So I've recently stumbled upon the discovery of Stirling Engines & wanted to try my hand at building some myself. I didn't want to buy a pre-made model of one as those aren't much more than desk ornaments. Ideally I hope to build a few relatively large engines to do a few tasks. One to run a cars alternator to charge up a bank of deep cycle batteries & a second to perform physical work via adapter pulleys hooked up to various power tools such as saws, sanders, mixers, or anything else that requires some spinning force to get it to function.
All that aside, I have questions about the first S.E. that I hope to make.
I picked up two identical bicycle air pumps with the handle on top and the little plastic extensions that you stand on while pumping it so it doesn't fall over. The main metal tube of each is roughly 17 inches long & they are 1.5 inches wide. I hope to use these as the pistons as I do not have access to a lathe, mill, or welder to fabricate those parts & figured that they are already sealed for pressurized air & have the ability to extend/contract. Does anyone see a reason why these wouldn't work as the power piston & displacer?
So both handles will attach to the flywheel & might use the existing rubber tube on the power piston to connect the airflow from one to the other (something tells me i may need to replace this with a copper/metal tube due to the high temps.) The pumps have 15 inches of 'extension' from their TDC to BDC if that makes any difference.
I don't think I will need to mod the power piston really at all but the displacer i plan on removing the plastic wings on the bottom & get a metal tube the same diameter to attach to the bottom & be the part that the heat source heats up as the internal components are probably plastic & i'm afraid they would melt if directly over the fire of the heat source. As these are air tight i'll have to remove some of the 'ring'? that makes the seal as I know the air needs to move around the displacer piston.
So i've seen some videos of people using rolled up steel wool as displacer pistons so i ask would that work in my application or do i need to make a displacer piston that is hollow on the inside but sealed as to take up as much space as possible inside the piston chambers as there's already 34 cubic inches of air to be moved back & forth between the two cylinder chambers?
I figure i'll need at least 6 inches for the 'burn tube' & will probably use high temp silicone to seal it to the displacer tube. Is there any benefit to using a longer tube vs as short of one possible without burning the parts that may be inside the bike pump?
Will a short tube work or do i need to match the 15 inches of extension that is already present in the pumps? I'm trying to wrap my head around the relation of the displacer size to the total C.I. of the two cylinder chambers combined.
Thanks in advance for any wisdom/input you all may have.
Well hello there Stirling engine makers.
Well hello there Stirling engine makers.
Last edited by Pappy on Mon Jul 29, 2024 2:17 pm, edited 1 time in total.
Re: Well hello there Stirling engine makers.
https://external-content.duckduckgo.com ... ipo=images
These are the pumps I am using. They are a thin metal that i assume is either tin or steel.
These are the pumps I am using. They are a thin metal that i assume is either tin or steel.
Re: Well hello there Stirling engine makers.
First question has got to be which style of Stirling do you plan to make? (Alpha, Beta or Gamma)
Then, what's your heat source, and/or cooling mechanism?
Then, what's your heat source, and/or cooling mechanism?
Re: Well hello there Stirling engine makers.
It seems like any type of tube can be made into a Stirling Engine. Some things that might help are:
Build the displacer chamber first. Operate by hand to see how much pressure it develops. Watch out for leaks, especially in the pushrod to cylinder cap seal. Tire pumps are designed to be very leaky in that area. Some have holes in the cap to let air in. A good seal in that area, called a gland, is very long and tight fitting while avoiding friction. The smaller the push rod and hole the less leakage. The longer the hole, and gland, the better the seal and higher the friction. Compromise, guessing and testing, are helpful.
A leak test can be done in a bathtub by pressurizing it with the other pump, if needed.
Long skinny displacers are better with high temperatures. Pancake displacer chambers are better for low temperatures. You will be building a long skinny one. Higher temperature materials will be appropriate, such as steel, stainless steel for the hot areas. Not aluminum, solder, or plastics. But you know that. Think, red hot. Welding may be necessary. I don't know if those pumps can be welded.
