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Engines that run on compressed air

PostPosted: Sat Dec 06, 2008 7:58 pm
by Martin R

PostPosted: Sat Dec 06, 2008 10:57 pm
by Petter
Probably fact. Some months ago there was a writeup about a small indian car which was stated to run on compressed air. The max travelling distance on a single "fill up" was stated to be around 100km, if I remember correctly, which should compare well with some of the electrical cars presently on the market.

Petter
CV8 112-2448
Interceptor convertible 2311-1769

PostPosted: Sun Dec 07, 2008 1:40 am
by Firebird1900
Yes there are people looking at compressed air as an energy source (or I should say energy storage) for cars and prototypes have been built. Problem is storing enough of it to get decent range, and the pressures are high which means thick tanks which means weight.

PostPosted: Sun Dec 07, 2008 9:13 am
by JonathanL
Firebird1900 wrote:Yes there are people looking at compressed air as an energy source for cars and prototypes have been built. Problem is storing enough of it to get decent range, and the pressures are high which means thick tanks which means weight.


There are toy aircraft you can buy which have litte piston engines which run on compressed air.

PostPosted: Sun Dec 07, 2008 10:38 am
by Martin R
I felt it looked reasonable enough to be true but nowadays there is so much stuff that is simply not true on the Net, I wasn't 100% sure.

Seems a good idea though and ideal for city driving etc.

PostPosted: Sun Dec 07, 2008 1:10 pm
by funnycar
Possible.

It can be calculated.

V roughly from the compression ratio, er no. Petrol expands to 25 [verification required] times its volume when combusted with oxygen in the transformation from liquid to gases and generates about 8 bar [verification required].

So the chamber volume at TDC is the charge volume of compressed air at 25 bar.

Then think of the number of cylinders and the engine speed.

A regular compressed gas cylinder hold air at 200 bar.
A carbon fibre cylinder could hold 300 bar.


Back in the eighties when I was a young, wet behind the ears engineer, Lucas Research built a ceramic engine in co-operation with Cookson. It was SiAlON, a ceramic formed from Silicon, Aluminium, Oxygen and Nitrogen - easy to remember.

The thing didn't wear out and could take a stratified 25:1 AFR.
We doubled the mpg of a traditional engine powered car.

Lucas also had a GDi injector and Plasma discharge ignition, well before anyone else.

If the Air car engine was SiAlON, it would be half the weight and NEVER wear out.

Food for thought ?????

The trouble with SiAlON, it can only machined with Diamond tools !!

PostPosted: Sun Dec 07, 2008 6:11 pm
by Petter
Here is the writeup I mentioned regarding the car produced in India:

"The Compressed Air Car, developed by Motor Development International (MDI) Founder Guy Negre, might be the best thing to happen to the motor engine, and people all over the world.

The $12,700 CityCAT, one of the planned Air Car models, reaches 68 mph, goes for a range of 125 miles. It will take only a few minutes for the CityCAT to refuel at gas stations equipped with custom air compressor units. MDI says it should cost only around $2 to fill the car up with 340 liters of air!

The Air Car will be starting production soon, thanks to India 's TATA Motors. Forget corn! That's a joke. There's fuel, user friendly, pocketbook friendly fuel! What can be better than air? Cool Concept. 6-seater taxi should be available in India in 2008: will even take a tuba!"

This looks interesting as an alternative to the pure electrical cars presently available, as far as I can tell. A colleague at work had to replace the batteries of his approximately xxx£20.000 electrical car, they turned out to cost around xxx£15.000, this seems way too high, even if in his case he was able to use his insurance to cover the claim :shock: .

The engine shown at the end of the video clip seems to be a variant of the Wankel rotary engine principle, which has been around for a while.

Petter
CV8 112-2448
Interceptor convertible 2311-1769

PostPosted: Sun Dec 07, 2008 6:17 pm
by Julian_S
funnycar wrote:

The trouble with SiAlON, it can only machined with Diamond tools !!


Interesting stuff, I don't think diamond tools would represent much of a problem today - the J&L catalogue has a host of stuff available, mail order, for a few quid!

Getting back to the air powered car: I think that the link is a hoax, on the test drive you hear the driver revving the engine and talking about the gear changes. A pneumatic motor (''engine'') would surely have similar operating characteristics to a steam engine. ie it would produce max torque at zero revs - hence a clutch and gearbox would be unnecessary - just like a steam loco.

Julian.

