Polymer lung clears diesel engine smoke.

Polymer lung clears diesel engine smoke

The grimy fumes of diesel engines blacken the air, irritate the senses and spew particles that may cause cancer. Cleaner diesel exhaust would clearly represent a welcome improvement.

Engineers at Argonne (Ill.) National Laboratory have now taken a step toward eliminating the sooty smoke. Bundles of semipermeable, spaghetti-thin tubes hooked into a diesel engine can serve as an antipollution "lung" by enriching the oxygen content of air entering the combustion zone, they report. With the extra oxygen content -- about 35 percent instead of the normal 21 percent--a stationary test engine equipped with the polymer lung "completely" burned diesel fuel, dramatically decreasing most exhaust emissions, says Raj Sekar of Argonne. He contends that turbochargers, which produce related effects by forcing larger volumes of air into an engine, have reached their performance limit.

Though optimistic that the lung technology could lead to a fleet of cleaner diesel vehicles, Sekar admits that environmental and technical obstacles remain.

The good news: A test engine fitted with the lung ran just as efficiently as an unfitted engine, but spewed only one-seventh the amount of smoke particles and fewer than half the smaller particulates linked to human cancers in an EPA report issued last summer. The test engine also released virtually no carbon monoxide.

The bad: In their present form, the lungs are so bulky that truck designers would have a hard time finding room for them. Moreover, with higher oxygen levels, diesel engines operate at higher temperatures, producing more nitrogen oxide pollutants, which contribute to acid rain and smog. But Sekar says that reducing the combustion temperature by mixing the fuel with a little water, or by adjusting the fuel injection timing, can keep these emissions at typical levels.

And the not-so-ugly: "The characteristic black exhaust of a running diesel becomes clear when the oxygen enrichment system is used," Sekar says.

He and his co-workers completed their first testing phase in October, using a single-piston stationary diesel engine. Next, they plan to add lungs to a six-cylinder engine. Each lung includes about 20,000 tubes, made primarily of the polymer polysulfone. As intake air pushes through the tubes, oxygen molecules permeate the polysulfone walls more rapidly than nitrogen molecules, says Earl Beaver of Permea, Inc., in St. Louis, which markets the polymer. The oxygen-enriched airstream then feeds into the diesel engine, which emits a barely visible exhaust, Sekar says.