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GM Engine Tech: 15 Percent Better?


After years of trial and error and secrecy, General Motors is ready to talk publicly about a combustion process that could increase fuel economy in conventional engines by up to 15 percent.

Uwe Grebe, executive director for GM's powertrain advanced engineering, told TheCarConnection.com that doesn't have a specific timetable for rolling out an engine with a homogeneous charge compression ignition, or HCCI, as the system is called. However, the fact GM has put experimental engines into a pair of demonstration vehicles suggests the technology could ready by the beginning of the next decade.

GM senior management is putting more and more emphasis on better fuel economy across its model line in an attempt to catch up with Asian rivals, which have long owned the franchise on fuel efficiency in the minds of most consumers.

The HCCI engine has several advantages that help make it more efficient, said Grebe. It doesn't need spark plugs inside the combustion chamber since the fuel is ignited by pressure, and it burns all the fuel inside the chamber completely, which eliminates the need for extensive pollution controls, Grebe said. The low-temperature, flameless energy release in the combustion chamber also means the engine uses less fuel, according to Grebe.

“Additional development costs, including research and testing programs, are required to make the technology ready for the great variety of driving conditions that customers experience,'' Grebe said.

When HCCI is combined with advanced technologies such as direct injection, electronic cam phasing, variable valve lift, and cylinder pressure sensing, it can provides up to a 15-percent fuel savings, GM said. It is almost as efficient as a diesel engine but doesn't require the kind of extensive and expensive after-treatment of the exhaust necessary on diesel engines.

Richard Wagoner, GM chairman and chief executive officer, said recently that the cost of diesel engine pollution equipment makes it very difficult to use small diesel engines in theU.S. where consumers don't have much of an inclination to pay extra for the technology.

GM's experts, like those at other automakers, have experimented with the technology behind HCCI engines for more than two decades. Only recently, however, have advances in computer software made it feasible to use the engines on production vehicles, Grebe said. The software helps smooth over the variability in combustion that occurs when the engine heats up or the atmosphere around the car changes.

Tom Stephens, group vice president GM Powertrain, said that while improvements in the standard internal combustion engines aren't very glamorous, they are cost-efficient. Standard gasoline engines are less expensive to build and offer excellent horsepower versus diesel engines.

Stephens said "there is no silver bullet" for improving fuel economy. GM, however, is committed to a broad strategy that will boost efficiency of engines and reduce emissions.

As part of the strategy, GM will introduce 14 new engines and transmissions for the 2008 model year, including eight that will be used exclusively in the North American market.

GM's two-mode hybrid system will debut  on the full-size Chevrolet Tahoe and GMC Yukon on or about Nov. 1 and will be matched up with a new 6.0-liter V-8 engine, but will still get 25 percent more miles per gallon than a full-size SUV without the two-mode hybrid system.

"It will get better than 20 miles per gallon, even under the new EPA test," Stephens added. The EPA has made its test for calculating mileage tougher for the 2008 model year and the fuel-economy rating for many models, such as the Toyota Prius hybrid, are expected to drop.

The new hybrid system, which was refined at the hybrid development center operated jointly by GM, Chrysler and BMW in Troy, will be the first hybrid system used on full-size SUVs, which have become symbols of gas-guzzling in the ongoing controversy over fuel efficiency.

"The hybrid Tahoe is genuine SUV, only it’s 25 percent better fuel economy," he said. The Chevrolet Tahoe and GMC Yukon hybrids will also deliver up to 40 percent better fuel-efficiency in city-driving, Stephens added.

Stephens also said GM plans to extend the use of the hybrid system to the Cadillac Escalade and crew cab versions of the Chevrolet Silverado and GMC Sierra during 2008.

Chrysler also is making plans to launch a hybrid version of its Dodge Durango, which uses the same basic system. The Chrysler system, however, has different formatting.

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