• May 26th 2009 at 2:00PM
  • 26
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]



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    • 1 Second Ago
  • 26 Comments
      • 6 Years Ago
      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.
        • 6 Years Ago
        Huh. Thanks for the clarification. I thought direct injection "was like a diesel". Good to see that GM is still innovating.
        • 6 Years Ago
        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.
        • 6 Years Ago
        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.
        • 6 Years Ago
        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.
        • 6 Years Ago
        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?
      • 6 Years Ago
      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...
        • 6 Years Ago
        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
        • 6 Years Ago
        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....
        • 6 Years Ago
        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.
      • 6 Years Ago
      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.
        • 6 Years Ago
        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.
        • 6 Years Ago
        @ 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.
        • 6 Years Ago
        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.
        • 6 Years Ago
        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.
      danwat1234
      • 3 Years Ago
      Wow, this technology with HCCI is intriguing. A lot of the comments on here give lots of ideas on how to make an HCCI engine. It is now over half-way through 2012, and no HCCI engines in sight. Lots of manufactures have Direct Injected OTTO cycle engines, and a lot of hybrids available that have atkinson-cycle engines. Toyota's 3rd generation Prius engine is ~38% efficient, being multi-port injected and they are aiming for the 4th generation Prius to have an engine that is 42% efficient, via Direct Injection and possible a longer stroke but smaller bore. Used Priuses are getting cheap on craigslist,Hurrah! I hope one day a Prius or other 'regular sized' 4-wheeled hybrid car can achieve 60MPG on the USA EPA highway and city test cycle. This can only be achieved I think with HCCI engines and high-tech steel alloys to save weight, along with aluminum or carbon fiber where it makes sense. In the coming years, engines and engine controls will become more and more complex, along with infotainment, collision avoidance and collision safety equipment. I question the long term reliability maintenance costs of future cars, and whether, despite the great fuel economy of a 2020 Hybrid Prius, would the net maintenance costs still save me money versus just keeping my 1999 Civic for another 20 years and doing the basic maintenance it requires? Chances are I would still save money with the new hybrid, I hope so.
      • 6 Years Ago
      i wonder if any thought has been given to making the Aura the entry-level Buick for a few years. it's a really good looking car, and with a few tweaks, could be a new Buick compact.
      • 6 Years Ago
      I am old enough to remember the disaster of the Olds diesel. Exactly why will converting a block from it's initial design pressures and stresses work this time?

      They supposedly really beefed it up the last time. Another engine like that and GM is gone.
        • 6 Years Ago
        That's not really an appropriate comparison. An HCCI engine fueled by gasoline doesn't require (or generate) anywhere NEAR the pressures in a diesel engine. Lots of the engineering development in gasoline engines over the last few decades has been to PREVENT them from spontaneous ignition within the cylinder (allowing higher compression ratios and temperatures and leaner mixtures.)

        The GM small-block diesel disaster was inexcusable. It wasn't some sort of technology breakthrough, as GM at the time made some of the best diesel engines in the world, just not ones suited for automotive use. This is a very different idea and should not be tarred with the same brush as the Oldsmobomb diesel.
      • 6 Years Ago
      It sounds as if this engine will work also like a DI gasoline spark-ignition system some of the time, not HCCI all of the time.

      If it can have the performance of a gasoline engine for stop-and-go, and accelleration power up to a gasoline-type redline, ie, drive like a normal car...

      And then switch to HCCI non-spark ignition when cruising in top gear under 3000rpms, that sounds like a real improvement.

      So far diesels behave like diesels, and gas engines behave like gas engines, and they behave distinctly differently in power delivery.

      If this makes a gasoline engine "switchable" to behave normally or somewhat pseudo-diesel HCCI for cruise... that could be very good, and like DI, an honest move forward in engine tech.
      • 6 Years Ago
      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?
        • 6 Years Ago
        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.
        • 6 Years Ago
        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.
      • 6 Years Ago
      Compare this HCCI engine to Fords EcoBoost Twin-Turbo with Direct Injection that is now in production and saves up to 20% MPG and delivers V8-like performance = Better Solution! Especially if EcoBoost can be deployed across different engine sizes I4 and V6 and brought to market at less than $1000 premium in volume in the next few years, which is exactly Fords plan. (Ford didn't invent it, they are just first to deploy it in big volume at reasonable cost vs. performance-only premium platforms in Europe).
        • 6 Years Ago
        Wow...yeah, Ford has really advanced the game by adding direct injection and twin turbos!

        Oh wait a sec...GM builds the Solstice GXP (for the time being), which comes with a 2.0L DI single-turbo 4 that gets 260hp. The base car has a 2.4L NA four with 172hp.

        The 2.4L gets 19/25 EPA mpg, while the turbo DI 2.0L gets 19/28 EPA mpg.

        Sounds like GM cracked the technology in 2007, actually. They use only one turbo to get V6 power out of a four, with 51% more power and 12% better economy than the 400cc-bigger 2.4L.

        But as soon as Ford can get this tech in a vehicle that costs less than $35k, it'll be something. HCCI is going to be a MUCH cheaper technology, AND an advancement beyond Ford's EcoBoost, because it uses NEW technology, not just a certain combination of technologies that have existed for years.
        • 6 Years Ago
        An HCCI engine can be ecoboosted (a.k.a. "turbo-boosted") as well. Imagine the upcoming Cruze with its 1.4 L turbo engine at 40 MPG. Make it an HCCI-equipped 1.4 L turbo, and that makes it 46 MPG. Not bad at all when there aren't too many expensive powertrain add-ons needed such as batteries, separate electric motors, diesel particulate filters, etc. Just a few sensors and software.
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