100 comments on The Air Car - A Breath Of Fresh Air Or A Waste Of Breath ?
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LPG is at a similar pressure and has trundled around in the back of cars for decades. Of course, they don't have 300lt tanks, but rather 30-75lt, but still.
I've yet to hear of a hot water system's explosion "destroying a house". The wiring or gas can go wrong and start a fire, but that's why - here in Victoria at least - they legally have to be outside the house.
Absolutely having all that air under pressure would be a safety concern. But so is having 40-75lt of petrol or LPG, travelling at 100km/h, and so on. We try to make those safe.
Me, I'd rather we were rid of cars entirely, even if they were powered by sunshine, strawberries, and pretty girl's smiles. But I'm not optimistic that'll happen any time soon, so instead I'm interested to hear of ideas like this - it's just a pity they always turn out to be some geek's wet dream.
I can assure you that 300l of hot water/steam can do a lot of damage if they explode. I used to work in the elect industry and have had quite a lot to do with how water systems. In NSW at least, it is quite legal to have HWS inside a house and they do make a good drying cupboard and also improve eff through lower losses.
I agree LPG is under high pressure but there have a few accidents but they are few.
However, it is only postponing the inevitable, we have to get off the car dominated society.
So they "do a lot of damage", they don't "destroy the house". Those are two very different things.
NSW is a dangerous and savage land. HW systems should be outside the house, not in it.
If we can use a high pressure flammable gas safely, then we can use a high pressure non-flammable gas safely.
I agree that cars suck. Here I rant about how and why I hate them ;)
Agreed on all counts :-)
Welding cylinders run 2000 psi+ and are trucked around regularly with safety.
Actually, they are exceedingly dangerous in a vehicle fire, especially acetylene which is not stored at very high pressure because it will spontaneouly explode.
In the UK nobody will go anywhere near a fire with welding cyliders involved - that includes the fire brigade.
Several times this year alone major motorway routes have been closed for twenty four hours after a vehicle has been left to burn itself out before anybody will go within several hundred metres of it.
http://www.youtube.com/watch?v=akqvaZ5J1aY&feature=related
Oh, they certainly have the potential to "destroy a house." But the trick is that with 40 gallons or so at 300psi and umpteen degrees...when the pressure is released - it flash boils. So you get that first crack in the water heater and it all turns into water vapor KAPOW! So the power there comes from 40 gallons of liquid turning into a gas - there's some serious expansion there. The MDI car's tank is designed to rupture in a certain way to direct the explosion and diffuse it as much as possible. At 3000 psi though, it's still a fricken bomb.
"The MDI car's tank is designed to rupture in a certain way to direct the explosion and diffuse it as much as possible."
One of the miracles of composite materials. CNG is also stored at this pressure on vehicles with few safety concerns, so given that air is a significantly less flammable gas I'm not so concerned.
Water? Outdoors? But it will all freeze solid in the winter! And in parts of fall and spring, too At least where I live it would. :) In the non-tropical parts of the world, the hot water heater is indoors and a matter of course.
LPG is at a similar pressure and has trundled around in the back of cars for decades. Of course, they don't have 300lt tanks, but rather 30-75lt, but still.
From Wikipedia:
Even taking the higher number for propane, 2.2 MPa is 13.5 times lower than the 30MPa used in the above calculation. 30MPa is 300atm. or the pressure exercised 3000 meters below sea level. An explosion of such a tank would be a dangerous thing to happen.
Let's assume that they can get 80% efficiency out of their expander, and they need a range of 150 miles, at about 100 watt-hours per mile. These are all optimistic assumptions.
So we're talking about most of 69 megajoules, the energy equivalent of 1/2 gallon of gasoline, released in a fraction of a second.
A better comparison may be - that's the energy equivalent of 36 pounds of TNT.
edit: corrected for higher efficiency
I am sure that there will be many on this thread who will do the simple math and also point out that for reasons of safety, short range, massive difficulties in repressurising and sheer inefficiency this is yet another example of why there are, as yet, still no adequate alternatives to gasoline or diesel for road transport.
It seems we have no option but to make gasoline somehow or other. This is why the only currently suitable alternatives to fuels from crude oil are the limited sources of ethanol, bio-diesel or gasoline from tar.
To give you some idea what all the potential alternatives are up against remember gasoline is a highly concentrated energy source, it is also relatively cheap.
Drive into a garage and the petrol pump will fill up the tank at a rate of about 1 litre per second.
One litre of petrol yields 34,000,000 joules of energy when it is burnt.
A petrol pump could therfore supply energy at a rate of 34 million watts. This is an huge amount of energy,
A typical coal-fired power station might only supply at a rate of 2000MW - this is the equivalent of roughly 60 petrol pumps!
"there are, as yet, still no adequate alternatives to gasoline or diesel for road transport."
"... for road transport of individuals in a one-tonne vehicle", I think you meant to say.
Because otherwise, you know, we have these things called "legs", and later inventions like a "bicycle" or a "bus" (they can make those electric, too - with batteries, and/or overhead lines).
Oh yes, I was just keeping it to the point of compressed air car, or any other potential alternative energy private car. :-)
Can you even imagine a compressed air powered 42 tonne delivery truck or a 'road train'?
Actually, there are around 6,000,000,000 people in the world who already don't travel much by car - if you have a car you are one of the all time lucky few, make the most of it.
I am surprised no one seems to have brought up flywheels as a more efficient way of storing rotary energy. Take a look at this article about http://en.wikipedia.org/wiki/Flywheel_energy_storage
Main points :
For both approaches, a tram or a bus is a more appropriate vehicle.
I think the real advantage of compressed air is low cost. It can very well be some limited kind of solution for third world countries.
Flywheels would be much more expensive and have certain safety issues too (albeit more manageable).
"Me, I'd rather we were rid of cars entirely, even if they were powered by sunshine, strawberries, and pretty girl's smiles."
It would be a horrible waste to use that for driving cars!
After the corn runs out.....