Stirlingengineforum.com

I have made a few duct tape tin can style toys but am looking to make my first real engine/generator. I have access to a decent machine shop and the skills to use it.

I have a small concentrated solar setup that puts out around 200 Wth at around 200 degrees C. I am looking to make a small engine/generator to harvest some electrical power during the transfer from the hot collector to a radiator inside during winter. Minimally, this will power a pump for the water lines and ideally would be enough to store something usable as a backup trickle charge for a battery bank etc.

Right now, I am thinking a free piston beta style is best suited. The geometry fits nicely into my space and is easy to machine with the tools I have. It is also a simple design without lots of linkages to build and maintain. It seems like most of the commercial generators and cryocoolers use this geometry correct? In the end I would like to couple this to a linear alternator; again, this seems to be the norm on commercial units of this type. I am open to arguments against this design.

Mostly, I am looking for a good 'cheat sheet' or FAQ for design dimensions like displacer size, power piston size, compression ratio, delta T, expected power output etc. I'm sure these have been answered somewhere but all I am finding are bits and pieces buried about.

Can't help with figures, I have a free piston Gamma motor with a linear alternator, it's built to the normal ratio for a high temp Stirling Engine of 1.5 : 1, but I think the power piston diameter could do with changing, I think a larger bore/shorter stroke would help to increase the frequency, at the moment it is below 1000/per minute, I would like 3000/per min. It has a bore of 1 1/4" dia. Heated with LPG. Electrical out put, about 1 Watt max, it will run a little transistor radio.
The power piston is sprung against the like poles of two magnets (magnets salvaged from an old Microwave Oven). The displacer is operated the same as in a Ringbom Motor with a fat rod through the gland in the cold end.
Ian S C

Ian S C wrote:...the normal ratio for a high temp Stirling Engine of 1.5 : 1, ...

You are referring to the swept volume of the displacer being 1.5 times the swept volume of the power piston correct?

This is exactly the type of number I am looking for. I understand the fundamental concepts of Stirlings fine, but if there was a quick list of these 'normal' ratios and values that would make a great sticky for this forum...

You bring up another good point. What is the ideal frequency? How does performance change with frequency within the bounds of physical engineering. Say, the difference between 100 Hz and 1000 Hz.

I don't think there is much change in the power of the motor with the change of design frequency, the reason for the wanted increase is for easier, and more efficient rectification to smooth DC current.
The only other formula that I use is the dimention/ shape of the displacer. The length should be about 3 times the diameter. The ones that are a guess are (1) the diameter of the rod for the displacer of a Ringbom motor. (2) the hight to diameter ratio for the Heylandt Crown for the hot piston of an ALPHA motor.
Ian S C