MIT researchers say HCCI cleaner, more efficient engine
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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Reader Comments (Page 1 of 2)
Will 3:40PM (8/04/2007)
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".
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Preston M 4:19PM (8/04/2007)
I'm very excited to see this technology applied. Tired of changing spark plugs.
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rgseidl 4:34PM (8/04/2007)
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.
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Preston M 8:24PM (8/04/2007)
I was kidding, i never change my spark plugs or oil.
why not the LS2LS7? 8:49PM (8/04/2007)
I'm with you man. The Japanese work on "lean burn" for 20 years and MIT chimes in and says "this looks good".
Derek 11:29AM (8/05/2007)
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.
naggs 5:33PM (8/04/2007)
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.
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ShaamanRyu 5:54PM (8/04/2007)
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
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why not the LS2LS7? 8:57PM (8/04/2007)
GM shipped this in the 60s, using methanol.
http://www.dieselsite.com/index.asp%3fPageAction=VIEWCATS%26Category=300
goat 5:54PM (8/04/2007)
The problem is, you still need gasoline, right?
The other advantage of diesel engines is the inherent flexibility of the fuels that can be burned.
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Bill 7:14PM (8/04/2007)
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.
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Derek 11:29AM (8/05/2007)
It's already been in production vehicles from what I've read. IIRC, Mitsu made a pickup in the early 80's that would run in HCCI up to ~25% throttle. After that it transitioned back to spark ignition.
Read GM's website, they claim to have HCCI engines running up to ~70% throttle under HCCI in the lab.
naggs 1:39PM (8/05/2007)
50 state legal diesels cost almost as much as a hybrid and wont be 50 state for very long. the up comming california standards are so far beyond the tier 2 bin 5 that noone has any idea how to meet them with diesel. for the forseable future, those standards ban diesels from california and any other state that adopts them.
Bill 12:14PM (8/06/2007)
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.
MikeW 8:20PM (8/04/2007)
I wonder if BMW will bring back valvetronic, for the exhaust valves to control residuals.
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MikeW 9:06PM (8/04/2007)
Diesel still have a flame front, that is why the diesel fuel system is key to mileage, performance, and emissions.
1min:51sec
http://video.google.com/videoplay?docid=-8849302132196496602&q=site%3Avideo.google.com+audi+R10+tdi&total=19&start=0&num=10&so=0&type=search&plindex=5
It might not be the actual engine, but it is representative of actual combustion.
Definately not those new piezo injectors can provide up to five injections per stroke.
naggs 1:35PM (8/05/2007)
diesels have a flame front because the fuel is injected into an enviroment where it will burn. in hcci, the air fuel mixture is already in the cylinder and it just knocks at the right time. the entire mixture burns as soon as the critical temp is achived
pbrown 8:24PM (8/04/2007)
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.
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cowboy bob 8:40PM (8/04/2007)
The future is electric. Quit wasting time and reasorces on bio-diesel, ethanol, bla, bla bla. Plug me into the windfarm baby!
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Imp 9:19PM (8/04/2007)
I'm with you, cowboy.