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Duct Taper
11-15-2007, 01:46 AM
I saw a program on TV tonight about energy efficient cars. One of the cars had an engine that ran on compressed air. I don't recall the range it had, but I was wondering if something like that would be possible to make to use on a three wheel mobility cart for old people or the handicap, or me who wants transportation to the coffee shop in the morning without having to fire up the pickup truck. Gas prices make expensive coffee stops!

Has anybody here tried to make an engine that runs on compressed air? Not like the turbine-type air tools but more like a steam engine with valves and piston.

bhjones
11-15-2007, 02:29 AM
Judging this by the air used by my air tools, I wonder how many thousands of cubic feet of compressed air you'll need per mile...

On the face of it I'd say it's impractical, but I'm no engineer.

darryl
11-15-2007, 02:42 AM
There are lots of ways to make compressed air motors. The more efficient of them use some means of keeping heat in the air as it expands to do the work. The same goes for supplying the air- as it's compressed, you keep it as cool as it can be, so you're not throwing heat energy away. This might sound like an oxymoron, because to keep the air cool, you'd have to draw the heat of compression out of it, and there goes the heat. What does happen is that it makes it easier for the compressor to push more air into a tank with less energy, so there's a savings there.

There's a name for this - it's adiabetic, if I'm not mistaken- someone correct me- and it's not the easiest thing to do. You're paying for a lot of energy that you'll be throwing away, both during charging of the (air) tank, and usage of the compressed air through the motor. I think it would be cheaper to use propane, first as a pressure that operated one pair, or a triple of pistons, similar to a standard air motor, then ignited as a fuel to drive another set of pistons. The waste heat would go largely towards warming the propane wherever it cools as it exits the tank.

Anyway, now we're (or I'm) talking about a fuel tank on board, something ignitable and dangerous, not to mention toxic in the way that exhaust gasses are. Leaks obviously pose problems, and it only takes a couple looks at 'compromised' propane systems to scare anyone away. Spectacular fireballs, buildings blown completely apart, many killed, etc. Still, I like the idea of it. The propane can be used to start the 'engine', since it runs partly on the expansion of it, so there's no need for a starter. It can also be fairly quiet.

I'm coming around to electric- when power requirements aren't massive (such as propelling a 4000 lb vehicle to transport a 200 lb person, it has a lot going for it. Recharging is relatively cheap, it's quiet, modern electric motors are efficient and can be very light, even the batteries can be lots lighter, if we wold ever be allowed to use one of the modern technologies without paying an arm and a leg for it- At any rate, for the slower speeds and smaller vehicles, which I might coin a name for, like Pet (personal, efficient transportation) electric seems to be about the best option. MHO

NickH
11-15-2007, 04:27 AM
Adiabetic?
A mechanism with no problems metabolising and storing sugar then using it later for energy?
That sounds like a groundbreaking area of research for automotive transport, it's certainly worth thinking about :D
Nick

Tuckerfan
11-15-2007, 05:35 AM
If you're talking about this car (http://www.theaircar.com/), then be advised that it's most likely a scam. They've been "beginning production in the next few months" for about a decade now.

Evan
11-15-2007, 07:13 AM
As I have said and repeat again compressed air is about the least efficient energy storage method possible. You would do better with a gang of hamsters.

DickDastardly40
11-15-2007, 08:04 AM
I have a quite a lot of experience in recharging breathing air bottles used for fire-fighting to 300 bar as well as HP air compressors associated with them. To charge the vehicle in 3 minutes or less at a filling station as the manufacturer's website suggests while possibly possible would result in a very hot pressure vessel. As the temp reduces so does the pressure within resulting in say 2/3 the original pressure.

This whole concept may mean that the vehicle does not pollute but whatever provides the motive power for the compressor.

If this pipe dream could become a reality, any Brits can be sure the our government would also tax us to the hilt for air as well as every other energy source.

A.K. Boomer
11-15-2007, 10:25 AM
As I have said and repeat again compressed air is about the least efficient energy storage method possible. You would do better with a gang of hamsters.


