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Why do 'environmentally friendly' cars always look like something noddy would drive.
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Oi stop nicking my post! ;-)
Soooory.
Mods please zap my dupe :-)
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Zippy hope you don't mind me locking yours, THe link needed to be "tinied" and the OP had already done it here. Nicked your punchy subject line though.
Edited by Pugugly {P} on 05/01/2008 at 11:06
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To compress the air either a diesel or electric compressor is needed, both of which pollute the environment.
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>>To compress the air either a diesel or electric compressor is needed, both of which pollute the environment.
True, but if we move to wind powered generation and electric pumps at the fillng stations some of the polution chain may be reduced.
Would like to know a bit more about the technolgy though.
Of course the whole basis of taxing fuel would have to change otherwise home pumps would get away from being taxed and of course the govt could finally tax the air that we breathe.
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>>of course the govt could finally tax the air that we breathe
Please don't give them ideas!
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How easy would it be to convert an existing diesel engine to this?
A diesel would seem easier due to no spark plugs but I'm just hypothesising.
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How easy would it be to convert an existing diesel engine to this?
Difficult or impossible I should think - the difficulty of making such a car work at all is immense without building it around an engine designed for IC - though I believe somebody did propose and maybe even patent a compressed air/IC hybrid a few years back - no idea whether it ever got made.
As is often the case the story is presented in a pretty dumb way for what is a seriously brilliant achievement. It implies that a few minutes on a garage tyre inflator is going to refuel it - a moment's thought is required to realise that you would either have to be there for hours refilling an enormous tank at the 200psi or so that is normally used, or that a much higher pressure is needed (which I am sure is the case).
Commercial filling stations could presumably use "industrial" grade compressors to provide the ?000 psi and volume of air needed, or perhaps the car carries its own small compressor which can run off electricity - probably taking hours rather than minutes to "recharge". One could have a compressor at home too, though one would not need a big one if it had all night to recharge.
Good Number_Crunching opportunity here;-)
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Oh right, I was thinking that as the valves etc will still be moving in their set timing pattern and with air there isn't a combustion cycle as such it would be easier.
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Compressed air forcing water through a rear facing nozzle would be my approach
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mss1tw, you might be right for all I know - I'm not claiming any special knowledge, and you probably could get it to work after a fashion. You wouldn't need the inlet and compression strokes though the engine could be allowed to 'idle' through them.
The engine would presumably run cooler than ambient rather than hotter, due to the adiabatic cooling of the expanding air, which would have some implications for lubrication (and heating the occupants!).
Efficiency aside, how feasible it would be to use what you already have would depend on creating a similar average cylinder pressure to the diesel power stroke. I have a vague recollection that petrol ngine peak pressures are in the order of 2000psi - turbo diesel would be higher due to inlet boosting and the higher nergy content of diesel. The air engine could maintain a more even pressure so might well be able to operate at say 2000psi and produce enough torque to move the car along satisfactorily.
Other things being equal, the torque would drop as the pressure of the air reservoir fell. So you'd presumably have to keep changing down. CVT and an air engine that is effcient across a very big rev range might provide a way round this, (apart of course from the solution I haven't thought of and the french bloke has, whatever that is).
The BBC video is very frustrating if you want to know how it works!
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I see TATA have invested in it, should have a chance of being a viable proposition then, with their financial backing
Edited by Westpig on 05/01/2008 at 14:44
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would this work like the old steam engines where high pressure steam went into a small piston and as the steam lost pressure the pistons got bigger to compensate for it.
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would this work like the old steam engines where high pressure steam went into a small piston and as the steam lost pressure the pistons got bigger to compensate for it
Steam locos evolved a 'compound' system whereby the steam was first used a in a high pressure cylinder then exhausted, still at pressure, into a low pressure cylinder to do some more work. I think this is principally about thermodynamic efficiency. If you release all the pressure in one go you get a big cooling effect on the gas/steam and the cylinder. The cylinder then heats up again when the new charge is let in. This constant heating and cooling is inefficient and spreading it out allows more expansion and less cooling of the charge so improving efficiency (E&OE - I'm not a steam engine designer).
The air engine might well use this principle but it would be about efficiency rather rather than maintaining torque as the pressure falls. The steam loco engine would be intended to run at a fairly constant steam pressure I should think.
