Zero-Emissions Automobile a Dream Machine Driven by Air

It sounds too good to be true, but that hasn’t stopped a handful of engineers from trying to produce a car that runs, quite literally, on air. That would be a true zero-emissions vehicle.

Here’s the idea: Compressed air fed into an expander (much as in the old steam engine) would drive a shaft that turns the wheels, and the only byproduct would be very cold air. That cold exhaust could also provide air-conditioning.

As longshots go, this one is way out there. An airmobile probably is not in your future. But the thing is, it works.

Thomas Hanson got into designing air-powered vehicles soon after retiring a few years ago from a 40-year career in engineering. It all started, he said, when he began making a list of the things he could “pull out of that electrical outlet” in his Newhall home.

Hanson suffers from a mild case of emphysema, so he has more than a passing interest in cleaning up the air. Cars that run on electricity are seen as one way to help achieve that, but Hanson found fault with that solution.

“The battery is the worst way of doing it,” he said in an interview. “It’s heavy, and you’ve got to have highly reactive chemicals or you don’t have a battery. And highly reactive chemicals are pollutants.”

Hanson found the answer he was searching for in his own home workshop--an air compressor. And he also found that many of the components he needed for his airmobile were readily available. Natural gas canisters engineered to hold compressed gas at more than 3,000 pounds per square inch have already been developed, and two or three of those could provide storage for enough compressed air to run a passenger car.

“You would have a compressor in the garage, and when you came home, you would plug your car in and the compressor would run during the night,” Hanson said. He has designed a high-performance compressor he says would fill the bill.

His calculations showed the car would not run very far, maybe about 60 miles, but a small internal-combustion “cruising engine” could extend the range to better than 200 miles and still produce practically no emissions.

The powerful air motor would provide acceleration and hill-climbing capabilities, and the cruising engine would take over when very little power was needed.

Hanson started bouncing his idea off anyone who would listen, but he found himself with a very small audience. None of the major auto makers, for example, even answered his letters, he said. And despite his years of engineering experience, he was dismissed from one public hearing as just another crackpot.

One who did listen was Paul Trentham, a consulting engineer in Missouri who was working with a Joplin firm to develop such a vehicle. The two pooled their resources to build a car that runs on air.

An air motor he designed delivered so much thrust that “you could blow the wheels off” every other car on the road, Trentham said.

Unfortunately, that terrific performance only lasted “four or five seconds,” he said. “It makes a great dragster for a short trip, but you use [the compressed air] up in a hurry.”

At first, Trentham was puzzled by the brevity of the performance, then he figured out something that, he said with some embarrassment, he should have anticipated. As he drew air out to run the motor, the air pressure in the container dropped, which he had expected. But as the pressure dropped, so did the temperature inside the container, thus reducing the air pressure further and robbing the system of much of its stored energy.

A heat exchanger could restore the heat to the container, thus reclaiming the energy. But an efficient heat exchanger needs at least one loop of liquid, and his vehicle produced only air.

“That was the killer to me,” said Trentham, who has since given up on the idea of running a vehicle with compressed air.

But that’s not the end of the story.

Trentham sent one of his air motors off to the University of Washington, where engineers in the department of aeronautics and astronautics are working on a similar system. They are using liquid nitrogen to run an ancient air motor that powers a converted mail truck.

At -320 degrees Fahrenheit, the liquid nitrogen has more than twice the stored energy of compressed air, Trentham said, and because it is a liquid, it can be used in a heat exchanger to maintain the correct temperature inside the automobile’s fuel tank.

Under a $360,000 grant from the Department of Energy, engineers at the university have shown that nitrogen fed into the air motor expands rapidly enough to run the vehicle.

Adam Bruckner, chairman of the department of aeronautics and astronautics at the university, said Trentham’s motor--which is technically called an expander--is expected to yield “a fivefold improvement in fuel consumption” over the air motor that was used in the old mail truck.

But others voice concerns about safety because liquid nitrogen would have to be housed in vacuum bottles aboard the vehicle and kept at -320 degrees. That’s cold enough to make your fingers brittle.

And an entirely new infrastructure would have to be built to provide liquid nitrogen at your corner filling station. So, as one top Energy Department official put it, don’t bet on the future of this technology.

But it wouldn’t hurt if a few more people took it seriously enough to look at the problems on a broader scale than has been done so far.

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Lee Dye can be reached via e-mail at leedye@compuserve.com.