Hey everyone! I just have a few general questions regarding a Gamma engine
1) What are the recommended ratios for:
displacer piston length to diameter
displacer cylinder length to diameter
power piston length to diameter
power cylinder length to diameter
displacer cylinder diameter to cooling fins outer diameter
number of cooling fins to each fin's thickness
radius of flywheel to the connecting rod length for both displacer and power sides
2a) Using a graphite power piston, what would you make the cylinder out of? an oil-lubricated bushing? or no lube since the graphite's already self-lubricating?
2b) and with that graphite power piston, i'm assuming i'd still need a bearing to align the rod so that the piston does not wear against the bushing too much, right?
3) What's the best way to seal the displacer side?
It's safe to assume in your answers that i may be missing some fundamental info about stirling engines since this is our first one. Please don't be afraid to dumb down your answers if you think that'll help me understand it better, especially when it comes to terminologies. For example, one of the words i keep hearing is "gland" but i'm not sure what part that's referring to.
All help is appreciated. Thanks!
First Gamma Engine
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stirlinguptrouble
- Posts: 3
- Joined: Sat Nov 05, 2011 11:50 am
Re: First Gamma Engine
One more thing, we're performing a Schmidt Analysis via Matlab, and we're trying to figure out how to estimate the temperature ratio of the gas at the cold end to that of the gas at the hot end. I figure i can estimate the hot gas temperature to be the same as the temp of the flame, and the cold gas temp can be approximated by the temp of the inner walls of the cylinder. I can simulate the temperature distribution across the walls through the cooling fins, but i'm not sure how i'm going to assign the convection boundary condition for free and forced convection. can anyone shed some light on this? thanksss
Re: First Gamma Engine
Stirlinguptrouble, first recomendation:If it's your first engine, get a published design from a proven designer like James G. Rizzo, or someone similar. 2, is the motor being built in a workshop with machinery, ie., a lathe, and brazing gear. 3 its important to use the correct materials to get the best perfomance from your motor, stainless steel for the displacer cylinder. You mention graphite for the piston, some say glass for the cylinder, but steel,either plain carbon, or stainless would be good,polish the bore, it must be very accurate in diameter, no taper, and round, bore it in the lathe, then lap it . Now make the piston to fit, ideally you are working to tenths of a thou. I believe that the final polish on the piston is done with plain paper. I use cast iron for my pistons, and a steel cylinder.
For a high temperature motor the ratio between the displacer and power piston is 1.5: 1. The displacer should be about three times as long as its diameter. The power piston should be a little longer than its diameter, but I find that the piston on a vertical motor can be a little shorter. Try and keep the con-rod on the power piston reasonably long to reduce the angle there by reducing the side thrust on the piston.
The motors that I worry about power I judge by looking at the hot end, is it running at red heat, and the cold end, is the water in the cooling system below boiling. Short of fitting thermocouples etc its a bit of a waist of time. If the displacer is made of steel, the hot end should be blue or even past that, and the colours fadeing down , and disapearing at about half way. Ian S C
For a high temperature motor the ratio between the displacer and power piston is 1.5: 1. The displacer should be about three times as long as its diameter. The power piston should be a little longer than its diameter, but I find that the piston on a vertical motor can be a little shorter. Try and keep the con-rod on the power piston reasonably long to reduce the angle there by reducing the side thrust on the piston.
The motors that I worry about power I judge by looking at the hot end, is it running at red heat, and the cold end, is the water in the cooling system below boiling. Short of fitting thermocouples etc its a bit of a waist of time. If the displacer is made of steel, the hot end should be blue or even past that, and the colours fadeing down , and disapearing at about half way. Ian S C
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stirlinguptrouble
- Posts: 3
- Joined: Sat Nov 05, 2011 11:50 am
Re: First Gamma Engine
yes, we are building it in a machine shop. we're having a lot of trouble estimating the temperature ratio of the gas between the hot end of the displacer and the cold end of the displacer. what would be the best approach? we need this temp ratio for the schmidt analysis which will help us determine the swept volume ratio we need to use. we're thinking of using aluminum fins (machined out of our aluminum engine block) with free convection cooling and a flame of about 2500 degF as our heat source.
