Is anybody on this forum building Stirling Cycle engines?

[ratty2e]

It does look like you had some choking inyour transfer pipes, as now with more surface area you acheived 20% more power.

What is the reason for using different materials for your expansion and compression cylinders? Have you experienced problems with thermal expansion and binding of the piston/displacer? You are using Rulon LR for your piston rings; did you know that running Rulon lr in cast iron isn't the ideal combination,as they class cast iron as a soft surface. The reccomended Rulon for that material is Rulon J or Rolum XL, you probably won't have a problem with the Rulon LR in the short term, but if you want your engine to run for thousands of hours then I would go for Rulon J or XL.

Are you using slots for your expansion and compression exchangers? I have found that if you have slots any wider than 0.5-0.6mm then it reduces the performance of the engine; what width /depth do you have in you engine?

There are many different materials which can be used for regenerator (wire guaze,foil,metal foam,wirewool etc),all have there merits and disadvantages; what material did you choose? Have you done any experimenting with porosity/fill ratio of you regenerator and what effect did it have on performance?

At last somebody doing real stirling engine work and not just playing about with bean can engines.

keep up the good work, the world needs people like you for when the hydrocarbon start drying up!

[Geoff V]

Hello Ratty2e

The reason for the different cylinder materials, displacer cylinder runs very hot at the top end so cast iron was selected, the compression cylinder in ally is a recent mod to get over the problem of loosing compression with a cold engine. You are quite right about Rulon LR in cast iron but i'm using up old stock, it's fine on hard anodising (rockwell 60-70).

Heat exchanger slots are 0.5mm wide and 5mm deep 46mm long and the regenerator matrix is 0.002" SS foil 18% fill factor, I plan to try to increase this to 25% but it's running so nicely at the moment I want to get it in my boat and enjoy it.

Geoff V

[ratty2e]

in a previous reply you mentioned that you are using a three ring system with spring preload. Can you please give more information on how this works as i don't think i have come across it before. I have been using a combination of either lip seal or normal Rulon pston ring but with a over lapping joint to stop the gas path.
The advantage with lip seal is that they aid self pressurisation from the sealed crank case, and minimise the crankcase pressure swing.

Do you use Rulon bearer/rider rings on both piston and displacer? Or as you are using a cast iron piston/hard anodised cyl, just rely on its self lubricating properties to support it in a closely toleranced fit? If you do use bearer/rider rings ; do you have them fully floating or glued to the piston/disp? Rulon is a great material but it does have an awful lot of thermal expansion compared to other materials; so it would be interesting for you to start another thread explaining how you made your three ring system.

[Geoff V]

Dear Ratty2e

I went for a lip seal on the compression piston for the very reasons you suggest, originally I had external plumbing to pump the crankcase down and the working volume up, this piping and the associated dead space is now redundant. Regarding bearer rings, they are just split Rulon rings floating in their grooves.
There is a video on youtube of the internal workings.
http://youtu.be/jAQ5kr_yFwo or search cnc3d49.

Geoff V

[ratty2e]

Your engine looks excellently made, if it performs as well as it looks then you have a little cracker!

Did you have the expansion slots wire cut?

When I have used thin stainless steel shim as a regenerator, I indent dimples into the surface with a seamtresses spiked wheel (what they use to make paper paterns).However when i come to wind it around into an annulus I have found that the way you wind it (either dimples in or dimples out) has a massive effect on the way it performs as a regenerator and hence engine performance. Have you seen a similar observation when you wind your regenerator?

do you have any power and torque curves that you could post? I would be interested in how flat your torque curve is and at what speed the maximum torque is acheived

[Geoff V]

Ratty

I cut the slots with a solid carbide slitting saw mounted on a much modified Chinese mini milling machine, unfortunately I don't have and pictures of the machine at the moment, lost them when a hard drive failed!

My regenerator is manufactured as you described, but being of 0.002" foil it doesn't curve in on it's self which ever way it's wound, unlike 0.001" foil.

Regarding power curves, all testing todate has been by driving a prop in a water butt, having first calibrated the prop power absorbtion curve with an electric motor. The great advantage of this method is one can track improvements instantly by just measuring the rpm. I will construct a prony brake at some time and generate some proper power curves but for now I only have 'spot' readings.

Geoff V

[mark]

you say that you engine was designed to have a volume ratio of 0.64. Why did you go for such a low figure as all of the conventional knowledge (schmidt theory,Organ,walker) says that you have have a volume ratio of at least unity or above. Did you know about their theories or was you design just a guess? Can you please elaborate why you went for such a low volume ratio as i find it hard to beleive that it will give maximum power, but i would like to hear your reasoning behind you decision.
at what temperature does you engine need to run? and what free speed does it produce at atmospheric(if it runs at atmospheric) and at 1barg and 2barg etc?

great looking engine though, and you must be doing something right to get the power you are getting.

[Geoff V]

Hello Mark

My engine was originally designed with a Lambda of 0.84 but would only just run if very hot and at least 3barg precharge, from past experience I suspected that Lambda was too high and so I reduced the compression bore to 48mm which gives a Lambda of 0.64, if you have seen my video, the engine is running with this the reduced lambda. I have covered this issue in more detail in posts over the last few days, you my like to read them.

I am very fortunate in knowing Dr Allan Organ very well, infact we had a pow-wow over coffee just yesterday. He was as puzzled as you at first but having given it much thought I believe he now thinks that the process is very unlikely to isothermal and that the schmidt analysis is probably not appropriate, you really should ask him yourself as I don't like second guessing his current thinking.

