An air car? I don't think so.

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Unfortunately, air cars are not in our future.

As editor of Hydraulics & Pneumatics, one of my roles is to be promote the increased use of fluid power technologies. But I'm sorry, I just can't get behind the concept of using compressed air as a practical means of driving a car.

A golf cart? Maybe. But you just can't store enough compressed air to give a car any appreciable range. I haven't crunched the numbers, but this video explains that one of the leading air car prototypes uses three cylinders of compressed air at 300 bar (roughly 4350 psi). The cylinders are made of a carbon fiber composite for light weight. The car's engine and frame are made primarily of aluminum, also for light weight. The video doesn't mention how safe such a vehicle would be in a collision. The host does mention that the composite cylinders would be safer than steel ones, but I wouldn't want to be anywhere near that much stored energy being released in an instant.

The host also mentions the car will have a range of about 200 km (just over 124 mi), and top speed would be about 110 km/hr (a little over 68 mph). This might be fine for driving to and from work, and running a few errands under ideal conditions. But most commutes and errand running involves conditions that are far less than ideal. You'd have a lot of stop-and-go traffic, hills, and inclement weather. Furthermore, you'd frequently need air conditioning or heat, which would substantially reduce range. Even windshield wipers would reduce your range.

You'd still need some sort of variable transmission to provide enough torque for decent acceleration from rest and also provide enough rotational speed for highway travel without gobbling up all the compressed air within a few miles. And don't forget, you'd need electricity for lights and such, so you'd have to tap into the compressed air to drive a generator — another drain on range.

The host mentions that the air car might incorporate a small internal combustion engine to increase acceleration. This implies that the vehicle would be more of a dog than the '63 Corvair I had as a teenager. (That thing wouldn't even burn rubber on wet leaves.) The website of MDI Enterprises mentions that some versions of the air car would incorporate an internal combustion engine for highway driving. Again, this confirms that a car powered by air alone cannot meet the requirements of today's typical car.

And of course, the energy needed to compress the air or nitrogen into the storage cylinder would be substantial. So unless the compressor was powered by solar, wind, or other type of clean energy, a compressed air car wouldn't be as environmentally friendly as it might seem.

Compressed air will continue to be a clean, safe, and practical means of  factory automation. However, I think it's primary role in the drive train of cars will be limited to the insides of tires.

Discuss this Blog Entry 2

Chris Kelley (not verified)
on Oct 8, 2012

Sorry, Alan, but I gotta disagree on the potentials of this idea. Ever since watching Youtube videos of the French air car last year and Gizmag news on the newer work in this field - and ESPECIALLY since the infrastructure EXISTS in the form of gas station air compressors already out there; I think this is an excellent path for urban / inner-city transportation.

PS: Still with H&P magazine, huh? We communicated when I was writing up results on flushing we were developing at MARCO Shipyard in Seattle in 1989/90. Time sure flies, huh? Now I'm working mobile equipment in NC.

Cheers!

on Oct 18, 2012

Thanks for commenting, Chris. I hope you're right because an air powered car would be great for the environment and the pneumatics industry.
It would be interesting to see a study about how much energy is contained in a large cylinder of high-pressure nitrogen. You could use that to determine how far you could transport a vehicle of, say, 2000 to 2500 lb (including passengers) at varying speeds over varying grades and account for wind and road surface friction and reasonable inefficiencies of the drive train itself.
One thing I think you'd need is a smart pressure regulator. It would provide air at high pressure to give you reasonable starting torque, then provide higher flow at lower pressure as vehicle speed increases. That might reduce air consumption enough to give you decent range on the highway.

PS: Yep, I remember. I don't remember all the articles I've worked on, of course, but I tend to remember the better ones, and yours was a dandy. I even pulled out the archive to reread it.

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Alan Hitchcox

Alan joined Hydraulics & Pneumatics in 1987 with experience as a technical magazine editor and in industrial sales. He graduated with a BS in engineering technology from Franklin University and...
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