Compressed Air "Batteries"

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Compressed Air "Batteries"

Postby k81ng » Sun May 27, 2007 4:59 pm

Compressed air technology or CAT could replace our current battery technology. If you'd like to discuss this technology or the recent article posting (http://www.bevob.org.uk/wordpress/2007/05/27/thinking-outside-the-box-can-compressed-air-be-the-next-battery/), have your say here!
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Postby anachrocomputer » Sun May 27, 2007 6:13 pm

I saw a similar vehicle being demonstrated by a university professor, maybe a year or so ago. He'd come up with the idea of using compressed oxygen as a way to drive a vehicle, so that the exhaust was pure oxygen. Seemed a bit daft to me, expecially since it had a range of a few hundred metres! But, it made the news and got the academic a bit of positive coverage in the media. But as a practical way to drive a vehicle, it looked like a non-starter.

Now, is the compressed air vehicle truly practical and useful, or is it just a way to get headlines?
1994 Suzuki Cappuccino
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Postby k81ng » Sun May 27, 2007 6:51 pm

anachrocomputer wrote:Now, is the compressed air vehicle truly practical and useful, or is it just a way to get headlines?


Well, judge the CityCat for yourself:
* Cost about £ 6,500 for the high-end model before tax
* Top speed: 68 mph
* Range 124 miles
* On board compressor fills the tank from power off the grid in about 4 hours
* Refill the tanks from a high-powered air compressor in about 3 minutes
* Dual fuel systems might go as far as 800 miles on 1.8 litres of fuel

Many people in London have judged the G-Wiz perfectly practical for city life. What if you could get a G-Wiz that could go 68 mpg for up to 124 miles? That seems quite practical and useful to me. Moreover, how would your City El perform with a such a system?
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Postby aminorjourney » Sun May 27, 2007 7:04 pm

The aircar concept could be just what the petroleum companies are looking for. After all, air filling stations could theoretically take the place of petrol pumps. However, with the fact you can 'charge' the car at home in four hours it could live side by side with EVs, using their infrastructure. Will it catch on? It's hard to say, but I'd certainly like to see one in the flesh. The YouTube videos of the various air cars showed that some were rather noisy. Perhaps when the engines have been quietened a little they'll have more appeal.

But is it a cool, up and coming technology? I think so. I want to see where it ends!
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Further Info

Postby k81ng » Sun May 27, 2007 7:05 pm

According to the Wikipedia entry, (http://en.wikipedia.org/wiki/Air_car),
The Air car range will be sold by MDI as well as by ZevCat, a US company based in California. Licenses are for sale, entitling the licensee to manufacture the Air car in other countries. Currently licences for manufacture and distribution have been sold to companies in Spain, Portugal, Brazil, South Africa, India, Great Britain, France, and the United States.


Woot!
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Postby qdos » Sun May 27, 2007 7:51 pm

I've been following ADI for quite some time now and the Tata tie up should be good. There's also a guy in Australia working on a compressed air engine too only his is a Wrankle engine which weighs all of 12kg and could be down to 6kg.

I was going to put a comment on the main site with a copy of the video but the comments are closed and I can't put HTML on here in the forum :(

I'll try and find you the link in the meantime you could go to QCarClub.com where I've got the video online here http://qcarclub.com/wordpress/?p=86

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Postby aminorjourney » Sun May 27, 2007 8:51 pm

Done! I've embedded the video on the BVS homepage :)

N

Yes, it does appear that you and Kate view the same sites!
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Postby EVguru » Sun May 27, 2007 9:01 pm

The physics just don't add up

P1*V1/T1 = P2*V2/T2

When you compress a gas it gets hot, that's part of the energy you've put into the system. If you allow the gas to cool you've lost that energy.

The only way to get any kind of resonable energy density is to use non metalic storage tanks, but there's no way that with current materials technology a composite tank can handle 300 bar at 2-300 Celcius. The gas passes through a heat exchanger as it comes out of the compressor and is cooled to as close to ambient as possible. It then gains some heat due to friction in the pipework and the air in the tank will be 'warm'.

When the air is let out of the tank it expands and cools. They try and use heat exchangers to take heat from the ambient air, but there's a limit to the size (and weight) of the exchangers so you can only gain so much heat (and therefore energy) back and a limit to how fast you can do so. Frosting is a real problem in cool humid conditions.

Guy Negre has been pushing this technology for many years and with some very dubious claims 'Further and faster than any EV'.

The energy efficiency makes fuel cells look positively miraculous!

The ONLY thing is has going for it is the fast re-fill although that's at the cost of still worse energy efficiency.

Air tools are used because they're light compact and powerful, but their energy consumption sucks. Use them in cold weather and you're prying your frostbitten fingers off the tool in short order. You need a 3hp compressor to run an air drill non stop.

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Postby k81ng » Sun May 27, 2007 9:46 pm

Your post makes a few assumptions that don't quite add up. The tanks would obviously warm when charged and cool when discharged, but the inefficiencies in moving all of that air around could be used in other systems. The temperature differences could be used to power heat pumps for heating and cooling for surrounding buildings and the car you're traveling in. Part of the whole point of EVs is that we aren't living in a vacuum; our transport choices have an impact on the world around us. We shouldn't make the same mistake with potential new options for storing energy by viewing them in strictly scientific box of PV = nRT.

As for tanks, carbon fiber tanks have been used in many different applications from paintball guns, to medical purposes, to long-term gas storage. I doubt anyone is planning to drive around with a 300 C tank.

As for frostbitten fingers, one of the videos demonstrated a presenter with his hand on an engine while it was operating. While I doubt that he would want to do this after the engine had been running for a long time, I wouldn't want to do it with a petrol motor, an EV motor, or my computer's CPU either. With engines mounted behind a thin "frost wall," I seriously down this could be a problem.

Lastly, your post seems to indicate that efficiency is the most important feature of transport. While this may be true for some EV enthusiasts, I don't believe that is true for the general populous, nor should it be. If transport were 95% green and did exactly what today's modern cars can do, but only 70% efficient, wouldn't that be better than today's petrol-based cars? Sure, compressed gas systems aren't as efficient, but if they can do the job we need them to do cleanly, how does the 10-20% difference in efficient really hurt?
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Postby qdos » Sun May 27, 2007 10:01 pm

Hi Paul,

I must say I've been rather intrigued as to the range of these compressed air machines and the air pressures in the tanks scare the pants off me but hey they've invested a lot of money and have real road going vehicles running about.

The Wrankle engine looks interesting to me as I really do think there has to be a better design than the 4 stroke ICE or what is basically a variation on the piston going up and down ludite approach. Have you seen the Free Piston Engine? there's also another spherecle engine I came across which is very very small but I can't recall the name at the moment but I've got it book marked somewhere.

At the end of the day one way or another we have to generate electricity to charge our batteries from somewhere, although there's lots of renewable means of producing a lot of it but we'll always have a demand for producing it instantly from some other source.

Unfortunately the world wants more and more things instantly. The more we get things quick, the quicker we forget about waiting a while and simply want things even quicker next time.

Me, I'm used to waiting and I'm perfectly content to wait for things but then I'm a bit different to most folk in that respect.


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