# 4-Cylinder Stirling engine



## tinyvdboom (Jun 1, 2013)

Hello, I'm Tiny van den Boom, 57 years old and really keen on building Stirling engines and flame eaters since 2009.

I've named this Stirling engine with 8 tumblers 'Spider' because it looks like a giant spider when you're looking at it. This engine is an own design, based on earlier models I've made. I've translated the corresponding principles of operation into an own 4-cilinder Stirling engine. Some of the parts are made on the basis of Jan Ridder's drawings. The challenge for me was to design and build a Stirling engine myself which should be working with 4 heat- and working cylinders. These 8 cylinders in total would be balanced by means of a large camshaft which would translate the rotation to a flywheel through a belt. The whole machine is built using a conventional milling machine and a conventional lathe.

The heat cylinders and displacers are made of so-called Pirex glass so the operation of the cylinder can be seen easily. This Pirex glass also takes care for the preservation of the heat when the flame is extinguished. To use the heat of the flame as efficient as possible I've also made wind glasses, which centralizes the heat below the Pirex glass. These wind glasses make it possible to use the Stirling engine outside too. For a correct height adjustment of the focal point of the flame I've made the burners adjustable. This also makes it easy to position the wind glasses after the wicks are lit.

By placing the tumblers at such a height I have managed to limit the friction between the rods and camshaft to a minimum because the rotation between rod and tumbler remained small. In addition, these rods have sufficient length so an optimal alignment could be generated. To let the engine run as smooth as possible, I put ball bearings in the most important pivot points, including the tumblers.

The air movement from heat- to working cylinder flows through a pipe outside the mounting plate for the purpose of manufacturability. Additionally, this gives the product an extra technical look. By means of a valve between the heat- and working cylinder, the pressure can be regulated so the RPM of the flywheel is adjustable. It's also possible to drive something with this Stirling engine by means of a pulley I've made on the axis of the flywheel.

If there are interested people for the (approx. 35) drawings of this Stirling engine, do not hesitate to send me an email. The drawings are available for a fee. My email address is: [email protected]






















Video: [ame]http://www.youtube.com/watch?v=fKVUSy29X5A[/ame]

Some more specs:

Amount of production hours: 250 hrs
Amount of o-rings: 32 
Total amount of parts: 508
Max RPM: 700
Bore x stroke working cylinder: 10 x 20 mm
Dimensions: 215 x 275 x 270 mm
Used materials: Aluminum, brass, bronze, Pirex-glass, copper, Corian and stainless steel.


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## Karlas (Jun 3, 2013)

Hello Tiny,

this is truely a fascinating engine ...............

Although it is far out of my reach, I would love to have your plans, please.

Karl


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## Herbiev (Jun 3, 2013)

Hi Tiny. A very impressive engine indeed. Welcome to the forum.


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## jwcnc1911 (Jun 3, 2013)

I've been trying to comment on this from my phone for two days...

Finally back behind the laptop, so:

Man this is freakin awesome!  I'm so into Stirlings right now and this is new and different!

Love it!  5 stars!


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## aarggh (Jun 3, 2013)

This is just a spectacular engine! Beautiful work and design!

cheers, Ian


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## jwcnc1911 (Jun 3, 2013)

After looking at this again and again... what are the valves between the power piston and displacer for?  Some kind of regenerator?


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## AussieJimG (Jun 4, 2013)

That is  beautiful engine Tiny

Jim


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## Septic (Jun 4, 2013)

I Especially like the compact cylinder layout and tall, yet stable rocker posts that give the design great aesthetic appeal.


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## Orrin (Jun 14, 2013)

Well done, Tiny!  The design is unique and your craftsmanship is superb!  Your Stirling is beautiful.

Best regards,
Orrin


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## tinyvdboom (Jun 16, 2013)

jwcnc1911 said:


> After looking at this again and again... what are the valves between the power piston and displacer for?  Some kind of regenerator?



The valves are for regulating the amount of RPM which is generated and for shutting off one of the cylinders if necessary (in case the fuel tank is empty).


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## jwcnc1911 (Jun 16, 2013)

Ok, further curiosity.  I can see adjusting rpm's by restricting flow.

I don't understand why you would want to shut one cylinder off.  Even if out of fuel.  In my thinking, depending on where the piston is in phase it could either cause a slight pressure or a slight vacuum on the power piston - in my reasoning making more resistance for the other running cylinders.  If you don't valve it off, it's essentially just moving air.

Can you explain please?

I'm also more curious, how did you calculate piston volumes? PV=nRT?  Or did you find a formula for calculating cylinder volumes?  Or did you measure another engine and go from there?

