Posted on 03/14/2007 1:31:43 PM PDT by Red Badger
A new engine design could significantly improve fuel efficiency for cars and SUVs, at a fraction of the cost of today's hybrid technology.
For Daniel Cohn, a senior research scientist at MIT's Plasma Science and Fusion Center, the century-old internal-combustion engine is still a source of inspiration. As he strides past the machinery and test equipment in the MIT Sloan Automotive Laboratory, his usually reserved demeanor drops away. "An engine this size," he says, pointing out an ordinary-looking 2.4-liter midsize gasoline engine, "would be a rocket with our technology."
By way of explaining that technology, he shows off a turbocharger that could be bolted to the 2.4-liter engine; the engine, he adds, uses direct fuel injection rather than the port injection currently found in most cars. Both turbocharging and direct injection are preëxisting technologies, and neither looks particularly impressive. Indeed, used separately, they would lead to only marginal improvements in the performance of an internal-combustion engine. But by combining them, and augmenting them with a novel way to use a small amount of ethanol, Cohn and his colleagues have created a design that they believe could triple the power of a test engine, an advance that could allow automakers to convert small engines designed for economy cars into muscular engines with more than enough power for SUVs or sports cars. By extracting better performance from smaller, more efficient engines, the technology could lead to vehicles whose fuel economy rivals that of hybrids, which use both an electric motor and a gasoline engine. And that fuel efficiency could come at a fraction of the cost.
Cohn says that his colleagues--Leslie Bromberg, a principal research scientist at the Plasma Science and Fusion Center, and John Heywood, a professor of mechanical engineering and director of the Sloan Auto Lab--considered many ways to make internal-combustion engines more efficient. "And then, after a lot of discussion, it just sort of hit us one day," Cohn recalls. The key to the MIT researchers' system, he explains, was overcoming a problem called "knock," which has severely limited efforts to increase engine torque and power.
In gas engines, a piston moves into a cylinder, compressing a mixture of air and fuel that is then ignited by a spark. The explosion forces the piston out again. One way to get more power out of an engine is to design the piston to travel farther with each stroke. The farther it travels, the more it compresses the air-fuel mixture, and the more mechanical energy it harvests from the explosion as it retreats. Overall, higher compression will lead to a more efficient engine and more power per stroke. But increasing the pressure too much causes the fuel to heat up and explode independently of the spark, leading to poorly timed ignition. That's knock, and it can damage the engine.
To avoid knock, engine designers must limit the extent to which the piston compresses the fuel and air in the cylinder. They also have to limit the use of turbocharging, in which an exhaust-driven turbine compresses the air before it enters the combustion chamber, increasing the amount of oxygen in the chamber so that more fuel can be burned per stroke. Turning on a car's turbocharger will provide an added boost when the car is accelerating or climbing hills. But too much turbocharging, like too much compression, leads to knock.
An alternative way to prevent knock is to use a fuel other than gasoline; although gasoline packs a large amount of energy into a small volume, other fuels, such as ethanol, resist knock far better. But a vehicle using ethanol gets fewer miles per gallon than one using gasoline, because its fuel has a lower energy density. Cohn and his colleagues say they've found a way to use both fuels that takes advantage of each one's strengths while avoiding its weaknesses.
The MIT researchers focused on a key property of ethanol: when it vaporizes, it has a pronounced cooling effect, much like rubbing alcohol evaporating from skin. Increased turbocharging and cylinder compression raise the temperature in the cylinder, which is why they lead to knock. But Cohn and his colleagues found that if ethanol is introduced into the combustion chamber at just the right moment through the relatively new technology of direct injection, it keeps the temperature down, preventing spontaneous combustion. Similar approaches, some of which used water to cool the cylinder, had been tried before. But the combination of direct injection and ethanol, Cohn says, had much more dramatic results.
The researchers devised a system in which gasoline would be injected into the combustion chamber by conventional means. Ethanol would be stored in its own tank or compartment and would be introduced by a separate direct-injection system. The ethanol would have to be replenished only once every few months, roughly as often as the oil is changed. A vehicle that used this approach would operate around 25 percent more efficiently than a vehicle with a conventional engine.
A turbocharger and a direct-injection system would add to the cost of an engine, as would strengthening its walls to allow for a higher level of turbocharging. The added equipment costs, however, would be partially offset by the reduced expense of manufacturing a smaller engine. In total, an engine equipped with the new technology would cost about $1,000 to $1,500 more than a conventional engine. Hybrid systems, which are expensive because they require both an internal-combustion engine and an electric motor powered by batteries, add $3,000 to $5,000 to the cost of a small to midsize vehicle--and even more to the cost of a larger vehicle.