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I think that the technology to run an engine on compressed air is actually quite old.
In the 19th C. I believe shunting engines were run on compressed air.
On the cycle track by Lake Annecy (an old railway line) there is such an old locomotive.There is no firebox.Where the boiler would be is a large tank.
The running costs and range for a similar car would seem to depend on the energy used to fill the tank and it's size.
An exploding compressed air tank could be just as damaging as a petrol or hydrogen tank going up,don't you think?
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> I think that the technology to run an engine on compressed air is actually quite old.
You're right, it's very old and no-ones managed to make it work yet. The main problem is that compressed air has a very low energy density in comparison to say, petrol. Also, compressing air is in itself an inefficient process.
MDI have been touting their air cars for a long time and nothing's really come of it. See this page from 2002, for example:
news.bbc.co.uk/1/hi/world/europe/2281011.stm
Perhaps things will change now TATA are onboard, but I won't be holding my breath!
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The power train can only be a reciprocating piston engine, like a steam engine, or a turbine. The size and structural integrity of the reservoir needed to get more than a very short driving range would pose problems. Life-threatening explosions would be a possibility. Looks a non-starter to me.
Steam itself is a much better idea and in the early days of motoring provided some of the smoothest, fastest-accelerating power available. I read a few years ago that someone was trying to update the steam car but it doesn't seem to have got anywhere.
Edited by Lud on 05/01/2008 at 15:20
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I don't see why an air engine is a problem - it's really the trade offs around range, power, tank size/weight etc that have to be optimised to compete with a typical ICE. The tank just has to be strong enough not to burst when knocked about a bit, and perhaps have some means of releasing pressure non-explosively in a fire!
Steam sounds more fun, but works better for constant load and especially continuous running. The great thing about ICEs is that the heat is created instantly and directly inside the cylinder as it is needed - a regular petrol or diesel engine has fantastic controllability - it is brilliant at starting and stopping, and varying its output. A traditional steam engine isn't going anywhere until it has made some steam. The engine side of steam engines was pretty well evolved before they started to fall out of use - future development would probably be of most use on the boiler/steam generation side. Maybe lots of "little boilers" that could be turned on and off to aid efficiency (one big boiler capable of generating enough steam for say 100hp would not only be slow to get going but would be very inefficient when producing the 10-20hp which is needed most of the time for just trundling along).
And what would you use for fuel - petrol or diesel? I can't see coal-shovelling catching on, or chucking on 50lb or so of wood every hour.
Edited by Manatee on 05/01/2008 at 17:00
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Just a thought - turbocharging compresses air to get more into the engine giving more power and/or smaller engine for given output.
Wouldn't it be possible to run a two-stroke (without crankcase compression) on compressed air - with direct injection of air and fuel, it would only need an exhaust valve.
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Seeing that with current air motors it takes about 10cu/ft/m to give the equivalent of 1 hp [750W] and that the manufacturers are hinting that it's fed from diving bottles at around 4000lbf/sq/in - then how many tons does the thing weigh [a 50cuft bottle weighs around a hundredweight] and how many yards does it go before it grinds to a halt.
The inefficiency of air compressors is legendary; to cover one mile would cost about £30 in electricity. It might, however, have some limited use in high-fire-risk industrial envirionments as it could be made totally sparkless.
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I think that the technology to run an engine on compressed air is actually quite old. In the 19th C. I believe shunting engines were run on compressed air. On the cycle track by Lake Annecy (an old railway line) there is such an old locomotive.There is no firebox.Where the boiler would be is a large tank.
Compressed air locomotives were used in coal mines until quite recently. These usually had multiple air cylinders a foot or so in diameter and several feet long.
For fire-risk areas above ground (refineries, for example) 'fireless' locomotives were used; these had a boiler periodically recharged from a static boiler plant which was outside the hazard area, possibly the one near Lake Annecy is one of these?
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Sounds like a non-starter, it would require more energy to compress the air than we use in an existing motor or engine. Plus we would need large battery to power ancillaries anyway.
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what if you ran out of air? you could use the air in the spare wheel to get you home :) now thats what i call duel functionality
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mj
Yes; that would work - if you were only about two feet from home.....
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