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GM testing engine that could up fuel savings by 15 percent

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GM Takes New Combustion Technology Out of the Lab and Onto the Road

PONTIAC, Mich – Engine experts have dreamt about it, talked about it and lectured about it, and today – for the first time – General Motors is letting outside parties drive the “most awaited advanced combustion technology” of the past 30 years.

GM demonstrated the combustion process, known formally as homogeneous charge compression ignition, or HCCI, for the first time in two driveable concept vehicles, a 2007 Saturn Aura and Opel Vectra. When combined with the enabling advanced technologies such as direct injection, electric cam phasing, variable valve lift and cylinder pressure sensing, HCCI provides up to a 15-percent fuel savings, while meeting current emissions standards.

“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.

In an integrated engine concept, 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 burning fuel 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.

The HCCI-powered concept vehicles – a production-based Saturn Aura and the Opel Vectra, both with a modified 2.2L Ecotec four-cylinder engine – drive like conventionally powered vehicles, but offer up to 15 percent improved fuel efficiency relative to a comparable port fuel-injected engine. (This fuel efficiency improvement will vary depending on the vehicle application and the customer driving cycle.) The driveable concept vehicles represent some of the first tangible demonstrations of HCCI technology outside of the laboratory.

“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 and variable valve timing and lift all help improve the fuel economy and performance of our internal

combustion engines. I am confident that HCCI will one day have a place within our portfolio of future fuel-saving technologies.”

Highlights of HCCI technology include:

  • Diesel-like engine efficiency 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.

How HCCI works

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. The lean operation of HCCI helps the engine approach the efficiency of a diesel, but it requires 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.

The prototype vehicles

GM demonstrated the adaptation of the HCCI technology in driveable concept vehicles based on conventional, production-based products like the Saturn Aura and Opel Vectra. The Aura features an automatic transmission; the Vectra, which is aimed at the European market, has a manual transmission. Both vehicles are powered by a 2.2-liter Ecotec engine (180 horsepower [134 kW] and 170 lb.-ft [230 Nm] of torque) that 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. The transition between the combustion processes is notable in the demonstration prototypes, but production versions are intended to deliver an imperceptible transition while driving, similar to the deactivation performance of GM’s Active Fuel Management system.

Currently, the GM demonstration prototypes can operate on HCCI up to approximately 55 mph, transitioning to spark ignition at higher vehicle speeds and during heavy engine load. An extended range for HCCI operation is intended as further refinements to the control system and engine hardware are made. “Perhaps the biggest challenge of HCCI is controlling the combustion process,” said Prof. Dr. Uwe Grebe, executive director for GM Powertrain Advanced Engineering. “With spark ignition, you can adjust the timing and intensity of the spark, but with HCCI’s flameless combustion, you need to change the mixture composition and temperature in a complex and timely manner to achieve comparable performance.”

GM’s global HCCI team will continue to refine the technology in the wide range of driving conditions experienced around the globe, from extreme heat and cold to the thin air effects of driving at high altitude. “Although our development costs for HCCI have been substantial, we have made tremendous strides in bringing this most awaited combustion technology out of the lab and onto the test track with the Saturn Aura and Opel Vectra vehicles. 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,” said Prof. Grebe.

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GM testing engine that could up fuel savings by 15 percent

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Maybe I'm missing something... but it sounds like this is just a diesel engine made to run on regular unleaded fuel?

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no you are missing something... its not really a new engine... but a new way of ignition/combustion...

see the current diesel combustion is very dirty... makes a lot of chemicals... doesnt burn it completely... by using a different method of combustion... gm is saying it doesnt require as many emission blockages... thus allowing it to run more smoothly without stupid emission add ons... also since its a cleaner burning, that means more % of it to give power so meaning, more power & more efficency, along with less polutants

one example that i can show you... is that if you throw a match in a pool of gasoline... the bi product is carbon dioxide and water... but because of the way it ignites in an engine it doesnt burn 100% and instead of having Carbon monoxide and other polutants...

so something could be learned to alter this process for gasoline or diesel... one could effectively reduce the amount of polutant filters like catalaic converters, erg valves, etc...

Edited by Newbiewar
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It is a lot like a diesel. Daimler calls their version Diesotto, since they are a combination spark ignition and compression-ignition engine. It is more than a diesel tuned to run on gasoline however. The trick is the homogenous charge for complete, efficient, and clean combustion, something neither conventional diesel nor otto-cycle engines can do.

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So there is still a spark? The article talked like it was simply ignition from compression which causes heat. That's a diesel... Not that the article was particularly forthcoming with details.

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So there is still a spark? The article talked like it was simply ignition from compression which causes heat. That's a diesel... Not that the article was particularly forthcoming with details.

