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Old 05-06-2008, 05:06 PM   #1
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GM moves closer to HCCI engine production

Imagine getting V6 fuel economy from your V8 Camaro. It could happen sooner than later with HCCI engine technology

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Previously we reported on a new technology dubbed homogeneous charge compression ignition, or HCCI, which allows petrol cars to improve fuel efficiency by as much as 15% by achieving combustion with only compression of the air-fuel mix rather than using a spark plug. The technology was pioneered almost 30 years ago but has only recently been subject to a great deal of interest from the auto industry, most notably from Mercedes-Benz and GM.

GM’s commitment to HCCI technology is especially strong, with the General implementing the technology into prototypes, including the Saturn Aura (pictured). In a new breakthrough, GM has announced it has engineered the technology to operate while a car is idling (previously it could only operate while a car was in motion), increasing fuel savings even further.

The HCCI system can now be used while idling and up to speeds of 55mph, but at speeds greater than this or when more vigorous acceleration is required, a traditional spark-plug system will be used. This means that HCCI equipped cars will have both technologies under the hood.

If combined with other fuel-saving technologies such as low-resistance tires and hybrid systems, the savings from HCCI could add up to be very significant.

While GM has been eager to develop the technology, other companies have adopted a ‘wait and see’ attitude towards HCCI, including BMW who is researching alternative methods to reduce the dependence on oil such as its hydrogen program.

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How HCCI works

HCCI, along with other enabling advanced technologies, approaches the engine efficiency benefit of a diesel, but without the need for expensive lean NOx after-treatment systems. Its efficiency comes from reduced pumping losses, burning fuel faster at lower temperatures and reducing the heat energy lost during the combustion process. Consequently, less carbon dioxide is released because the vehicle’s operation in HCCI mode is more efficient.

Highlights of the technology include:

- Engine efficiency approaching the benefit of a diesel with substantially reduced after-treatment cost
- Builds off proven gasoline direct-injection and variable valve actuation technologies
- Adaptable to conventional gasoline engine architectures
- Requires only conventional automotive exhaust after-treatment
- Compatible with all commercially available gasoline and E85 ethanol fuels.

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 HCCI operation. During HCCI mode, the mixture’s dilution is comparatively lean, meaning there is a larger percentage of air in the mixture. This reduces the throttle losses of a conventional spark-ignited engine at low loads, helping the HCCI engine approach the efficiency of a diesel, but requiring only a conventional automotive exhaust after-treatment. Diesel engines require more elaborate and more expensive after-treatment to reduce emissions.

HCCI builds on the integration of other advanced engine technologies - some of which are already in production and can be adapted to existing gas engines. The cylinder compression ratio is similar to a conventional direct-injected gas engine and is compatible with all commercially available gasoline and E85 fuels.

“I am pleased with our engineering team’s progress,” said Stephens. “It is another initiative in GM’s advanced propulsion technology strategy to lessen our dependence on oil. HCCI, direct injection, variable valve timing and lift, and Active Fuel Management all help improve the fuel economy and performance of our internal combustion engines. I am confident that HCCI will have a place within our portfolio of future fuel-saving technologies.”

Achieving HCCI operation at idle has long been a challenge for HCCI engineers, because the relatively low-temperature and light engine load characteristics generally inhibit the proper thermodynamic conditions for successful, controllable autoignition. Also, heat is needed at start-up and idle to light-off the catalytic converter.

GM’s engineers overcame these challenges with advanced control of the direct injection system and a HCCI-specific cylinder pressure sensor system. After spark ignition is used to start the engine, the engine’s sophisticated control system manipulates the combustion process via input from the cylinder pressure sensors so that auto-ignition can occur during idle.

“Fuel consumption with a spark ignition engine is relatively high when idling, so this new development in our HCCI process helps to enhance fuel efficiency,” said Dr. Matthias Alt, HCCI program manager, GM Powertrain.

The emerging HCCI technology offers several paths for implementation in a production vehicle. GM’s strategy combines the efficiency enhancements of HCCI and the power-on-demand attributes of spark ignition. This combination delivers enhanced fuel savings over a comparable, non-HCCI engine, but with the performance consumers have come to expect during higher engine load situations, such as passing or entering a freeway.

“GM’s HCCI development focuses the technology where it will deliver the most benefit at the most reasonable cost for the consumer,” said Alt. “An HCCI engine that uses HCCI in the entire operating mode would be heavier, noisier, more costly and would not deliver the performance experience people expect from a modern car.”

With GM’s technology, proven gasoline engine technology is retained and the engine has spark plugs and a conventional ignition system. The vehicle operates in HCCI mode up to about 55 mph (88 km/h) and switches to spark-ignition for higher-speed, higher-load conditions. It also engages spark ignition mode for passing at lower speeds and other higher-load demands.

The Aura concept is powered by a 2.2-liter Ecotec engine that makes 180 horsepower (134 kW) and 170 lb.-ft of torque (230 Nm). It features a central direct-injection system, with variable valve lift on both the intake and exhaust sides, dual electric camshaft phasers and individual cylinder pressure transducers to control the combustion as well as deliver a smooth transition between combustion modes.

A sophisticated controller, using cylinder pressure sensors and GM-developed control algorithms, manages the HCCI combustion process, as well as the transition between HCCI combustion and conventional spark-ignition combustion.

