The BBC and the Times of London are all ahoo over the possibility that French inventor Guy Negre may have finally developed a commercially viable car that runs on compressed air. I say “finally”, because Negre, who used to be a Formula One engineer, has spent 15 years trying to bring his air car to market. In 2003 he was promising air cars as soon as “next year” in Germany. Still, he now claims to have a made a breakthrough, and apparently he’s convinced the owner of Indian car maker Tata and an Australian auto maker that he’s got the real deal, and both are hoping to produce air cars for their local markets possibly by the end of this year, or early 2009. We’ll see about that.
Is it even a good idea?
First, the specs: The OneCAT, as the car is named, will weigh 772 pounds (compared to 2,700 lbs. for a Mini Cooper) and carry up to five passengers. It has a range of 125 miles a day, and a top speed of 70 miles per hour. It works by replacing the hot gases of the internal combustion engine with compressed air. Pipe the compressed air under pistons, the air expands, the pistons move. The pressurized air is stored in carbon fiber tanks in the chassis. The range can be increased to 800 miles with the use of a liquid fuel burner that heats the air after it’s released. (Recall Boyle’s Law: hot air expands, causing more pressure, and allowing more power). On a long range trip using the burner, the car gets the equivalent of 120 mpg, and it can burn any liquid fuel. When the tank goes flaccid, OneCAT owners can bring them to filling stations with an industrial air compressor, and it should take 3 minutes to refill a tank, or they can plug the car in to an electric socket and use the engines own compressor to refill itself in about 4 hours, using 22 kWh of electricity in the process. It’s expected to cost $4,800 (US) in India.
On the upside, the OneCAT is a zero emission car, at least in terms of city driving. The air does have to be compressed at the filling station, and it takes electricity (usually) to do that, so critics argue that it just moves the pollution somewhere else, like coal plants in Tennessee. That doesn’t worry me because, as loyal Molluscovites know, I argue we can solve that problem with the application of solar cells and wind turbines. Anyway, it’s 125 mile range easily covers the average American commute of roughly 40 miles roundtrip, plus some miscellaneous driving. That distance would even get me from San Diego to Los Angeles, one way. Some blog commenters have worried about the explosive possibilities of carrying air under so much pressure, but carbon fiber is very strong, and it has the advantage that if punctured, it will shred, like cloth, rather than burst, like steel. Also, gas is flammable, and we seem to have gotten used to carrying around 12 gallons of that wherever we go. As a bonus, when the engine is exhausting the air, it is cool, which means free air conditioning.
On the downside, the car is little. While it has roughly the same power-to-weight ratio of as other super compacts, it’s really light. That means that as soon as you put people in it, their weight will have a big impact on things like range, top speed, and fuel efficiency. Since the company put forward those 125 miles and 70 mph figures, we can safely assume those are best case scenarios, and they’re probably much worse when carrying a real load. Also, when refueling at an a big air compressor, the air will get hot as it’s put into the tank. As it cools, the air will lose some volume. Thus, the big compressor fills quickly, but less well. Also, we’re not using solar power yet, so the electricity will be generated by coal plants, most likely.
By comparison, Tesla Motors’ electric car will get the equivalent of 135 mpg, 220 miles per charge, and cost 2 cents a mile. It also take 3.5 ours to recharge, but there’s no speed-charge option like with OneCAT. The Tesla weighs 2690 pounds, so while it’s still light, it’s quadruple the OneCAT, and it comes with the kind of snazzy luxury features Americans like. The Tesla retails for around $100,000, but it has the distinct upside of actually existing.
[Thanks Sam, for the link, and I hope this answers your question!]