Simple Stirling 1 performance with and without regenerator
June 9, 2008 – 12:02 pm
I’ve tried a variety of regenerators on the Simple Stirling 1 engine and the one shown in the photo is simple to make and performs as well as or better than all of the other ones I’ve tried. The test results on the engine with the original displacer and with the modified displacer containing the regenerator are shown in the plot. As you can see for the same delta T (temperature difference between the hot and cold plates), the displacer with a regenerator provides much higher RPM.
Ideally, a regenerator makes a Stirling engine more efficient because it performs part of the heating and cooling of the working gas as the displacer cycles it back and forth between the hot and cold chambers. After the gas leaves the regenerator it enters the active heating or cooling regions. A regenerator is a passive component. It cools the hot gas as it flows in one direction through the regenerator and heats the gas when it returns back the other direction. The heat is transferred to the steel wool in the regenerator I’m using and is transferred back on the return trip.
The regenerator isn’t totally free. The steel wool material causes some friction with the air, causing a larger pressure differential on the two sides of the displacer that makes additional work for the engine. The volume taken up by the regenerator also adds dead space to the engine, making the engine slightly less efficient. Despite these disadvantages, the net gain is substantial.
Incidentally, making more clearance around the side of the displacer to make the air flow easier (with no regenerator) actually caused such a large drop in power the engine wouldn’t run at any reasonable temperature. I cut the displacer down from approximately 3.4″ diameter to 3.25″. The reason it causes such a drop in power I believe is because the tight clearance between the displacer and the cylinder wall accelerates the air as it flows past. The air speed is high enough to make the air swirl around in the hot or cold chamber and have good heat transfer with the hot or cold plate. The larger clearance reduces the air speed, possibly causing laminar flow instead of turbulent flow, and reducing the heat transfer.
Modifying the displacer to add the regenerator is probably self-explanatory if you look at the photos. I used a spade bit to drill the four 7/8″ diameter holes. You could probably use a 3/4″ hole instead of 7/8″. To keep the steel wool in place I used 5 minute epoxy to attach a disk of aluminum window screen on the bottom of the displacer and then divided up 0.6 grams of #0000 steel wool among the 4 holes. Try to fluff it up to fill the volume and make sure there are no straight through holes where the air can go without going through the steel wool. Test run the displacer to make sure you’re getting reasonable performance and then epoxy a screen on the top of the displacer to lock the steel wool in. In the photos you can see that I put masking tape on the screen to mark the circle and hold the screen in a circular shape.
If you test your engine without the regenerator and then add it, you’ll probably be as blown away as I was that 0.6 grams of steel wool (this is almost nothing) can make such a huge difference.
It’s quite possible you may be able to come up with a regenerator that works even better. I’m still planning to try some fine copper wool.
25 Responses to “Simple Stirling 1 performance with and without regenerator”
Nicely done! Torque remained constant?
By DU on Jun 9, 2008
I don’t have a way to measure torque on this engine, I’m just measuring unloaded RPM. The engine accelerates until the torque balances the friction. It would be nice to measure the torque–I’ll have to think about that.
By admin on Jun 9, 2008
Hallo Doug,
In one of my LTD Stirlings I used succesfully Scotch Brite cleaning pad as regeneratormaterial.
see:
Http://home.hccnet.nl/hvisser.5
next-Gallery- model 23
Greetings from Zeeland, Holland
Huib Visser
By Huib Visser on Jun 15, 2008
Hi Doug,
As air passes through the regenerator as well as around the displacer, could the speed gain be due to less air resistance?
Would it be more efficient to increased the diameter of the displacer, so more air passes through the regenerator?
nice work btw
Al
By Al on May 17, 2009
Hi Doug, I am not an engineer, but i think the size of the displacer and the size of the power piston are directly related. I also think that the space between the displacer and displacer wall is critical to the amount of pressure created to the power piston. Also i believe the sizes of the two pistons are relative to each other. if u change the size of one u must change the size of the other, directly perportional ???
good job even i can understand it….
By Dave on Jun 5, 2009
Hi All
Cheers, John
I’m recently interested in Stirling engines for generation of charging current for electric assist pedal trikes.
