Hey!
I'm from Romania and i want to build a stirling engine!
I work at a company where I can work up the metal on the lathe and milling!
Following documentation we concluded that gamma stirling engine is easier to build.
Something like
Gamma engine
FY_Main.jpg (76.12 KiB) Viewed 7288 times
Can someone help me with drawings or sketches?
Last edited by navodlom on Mon Feb 17, 2014 1:36 am, edited 1 time in total.
Navodlom, that's quite a nice looking little engine. There is another variation of the GAMMA motor, using the photo as a basis, leave the displacer where it is, and take the power cylinder, and move it, either up or down, so that it is at right angles to the other cylinder. Both the connecting rods can then operate on the same crank pin, this makes the motor simpler, and leaves one end of the crankshaft free for you to fit a pulley if you wish.
When designing Stirling Engines, the basic rules are: ratio displacer swept volume to power piston swept volume is 1.5 : 1 . The length of the displacer should be about three times its diameter.
For an example, a motor with a power piston of 30 mm diameter, a stroke of 20 mm would be a good one to try.
Best metals: displacer cylinder hot end, and the displacer, thin walled stainless steel, you can go to something between .25 mm and .5 mm thick. The power cylinder could be steel, or cast iron (best), the power piston is best made of cast iron.
The cold end of the motor can be made of aluminium, although steel, brass, or some heavier metal is best for the flywheel. Ian S C
sorry forgot that bit, just a bit of tube, it can be copper tube, plastic, or rubber, it gets connected to the cold end of the displacer cylinder, to the top of the power cylinder. Ian S C
I decided:
-power cylinder: 30 mm diameter, 40 mm long; (cast iron)
-power piston: 20 mm long; (cast iron)
-displacer cylinder: 25 mm diameter, 40 mm long (stainless steel);
-cold cylinder:25 mm diameter, 40 mm long (aluminium)
-dysplacer piston: 23 mm diameter, according to my calculations length is about 49 mm
I would say that your displacer is a bit short, for 23 mm dia. it should be around 70 mm long. It will need a longer stroke than the power piston, as the swept volume of the displacer should be about 1.5 to 1 of the power cylinder volume, I'll let you do the maths for that. Leave around 1.5 mm each end of the displacer, and it should be OK, so the displacer cylinder will be the length of the displacer, plus the stroke, plus the end clearances, about 3 mm. The reason for the length is that it (A) keeps the hot end as far as possible from the cold end. (B) acts as a regenerator. This explains why stainless steel is the ideal material for these parts, because of its high thermal resistance. This resistance is not important at the hot end, the heat has only part of a mm to travel.
If nothing else is learned from these little motors, you should learn about thermodynamics, and the use of different metals affected by heat, and friction.
With the power piston, if you can use cast iron, it will need next to no extra lubrication. Don't use WD-40, it will work well first run, and the next few if they are within a few days of the first, but leave the motor a few weeks and you probably wont be able to turn it, it will be gummed up, the light liquid all gone. If you really need it, some very light -sewing machine oil, just one or two drops will last a number of hours running. 3 in 1 oil has a similar effect as WD-40. The gland where the displacer rod comes out of the cylinder may need some oil too. Ian S C
You could insert a spacer between the hot cap, and the cold end. Its not a mistake, it is research and development, Just make sure there are no leaks in the joints. You could shorten the displacer by a few mm, but try for better that 60 mm. If your power stroke is 20 mm the volume is 14.14 cc (I think), so the volume for the displacer should be about 22 cc, I'll let you work out what stroke the motor needs, even people who didn't like maths at school get to find its not so bad when using it for something we like doing. Ian S C