PostPosted: Sun Dec 07, 2008 6:19 pm
by Julian_S
JonathanL wrote:[

There are toy aircraft you can buy which have litte piston engines which run on compressed air.


Toy = Model?

From my yufff I remember them running on CO2, not compressed air - but I'm a bit rusty nowadays...

Julian.

PostPosted: Sun Dec 07, 2008 8:41 pm
by Julian_S
A quick Google reveals this link:

http://www.futurepundit.com/archives/000129.html

This hyperbole from MDI dates back to 2002! And still no product.

I think a little ''common sense'' reasoning would probably lead you to conclude that the amount of energy stored in the air tanks would equate to little more than a mug of petrol or Diesel, ie enough to move the vehicle about 1 mile....

PostPosted: Sun Dec 07, 2008 9:55 pm
by Firebird1900
verey very approximate .........

If you are storing air at 300 bar (which is pushing it!) then a cubic metre (1000 litres) of stored air will give you 300,000 litres at atmospheric

so if you have a one litre engine ............ and u assume u use it all ........ and it all ends up at atmospheric ............ and its a two stroke engine .......... thats 300,000 revolutions (in practice u would get a lot less than this because the cyliners would be above atmospheric at end of stroke and you would need some residual pressure in the tanks)

for simplicity say you do 3,000 rpm thats 100 minutes of driving.

ball park guesstimate suggests that its not impossible but it is beyond what is possible today to get a sensible range with a sensible pressure / volume.



alternatively u could work it out from stored energy but someone else can have a go at that

PostPosted: Mon Dec 08, 2008 10:48 am
by JonathanL
Julian_S wrote:
JonathanL wrote:[

There are toy aircraft you can buy which have litte piston engines which run on compressed air.


Toy = Model?

From my yufff I remember them running on CO2, not compressed air - but I'm a bit rusty nowadays...

Julian.


They're called Air Hogs. Think I got my nephew one once. Stopped making them recently, I think.

http://cgi.ebay.com/Spinmaster-Air-Hogs ... 7C294%3A50

Apparently, it's not a new idea;

http://blog.modernmechanix.com/2007/11/ ... essed-air/

PostPosted: Mon Dec 08, 2008 3:13 pm
by Julian_S
JonathanL wrote:
Julian_S wrote:
JonathanL wrote:[

There are toy aircraft you can buy which have litte piston engines which run on compressed air.


Toy = Model?

From my yufff I remember them running on CO2, not compressed air - but I'm a bit rusty nowadays...

Julian.


They're called Air Hogs. Think I got my nephew one once. Stopped making them recently, I think.

http://cgi.ebay.com/Spinmaster-Air-Hogs ... 7C294%3A50

Apparently, it's not a new idea;

http://blog.modernmechanix.com/2007/11/ ... essed-air/


I've just found what I used:
Image

Rather more business like than the modern toy! I guess HSE has banned them in case Little Johnny gets a square millimeter of frost bitten skin when refilling from the Soda Syphon bottle!

Julian.

PostPosted: Mon Dec 08, 2008 8:05 pm
by Julian_S
Firebird1900 wrote:verey very approximate .........

If you are storing air at 300 bar (which is pushing it!) then a cubic metre (1000 litres) of stored air will give you 300,000 litres at atmospheric

so if you have a one litre engine ............ and u assume u use it all ........ and it all ends up at atmospheric ............ and its a two stroke engine .......... thats 300,000 revolutions (in practice u would get a lot less than this because the cyliners would be above atmospheric at end of stroke and you would need some residual pressure in the tanks)

for simplicity say you do 3,000 rpm thats 100 minutes of driving.

ball park guesstimate suggests that its not impossible but it is beyond what is possible today to get a sensible range with a sensible pressure / volume.



alternatively u could work it out from stored energy but someone else can have a go at that


Have a look at some of the comments here when you get a mo:

http://www.popularmechanics.com/automot ... 17016.html

It would appear that essentially the whole thing is just a scam to get money from investors with no scientific knowledge.(as I suspected) They have not managed to get the vehicle beyond the 5 mile barrier at the mo, and they've been at it since 2002! Air is a hugely inefficient energy storage medium.

Julian

PostPosted: Tue Dec 09, 2008 12:55 pm
by Martin R
Interesting reading - it would appear that whilst some work has been done, early predictions have turned out to be unfounded and as time has passed by, they obviously realised that technically, they were missing the mark.

Usually, when something appears to be too good to be true, it is.