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Thread: Compressed air engine

  1. #1
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    Compressed air engine

    Hello to all,

    I just wanted to show a project I was proud of. It isn't quite a robot, but it does incorporate a Basic Stamp 2 and some solenoids!

    I did this project for my 5th year in high-school. The project was very lose on the subjects, so I decided to build a compressed air engine. This is only my first prototype and due to some $ limitations, I couldn't make it any better.

    The Objective of my project was to build a prototype of an engine that could replace a conventional combustion engine. Since the compressed air engine needs lot's of... You guessed it, compressed air, I figured I was better to plan for something like and 18 wheeler or a city bus since they have lot's of space.

    So the first step is to build air muscles. I used some 30 mm in diameter air muscles. These are roughly able to lift 150 pounds while contracting 27% of their length. To say the truth I kinda guesstimated the lift capacity because I didn't have a way to test the muscle with 150 pounds. I used the stats from Shadow Robot (http://www.shadowrobot.com/airmuscles/techspec.shtml).

    Here is my nicely done muscle 30mm (but it's less efficient) next to the mini-muscles :




    This was also more practical for all the calculations that I will show later.

    So I made a Basic Stamp 2 breadboard to control valves (http://forums.trossenrobotics.com/showthread.php?t=1250&highlight=solenoid+basic+sta mp&page=15 thread)



    This was a huge milestone for me, I, for the first time, managed to do something concrete with a micro-controller. Thanks to all of you! Wouldn't have been possible without you guys!

    Then I made the frame. I decided to make the frame a triangle since it can't move. For example, a square could become a parralelogram if you push hard enough. I used 6 * 24 inch metal sheets (2 inches * 24 inches * 1/8 inch). Used long screws with nuts to hold the double layer of metal and some big spacers and the corners of the triangles. These were used to hold the air muscles.

    Here is the image of the frame :



    Here is the image of the air muscle that is efficient on the frame : (although very ugly)



    So I put it all together. I used 1 second intervals to open the valves. So, the engine does 1 turn in three seconds, or 20 RPM. After calculating the torque, I figured out that the engine was producing a measly 0.15 horsepower! But after reading about the combustion engine, I learned that Enrico Bernardi (who built the first combustion engine) engine only produced 0.024 CV, so it's not that bad. My engine could produce a lot motor power, all I needed was better valve (that pass more air) because the ones I had took about 1 second to fill the artificial muscle. But those are about 500$...

    Here is a video.









    So the motor breaks down at the end because I used a metal piece that was too small. (won't make that error again!)

    Calculations :

    These are estimates made with the data I found.
    The green cylinders in the 3D models are compressed air reservoirs made of carbon fiber.

    I made three models :

    18 wheelers :

    I estimated with a 32 muscle motor :

    Amount of compressed air : 5200 liters.

    Adds a total of 850 kg to the 18 wheels.

    It can run over 300km and reduces the cost of fuel of 30% to 80% depending on the truck.






    City Bus :

    Amount of compressed air : 3300 liters.

    Adds a total of 500 kg to the bus, which is about the same weight as the hybrid buses in my city.

    It can run over 200km and reduces the cost of fuel of 65% to 75% depending on the conditions.






    UPS style truck:

    Amount of compressed air : 1800 liters.

    Doesn't add any weight.



    It can run over 200km and reduces the cost of fuel of 65% to 70% depending on the conditions.





    I gave in a 30 000 word "Rapport" explaining pretty much everything (the problem is it's in French.)

    What do you guys think?

    Sam
    Last edited by sam; 09-03-2009 at 08:59 PM.

  2. #2
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    Re: Compressed air engine

    They have air buses and taxis in Europe somewhere but using
    air turbines.
    http://www.mdi.lu/english/moteurs.php
    this mobs using cranks.
    If you put a quick release valve on the output air and another muscle opposite the first
    you end up with something like a double acting steam cylinder .
    means two valves per muscle but it works a lot better, more revs.
    Last edited by RevBryce; 09-03-2009 at 09:23 PM. Reason: typos
    Necessity is not the mother of invention.
    laziness is.

  3. #3

    Re: Compressed air engine

    Its a very interesting concept I saw mention of in a show on Disc, NatGeo or one of them not too long ago, It certainly peeked my curiosity very interesting to see it in practice! Where are you getting your compressed air? Cheapy air compressor?