No, there is no spark. The gas is ignited like a diesel engine, by compression. But HCCI is a new technology where the gas burns evenly, with no hot spots in the combustion chamber, which isn't even available on diesels.
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Does HCCI require direct injection?

If so, does the 15% extra efficiency stack on top of the DI gains?

Gasoline feedstocks vary considerably. Just switch gas stations to see that.

Ethanol, in comparison, is quite uniform in chemical structure and reactivity. Just switch bottles of Jack Daniels to see that.

That high level of uniformity should greatly benefit HCCI.

Ethanol also exhibits a pronounced cooling effect when sprayed into the combustion chamber.

Which in this application, should also be quite beneficial.

Ethanol has a much higher flash point and ignition temperature than gasoline, but are highly consistent from one batch of ethanol to the next.

So....should we expect to see ethanol-fueled HCCI motors around the corner?

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Does HCCI require direct injection?

If so, does the 15% extra efficiency stack on top of the DI gains?

Gasoline feedstocks vary considerably. Just switch gas stations to see that.

Ethanol, in comparison, is quite uniform in chemical structure and reactivity. Just switch bottles of Jack Daniels to see that.

That high level of uniformity should greatly benefit HCCI.

Ethanol also exhibits a pronounced cooling effect when sprayed into the combustion chamber.

Which in this application, should also be quite beneficial.

Ethanol has a much higher flash point and ignition temperature than gasoline, but are highly consistent from one batch of ethanol to the next.

So....should we expect to see ethanol-fueled HCCI motors around the corner?

the ethanol hcci would take a different comp ratio to have this work, surely... aka different internals/head i don't think we'll see that here for a couple years after gas or diesel engines have it.

get it working for bio diesel!!! heck, wouldn't hcci save trucking and train companies lots of money too?

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It is my understanding that the diesel combustion process is hotter than spark ignition and that in turn leads to increased nirous oxide emissions. Hydrocarbon, carbon dioxide, etc are lower. Diesel fuel istself is dirty more so than the ignition process.

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Where's JamesB... he's always well versed in this kind of cuttingh edge stuff!

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HCCI requires a lowr compression ratio than a diesel, and with a different type of fuel doesn't produce the same particulates or NOx that a diesel engine does. There is a spark though, as the engine doesn't operate in HCCI mode all the time. Even in the final optimal version there will still be a spark-ignition mode during start-up at least. Take note though—this development engine operates in HCCI mode only during it's midrange (a band around 3000 rpm or so), yet peaks at 180 hp and 170 lb-ft somewhere above that (i.e. in DI spark ignition mode), a nice boost on the current 2.2 L DI engine.

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From GM's press release:

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. The lean operation of HCCI helps the engine approach the efficiency of a diesel, but it requires only a conventional automotive exhaust after-treatment. Diesel engines require more elaborate and more expensive after-treatment to reduce emissions.

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Does HCCI require direct injection?

If so, does the 15% extra efficiency stack on top of the DI gains?

Gasoline feedstocks vary considerably. Just switch gas stations to see that.

Ethanol, in comparison, is quite uniform in chemical structure and reactivity. Just switch bottles of Jack Daniels to see that.

That high level of uniformity should greatly benefit HCCI.

Ethanol also exhibits a pronounced cooling effect when sprayed into the combustion chamber.

Which in this application, should also be quite beneficial.

Ethanol has a much higher flash point and ignition temperature than gasoline, but are highly consistent from one batch of ethanol to the next.

So....should we expect to see ethanol-fueled HCCI motors around the corner?

The short answer is yes.

DI in and of itself does not increase power. What it does is that it allows extremely good knock resistance and hence permit about 1~2 points of additional compression to be used. This is where the roughly 7~10% of torque and power increase comes from. Just very roughly you get 3~5% per point of compression increase.

In order to achieve compression ignition, HCCI will have to operate at an even higher compression in compression ignition mode. Diesels operate at about 22:1 compression. I am presuming that HCCI will operate at a compression ratio around 15~17:1. DI or not, advanced combustion management or not, this kind of compression is probably not possible without uncontrolled knock at full load and/or at certain RPM ranges. I suspect this is why the engines incorporate variable valve lift (ala VTEC). One of the possibilities is to switch over to a cam profile which close the intake valves way into the compression stroke when compression ignition is not desired or possible. This will let the piston kick some of the air back out of the cylinders. Assuming that 25% of the air is pushed back out of the intake ports by the piston because the intake valves closed late, the effective compression ratio will drop from 15:1 to about 11.25:1. At this point compression ignition won't happen and the spark plug is used.

Edited by dwightlooi
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barely off topic....is the 2.2DI going to kick out the 2.4 used in the BAS hybrids?

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The short answer is yes.

DI in and of itself does not increase power. What it does is that it allows extremely good knock resistance and hence permit about 1~2 points of additional compression to be used. This is where the roughly 7~10% of torque and power increase comes from. Just very roughly you get 3~5% per point of compression increase.

