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Mercedes Dies-OttoRewriting the rules of internal combustion

By JEFFERY P. VETTRAINO

AutoWeek | Updated: 07/25/07, 4:02 pm et

The demise of the internal combustion engine has been greatly exaggerated, or so Mercedes-Benz thinks.

The company’s position stems from empirical observation, based on all rational evidence: Internal combustion will remain the workhorse in transportation and power equipment for decades to come. Beyond this conclusion, Mercedes’ advanced engineering staff believes the efficiencies in both spark-ignition and diesel engines are a long way from tapped out, even after 100-plus years of development.

To demonstrate its point, Mercedes is developing a new, small-displacement engine known internally as the Dies-Otto. The Dies-Otto will debut in an S-Class sedan at this year’s Frankfurt motor show and could be in production long before alternatives like fuel-cell propulsion.

“The deepest potential in internal combustion has yet to be exploited,’’ says Herbert Kohler, vice president of advanced engineering and chief environmental officer at Daimler AG. “We have diesels that are as clean as gasoline engines, and we expect gas engines as efficient as diesels. Dies-Otto is one of several possible next steps.”

The Dies-Otto is fueled by direct gasoline injection and operates as both a four-stroke (Otto Cycle) spark-ignition engine and compression-ignition (diesel) engine. While the dual-mode ignition is its defining trait, the Dies-Otto actually integrates and optimizes nearly every significant internal combustion development of the last 20 years, including direct injection, piezo injectors, variable valve operation, serial turbocharging and advanced electronic controls, with a new twist called variable compression. According to Mercedes, the Dies-Otto delivers a previously unattainable mix of horsepower, torque and efficiency, with several advantages over conventional diesels.

This four-cylinder engine displaces just 1.8 liters, or considerably less than we’d expect in a hefty S-Class sedan. Mercedes expects to bury the old, “no-replacement-for-displacement” adage with an advanced turbocharging system. Yet the Dies-Otto’s two turbos are neither sequential nor parallel. Each one is optimized to work at certain engine speeds, with either one or the other pumping air into the cylinders at a given moment.

The big news is something Mercedes calls auto ignition, or compression ignition with gasoline fuel, at a substantially lower temperature than the latest-generation diesel engines. The process involves a host of parameters, including injection timing, variable valve operation and a shorter exhaust stroke that leaves a high quantity of exhaust gas inside the combustion chambers. The key is a variable compression system, which changes compression ratio on the fly. For now, Mercedes is keeping the specifics to itself.

Maximum output comes with spark ignition, while maximum economy comes with compression ignition. The Dies-Otto cycles between the two as conditions or driver demands warrant, though development is currently focused on maximizing time during which the engine operates with auto-ignition.

As presented in the S-Class, the 1.8-liter Dies-Otto delivers specific output of 134 horsepower per liter and torque at 160 lb-ft per liter, with about 40 miles per gallon. Mercedes says it motivates the 4500-pound S-Class from 0 to 62 mph in 7.5 seconds.

Moreover, it generates almost no nitrogen oxide and less carbon dioxide per liter of fuel consumed than current diesel engines, according to Mercedes. Because it runs on ordinary gasoline, it could also eliminate the infrastructure or capacity bottlenecks posed by diesels. It would be cheaper to build than the latest passenger-car diesels, largely because it uses a conventional three-way catalyst and requires no expensive particulate treatment. Finally, it could run on biofuels like ethanol, though Mercedes is not yet sure in what ratio.

Mercedes’ Kohler says transportation’s future includes a combination of electric power, hybrids, biofuels and, perhaps within a decade, the first fuel cells. Still, whether it is spark ignition, diesel or a combination of the two, internal combustion will remain the primary source of transportation power for decades beyond that.

The next stage, according to Kohler, might need to be a focus on vehicle efficiencies. In many respects, as manufacturers have focused on engine development and emissions, vehicles have gotten short shrift. It could require similar investment to reduce the amount of energy that various vehicle systems drain while maintaining the level of safety, comfort and performance the market has come to expect.

[aaaantoine]

I really enjoy reading about new engine technology.

If you can really get 40 mpg in an S-Class without going hybrid, there is hope for the future yet.

[Drew Dowdell]

incredibly interesting to see europe's take on what "hybrid" means.

[haypops]

GM is working on a gas fired compression ignition engine that we know of. Probably working on lots of this stuff that we don't know about too.

[Intrepidation]

As presented in the S-Class, the 1.8-liter Dies-Otto delivers specific output of 134 horsepower per liter and torque at 160 lb-ft per liter, with about 40 miles per gallon. Mercedes says it motivates the 4500-pound S-Class from 0 to 62 mph in 7.5 seconds.

That is extremely impressive...if I did teh numbers right, it means that the 1.8L will produce 242 horsepower, and 288 lb.-ft. torch...while getting 40 mpg. In your face Lexus.

[Drew Dowdell]

That is extremely impressive...if I did teh numbers right, it means that the 1.8L will produce 242 horsepower, and 288 lb.-ft. torch...while getting 40 mpg in an S-class. In your face Lexus.

missed an important point there. Imagine what'd it do in a C-class.

[haypops]

I'm just talking out of my butt, but I think that in thirty years from now the money spent on hybrid technology and especially hyfrogen will be thought of as a mistake.

[the_yellow_dart]

I'm just talking out of my butt, but I think that in thirty years from now the money spent on hybrid technology and especially hyfrogen will be thought of as a mistake.

Well... you still gain engineering experience as a firm.

Do you think GM's Wankel research was a mistake?

[haypops]

Well... you still gain engineering experience as a firm.

Do you think GM's Wankel research was a mistake?

That is an interesting question. I think if there were infinite, even a reasonable amount, resources then it wasn't a mistake. However, resources are severely restricted. That shortfall is obvious now, but was probably always in place for the research end of things.

Edited July 26, 2007 by haypops