The displacer can be completely a regenerator, and out of stainless steel wool. It can also be a tight fitting smaller tube, with the regenerator held internally. It may need an internal roller to prevent dragging. The regenerator can also be fixed to the cylinder with a second cylinder inside for the displacer, or external and separate to the whole cylinder. Remember if it is on, or in, the displacer it will have a large shaking force at high speeds. Experiment with and without a regenerator, see what gives more kick?
The bottom of the pump has a one way valve in it and must be removed on both pumps. I assume you know that too.
The piston in a Stirling is bidirectional. The tire pumps are one way. You might be able to disassemble them both and combine them. They tend to be higher friction and need some sort of lubricant. Silicone? Experiment with others seals if necessary. Good luck with that. I would need to experiment there. The displacer should be dry, except maybe a little lube on the gland. Lubricant adds viscosity friction but helps seal.
Connect it to the displacer chamber with as short a tube as practical. I've had difficulty finding fittings for those sizes. If you find a link let me know. Otherwise you can make some with skinny tubes and solder. Maybe nuts and bolts and a drill and glue.
Operate the displacer by hand to see what kind of travel you will get. Experiment with stroke and crankshaft after that. This will allow you to build test and debug each part individually.
Leaks on the piston pushrod and cap are not important. Friction is. If the stoke is long and connecting rod short, there will be more friction at mid stroke.
You probably won't pressurize this engine but, if you do, a bigger flywheel will be needed.
Hope this gets started.
Build the displacer chamber first. Operate by hand to see how much pressure it develops. Watch out for leaks, especially in the pushrod to cylinder cap seal. Tire pumps are designed to be very leaky in that area. Some have holes in the cap to let air in. A good seal in that area, called a gland, is very long and tight fitting while avoiding friction. The smaller the push rod and hole the less leakage. The longer the hole, and gland, the better the seal and higher the friction. Compromise, guessing and testing, are helpful.
A leak test can be done in a bathtub by pressurizing it with the other pump, if needed.
Long skinny displacers are better with high temperatures. Pancake displacer chambers are better for low temperatures. You will be building a long skinny one. Higher temperature materials will be appropriate, such as steel, stainless steel for the hot areas. Not aluminum, solder, or plastics. But you know that. Think, red hot. Welding may be necessary. I don't know if those pumps can be welded.
The displacer can be completely a regenerator, and out of stainless steel wool. It can also be a tight fitting smaller tube, with the regenerator held internally. It may need an internal roller to prevent dragging. The regenerator can also be fixed to the cylinder with a second cylinder inside for the displacer, or external and separate to the whole cylinder. Remember if it is on, or in, the displacer it will have a large shaking force at high speeds. Experiment with and without a regenerator, see what gives more kick?
The bottom of the pump has a one way valve in it and must be removed on both pumps. I assume you know that too.
The piston in a Stirling is bidirectional. The tire pumps are one way. You might be able to disassemble them both and combine them. They tend to be higher friction and need some sort of lubricant. Silicone? Experiment with others seals if necessary. Good luck with that. I would need to experiment there. The displacer should be dry, except maybe a little lube on the gland. Lubricant adds viscosity friction but helps seal.
Connect it to the displacer chamber with as short a tube as practical. I've had difficulty finding fittings for those sizes. If you find a link let me know. Otherwise you can make some with skinny tubes and solder. Maybe nuts and bolts and a drill and glue.
Operate the displacer by hand to see what kind of travel you will get. Experiment with stroke and crankshaft after that. This will allow you to build test and debug each part individually.
Leaks on the piston pushrod and cap are not important. Friction is. If the stoke is long and connecting rod short, there will be more friction at mid stroke.
You probably won't pressurize this engine but, if you do, a bigger flywheel will be needed.
Hope this gets started.
Re: Well hello there Stirling engine makers.
I would recommend starting with a tin can engine first. The Jim Larson book 'Eleven Stirling Engine Projects You Can Build' would be a great place to start.
After building one or two you might have a totally different approach for a more advanced model.
After building one or two you might have a totally different approach for a more advanced model.
Re: Well hello there Stirling engine makers.
I guess I should have specified that this is for an Alpha Style S.E.
