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  • Compressed air motor

    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.

  • #2
    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.
    Brett Jones...

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    • #3
      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
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        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
        Nick

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        • #5
          If you're talking about this car, 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.

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          • #6
            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.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              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.

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              • #8
                Originally posted by Evan
                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 ,,, 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...

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                • #9
                  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.
                  Excuse me, I farted.

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                  • #10
                    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.
                    Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                    ~Practitioner of the Electromechanical Arts~

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                    • #11
                      Wes...

                      Now that's a idea.. using someone elses energy.. ha..
                      Excuse me, I farted.

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                      • #12
                        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.

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                        • #13
                          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.
                          It's only ink and paper

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                          • #14
                            Originally posted by Carld
                            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.
                            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."
                            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                            ~Practitioner of the Electromechanical Arts~

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                            • #15
                              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......

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