Re: First Gamma Engine
You can get some idea of hot end temperature by the colour of the displacer, find a chart of tempering colours for steel (thats if the displacer is steel), for the cold end, i think you can get a non contact IR thermometer, The hot end won't be much more than 700*C or so, and the cold end, with effective cooling should be less than 100*C, I'm affraid that I'm not hi tech, I follow the basic design parameters, use the best I can get / afford in materials, an go for it, some motors go well, others go, if you think things through and work carefully, its hard to make a motor that won't go eventually. Ian S C
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R-WIN DEVELOPMENT
- Posts: 4
- Joined: Sun Dec 18, 2011 7:53 am
Re: First Gamma Engine
Gamma type,big fly wheelstirlinguptrouble wrote:Hey everyone! I just have a few general questions regarding a Gamma engine
1) What are the recommended ratios for:
displacer piston length to diameter
displacer cylinder length to diameter
power piston length to diameter
power cylinder length to diameter
displacer cylinder diameter to cooling fins outer diameter
number of cooling fins to each fin's thickness
radius of flywheel to the connecting rod length for both displacer and power sides
2a) Using a graphite power piston, what would you make the cylinder out of? an oil-lubricated bushing? or no lube since the graphite's already self-lubricating?
2b) and with that graphite power piston, i'm assuming i'd still need a bearing to align the rod so that the piston does not wear against the bushing too much, right?
3) What's the best way to seal the displacer side?
It's safe to assume in your answers that i may be missing some fundamental info about stirling engines since this is our first one. Please don't be afraid to dumb down your answers if you think that'll help me understand it better, especially when it comes to terminologies. For example, one of the words i keep hearing is "gland" but i'm not sure what part that's referring to.
All help is appreciated. Thanks!
[BBvideo 425,350]http://youtu.be/42RrqapTLSU[/BBvideo]
Gamma type,big radiator
[BBvideo 425,350]http://youtu.be/hxXO1sq2ifY[/BBvideo]
Best regard
Re: First Gamma Engine
(1) displacer, this should be three times its diameter long. The displacer cylinder length depends on the length of the stroke,ie., if the stroke was 1", the length of the cylinder would be the length of the displacer, plus the length of the stroke, plus the gap at each end.
(2) piston, 1:1 is a fair enough measurement to start with, maybe a little more in length.
(3) usually depends on what metal you have, but 1/2" deep fins on a 1" diameter cylinder would look OK.
(4)Thickness of fins, and gap between fins, say about 1/16" fin, 1/8" gap, it seems more art than engineering as far as the fins on my only engine with fins (I usually use water cooling).
(5) flywheel radius ? thats a bit of trial and error (more error). Don't use too much weight, but keep the diameter up. One good test for a motor is getting it to run with no flywheel, if it runs,it will go quite fast, but with very little power. Theres enough flywheel effect with the crank, and big ends of the con rods.
The motor in the You-tube clip could be conciderably more powerful if it had a propper burner that wrapped right around the hot end, the torch on its own is OK to just get it going, but to finish the motor a burner is an important part.
Make the power cylinder out of steel with a polished inside (if you can get old car shock absorbers grab them), get to work with a hack saw just above where the inner rod comes out, do it outside, be careful as you break through to the inside, theres air and oil under pressure (I think the usual saying is "Don't do this at home), don't blame me if you get covered in oil. Inside there you will find a tube perfect for a cylinder, plus you'll get some very good steel. If you use a bronze bearing bush, it must be a plain one, you must not use oil, specially on a graphite piston NO OIL.
Gland,Thats a bit similar (well its the same) to the part of a water tap thet the spindle goes through that is sealed to stop the water leaking out while the spindle can turn, on the displacer it allows the rod to go in and out, but keeps the air inside. Ian S C
(2) piston, 1:1 is a fair enough measurement to start with, maybe a little more in length.
(3) usually depends on what metal you have, but 1/2" deep fins on a 1" diameter cylinder would look OK.
(4)Thickness of fins, and gap between fins, say about 1/16" fin, 1/8" gap, it seems more art than engineering as far as the fins on my only engine with fins (I usually use water cooling).
(5) flywheel radius ? thats a bit of trial and error (more error). Don't use too much weight, but keep the diameter up. One good test for a motor is getting it to run with no flywheel, if it runs,it will go quite fast, but with very little power. Theres enough flywheel effect with the crank, and big ends of the con rods.
The motor in the You-tube clip could be conciderably more powerful if it had a propper burner that wrapped right around the hot end, the torch on its own is OK to just get it going, but to finish the motor a burner is an important part.
Make the power cylinder out of steel with a polished inside (if you can get old car shock absorbers grab them), get to work with a hack saw just above where the inner rod comes out, do it outside, be careful as you break through to the inside, theres air and oil under pressure (I think the usual saying is "Don't do this at home), don't blame me if you get covered in oil. Inside there you will find a tube perfect for a cylinder, plus you'll get some very good steel. If you use a bronze bearing bush, it must be a plain one, you must not use oil, specially on a graphite piston NO OIL.
Gland,Thats a bit similar (well its the same) to the part of a water tap thet the spindle goes through that is sealed to stop the water leaking out while the spindle can turn, on the displacer it allows the rod to go in and out, but keeps the air inside. Ian S C