PHEV-type car that is powered by compressed air is reported in this CNN story:You've heard of hybrids, electric cars and vehicles that can run on vegetable oil. But of all the contenders in the quest to produce the ultimate fuel-efficient car, this could be the first one to let you say, "Fill it up with air." That's the idea behind the compressed air car, a vehicle its backers say could achieve a fuel economy of 106 miles per gallon. : : The compressed air car will get a chance to prove itself next year when it competes for the Automotive X Prize. The multimillion-dollar award will go to the team that "can win a stage race for clean, production-capable vehicles that exceed 100 mpg equivalent fuel economy," according to the X Prize Foundation. The air-car concept has also drawn the interest of Tata Motors, India's largest automaker. The company announced an agreement with MDI last year to further develop and refine the technology. However, the cars have yet to hit the streets in India or anywhere else in the world.
This sounds a lot like the compressed nitrogen car that the EPA developed in the 90s with the help of Ford Motor. They probably have patents on it. The nitrogen is compressed as a mechanical storage mechanism analogous to a battery. Two UPS trucks have been tooling around Manhattan for the last year using this storage method. Anyone else see the similiarity?
The 4500 psi number seems really dubious. You'd need a very strong (and heavy) pressure vessel, along with a massive compressor.
Hydrogen/Fuel Cell cars need about 10,000 psi to have enough energy density to be worth the trouble, so there's been a lot of research into lightweight pressure vessels in the past 8 years or so. My information is about 5 years old but that was one of the chief research areas H2 fuel cell cars then.
The tanks in the MDI car are carbon fiber - strong but not heavy. There is no reason the compressor would need to be "massive" to achieve 4500psi. I Googled "5000 psi air compressor" and found numerous companies making systems for scuba divers. They were not overly large and could easily be put in a garage. I'm sure the designers have considered these issues. Zero Pollution Motors - Air Car
No information was given on how electricity is generated, or if there is any plan to provide cabin heat or defrosting.
Power would be gereated by an alternator of some sort off the motor. Doesn't take much power to compress air. It's all about mechanical advantage. We go up to 10K all the time with a feed pressure of >1000psi, we don't like to run the tanks down below 1k because it gets hard on the pump.. The key is volume. Our firefighting air tanks are pumped to 4.5k and takes about 2 minutes, they're the size of scuba tanks and last about 45 minutes.
That is cool. The question still remains, how much electricity does it take to run the pump over that time? I like the concept of the air car. I just want to find out how much energy it takes to run.
We use a ludacris amount of power for the tanks, but of course we're trying to fill 500 tanks as fast as possible and we're using 4 fill stations filling them 2 at a time at each. In the shop when we go to 10K we're not using alot of volume, testing things not trying to kill people, so it also doesn't take too long, only a couple minutes from an "empty" supply bottle. Empty being <1k, full being >2200. Power consuption being very little. If we tried to fill a firefighting tank with the shop unit it would probably take about 15 minutes on a fresh supply bottle. Again it's about volume not pressure. There's no way I would try to pump up car tires using this unit. The pump would more than likely burn up. Car tires have ALOT more volume than a scuba tank. The shop "pump" only outputs maybe 3sqin per cycle. So until pressure built up it would be cycling at 0 psi. The air compressor in the garage takes about 10 minutes to get to 150psi, but there's a ton of volume. If you had a small hybrid compressor it shouldn't take that much power. When I say hybrid I mean run electric until the pressure built to about 150psi or so and then run hydraulic to take it the rest of the way. Of course it wouldn't take near as long if you didn't have to use atmosperic pressure.
The short answer is more than you get back when you run the car. That part is obvious. To answer your question in more detail, we need to look at the losses: Compression losses: 1) Losses in the engine or motor that powers the compressor. 2) Frictional losses in the compressor. 3) Frictional losses in moving air through the compressor. 4) Adiabatic heating losses. Air engine losses: 5) Frictional losses moving air from storage through the engine. 6) Frictional losses in the regulator/controller. 7) Frictional losses in the air motor. 8) Normal automobile losses not unique to the air car. This adds up to a lot of losses. Of course there are a lot of losses in any car. Adiabatic heating and frictional air losses are the big ones unique to the air car concept. I can't imagine that these losses will ever be less than those found in a good battery-electric car. The attraction will be the lower level of technology required to manufacture and use air cars, not overall efficiency. Tom
In one of the earlier reports about this car I read a $2 worth of compressed air will give a 200km range. This will be good solution as a city car in India where heating is not needed in most parts and moderate speed will do. However Tata keeps this project very low-key. I wouldn't get my hopes up till it's show-cased.
