Air Powers Engine

Air Powers Engine

Brown, Alan S

Air has been powering torpedoes since 1866 and mine locomotives even earlier. Now, inventor Angelo Di Pietro of Engineair Pty. Ltd. of Melbourne, Australia, says he is developing an air motor efficient enough for wider practical use.

Vehicles driven by compressed air have an obvious advantage: They generate no pollution. They can run indoors or in crowded locations where it’s a good idea to avoid noxious fumes (like Enginair’s first testbed, Melbourne’s wholesale produce market). Air-powered vehicles fuel up much faster than battery units, which take hours to recharge.

In addition, Di Pietro said, his motor generates high torque at low revolutions per minute and produces little noise. It also weighs a fraction of traditional piston motors and costs less to produce. Di Pietro claims that the Engineair motor is one-seventh the size of most piston-based air motors and is more efficient.

The secret is in the design. More than 35 years ago, Di Pietro worked on rotary Wankel engine development at Mercedes-Benz. After a few years, he moved to Australia and founded a construction company. Yet he kept coming back to the idea of a rotary engine based on air rather than combustion gases.

The Di Pietro motor is a rotary piston. It consists of a cylindrical piston (which drives the shaft) that rotates eccentrically inside a cylindrical stator.

The space between the rotor and stator is divided into six expansion chambers by pivoting dividers, which open and close as they follow the motion of the rotor as it rolls against the stator wall. A thin film of air cushions the stator as it rolls (so it takes only 1 psi to overcome friction).

A slotted timer mounted on the output shaft controls the flow of air in and out of the expansion chambers. The greater the inlet flow, the higher the engine torque. Shorter inlet cycles let in less air, but the expansion of the air in the chamber is more efficient.

Di Pietro points to a study at Monash University in 2002 which found that his air engine used 770 liters per minute per horsepower. He has built several new prototypes since then, and believes that he will eventually be able to quadruple efficiency over those levels.

Potential applications range from commercial vehicles used in the mining, petrochemical, and pharmaceutical industries to scooters, buses, boats, trains, and cars. Di Pietro plans to put the engine into a carbon fiber two-seat car and use it to commute to work.

Copyright American Society of Mechanical Engineers Mar 2008

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