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David Kerzel,     Pompano Beach, Florida     david@FloridaAME.org

Vertical CO2 type compressed air engine  First posted 8/10/2003

This engine started as a personal challenge to see if I could make smaller parts. It started one day when I had been thinking about the little engine Steve Peirce has been building, like his Liberty.  I started to sketch a piston and connecting rod.  The parts were slightly smaller than any I had made before but they would need to be very accurate for the engine to actually run.  I made the parts the next weekend, they came together quickly  and I was amazed at how accurate they were.  Steve had commented about how quickly these engines go together, but I had been skeptical. 

 

During the next week I started plans for a engine that would use my piston and rod.  The sizes were good enough and the engine was planned .25 inch bore X .25 inch stroke.  The crankcase will be made from 1/2 X 1/2 the engine will be 1 3/8 high and have a 1 inch flywheel.  The design had 3.5 to 1 Compression, but previous CO2 engines all seem to run at half the calculated value.  When the piston moves up it compresses the air in the cylinder, If that pressure is more than the supply air pressure the ball opens and the engine pumps out air and does not run.  When the pin opens the valve the higher pressure air pushes the piston down on the next stroke.  The more the piston / cylinder leak the lower the operating pressure and efficiency.

The engine did not run reliably on the first try, then I realized the space above the ball was to large and the air flow could  hold the ball in the open position.  I quick fix with a drop of epoxy and the engine now just runs.  It favors one direction but runs in either.  It will run at pressures of over 24 PSI and hums at 40 PSI.  Air consumption is very small.

The project went very fast, less than 20 hours to build it and about 8 hours to draw the plans.
It is a quick build and defiantly sharpens accuracy and machining skills. Being a compressed air engine it just starts and runs with no fuss. This type of engine has a lot of fun easy possibilities for modifications and more complex designs. 

The free plans can be found by clicking Mini_V1 Plans.  The plans are accurate, but I would recommend using them as a staring point for your own ideas.  The cylinder looks long,  the head could be screwed to the cylinder, it could have multiple cylinders. it could.....

     

Copyright 2003,  Florida Association of Model Engineers and engine builder as noted above, All rights reserved.