The Death of Diesels?

[Orange Crush]

Mercedes Dies-Otto
Rewriting the rules of internal combustion

By JEFFERY P. VETTRAINO

AutoWeek | Published 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.

From:
http://www.autoweek.com/apps/pbcs.dl...004/1024/rss01

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.

1.8 * 134HP/L = 241HP
1.8 * 160TQ/L = 288FT-LBS

[Overide]

im confused... and i am a mechanical engineer! I would have to see more info on how they are able to change the compression on the fly like that...

[BK19702]

Originally Posted by Overide

im confused... and i am a mechanical engineer! I would have to see more info on how they are able to change the compression on the fly like that...

Ditto on all accounts. It almost sounds like the old Perpetual Motion Machine from Thermodynamics (i.e. too good to be true).

[Overide]

Thermo was such a tough class... the lab was cool though.

[t22a80]

Very interesting. Its almost like they took just about every idea thats been on the market and put it all together and this is what they came up with. At first I wasnt very impressed with those HP and TQ numbers until I read it again and it was "per liter".

Could be very interesting if its proven reliable. My only question is how much will they charge for this? If you want a diesel in a truck its an expensive option, one that often doesnt pay off unless you put on a lot of miles. I have a feeling this could be a similar situation.

[Orange Crush]

Frankfurt Motor Show starts on Sept 13 so we'll have to wait until the to get more details.

Re: Variable compression

http://www1.eere.energy.gov/vehicles...vcr3_29_01.pdf

&

http://www.mce-5.com/vcr_strategy/vc...principles.htm

P.S. The MB Dies Otto powered SClass (4500+ lbs) has achieved 39 mpg.

[KYDeepwater]

I think to change the compression, they use hydraulic servos to move the top half of the engine, putting it on a slight angle and reducing the volume above the cylinder. Saab did this a few years ago to chagne displacement and change the valve lift. It will be curious to see how reliable all of these extra engine management systems will be.