Hello,
I built a Stirling engine using a 50CC motorbike cylinder and a piston. Although the mechanism is not as smooth as i expected it to be, i want to give it a try to see if i can get it to run. I used a 2.25" galvanized pipe as the hot end cylinder and its length is around 12". Another galvanized pipe of around 1.8" diameter runs inside this cylinder as the displacer. Hot end cylinder is connected through a copper pipe to the cold cylinder which is around 1.25" in diameter. Piston and displacer are coupled through a mechanism.
The main thing i want to know is how much do you think i should heat the hot cylinder for this to at least move? i tried heating it up with a gas burner (used in the kitchen), but it did not move. I am new to this area and really appreciate if some one can help me with this.
advice on a newly built sirtiling
Re: advice on a newly built sirtiling
Manusha, is you hot end thined down, or is it full thickness? What is the gap between the bore of the hot end and the diplacer? On your power piston, is it the origional motor cycle one, with rings?
The motor ifits going to run should be able to turn quite easily, and if the motor can be relieved of pressure ie., remove the copper connecting tube, it should be free to rotate a number of revs when you flip the flywheel. One thing I can see so far that will stop this is the power piston with rings, get rid of it, or you may get away by removing the rings and replacing them with Teflon plumbers tape, twist it up, then wrap it round the ring grooves. Ordenary rings create too much friction. Better than that would be to get some cast iron bar, and make a new piston, make it a very close fit, it must just slide through the dry cylinder under its own weight, and stop if you seal the end with your hand.
Friction is the biggest killer, then air leaks. Make sure the timing is correct, the displacer leads the power piston by 90*. The galv pipe will be OK to get the motor running if thinned down to say .020"/.030"at the end where it is heated, the complete displacer should be a similar thickness, Better still they both would be better made of stainless steel, this having better performance with heat (red hot), and reduces the heat conduction from hot end to cold. The swept volume of the displacer should be about 1.5: 1 for the power cylinder. You might find something amid that load of thoughts of mine that might help. Ian S C
The motor ifits going to run should be able to turn quite easily, and if the motor can be relieved of pressure ie., remove the copper connecting tube, it should be free to rotate a number of revs when you flip the flywheel. One thing I can see so far that will stop this is the power piston with rings, get rid of it, or you may get away by removing the rings and replacing them with Teflon plumbers tape, twist it up, then wrap it round the ring grooves. Ordenary rings create too much friction. Better than that would be to get some cast iron bar, and make a new piston, make it a very close fit, it must just slide through the dry cylinder under its own weight, and stop if you seal the end with your hand.
Friction is the biggest killer, then air leaks. Make sure the timing is correct, the displacer leads the power piston by 90*. The galv pipe will be OK to get the motor running if thinned down to say .020"/.030"at the end where it is heated, the complete displacer should be a similar thickness, Better still they both would be better made of stainless steel, this having better performance with heat (red hot), and reduces the heat conduction from hot end to cold. The swept volume of the displacer should be about 1.5: 1 for the power cylinder. You might find something amid that load of thoughts of mine that might help. Ian S C
Re: advice on a newly built sirtiling
>> is you hot end thined down
No. The thickness of the pipe is around 1mm.
>> What is the gap between the bore of the hot end and the diplacer
Around half a centimeter.
>> On your power piston, is it the origional motor cycle one, with rings?
No rings are removed.
The piston moves quite easily and its lubricated with engine oil and is sealed well. Why do you think that the displacer should be thinned as well? I did not check for air leaks, so will do that too.
No. The thickness of the pipe is around 1mm.
>> What is the gap between the bore of the hot end and the diplacer
Around half a centimeter.
>> On your power piston, is it the origional motor cycle one, with rings?
No rings are removed.
The piston moves quite easily and its lubricated with engine oil and is sealed well. Why do you think that the displacer should be thinned as well? I did not check for air leaks, so will do that too.
Re: advice on a newly built sirtiling
The gap between the displacer and its cylinder is far too big,1.5 mm, or maybe 2 mm is about right. The displacer cylinder at 1 mm is OK. The displace its self must be as light as possible, and no leaks, I'm affraid that I often, when making mild steel displacers end up making two or three, because I make them too thin, and end up with zero thickness, .010" is usually what I'm aiming at. My best ones are made of thin walled stainless steel with the end TIG welded on, that goes for both displacer, and cylinder. The metal is between .005" and .010", my friend with the TIG welder is'nt too keen on the .005 stuff!
