Benz's DuoTec: Clean, Powerful and 40 MPG

Engine Blends Best of Gasoline and Diesel Technologies


This glimpse into tomorrow comes courtesy of the brains at Mercedes-Benz, hosts of a recent technical presentation on alternative technologies and the future of the internal combustion engine.

The message was clear. Don't write off the gas-burner.

"Suck-squeeze-bang-blow," the process that moves the modern world, is still being refined, and in one form or another will be with us well after our children are adults, perhaps even after their children are grown.

But there's still room for improvement, and much of the discussion at Mercedes' tech-fest centered on a new fuel-efficient engine that will debut at the 2007 Frankfurt Auto Show.

Two Technologies Made One It's called DuoTec in the literature, but the engineering brass referred to the prototype as "DiesOtto," reflecting the combination of technologies that were applied to a conventional "Otto cycle" engine (suck, squeeze, bang, blow) in order to achieve the fuel economy of a diesel engine, the emissions of a super-clean gas engine and the power to satisfy even the lead-footed.

And while the prototype is a smallish four-cylinder that displaces just 1.8 liters, it's not just for some lightweight econocar. Instead, Mercedes is showing DuoTec for the first time in an S-Class sedan, underlining the point that cylinder count will cease to be a measure of performance and fuel efficiency.

As it sits in the S-Class, the new engine puts out 134 horsepower and an impressive 160 pound-feet of torque — per liter. That's a total of 241 ponies and an impressive 288 lb-ft packed into an engine the size of a Honda Civic's. This small engine is capable, Mercedes executives say, of propelling the big sedan from zero to 60 mph in 7.5 seconds while delivering fuel efficiency of around 40 miles per gallon.

The DuoTec engine runs on conventional gasoline and will be less expensive to build than a diesel — which requires costly combustion after-treatments — and, most important to the guys trying to sell it, will deliver the range and power demanded by most car buyers.

DuoTec is still five to seven years from series production, but it will likely beat the fuel cell to the retail market. When it does appear, it could have a more immediate and much larger impact than alternative fuels on both fuel economy and emissions levels.

Secretive Think Tank Is Incubator The alternative technology presentation was conducted in one of the high-security buildings at Mercedes headquarters in the Untertürkheim district of Stuttgart. (To gain entry, we surrendered cameras and cell phones and enjoyed a polite pat-down.) The PowerPoint shows on alternative technologies were narrated by guys who peer over time's murky horizon in order to find answers to questions that aren't even being asked yet.

"Why didn't we think of that?" is verboten in these hallowed halls.

The strategies employed for the prototype DuoTec include downsized displacement, twin turbocharging for power boosts at both low and high rpm, direct gas injection, variable valve timing and lift, and a trick adjustable cylinder head that changes compression ratio depending on whether the engine is being fired by its spark plugs or — and this is the really cool part — by compression ignition, just like a diesel.

How's that work?

When the DuoTec engine is starting or laboring under full load, the fuel and air mixture is ignited by conventional spark plugs; then, when the engine is under partial loads, combustion changes to what Mercedes calls "controlled auto-ignition," similar to the compression ignition of a diesel engine. This combination results in great fuel economy, excellent power across the rpm range, reduced combustion temperatures and extremely low nitrogen-oxide and carbon-dioxide emissions. It also allows the use of conventional catalytic converters so the engine can meet all European and U.S. air-quality regulations.

The Hitch This two-mode operation depends on complex electronic controls that can only be developed on the world's most powerful computers. It also requires a new, extremely sensitive pressure sensor that provides unprecedented levels of information about what's going on in the combustion chamber.

DuoTec is modular in concept, meaning its technologies can be applied to other engines. Neither cylinder count nor displacement is restricted to the 1.8-liter, four-cylinder configuration that will appear at Frankfurt.

Why DuoTec Matters With the number of cars on the road growing at a rapid clip — there will be about 2.2 billion vehicles on the world's streets by 2050, says Dr. Joachim Schommers, director of passenger car development at Daimler — something must be done to cut their appetite for petroleum-based fuels.

That's especially critical, as many pundits believe peak oil production has already arrived or is looming just around the next hazy bend in the energy road. Add to that the national concern over dependence on an oil supply increasingly controlled by the OPEC nations, many of whom are not exactly our friends.

Technologies such as the DuoTec engine are aimed at cutting our oil dependence, thus boosting our energy security without dramatically impacting our mobility.

No Single Answer But no single alternative technology can solve all the needs of every market — and right now not even all the available alternative fuel sources combined could supplant gasoline and diesel as the most efficient and cheapest means to power the world economy.

A multi-pronged approach is likely the only rational course of action.

Daimler has been spending an average of 5.6 billion euros ($7.5 billion) a year on a variety of alternative technologies since 1990. In that time, the Mercedes-Benz passenger car fleet's carbon-dioxide output has been cut by 30 percent, and other emissions are down by 90 percent. That kind of performance, along with new technologies such as the DuoTec engine, helps bolster the automaker's argument that it is the leader in this effort.

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