Challenges for production

The biggest challenge of HCCI is controlling the combustion process. With spark ignition, the timing of the combustion can be easily adjusted by the powertrain control module, with control of the spark event. That is not possible with HCCI’s flameless combustion.

The mixture composition and temperature must be changed in a complex and timely manner to achieve comparable performance of spark-ignition engines in the wide range of operating conditions. That includes extreme temperatures - both hot and cold - as well as the thin-air effect of high-altitude driving.

Advancements such as idle operation and improved noise, vibration and harshness bring HCCI technology one step closer to production. GM’s global HCCI team will continue to refine the technology in the wide range of driving conditions experienced around the globe.

“Our development costs for HCCI are very expensive; however, we have made tremendous strides in bringing this much awaited combustion technology out of the lab and onto the test track with the Saturn Aura concept vehicle,” said Prof. Dr. Uwe Grebe, executive director for GM Powertrain Advanced Engineering. “More research and testing are required to ensure the technology is ready for the great variety of driving conditions that customers experience.”
http://www.motorauthority.com/news/t...ci-technology/
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Old 05-06-2008, 05:18 PM   #2
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Hmmm Interesting
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Old 05-06-2008, 05:38 PM   #3
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+2; very interesting. You know the bug-eaters are having their way when a gas engine runs like a diesel. J/K
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Old 05-06-2008, 11:16 PM   #4
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I wonder how much gas would this system save?
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Old 05-06-2008, 11:20 PM   #5
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Sounds like diesel technology. Heat up the cylinder and then use compression to combust the fuel. It's a diesel engine that uses gasoline, right?
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Old 05-06-2008, 11:34 PM   #6
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I think the 305 in my 3rd Gen had this technology. Every time I let someone else drive it, when I got it back it would run after I shut the engine off. That was working at idle for about a minute anyway... if I kept giving it gas I bet it would have done it longer.
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Old 05-06-2008, 11:36 PM   #7
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Quote:
Originally Posted by DGthe3 View Post
I wonder how much gas would this system save?
"or HCCI, which allows petrol cars to improve fuel efficiency by as much as 15%"


The current, non-HCCI, 2.2 in the Cobalt XFE gets 25city/36hwy...so 15 percent increase: 28/40? Plus the DI and the VVT they've included in the Aura's test engine,...I'd say we're looking at an easy 45mpg four-banger.

Eat that, Prius!!!
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Old 05-07-2008, 12:15 AM   #8
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Quote:
Originally Posted by Dragoneye View Post
[I]

Eat that, Prius!!!

Amen to that!
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Old 05-07-2008, 09:54 AM   #9
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Quote:
Originally Posted by sterlingnotes View Post
I think the 305 in my 3rd Gen had this technology. Every time I let someone else drive it, when I got it back it would run after I shut the engine off. That was working at idle for about a minute anyway... if I kept giving it gas I bet it would have done it longer.
LOL; dieseling for the win!!! See, and no one like the LB9s (is that right?...) and L98s back in the day.
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Old 05-07-2008, 10:27 AM   #10
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I'd love to see this happen. It's technology like this that makes me think GM will overcome new regulations on efficiency. Plus, more efficiency is always good.
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Old 05-07-2008, 12:53 PM   #11
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Interesting, well that puts it back in my mind when it was mentioned early on that the Camaro could have 30 MPG, this sorta development now makes me think maybe it wasn't the 4 cyc that was only suppose to do that kinda mileage. Hmmmm..

Wow if this is in the new Camaro. I'm just losing my mind, is it April 2009 yet?!?!?!?!
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Old 05-07-2008, 01:47 PM   #12
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Hmm.

There's something I still haven't been able to fathom yet. My '91 vert I had (305 TPI) got 21+ MPG on the highway, and this was 17 years ago in a CONVERTIBLE. My 400+ HP Supra got 25 MPG hwy, and it was a '94. early 90's HOndas could easily get 40 MPG on the highway...so why are these numbers so hard to believe now? I know cars are heavier now (duh, make them lighter and save gas folks!) but there's got to be something else wrong with the picture here that it's so difficult to fathom a V8 making over 25 MPG.
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Old 05-07-2008, 01:49 PM   #13
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It mentions the added benefit of not using expensive diesel emissions systems. It also so should mention the benefit of diesel efficiency without diesel prices.

I'd pay a little extra to get this system in my Camaro.
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Old 05-13-2008, 11:49 AM   #14
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Actually, the large arguement for HCCI is the improvement in emissions.

Normally combusted gasoline burns, producing HEAT andthus NOx emissions. HCCI doesn't burn the charge, but actually harnesses the compression energy to combust the entire charge simultaneously. Because it doesn't technically *burn* (like in a diesel) there is actually very little heat produced.

They already have these engines running, but only for certain drive cycles. They are working on a way to get them to run under more conditions.

Essentially, using computer controlled forced induction and constantly monitoring cylinder temperature, intake charge temperature, and barometric pressure they can calculate how much intake duration (valve control) they need to get the engine to 'knock' at the right time.

Differenced between this and diesel... Much lighter block, less torque (no sustained burn). Ignition timing isn't adjustable by adjusting fuel, it's all computer controlled.

I don't know if that made any sense, but when I learned about this technology in class I geeked out. I'd be more excited in looking at what kind of POWER you can get out of your V8 than what kind of fuel economy you can get. HCCI engines produce vastly more power than standard combustion because of the energy that isn't lost as heat. However the engine sounds a little different :S
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