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As automobile companies in the US clamor for taxpayer bailout dollars, they’re extolling the virtues of hybrid vehicles and imminent electric cars such as the Chevrolet Volt. In spite of the fact that test drivers adored General Motors' ill-fated EV1 electric vehicles, GM contends its predecessor design was unworkable and too expensive.

So, while GM and other carmakers pitch their wares and thrash about for funds, developers elsewhere in the world are implementing some sensationally different techniques for powering vehicles.

Simply Pneumatic

One of the most fascinating developments is the compressed air engine. In France, University of Orleans students are already building prototypes. These hybrid pneumatic engines use conventional fuel, but contain an extra intake valve dedicated to compressed air. If a car is braking or coasting, the engine's cylinders use this valve to pump air into a pressure tank. When not braking, this compressed air is fed back into the engine to help drive the cylinders. Alternatively, the compressed air can supercharge the internal combustion engine, feeding its fuel-air mix into the cylinders under pressure.

In Switzerland, researchers at ETH Zurich are also working on pneumatic hybrid engines. ETH's motors are also internal combustion engines, and they're connected to compressed air tanks, too. Like the University of Orleans' pneumatically-supercharged engines, ETH's motors use compressed air when the vehicle is starting off from rest, or accelerating. At that time, compressed air flows into the engine through an additional valve, along with gasoline.

Fore and Aft Superchargers

ETH's experimental engines are also supercharged by turbochargers driven from the car's exhaust. Initial findings indicate this dual supercharging scheme can result in as much as a 50% fuel saving, especially in city driving situations, where the engine can pump air into the car's compressed air tank during frequent braking.

These air-assisted engines are also physically small. ETH says no more than about 30 hp is typically needed for everyday driving. In ETH's car, that translates to a small 2-cylinder engine, one with markedly lower frictional losses than a 4-cylinder counterpart.

Moving beyond academia, Europe’s Motor Development International is well along in its efforts to create workable pneumatic vehicles. MDI's 4-door CityCAT Air Car, to be built in India, uses compressed air exclusively to drive its engine's pistons. Here’s a photo of a typical MDI air engine.

In use, it takes mere minutes to fill an MDI car's composite air tanks, using high-speed electrically powered air compressors. MDI contends it could cost only about $2 from a commercial pumping station to fill a CityCAT's tanks with air compressed at over 4300-psi. Alternatively, a built-in compressor, powered from any convenient electrical outlet at home, could refill a CityCAT’s tanks in a few hours.

MDI anticipates selling its air-powered cars in the US for less that $20,000. For that price, you'd get a small, but 100-mph, hybrid car with the compressed air equivalent of a 75-hp engine.

For MDI’s long-range models, a small gasoline engine, similar to that used in the Chevy Volt to recharge its battery, would operate an on-board compressor. MDI asserts that one small tank of gasoline could take six passengers from New York to California with ease.

Click on this YouTube video to see MDI's vehicles in action. Decide for yourself whether this is a bunch of hot air.

At the upcoming SAE World Congress 2009, a number of pneumatic hybrid engine designs will be discussed. In addition to a report from the University of Orleans, papers will be presented from Lund University in Sweden, the National Taipei University of Technology, the University of Waterloo, Canada, and England's Brunel University.

The list of technical sessions, with lots of meat and potatoes for electronics engineers, includes quite a variety of technology alternatives to the conventional internal-combustion engine automobile.

Comments? Observations? Write me at amm at en-genius dot net, or post your comments on our blog.