When I finish the projects I have going I will be building a Stirling.  I'm considering designing my own.

Thanks for the reply!


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## chizz (Jun 30, 2013)

Hi Tiny,

what a brilliant looking engine, great machining.


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## Hopper (Jun 30, 2013)

jwcnc1911 said:


> Ok, further curiosity.  I can see adjusting rpm's by restricting flow.
> 
> I don't understand why you would want to shut one cylinder off.  Even if out of fuel.  In my thinking, depending on where the piston is in phase it could either cause a slight pressure or a slight vacuum on the power piston - in my reasoning making more resistance for the other running cylinders.  If you don't valve it off, it's essentially just moving air.
> 
> ...



Formula for calculating volume of a cylinder is V = L*Pi*R(squared)
Or there are web cylinder volume calculators online.
On Strilings you usually look at the swept volume of the piston/discplacer, using the stroke as L and half the piston/displacer volume as R.
Common rule of thumb is that displacer swept volume should be 1.5 times the power piston swept volume.


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## jwcnc1911 (Jul 1, 2013)

Hopper said:


> Common rule of thumb is that displacer swept volume should be 1.5 times the power piston swept volume.



That's what I was looking for.  I was going back to Chemistry class on the ideal gas law there.  The more I study them the more forgiving the design appears.  I just didn't know how deep people were getting in the design of these little engines.  Obviously there has to be enough volume in the displacer that when heated it supplies enough pressure to move the power piston.  So it would have to be greater volume or much higher temperature is required.  That's why all of those LTD's have such huge displacers and tiny work pistons.

I also theorize (and will put to practice given time) that if you increase the stroke of the displacer, increase the volume of the displacer therefor moving the gas farther away from the heat source you would have a more efficient engine.  Given this is a beta type, I don't know about a gamma.  I figure the dead space would cool the gas before it could work if it's too far from the heat source.

Any way, thanks for the rule of thumb!


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## Longboy (Jul 1, 2013)

jwcnc1911 said:


> ..........
> I don't understand why you would want to shut one cylinder off. Even if out of fuel. In my thinking, depending on where the piston is in phase it could either cause a slight pressure or a slight vacuum on the power piston - in my reasoning making more resistance for the other running cylinders. If you don't valve it off, it's essentially just moving air.
> 
> Can you explain please?
> ...


 This premise I agree with. Closing off the passageway between displacer and power cylinder. Not an issue on the displacer side but with a sealed power cyl. would generate compression/ vacuum depending on where in the stroke those valves are closed creating drag for the active cylinders. If the builder witnessed the other cylinders carring over the the inactive cyl then these valves may be an inconclussive stratagy.


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## Hopper (Jul 2, 2013)

jwcnc1911 said:


> That's what I was looking for.  I was going back to Chemistry class on the ideal gas law there.  The more I study them the more forgiving the design appears.  I just didn't know how deep people were getting in the design of these little engines.  Obviously there has to be enough volume in the displacer that when heated it supplies enough pressure to move the power piston.  So it would have to be greater volume or much higher temperature is required.  That's why all of those LTD's have such huge displacers and tiny work pistons.
> 
> I also theorize (and will put to practice given time) that if you increase the stroke of the displacer, increase the volume of the displacer therefor moving the gas farther away from the heat source you would have a more efficient engine.  Given this is a beta type, I don't know about a gamma.  I figure the dead space would cool the gas before it could work if it's too far from the heat source.
> 
> Any way, thanks for the rule of thumb!



See if you can get hold of a copy of James G Rizzo's book The Stirling Engine Manual . It is out of print and expensive to buy, but my local library got a copy in for me from the state library. It has all the design theory and parameters  you need to get started.

Yes you can play with different strokes for displacer and power piston as you suggest, as long as overall volume is ballpark correct.

A few further rules of  Stirling thumb:
Displacer length should be about three times the diameter.
Displacer clearance to the end of each chamber should be minimal (.015" or less) 
Displacer clearance to displacer chamber should be minimised, maybe .020 all round.
Hot end of displacer chamber should be about half to two-thirds of teh total displacer chamber length. The remaining half/third is the finned cold end.
Keep 'dead space' to a minimum, eg on gamma engine, keep the two cylinders as close togehter as possible and use a 3/16" hole to connect the two as directly as possible. 

Common materials are:
Piston: Brass or graphite in steel or iron bore
Displacer chamber hot end: thin stainless steel. 
Displacer: Thin stainless steel
Displacer chamber cold end, finned aluminium or water jacket.

Have fun.

Commonly used materials


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