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Author Topic: Compressed air car: Car of the future?  (Read 4893 times)

Offline McQueen

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Compressed air car: Car of the future?
« on: 20/10/2007 09:02:30 »
Will you take a look at this  site it is definitely the coolest idea for a car engine that I have seen anywhere. It is not a scam it will work. I was as great a sceptic as you could expect to find anywhere, but after studying the concept I believe that every word on the MDI air car found at the web-site is a hundred per cent true. The facts are stated without exaggeration, this is surely  the great breakthrough that the automobile industry has been waiting for.  Briefly the car runs off compressed air. Compressed air at 4200 psi (330 bar) is stored in a tank and supplies the engine, which works very much like an IC piston engine. Using a 320 litre tank of air compressed to 300 bars, the car can run at equivalent speeds to a normal car with a 1 litre cubic capacity for 7-8 hours at a minimum. The tank can be recharged using a small portable 4KW compressor in 3 – 4 hours or in 2 minutes using a specialized compressor running at 500 KW. It is no more dangerous than carrying around a couple of filled scuba tanks in the car.
« Last Edit: 20/10/2007 16:09:48 by ukmicky »


 

Offline DoctorBeaver

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Compressed air car: Car of the future?
« Reply #1 on: 20/10/2007 09:25:23 »
May I suggest you edit your post and remove the quotes from the URL.

My knowledge of this subject is zero but, I must say, the site looks genuine.
« Last Edit: 20/10/2007 09:28:12 by DoctorBeaver »
 

lyner

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Compressed air car: Car of the future?
« Reply #2 on: 20/10/2007 12:09:09 »
Yes, it will work. But the efficiency is not too good; there is a lot of energy wasted in the compression process, which has to be dissipated from the compressor and by cooling the cylinders.
I am not too happy with the risk of the high pressure cylinders in accidents. Every now and then, scuba cylinders explode, horrifically, in car accidents but there are not many around so it isn't a significant problem at present.
And, of course, the actual quantity is very different (scuba cylinders hold about 10litres) -hence the energy of any explosion would be greater.
The numbers you quote are optimistic - 4kW for 3-4 hours is - say 16kWhr, and all that  energy wouldn't go into the  compressed air. Someone might help us with the amount???
16kW is a low power for a car to run at high speed so you'd get much less than 1 hour on a motorway at modest speed.
A good possibility for short running bus services in town centres, perhaps.  No smells!
 

Offline McQueen

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Compressed air car: Car of the future?
« Reply #3 on: 20/10/2007 13:59:12 »
Quote
I am not too happy with the risk of the high pressure cylinders in accidents. Every now and then, scuba cylinders explode, horrifically, in car accidents but there are not many around so it isn't a significant problem at present.

Granted this might be a problem, but the information at the web-site tells us that this problem has been solved and that the tanks will not explode. Although, exactly how they might manage this is something of a mystery to me.
Quote
The numbers you quote are optimistic - 4kW for 3-4 hours is - say 16kWhr, and all that  energy wouldn't go into the  compressed air. Someone might help us with the amount???
16kW is a low power for a car to run at high speed so you'd get much less than 1 hour on a motorway at modest speed.
All I did was to calculate how long it would take to fill a tank of that size to that pressure (300 bars) approx. 4200 psi. and the information at the site seems to be more or less in keeping with this.
Quote
16kW is a low power for a car to run at high speed so you'd get much less than 1 hour on a motorway at modest speed.
Start at the other end, you have a tank filled to 4200 psi, the pressure you need to drive the cylinder is 500 psi, even at 4000 rpm that gives, a perfomance similar to a 1 litre IC piston engine car for 7-8 hours at a minimum! So this technology looks good. The web-site also states that the air car might be on the road by next year 2008 !
Apart from that think of the advantages, the IC piston engine as you know, has an on the road efficiency of less than 20%, while the steam turbine that generates electricity has an efficiency of  close to 90% ! So what this means is that you could fill your tank much more cheaply with compressed air than with petrol. In other words if it costs 50 euros to go a certain distance using petrol, it would cost only 4 euros or less to go the same distance using compressed air ! Which is a significant saving. Further, the electricity that you will be using originates from a centralized location (i.e., the power station) so it is that much easier to control pollution. I feel that this car design has really serious potential.




