Car that runs on air, from the makers of the world's cheapest car
trak.in
trak.in
(My calculation: gasoline stores about 3000 times as much energy as compressed air per volume. But a gasoline engine is also only 10% efficient, an air engine would be much more efficient. Assuming 100% efficient, then gasoline stores 300 times as much. I can go about 300km using 11 or so gallons of gas. Lets assume a lighter car, so 5 gallons per 300km * 300 = 1500 gallons of air, which is about 5.5 cubic meters. So you'd need a box 1.75 meters on each side. Which is about 1/3 of a car.)
Obviously if they can store the air at a higher density then the box can be smaller, but if they did that it would also have to be stronger and thus heavier. (Edit: they are running at about 1/3 more pressure than my numbers assumed.)
And now comes the bigger problem: you waste a tremendous amount of energy by heating the air when you compress it.
And then you let the air cool, and lose again, because as it expands it gets _really_ cold, and won't expand as much. On the plus side running the A/C will be free. But forget about heat in the winter.
Using higher compression makes this much worse.
All in all, I simply don't think this will work for that distance. Maybe as a 30km car it would work fine (and there's a large market for that), but not 300km.
And the heating/cooling losses are really going to hurt efficiency.
And as an aside using vegetable oil is a bad idea. Unless you can seal it away from air (doubtful) it will oxidize and won't be oil anymore.
Now please tell me if I made any mistakes in my calculations.
One big thing is that your current vehicle doesn't push the technical mileage limits as far as the Air Car does.
You've assumed the car is the same weight. Cars can be made much lighter than those currently on the market today. You can get well below 1000 pounds. For example, one design prototype is the Volkswagen 1-liter car, which gets 282 mpg. (http://en.wikipedia.org/wiki/Volkswagen_1-litre_car). This design uses a variety of techniques to get the mileage up, and does so quite wonderfully.
With an Air Car it's even easier: you can even do it in a production, mass market system. You need not have a transmission, or an electrical system, or an air conditioning system, so you can get a very good car, a production car, for under 1000 pounds.
Also, unlike gasoline engines, it's a comparatively simple matter to have breaks which recover power. Power recovering breaks become simply a system for compressing and releasing a piston: a fairly mature technology actually. So breaking is not as much of an issue, and the energy you'd lose for it can be recovered at about the 70% efficiency level.
Also, compressed air, at 300 bar (4500 psi) stores approximately 16 kwh per 300 liters, (via wikipedia http://en.wikipedia.org/wiki/Air_vehicle#Storage_Tanks), giving an energy density of 0.0056 of gas (in liters). In other words, gasoline takes 176 times less space, not 3000 times, as you guessed. And given modern tanks, the air is lighter than it is large (compared to gas), though weight is a property of the tank, and does not scale linearly. I haven't factored the efficiency of gas versus air engines into this calculation, as both technologies are varied and evolving.
When these factors combine, you can get a much, much more efficient vehicle than ordinary. Getting around 80 km is a no-brainer, and 300 km is well within the realm of possibility. You might go up to 1000km before you start to hit fundamental limits.
To address some of your other concerns.
The temperature regulation of the compressed air tank is not as much of an issue as you think. There are two temperature regulation problems. The first is heating the tank as you compress it. This is not a fundamental problem, but it's actually a technical detail that I think I've solved, and I want to develop it for my startup. You'll just have to trust me that there's a way to heat this cost effectively. The second direction is when the air is expanding. While the expanding air leaving the tank is quite cold, the tank itself doesn't expand very fast, and air simply doesn't have much heat capacity. Oil and water have a far greater heat capacity, and so running a radiator in a gasoline car is actually a much more significant problem.
Also, the oil they use is actually a vegetable oil derivative. They use a combination anti-oxidant and mineral (anti-corrosion) additive (such as http://www.hexion.com/products/technicaldatasheet.aspx?id=39... though I don't know the exact product).
Additionally, there are wonderful, wonderful ways in which to improve the energy economy of these vehicles as compared to gasoline (or any other comparable vehicle, including electric). Email me, if you might be interested, since I am working on them, and actually looking for more mechanical engineering and organizational talent, or funding, or mentorship.
But I still maintain that the heating/cooling losses from compressing the air are going to hurt efficiency a lot. It's really hard to do anything with waste heat, especially since this car probably won't be sold in cold climates, so the waste heat can't be used for heating.
But, since an air engine is so much more efficient than internal combustion, it might work out.
But if it works so well, I wonder why no one did it before now - is the tank the problem?
Does it make sense to use a larger, lower pressure tank?