Im really surprised at people and how they do not imediately recognize this as a total flop --- even my nieghbor told me about it like a half year ago, real nice guy but get a clue -- he was actually talking like its "for free",,,

It is one of the worst concepts out there, Its hard for me to think of something more inefficient but I'll try -------- How bout a jet turbine that runs a generator that charges capacitors that then runs an electric motor that then runs a compresser to fill an air tank that then runs a compressed air motor --- and put it all in a hummer package, sad thing is is you could, and still have enough room left over to carry 7 people:rolleyes: ,,, with the vehicles efficiency hovering around 1.25% you could creep down the road at 3 MPH (full throttle) and use it to melt all the snow off the roads in the winter, keep in mind in the summer months your going to take a hit in efficiency to .75% due to running all 9 AC compressers to keep the people inside from starting on fire... Too bad we cant run all that AC in the winter months --- we could really use the extra heat to melt the snow faster...

Dawai
11-15-2007, 10:45 AM
A steam engine will run on compressed air. Not as efficient since the specific gravity of air is much less than steam.

Actually, in a multi-fuel-storage system, air makes much more sense than a hydraulic accumulator. Air weighs less to carry around. INstead of braking, pump the tank up. You can get by with a much smaller engine.

NOW, a gps system and software to analyze the forward terrain would allow a motor to run wide open and build energy to pull a big hill on the trip planned by gps. Meaning a 6-10hp engine could power a small car.

Now wheelchair? just go to a 3rd world country and buy a kid. His whole life could be just to take care of a elderly/disabled person. With all the expense of electric wheelchairs, nurses, and other crap they have to have assisted living in the long run it'd be much cheaper.. and the person from the other world would be much better off.

Weston Bye
11-15-2007, 10:51 AM
As a 10-year old back in the '50s, I had daydreams of an air powered bicycle. Just recharge on "free" air from the gas station, and plan my travels to take me from station to station. I could imagine well enough - but just didn't have the wherewithal to make it happen.:(

Dawai
11-15-2007, 11:25 AM
Wes...

Now that's a idea.. using someone elses energy.. ha..

tony ennis
11-15-2007, 11:54 AM
Ultimately, that's what all our engines are about - using energy stored or produced by someone else. Whether it is Mother Nature compressing plants into oil, or a boy's dream of using compressed air from the filling station for his bike. All the same.

Carld
11-15-2007, 12:52 PM
How about a hot air engine. Say an ultra light bus for 20 passengers that are constant talkers and full of hot air. The thing should run 24/7 on just food and drink. you could drop off passengers and pick up new ones at designated stops.

Sounds great to me and think of all the great things you could learn from all the conversation.:D :rolleyes:

Weston Bye
11-15-2007, 01:01 PM
How about a hot air engine. Say an ultra light bus for 20 passengers that are constant talkers and full of hot air. The thing should run 24/7 on just food and drink. you could drop off passengers and pick up new ones at designated stops.

Sounds great to me and think of all the great things you could learn from all the conversation.:D :rolleyes:

Reminds me of the saying:"After all is said and done, there is more said than done." Such a bus could prove to be the exception.

It might be a hard ride, though, as Mark Twain observed during one of his lectures: "It's a painful death to be talked to death. - I will pause here to let some of you escape."

Duct Taper
11-15-2007, 01:12 PM
Gee whiz, what a bunch of skeptics!
At the end of that part of the TV program that covered the air car I thought I heard the narrator say that the engine could run a generator that could power a compressor that could provide the compressed air to run the engine.... so it was FREE!!! Man, who can be skeptical about that? Perpetual motion is possible after all. Eh? ?????

I don't think I will spend much more time trying to figure out how to make one of those engines......

RPease
11-15-2007, 01:38 PM
........You would do better with a gang of hamsters.

Sorry Evan.........that's not possible.......You can have a "gang of elk", but not hamsters. It would be a "horde of hamsters". Of course, if you wanted to use guinea pigs....you could have a "group of guinea pigs".........LOL


:D :D :D

Evan
11-15-2007, 02:49 PM
OK. What's the singular of "horde"? My hamster wants to know...

http://vts.bc.ca/pics/hw1.gif

heavysteamer
11-15-2007, 03:29 PM
When I was a kid one of my "rich kid" friends had an air powered model car. It had an air pump in the back to pump it up and then ran using a very well made and finely machined engine. Was real neat, we just didn't notice that it would have gone better if we had just pushed it instead of pumping it.

