GM's homogeneous charge compression ignition (HCCI) - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 08-27-2007, 01:20 PM Thread Starter
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GM's homogeneous charge compression ignition (HCCI)


"The star of General Motors’ Powertrain Technology Show is homogeneous charge compression ignition (HCCI). It took 30 years to make this engine a reality. The idea of this engine hasn’t been very secret. Tinkers and high-quality teams have tried to perfect it, but the GM team led by Uwe Grebe, executive director for GM Powertrain Advanced Engineering, has succeeded.

“I remember debating the limits of combustion capability when I was in college,” said Tom Stephens, group vice president, GM Powertrain and Quality. “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. By combining HCCI with other advanced gasoline engine and control technologies, we can deliver a good fuel-savings value for consumers.”

GM says, “An HCCI engine ignites a mixture of fuel and air by compressing it in the cylinder. Unlike a spark-ignition gas engine or diesel engine, HCCI produces a low-temperature, flameless release of energy throughout the entire combustion chamber. All of the fuel in the chamber is burned simultaneously. This produces power similar to today’s conventional gas engines, but uses less fuel to do it. Heat is a necessary enabler for the HCCI process, so a traditional spark ignition is used when the engine is started cold to generate heat within the cylinders and quickly heat up the exhaust catalyst and enable.”

We drove one of the two concept vehicles with the HCCI engine at the company’s proving ground. It seemed like a regular car, which we drove to 70 mph. In idling, however, the engine didn’t sound a growl. GM says HCCI provides up to a 15 percent fuel savings and meets current emissions standards. GM didn’t say when the HCCI would appear in vehicles for sale.

GM revealed that it will launch 14 new or revised powertrains for 2008, including five 1.0-liter to 2.0-liter small-displacement engine variants, seeking to save fuel and improve performance in GM cars and trucks. That powertrain includes hybrids, clean diesels and fuel-saving technologies such as direct injection, six-speed transmissions, renewable biofuels and small-displacement engines for Asia, Europe and Latin America."
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post #2 of 3 (permalink) Old 08-27-2007, 01:32 PM
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This from Wikipedia:
HCCI is closer to the ideal Otto cycle than spark-ignited combustion.
Lean operation leads to higher efficiency than in spark-ignited gasoline engines
Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions. In fact, due to the fact that peak temperatures are significantly lower than in typical spark ignited engines, NOx levels are almost negligible.
Since HCCI runs throttleless, it eliminates throttling losses

High peak pressures
High heat release rates
Difficulty of control
Limited power range
High carbon monoxide and hydrocarbon pre-catalyst emissions
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post #3 of 3 (permalink) Old 08-27-2007, 02:40 PM
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I'd stay away from first years of production.

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