In order to achieve compression ignition, HCCI will have to operate at an even higher compression in compression ignition mode. Diesels operate at about 22:1 compression. I am presuming that HCCI will operate at a compression ratio around 15~17:1. DI or not, advanced combustion management or not, this kind of compression is probably not possible without uncontrolled knock at full load and/or at certain RPM ranges. I suspect this is why the engines incorporate variable valve lift (ala VTEC). One of the possibilities is to switch over to a cam profile which close the intake valves way into the compression stroke when compression ignition is not desired or possible. This will let the piston kick some of the air back out of the cylinders. Assuming that 25% of the air is pushed back out of the intake ports by the piston because the intake valves closed late, the effective compression ratio will drop from 15:1 to about 11.25:1. At this point compression ignition won't happen and the spark plug is used.

i think your patially right... but from my understanding the direct injection technology is old... the only reason they are beginning to use it, is because as the fuel enters the cylinder it helps too cool the cylinder, allowing for additional cooling... this of course allows the engine to be put at a higher compression ratio...

but this is how gm describes it...

Inject the fuel directly into the cylinder like a diesel, Allow the engine to breathe more air for greater torque and horsepower, Have increased compression ratio (for improved performance and fuel economy)

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i think your patially right... but from my understanding the direct injection technology is old... the only reason they are beginning to use it, is because as the fuel enters the cylinder it helps too cool the cylinder, allowing for additional cooling... this of course allows the engine to be put at a higher compression ratio...

but this is how gm describes it...

Inject the fuel directly into the cylinder like a diesel, Allow the engine to breathe more air for greater torque and horsepower, Have increased compression ratio (for improved performance and fuel economy)

Well, the benefits are many and charge cooling is only a small part of it.

If you think about it, DI or not, roughly the same amount of fuel is injected to be burned with a given amount of intake air charge. Whether the fuel is injected at the intake ports or directly into the cylinders its vaporization removes heat from the intake charge. The only advantage DI has is that 150 bar injection allows for slightly more even and more complete atomization of fuel than 3~5 bar injection. Nonetheless, the specific latent heat of vaporization is the same since the fuel is the same so it is not going to be a huge difference.

DI allows for a few things which port injection does not. The first is that the window of opportunity to inject fuel is from the beginning of the intake stroke to the end of the compression stroke. For port injection, the window of opportunity lasts only till the end of the intake stroke. In fact DI engines typically favor late injection (during the compression stroke). This has a big advantage in resisting knocking because unlike port injected engines where the cylinders are filled with combustible fuel-air mixtures from the beginning of the intake stroke through the end of the compression stroke, the DI engine only has fuel in cylinders in the last 25~50% of that period. No fuel means nothing to detonate with during that period.

If you are planning on burning ultra lean mixtures you can also direct the injection very late into the compression stroke just before the spark event in s narrow jet to create a local enrichment around the spark plug so the mixture near the tip will ignite while the rest of the cylinder is almost devoid of fuel. This is called stratified injection and is used in many DI engines for economy gains. The GM engines however does not do it mainly because lean burning makes you fail emission rules unless you scrub the oxides of nitrogen from the exhaust. Doing so requires special catalysts that cost a lot and which is absolutely in compatible with sulfur in the fuel (which US gasoline has a $h! load of).

Thirdly, DI allows for an injection shot which is not obstructed by the intake valves and the bridge between the two intake valves (in multivalve engines). This "straight shot" allows the designers to use strategies like jetting onto a dished surface cast into the piston tops so the fuel cloud mushrooms back up and promote better mixing.

Lastly, of course, more finely atomized fuel in and of itself burns more evenly.

You are right that it isn't new. In WWII many German engines were direct injected using a Bosch Mechanical direct injection system. The Daimler-Benz DB601/603/605 aircraft SOHC 4-valve inverted V12s were direct injected. The Junkers-Jumo 211 and 213 aircraft SOHC 3-valve Inverted V12s were direct injected with twin sparking plugs. Even the Maybach HL230 V12s used in the Pzkfw V (Panther) and PzKfw VII (King Tiger) were direct injected.

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The short answer is yes.

DI in and of itself does not increase power. What it does is that it allows extremely good knock resistance and hence permit about 1~2 points of additional compression to be used. This is where the roughly 7~10% of torque and power increase comes from. Just very roughly you get 3~5% per point of compression increase.

