Big Beta Stirling 1kw, 100degC to 400degC

[Ante]

If that drawing is to scale, the displacer should be much longer.
I don't understand what you mean,"my linkage is rotated 90* (vertical engine). Ian S C

"my linkage is rotated 90*" that means that pistons goes up and down not left and right like in zivko engine on pictures.

in excel file zivko piston movements are vertical. -red line on right graph represent movement of conecting rod of displacer and blue line represent movement of conecting rod of working piston. (conecting rods are mising)
so all red numbers are conected to displacer and all blue numbers are conected to movement of piston.

xcl with yellow and green dots is updated. conecting rods are missin but i dont have time to math them. vertical movement of yellow points is close enough to movement of pistons to get easy stroke ratios and phase angle.

My opinion is that pistons dont need sinusoidal movement but it will be better that phase angle is around 90 degrees.

PS zivko i send you mail on forum before 2 days, you did not replay me, i dont know did you get it?

I am going to mountain so that is all of me util monday.

Salute!
And sorry for my bad comunication :)

[zhivko]

Hi Ante,

I am still getting used to use forum - thanks for PM - I just responded.

And for you last worksheet - now everything is clear and I found worksheet very usefull.

Best regards,
Klemen

[zhivko]

If that drawing is to scale, the displacer should be much longer.
I don't understand what you mean,"my linkage is rotated 90* (vertical engine). Ian S C

"my linkage is rotated 90*" that means that pistons goes up and down not left and right like in zivko engine on pictures.

in excel file zivko piston movements are vertical. -red line on right graph represent movement of conecting rod of displacer and blue line represent movement of conecting rod of working piston. (conecting rods are mising)
so all red numbers are conected to displacer and all blue numbers are conected to movement of piston.

xcl with yellow and green dots is updated. conecting rods are missin but i dont have time to math them. vertical movement of yellow points is close enough to movement of pistons to get easy stroke ratios and phase angle.

My opinion is that pistons dont need sinusoidal movement but it will be better that phase angle is around 90 degrees.

PS zivko i send you mail on forum before 2 days, you did not replay me, i dont know did you get it?

I am going to mountain so that is all of me util monday.

Salute!
And sorry for my bad comunication :)

[zhivko]

Here is excel with correct values you will find arm L disconnected - also how do specify arm angle? In my design it's 90deg, but in excel I don't see this option to be specified...

[Ian S C]

To get the diplacer / power piston ratio correct, the simplest way would be to reduce the power stroke, this could be used to give you more room to lengthen the displacer, even if the skirt of the power piston comes quite a good few MM out of the bore, say up to a third of its length. By reducing the power stroke, you stand a chance of increasing the rpm. Ian S C

[zhivko]

To get the diplacer / power piston ratio correct, the simplest way would be to reduce the power stroke, this could be used to give you more room to lengthen the displacer, even if the skirt of the power piston comes quite a good few MM out of the bore, say up to a third of its length. By reducing the power stroke, you stand a chance of increasing the rpm. Ian S C

Power piston could not came out of bore since there are two piston rings in place (pfte graphite material).
Thanks Ian, I made a check once again but from movie recorded in current situation could be seen that displacement ratio of power piston and displacer piston is already in 1:1.5 relation - have I understand correctly that displacement ratio should be in ratio 1:1.5 or compression should be 1.5 ?

1) Ian could you check and please confirm this?

It could be that compression ratio is too big and that phase delay is not 90 degrees. Also its question for me if motion should be strictly sinusoidal? This could also be a problem - can you comment please.

But reducing a power stroke means to recreate linkage (new linkage) - could it be better to try first with changed heater and steel wool displacer? I am thinking of creating spiral heater in the length of 250mm as you suggested.

