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Author Topic: The Compressed air engine: Is it a scam?  (Read 30360 times)

Offline McQueen

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The Compressed air engine: Is it a scam?
« on: 08/09/2007 16:12:44 »
According to the manufacturers and the article at Wikipedia it uses compressed air to drive the pistons in a modified piston engine. The compressed air is supplied from an onboard tank filled with air at 3000 psi , this compressed air is injected into the piston cylinder and used to push the piston down giving the motivating power. The only emissions from such an engine are air. The downside to using such an engine is that since there is no heat to speak of it will be difficult to heat your car, the upside is that if you happen to live in a country with a hot climate, air-conditioning would be one side effect of the expanding air, that could be used to air-condition your vehicle. The compressed air car has already gone into collaboration with an automobile company in India : Tata’s who are going to produce the ‘city cat’, some time in the near future. What do you have to say about such an engine? Will it work or is it a scam? McQueen.
« Last Edit: 08/09/2007 16:14:20 by McQueen »


 

Offline syhprum

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The Compressed air engine: Is it a scam?
« Reply #1 on: 08/09/2007 17:16:59 »
Compressed engines are of quite possible we boys used to use them to power our model aircraft during WWII but the amount of power you can store in a compressed air bottle is pretty limited.
Much more can be stored in compressed Helium but the cost is prohibitive and it is only used by military and space agencies.
 

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The Compressed air engine: Is it a scam?
« Reply #2 on: 08/09/2007 17:50:22 »
But, like hydrogen powered cars, compressed air is merely a means of delivering power that has been generated elsewhere - it is not a primary means of generating power.
 

Offline syhprum

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The Compressed air engine: Is it a scam?
« Reply #3 on: 08/09/2007 18:32:41 »
Both liquid air and electric light cars were quite common at the turn of century and probably outnumbered steam and petrol propelled vehicles for town use.
The big problem with liquid air is that a source of heat is required but for a ladies dog cart or tete a tete limited by law to 12 mph not much power was required and a 'radiator' operating in the reverse manner to which they do today sufficed.
Where Helium wins out it can be compressed to a great degree without liquefying.
 

Offline Bored chemist

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The Compressed air engine: Is it a scam?
« Reply #4 on: 08/09/2007 19:50:03 »
Much more can be stored in compressed Helium
Why?
I can see that it's lighter than air but the weight of the tank will be  much bigger than the weight of the gas anyway.
Also, since nitrogen and oxygen are well above their criticl temperatures in normal air, they cannot be liquefied by compression.
 

Offline syhprum

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The Compressed air engine: Is it a scam?
« Reply #5 on: 08/09/2007 20:40:02 »
I have been trying to find the source my information without success, I have seen an article probably in the 'Scientific American' depicting spherical containers that are filled with highly compressed Helium which comprised an energy storage system that stored more energy per Kg than any batteries.
 

Offline lightarrow

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The Compressed air engine: Is it a scam?
« Reply #6 on: 08/09/2007 21:08:27 »
When I was 15, I had the same idea for an engine with compressed air. At that time no one among friends and school mates knew much about this (I didn't know it was exploited in the IIWW). They said I was crazy. So I stopped thinking about it. Now I see it again!

Ok, so, another idea I had at those times for an engine: a  couple of big disks, one over another, spinning in opposite directions. No pollution (from the veichle, not from the energy plant of course), virtually no noise, very high torque.

Of course, as George wrote, they are just a means of delivering power that has been generated elsewhere; the convenience is in the possibility to centralize the production of power, making this process more efficient; let's remember that in a car's combustion engine only ~ 20% of the petrol's energy is converted into the veichle's movement.
« Last Edit: 08/09/2007 21:10:05 by lightarrow »
 

Offline syhprum

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The Compressed air engine: Is it a scam?
« Reply #7 on: 08/09/2007 21:22:21 »
Flywheel power storage has certainly been used on vehicles, I remember TV coverage of a railway shunting engine that stopped at an electricity supply, spun up its counter rotating flywheels and then went to work.
these were common low tech wheels but since then high vacuum enclosed ones have been developed
 

Offline McQueen

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The Compressed air engine: Is it a scam?
« Reply #8 on: 09/09/2007 04:54:37 »
Syhprum
 
Quote
Compressed engines are of quite possible we boys used to use them to power our model aircraft during WWII but the amount of power you can store in a compressed air bottle is pretty limited.

