Kerzel's V2 CO2 engine

[stevehuckss396]

How high is the ball being lifted off the seat? At one to one scale the ball is lifted .010. At 3X I think I would start with .025 and maybe decrease it some depending on if it seems to want to go. The fact that it seems to be kicking back and locking up would make me check the lift.

 

[kvom]

I bought a height gauge recently on eBay. When it arrives I'll try to get a good measurement.

 

[kvom]

I decided to use my smallest ball (3/16") to reduce the amount of force needed to lift the ball.. Since I needed to bore the other cylinder and make a new piston to fit, I did that today. I also made a new valve seat to fit the smaller ball. Testing with the head I get a good seal, so once I get the new piston lapped in I can try it. out. I will need to turn a smaller lift pin in order to leave room for the gas to enter the cylinder.

 

[kvom]

I assembled the cylinder, head, valve seat, and small ball today. The assembly is airtight but still doesn't run. However, I haven't tweeked the lift yet. I did get my height gauge, but the top of the ball is below the level of the valve seat, so measuring the total lift is a challenge I haven't solved.

I was getting some binding between the piston rod and the crank pin, as my crankshaft bushings weren't absolutely straight. So I turned, drilled, and reamed a 1-piece bushing from some brass rod to get a tight press fit with the crankcase. That certainly loosened up the mechanism. It appears to me that any tightness anywhere will inhibit the engine from running.

The entire process is challenging, but frustrating as well.

Tomorrow I'm on an all day trip to help a friend pick up a Bridgeport mill he found in NC.

 

[ksouers]

However, I haven't tweeked the lift yet. I did get my height gauge, but the top of the ball is below the level of the valve seat, so measuring the total lift is a challenge I haven't solved.

How bout a dial indicator?

 

[kvom]

I am going to abandon his project for at least the time being, as I suspect the physics may be against me.

I did find a way to measure the lift and it was .045. With some filing on the pin I reduced it to .02, but no improvement. Even at 80 psi there does not seem to be enough force on the piston to complete a revolution. It might work with a much more massive flywheel and higher pressure still, but I have reached my frustration level for the moment.

 

[vlmarshall]

Do you think that testing with CO2 instead of air would help? Perhaps CO2's continuous expansion from liquid to gas as it warms would help your engine get over the 'hump'.

Just a thought. Great build so far, I hate to see ya quit. :-\

 

[kvom]

Here are the issues as I see them:

1) The ball has to be small, otherwise the pressure acting on it will be too great for the pin to lift

2) If the ball is small, the the inlet hole is also small, limiting the input gas flow into the chamber.

3) The lift has to be small. If it's too high then the gas enters to early in the cycle and kicks the piston opposite the way it needs to go. But when it's low then issues 1 and 2 come into play.

The 3x scaling problems are these:

1) The chamber diameter is now 3**3 larger, or 27 times the volume of the original scale. That means 27x more gas needs to enter to result in the same pressure.

2) If I could scale up the ball and hole 3x then it would allow 8x the flow. But I would also have 8x the force acting on the ball.

3) The mass of the piston/crank assembly is also 27x the original, meaning the for a given pressure in the chamber I would have a smaller velocity.

The only "solution" that would seem to have a chance is to have an extremely heavy flywheel whose momentum could carry the cycle around, and the pressure would likely need to be quite high as well.

I have a pretty heavy round piece of steel that I could use to try it at some point, but the esthetics of the engine would be poor.

 

[radfordc]

In the past I constructed a 2X version of Kerzel's Mini V1. It never has run well....I think I know why now.

Charlie