Bluetec Drives Award-Winning DC Turbodiesel

Special Report

Story Behind 10 Best Engines

The Ward’s 10 Best Engines competition celebrates 13 years of recognizing outstanding powertrain development. In this third of a series, Ward’s highlights the Bluetec emission-reduction strategy that sets the Mercedes 3L V-6 turbodiesel apart from its competitors. Watch for features on the other 2007 winners throughout the year.

Proponents say new-generation diesel technology is the most viable, most readily deployable answer to reducing fuel consumption in U.S. light vehicles.

Those advocates are countered by concerns about diesel emissions, infrastructure and consumer perception.

DaimlerChrysler 3L DOHC V-6 turbodiesel performs on par with similar-sized gasoline engines.

DaimlerChrysler AG can’t directly improve the nation’s diesel-fuel infrastructure, but on the other two matters, the company’s all-new 3L DOHC V-6 turbodiesel – a 2007 Ward’s 10 Best Engines winner in its first year of availability – stands ready to dispel any doubts.

DC’s new V-6 turbodiesel has the performance and refinement to emphatically dispatch issues of customer satisfaction and stands poised with advanced new low-emissions technology that soon will make diesel power available to buyers in all 50 states, even those with the strictest emissions standards.

For 2007, DC offers the 3L V-6, developed by the auto maker’s Mercedes-Benz unit, in the Mercedes E320 Bluetec, ML320 CDI, R320 CDI and GL320 CDI, as well as the Jeep Grand Cherokee CRD (Common Rail Diesel). The V-6 configuration represents a new direction for Mercedes, as all its prior 6-cyl. diesel engine families had been inline architectures.

Gerhard Doll, Mercedes-Benz senior manager-project coordination development, V-6 diesel, says Mercedes selected the “V” arrangement for a variety of advantages over its historically significant I-6 diesel layout:

The industry has come to expect technical innovation from engineering-driven Mercedes, and the new 3L V-6 turbodiesel doesn’t disappoint. This power-dense and frugal new diesel architecture incorporates a host of new technology and design features that help make it worthy of spearheading the diesel charge in North America.

Doll says the new V-6 diesel engine family – which, curiously in this age of increasing modularity, owes nothing to the company’s highly regarded current lineup of V-8 diesels – was developed in approximately 40 months, gestated by the Mercedes-Benz Development System, the company’s Computer Assisted Engineering (CAE) product-development process.

From its very foundation, the new 3L V-6 turbodiesel strives for technical superiority. Consider, for instance, the unusual 72-degree V angle. Conventional wisdom points to a 60-degree V angle as optimal for a V-6 to achieve even ignition firing and minimize vibration. But Doll says Mercedes engineers decided on the unique 72-degree layout as “the ideal compromise between installed width and height.”

A balance shaft, rotating opposite the crankshaft at the same speed, compensates for intrinsic V-6 imbalance.

Mercedes claims this engine is the first V-6 turbodiesel to feature an all-aluminum block; the company built on its aluminium-diesel experience from 3-cyl. powerplants for its Smart unit and 4-cyl. all-aluminum turbodiesels in the A-Class.

Even with its cast-in iron cylinder liners, the V-6 turbodiesel block, supplied by Alucast, weighs just 90.4 lbs. (41 kg), and the entire engine weighs just 459 lbs. (208 kg) – less, says Mercedes, than the inline 2.7L I-5 turbodiesel the new V-6 supplants in many European models.

Engineers also applied CAE extensively to engine internals, from the friction-cutting roller-finger followers for the DOHC/4-valve cylinder head to the specially machined crankshaft, with crankpins with rolled radii to maximize strength. The new 3L V-6 turbodiesel’s crankshaft is said to be more than twice as stiff in flexural and torsional rigidity compared with the previous family of inline diesels.

This intricate structural attention is largely responsible for the new turbodiesel’s outstanding noise, vibration and harshness “signature.” Ward’s 10 Best Engines testers all highlighted the V-6’s almost nonexistent levels of idle clatter and general mechanical gnash.

Some may think U.S. customers continue with longstanding revile for diesel NVH characteristics, but none could object to the NVH of this all-new diesel mill, and almost anyone would be challenged to distinguish its noises from those of a gasoline engine – even at idle.

Much credit also goes to the outstanding new piezohydraulic fuel-injectors, fed by a common rail, whose repertoire of multiple injection events comes at an efficiency- and power-enhancing maximum of 23,200 psi (1,600 bar).

The 8-hole piezohydraulic injectors, developed by DME, a unit of Robert Bosch GmbH, can generate as many as five injections per combustion event, including two “pilot” injections, less than a millisecond apart, that all but eradicate the infamous compression-ignition clatter. Mercedes and Bosch also collaborated for the engine-management system, says Doll.

But the most pressing matter in the diesels-for-the-U.S. debate is emissions. Although DC’s 3L V-6 currently is one of only two diesels offered for any U.S.-specification light vehicle in ’07, it is available for sale only in 45 states.

The new engine offers an impressive array of emissions-control technology, including cooled exhaust-gas recirculation and a particulate filter to help reduce oxides of nitrogen and particulates, which diesels produce in excess compared with a gasoline engine.

An even greater degree of sophistication is required to reach particularly stringent California LEV II and federal Tier II, bin 5 emissions standards.

For that, DC, along with partners Volkswagen AG and Audi AG, will introduce Bluetec, a suite of emissions-control technologies that will take diesel to the final level of cleanliness, making its tailpipe emissions essentially as clean as those of a gasoline engine.

Currently, the E320 Bluetec employs most of the modular Bluetec emissions-control system components, including a NOx-reducing “DeNOx” catalytic converter and a selective catalytic reduction (SCR) converter.

SCR involves periodic infusion of a reducing agent that allows a special converter to chemically reduce NOx to harmless nitrogen and water.

Today’s Bluetec system allows the E320 Bluetec to emit at Federal Tier II, bin 8 levels, permissible until 2009 in 45 states.

To achieve Tier II bin 5 compliance, which effectively allows diesel-engine sales nationwide – Mercedes promises it will launch bin 5-capable diesel models next year – the Bluetec system injects a urea-based fluid called AdBlue into the exhaust stream before it enters the SCR converter, cutting the nasty NOx to bin 5 levels.

There are meaningful costs associated. But Doll says, “The savings achieved through significantly lower fuel consumption, when compared with comparable gasoline models, very soon pay off for the customer.”

With an E320 Bluetec priced just $1,000 more than the equivalent gasoline-engine E 350, promise of swift payback for the customer is not hyperbole.

Bluetec-equipped diesel-powered vehicles are expected to be launched next year as ’09 models, which will be available for sale in all 50 states.

And despite the obvious emphasis on optimizing diesel emissions (and NVH qualities), Doll says performance advances also will not stand still. At 208 hp in the Mercedes E320 Bluetec, the new 3L DOHC V-6 turbodiesel develops almost 70 hp/L – an almost unthinkable figure less than a decade ago, while fuel economy of 26 mpg (9 L/100 km) city and an astounding 37 mpg (6.3 L/100 km) highway are more than 30% better than the same car using Mercedes’ gasoline-fueled 3.5L DOHC V-6.

“Some time ago, journalists were asking whether 60 hp/L and compliance with more stringent emission standards were possible, and we responded optimistically at the time,” Doll says. “Today we are talking about 70 hp/L and Bluetec technology which is able to meet the most stringent exhaust emission standards worldwide.

“The development of the diesel engine has by no means come to an end yet. You can look forward to interesting developments over the next few years. Until then we must ask (the auto industry and consumers) to be patient,” Doll says.