Oscillating engine designing questions

[Alex]

Hello every one!

I've been away from this forum too long and thought it would be time for a comeback.
Still looking at different engine designs and no complete engine yet, just various parts laying around. Among them a cylinder I made some months ago. Can't remember which ozzy it belongs to so I thought that it might be possible to sort out the rest of the parts on my own.

So, to my questions; does it matter how close the piston goes from the cylinder top when at top dead center and how does the stroke affect the running?

Maybe this has been asked before and if so please forgive me.


/Alex

 

[Brian Rupnow]

On an oscillating engine, where the ports come thru the side of the cylinder, as in the model I have shown, the piston must not go up past the "port", otherwise no air or steam will be able to enter the cylinder.---Brian

 

[stevehuckss396]

On an oscillating engine, where the ports come thru the side of the cylinder, as in the model I have shown, the piston must not go up past the "port", otherwise no air or steam will be able to enter the cylinder.

I'm not sure it matters. When the piston is at top dead center the cylinder is centered between the ports and no air will flow anyway. I would think that as long as the piston is out of the way when the port is uncovered things would be fine.

Does this sound OK? or am I thinking wrong?

 

[Brian Rupnow]

This is the same engine with the piston at "Top Dead Center". You can see that half of the port is still exposed. If the piston or connecting rod is designed so that the piston totally occludes the port, (by coming too close to the end of the cylinder) then no pressure can get into the cylinder to force the piston down.

 

[stevehuckss396]

All of the wobblers i have built would have the port centered at top dead center and nothing would flow. With this design it would'nt matter. With your design it does matter.

I would like to change my reply to

Maybe depending on the port configuation.

 

[NickG]

If the piston goes right past the port though, it will be trying to compress any air above the port so it'd be a bad design. On my designs I do it so it comes level with the bottom of the port. Steve is right though at TDC the cylinder port is bang in the middle of the inlet and exhaust, as soon as it moves past TDC it should start to overlap with the inlet port. That is the ideal situation, this sort of engine will tolerate a bit either way as long as it's not too bad!