Thanks,
zhivko

[Ian S C]

Zhivko, the displacer 1.5, to the power piston 1, if its the other way it won't work. It's sometimes worth experimenting if the design allows with the phase angle. First set at 90*, then move gradually in one direction and note the effect, then go back to the 90* mark, then change the angle in the other direction, there is a good chance that the 90* mark will be as good as you get. I would suggest that the test be done with the load the motor is designed for, as the angle may differ at different loads. Ian S C

[Ante]

Here is excel with correct values you will find arm L disconnected - also how do specify arm angle? In my design it's 90deg, but in excel I don't see this option to be specified...

Zhivko because this is modified ross-yoke xcl sheet i did not put option to change L arm angle, I will try to solve that in few days if you need.
I was watching your "zivko1 corrected values" you put for "center" and "con rod" different values i putt sketch to see what that means:

If you dot wont that type of L arm then correct it

about sine movement my opinion is that it is not important that pistons have sine movement but it is very important to they have phase angle about 90 degrees.

about compression ratios/stroke ratios
first picture:
[album]97[/album]
(not in scale)

normally we make gamma engines (left picture) and there pistons do not have overlapping, than we say that is best way to get good working engine is to have displaced volume (Vd) 1.5 volume and working volume (Vwp) 1.
That gives compression ratio of: Vmax is Vd+Vwp=1.5+1=2.5 and Vmin is Vd=1.5 so compression ratio si Vmax/Vmin=1.66
and we do not make difference between strokes and volumes

If we have beta engine (right picture) with same displacer and if we design it with same compression ratio because of overlapping of pistons this engine should have more longer stroke of displacer to keep compression ratio. (because of that, engine will have bigger displaced volume).

So my opinion is that you need larger stroke ratio to get compression ratio 1.666 or 1 working vs. 1.5 "dead space"
because of that I put to you "stirling pistons beta sheet"

If I am wrong please someone tell me (us)

Salute Ante

[zhivko]

Ante thanks,

I still examining your post, you say:

So my opinion is that you need larger stroke ratio to get compression ratio 1.666 or 1 working vs. 1.5 "dead space"
because of that I put to you "stirling pistons beta sheet"

Is there suppose to me some additional excel file in this post?

Ante please check my last excel file - I did construction of crank design by following

my_crank.jpg (41.71 KiB) Viewed 7703 times

and the values for my design are in:

zivko1_correctValues.zip

MyCrankCalculation

(159.56 KiB) Downloaded 291 times

.

Still need to modify excel so L arm and radius, and crank would be displayed apropriately.

Best regards,
zhivko

[zhivko]

Here is excel corectly visualizing crank movement for different parameters.

myCrankMechanism.png (223.2 KiB) Viewed 7700 times

[Ian S C]

If your volume ratios are not correct (or near enough), all the mathimatical formula in the world won't make it work. Ian S C

[Ante]

Here is excel corectly visualizing crank movement for different parameters.

The attachment myCrankMechanism.png is no longer available

sending file for comparison (I can not send it on PM)

Salute

[zhivko]

Hi Ante, geofv, Ian and all other that are reading this topic,

This is my latest geometry,

ModifiedVersion.jpeg (71.43 KiB) Viewed 7691 times

made by modifing excel sheet attached in previous post. I tried to acknowledge all the pointers you gave me so here is now latest geometry that mainly changes following:

stroke ratio is now 2,1
phase difference is now 90 degrees
(Ante as you said "this engine should have more longer stroke of displacer to keep compression ratio than 1.5" and you didn' explicitly mention how big it should be) - so I ask everybody should ratio of 2.1 be enough (big)?

piston diameter is 250mm
piston stroke is 107mm
displacer stroke is 227mm
other data:

ModifiedVersion_Data.jpeg (208.01 KiB) Viewed 7691 times

displacer is extended to 2 times diameter (but its diameter is still 230mm) - still missing some experience regarding steel wool? How to modify displacer to incorporate it? Should displacer be also 250 and should I put 3 holes where steel wool should be placed? It seems to me that direct air flow to piston are would result in better heat transfer and less pressure drop compared to if air is directed on sides of displacer? Comments anybody?