As for a heat source i'll have different sources depending on which S.E. i'm using & as this project evolves. I didn't want to bore anyone with the details so omitted that before. So i'll probably build a rocket stove for the first heat source or basically just have something to direct the heat of a small camp fire to the S.E. Eventually plan on building a "wood gasifier" to replace it in time as they pull more energy out of the firewood/are more efficient. Also during the hot summer months plan on fabricating some form of solar oven to be a free heat source but all that's WAY down the road. But the man fuel source will be firewood.
As for cooling, nothing at first but again this is to be an evolving project.
If it is required i planned on taking metal strips & affix them longways on the OUTSIDE of the power piston spaced at 45-degree intervals so they can act the same way the cooling fins on an air cooled motorcycle engine works. If further cooling is needed, another plate across the top two & sealing off both ends. This will make a channel that coolant can flow through & I have a small heat exchanger taken out of a trucks A/C unit that can be used for this. Was thinking adding fan blades to the flywheel to force air over this heat exchanger/radiator looking thing.
I live in a camper in a remote/rural area so access to things people often view as 'normal' are not options to me (just wanted to clarify that)
I have half an acre of land so if the engine/engines are unusually large that is of no concern as the wood pile to fuel it will end up being large as well.
Having limited fabrication methods I was hoping to use things that are 1-cheap & 2-already (to an extent) built for the application at hand. Figured these pumps fit that bill well.
Somebody mentioned fittings for unusual sizes of pipes. There are 304 food grade stainless steel tubings that one can order on Amazon that are 'normally' used in the brewing industry. Having worked in that industry they can handle 50-PSI no problem & have 'tri-clamp' fittings that have gaskets to connect them to each other to allow for custom applications. (make them whatever shape you may need such as going around a corner or whatnot) These gaskets aren't made for red hot temps but can/do withstand boiling temps on the regular.
As for a flywheel I basically have two options. The first one being a simple bicycle tire or if that isn't going to be heavy enough I planned on using an old brake rotor from a car. (because these are what I have or can get for free)
Pardon me for not having a picture or a nice diagram but to explain what I have in mind is the two pumps parallel to each other laid down sideways with their hand pumps connected to the flywheel that sits inbetween them. The displacer tube being a bit longer than the other for having a "burn tube" attached to it & have a somewhat small diameter tube connecting an air passage between the two bike pumps. A small rocket stove to sit underneath the burn tube.
Once I have it to the point of where it is built and running somewhat reliably, I have the old timing chains & 2 matching sprockets from an old Ford Triton motor. Figured I could attach one sprocket to the flywheel & use it to power something or I might hold off on these for a larger engine. This first engine I will be more than happy if it can via the right size pulleys, spin a cars alternator to charge a battery bank using firewood.
Eventually I'd like to build something on the level of this engine here.
https://2.bp.blogspot.com/_4SFgj1O1Abs/ ... G_4962.JPG
Given this picture is of a 1/4 scale version but the original I think was Stirlings 4th engine and had like 45-HP & was used to power a plant of some kind for 3 or 4 years until somebody overheated part of it & they replaced it with something else.
The walking beams and the dual action power piston on it are beyond my fabrication ability/budget right now but I guess one could say that my end goal is to build an engine capable of replacing a gasoline burning 20-KW generator. So yes, I am aware that the final S.E. I end up having will have a pretty big footprint. As mentioned before I have half an acre so if it's as big as a car or two i'm completely good with that. I don't mind giving off the 'crazy steampunk guy' type of vibes to the neighbors anyways.
Thanks again for the replies.
As for a heat source i'll have different sources depending on which S.E. i'm using & as this project evolves. I didn't want to bore anyone with the details so omitted that before. So i'll probably build a rocket stove for the first heat source or basically just have something to direct the heat of a small camp fire to the S.E. Eventually plan on building a "wood gasifier" to replace it in time as they pull more energy out of the firewood/are more efficient. Also during the hot summer months plan on fabricating some form of solar oven to be a free heat source but all that's WAY down the road. But the man fuel source will be firewood.
As for cooling, nothing at first but again this is to be an evolving project.
