Pneumatic Hybrids: Inexpensive Gasoline + Compressed Air System Could Reduce Fuel Consumption by 32%

Pneumatic Hybrid Cars
Engineers have been looking for ways to use compressed air to save fuel for a long time. Turbochargers and superchargers can do that when you use them to downsize a vehicle's engine, but an even better system that offers bigger improvements and fewer downsides is under development at the Swiss Federal Institute of Technology in Zurich.

Read on for an overview of how it works!A New Hybrid System on the Horizon?
One problem with traditional gasoline/electric hybrids is the high cost of batteries. Another is the increased complexity of needed two propulsion sources, adding to costs. What if you could get rid of the electric motor altogether, and store energy in something less expensive than batteries?

That's the thinking behind the pneumatic hybrid system (gasoline and compressed air) developed by Lino Guzzella, a professor of mechanical engineering at the Swiss Institute, and his team (he developed the PAC-Car II, a hyper-efficient vehicle).

Pneumatic Hybrid Technical Details
The principle of the pneumatic/compress-air hybrid is fairly simple: You use the engine's pistons to compress air that is then stored in a tank. When needed, that air is used to give the engine extra power (in a way similar to a turbo-charger, but without the lag). This would allow car makers to use much smaller engines yet still get similar performances (the power of big engines is mostly wasted while cruising -- it is only used during acceleration).

It's still early in the R&D;, but:

Guzzella says that the system will add only about 20 percent to the cost of a conventional engine, whereas the extra components required in hybrid electric vehicles can add 200 percent to the cost. Computer simulations suggest that the design should reduce fuel consumption by 32 percent, which is about 80 percent of the fuel-savings of gas-electric hybrids, he says. Initial experiments have demonstrated that the design can be built.

What this system does better than previous ones is to control with a high degree of precision the flow of air to reduce losses as much as possible. So you have less complexity, less weight, and fuel savings close to a regular gas electric hybrid (32% might not seem like much, but remember that hybrids use more than one trick; lower drag coefficient, reduced weight, low rolling resistance tires, etc.. All of which can be used in combination with a pneumatic hybrid engine).

About 80 percent of the efficiency gain in Guzzella's system comes from using the small engine. Some of the rest comes from capturing energy from braking and then using it for acceleration--over short distances the car can be propelled by compressed air alone, using no fuel. Fuel is also saved by adjusting the load on the engine to keep it running at optimal efficiency, either by increasing the load by using some of the pistons to compress air, or by decreasing the load by using some compressed air to drive the pistons. Finally, compressed air can be used to restart the engine, making it practical for the system to turn the engine off whenever the car comes to a stop, rather than idling.

In Guzzella's test engine, a 2-liter gas engine was replaced by a 0.75-liter pneumatic hybrid, and the most beautiful thing about it is that the pneumatic system only requires control to manage the air, an extra valve in the cylinders and an air tank. The regular engine does all the rest. And unlike some other compressed air cars, you still have a long range and enough power for highway speeds.

Via Technology Review

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