big gamma stirling engine

[little john 1]

reet here goes

i recently went to a museum full of old steam and stirling engines and saw many examples of stirling engines wich used to run small mills and brewerys and such and got the seed of an idea planted in my daft head

over the last 5 years i have been collecting oldschool engineering tools ( hence my forum name ) as i own a raglan little john lathe mk1 wich forced me to build a small shed to house it and get away from the missus ( snigger )

now i have had to extend the shed due to my collection of tools and stock metal acquired from scrap merchants n skips and i have an empty corner where i used to have a dustbin full of stock now been moved and racked pretty neatly

now 3 years ago i built a wood burner out of an old propane cylinder then developed it to run on used engine oil using the ozzirt design but heavily modified wich at full pelt on a drip feed it kicks out about 485 degrees on the secondary burn chamber with no visible smoke from the flue ( not a clue what the co2 is like ) but it does a fantastic job of keeping the place warm in winter

now seeing these stirling engines i want one to build into this heater but powerfull enough to run a line shaft to the bench at the back of the shed to run an old grinder i have and eventually a power hacksaw ( ambitious to say the least )

can anyone shed any light on the ideal capacity differences between the displacer and power cylinders please as im currently faffing around with a 4" x 8" heavy gauge steel displacer and a 3" x 1" power cylinder and the crankshaft out of a briggs and stratton lawnmower

would this work

[Ian S C]

Hi little john, welcome aboard. Lineshaft, you'll be lucky! for a unpressurized motor you'r looking for BIG.
There are some ratios that should be followed fairly closely. (1) Displacer, this should be about three times longer than it's diameter, and light as possible, made of steel, or better stainless steel. This fits into the hot cap, with a small radial gap, also a gap at each end of its stroke.
(2) The power piston should be reasonably light in weight, and made of cast iron, with no piston rings, and lapped until it will just slide down the cylinder under its own weight. The cylinder should be either steel, or cast iron(latter is best).
(3) The next ratio is that between the displacer, and power piston, the swept volume, this should be as near as possible to 1.5 : 1, this is the ratio used by Robert Stirling in his motors.

Before you build a big one, try(if you have not already) building a smaller one, If you look in my gallery you will see a vertical one on 4 legs, it has a 2 1/4" bore, and is a BETA type motor. If I pushed it, it might get up to 10Watts out put. Ian S C

[little john 1]

im thinking big as i have recently acquired some kind of cast iron 20" wheel looks like its off some kind of small train ( possibly a mine cart ) and weighs approximately 40 kg

i have already begun messing at making a smaller one but i dont think i have the displacer cylinder at the right size as the engine tries to run but just wont keep going or it could be my water cooling jacket that is just too good ( fresh water cold at one end roughly 4 degrees c ) and glowing red hot at the other end at 4" diameter and 8" long

just cant figure out whats going wrong or where im calculating wrong im now looking at a large 9kg fire extinguisher shell and thinking of using that for a displacer cylinder ( hot cap ) and i have a 2ltr stainless thermos flask thats going to get the chop for the displacer and wrapped in steel wool to see if that will help by acting as a recouperator built in to the hot cylinder

im also going to use your ratios and totally rebuild the smaller engine after a trip to my favourite scrap metal merchants this coming weekend for some more brass