In order to achieve compression ignition, HCCI will have to operate at an even higher compression in compression ignition mode. Diesels operate at about 22:1 compression. I am presuming that HCCI will operate at a compression ratio around 15~17:1. DI or not, advanced combustion management or not, this kind of compression is probably not possible without uncontrolled knock at full load and/or at certain RPM ranges. I suspect this is why the engines incorporate variable valve lift (ala VTEC). One of the possibilities is to switch over to a cam profile which close the intake valves way into the compression stroke when compression ignition is not desired or possible. This will let the piston kick some of the air back out of the cylinders. Assuming that 25% of the air is pushed back out of the intake ports by the piston because the intake valves closed late, the effective compression ratio will drop from 15:1 to about 11.25:1. At this point compression ignition won't happen and the spark plug is used.

I think your compression ratios must come from a 20-year old textbook. Only the most ancient Chinese and eastern European diesels use a 22:1 compression ratio. A modern common-rail diesel should be running no higher than 18:1, and a newer engine between 15:1 and 17:1. GM's latest 6.6 L Duramax runs at just over 16:1. Even VW's pump-injection engines can operate at around 18:1 compression ratios.

A modern spark ignition engine will often run between 10:1 and 11:1 with port injection, and flex-fuel engines optimized for E100 in Brazil at well over 12:1, without direct-injection. GDI engines typically run at just over 11:1 to a little over 12:1 compression ratios, closer to 10:1 with forced induction. An HCCi engine will probably run at around 13:1, perhaps lower. Note that your strategy for lowering the compression ratio is not being use when the engine is running in spark-ignition mode—it is the ability to create an homogeneous charge in a lean air-fuel ratio that allows compression ignition at such low compression ratios, and why getting it to work over a wide operating range has been so difficult in the past. As you say, at higher compression ratios you get knocking. HCCI allows compression ignition at a much lower compression ratio compatible with spark-ignition direct injection—the problem lies in creating a homogeneous charge that will ignite over a wide enough range to be worth the effort.

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I think your compression ratios must come from a 20-year old textbook. Only the most ancient Chinese and eastern European diesels use a 22:1 compression ratio. A modern common-rail diesel should be running no higher than 18:1, and a newer engine between 15:1 and 17:1. GM's latest 6.6 L Duramax runs at just over 16:1. Even VW's pump-injection engines can operate at around 18:1 compression ratios.

A modern spark ignition engine will often run between 10:1 and 11:1 with port injection, and flex-fuel engines optimized for E100 in Brazil at well over 12:1, without direct-injection. GDI engines typically run at just over 11:1 to a little over 12:1 compression ratios, closer to 10:1 with forced induction. An HCCi engine will probably run at around 13:1, perhaps lower. Note that your strategy for lowering the compression ratio is not being use when the engine is running in spark-ignition mode—it is the ability to create an homogeneous charge in a lean air-fuel ratio that allows compression ignition at such low compression ratios, and why getting it to work over a wide operating range has been so difficult in the past. As you say, at higher compression ratios you get knocking. HCCI allows compression ignition at a much lower compression ratio compatible with spark-ignition direct injection—the problem lies in creating a homogeneous charge that will ignite over a wide enough range to be worth the effort.

Two things...

(1) Most of the current breed of DI Diesels run at 16~18:1 static compression, but that is not because it is preferable or that somehow compression ignition at these compression ratios was not possible before. It is because they are all turbocharged!

(2) 13:1 is not all that high. In fact, 13:1 is low enough that it can be reliably spark ignited on premium 91 octane without risk of detonation. Homogeneous charge or not, the problem with compression ignition with gasoline is that the theshold between compression induced conflagration (which is what you want) and detonation (which is true knocking) is very narrow. Gasoline also burns faster and detonate "harder" when it detonates. Diesel for instance won't even burn if you light the fluid with a cigarette lighter.

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The "trick" behind modern engines is something very simple. To run high compression for when you need it and can use it is to be able to disable it for when you can't.

Some of you may understand the concept, others won't but there is a difference between static compression ratios and a running compression ratio. And it's related to valve timing and overlap.

Ever wonder how electric fuel pumps are inside a fuel tank and the fuel is "plumbed" through that electric motor and there is absolutely no danger of it igniting?

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The "trick" behind modern engines is something very simple. To run high compression for when you need it and can use it is to be able to disable it for when you can't.

Some of you may understand the concept, others won't but there is a difference between static compression ratios and a running compression ratio. And it's related to valve timing and overlap.

Ever wonder how electric fuel pumps are inside a fuel tank and the fuel is "plumbed" through that electric motor and there is absolutely no danger of it igniting?

or just have a variable compression engine... like one prototype that catapillar made.
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Ever wonder how electric fuel pumps are inside a fuel tank and the fuel is "plumbed" through that electric motor and there is absolutely no danger of it igniting?

because liquid gasoline doesn't burn - fumes do. No oxygen = no combustion.

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or just have a variable compression engine... like one prototype that catapillar made.

Far easier to just control the amount of combustable gasses introduced into the engine.

Think about it, when you have EGR, you already have the inert gasses that effectively reduce the "displacement" of the combustion chamber.

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