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    Re: Compressed air engine

    There are several inventors around these parts claiming to have working vehicles. I haven't ever had a chance to dig into their shorts.

    You, however, get a +rep for posting a WORKING prototype that is open and very obviously visible without a bunch of black magic behind it. This is an outstanding high-school science faire-like project, and should have won Nationals here in the US with a proper write-up behind it.

    Kudos, continue your investigations! Big +Rep!
    I Void Warranties�

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    Re: Compressed air engine

    Great project. Keep up the work and keep posting.

    One question how do you power the compressor and does that count into HP rating of the engine?

  6. #6
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    Re: Compressed air engine

    If you power it off the wall and store it in a tank, you get to "ignore" the power requirements. Just like every other vehicle out there. If we counted that, every car in the world would have negative horsepower.
    I Void Warranties�

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    Re: Compressed air engine

    Yup that makes sense.
    "The green cylinders in the 3D models are compressed air reservoirs made of carbon fiber."
    Missed this on the first read thru. Thought it had on a onboard compressor constantly going.

  8. #8
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    Re: Compressed air engine

    I'm being a bit dodgey because this is a major hot-button topic for me. I believe that an awful lot of "alternative energy" pulls claims from its collective proverbial butt. To arrive at true energy density and efficiency we need to look at the number of conversions and the losses in each conversion. Unfortunately, the marketing departments override that and just run rampant.

    I think your question is absolutely valid, but I think it's beyond the scope of this project. It's an area of investigation that will require someone _not_ building an air engine to explore it and come up with the most efficient mechanism of getting there, then measure the cost of conversion vs density...

    That said, I love the "reduction to practice" that this project represents. It's not an idea, it's an idea that became a WORKING prototype. Gotta love that. If I ever find myself back in the financial position I'm used to, I'd fund this just on a flyer.
    I Void Warranties�

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    Re: Compressed air engine

    Quote Originally Posted by nagmier View Post
    Its a very interesting concept I saw mention of in a show on Disc, NatGeo or one of them not too long ago, It certainly peeked my curiosity very interesting to see it in practice! Where are you getting your compressed air? Cheapy air compressor?
    Sadly... No, I had to pump it by hand! lol

    The compressor I presented for the real world thing would be this monster :

    http://www.rixindustries.com/pdf/2DS%20Flier.pdf

    SPECIFICATIONS
    Horsepower Range: 500 BHP
    Pressure Range: 7500 PSIG (500 Bar)
    Displacement: 1200 CFM (2-3 Stage) or 600 CFM (4 Stage)
    Cylinders: 1 to 4 Stages, Diameters to 18”, Single or double-acting
    Stroke: 8 inches (203 mm)
    Speed: 200 – 510 RPM
    Typical Gases:
    Oxygen, Hydrogen,
    Argon, Nitrogen, Helium,
    Natural Gas, Breathing Air

    But, if I recall correctly, I needed to have an inlet pressure of 125 PSIG, so you would need a centrifugal compressor (low pressure but huge volume) to compress the air to 125 PSIG.

    Sam

  10. #10
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    Re: Compressed air engine

    Quote Originally Posted by Adrenalynn View Post
    There are several inventors around these parts claiming to have working vehicles. I haven't ever had a chance to dig into their shorts.

    You, however, get a +rep for posting a WORKING prototype that is open and very obviously visible without a bunch of black magic behind it. This is an outstanding high-school science faire-like project, and should have won Nationals here in the US with a proper write-up behind it.

    Kudos, continue your investigations! Big +Rep!
    Thanks a lot!

    Sadly I didn't go to my schoolboard's science fair (a pretty big one). I just completely forgot it existed. It kinda pisses me off because now I'm in college (only 5 years of high-year here), so I can't participate.

    I do have a full (very good) 4000 word document I wrote about all the project. It goes up to 12 000 with the annexes. I also have a 8 000 word documentation of my process and another 10 000 words of stuff I cut out because I had too many words.

    Now that it's been a few month that I haven't thought about the project (took me almost a whole year to complete it), I think that maybe I will make a second prototype that is faster and stronger... but it's still passing through my head, dunno if I should.


    Sam
    Last edited by sam; 09-04-2009 at 10:42 AM.

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