Stirlingengineforum.com

Which type of stirling engine will be more efficient?

two power piston type stirling engine or displacer and power piston type stirling engine?

santu398, generally I feel that the ALPHA motor is the more efficient, ie., more power to weight, don't know about fuel efficiency, but it proberbly wins there too. ALPHA two power cylinders, BETA, and GAMMA, power piston and displacer. Ian S C

Thanx a lot...

santu398, if you plan on making an ALPHA motor, you really need, or have access to a lathe, and be reasonably compenent in its use, you can make a GAMMA motor with very little amount of tools, a BETA motor requires a bit more work, and would require a lathe to make the power piston, and the part of the cylinder that the piston works in. With the GAMMA type, you can replace the piston with a diaphram (bit of a balloon), and the rest can be made of tin cans, and bits of wire. Read all you can on Stirling Engines, understand how they work, then work carefully, and you should have little trouble getting a motor that works. Ian S C As I don't know you, I may be trying to tell you things you already know, best wishes anyway.

Thanx a lot sir...

I want to do 2piston type stirling engine as mini project...for this i purchased two cylinders with pistons...i am thinking to connect the cylinders through a pipe by making holes to the piston....now the problem is how to connect the cylinders...

that is at what position it is better to make holes to the cylinder? As the fire is kept at the bottom of hot cylinder can i make holes at the bottom of the cylinder or will it have any effect?

The holejoining the two cylinders is at the TDC of both pistons. The hot piston has a piece on top of it constructed in a similar way to the displacer in a BETA/GAMMA motor, this is called a Heylandt Crown, among other things it keeps the heat away from the head of the piston. The heated area is near the top end of the extention bit. There are photos of a Ross Yoke ALPHA motor in my gallery. Ian S C

Thanq sir...

Before working for the project i was struck with a small doubt...

How to manufacture a piston that fits the cylinder air tight (so that the gases dont escape)?

Can we manufacture the piston air tight by using lathe?

Please suggest any simple technique to manufacture a cylinder with piston that is air tight?

You are in luck, having a lathe makes pistons much easier. First make the cylinder smooth as possible, and parallel, the exact bore is not that important, next turn the piston down until it just won't fit, now polish it down to size with fine wet and dry paper, I finish off with 1200 grit. The piston should slide through the cylinder under its own weight, and if you put your finger over the end it should stop, or move very slowly. Again the dimention is not important, but the clearance is just a fraction of a thou. Depending of the heating patten of the motor, it's possible that you may need to polish it just a little more if its too tight, but if you can just let it run its self in, after a few hours running the motor will speed up, and gain power. Ian S C

Thanq sir

Can we make hot cylinder with the steel or cu metal or it should be made of glass because of expansion effect?

If that is your choice of materials to make the cylinder, use steel. Copper is a poor choice as it has a high amount of friction, and is fairly soft. Glass is hard to work with,ie., lapping the bore to fit the piston. If you get one of the Airpot cylinders and its graphite piston you'v got no trouble, its all done for you. Glass expands quite a bit on heating, but in a hot air motor it should not be a problem.
Steel, and try and get a bit of cast iron for a piston. There is a picture of one in my gallery, the one there is 35 mm dia, the skirt is about 1 mm thick, and the crown is 3 mm thick, this piston is made from a cast iron window weight, and runs in a cylinder made from the inside tube of a car shock absorber. Ian S C

Sir,

Which metal is better to connect two cylinders so that it can serve the purpose of regenerator also?

I would suggest stainless streel, and if of large enough bore, either stainless foil, or stainless wire fitted inside. The idea being to keep the hot end of the regenerator as hot as possible, and the cold end as cool as possible. That way the air can pick up heat as quick as possible. Ian S C

what should be the length of connecting rod for a stroke of 80mm and crank radius 40mm?

Please reply

The length of the con rod depends on the distance the crank is from the cylinder, try and keep it fairly long, this reduces the angle of the thrust on the piston, thereby reducing the friction in the cylinder. Just make sure that there is a little (mm or 2) clearance at the top of the stroke. Ian S C