I think that what Syhprum has to say is more or less correct, although there are several other things in the literature about the air-engine that I find hard to believe. If I am not mistaken the model aircraft that Syhprum is talking about used compressed air in the same way as an inflated balloon, (i.e) the reactive forces of the gases escaping from the nozzle push the balloon (plane) in the opposite direction. Such toy planes are still available today.  The literature on the air-car says that 340 litres of compressed air are stored at  4500 psi. OK, so 340 litres corresponds to a tank 2.25’ x 2.25’ x 2.25’ or 19,683 cu ins of compressed air approx. Let us suppose that the cylinders in the engine are 3” x 3” so they have a volume of  21 cu ins approx. A normal car works at the following rpm. Starting speed 300 rpm, idling speed 1000 rpm, slow speed ( about 20mph) 2400 rpm, moderately high speed (30- 40 mph) 3600 rpm. Since most of us drive at or about 30 mph (45km/hr) we take this as the bench mark. 3600 rpm means that the engine fires 60 times every second, this gives 60 x 21 or a usage of 1,260 cu ins per sec. And 75,600 cu ins min. Since the amount of pressure needed to run the engine is 500 psi and the pressure in the tank is at 4500 psi, we divide 75,600/8 (approx) = 9,450 cu ins are used by the engine every minute. Since the tank has a capacity of 19,683 cu ins, the engine will run for 19,683/9,450 = 2 mins. The point is there is no way to replace this compressed air, compressed air is similar to generating electricity, if you try to compress to a higher pressure, you need more power and to compress to 4500 psi or even 450 psi would require a huge amount of power ! The second thing is how far can you go in 2 minutes, it takes two minutes just to get out of the garage, although theoretically, if you had a straight road you could go 60 kms in that time.  Apart from the huge amount of energy that would be needed to fill the tanks, there is the question of heat. A diesel engine compresses to about 16 : 1 or about 240 psi, during compression temperature rises to 500 degrees centigrade. The literature tells us that the air tank can be filled in 2 minutes! The temperature must rise to several thousands of degrees centigrade at the very least! Now the Dunlop Aviation Services,  Tyre factory in England when it first opened tried to use compressed air to test the bursting point of  airplane tyres, these are some of the toughest tyres in the world. The tyre exploded when the pressure reached 800 psi demolishing most of the test facility with it, nowadays they use water instead of air to inflate the tyres to bursting point ! The point I am trying to make is that that amount of pressure (4500 psi) at that temp (3000 degrees C?) is just not safe, every car would be like a 1000lb bomb waiting to go off. McQueen.





 

Offline syhprum

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The Compressed air engine: Is it a scam?
« Reply #9 on: 09/09/2007 06:01:19 »
Our model aircraft used twin cylinder horizontally opposed engines about 2 cc displacement with the air intake controlled by a rotary sleeve valve.
Details could probably be found in the modellers magazines of the period
 

Offline McQueen

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The Compressed air engine: Is it a scam?
« Reply #10 on: 09/09/2007 07:45:54 »
Quote
Our model aircraft used twin cylinder horizontally opposed engines about 2 cc displacement with the air intake controlled by a rotary sleeve valve.Details could probably be found in the modellers magazines of the period
Wow! That's sommething I'm hearing for the first time. How long could they stay in the air ? Quite interesting I'll look it up, if I can. McQueen
Yes Syhprum , you were right, here is a link. Quite fascinating!
« Last Edit: 09/09/2007 08:07:08 by McQueen »
 

Offline DoctorBeaver

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The Compressed air engine: Is it a scam?
« Reply #11 on: 09/09/2007 08:10:04 »
Our model aircraft used twin cylinder horizontally opposed engines about 2 cc displacement with the air intake controlled by a rotary sleeve valve.
Details could probably be found in the modellers magazines of the period

I've only come across electric or petrol engines for model planes. Or, of course, elastic bands!
 

Offline Bored chemist

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The Compressed air engine: Is it a scam?
« Reply #12 on: 09/09/2007 13:23:20 »
A long time ago a friend of mine had a model aircraft engine that ran like a steam engine but on the little CO2 cylinders you could get for making soda water. I never saw it in use in a model so I don't know how well it worked.

Incidentally, it's true that a high pressure air tank in a car would make it a potential bomb. The next question is, what does the gasoline tank do that's different?
In order to propell the vehicle you need stored energy; however you do it that is a potential danger.
 

Offline McQueen

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The Compressed air engine: Is it a scam?
« Reply #13 on: 09/09/2007 14:31:19 »
Quote
incidentally, it's true that a high pressure air tank in a car would make it a potential bomb. The next question is, what does the gasoline tank do that's different?
In order to propell the vehicle you need stored energy; however you do it that is a potential danger.
True! In many respects, the air-car engine is something that we all appreciate. But   in many respects it places us in the position of the poverty stricken vicar who visited the Manor and was given a bad egg for breakfast, for the amusement of the Lord. When asked what his breakfast was like. He replied "Well......it's good in parts!"  So, yes the aircar is a good thing, but it can power the engine for only a minute or so and then you need to think about refuelling. The rest of the time it runs on a gasoline engine. So what's the difference, not much. The Rotary Pulse Jet Engine would probably be much a better  alternative and more practical! McQueen
« Last Edit: 09/09/2007 14:34:12 by McQueen »
 

Offline ukmicky

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The Compressed air engine: Is it a scam?
« Reply #14 on: 09/09/2007 14:36:14 »
Look at the positives if you happen to take a dip in your local lake and forget to remove your car all them air tanks in your boot will stop you sinking. :)
 Or if it did still sink your engine would still work so you could drive back out. ;D
 

Offline DoctorBeaver

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The Compressed air engine: Is it a scam?
« Reply #15 on: 09/09/2007 16:22:43 »
Look at the positives if you happen to take a dip in your local lake and forget to remove your car all them air tanks in your boot will stop you sinking. :)
 Or if it did still sink your engine would still work so you could drive back out. ;D