DisplacerSteelWool.jpg (12.77 KiB) Viewed 7691 times

Video available at:
video

regards,
zhivko

[Geoff V]

zhivko

A displacement ratio of 2:1 will be good for the temperatures you intend using but be carefull how you measure this. It is the ratio between the maximum volume in the heater (bore x stroke of the displacer) and the maximum volume in the compression space (piston bore x the maximum gap between the top of the piston and the bottom of the displacer) which on a beta will be less than the piston bore x it's stroke, and don't forget to subtract the volume of the displacer rod.

Heat transfer takes place in the annular gap around the displacer, there is no point in heating the end of the heater! The amount of heat transfer is also dependant on the gap, as the gap gets bigger the heat transfer decreases.

IMAG0396.jpg (140.04 KiB) Viewed 7687 times

Do not try to get too higher compression ratio, the heat transfer process is almost all adiabatic (not isothermal as most text books say) if the compression ratio is too high it will overload plain heat exchangers and the engine will not run!

Regarding the phase angle, 90deg is not critical, like Andy Ross we have run engines from 35deg to 105deg and are currently using between 45 and 51deg kinematic phase angle. The phase angle changes the characteristics from gentle, lower power, easier to start at 35deg to harsh, difficult to start, yet more power at 105deg and the best angle varies between engines of different designs.

Finally, if you have not already done it, disconnect the piston rod, apply heat to the sides of the heater and turn the engine by hand to measure how far the piston moves, this will tell you more than all the spreadsheets on the Planet.

GeoffV

[vamoose]

Crikey zhivko, you have really been doing some work on this baby,
I studied autocad a few years ago but haven’t had a reason or a copy or a decent computer to run it on for a while (although I wish I had a working copy of late). I can appreciate the effort you have made, also I used to work in the metal fabrication industry and i like what you have done so far (sweet!).
I have been reading your topic with interest and have had a few thoughts about some possible retrofit ideas. That being said I don’t want to distract you too much from the good ideas and possible alterations to geometry that the other guys have suggested. Its very solid information from some very experienced fellows, so take my ideas with a grain (or bag) of salt, also if my thoughts are bad ideas, I hope they will say so, so that I don’t lead you too astray.

Firstly as another option for placing steel (or other type wool) around the displacer, here's a possible alternative

Here is a possible material for regenerator use. Its called 'termimesh' in Australia (and is a termite barrier material used in the construction industry). It is a stainless steel interwoven mesh that is around 300 microns in thickness, with strands 150 microns in diameter and has about 22 strands per 10 mm. It can be cut with heavier duty scissors, its not too rigid and can be manipulated into shape as its quite malleable. I guess it might be available from pest controllers in other countries with termites. I've been informed its not covered in any chemicals but is just a physical penetration barrier.
(I just picked it up off a job site rubbish pile)
vamoose

had a closer look and it's 15 threads every 10mm, don’t know how I got it so wrong, I must be in need of a monocle ...or 2.

vamoose

(from what i've found) The width of the mesh is 300mm and comes in a basically a continuous length, And as opposed to steel wool you shouldn’t get the particles from the wool that can become free floating ebrasives, also I think it may be able to be wound so that it conforms to the displacer radius fairly closely . I'm not suggesting this is a great alternative but its an option.

Also another alternative (disregarding the first suggestion)- possibly, if there is enough room you could introduce a thin sleeve with a small clearance between it and the displacer (with the larger gap between the sleeve and the cylinder wall), and then wind mesh “bandage wound” around the sleeve outwardly to firmly fill the gap between the sleeve and the cylinder wall (and then 'insert' into the cavity). This could then possibly act as a hot end heat exchanger, regenerator, and then cold end heat exchanger (you could also divide the mesh into 3 different sections (rolls) so they are more physically isolated from each other).This insert would obviously have to end at the point of the top stroke of the power piston.
A loose (or firmish) seal could then be located between the small gap of the displacer and sleeve to encourage the working gas to flow through the new outer 'manifold' and the hot and cold ends (and regenerator).

Just some thoughts
vamoose