display at the IAA International Motor Show in September 2007 will have gained insight into the fourth challenge developers face: the need to link BLUETEC with other technologies, such as hybridized diesel drives and start-stop mechanisms. Both of these technologies reduce consumption and thus CO2 emissions. However, both of them also affect the temperature of the exhaust flow, and therefore the effectiveness of the treatment process as well. | ||||||||
While Lindemann considers this problem an obstacle, he also views it as one with hidden potential. He refers to this dilemma as a "mutual blocking" between concepts for reducing CO2 emissions and those for lowering other pollutants. "The two approaches can actually support each other," he says. "For example, an effective treatment system allows you to choose an engine setup that is consistently optimized in terms of CO2 emissions. Conversely, the use of such a system in a hybrid drive makes it possible to implement temperature management measures that further increase the effectiveness of exhaust treatment." In other words, the next round of the classic tradeoff — the need to offset (or even more than offset) the increase in fuel consumption that inevitably results from an emissions reduction — is about to begin. Lindemann says he’s ready for the challenge: "Thanks to BLUETEC, we can balance this tradeoff in a different way — at an extremely low emissions level."
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