Wednesday, February 11, 2009

Cheap Hybrids Minus Pricey Batteries - No Hot Air

The Swiss Federal Institute of Technology is developing a new type of hybrid vehicle that's affordable, and is close to achieving the same fuel saving. The catch? Throw out the sowing machine size electric motor and its pricey companion, the uper-duper expensive battery.

Sounds like a lot of hot air. Well, it takes air and a novel, yet seemingly low-tech (but difficult) paradigm buster that's going to make you slap your head, and say, "Why didn't I think of that?"

The Swiss Institute is developing a car that stores energy by using the engine's pistons to store compressed air. Later, when needed - you guessed it - the air is released and the car is propelled along. This nifty feature adds 20% to the engine's cost; for gas-electric hybrids, the electric motor and its pricey battery companion add 200%!

Some info. from the article is below (link):

The overall idea of air (or pneumatic) hybrids isn't new, but making them efficient has been challenging. "It's difficult to keep the [energy] losses involved in moving air around small enough that it looks attractive," says John Heywood, a professor of mechanical engineering at MIT who has also worked on developing air hybrids. What's more, tanks of compressed air store far less energy than batteries, severely limiting the fuel savings in typical air-hybrid designs, says Doug Nelson, a professor of mechanical engineering at Virginia Tech. This is one of the major drawbacks of cars designed to run solely on compressed air.

Guzzella's new air-hybrid design makes use of advanced control systems to more precisely control the flow of air, improving overall efficiency. To overcome limited storage capacity, the design relies less on capturing energy from braking than other hybrids, and more on another approach to saving energy: using pneumatic power to boost the performance of smaller, more efficient gasoline engines.

[...]

Guzzella's design replaces a two-liter gasoline engine with a very small 750-milliliter one that's adequate for cruising speeds. It uses compressed air to provide boosts of power for acceleration. The dense, compressed air provides the oxygen needed to burn larger amounts of fuel than usual, a technique called supercharging.

A similar approach is already used in some production vehicles, where exhaust gases drive a turbocharger. But turbochargers are known for a problem called "turbo lag"--a noticeable delay between when the accelerator is depressed and when the extra power kicks in. The lag is the result of the time it takes for the turbine in a turbocharger to start spinning fast enough. Guzzella says his system suffers no such delay, providing extra power instantly. That's could make the technology more appealing to consumers, says Zoran Filip, a professor of mechanical engineering at the University of Michigan, who was not involved with the research.

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.

[...]

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.

- Brewskie

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