Kerzel's V2 CO2 engine

[kvom]

I have been trying to build a triple scale version of Dave Kerzel's 2-cylinder CO2 engine.  Here's an in-progress pic from a few weeks ago:



I think I may have run into some intractable laws of physics.  The picture shows my initial fitting with a 3/8" ball as the valve.  For reference, the base of the engine is ~2.5" wide, and the bore is 3/4".

With this size ball, the air pressure at 40 psi puts such force that I can't move the ball by turning the flywheel by hand.  So it became quickly evident that I would need a much smaller ball.  So after making 4 or 5 different valve seats I'm using a 3/32" ball.  At 25 psi I can lift the valve fairly easily by hand turning the flywheel, but the engine still doesn't run. 

So I need to experiment with how much lift is needed.  If there is too much lift then the ball rises too early in the cycle and the pressure kicks the piston back in the opposite direction.  Too little and there is not enough gas introduced to force the piston back around again.  I am also concerned whether there is enough space around the lift pin for enough air flow into the cylinder.  I might also need a very heavy flywheel to maintain the angular momentum.

If anyone has had experience with larger CO2 engines I'd be happy for their feedback.

I've enjoyed the machining part of building the pieces, but it gets frustrating solving the physics of scaling up.  Perhaps I've bitten off more than is chewable.

FWIW, materials are:  crankcase, cylinders and heads, crank are 6061 aluminum.  Pistons, valve seats, lift pins are 360 brass.  Crankshaft, crank pin, connecting rod, wrist pins are silver steel, flywheel is 3x1" 12L14 steel.

[vtsteam]

Seems silly to dredge up a post that's 5 years old, and one nobody ever answered. But this engine is so like one I started working on last summer, that I just had to bring it back for another look, and maybe more of a jaw session than it got when posted.

Now a CO2 engine is close kin to a steam engine, and compressed air engine. But maybe because the type wasn't familiar, no one answered?

This one seems to be a bash valve engine, and I also see what look like some tiny uniflow ports drilled low on the cylinders for exhaust. The twin I was working on was also supposed to valve with bash intake and uniflow exhaust. It isn't finished yet, so I can't say for sure whether it will have the same problems. But I can comment on the questions posed here -- from my own understanding.

The question about valve pressure has less to do with the size of the ball (I believe) than the size of the port. So changing the ball size -- I'm guessing -- really meant KVOM made a new valve altogether with a smaller port, as well as the ball. If not, then the crank pressure wouldn't have reduced much. I do think an engine like this one would need fairly high pressure to run, and definitely a good sized flywheel.

And I believe this engine needs to have extra clearance volume. If the volume is too small, yes, the valve opening early would stop the piston, and reducing the dwell would not provide enough gas to follow through. I'm guessing the clearance volume wasn't sufficient.

I think the uniflow ports look small, and that could also prevent cycling since not enough of the gas charge might hve been exhausted.

I do think this engine could have been run (maybe it was eventually) with modifications, so I hope it wasn't abandoned!

[SwarfnStuff]

I made a simple single cylinder one of these from looking at this web site.  http://www.animatedengines.com/
 You may find it worth a look as it covers various engine types with animated drawings.
I did get it running and it does need more air than my tiny compressor can supply. Still, I was happy as it was my first attempt at any engine. 
Regards,
John B