GM's HCCI Tech Could Put the Company Ahead Of Competition In Engine Development

Even with its June 1 deadline around the corner, General Motors continues to work on a new gasoline engine that runs like a more-efficient diesel unit. Known as the HCCI, the technology improves fuel-economy by 15 percent and releases fewer emissions - something that could help the future GM comply with the new proposed fuel-economy regulations announced by Obama.
HCCI, which stands for ‘homogenous charge compression ignition,’ works by igniting a mixture of air and fuel inside the engines cylinders and doesn’t use a spark-generated flame. The process uses less fuel and more air to generate power by using advanced technologies, direct injection, electric cam phasing, variable valve lift and cylinder pressure sensing.
While GM has been able to report a top speed of 60 mph with the HCCI in a Saturn Aura test-mule, there are still many challengers including controlling the process at high altitudes and high temperatures.
No word on when GM plans to have the HCCI technology ready but look for it sometime after the Chevrolet Volt

Driving an HCCI vehicle is similar to a car powered by a conventional engine. We took a brief test run in a Saturn Aura mule outfitted with the technology, working with a 2.2-liter Ecotec engine, and it responded agreeably. All told, about two-thirds of our time behind the wheel was spent running in compression ignition.

GM appears to be at the forefront of the technology, but it is far from alone in considering its potential. Daimler developed an engine called “DiesOtto,” and it was shown in the Mercedes F700 concept in 2007. VW has also prototypes of a similar engine.
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Joe_Limon - 5/21/2009 3:31:06 PM

0 Boost

I was helping one of my university professors set up and run some hcci tests. It's a very very finicky way of running the engine. Best suited for a hybrid system where it runs at a constant best efficiency rpm.

inspirion7 - 5/21/2009 3:54:52 PM

+1 Boost

Would you say that if used in a standard application, it wouldn't yield the same results we should get in daily use at this point? What would make it more flexible in its performance outcome to meet daily efficient output we would benefit from?

holmstar - 5/21/2009 4:19:27 PM

+2 Boost

@inspiron7

HCCI engines are NOT ready for use in automobiles right now. Basically, you are running a car by using "knock" (the air/fuel mixture self-ignites due to high temperature and pressure) as the normal way of igniting the air-fuel mixture rather than using a spark plug. The problem is that it is rather difficult to get the mixture to ignite exactly when you want it to. Thus it is easy to have the mix ignite too early and send a rod through the block... not good. I'm sure that this 60mph test was executed under VERY controlled conditions, and not at all like the way a normal person would drive a car.

Diesels get around this issue by compressing the air first and injecting the fuel into the superheated compressed air in the cylinder. But since the air fuel mixture is not homogeneous, the fuel does not burn cleanly and a lot of soot is produced.

Joe_Limon - 5/21/2009 10:48:30 PM

0 Boost

The good thing about hcci engines is that the flame starts uniformly throughout the cylinder, allowing it to build up pressure the fastest and thus get the most energy out of the given amount of fuel possible. The trouble lies in controlling the ignition. It doesn't use a spark plug so you can't adjust ignition timing the traditional ways. A couple ways that are used to control ignition are by using vvt and allowing more or less air into the engine. Thus allowing different compressions and thus retarding or advancing the engine. A second method entails having a variable displacement combustion chamber. By having a plug that slides in and out of the top of the cylinder you can also increase or decrease cylinder pressure. At the current state however hcci remains an amazingly difficult state to acheive, especially in variable conditions (i.e. different loads, speeds, and throttle positions). Thus to maximize the usefulness I could see a small hcci generator that runs at only one load and engine speed being run to charge a battery. Another thing about diesels, the fuel is injected over an interval of time. Meaning that you are losing pressure and thus efficiency as you squirt fuel into the engine. The only reason why they are more efficient then traditional gasoline engines is that they do run at a much higher compression. If one could make a gasoline engine run at that that compression level you would have a much more efficient engine. (though not as efficient as hcci at a constant speed).

ThierryHenry14 - 5/21/2009 4:41:05 PM

-1 Boost

Now if GM can only put the company ahead of the competition in other areas...

inspirion7 - 5/22/2009 10:52:28 AM

+2 Boost

a step at a time...

dodgedart - 5/22/2009 10:53:10 PM

0 Boost

looks like a little dies-otto engine would be a great generator in the volt!