Compressed air cars. Puff puff.

[Kinglet]

I recently stumbled upon the concept of cars powered by compressed air. The technology seems very promising, and is even cheaper to produce than combustion engines. Battery powered cars which have very high production costs and high amounts of greenhouse gases are released during production of them. However air cars are not developed enough yet as, for some reason, they are barely known. I think they would be much more effective than battery powered cars if they get developed enough and large fusion power plants produce cheap and ecological energy.

What do you think?

[Kryten]

Compressed air tanks are heavy, and the energy density is poor. Like, lead-acid battery level poor.

[Kinglet]

Compressed air tanks are heavy, and the energy density is poor. Like, lead-acid battery level poor.

It can be stored in carbon fibre tanks, which can store air at reasonable pressure at relatively low weight. You can increase energy of compressed air by heating it, so sunny regions would profit from compressed air cars.

Also, there is a surprising lack of research going into air cars right now, and every company that did research into it got mysteriously murdered or something.

[11of10]

What about safety?

[magnemoe]

Compressed air tanks are heavy, and the energy density is poor. Like, lead-acid battery level poor.

yes, and they have poor efficiency compared with batteries. You loose a lot of energy compressing and decompressing air.

They used compressed air locomotives in mines back in the 19th century, they was replaced by battery powered ones as soon as they got the technology. Safer, cheaper and less energy loss, bonus in that it was easier to recharge them than compress air even if slower so you could put an charging station where you filled the train deep inside the mine.

[Kinglet]

What about safety?

"It was reported on Seven Network's Beyond Tomorrow that on its own carbon-fiber is brittle and can split under sufficient stress, but creates no shrapnel when it does so."

I am aware that the energy density of air powered vehicles is low, but it can also be used in hybrid with other propulsion methods.

[lajoswinkler]

I recently stumbled upon the concept of cars powered by compressed air. The technology seems very promising, and is even cheaper to produce than combustion engines. Battery powered cars which have very high production costs and high amounts of greenhouse gases are released during production of them. However air cars are not developed enough yet as, for some reason, they are barely known. I think they would be much more effective than battery powered cars if they get developed enough and large fusion power plants produce cheap and ecological energy.

What do you think?

This is an old concept that somehow surfaces every now and then, and then the media made up out of part time scribblers feeds it to the general public which has memory ability of a goldfish.

Energy density of such power sources is laughably low, which is pretty much the most important thing to consider. It makes these things inefficient and therefore such system applied to a town would require more energy and more often charging.

(Also, there is no such thing as ecological energy. Ecology is a science that does not deal with power production and environment protection. Proper term is environmentally friendlier power source, because none is friendly).

[magnemoe]

It can be stored in carbon fibre tanks, which can store air at reasonable pressure at relatively low weight. You can increase energy of compressed air by heating it, so sunny regions would profit from compressed air cars.

Also, there is a surprising lack of research going into air cars right now, and every company that did research into it got mysteriously murdered or something.

Then you loose say 30% of the energy compressing and 30% then you use the energy it don't require conspiracies to explain why such projects fails.

Add that an charging station will become far more complex than an power outlet.

it win in price over an normal electrical car, but the total energy use will be higher than an petrol one because of inefficiency.

[KSK]

I recently stumbled upon the concept of cars powered by compressed air. The technology seems very promising, and is even cheaper to produce than combustion engines. Battery powered cars which have very high production costs and high amounts of greenhouse gases are released during production of them. However air cars are not developed enough yet as, for some reason, they are barely known. I think they would be much more effective than battery powered cars if they get developed enough and large fusion power plants produce cheap and ecological energy.What do you think?

That's a couple of fairly large 'if's at the end there, especially the one about fusion. I think range is going to be an issue too even with substantial development. Compressed air might eventually become feasible for municipal vehicles but I doubt there'll be much consumer demand for them.

Edit: I suspect poor economics did more to kill air car development than some mysterious murderer.

[Streetwind]

I think they're impractical due to the immense energy requirement to "refuel". Just look at the wikipedia article... a 360 kW compressor running for 5 minutes (that's 30 kWh of energy) just to put 2.5 kWh worth of air into the car's tank. 2.5 kWh... A Tesla Model S carries 85 kWh onboard with a full charge!

This is crippling. Because ultimately, if your energy source is clean (like solar), it all boils down to how you can best use that energy. And a li-ion battery with an electric motor just converts so much more of the harvested solar power into actually moving your vehicle. Even if mentioned theoretical improvements are realized, air compressors aren't going to get to that level. Ever. And battery technology isn't maxed out yet either, so citing theoretical future improvements equalizing the imbalance is moot. If anything, I'd put my money on batteries increasing the gap. (This is actually a trend that has been crystallizing itself during the last 2-3 years - it's increasingly becoming clear that pure electric will begin to significantly outperform all other sensible options in the near future. Even hydrogen fuel cell tech is seeing its advantages in energy density melt away before the first series vehicles even hit the road, and efficiency-wise fuel cells were already worse. Battery tech is hauling ass right now.)

