• Aug 4, 2007
We're not gonna try to explain all the physics involved in this new engine design. That's for all you Autoblog readers with engineering degrees to do in the comments. But, from what we understand, MIT researchers have taken a long hard look at an engine design called homogeneous charge compression ignition (HCCI) and say it could run cleaner and more efficiently than current popular engine designs.
Conventional gasoline engines work by pistons compressing a mixture of fuel and oxygen that is ignited by a spark. Diesel engines work by injecting fuel into hot, compressed air which then ignites. HCCI is a mixture of the two methods. Air and fuel are mixed, injected into cylinder, then ignited by pressure from the piston.

One MIT researcher says HCCI could get 25% better fuel economy over a gasoline engine, while running cleaner than most diesels.

The article from MIT's Technology Review says several automakers are currently researching HCCI engines. Volvo has been testing an engine that can switch between spark ignition and HCCI. AutoblogGreen just recently wrote that Mercedes is working on what they call DiesOtto, which is basically HCC, as welI.

[Source: MIT Technology Review]


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    • 1 Second Ago
  • 25 Comments
      • 7 Years Ago
      It looks like to me the system can create a variable fuel mixture during the combustion event. This is just my hypothesis. No facts here, but what do you think???

      At the point of initial fuel injection & combustion it would be richer and less prone to detonation. The piston has very little downward motion at this time. This is a good thing, no knock! Higher compression ratios are possible.

      As the flame progress it will lean and burn faster. At the same time the piston travel is accelerating downward allowing a steady downward force rather than a "bang".

      The end of the combustion cycle would be over-lean to improve the emissions.
        • 7 Years Ago
        Not sure if i understood what you're saying, and if I'm wrong, i apologize in advance.

        I think you're assuming that as fuel burns, nothing else happens. The truth is, oxygen is also being consumed as part of combustion, so once the valves close, the equivalence ratio (richness) of the air/fuel mixture can't cross over the rich/lean boundary. That is, a rich mixture that burns will only get more and more rich, since oxygen and fuel burn stoichiometrically (always the same ratio for a given fuel). Same for lean mixtures becoming more lean.

        I totally agree with the first statement you had though. I think the variable fuel mixture is the whole key to this technology, since by changing the air/fuel ratio, you can change the point at which spontaneous combustion occurs. Thus, you can achieve an effect similar to variable valve timing.

        Of course, this is all theoretical, which is probably why there's so much trouble with HCCI. Things are easy when you assume uniform pressure and temperature in a combustion chamber, but that never happens in practice.
      • 7 Years Ago
      The other, other, hybrid engine.

      I look forward to seeing these in the real world. It sounds like there's real potential here, a dramatic improvement in efficiency without the tradeoffs normally associated with going "green".
      • 7 Years Ago
      HCCI is still years away from appearing in a production vehicle.

      But in less than a year we'll see 50-state approved diesels start appearing here in the U.S.
        • 7 Years Ago
        No one knows how much clean diesel will cost until they come out here in the U.S. (VW's first, IIRC)

        As for CARB, when it becomes apparent how much more fuel-efficient clean diesels are than gasser, I fully expect the federal government to effectively freeze emissions at LEV II levels for clean diesel vehicles.

