When Dimitrios Dardalis was a boy growing up in Athens, Greece, he chanced upon a book describing a British fighter-plane engine with a moving cylinder.

That idea remained in his mind until he became a graduate engineering student at the University of Texas-Austin, where Mr. Dardalis decided to design a new-age, rotating cylinder-liner engine.

Mr. Dardalis, 30, started investigating the idea seriously in late 1997 and with the aid of an $89,000 advanced research program grant from the State of Texas, recently received a patent for his RLE design that promises to increase fuel efficiency of big diesels that power today's 18-wheelers by 4.5% to 5.5%.

“That may seem like a small number, but it's actually huge,” says Dr. Ronald Matthews, professor of mechanical engineering and head of UT Austin's engine research program. He notes that a truck driven 120,000 miles (193,000 km) per year, averaging 6.5 mpg (36.2L/100 km), could save $2,000 in fuel costs. Companies with fleets of trucks could reap enormous savings.

Mr. Dardalis has yet to build a prototype of RLE — his work has been done with computer design and simulations. But it is promising enough to win a presentation to Cummins Engine Co. Mr. Dardalis is looking for a $70,000 grant to build a functioning prototype within six months.

The grad student says the concept is counterintuitive, but he is convinced it will reduce friction and improve fuel economy.

Mr. Dardalis does not claim to have originated the concept. It was used in the engines of Bristol and Napier World War II fighters to reduce maintenence. Rolls-Royce also began work employing this principle, but aborted the project before it was completed.

The Texas design uses rotating liners that protect the cylinders in which the pistons move. Conventional heavy-duty diesels have fixed cylinder liners tightly pressed into precast cavities. Although the piston rings typically are well-lubricated, the force of combustion and billions of piston cycles produces considerable friction. And as a conventional piston ring reaches zero-velocity near the top of its cycle, lubrication all but disappears at the very moment cylinder combustion pressure skyrockets.

The Dardalis design creates a constant, evenly distributed lubrication film between the piston and inner liner wall as the liners are rotated throughout the cycle. In addition to increased fuel economy, friction and wear are reduced, as are exhaust emissions.

The RLE technology can be used in any type of diesel engine, says Mr. Dardalis, who claims RLE-designed engines would last longer and require less maintenance.