Wednesday, July 15, 2009

air powered bike update

This is a video of someone actually running an air powered trike.

But this video below shows more promise.

In this video he is sort of on the right track. Forget the selenoid at the top where the spark plug goes. They are only good for so many cycles and will wear out pretty quickly. Besides, the 4 stroke engine already has great valves in it. And he makes the intake and exhaust work together for air power by adding the lobes on the cam shaft. I can't see it getting more efficient than that. You just need a cheap air compressor and a scuba tank or better, a carbon fiber tank. I like the idea of using compressed air instead of batteries. And imagine doing conversions on cars. You take the camshafts out, add the lobes and grind them smooth. Take the gas tank out and replace with a 10,000 psi carbon fiber tank. Have a double reducer on that that goes down to 100 to 150 psi. You could fill up at a welding shop or at home if you have a high pressure compressor. And once you pressurize a tank, it doesn't lose its power like batteries do even just sitting there. Gas stations could start adding high pressure tanks and compressors so they could fill up the new vehicles.


  1. The reason he used a solenoid valve, and not the usual valves of a 4 stroke engine, is that they aren't meant to resist pressure in the manifold. Enough pressure in the manifold to get some real power out of the engine, and the valves will just lift off their seats. Just like the safety valve on your water heater...

    On the right sort of engine, you could flip the head on its side, with the manifold connecting to the cylinder, and feed your tank to the combustion chamber side. (just takes a couple of plates the same size as the head.

    You want an overhead cam engine, that doesn't displace or combine the ports excessively. Keeping the valve seats from just blowing out and getting oil to the cam bearings and followers is left as an exercise for the reader.

    Other things to think about if you want to do serious amounts of power - you will need a high volume of gas thru your regulator. High flow regulators are truly rare birds. If you want real range, you will need a multi stage engine, as you want to expand to as close to atmospheric pressure as you can. (look up triple expansion steam engines). Keeping things from icing up (you expand gas to cool it, its how refrigerators work) is another exercise for the reader.

  2. Not to be a pessimist, but more of a realist.
    Compressed air does seem like an ideal solution, but there are a few issues that make it not so ideal. The biggest is that compressed air is a bomb waiting to happen. The energy stored is proportional to the volume of the tank, and proportional to the SQUARE of the pressure. Assuming a 15gal tank, at 10K psi we have 3.9Mjoules. That's the equivalent of a kilogram of TNT, just waiting to go "BOOM".
    It's not a matter of 'if', it's a matter of WHEN.
    The next is that it is not very dense. That same tank above contains 1/30th the energy of a single gallon of gasoline, or 1/500th the energy of that same tank filled with gasoline. Granted, the gasoline engine and drive train waste 80% of that, but taking that into account and assuming 100% efficiency for the air engine, that still leaves gasoline 100 times more dense than air.
    On the plus side, you get free AC (just use the engine and other expansion components as heat sinks)

    TL;DR: I applaud your creativity and concern for the environment, and I encourage you to keep furthering the causes, but unless you come up with a truly groundbreaking development, don't expect any investors to come knock down your door.

  3. Good points, but the carbon fiber tanks don't explode. They can withstand a 357 magnum at point blank. Something could pierce it and make a hole, but it doesn't crack and fracture. So in a car wreck, you might have a hole with air loudly escaping. But in a normal gasoline powered car, a car wreck could yield gasoline pouring all over you and then igniting.

    I do agree about the energy density, though. There is just no beating gasoline. That is why "peak oil" is going to affect us much more than we hoped. There is no substitute for oil no matter how you slice it. All we can do is just be adaptive and make the best of things.

    TL and DR? Who is that?

  4. Guinevere, you are right. I forgot that the only thing keeping the valves shut is a spring. The more power you need, the stronger the spring would need to be. So, this second video might work for a bike, but nothing larger. You bring up some good points about what needs to happen for more power. I wonder if someone could make a "poor man's" high volume regulator? :)

  5. This is a fantastic idea! Air tanks are easy enough to source and I can think of all sorts of emergency power situations for these things. I have two dead weed whacker engines just begging for a conversion!

    To chip in my 2 bits, I don't see how excessive air pressure could cause a valve to blow open in a conventional 4 stroke, there is no risk of them popping open under the normal explosive forces of conventional combustion. In the same way that airliner doors open inwards so they form a "plug" that seals the door closed when the cabin is pressurised, the valves are seated so that the high pressures of the compression/ignition strokes work to seal the inlet and exhaust valve even more tightly into their seats, thus creating a tighter still seal. In the same way, compressed air pumped into the cylinder would push the valves shut. The springs on the valves are to firmly and quickly reset the valves in time for the next compression/ignition stroke, the forces in the cylinder and head do the rest.

    Thanks for the post!