Comressed air powered car conversion

[Hondo]

I guess my point is, would the tanks in an air powered car be more dangerous than the gas tank in an ICE powered car?

[MazdaMatt]

Oh... well i've never been very fond of the idea of burning to death in a car crash... Realistically, i think you're far more likely to burn to death in a car crash than be exploded to death by one of these cylinders. Compressed air is a big industry with big safety and those cylinders are pretty hardcore. The worst it would do it knock off a valve and deafen you with the venting air pressure... or kill you with the knocked off valve...

[Hondo]

Originally Posted by MazdaMatt

This discussion inevitably turns to efficiency. I know that a 68cu air cylinder filled to 5000psi in half a minute gets HOT. That isn't coming from the compressor, but from the source tanks that were at room temp. I'm pretty sure that is an indication that the process is rather lossy, but i'm no compressor engineer.

I can understand the cylinder getting hot if it is filled from the compressor, but I can't quite figure out how it would get hot just from equalizing with the pressure in the big tank. If you have 3K psi in the big tank decompressing into another tank, that should cause a cooling effect. Where does the heat come from?

[aerohead]

There's a professor across the street that toyed with one but he used an air motor,much like an impact wrench might use.The power supply was liquid nitrogen,run through an expansion device to gasify it under relatively high (to the atmosphere) pressure.It was very loud,had very limited range,was expensive to fuel and I believe the whole project has been abandoned.Seems like when the whole energy path was analyzed,the system had terrifically low mechanical efficiency.----------- I personally think that an air motor device,recharged slowly between traffic lights(if we must have them),could assist a small engine or electric motor,acting like a supercharger or turbo,only for acceleration,then taken off line after the car achieved cruise.There would be an issue with mass and I think it may be the reason for electric hybrid,because of the highest efficiencies demonstrated with electric and electronic devices.

[Big Dave]

This falls under the heading of "there's one born every minute."



Two things kill compressed air cars:


Air compressors are not particularly efficient devices - around 25% for commercial compressors.

Air tanks are very heavy for the energy they store.


Gasoline and diesel did not come to dominate because of some deep dark conspiracy. They simply work better and always have.

[bennelson]

Originally Posted by Big Dave

Gasoline and diesel did not come to dominate because of some deep dark conspiracy. They simply work better and always have.

The do NOT work better. They work fine. In the early days, they were TERRIBLE! It wasn't until after both the electric starter and the muffler were invented that they really became practical vehicles. They are not nearly as efficient as an electric car. They do let you drive REALLY FAR REALLY fast. (And have good heat in the winter!)

Petroleum vehicles are not efficient, but they don't have to be because the fuel contains so much energy.

To power a vehicle from an alternative, renewable, form of energy, efficiency becomes much more important.

Even if an air compressor is not as efficient as it could be, what if it could be run mechanically from a windmill, or other source of "free" energy?

Perhaps the wind could "pump up your car" for you automatically? That's something you can't do with gasoline.

Here's a related project on INSTRUCTABLES I thought was interesting.

[Hondo]

Originally Posted by Big Dave

This falls under the heading of "there's one born every minute."



Two things kill compressed air cars:


Air compressors are not particularly efficient devices - around 25% for commercial compressors.

Air tanks are very heavy for the energy they store.


Gasoline and diesel did not come to dominate because of some deep dark conspiracy. They simply work better and always have.

Not enough range and too heavy, isn't that what they used to say about electric cars? Now we have the technology to take a car over 200 miles on a single charge (Tesla Motors). Technology in compressed air is also getting better and light weight tanks (like the new scuba tanks) are being produced. I'm more interested in finding a way to make it happen instead of throwing up my hands, saying it won't work and continue burning fossil fuels.

[Ryland]

The air tank gets hot because of physics, any increase in pressure is going to create heat, a decrease in pressure is going to have a cooling affect, part of why air powered cars don't tend to work well in states that have winter.

Originally Posted by Hondo

I can understand the cylinder getting hot if it is filled from the compressor, but I can't quite figure out how it would get hot just from equalizing with the pressure in the big tank. If you have 3K psi in the big tank decompressing into another tank, that should cause a cooling effect. Where does the heat come from?

[Hondo]

Ben, we think a lot alike. I have been designing a vertical wind turbine based on a patent from the 70s (public domain). I have been testing different blade and deflector shapes in my home-made wind tunnel. My building that my business is in has a large flat roof, and every time I got up there to fix a leak or work on an exhaust fan, it was windy. I thought it would be great to put up a wind turbine to charge the batteries in my electric Fiero. I just needed a way to store all that energy. I didn't like the idea using a big bank of batteries, so I thought why not compressed air. Big propane tanks are relatively cheap and easily hold 300psi, as the burst pressure is 925psi.

[Bicycle Bob]

Gasoline or even hydrogen has to mix with air to release its energy. Compressed air is the equivalent of high explosive. SCUBA tanks are far more tightly regulated than aircraft parts. They say that carbon tanks don't turn into shapnel, they "just split." OK, so then the car turns into shrapnel, and you hope there is not another air car nearby. I'd hate to see traffic jams go off like fuses and detonate the parking lots.

An actual test of the Air car revealed that the range was 39 km, not 200. The air-powered locomotives used existing steam technology, which had to be regulated for safety, and had very short range. The great insurance companies got their start by inspecting the boilers of their policyholders.