If it is required i planned on taking metal strips & affix them longways on the OUTSIDE of the power piston spaced at 45-degree intervals so they can act the same way the cooling fins on an air cooled motorcycle engine works. If further cooling is needed, another plate across the top two & sealing off both ends. This will make a channel that coolant can flow through & I have a small heat exchanger taken out of a trucks A/C unit that can be used for this. Was thinking adding fan blades to the flywheel to force air over this heat exchanger/radiator looking thing.
I live in a camper in a remote/rural area so access to things people often view as 'normal' are not options to me (just wanted to clarify that)
I have half an acre of land so if the engine/engines are unusually large that is of no concern as the wood pile to fuel it will end up being large as well.
Having limited fabrication methods I was hoping to use things that are 1-cheap & 2-already (to an extent) built for the application at hand. Figured these pumps fit that bill well.
Somebody mentioned fittings for unusual sizes of pipes. There are 304 food grade stainless steel tubings that one can order on Amazon that are 'normally' used in the brewing industry. Having worked in that industry they can handle 50-PSI no problem & have 'tri-clamp' fittings that have gaskets to connect them to each other to allow for custom applications. (make them whatever shape you may need such as going around a corner or whatnot) These gaskets aren't made for red hot temps but can/do withstand boiling temps on the regular.
As for a flywheel I basically have two options. The first one being a simple bicycle tire or if that isn't going to be heavy enough I planned on using an old brake rotor from a car. (because these are what I have or can get for free)
Pardon me for not having a picture or a nice diagram but to explain what I have in mind is the two pumps parallel to each other laid down sideways with their hand pumps connected to the flywheel that sits inbetween them. The displacer tube being a bit longer than the other for having a "burn tube" attached to it & have a somewhat small diameter tube connecting an air passage between the two bike pumps. A small rocket stove to sit underneath the burn tube.
Once I have it to the point of where it is built and running somewhat reliably, I have the old timing chains & 2 matching sprockets from an old Ford Triton motor. Figured I could attach one sprocket to the flywheel & use it to power something or I might hold off on these for a larger engine. This first engine I will be more than happy if it can via the right size pulleys, spin a cars alternator to charge a battery bank using firewood.
Eventually I'd like to build something on the level of this engine here.
https://2.bp.blogspot.com/_4SFgj1O1Abs/ ... G_4962.JPG
Given this picture is of a 1/4 scale version but the original I think was Stirlings 4th engine and had like 45-HP & was used to power a plant of some kind for 3 or 4 years until somebody overheated part of it & they replaced it with something else.
The walking beams and the dual action power piston on it are beyond my fabrication ability/budget right now but I guess one could say that my end goal is to build an engine capable of replacing a gasoline burning 20-KW generator. So yes, I am aware that the final S.E. I end up having will have a pretty big footprint. As mentioned before I have half an acre so if it's as big as a car or two i'm completely good with that. I don't mind giving off the 'crazy steampunk guy' type of vibes to the neighbors anyways.
Thanks again for the replies.
Re: Well hello there Stirling engine makers.
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Actually picture something pretty similar to this cept the red parts are the bike pumps.
Actually picture something pretty similar to this cept the red parts are the bike pumps.
Re: Well hello there Stirling engine makers.
Both those pictured engines, and the one you described in the opening post are Gama Stirling Engines. Characteristics are a separate power piston, and separate displacer chamber with regenerator.
An Alpha has two pistons with associated piston rings. One hot cylinder and one cold cylinder. It has a regenerator in the interconnection tube.
This is good, as an Alpha probably would be very hard to build from the two tire pumps, or at least harder.
An Alpha has two pistons with associated piston rings. One hot cylinder and one cold cylinder. It has a regenerator in the interconnection tube.
This is good, as an Alpha probably would be very hard to build from the two tire pumps, or at least harder.
Re: Well hello there Stirling engine makers.
Also, if you can keep the piston and displacer vertical. It will reduce side friction. Heat the bottom of the displacer and cool the top. Your pumps include several low temperature parts, so I recommend connecting the piston cylinder to the cold side of the displacer. Similar to the first photo. All three are vertical.