Help required

[santu398]

Thanq :)

I made two cylinders(dia 40mm) with mild steel and pistons with aluminium... i connected the two cylinders with a stainless steel pipe(20mm dia) (including sudden compression fitting(10mm dia) at the bottom of cylinders) from the bottom of the cylinders... I want to fill the cylinder with helium gas... Till what pressure the gas should be filled?

[santu398]

What are the preferable dimensions of crankshaft radius for a cylinder of 40mm dia and 100mm length with a connecting rod of 8mm diameter?

plzz help me

[Ian S C]

Thought you had desided on a stroke of 80 mm/40 mm throw of the crank ? May be a good idea to show us a sketch of your motor so far, to give us an idea of what you have. Ian S C

[santu398]

sorry i cannot post the pics of the motor...

Can u please tell me at what pressure helium gas should be filled in the cylinder?

[Ian S C]

How long is a bit of string? You'll have to work that out your self as you design the motor, but I would start at 1 Bar, and move up slowly by say 10 psi at a time, testing the motor for torque and revs at each stage, by the time you get to 100psi you start to get to the need for pressure testing, as pressures can reach toward 200psi, so a 300 psi test would be adventageous. Pressure questions asside2000psi would be possible, but would require very high quality engineering, and design. If this is your first pressurised engine, stick to air, Its free, and easier to manage unless you have expiriance in working with pressurised gas. Ian S C

[santu398]

Thanx a lot Sir...sorry for late reply..i stopped working on the engine these days hence no reply...we were asked to submit the engine by 30th of this month...
The pistons are very tight and we were left with a doubt whether the engine can run with air as working gas :(

[Ian S C]

To run your motor its GOT to have the absolute minimum friction, the pistons must fit without leaks, but slide through the cylinder under its own weight.
To use the motor pressurised it MUST be sealed, the seals on the crankshaft bearings is difficult, and its doubly difficult with helium, I'm not sure if its like hydrogen, and will pass through some metals. For your engine, air is the gas of choice (its cheap, its everywere). Unless you have succesfully built a number of atmospheric motors, I would forget about trying to build a pressurised one.
Please try and get the motor going, even unpressurised, you will find it will give you great pleasure. Ian S C

[santu398]

http://lh5.google.com/-VXTcFxXqCS4/UGa1 ... to0500.jpg

Sir this is the model of my engine ( did not assemble fully )

This is my first engine...the only reason why i want to fill with helium gas is because the pistons are tight..they dont slide on their own weight... Now please suggest me which is the better gas to fill...the engine is provided with a valve to fill the gas easily....

[Ian S C]

I don't like the idea of aluminium for pistons. One reason is the high coefficient of friction, another that I heard recently, aluminium oxidises almost instantly (this forms a protective layer), al oxide is an abrasive used commonly on machineshop grinders. There are expensive ways around the problem.
To get yor motor going, take the piston out and polish it with fine wet and dry paper, until it fits.
Cast iron, or brass in a steel cylinder would be better.
I don't actually understand how you are going to make the motor work, one cylinder requires to be heated, to proberbly 500-600*C, while the other needs to be quite cool.
As for the con rods, they need a guide (some bits of wire wrapped around the crank each side), so that they stay central. Ian S C

[santu398]

Ok..i will try to change the piston material

The aluminium piston does not contact the cylinder...it is surounded by a O-ring..

What approximately should be the temperatures of hot cylinder and cold cylinder??

[santu398]

sir please tell me what should be the temperature of hot and cold cylinder..the cylinders are 3-4mm thick made of mild steel

[santu398]

Do you want me to use helium as working fluid so that no formation of aluminium oxide takes place?

[Ian S C]

No helium needed, this type of motor can not be sealed, and pressurised. If your piston has an O ring, this must be fitted very carefully, the outside diameter must be only just touching, but must seal, the slot in the piston must be wider than the ring to allow movement, another way to do it would be to take out the O ring, and replace it with teflon tape, the type that plumbers use for sealing pipe joints, roll it into a string, wind it in the groove, and pack it in tightly, force the piston into the cylinder, and work it up and down a few times, until it frees up a bit.
Just looking at the crankshaft, are the cranks at 90* to each other?
Have you any access to books on hot air engines that could give a clearer idea of whats required, maybe you should down load (its free) Andy Ross's book " Making Stirling Engines", this will show what is required to get an ALPHA motor going.
The best motor to start with is a GAMMA type. Ian S C

[santu398]

Ok sir...done as u said but its not working :( i guess the problem is with flywheel

What should be the size and weight of a flywheel for a bore of 40mm and stroke length of 70mm?

[Ian S C]

You could make the flywheel from plywood or MDF, say 200 to 250 mm diameter, by 15 to25 mm thick, and as the weight required is that nearest the rim, some holes (6 is easy) say 50 mm dia, could be cut near the hub, forming spokes. The weight of a flywheel is that at the rim.
A metal(not aluminium, too light), 150 to 200 mm dia, weighing up to 2 Kg,or better, two wheels 1.5 to 2 Kg each, one each end of the crankshaft.
The light weight of the crankshaft, and the long distance between the bearings is a bit of a worry! I still don't understand how the motor is heated and cooled, and the cylinders are far too heavy, you have to get the heat in and out quickly, without too much being conducted along the length of the cylinder. Ian S C