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GM Develops New High-Efficiency Engine

HCCI engine sips fuel like a diesel, but without the sooty exhaust

By Joe Benton
ConsumerAffairs.com

August 24, 2007

The engine sips fuel like a diesel, getting 15 percent better fuel economy than ordinary gasoline engines but produces low emissions like a gasoline engine and will not need the expensive exhaust treatment that diesel engines require.

GM demonstrated two working concepts of the engine known as the homogeneous charge compression ignition (HCCI) engine.

In an HCCI engine, gasoline is ignited inside the cylinder using compression and the engine's own heat without the need of a spark. This is the same way that a diesel engine ignites diesel fuel.

This type of ignition produces energy because the fuel burns with less heat, which wastes energy. There is more compression when the fuel is ignited and power is produced as the fuel and air expand.

The vehicles GM used to show off the HCCI technology are a Saturn Aura and an Opel Vectra, two sedans equipped with 180-horsepower 2.2-liter four cylinder HCCI engines.

"I remember debating the limits of combustion capability when I was in college," Tom Stephens, group vice president, GM Powertrain and Quality, said in a company statement. "HCCI was just a dream then. Today, using math-based predictive analysis and other tools, we are beginning to see how we can make this technology real."

The HCCI engine, which burns gasoline or E85 ethanol, runs in compression ignition at speeds as high as 55 mph, GM said. At higher speeds, or under heavy loads, the engine switches to spark ignition mode.

GM said it is continuing to refine the technology but did not commit today to a production timetable for the HCCI engine.

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