Trying a Stirling

[dgjessing]

Well to follow up, I must say I'm kinda disappointed that I can't get it to run on a flame in a cup, but I've come to grips with that. Someday, I want to do another one that will run on a candle flame ;D

Anyway, this afternoon I made a new power piston for it, a couple of thousandths bigger, and that makes a huge difference - a whole lot less blow-by and no need for a big dollop of oil on top of the piston. With the new piston I can run it for 10 minutes or so before the entire thing gets really hot and it coasts to a stop. I think it could run forever but I don't have the patience to stand there blowing compressed air on the cold end's cooling fins (which extends the 10 minutes).

So what I've learned:

- "They" ain't kidding about keeping the friction down to a minimum; not a lot of power here, every little bit helps.

- The scotch yoke thing is probably a mistake, unless it's done with great precision (which mine ain't). Too much friction, too much bangin' around.

- This engine runs best when the "cold end" is a lot hotter than I expected would be good. If my HF non-contact thermometer is to be trusted, the best performance is achieved when the cold end is roughly 170 f and the hot end is about 400 f.

 

[Chaffe]

another way to extract the most power i found is by adjusting the piston to displacer timing, prehaps a consideration when building another engine to make this a controllable peramiter, good work with your completed model though.

 

[NickG]

Never played with the timing on a stirling but guess the easiest way would be to just have the two cylinders run off seperate cranks.

I set out to make mine run on a candle too but you need something with a much bigger displacer if you want that. Look at the LTD ones - larger ratio of swept volumes from displacer to power piston.

Nick

 

[Chaffe]

Never played with the timing on a stirling

see my picture at the top of the post mate, timing is controlled by two crank discs, it wont run AT ALL if it is minutly out

 

[NickG]

What is the timing set at though? 90 Deg apart? Presumably it will run at that as that is the whole point of a gamma type stirling like the one in this thread. The power and displacement cylinder centrelines are 90 deg apart running off a common crank giving you the 90 degree phase difference.

I can imagine 90 deg isn't the optimum for every engine but I would have thought most engines would work reasonably well at that angle.

Nick

 

[Chaffe]

What is the timing set at though? 90 Deg apart? Presumably it will run at that as that is the whole point of a gamma type stirling like the one in this thread. The power and displacement cylinder centrelines are 90 deg apart running off a common crank giving you the 90 degree phase difference.

I can imagine 90 deg isn't the optimum for every engine but I would have thought most engines would work reasonably well at that angle.

Nick

You set the timing to the optimum setting by adjusting until it runs best. There is no way of saying what is the exact angle as the whole physics of the engine would vary the timing. Its similar to a four stroke engine, in theory the exaust valve and inlet valve should never be open at the smae time, but after experimentation it has been proven that overlap needs to occur for best performance.