Reducing power is what you think the problem is?

Spark ignition engines aren't efficient at part throttle either.

And the Swedes drive their Gotland-class subs with -- certainly must have a throttle.

Think of it as a closed loop. Inside the large glass bulb in a smaller bulb that moves back and forth to close off the glass chamber between the two glass bulbs. When the air inside the glass bulb becomes hot it pushes the smaller glass bulb inward while the air inside is expending due to heat and rushing out of the chamber as it closes. Then the hot air flows to the cold piston where the hot air will first push the piston out. When the air inside the cylinder cools it contracts pulling the cylinder back in and the same air goes back to the bulb pushing it open for the cold air to enter the chamber and repeat.

The engine can use any heat source.... just got to get it under/around the glass bulb.

You Tube has plenty

But it costs toooooooo much

Just by pinching off the connection between the displacer and the working cylinder. You could basically build in something like that on any stirling engine, wether it is a ringbom engine (like this one) or not.

They're handy for driving generators. I've seen some people use them to charge their phones

They used them during the war to run radii generators be dam if I can fine one on line. Or in england they use them to drive mine water pumps.

OMG !!!! DRY UP !

Cope

Objection noted and promptly discarded.

What about dildos?

One can anthropomorphize ANYTHING! Sheesh! Even a rock!