Fuller Throttle

When it comes to producing fuel-efficient automobiles, mixing air and gasoline is a good thing. The more air allowed into the combustion chamber, the better a car's fuel economy, says Lino Guzzella, a professor of mechanical engineering at the Swiss Federal Institute of Technology (ETH) in Zurich. And his team has developed a supercharger that can give small cars more zip.

There are three ways to compress intake air heading for the combustion chamber. First, it can be done mechanically. That method is fast, Guzzella says, but inefficient because it too uses energy. So most automakers do something else: rely on turbochargers, which use exhaust fumes to turn a turbine that runs the compressor. The turbocharger's advantage is that it doesn't consume energy; indeed, it makes use of waste. But in going from idle to full acceleration, there is an annoying lag time. So engineers in the 1930s came up with a third method, the pressure-wave supercharger, which uses exhaust to create waves of pressure to compress the air directly. Like the turbocharger, it's efficient and makes use of waste. And it's also fast. Trouble is, it's also volatile and difficult to control. Too often, the clean air and the exhaust mix. "Then the engine starts coughing and doesn't run smoothly," Guzzella says.

His team has developed sophisticated controls — a network of sensors, actuators and microprocessors — that keep the supercharger under control. "We've taken an old idea and revitalized it using advances in microelectronics," he says. Indeed, Guzzella notes, car mechanics have changed little in 50 years; all the recent advances in automotive engineering have come about from employing microprocessors. The ETH supercharger keeps a model of the whole system stored in its memory, running a few milliseconds ahead of the device. It can then predict if the exhaust and air are about to mix and control the intakes accordingly. If it merely sensed when the exhaust and air were mixing, it would be too late.

Today's larger engines are excellent at delivering fuel efficiency at full acceleration, but most of the time we don't drive with our foot to the floorboard, Guzzella says. So automakers are downsizing, making smaller engines that need more open throttle and use more of their capacity. Alas, the smaller engines are less peppy and thus harder to sell. Guzzella's supercharger will mean that smaller, more fuel-stingy engines — that can average 27 kilometers to the liter — can also have the acceleration power that consumers demand.

Guzzella's team is working with Swiss Auto, a parts manufacturer. Swiss Auto supplies the mechanism; his team handles the electronics. Several major European automakers have expressed interest in the supercharger, but he's not at liberty to name them. The technology is ready, Guzzella says, and if funding to commercialize the supercharger becomes available, it could be on sale within three to five years. And European drivers will be able to buy cars that are as fast as they are economical.