New auto device cuts pollution

November 14, 1999

An inexpensive, wine-bottle-sized device could slash smog drastically in all kinds of vehicles, according to Massachusetts Institute of Technology (MIT) physicists. At a physics meeting this week in Seattle, they will report advances in a prototype device that they say could significantly reduce pollution from cars and trucks while being fully compatible with present engine technology. The researchers believe that their "plasmatron" device could offer many of the benefits envisioned for alternative vehicles--considerably sooner and at much lower cost.

If installed in current vehicles, the MIT scientists say the device could slash the emission of nitrogen oxides, the major component of smog, by 90%. The plasmatron was winner of the 1999 Discover Magazine Award for Transportation earlier this year, and has undergone more recent laboratory tests that have encouraged the researchers further.

The scientists say tests in late October of a prototype plasmatron on a commercial automobile gasoline engine at Oak Ridge National Laboratory have been promising, showing projected reductions in nitrogen oxide emissions and reliable operation of an improved version of the device.

MIT Plasma Technology Division Head Dan Cohn and his colleagues have proposed to demonstrate the plasmatron within a year in a natural-gas bus, with the aim of significantly reducing the nitrogen oxides emitted from those vehicles.

The researchers also project that the device could reduce emissions of hydrocarbons (incompletely burned fuel) by 90% during gasoline engine startup, the time at which most pollution emissions occur. The plasmatron works as soon as the engine is started, unlike catalytic converters, which significantly reduce pollution emissions in vehicles but typically require at least 30 seconds to warm up.

Along with co-inventors Leslie Bromberg and Alexander Rabinovich, Cohn has already done work indicating that use of the plasmatron with diesel engines (common in trucks) might significantly reduce pollution from those vehicles.

The physicists say their plasmatron should work in all vehicles that have spark-ignition engines, including conventional autos. They're even confident that it could be implemented in future vehicle designs such as hybrid electric-gasoline vehicles, hydrogen cars, and automobiles that run on fuel cells.

The scientists believe the device can, in fact, change the course of alternative vehicle development.

"We believe that our device could be a game-changer in the automobile industry," said Cohn, who will present the latest advances in the plasmatron at the American Physical Society Division of Plasma Physics Meeting on November 18.

For example, automakers are spending millions of dollars and many years of effort on fuel cells--devices that convert a fuel into useable energy through electrical and chemical processes. Such devices produce very little pollution, and are more than twice as efficient as conventional power generators. However, practical and cost-competitive fuel cell cars may well be many years away.

Cohn believes that the plasmatron could provide a reasonable alternative to fuel cells, considerably sooner and at much lower cost, by placing them in hybrid electric-gasoline vehicles. Such autos are further along in development and offer high fuel efficiency. According to Cohn, plasmatrons for hybrid vehicles could be developed and implemented at a fraction of the cost required to make fuel cell cars a reality.

However, other researchers point out that further development is necessary before determining if this device will truly operate in all the ways that its inventors envision.

"There's a large step between a promising idea such as this one and a device which makes sense for a vehicle," says L. Craig Davis, a researcher for the Ford Motor Company. "It's hard to tell how this device would work on real vehicles. There's always a lot of engineering nitty-gritty that needs to be worked out."

And others worry that hybrid vehicles already have enough complexity without the addition of the plasmatron. Hybrid vehicles have quite complex powertrain configurations that already optimize the control of the engine for maximum fuel efficiency and minimum emissions, according to Rod Tabacyznski, a Ford laboratory director.

Still, the researchers point to the simplicity of their device when making the case that it would be an attractive option to pursue. They estimate that the entire plasmatron system could cost no more than two to three hundred dollars, and that only a very inexpensive electrode component in the device may need to be replaced a few times over the average lifetime of a vehicle. Cohn says the procedure could be as simple as changing a spark plug.

A humble looking, wine-bottle-sized device, the plasmatron can be located, like a carburetor, close to the engine. It takes a portion of the fuel from a fuel tank, combines it with air, and generates an electric discharge that converts part of the air-fuel mixture into a plasma, a collection of electrically charged particles. The plasma accelerates chemical reactions which lead to the production of hydrogen-rich gas.

The hydrogen-rich gas travels to the engine along with untreated fuel. Because of hydrogen's favorable combustion properties, its presence enables the engine to run with a greater proportion of air--bringing about a lower engine temperature (greatly reducing nitrogen oxide pollutants) and better fuel economy (because air molecules enable fuel to burn more efficiently). In fact, an air-rich engine is 10-15% more efficient than one with less air, because the properties of air molecules allow for more efficient combustion. This increase in efficiency compensates for the power consumption of the plasmatron.

A future goal of the researchers is to incorporate the plasmatron into a slightly modified design of an automobile engine. In the cylinders of traditional combustion engines, there is a limit to the compression ratio (the ratio between the amount of volume above the piston at the bottom of its compression stroke in an engine cylinder to the volume at the top). Increasing the compression ratio would increase the engine's efficiency, but this causes traditional fuel to combust spontaneously, disrupting the engine cycle. The presence of hydrogen, however, enables operation with higher compression ratios, since the gas combusts more controllably under these conditions. And a higher compression ratio would further increase engine efficiency.
Another news release on this topic is being issued by the Massachusetts Institute of Technology. It can be obtained by contacting Elizabeth Thomson (617-258-5402, ).

American Institute of Physics

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