When the MIT group first hatched its idea, Bromberg created a detailed computer model to estimate the effect of using ethanol to enable more turbocharging and cylinder compression. The model showed that the technique could greatly increase the knock-free engine's torque and horsepower. Subsequent tests by Ford have shown results consistent with the MIT computer model's predictions. And since the new system would require relatively minor modifications to existing technologies, it could be ready soon. Ethanol Boosting Systems, a company the researchers have started in Cambridge, MA, is working to commercialize the technology. Cohn says that with an aggressive development program, the design could be in production vehicles as early as 2011.
While Cohn applauds the benefits of hybrids and says his technology could be used to improve them, too, he notes that the popularity of hybrid technology is still limited by its cost. Cheaper technology will be adopted faster, he suggests, and will thus reduce gasoline consumption more rapidly. "It's a lot more useful," he says, "to have an engine that a lot of people will buy."
I would LOVE to see that!
I never got that far. Lucas (Prince of Darkness) electrics brought me to tears.
Drive it home from the dealership, get up the next morning @ 0500 to start a commute to work, put the key in and.....nada! Borrow a car, have the MG towed to the dealership (20 miles away!) where they say "Ahhh, the 'ol seat-belt interlock problem....". That happened three (3) times and I held my breath everytime I went to start it.
No instrument lights for a month and the dealer says "Ahhhh, the 'ol fuse block problem......"
Coming back across the squirrly Half Moon Bay hwy 92 in the wee hours of the morning after too many adult beverages.... no headlights!!!! Got to a turnout via the lights of the car behind me (who kept going) and after I stopped shaking, I reached up under the dash and jiggled the wiring harness....
LIGHTS!!!
I traded it in on an Audi 4000 - which I still own today!!!
You're doing a smashing job, dighton.
I move that the Coöperative reëlect you for another term.
Speaking of thermodynamic efficiency, remember back in the 80's when Smokey Yunick was working on an "adiabatic" engine? No cooling at all. He was talking about needing ceramic technology. I wonder what happened with that.
they're going for economy. turbos don't run constantly, can be controled from inside the vehicle, and when they are running, they're not pulling hp away from the engine by running off the crank.
The cooling effect of the alchohol injection is interesting, to say the least.
I don't know... High compression engines have been around for a long time, as is direct injection, and the technology is extremely mature. It's the technology currently in use in diesels. It's not unusual for a diesel to have a compression ratio in the neighborhood of 20:1 or higher, as opposed to less than 10:1 for most gasoline engines.
As mentioned earlier though, I'm not so sure about using a turbocharger: A supercharger would help keep the temperature of the intake charge down, which is the whole reason for the alcohol injection in the first place. Remember, it's not being used as a fuel, or even an oxidizer, though it has both properties: It's to help the intake charge resist premature detonation.
Mark
Because if someone were to come out with a high compression diesel, complete with a turbocharger and direct injection, the response would be, "We had that back in the 1990s... So what's new about this?"
Mark
"Remember, it's not being used as a fuel, or even an oxidizer, though it has both properties: It's to help the intake charge resist premature detonation."
I think this is the "aha" of this innovation. It cools, like water injection, but has energy content which HELPS the engine fire.
I wonder what the physics are behind having to direct inject it, rather than having it premixed with the gas?
Chrysler bought the design from Smokey sometime in the 80's - but I do remember being in Smokey's shop in 88 or 89 and he had 2 of the adiabatics left, all built and stored away, in addition to the one in the car he drove daily
oh yeah, and Smokey got 80-90 mpg with the little Horizon he was driving - thats what he told me himself and I for one believed him, was and never will be a better engineman than Smoke
It melted!
Seriously, we already have that in a gas turbine. It is possible to design such an engine with a regenerative heat exchanger that transfers exhaust gas heat to the incoming air stream. Efficiency is quite good at constant load but suffers under variable load conditions.
Regards,
GtG
This evidently really happened...Fiat was doing a world wide search for an electronics supplier to replace the notoriously falure prone Marconni electronics on their car line. They looked at Delco, Bosch, a couple of Japanese suppliers and....Lucas. They picked Lucas! So much for decisions by committee.
Listening to a carnut oriented radio program a few years ago and the guests were a couple of Brits. One of them mentioned that it was a shame that Lotus had gone bankrupt again - for the eighth time. The other chimed in that it was indeed too bad since they had great engineering but, he said, "you know what Lotus stands for don't you?" "Lots Of Trouble - Usually Serious"
Cheers
This is the first I've heard of it. I'm not an engine expert, but it looks like its potential is being greatly exaggerated.
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