TURNING about a quarter of ordinary fuel into a hydrogen-rich gas before it鈥檚
burnt could be the key to building clean-running cars, engineers from the
Massachusetts Institute of Technology told a meeting of the American Physical
Society in Seattle this week.
Hydrogen is not only a very attractive fuel in itself. When it is combined
with petrol or diesel in an engine, the mixture burns efficiently, giving off
very low levels of the nitrogen oxides that are otherwise emitted by vehicle
exhausts, and which create photochemical smogs.
The big problem with hydrogen, however, is storage. Because it is a very
light gas, to store a sensible amount you have to keep it at very high pressures
in tanks with massively thick, heavy walls. Such tanks are impractical for
cars鈥攕o the MIT team decided to generate hydrogen using a car鈥檚 own fuel
supply instead.
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To do this, the researchers have developed a wine-bottle sized 鈥減lasmatron鈥�.
It uses an electric discharge to ionise a mixture of air and hydrocarbon fuel,
creating a hot plasma. This plasma is then partially oxidised to form carbon
monoxide and hydrogen. The plasmatron has been successfully tested in a
conventional car engine. Next year, the team will test it on a methane-powered
bus.
The hydrogen-rich gas created by the plasmatron flows into the car鈥檚 engine,
where it mixes with air and more fuel. The gas helps the hydrocarbon fuel burn
more completely. 鈥淚t takes energy to produce the hydrogen-rich gas, but the
engine runs more efficiently, so there鈥檚 no overall loss or gain,鈥� says Dan
Cohn, head of the plasma technology division at MIT鈥檚 Plasma Science and Fusion
Center.
Reducing pollution is the plasmatron鈥檚 main aim. The catalytic converters in
cars don鈥檛 work when they are cold, so they don鈥檛 break down pollutants in the
exhaust of a car that鈥檚 just been started. Using only the hydrogen-rich gas when
the car engine starts cuts hydrocarbon emissions by 90 per cent, says Cohn.
After a few minutes, the 鈥渃at鈥� warms up enough to do its job, at which point the
MIT engine shifts to a mixture of one part hydrogen-rich gas and three parts
hydrocarbon fuel.
鈥淲e can now take a low-quality fuel and convert it into a high-quality fuel,鈥�
claims Cohn, citing successful hydrogen-enrichment experiments with diesel and
corn oil. The bus tests planned next year will assess how well the plasmatron
can reduce the nitrogen oxides produced by burning methane, an otherwise clean
fuel.
Cohn thinks the plasmatron鈥檚 biggest potential will be in low-emission,
high-efficiency hybrid vehicles that will use both hydrocarbon fuels and
electric power. He says that cars using hydrogen-enriched fuel would cost less
and be available sooner than the hydrogen fuel cell cars being developed by
companies such as Daimler-Chrysler and Ford, which both plan to launch models in
2004.