Going Green with Blue

While Ford, GM and DaimlerChrysler provide excellent small-displacement diesel engines as options for the European car buyer, not one has yet announced its intention to bring these clean, efficient, quiet, higher fuel efficiency engines here to the United States.

The U.S. Environmental Protection Agency's (EPA) emissions regulations for diesel engines have been a big stumbling block for OEMs who want to bring in their high-tech diesel automotive power plants from Europe. That fact may be changing, however; EPA recently signaled an easing of these tough emissions standards, which would permit these diesel engines to be part of the nation's alternate fuel strategy.

GOING BLUE

The BLUETEC technology is a comprehensive system of diesel emissions control that uses the latest electronic control concepts, as well as some new components in the design of the fuel injectors. Diesel exhaust aftertreatment also is an essential part of the BLUETEC concept, as is the proposed addition of a urea-injection subsystem that cleans up tailpipe emissions to meet the originally proposed EPA diesel limits on emissions for all 50 states, which can be difficult to meet. But more on that a little later.

The M-B 2007 E320's BLUETEC-configured engine combines several technologies to minimize exhaust emissions, and it is a newly designed V6 turbocharged direct-injected diesel engine. BLUETEC is a concept based on advanced engine design which includes four valves per cylinder, centrally located piezoelectric injectors, third-generation CDI, a turbocharger with variable nozzle turbine and exhaust gas recirculation (EGR). This new V6 engine develops 221 horsepower (hp) and 376 lb.-ft. of torque.

ELECTRONIC FI THE KEY

The leap to electronic fuel injection means that a modern diesel engine may now be made cleaner, quieter and more powerful than earlier mechanically injected diesel engine designs. Diesel powerplants produce 20 percent to 30 percent lower carbon dioxide (CO2) emissions and significantly lower carbon monoxide (CO) emissions compared with gasoline engines. But until now, diesels have produced more oxides of nitrogen (NOX) and particulate matter (PM) at the tailpipe. However, with precise electronic control of fuel delivery, coupled with an oxidation catalyst and exhaust-stream aftertreatment, the BLUETEC diesel engine with the AdBlue urea injection system could pass EPA's 50-state emissions standards.

NOT JUST ANY DIESEL FUEL

The BLUETEC system depends on the use of ultraclean diesel fuel with less than 15 parts per million (ppm) sulfur. Low-sulfur 15 ppm diesel fuel – as mandated by EPA – is now entering the U.S. fuel distribution system and should be available nationally by the late fourth quarter of 2008. Sulfur is a natural element in most mineral oils, but it has a corrosive effect on engines. Sulfur also increases particulate emissions. The imminent availability of very low-sulfur fuel enables the use of reliable particulate filters and efficient NOX after-treatment technologies.

Critical parts of this diesel engine's emissions control system are three after-treatment units located in the exhaust stream:

• An oxidizing catalytic converter.
• A particulate filter.
• A de-NOX storage converter that temporarily absorbs NOX.

During brief regeneration pulses of a richer fuel-air mixture, stored NOX is released to react with other exhaust gases to form harmless nitrogen (N). Regeneration pulses also raise temperatures in the particulate filter, which effectively burns off the accumulated deposits.

The complete BLUETEC system includes one more module – AdBlue injection. The AdBlue liquid is a water-based urea solution carried in its own small tank and metered into the exhaust stream in minute quantities. The quantities are so small that the AdBlue tank only needs to be refilled during routine scheduled maintenance at prescribed periods, say M-B engineers.

When AdBlue is injected into the already precleaned exhaust gas stream, ammonia (NH3) is released. This converts NOX into harmless N and water (H2O) via a downstream catalytic converter. Called Selective Catalytic Reduction (SCR), this process creates the most effective method of exhaust gas aftertreatment currently available. While AdBlue has not been approved – yet – for use in the United States, AdBlue injection has already proved to be effective in tests run by more than 10,000 Mercedes-Benz commercial vehicles in Europe.

AGENCY RELUCTANCE

EPA's main objection is that anything involved in emissions control that requires the owner of a vehicle to do anything other than fill it up with fuel and get periodic emission tests is impractical. The Agency says that most motorists will not voluntarily do anything to keep the emissions system operating properly as designed, even in the interest of air quality compliance.

That's why EPA has not yet approved the AdBlue subsystem. But that could change, especially if the Agency buys into replenishment of the AdBlue urea liquid as part of the engine's periodic maintenance schedule. In addition, another warning light may be added to the dash to advise the motorist when it's time to get a new supply of urea after-treatment additive.

ELECTRONIC FI THE KEY

The new high-torque M-B diesel engine is quiet and delivers high fuel efficiency as it achieves much lower exhaust emissions than previous diesels. The turbocharged V6 powerplant uses full electronic fuel injection (FI), considered technically impossible on a diesel less than a decade ago. Relying purely on the heat of highly compressed intake air to ignite the fuel, diesel engines operate without spark plugs or other ignition-related parts.

The leap to electronic fuel injection means that a modern diesel engine may now be made cleaner, quieter and more powerful than earlier mechanically injected diesel engine designs. Diesel powerplants produce 20 percent to 30 percent lower CO2 emissions and significantly lower CO emissions compared with gasoline engines. But until now, diesels have produced more NOX and PM at the tailpipe. However, with precise electronic control of fuel delivery, coupled with an oxidation catalyst and exhaust-stream aftertreatment, the BLUETEC diesel engine with the AdBlue urea injection system could pass EPA's 50-state emissions standards.

REAL-WORLD BENEFITS?

M-B sources tell us that not only is BLUETEC now the cleanest diesel emission control technology in the world – one which can meet the most stringent emissions standards – but it also helps customers enjoy tangible fuel savings and helps to reduce our dependence on imported oil. With its super-clean exhaust, the technology also may increase the appeal and the future availability of diesel-powered vehicles.

In fact, industry watchers now predict that the market for diesel-engine cars in the United States will quadruple in the coming decade; currently, it ranks about 3.4 percent of the total market. Energy costs are expected to continue rising, and because diesel engines get between 20 to 40 percent better fuel mileage than gasoline engines, their popularity can only grow.

But growth is going to take several things to make it happen. Volkswagen is the only OEM that now offers diesels in some of their cars, and even that engine will be dropped for the 2007 model-year. M-B discontinued the E320 TDI inline six en-gine a few years ago. The new E320 V6 BLUETEC will go on sale later this year.

Ford and GM could make diesels available if the new EPA diesel regulations were eased; it could qualify their diesel engines now sold in Europe. Nissan also offers some high-efficiency, high-mpg small diesels in Japan. Audi is rumored to have a small diesel ready for the coming 2008 TT sports car, but it is not likely to be an early engine option. And don't forget that DaimlerChrysler's U.S. divisions of Chrysler and Dodge could easily provide an opportunity for the BLUETEC engine to find its way under some Jeep and Dodge hoods, as well.

FUTURE IMPLICATIONS

In Europe, where fuel prices are at least twice as much as in the United States, more than half of all new-car buyers opt for a diesel-powered car. As fuel prices here continue to increase in the coming years, fuel economy is likely to become an even more important factor in the purchase consideration. That's why analysts conservatively see the market share for diesel cars growing by at least 12 to 14 percent by 2015.

What's more, M-B believes consumers are beginning to realize that diesels can get even better fuel mileage than hybrids, especially when they are driven over long distances. The pulling power and fuel economy of the new-generation diesels are ideally suited to vehicle types such as large sedans, light-duty trucks and SUVs that are so popular here.