At those pressures any air escape would basically be an explosion and would turn the car briefly into a rocket...

Time to bust out the calculator, methinks...

Hmm. Since normal atmospheric pressure is about 15 psi, this is 290 atmospheres of pressure, which is pretty extreme. And if that 340 L of air was measured at normal pressure, then the tank would only be about 1.17 L in size once the air was compressed.

That seems pretty tiny, so let's try it the other way around (which makes more sense in terms of the energy to run a car: assume the tank itself is 340 litres. That's pretty big - about one and a half 44 gallon drums.

But if that's the case you'd have the equivalent of 98,600 L of air at normal pressures compressed into the tanks. That's about 4,400 mol of gas. If we treat air as being all nitrogen (which is fairly close), that's 4,400 x 14 x 2 = 123,250 grams = 123 kg of air, which is not too bad, although it's a lot more mass of fuel to lug around when full than a tank of petrol.

{to be continued}

Have to admit, I'd only read the thread, not watched the video. The video showed the size of the tanks, and the 340 L tank size seems about right. But the video was also filled with extremely bad science (perpetual motion?) and plain nonsense (free fillups).

The concept itself, separate from its promotion by people who don't understand the science and technology, is a very intriguing one... but it's still only an energy transfer technology, and the original energy has to come from somewhere. As Shane pointed out, the possibility of coupling this technology with clean energy generation is also there, but I suspect technologies that provide clean energy directly in cars might have more potential... or hydrogen solutions. After all, no matter what we say about the strength of the tanks, that much pressure is basically an explosion waiting to happen... and as Mel has pointed out, most of our current solutions for solving that problem are made of large masses of metal. So really, the key technology here might be, not the engine, but the 'fuel' tanks.

Right on Bravus!

Let's do some rough calculations!

A 1 litre engine running @ 2000 rpm (2 cycle basis)@ 200 psi would use 2000 litres per minute. Your 340 litre tank reduced to 200 psi would give you around 7000 litres. Have I made a mistake here somewhere Bravus? What does your calculator say?That would give you less than 4 minutes run time. mel

I think that's correct, but why reduce the tank pressure to 200 psi? Their claim is 4350 psi in the tanks, presumably reduced to 200 at the engine. If my calculations are correct the roughly 99,000 litres would give about 50 minutes run time at 2000 litres/minute.

(erm, that's short of 200 miles, unless it is doing 240 mph - at 2000 rpm!)

I meant to show that 200 psi at the engine only gives you around 7000 litres from the 340 litre tank at 4400 psi. (4400 divided by 200 times 340)

Whether 200 psi at the engine is enough I have no idea. I presume the engine would actually be a low speed large bore long stroke configuration similar to steam power but the usage would be the same.

I spent an hour googling air car actually. mel

Ah, OK, I get you know. I was calculating it back to room pressure, but of course you're right that the input pressure to the engine needs to be higher since that does the work.

This discussion, and particularly the video that started it, has made me realise one thing: I don't think there's anywhere in Australian junior high science that we discuss thermodynamics and state that perpetual motion machines are impossible - but we definitely need to start doing so. That will help innoculate people to snake oil as we move to alternative forms of energy.

Con men always give you a little something for a bigger something in return. Anyone remember the rainmaker?