Also: air compressors are freaking loud, especially in the hundreds-of-kilowatts range. Compressed air decompressing and exhausting is loud. Electric charging is noiseless. Electric motors are very quiet. I know which one I prefer for my driving and housing comfort!

[GDJ]

Just my 2¢ here, but I'd rather see Fuel Cells get a better stronghold in ground transportation. Yes, they have flaws, but far more promising in the long term.

[peadar1987]

Compressed air is a rubbish way of storing energy. The isentropic efficiency of compressors is around 80-90% in the best case scenario, as is the isentropic efficiency of turbines, so you lose 20% straight off the bat. Compression also heats up the air. Compressing air from 1 to 100 bar heats the air up 700K. That heat is just lost as the air is cooled and liquefied.

[KerikBalm]

I was dissappointed by this:

http://blog.caranddriver.com/deflated-peugeot-citroen-shelves-its-air-hybrid-technology/

I don't see why operating an air pump would be so energy inefficient?

It should work well if truly cheap solar or fusion power became a reality.

I'm still waiting for the "revolution" to happen from cheap "printable" thin film PV systems :/

[The Yellow Dart]

The only way I see Air Cars ever being used on a large scale in the world would be a "peak oil" crisis situation, where the entire world would experience a huge and worsening fossil fuel shortage. Air Cars would be a quick, cheap, simple, and effective way to keep world economies limping on without oil. Electric cars are better, but the price could only go down so much, and there isn't much of a second hand market for lower class people to buy at cheaper prices. Small Air Cars could be mass produced, distributed, and sold very cheaply to keep people going to work, keep goods moving, keep things working. In the long term, I think they are just too inefficient and as it is an extremely simple, mechanical technology, you can only increase its efficiency by a small bit.

Just my 2¢ here, but I'd rather see Fuel Cells get a better stronghold in ground transportation. Yes, they have flaws, but far more promising in the long term.

Just curious, not trying to ignite a debate, but what are your personal reasons for supporting hydrogen over batteries?

[AngelLestat]

Its clear that is not the best if we are looking efficiency, but this in India seems to be usefull, because the cars can be very cheap (more than gasoline cars).

But it will work for lightweight city cars, simple, whithout any luxury, which makes the works done..

It has many drawbacks but it works whithin its niche.

There are also other techniques to use air as energy storage without so much energy lost.

Take a look to this company:

http://www.lightsail.com/

[Kinglet]

Don't forget that you can increase energy density by heating up the compressed air inside the tank. This way electric cars could be equipped with large mirrors focused on the tank to keep the air inside warm. One power becomes environmentally friendly and cheap, poorer people in sunny regions could have good use for cheap aircars as their climate could be used to increase the car effeiciency.

[AngelLestat]

Don't forget that you can increase energy density by heating up the compressed air inside the tank. This way electric cars could be equipped with large mirrors focused on the tank to keep the air inside warm. One power becomes environmentally friendly and cheap, poorer people in sunny regions could have good use for cheap aircars as their climate could be used to increase the car effeiciency.

which increase the weight and reduce the overall efficiency.

Air cars does not have a future.. when batteries will become cheaper (that it will be in 1 or 2 year only), it will be pointless even in india.

[Nuke]

i tried building air cars out of lego, the results were not that spectacular. of course you cant get much air into a duct tape reinforced coke bottle without it exploding. had a car that could drive across the room before running out of air, it had this cumbersome trailer for the 3 coke bottles that powered the thing. i had 3 servos on there, one for steering and 2 to actuate the 3 speed + reverse transmission. i think i was running a 4 piston pneumatic engine but im not sure. drive time never exceeded 30 seconds.

[FleshJeb]

Have you seen this?

http://gas2.org/2008/10/28/ups-is-first-in-delivery-industry-to-test-hydraulic-hybrids/

[Streetwind]

Now that's a concept I can get behind, a regenerative braking assistance module working off of gas pressure.

- You can use gas with more convenient properties than pure air, without worrying about exhaust

- You don't have the abysmal 5% well-to-wheel efficiency of a pure compressed air car

- You can be competitive with electric hybrids because the system is simpler and more direct than dynamo -> battery -> motor

[peadar1987]

Yeah, in a hydraulic hybrid, you can insulate the tank, so the heat loss isn't significant when you compress the gas, and you don't have to rely on compressors and expanders that aren't 100% isentropically efficient. It's a far, far better concept.

[AngelLestat]

Now that's a concept I can get behind, a regenerative braking assistance module working off of gas pressure.

- You can use gas with more convenient properties than pure air, without worrying about exhaust

- You don't have the abysmal 5% well-to-wheel efficiency of a pure compressed air car

- You can be competitive with electric hybrids because the system is simpler and more direct than dynamo -> battery -> motor

Thanks, I dint know this technique.

So this thing does not need gearbox for what I can see, its like hydbrid electric engines which can provide a lot of torque, so they save energy in transmission and they add regenerative brake.

Not sure how much of the heat is used or if it has some extra besides insulation.

I wonder if this only has sense in large vehicles or it can be used at any scale.