Regarding running temperatures, I start the engine at 460c and about half a barg precharge, after a run, with the burner off it runs down to about 250rpm at 300c at atmospheric.

I hope you read my other posts especially regarding the work I have been involved in with another Beta engine with a variable goemetry crank mechanism.

Geoff V

P.S. free speed off load at 1barg 1600rpm, haven't tried it off load at 2barg.

[Ferraccio]

Geoff,
I'm entering now in discussion,
excuse me all.
for my poor knowlwdge of English I do not have read all messages in discussion, for so my notices may be are unappropriate.
At this stage I think to write this:
I'm buiding a 96 cc alpha engine, (so 1:1 ratio), air, atmosferic, but pressurizable (dimensioned) for 15 bar relative.
I've no one experience for burner.
Material used SS 316, 304, aluminium, bronze.
Angle levers to minimize lateral stresses on piston/diplacers.
The engine is foreseen "completely" pressurizable (generator too), avoiding sealing on shafts, and pumping.
For my problems my contruction is very slow and whith poor facility.
Till now I've poor experience in burner,

About in general Stirling engine:
S. E. is NOT competitivwe (now) related to other types of engines, using gas or oil:
Modern steam (alternative) (see Cyclone engine) using porcelain - h. tech matrls; or turbine (see Capstone Turbine) h. tech matrls, have superior yelds.
Stirling engine is good using not otherwise utilized heat surces (Sun, wood, twigs, straw, rice hulls), when yeld is not so important, cost of engine is very low, and overall the exaust heat is recovered (for cooking or heat).
Power from 5 up to 30 kW.
At this stage, for our experiments, of course we use gas.
Ian:
About coal: it is sure that, being pollutant or not the coal will be (sure !), it is the combustible of next centuries; (world reserves fo oil are for 50 - 60 years, coal is for 250 - 300 years), coal is NOT pollutant when used with (now yet existing) filtering (also quite expensive) devices.
Also: with (quite expensive) safe procedure (yet existing too - not pollutant) from coal can be extract gas and oil.
Is the "expensive not pollutant devices" wil be used is not depending by me ;-)).
True: the coal is dark, but to die, ... is more dark.
To explain as by me said: SE is external combustion engine: is rare to find a correct balance of imput energy (from combustible content) and exaust mechanichal one. Yeld is very low.
From Italy
Ferraccio

[Geoff V]

Dear Ferraccio

Thank you for replying to my thread.
How far have you got with the construction of your pressurised Alpha?
In light of my recent experiences, with several engines, I am concerned that you have selected a displacement ratio of 1:1. It is now clear to me that such an engine will require a very high heater temperature to run at all which will probably prevent you using low grade fuels. If your intention is to use high grade fuels which can achieve high heater temperatures, all well and good.
Regarding burner design, I have some experience with LPG burners, not that I consider myself a specialist but you are welcome to what little knowledge I have.

Geoff V

[Ferraccio]

Hello Geoff;
The choice of the 1:1 ratio is not due to the fact that I I plan to use fuels hy tech, but for the fact that the engine is alpha, obviously with medium to high temperatures, as we do in many.
The ratio 1:1 (reported in the literature) is (what in my judgment and my opinions certainly questionable) due to the nature of the Stirling engine. I repeat that these are only my opinions based on my knowledge (intuitive and therefore not certain) the physics of fluids.

1) The S. E. is a closed-cycle engine with a fluid confined, where the works of "pumping" useless are deleterious.

2) The engine (although not clear from the literature) uses a pulse cyclic "self sustained" (*), which I think can be easily damaged (this will become clear for realize very high level, where volume and geometry of the ducts sections can be decisive).

3) The reduction of the volumes in which it moves the fluid, (and therefore the dead volumes) is obvious way to have direct and strong pulses.
Other architectures use more interior volume of alpha, often with counter pulsation; in Alpha architecture the volumes are minimal and the flow is directed.

For the enormous complexity of step 2) can happen that a beta or gamma motor, built with the same level of an alpha, may be more performance than an alpha, but the same had "guessed" geometries and conducted, the alpha has certainly less against pulsation, less dead space than any other engine, and the flow is more direct.
Is clear also that the buildin of a SE is mainly an empirical work, for NASA too ...

As for the fuel "unconventional" the skins of hazelnuts, produced in quantity for the confectionery industry here in Italy, have among the major powers in calories, even more than some coal. The dried manure, or dry twigs when burned give excellent thermal power, but they are certainly low tech, in the sense that the flame is less manageable, and then the deposition of heat is less efficient. (yeld!!).
Alpha engine is simpler in some way...., more difficult in other.

(*) The thermoacoustic engines, such as those produced with very high efficiency by NASA for deep space applications, are simple "pipe" (without pistons or levers), but built with in very high technology "around" the spontaneous pulsation, using every physical and technology device to carry the focus of the pulse on piezoelectric plates.

I'll be happy to ear your considerations.
Ferraccio (bad iron)

[Ferraccio]

I correct myself:
"....but the same had "guessed" geometries and conducted, ...."
have to be coorected in:
"....but if the same engines had "guessed" geometries and conducted, ....

[Ian S C]

Geoff, you may have seen this site, but here goes, www.scientiareview.org/pdfs/168.pdf Optimization of Stirling Engine power output through variation of Choke Point Diameter and Expansion Space Volume. By Anna Brill of Massachusetts Academy of Math and Science. Ian S C

[theropod2]

Ferraccio,

Regarding coal as a fuel source, see gasification.

R

[Ian S C]

MANURE is good, see Chinese domestic (rural) gas generator. Ian S C