IOWOLF
11-15-2007, 03:42 PM
Air is no longer FREE at most gas stations,Where have you been?

tattoomike68
11-15-2007, 03:47 PM
People used to say the Wright brothers were nuts too.

http://www.youtube.com/watch?v=QmqpGZv0YT4

heavysteamer
11-15-2007, 04:29 PM
Wow! LA to New York on one tank of fuel.

Weston Bye
11-15-2007, 04:35 PM
Air is no longer FREE at most gas stations,Where have you been?

Thanks for the news flash.

IOWOLF
11-15-2007, 05:30 PM
Don't be a Dick head

Weston Bye
11-15-2007, 05:50 PM
IOWolf:

Perhaps my original post was unclear. My childhood daydreams happened back when, unlike the present, air was indeed provided free to the customers for inflation of tires and such. This apparently escaped your notice or understanding. I'm sorry.

I suspect that had that 10 year old kid achieved the air powered bicycle, that the gas station owner would have eventually caught wise to the excessive air use and chased the kid away. Back then, the majority of station owners actually worked in their own stations.

Joel
11-15-2007, 06:04 PM
I understood Wes perfectly without the need of further elucidation.


Don't be a Dick head
You gotta be kidding.

IOWOLF
11-15-2007, 06:19 PM
Wes,I was just saying that you can't Use someone elses Energy without Paying Now-a-days. So it is a Moot point.

Joel , let me repeat it for you also.

Joel
11-15-2007, 07:34 PM
Don't be a Dick head. :p

IOWOLF
11-15-2007, 07:53 PM
Don't be a Dick head. :p


Now That is original:rolleyes:

Can we move on to 2nd grade comebacks now?:p

bob_s
11-15-2007, 08:58 PM
Take a tour of some of the old coal mines in Southeast BC - Fort Steele comes to mind - compressed air powered locomotives abound.

wierdscience
11-15-2007, 09:54 PM
Sorry Evan.........that's not possible.......You can have a "gang of elk", but not hamsters. It would be a "horde of hamsters". Of course, if you wanted to use guinea pigs....you could have a "group of guinea pigs".........LOL


:D :D :D

I thought a hamster was a union guinea pig??:D

dicks42000
11-16-2007, 12:23 AM
Probably, we all could guess why air powered locomotives would be popular in coal mines. Think that mines needed a massive air supply for drills, jack legs, boring machines, etc. anyway...mine atmospheres were fairly hazardous to begin with due to methane and coal dust....It just makes sense.
Energy efficiency never really entered into it.
Porter, Ingersoll-Rand, even Hunslett made or at least played with pneumatic locomotives.

There used to be a Porter pneumatic loco on display at the museum at Kaslo BC. (One time mining town....).

Pneumatic and "fireless" steam locos were used where cleanliness or non-combustability was a requirement too. Places like munitions plants, typewriter factories (Yes, either Remington-Rand or IBM had one.)....

Air propulsion was practical in that instance for many of the reasons that can make hydrogen practical. It was a "byproduct" of a necessary or integral industrial process. It didn't require massive investment, tax subsidies, fraudulent claims, wishfull thinking etc. to make it profitable.

Rick

Duct Taper
11-16-2007, 11:55 AM
Thanks for the link, tattomike. I liked the version of the air engine developed by Angelo DiPietro that weighed only about 25 pounds, was small, and was very similar to the Wankel rotary engine. I could see this becoming a standard for in-factory or similar uses. If they could be cheap enough they could replace most vehicles in New Delhi, India where they have billions of three-wheeled jitneys that pump out unbelievable amounts of blue exhaust smoke. Not part of the Kyoto treaty of course.

But it is still too much to build at home I think.

Evan
11-16-2007, 12:10 PM
I don't think an air engine would be suitable even for transport in a factory floor situation. Electric is much better with far better range. You can't carry enough energy in a compressed air tank to go anywhere, even in a forklift at 10 mph. I seem to recall that the current record for the air car is a mile or so. That's barely enough to make a couple of trips back and forth in a large plant. It will never be cost effective for simple thermodynamic reasons.