 

lyner

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Compressed air car: Car of the future?
« Reply #4 on: 21/10/2007 00:28:10 »
Quote
Start at the other end, you have a tank filled to 4200 psi, the pressure you need to drive the cylinder is 500 psi, even at 4000 rpm that gives, a perfomance similar to a 1 litre IC piston engine car for 7-8 hours at a minimum!
This calculation doesn't actually state the amount of energy available.  You can't talk in terms of 'performance' if you don't consider actual power output.
If you really have only 16kWh stored then your vehicle will be severely under-powered, compared with a 1 litre IC engine, which can develop 40 or 50 kW, easily. - or it  will have less than 1/2 hour of running time.

What sort of material will be used for the cylinders?  They may claim to have solved the strength / safety problem but I question whether they can achieve it without some serious weight penalty.
btw, I just looked this up in Wiki and their estimate is that -weight for weight, the  energy storage capacity is similar to that of lead acid batteries if you use strong enough cylinders to satisfy safety requirements.
 The efficiency of a charge / discharge cycle of a battery could well be better than the efficiency of the  air-compression system if you throw away all the  heat produced from compression. Insulating the cylinders could reduce this loss mechanism, perhaps. They would get pretty hot when pumped to 300atmospheres, so your insulation would need to be good.
I am sure it would have some applications, though.  It could be good in tunnels, where the  exhaust (cool) air would make life more pleasant for passengers.
 

Offline McQueen

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Compressed air car: Car of the future?
« Reply #5 on: 21/10/2007 05:52:11 »
Quote
If you really have only 16kWh stored then your vehicle will be severely under-powered, compared with a 1 litre IC engine, which can develop 40 or 50 kW, easily. - or it  will have less than 1/2 hour of running time.
I don’t quite see what you are getting at, are you calculating this using kilowatt hours or by using some more arcane technique ?  As far as I know one kilowatt hour = 3 x 10 ^^6 watts. I used a much more basic method: If it takes a 500 KW compressor 2 minutes to fill the tank, then it will take a 250 KW compressor 4 mins. to fill the tank etc., So, extending the process, at 4 KW it takes 250 mins. Or 4 hrs 10 mins. This seems to correspond well with what the web-site says about how long a 4KW compressor will take to fill the tank. 
Similarly, I at first thought that the figure of 7hrs – 8 hrs running time on a single tank seemed wildly exaggerated. Until you remember that you need a volume of only 8 cc at 4000psi to expand 125 times to around 1000 cc and come to atmospheric pressure (i.e 32 psi).  If the engine is running at  4000 rpm it uses 8cc x 66 = 528 cc per minute.  320000/528 = 606 mins or around 10 hrs.  Take into account that you need a second expansion chamber to bring the pressure down to controllable levels at around 500 psi and the air in the tank will last until only 1/16 of the tank is full and it still gives a comfortable margin of around 7hrs – 8 hrs running time with a performance comparable to that of a 1 litre IC piston engine.  This by itself might not mean much but it seems to be exactly what is claimed ( more or less ) at the web-site and is what got me thinking.
The similarities, coincidences were two much to ignore, add to this the fact that a model air-plane using a CO2 engine and a 2cc tank runs for 4-5 minutes helped.
 

Offline neilep

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Compressed air car: Car of the future?
« Reply #6 on: 21/10/2007 13:20:03 »
Wiki Has a nice article about air engines http://en.wikipedia.org/wiki/Air_engine

and if you scroll down there's quite a few external links of which this is one of them.

http://edition.cnn.com/2005/TECH/03/30/spark.air.car/index.html

It does sound very exciting !!
 

lyner

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Compressed air car: Car of the future?
« Reply #7 on: 21/10/2007 22:33:22 »
I'm sorry, but just by talking about volumes, pressures and revs  you can't magic ENERGY out of nowhere. The car needs serious amounts of  energy to go 7 or 8 hours, if it is expending  tens of kilowatts in maintaining a reasonable speed (which I don't think you have included in your sums) and  it won't run for long on 16kWh.( And I am happy with your estimate of that amount of stored energy:  4 kW for 4hours = 16kWh.)  Yes, on a horizontal railway line at 10mph, it will go for ever and a day.  You could use a lawnmower engine to achieve the same thing. But that's not the scenario for a usable motor car.
I think the 'hole' in your argument is that you have quoted a possible value for engine revs but not taken it further with torque and gearing calculations and, hence, the actual power developed or required.
Energy (/power) is the bottom line, always and will always give you a good ball-park figure. Details of engine design etc can only help you approach this- not to exceed it.
The summary on the Wiki site suggests that the range for weight performance is about the same as for lead acid batteries. Fine for local delivery vans but not for long journeys at speed.
 

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Compressed air car: Car of the future?
« Reply #7 on: 21/10/2007 22:33:22 »

 

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