I'm very interested in these ideas, and I spend a lot of time dreaming up ideas - basically every time I have to fix something in my car I think of a way to design a car without that part. But I don't know if I could actually help you - I'm a computer programmer, I don't have experience with any of the skills you mentioned.
Additionally, none of the interested parties have figured out the last step: how to cheaply charge the thing (while recycling the waste energy). But I think I might have.
Your calculations are off: energy density of gasoline ~35 MJ/L, compressed air at 300 bar ~ .15, so per volume is ~230 times, so w 10x efficiency, it's down to 23X volume required: tank to be used is 340 L : divide by 23 ~= 15 L ~= 4 gal. Much closer to their claim, no?
The compression stations will have heat exchangers, so be able to use at least some of the wasted energy...
(Note: energy density figures from Wikipedia)
So yes, now I have to retract what I wrote about the size of the tank. I have new respect for the power of air.
With all the hype around the Prius, Tesla, etc, I wonder how we never heard of this till now.
If anyone is interested, email me for details.
Autoblog.com is a good start for the uninitiated.
It runs on some traditional power source and stores its energy in the form of compressed air.
Please take this story with healthy skepticism. Until we see it in mass production, it's more likely than not that this story is not what it seems.
In compressed air however it's the compression that contains the power to move the car. Drive an accident and the same power that moves your car will release its power with quite an unpleasant speed.
I'd much rather face any compressed air explosion than be soaked in burning gas.
In the middle of the fire, however, I'm not so sure.
However, in an accident, you'd want to pick the compressed air tank. The tanks are very strong. Gas tanks in cars are built with very flimsy steel.
Industries like welding has been using high-pressure tanks for decades, and bottles rarely fail.
Compressed air is far more dangerous than gasoline. Gasoline is not a guaranteed explosion more likely its a fire.
And that process will probably rob a lot of the explosive force.
Can you compress gas so much that if it exploded it would liquefy? With a quick google I couldn't find an equation relating pressure drop to temperature in real air (not ideal gas).
Gas is a low viscosity, oily (duh) substance held in flimsy metal or plastic containers that ignites easily and is hard to put out. We are comparing the danger of being injured by the compressed air explosion with the danger of being burned severely by sprayed or leaked fuel.
Sign me up for the shrapnel because burns suck huge.
Some of those tanks are both under extremely high pressure and contain explosive gases.
We intentionally put vast amounts of far more flammable compounds into gas tanks, welding, cutting etc.
How about driving a car?
Otherwise, compressed air is used in every car shop in the world for. Pneumatic tools may not require as much pressure as this car, though.
But we have plenty of experience in designing containers to hold gas under high pressures.
And don't tell me that doesn't happen, since I had that happen to me two times already, strangely enough the accidents were less than 2 weeks apart, and both times they were big SUVs(Navigator and an X5). Actually the same thing happened to a friend(in his case it was a Grand Cherokee). So accidents like this probably happen quiet often.
And yes before someone asks in all 3 cases, it was a soccer mom on a cell phone.
It's actually a mature technology.
Check 3:06 in this video: http://www.youtube.com/watch?v=QmqpGZv0YT4
I wouldn't call it bunk science - it's certainly nowhere near as bad as the 'runs on seawater' cars.
A pretty cool idea. I wonder how the compressed air is generated. I know that there are some < $100 compressed air generators that run off many other types of power(electricity, petrol etc). I wonder how energy efficient it is in terms of power. I mean, the energy use has just moved from the car to the compressed air generation plants.
It seems they have optimized the car for use in urban areas by making it as lightweight as possible. I wonder if it would pass safety tests in other countries -- with the car being held together with glue, and relying on wireless technology (zigbee maybe)?
Great ideas... it seems to have used a whole bunch of new technologies.
What is pressure stable?
And changing the type of gas has almost zero affect on how much energy you can store in it by compressing it.
So most paintball markers use CO2 because you need a simple regulator to get an even pressure for most of the tank. Some markers use plain air pressure, they require more complicated regulators because the pressure changes dramatically during the entire use of the tank.
So the dumb jocks say that the CO2 tanks are "pressure stable", I suppose because pressure in the tank is constant around 850psi so long as there is any liquid CO2 in the tank.[1]
I made this comment because this to me seems like a desirable property for a fuel gas in a compressed gas vehicle to possess. I will attempt to be more succinct in the future.
[1] And since we are nitpicking, I am in fact aware that that this figure of 850 is variable based on the temperature of the tank.
The only trouble with using a gas like co2 that liquefies easily is that once you reach that point (850psi) you pretty much can't go any farther. And they are running this thing at a much higher pressure than that - about 4500.
I'm sure there are gases that would liquefy at this pressure, but none that you would want to release into the atmosphere.