It's really difficult to make people realize that just because we can envision something being done doesn't mean it is always practical, possible or worth doing.

Tuckerfan
11-17-2007, 12:05 AM
Ford and UCLA (http://pfdietz.blogspot.com/2005/10/more-on-compressed-air.html) are apparently doing research on the "air car," but that doesn't mean it's actually practical, or will ever see the light of day.

Apparently, the Aussies have golf carts that run on compressed air. (http://www.engineair.com.au/)
You can get plans to convert your car to air power. (http://www.fuellesspower.com/air2.htm)


And here's a bad scan (http://usera.imagecave.com/tuckerfan/O2engine.jpg) of a newspaper clipping on air powered engine for cars.

aostling
04-29-2008, 06:39 AM
Yesterday I saw this compressed air locomotive outside the mining museum in Bisbee, Arizona. The museum was closed so I got no details of the engine's operating pressure, or range. No doubt the riveted pressure vessel was a limitation, which modern welded construction could overcome.

Does anybody know what the strange-shaped car is, coupled to the locomotive?

http://i168.photobucket.com/albums/u183/aostling/IMG_0182.jpg

Alan Smith
04-29-2008, 06:54 AM
Looks like it might be a blower of some sort, maybe for ventilation purposes. It looks as if it might have an air motor to drive it also.

Swarf&Sparks
04-29-2008, 08:10 AM
Allan, what makes you think that rivetted joints are somehow inferior to welds?

Twas in fact "economic" measures that drove rivetting from shipyards and boilermaking.

Ask yourself why rivets are still used in light aircraft.

Evan
04-29-2008, 08:32 AM
The real limitation on pressure is the diameter of the pressure vessel. They would have done better to use several smaller diameter tanks. The amount of hoop stress in a pressure vessel is proportional to the diameter. That's why you see small air compressors with two small tanks instead of one larger. Pressure tanks with a diameter of less than 4" aren't regulated because they have a tight enough radius that it is unlikely they will fail catastrophically.

Swarf&Sparks
04-29-2008, 08:57 AM
Agreed Evan, that "hoop" stress is 2x longitudinal, but how the hell are you gonna construct that long storage vessel efficiently, and get around the curves in the mine railways of that era?
Bear in mind, also, that the early (safe) mine locos were stored steam.

aostling
04-29-2008, 09:42 AM
Allan, what makes you think that rivetted joints are somehow inferior to welds?


It's not that I thought the joints weren't strong. But unlike a continuous weld, I thought there might be leakage between the discrete rivets if the pressure exceeded a certain level.

But I guess this depends on the design -- perhaps the pressure increases the sealing force. Do riveted pressure vessels employ some sort of soft metal seal?

A.K. Boomer
04-29-2008, 09:56 AM
"Agreed Evan, that "hoop" stress is 2x longitudinal, but how the hell are you gonna construct that long storage vessel efficiently, and get around the curves in the mine railways of that era?
Bear in mind, also, that the early (safe) mine locos were stored steam."






They could be bundled, I guess it would depend on application whether the higher pressures would be worth the lesser volume (per same external area) and extra weight but im thinking in most cases it would be as Evan has stated hoop stress gets out of control in a hurry, It makes you wonder were the cut off ratio is, I mean where's the magic formula for getting the most work done --- smaller tanks can hold much higher pressure and can just use regulators --- again lots of variables ----- what about internal "bundleing" what about a larger tank with an internal honeycomb structure that helps support the outside?

oldtiffie
04-29-2008, 09:56 AM
All "prescribed" pressure vessels are regulated in OZ and must be designed and pressure tested in accordance with the "Pressure Vessels" Code. This includes but is not limited to: compressors, LPG fuel tanks (including "in car" ans BBQ), boilers etc. etc. and must be designed/certified by a Registered competent experienced professional ME. All must be re-tested at prescribed intervals - many but by no means all are re-tested every 10 years - many are less.

I had my LPG tank in my car done about 4 months ago as I had it for 10 years.

I have tossed out small BBQ type LPG tanks at 10 years as it was better to buy a new one.

Oxy, acet, argon etc. bottles in the shop are owned by the suppliers from whom I and everybody else rents them. The supplier is responsible for the periodic testing.

