We take a quick spin in GM's latest HCCI engine prototype
by Sam Abuelsamid on May 26th 2009 at 2:00PM 
Since our first encounter with General Motors' HCCI (homogeneous charge compression ignition) engines in August 2007, the powertrain research engineers at GM's Tech Center in Warren, MI have continued plugging away at the technology, trying to turn it into a marketable reality. The basic premise of compression ignition is simple. Based on the Ideal gas law (PV=nRT), if you decrease the volume of a particular quantity of air, the temperature rises to the point where fuel will spontaneously combust.
The hard part is controlling the pressure, temperature and air/fuel mixtures precisely enough to manage that combustion without causing excess noise and engine damage. When we first tried the HCCI prototypes a couple of years ago, the engines had a fairly narrow band of HCCI operation with the engine running in basic spark ignition mode the rest of the time. Thanks to a newly developed mixed-mode HCCI feature and external EGR, the engines can now run in HCCI from idle all the way to 60 mph.
We had a chance to drive a Saturn Aura with an HCCI engine based on the 2.2-liter EcoTec four-cylinder around the streets near the Tech Center. The engine ran smoothly and transitions between HCCI and spark ignition really couldn't be felt. The only indication of a transition was a slight ringing sound over the first couple of power cycles after transition.
The basic hardware for a production HCCI engine is in place now, with the only new piece of hardware being a combustion chamber pressure sensor. GM is continuing to work on the control software to make this a robust system and even adapting the homogeneous charge and pressure sensors to diesel engines to reduce NOx emissions. GM says that HCCI engines can achieve about a 15% improvement in fuel efficiency compared to a similar spark ignition engine – at a much lower cost than a hybrid. The automaker hopes to have HCCI engines in production in about five years.
[Source: Green Fuels Forecast]
Reader Comments (Page 1 of 2)
why not the LS2LS7? 2:04PM (5/26/2009)
Here's a shorter summary:
HCCI works like a Diesel, both in how it ignites and by reducing throttling losses. It could give Diesel-like highway economy (per Joule, not per gallon, as Diesel has 15% more energy per gallon).
From another article I read, this engine can work in HCCI mode up to 3,000rpm. This may not seem like much, but if it can work in HCCI mode up to 3,000rpm and up to moderate loads, it'll cover virtually all of the "cruising"-type situations where the Diesel-style operation is a huge advantage.
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Tourian 2:11PM (5/26/2009)
Huh. Thanks for the clarification. I thought direct injection "was like a diesel". Good to see that GM is still innovating.
Nightcrawler 2:14PM (5/26/2009)
This sounds promising. Are other automakers known to be working on something similar, or is this an idea that could really give GM a leg up on the competition if it pans out as they hope?
why not the LS2LS7? 2:22PM (5/26/2009)
Tourian:
DI is kind of like a (DI) Diesel in how the fuel enters the chamber. However, in a standard gas DI engine, the fuel is still ignited by spark. More importantly, in a standard gas DI engine, the air to fuel ratio must remain close to stoichiometric (14.7:1) so that the engine doesn't knock. This means when you reduce the fuel entering the chamber you have to reduce the air too. That means closing the throttle plate. That is a problem because closing the throttle plate creates a vacuum that the engine must then work against to get air into the cylinder, wasting energy.
Since the amount of fuel used is very low at highway speeds, the amount of air in a gas engine must be restricted a lot and thus gas cars are at a disadvantage on the highway. Diesels don't have throttle plates, they just let in a full load of air each time, so they do far better in the highway.
An HCCI tries to work like a Diesel on the highway, by opening the throttle plate, reducing pumping losses a ton. The fact that it also uses compression (instead of spark) ignition is more of an inevitability than an actual advantage.
Sea Urchin 2:23PM (5/26/2009)
@ Nightcrawler
"This sounds promising. Are other automakers known to be working on something similar, or is this an idea that could really give GM a leg up on the competition if it pans out as they hope?"------------Dude as i pointed in another post GM sold 122 Chevy Silverado's Hybrids in first Quarter of 2009.
Silverado is GMs best selling vehicle and Hybrid variation is a BUST with capital B. GM better study why Silverado failed and make sure that this new car is not the same.
carlbolt 2:55PM (5/26/2009)
There is still a big difference between the way how diesel and HCCI ignite, Though both combustions are ignited by compression, the diesel is ignited at a single point, and then the flame front will propagate inside the cylinder, while the HCCI combustion will be ignited at every point at the same time, there is no flame front propagating, combustion is much more smoother, and highest combustion temperature is lower, which is good for reducing NOx generation.
Ian 3:22PM (5/26/2009)
Sea Urchin:
Is it a bust because, like the Tahoe Hybrid, its $5000 more than a fully loaded LTZ model? A lot of Silverados sold are base and mid models too, but when you take an LTZ, add hybrid and charge $5000+ more for like the Tahoe, you're not going to sell very many.
This goes back to my argument of, if I'm paying $5000+ more for it, how much am I really saving on gas? $23K prius or $15K Corolla? $8000 is a LOT of gasoline.
PJ 3:39PM (5/26/2009)
"From another article I read, this engine can work in HCCI mode up to 3,000rpm."
Thanks for clearing that up, LS2. I was wondering how this cycle would only work "up to 60 mph," as the AB post puts it, unless it had a *reeeeeally* tall first gear.
Sea Urchin 2:15PM (5/26/2009)
Wonderful, the only problem is that GM needed this engine 5 years ago, not 5 years from now.
Also, in 5 years cars will have to increase HPs, this is true for all cars, so overall the improvement will be below 15% or non existent at all. Sounds familiar, more HP, same MPGs?
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why not the LS2LS7? 2:25PM (5/26/2009)
You clearly failed to get it.
