Stirlingengineforum.com

The first is a question. I've seen that most Stirling engines out there use a fairly small chamber, which is heated to drive the piston with expanding hot air.
Why not add a long, thin pipe to the cylinder and heat that, instead. For instance, a thin pipe could be bent back and forth to fit inside a rocket stove, going down the chimney, back up after the bend, then back down, ect... Like a radiator. Seems like the whole radiator would get even heating from the fire. That pipe would be capped at one end and the other end would be tapped into the cylinder. Seems like a greater volume of air would be heated that way. Wouldn't more hot air cause more pressure/power?
For solar, a long, thin pipe in a solar trough, say, 6 feet long. One end is capped and the other end is tapped into the cylinder. The entire 6 feet of pipe would be heated evenly. Wouldn't that extra volume of heated air cause more power to the cylinder?

Or am I wrong about a larger volume of heated air adding more power?

Next question. Would it be possible to inject a small amount of water mist directly into the heated cylinder? Wouldn't that mist immediately turn to steam, hugely increasing the pressure? I'm not talking about a lot of water from a boiler. Just a light burst of mist that should immediately turn to steam, expanding , and driving the piston. No boiler. Just a mist injector tapped into the heat chamber. For safely, pressure plugs and multiple safety valves could be used. Also, the injector could be automated so as to inject only when the pressure is at or below a set level, reducing the risk of a blowout due to build up of too high a pressure. I realize this is more complicated than the home builder might be comfortable with, but there are commercial builders of Stirling engines. They could work it out.

Next question. Is a standard flywheel the best way to convert a Stirling's piston power to electricity? What if you put a magnet on the end of the piston, then drove that through a coil? That would also produce electricity. Or, use a stationary magnet to repel against the magnet on the piston? The stationary magnet would act as a stop for the piston. If coils were placed around the stationary magnet, they would produce electricity each time the stationary magnet's field got warped by the approaching magnet on the end of the piston.
If you look up the "Gap" motor on YouTube, you will see magnetic neutralization in action. It requires an input of electricity to neutralize the stationary magnet's repulsion, allowing an opposing magnet to approach it without the repelling effect. When the power is cut off, the magnets repel one another again, shooting the magnet that just approached away again. Adding this technique would give power to the back stroke of the piston. Seems like a perfect fit for a Stirling engine.

Third is a suggestion. You need heat on one side to drive the cylinder, cold on the other. Why not use ammonia as the working liquid so you can run the absorbsion cycle in a closed loop. The ammonia would be heated in the chamber, causing it to expand as it turns to a gas. The gas is exhausted to the cool side, where it condenses back to liquid. The gas condensing back to liquid will cause the area to become cold. So, the absorbsion cycle would power the motor as it is heated to a gas and it would also provide the cooling for the cold side, after which the liquid would be returned to be heated once more.
Maybe that could be worked into a closed loop system, maybe it can't. At the very least, an absorbsion cycle should be used to on the cool side, since waste heat will be available anyway. The absorbsion cycle could be run off that waste heat.

Fourth is also a suggestion. If running the Stirling in an area with winter conditions (freezing) use antifreeze, left outside overnight, to cool the cold side. A Stirling shouldn't be able to heat the antifreeze too much if the container holds enough and the outside temperature is freezing.


I'm no expert on Stirling engines. I study them because they're capable of running on a lot of different renewable fuels. They might become an important part of our lives in the future. I'm not saying I'm right about my suggestions, so feel free to respond honestly without regard for my feelings. I'm here to learn.

Nice to be here, btw. Lots to learn about these cool machines.

Mangyhyena, Q 1, some engines use a system of a large number of reletivly short narrow bore tubes, but the free space/ dead space must be kept to a minimum, your idea is not quite on target, but heading the right way.
Q2Forget it, you would have steam at the hot end, but condensate at the cold end. Its no stirling/ hot air cycle.
Q3No a flywheel is not essential, the free piston motor works quite well, I am rebuilding my one, its a GAMMA motor and uses a mechanical spring for the displacer, and a magnetic spring for the power piston(2 like poles) the moving magnet passes through a coil system. I have a number of other motors driving generators, or a water pump, or a power hacksaw with a junior hacksaw blade.
Q4You can try any sort of cooling you like, but its best to keep it simple(KIS, some add another S)stick to water cooling, yes you can add antifreeze if you wish, or go for air cooling, it can work quite well. With water, if it leaks, no problem. Can be a bit of a bother with other chemicals if it leaks.
The first thing I would suggest to someone wanting to study Stirling Engines, is to build a simple motor to a proven design, it can be one built with the use of a lathe, and use stainless steel for the hot cap and displacer, or it may be one of the tin can designs. Important, get the ratio of sizes correct, and use good design, to keep friction, leaks, and dead space to a minimum. Keep asking, Ian S C

Thank you, Ian.

The dead space is the air in the center of the pipe, the air not touching the inner walls of the pipe? Is that why I see people putting steel wool inside the chamber, trying to get more surface area for heating?

Would the steel wool work inside that pipe/radiator in the rocket stove to reduce dead air space? The idea to heat the air that drives the piston from outside the piston is not without precedent. Steam engines run off a boiler, not water heated inside the cylinder. Was just wondering if the same could be done with air.

Spaced washers might work in place of the steel wool inside a pipe, if the pipe is attached to the cylinder and heated evenly. Will have to try it out when I get a motor going.

A simple Stirling I build is coming soon. I'll have plenty of questions along the way, I'm sure, and I'll be asking in here.

Thanks again.

What I got from the video on the Gap motor was it is just a linear electric motor.You cant disconect it from its power source and reb it up to produce more electricity.If I missed that part you wouldnt need a stirling engine.The Gap motor could stand alone and run any appliance by its self.

He's claiming over unity for the GAP motor. However, my question is how much of its own energy is used to keep itself running. If he's got only enough extra to run a single lightbulb, it will have to be upscaled quite a bit, adding to the production cost quite a bit. And that is if he's correct about his claim of over unity.

I was just curious about his technique added to the Stirling cycle.

The Stirling seems well suited to recharging small electronic devices, but unless a way to get more power to the motor is found, TEG technology might be the best solution for users at the home level. That's why I asked about heating the air in an external radiator.