There is provision in the Code for riveted vessels but as said, most are welded.

Swarf&Sparks
04-29-2008, 10:02 AM
"I thought there might be leakage between the discrete rivets if the pressure exceeded a certain level."

Indeed, Allan, and in that lay their strength :)

Boilers, and ships, were "caulked" with a tool (air or hand) somewhat like a cold-chisel. This peened over the edge of the plates. As the ship and/or boiler aged, corrosion products actually improved the seal.

If you are interested in the subject, I can recommend the books of Prof J.E. Gordon: "The New Science of Strong Materials"
and "Structures"

Both still in print. I you are lucky, you may find them in the original Penguin editions at a secondhand book store or flea market.

interiorpainter
04-29-2008, 10:02 AM
From what i have heard.
City trips on compressed air.
Longer trip add a little gas during the process making even more gas.

The Swiss company already have got modular prototype engine ready.
Does not look like a hoax to me, the Swiss do not know how to.

Swarf&Sparks
04-29-2008, 10:04 AM
Ok, if you want really "efficient" pressure vessels, you'd use spheres :D

Don't mean to be facetious, but it just aint commercially viable.

A.K. Boomer
04-29-2008, 10:15 AM
Allan, what makes you think that rivetted joints are somehow inferior to welds?

Twas in fact "economic" measures that drove rivetting from shipyards and boilermaking.

Ask yourself why rivets are still used in light aircraft.




Actually I believe in such applications like tanks they are inferior to welds -- Rivets are in no way as sealed/strong/uniform or dependable --- they focus maximum strength on certain area's and leave weak "gaps" in others, They actually are inferior for both high pressure applications AND containment/sealing app's

Why rivets are still used on not only light but also commercial aircraft IS because its economic, to weld all the seams of aluminum on an aircraft would be both impractical and unsafe as it would suck the T rating from the material and also seal up any future repair options, most of the riveted panels cover up strategically placed systems underneath the skin, its common practice to gain access to just about anyplace on a craft by just simply drilling out the rivets and removing said panel, In doing this you keep the material strong and also dont have to discard entire assembly's if something goes awry underneath, aircraft construction and tanks are two totally different birds.

Swarf&Sparks
04-29-2008, 10:22 AM
Boomer, I can only refer you to the above J.E. Gordon volumes.

My dear old engineer mate from the Clyde is deceased, as is his BIL, who was a foundryman.

Foidermore, welded ships leak like sieves, unless caulked with polymers!

$$$$$

Evan
04-29-2008, 11:20 AM
The main reasons that aircraft are riveted are:

2000 and 7000 series aluminum isn't conventionally weldable.

A riveted aluminum structure has much better damping than a welded one.

The material properties are preserved.

It isn't practical to weld the types of structures used in monocoque construction aircraft even if it were possible.

It is far easier to repair.

Forrest Addy
04-29-2008, 12:01 PM
GETTING back to the OT - ahem - compressed air has some advantages if two conversion inefficiencies can be tolerated but not in a car requiring hundreds of miles in range requiring 2000 Kwhr of energy storage.

Aslo the air pressure will have to be in the thousands of PSI. Gas station air will not provide the energy density. You'l need air storge the size of a motor home. Nope air is even worse than gas as a prime mover in terms of energy but the real killer is the size of the "fuel" tank.

There's a big safety issue too. Imagine the hazard of high pressure air cylinders rupturing in a collision.

Is the noun of venery for linguists a "polyglot?" Machinists "curse?"

Swarf&Sparks
04-29-2008, 12:10 PM
I believe that what is now known as TIG welding, was developed during WWII, for aircraft monocoque welding. It was then "heliarc" and the aircraft had a very limited design life (slightly longer than the the guys that flew em).

The alloys used in those aircraft are beyond my ken, but I salute the guys that flew them and the people that kept them in the air.

interiorpainter
04-29-2008, 01:04 PM
You can use an airgun pump to get to 3000 psi without to much effort.
Volume can be fixed if you really want to.

Composite divetanks are around for years and are much safer than anything else.

Can anybody renew the link to the Swiss factory that makes one cylinder airmotors that can be linked to become a multi cylinder engine?
I was only kidding about the Swiss, BT can make me smile.