weed wacker engine running on air!!!!
 

ok so ii built a weedwacker engine that runs on compressed air yesterday, it runs ok but i have it set up so that the air comes in from the spark plug hole, so i am thinking that there is still compression resistance when the piston comes back up, therefor the piston is not reaching top dead center. it really shakes when its running so i am thinking that because the piston is not going all the way up that the engine is running back and fourth( left and right). anyone ever made one of these before? and suggestions on how to get the air out of the top of the piston when it comes back up?

Bobby

Re: weed wacker engine running on air!!!!
 

It's a 2 stroke engine, try blowing the air in where the carb would be and possibly the reeds will take care of it. I think you'll need pulses of air at an increasing rate to build up rpms. Running on gas this is how it works.

Re: weed wacker engine running on air!!!!
 

That probably will not work the way you want it to, engines do work by compressing an air/fuel mixture, but they rely on that air being heated by combustion at precisely the right time to push the piston back down, you might be able to figure out some way to inject the air just after TDC and that might work, but I don't think you are going to get the power output that you are expecting. Plus, your shop air is probably about 90 PSI, combustion pressures are much much higher, I'm not sure of the exact number, but figure a compression test on a typical engine is usually 150-200 PSI (and that is just the dead compression, not the pressure generated by the combustion).

Re: weed wacker engine running on air!!!!
 

the engine will idle well at 78 psi but if i go down to 75 it stalls out...but if i go up to 120 or 150 psi it does not idle up or anything i think that is due to the compression resistance problem i am having... they already have cars that run on compressed air over in europe... i am going to rebuild a briggs and straton 3-5 HP engine, make it run on air, and put it on a dirt bike for my senior project (we have to do that to graduate). but i have to mess around with the cam shaft so the intake valve will open on the down stroke and the exhaust valve will open on the up stroke, and also figure out how to keep like 300-400 psi into a tank.
i will try putting it on the carborator side and see what happens

Re: weed wacker engine running on air!!!!
 

If you do that with a four stroke engine, you'll need to open the exhaust valve at every stroke, otherwise the compression stroke will kill your power output. Finding a two cylinder and modifying it would probably work better...

Re: weed wacker engine running on air!!!!
 

i have to modify the cam shaft to make it essentially a 2 stroke, i have to make the intake valve open on the down stroke and the exhaust valve open on the up stroke....seems pretty simmple!!! SEEMS

Re: weed wacker engine running on air!!!!
 

You might try a rotary engine, I'd think one of those would work well on compressed air. If you look at most air tools, they use a rotary vane air motor... You might also be able to modify a turbocharger...