 

Offline lightarrow

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The Compressed air engine: Is it a scam?
« Reply #16 on: 09/09/2007 18:59:51 »
Flywheel power storage has certainly been used on vehicles, I remember TV coverage of a railway shunting engine that stopped at an electricity supply, spun up its counter rotating flywheels and then went to work.
these were common low tech wheels but since then high vacuum enclosed ones have been developed
Thank you for this information. It was not only science-fiction, then!  ;D
 

Offline lightarrow

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The Compressed air engine: Is it a scam?
« Reply #17 on: 09/09/2007 19:16:34 »
Look at the positives if you happen to take a dip in your local lake and forget to remove your car all them air tanks in your boot will stop you sinking. :)
 Or if it did still sink your engine would still work so you could drive back out. ;D
Or, if you have to stay deep under water for long time, you have enough air to breathe.  ;)
 

Offline Bored chemist

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The Compressed air engine: Is it a scam?
« Reply #18 on: 09/09/2007 20:25:20 »
"Apart from the huge amount of energy that would be needed to fill the tanks, there is the question of heat. A diesel engine compresses to about 16 : 1 or about 240 psi, during compression temperature rises to 500 degrees centigrade. The literature tells us that the air tank can be filled in 2 minutes! The temperature must rise to several thousands of degrees centigrade at the very least!"

Why on earth would the temperature need to be high?
It's perfectly simple to fit intercoolers on multi stage compressors. I regularly work with gases at 4500psi, they are practically at room temperature; if they ever got anywhere near 3000 C the steel tubing would melt.
 

Offline McQueen

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The Compressed air engine: Is it a scam?
« Reply #19 on: 09/09/2007 23:16:11 »
Quote
Why on earth would the temperature need to be high?
It's perfectly simple to fit intercoolers on multi stage compressors. I regularly work with gases at 4500psi, they are practically at room temperature; if they ever got anywhere near 3000 C the steel tubing would melt.
But could this be done in 2 - 3 minutes ? Surely filling a 340 litre tank with air at 4500 psi in that amount of time would have to resullt in some heat? McQueen
 

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The Compressed air engine: Is it a scam?
« Reply #20 on: 10/09/2007 13:53:02 »
When you compress air, the tank gets hot - diving bottles get hot and they use water to coolem. This is lost energy because you are using isothermal compression, effectively. The beauty of the IC engine is that it's adiabatic - more efficient.
Pneumatic engines  are pretty useful, though - what would your dentist do without his drill or how would they dig up roads so effectively without the lightweight pneumatic high-power breaker?
 

Offline Soul Surfer

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The Compressed air engine: Is it a scam?
« Reply #21 on: 10/09/2007 23:23:12 »
Remember if you are using air that is already compressed to 4500psi and at room temperature in a much larger cylinder you can rapidly fill the car tank with it because the overall filling process will not cause a large rise in temperature because the initial gas expanding into the empty tank will cool down and then warm up again as it is compressed by more gas entering the tank the only excess heat will be caused by the absorbtion of heat during the initial period when the gas is cold.  this could be prevented by making sure the tank is reasonably well insulated.
 

Offline McQueen

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The Compressed air engine: Is it a scam?
« Reply #22 on: 11/09/2007 15:38:58 »
Soul surfer
Quote
Remember if you are using air that is already compressed to 4500psi and at room temperature in a much larger cylinder you can rapidly fill the car tank with it because the overall filling process will not cause a large rise in temperature because the initial gas expanding into the empty tank will cool down and then warm up again as it is compressed by more gas entering the tank the only excess heat will be caused by the absorbtion of heat during the initial period when the gas is cold.  this could be prevented by making sure the tank is reasonably well insulated.
I am not too sure about this, what about Boyle's Law. Again look at the time constraints the tank has to be filled in 2 - 3 minutes. I can understand controlling the temp. if the filling took a longer time but......McQueen.
 

Offline syhprum

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The Compressed air engine: Is it a scam?
« Reply #23 on: 11/09/2007 17:03:46 »
Can anyone well versed in physics and good at arithmetic tell me how many Joules of energy are stored in 320 liters of air compressed to 300 Bar.
I don't think it amounts to a lot

I make it about 1.38 KW hours, a small slow vehicle might mamage on about 5 KW and run for 15 minutes or so ! 
« Last Edit: 11/09/2007 17:24:55 by syhprum »
 

Offline lightarrow

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The Compressed air engine: Is it a scam?
« Reply #24 on: 11/09/2007 20:25:41 »
Can anyone well versed in physics and good at arithmetic tell me how many Joules of energy are stored in 320 liters of air compressed to 300 Bar.
I don't think it amounts to a lot

I make it about 1.38 KW hours, a small slow vehicle might mamage on about 5 KW and run for 15 minutes or so ! 
Work done by the gas (assumed as ideal) on isothermal expansion ~ 5.48*107 J.
For adiabatic expansion is more complicated.
 

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The Compressed air engine: Is it a scam?
« Reply #24 on: 11/09/2007 20:25:41 »

 

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