No one has an HCCI engine yet, despite working on it since the 80s. GM cannot be faulted for not having one yet.
At any HP level, in a cruising situations (highway), an HCCI engine will always be more efficient than a regular gas engine. If HP output has to go up to cruise a car (perhaps higher weight or more drag), it will have to go up on gas, Diesel and HCCI engines alike and thus the HCCI will still be more efficient than a conventional gas engine.
Mr.Oak 5:30PM (5/26/2009)
Urchin: The Silverado/Tahoe two mode Hybrids would have been much more of a success in gas had stayed @ $4.00+ per gallon. Current economic free-fall has guaranteed that just about EVERY model of vehicle offered by all manufacturers are underperforming sales wise.
To GM: Folks looking for "work" trucks are not about to do the hybrid thing. It works for Escalade and Suburban (recreational), will not work for (work) trucks.
The target vehicles for the Two-Mode Hybrid system, should have ben the LAMBDAS. These are typically not used as work trucks. The recreational buyer would be more likely to take a chance on this "Hybrid thing" than professional crowd.
jon 2:25PM (5/26/2009)
if this is even a moderate step toward more efficient vehicles across GMs product line, i say more power to them. frankly, the planet needs this more than we need our cars to go from 0-60 in under 3 seconds. I really like the idea of this, however, it surprises me that this wasnt done years before (the ideal gas law is not new, thats for sure) i suppose technological barriers prevented it before, but nonetheless, this seems like an obvious evolution in gasoline engine technology.
as for the post about increases in HP over the years, i think you are missing a key point about the way technological increases work, technology becomes both faster/better and cheaper/easier to build at the same time, as time passes, this is what has allowed, for example, both computers and cars to become more efficient and faster over the years, while prices have either not grown (factoring inflation) or even dropped. this technology will merely help facilitate the normal way of things, which means more efficient cars that, at the same time, will indeed take us faster than we've ever gone before. the world is just awesome.
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Richard 2:38PM (5/26/2009)
It is fairly sad that, at least in the 'States, its hard to find efficient engines in a wider range of vehicles, yet there's no shortage of power to be had. Just google for the ABG review of the BMW 520d (approx. US price would be around $35K, gets around 45 US mpg, and has 0-60 in the 7-8 second range (all from memory)). It got slammed by many commenters for being "too slow," or "underpowered." Not that long ago, a 5 pass. luxury sedan doing 0-60 at that speed was just fine, and many of today's 540 drivers would never see a difference.
jon 2:46PM (5/26/2009)
i really agree with how crummy the fuel efficiency choices are here in the USA. even with president obamas new more efficient standards by 2016, we still will be far behind europe and japan. i for one am a level headed american who would gladly drive a diesel (so long as it is clean and environmentally acceptable) and even sacrifice speed (the BMW you described is one i would take in a heartbeat) americans need to realize that this is the future, and clean, efficient diesels are part of it.
Julius 3:51PM (5/26/2009)
@ jon...
Umm... Japan and Europe have those fuel-sipper choices because gas there is much more expensive and distances are much shorter than it is here.
If our gas had been at $4-5/gal like it did in Europe, the SUV boom never would have happened.
jon 4:22PM (5/26/2009)
i dont deny that whatsoever, they do have their reasons for being more fuel efficient, gas is much pricier in those places and distances are usually shorter. i suppose i argue that you dont need some distance or fuel cost related reason to be fuel efficient. fuel efficiency, regardless of the cost of gasoline, means lower costs for everyone. moreover, the main- and BY FAR most important- reason why we all need to be more fuel efficient, regardless of other factors, is because of the environment. anyone who denies that global warming is happening is either uninformed or denying the obvious facts, and reducing our carbon footprint, whether it be through emissions controls at power plants, or increasing fuel efficiency in our cars (the less gas we use, the less smog we emit) is- and dare i sound a little scary- paramount for the future of human existence.
im sure most of you agree with this, but i like to say it as much as humanly possible, even if only one person is educated, thats enough.
Aspherical 2:34PM (5/26/2009)
Interesting idea, yet a gasoline HCCI engine will not perform better than a diesel engine (torque, MPG). The only competition to this style I see is an Atkinson cycle engine. The HCCI engine only has the potential to sell in countries that don't have a good selection of diesel engines to choose from (i.e. the US). I don't get it...
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Ligor 4:29PM (5/26/2009)
let me spell it out
the diesel engine will still only rev to 4k, some of us like to see the engine freely rev to 7k+, the sound alone is enough for me
the HCCI will get you better milage, more torque and yet when you feel like it you can just slam on the gas and still have that high reving engine you like sine the engine will run in spark ignition mode if pushed hard, and likely there will be a button you can push that will make your engine stay in spark ignition for when you are feeling like having some fun
M-B was supposedly also working on this and they're supposed to come out with it a few years before GM. I don't know how the current market situations have changed that
Aspherical 4:46PM (5/26/2009)
Ok, so it is essentially "dieseling" at cruise speeds and then the sparks are turned on when you punch the gas. Hmmm... I like that idea better than carrying a gasoline engine AND a massive battery around like today's hybrids. I am curious to see how this turns out....
why not the LS2LS7? 5:48PM (5/26/2009)
MPG can't be helped, Diesel just plain has more energy per gallon. But an HCCI could match a Diesel on true efficiency (per Joule input energy), so that's a good thing.
If you want more torque from a gas engine, buy one with a longer stroke. This is done by increasing the crank offset, which forms a longer lever arm creating more torque at the expense of revs.
Gas engines generally do not do this because it reduces overall power output (HP) and thus reduces performance. But there's no reason that if it were found to be desirable to have more torque low and less HP that gas engines couldn't do as well as Diesels on this.