The aluminium piston will cause a bit of friction, and yet not be air tight enough. The hot air motor should run with out too much in the way of oil. Aluminium is a poor material for a piston in a hot air motor, cast iron is the ideal metal for this task, and can be made as light as an aluminium one, it does not need the strength of the piston in an IC motor. Use no rings, or grooves packed with Teflon tape, or a leather cup seal (like in a bike pump), with the latter two methods you can allow a thou or so clearance (not good practice), but it helps if you can't get the close tollerence required for the ideal piston. Oil is not good on the piston, it causes too much drag, a similar effect to friction. Try packing the ring grooves with Teflon tape, If there is enough metal at the bottom of the skirt of the piston, could you put another groove (just shallow), and pack that one too, this would keep the aluminium from the cylinder bore. Ian S C
The aluminium piston will cause a bit of friction, and yet not be air tight enough. The hot air motor should run with out too much in the way of oil. Aluminium is a poor material for a piston in a hot air motor, cast iron is the ideal metal for this task, and can be made as light as an aluminium one, it does not need the strength of the piston in an IC motor. Use no rings, or grooves packed with Teflon tape, or a leather cup seal (like in a bike pump), with the latter two methods you can allow a thou or so clearance (not good practice), but it helps if you can't get the close tollerence required for the ideal piston. Oil is not good on the piston, it causes too much drag, a similar effect to friction. Try packing the ring grooves with Teflon tape, If there is enough metal at the bottom of the skirt of the piston, could you put another groove (just shallow), and pack that one too, this would keep the aluminium from the cylinder bore. Ian S C
Re: advice on a newly built sirtiling
Could you please explain why the gap between displacer and hot cylinder matters that much.
Currently my displacer is pretty heavy as it is made of a galvanized pipe. So I decoupled it from the rest of the mechanism. Obviously I do not expect the engine to run now, but the cold cylinder should move away from the pressured side one stroke. Still it does not seem to happen. I even removed oil from the piston and checked for drag and its very low. Removing oil did not reduce the air tightness.
It seems like there is a leak in the hot cylinder. The rod driving the displacer comes out of the cylinder through a 1 inch long bush made of steel. The rod too is steel. I haven't done anything special to there to eliminate leaks. Do you have any suggestion for that? Would a bush made of aluminium work better than the steal one? I might be able to put an 'O' ring type rubber seal there but it would definitely increase friction.
Currently my displacer is pretty heavy as it is made of a galvanized pipe. So I decoupled it from the rest of the mechanism. Obviously I do not expect the engine to run now, but the cold cylinder should move away from the pressured side one stroke. Still it does not seem to happen. I even removed oil from the piston and checked for drag and its very low. Removing oil did not reduce the air tightness.
It seems like there is a leak in the hot cylinder. The rod driving the displacer comes out of the cylinder through a 1 inch long bush made of steel. The rod too is steel. I haven't done anything special to there to eliminate leaks. Do you have any suggestion for that? Would a bush made of aluminium work better than the steal one? I might be able to put an 'O' ring type rubber seal there but it would definitely increase friction.
Re: advice on a newly built sirtiling
For the displacer bush I use one of three different materials, brass, cast iron, and Teflon. Brass is possibly your best bet as availablity goes. Cast iron if you can get it, and can work with it. Get a brass bolt, and drill a hole through the length of it. You should not run steel against steel, or like metals against each other, except cast iron.
The space between the displacer, and its cylinder should be kept to a minimum (within reason), the excess is dead space.
Be careful when using galvanised pipe in an area where its being heated, zinc when heated is very toxic, and when heated inside the cylinder it becomes zinc oxide powder (white powder), and can block up the tube connecting the power cylinder. If the displacer is too heavy, the motor will jump around with the momentum. Ian S C
The space between the displacer, and its cylinder should be kept to a minimum (within reason), the excess is dead space.
Be careful when using galvanised pipe in an area where its being heated, zinc when heated is very toxic, and when heated inside the cylinder it becomes zinc oxide powder (white powder), and can block up the tube connecting the power cylinder. If the displacer is too heavy, the motor will jump around with the momentum. Ian S C
Re: advice on a newly built sirtiling
Thanks Ian.
I will remove the galvanized cylinder as well as displacer. There are heavy, not smooth and toxic as well (As you've indicated).
I will remove the galvanized cylinder as well as displacer. There are heavy, not smooth and toxic as well (As you've indicated).
Re: advice on a newly built sirtiling
Don't worry if the outer surface of the displacer, or the inner surface of the displacer cylinder are a bit rough, i have a theory (untested), that the rough surface enhanses the regenerative effect of the displacer.
A source of stainless steel cup shaped bits for the displacer cylinder is the kitchen ware department of shops, and pound/ dollar shops, and second hand shops, things like stainless sugar bowls, beakers, and for smaller motors, salt shakers. My latest motor uses the steel case of a AA NiCad battery for the displacer cylinder. The 2.5 cc motor in my gallery has a AA NiCad case for the displacer, this replaced the aluminium body of a white board marker. Ian S C
A source of stainless steel cup shaped bits for the displacer cylinder is the kitchen ware department of shops, and pound/ dollar shops, and second hand shops, things like stainless sugar bowls, beakers, and for smaller motors, salt shakers. My latest motor uses the steel case of a AA NiCad battery for the displacer cylinder. The 2.5 cc motor in my gallery has a AA NiCad case for the displacer, this replaced the aluminium body of a white board marker. Ian S C