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Old 08-28-2007, 11:09 AM   #1
tackepj
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Default GM experiments with new HCCI engine in Aura

Follow the link to an interesting article from Inside Line:

http://www.edmunds.com/insideline/do...ticleId=122346

Here is the text:

"DETROIT While the Volt plug-in hybrid has made lots of headlines for General Motors, the company wants us to know that it's still busily refining gasoline and diesel engine technology.

Its latest effort is the HCCI internal combustion engine, a spark-ignition piston engine that can operate as a compression ignition motor, similar to a diesel. GM installed a version of the engine in both a Saturn Aura and an Opel Vectra and let us drive them around its proving grounds in Milford, Michigan.

General Motors says HCCI (Homogeneous Charge Compression Ignition) can yield a 15 percent improvement in fuel economy. But there are a few caveats. First, GM Powertrain Chief Tom Stephens says the technology won't likely reach production before 2015. And second, this impressive number includes the cumulative efficiency of variable valve timing and lift as well as direct injection, both of which must be in place for compression ignition to operate.

Compression ignition is all about the temperature inside the combustion chamber. In compression-ignition mode, the exhaust valves close earlier, trapping some of the heated air from the previous combustion cycle. This warms the incoming fuel mixture sufficiently to produce ignition once it's compressed by the piston. Clever stuff. But when the engine is under load while accelerating, for example the engine must transition back into spark mode to make full power.

This translates into a very narrow window of operation for compression ignition. Both light and heavy throttle applications sent the Ecotech four-cylinder into its default spark ignition mode. In fact, we were seldom able to keep the engine running on compression ignition mode. There's no mystery about the onset of compression ignition, as the engine starts knocking like an ancient diesel.

At this point, HCCI attracts far more attention from the driver than it should, and we're not yet persuaded that its effect will be greater than simple cylinder deactivation. Still, the gasoline engine clearly has a future, and we give General Motors credit for giving us a run in what is still a laboratory rat.

What this means to you: Mercedes-Benz is about to announce this technology at the 2007 Frankfurt Auto Show, so count this as one way in which the General is leading the way into the future."

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Old 08-28-2007, 11:31 AM   #2
Gerry Proctor
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Default Re: GM experiments with new HCCI engine in Aura

Peccles posted this in the "general" Saturn a while back (http://www.saturnfans.com/forums/sho...d.php?t=105159). This is interesting technology, but has its place -just like hybrids. Paricularly; it's back to spark ignition with speeds over 55. No doubt, those city drivers would see the most benefits. It would probably be some interesting employment if combined with a hybrid.

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Old 08-28-2007, 11:49 AM   #3
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Default Re: GM experiments with new HCCI engine in Aura

Quote:
Originally Posted by Gerry Proctor View Post
Peccles posted this in the "general" Saturn a while back (http://www.saturnfans.com/forums/sho...d.php?t=105159). This is interesting technology, but has its place -just like hybrids. Paricularly; it's back to spark ignition with speeds over 55. No doubt, those city drivers would see the most benefits. It would probably be some interesting employment if combined with a hybrid.
Or with the E-Flex system (a la Chevrolet Volt concept), where it could be optimized to run in the sweet spot in HCCI mode to recharge the batteries...

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