        No need for legislation - they can simply blackmail CARB states by threatening to cut highway matching funds.
      • 7 Years Ago
      The future is electric. Quit wasting time and reasorces on bio-diesel, ethanol, bla, bla bla. Plug me into the windfarm baby!
        • 7 Years Ago
        I'm with you, cowboy.
        • 7 Years Ago
        Farmers should go Solar.
        They've got the land, and a solar panel can convert more sunlight to electricity then plant matter.
        There should be expansion kits for farmers.
        Buy 1 panel a month...
        • 7 Years Ago
        The future is electric only if we can get over our aversion to nuclear power. That probably won't happen until we can dispose of the current and future nuclear waste offworld.
        • 7 Years Ago
        Electric is nice and all but until someone invents almost instantaneous recharge times then how am I going to get from point A to point B if the distance is greater then the autonomy of one charge? Going to NY to LA will have to be a multi week trip lol. Alright I might be exagerating there. I'm getting ready to head out to Santa Fe from NYC. That'd be a lot of long stops to recharge if I were driving an electric car. I'd say for now the most efficient technology today is Diesel and like Bill said it's got a lot of possible fuels to choose from. People think diesel is slow but that's not always the case. Some engines produce 170+hp and close to 400lb-ft of torque out of 2.oL and still get more then 40mpg.
        • 7 Years Ago
        Considering that there are numerous locations around the world where we have performed aboveground and underground nuclear tests, there is no excuse for our inability to build a nuclear waste storage facility.
        • 7 Years Ago
        Sure that is the future, but we need Infrastructure to get that electric to the people. Plus that electricity comes from somewhere...most of you forget that "somewhere" is still largely COAL. Whether anyone likes it or not we are stuck with fossil fuels for a long while, manufacturers know this and that is why we will see fuel efficient diesels, hybrids and a load of other refinements over the next 20 years. Stop repeating what Digg tells you and look at the facts for yourself...yes electric would be nice but this is real life and we might be going that way but it takes time and money.
        • 7 Years Ago
        Windfarms kill condors though! But seriously, the electric will be mostly created by fossil fuels still.
      • 7 Years Ago
      a major reason why it is cleaner is there is no flamefront. when a traditional engine burns the air fuel mixture in the cylinder, the flame starts at the spark and moves through the mixture. the tempature at the flame front is much higher than the average cylinder tempature and some of the really bad chemicals like NOX only form at those extreme tempatures. ill leave the details on that to a chem degree. with the 'diesel' ignition method, there is no flame front. the entire mixture burns as soon as the temparture reaches ignition point. there is no flamefront so lower peak temps.

      the trick is to get all the factors to line up so that it goes boom at just the right time, you cant control it directly like with a spark so you have to constantly tweak all the factors involved.

      the main reason that it is more efficient is there is no spark needed after the engine gets up to temp.
      • 7 Years Ago
      File under no shit, Sherlock. HCCI has been stuck in manufacturers' R&D labs in Japan and Europe for 20+ years. Nice to see MIT has come down from its ivory MediaLab tower to assert the blatantly obvious.

      The difficult aspects of HCCI are timing control, combustion noise (higher than conventional diesel), mechanical stresses/life expectancy and transparent transitions between HCCI and conventional combustion modes. Solutions to all of the above have been developed over the past 5 years or so, now the challenge is making them cheap and robust enough for series production.

      Preston - HCCI and its myriad variations can only be used in part load and, not during engine warm-up. The portion of the map in which it can be applied has steadily increased but there are limits wrt both torque and engine RPM. If you really want to get rid of your spark plugs, you need to buy either a diesel or a pure EV.
        • 7 Years Ago
        This is not lean burn. Lean burn is just conventional spark ignition at high A/F ratios.
        HCCI uses no spark plug, the entire mixture just combusts spontaneously so in theory there is no flame front.
        • 7 Years Ago
        I'm with you man. The Japanese work on "lean burn" for 20 years and MIT chimes in and says "this looks good".
        • 7 Years Ago
        I was kidding, i never change my spark plugs or oil.
      • 7 Years Ago
      so...just to kinda...clarify....they're trying to get the fuel-air mixture to explode via "knocking"? well....it's actually pretty damn easy then.....just that, as rgseidl said, timing is an issue......though I think that if you make the stroke long enough.....it'll eventually have to knock.

      although there is an even better technology out there that Ford's researching on...I think you've all heard about it...turbo charging an engine with a long stroke, then just inject a bit of ethanol into the combustion chamber to cool the mixture to prevent knocking, then ignite it. With that, there's more power from the long stroke, but it's claimed to be able to rival economy of hybrids....

      The ethanol only needs to be added every time you do an oil change, so basically it works...just that it's still under research
      • 7 Years Ago
      If it could run on Gas ,Diesel,Ethanol,and combine it with a Hybrid and park itself and have enough room in back for an orchestra and we could sell it to the Chinese then you would have something and give it a fancy name like the FlexFuel500 HCCI Family Truckster Turbo.
      • 7 Years Ago
      I'm very excited to see this technology applied. Tired of changing spark plugs.
      • 7 Years Ago
      To Seoultrain,

      What I think you are not taking into account is that prior to injecting the fuel air mixture there is already compressed air or a prior fuel/air mixture in the cylinder.
      As the new air/fuel mixture is introduced it will start combustion and have a flame front. As this flame front travels it will reach what ever prior gas was in the cylinder. This will create a different mixture.
      So that means it could start rich and change to lean.
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