I was keen on a tiny diesel engine, but none seem to exist. Nevertheless, the Stirling engine seems ideal for the use of waste
vegetable oil (WVO). Using this in diesels is very problematic wrt engine life, whereas a Stirling should last as long as it’s
built to. I was wondering where the tiny amount of 0.6g of steel wool was derived. I was keen on using aluminium wool as it has
about the best thermal properties for this use, but on finding it costs about $250 for 5 lb, I thought I would compromise on steel
wool. Laying the strands across the flow rather than with the flow should make the axial conduction of heat as low as possible. I’m toying with a magnetic drive for the displacer and a diaphragm for the power piston. This way leaks can be avoided and friction cut. I’m still looking for sites which will give me volume ratios such as power piston displacement to total enclosed volume. The only mention of weight of regenerator mesh I’ve found is here, and I’m guessing that much more could be used, although ideally, the mass of regenerator material would be the same as the mass of air passed through it in proportion to the specific heats. Any comments eargerly absorbed
By John Riley on Jun 27, 2009
ps I just looked up the specific heat of air and it’s a bit more than twice that of iron on a weight basis, so ideally perhaps 2.5 to 3 times the weight of steel wool? j…
By John Riley on Jun 27, 2009
Hi,
I was looking at your Maker Faire 2008 Engine and it seems quite large however you state it only delivers 0.09W. I do not understand that.
Is that because you are only putting in a small amount of power or are there huge losses. For example, if you put in heat at a rate of 100W, how much power would the engine deliver? Thanks.
By Robert Virkus on Jul 2, 2009
Sorry to intrude – I have some real newby questions about all this if you don’t mind…
I have an off-grid house so energy from renewables is of special interest to me. A year or so ago, I saw something on TV about a generator powered by a Sterling engine at the focal point of a solar array (based on an old satellite dish).
I thought the process seemed fairly “developed” and looked for kits or something to come out. (Note – I have a degree in Music and am not allowed to handle sharp objects ’cause I’m accident prone, so trying to build something myself is not in the cards…) However, the discussion here makes me think that (for me) this would not be a practical addition to my system.
Lets face it – putting up a solar dish and engine in the front yard that only produces 1 watt would only irritate my wife while doing little to charge my batteries.
Is this technology just too “immature” to be of real use for someone like me? I’m looking for some alternatives to PV that I can use to expand my generation capacity. Water is not available, wind is good but windmills aren’t and generators based on the Tesla turbine seem to be “vapourware”.
Sorry if you feel this post is off-topic but I figured that you engineering types who are really working on this stuff would have the answers to my naive questions. Thanks for your patience.
Roger
By Roger Priddle on Aug 2, 2009
Hi all, its now quite a long time that i feel interested in ltd stirling engine. i first may fully thank the author of this edit to have physically test and further realised his results that confirm sumarize of Dr JR Senft theory about higher efficiency displacer that were including regenerators. I here may confess that i kept the study of the displacer at least because it was to my sense the most interesting part of the engine where improovments could significally change the output performance. I wont go through all the details of my search and studies about but i may give parts of my personnal conclusions about this subject. Most of it is relative to some information u could find in the book written by Senft about LTD Stirling engine and theory of heat engine efficiency.N92 and P19 seems to be quite good example of it.
First it seems clearly obvious that regenerators have an effect once aded to the displacer but one may consider that advantage comes oftenly with inconvenient. Therefore obtained results could differ relative to the architectural design, size, shape and mateer used to proceed.
Nevertheless regenerators seemed to bring out more than they cost. Sumurazine of the subject will say that they increase speed transfer of the gas, creating new acces instead of the unique circle peripheric gate (clearance between dispacer and wall chamber)Further to this idea, the complete transfer of the gas will be more balanced and potentially be done at a higher speed if opertures are done within the dispacer. Paradoxaly these new opertures are creating dead volume within the chamber that basically we may avoid. The all trick is then to find the good balance of it, i.e. to achieve a good design. One more advantage of creating such air gap through regenerators is to help avoiding or reducing lateral movement of the displacer when running, keeping more constant the clearance. This remarks ends up the velocity fluid transfer and aerodynamic aspect relative to the displacer.
Second, one may consider the thermal aspect of the regenerator whom first goal is to use part of the heat left by the gas to increase the efficiency of the Carnot Cycle. In this way regenerators may be considered as heat capacity storage unity that will release it during heating and expansion phase. Here the question occurs since everyone knows that main body displacer is made out of isolation foam that prevent body diplacer to get hot and to avoid making a heat transfer gate with the cold plate.Therefore its also obvious that displacer should never be in contact with neither of the plates at end positions of the cycle engine. This is apparently the good combination of regerator size, thihcness and peripheric clearance for gas flow that will improove the performance compared to a full displacer. Senft may precise that compensation relative to the diameter of the displacer would be done in case adding regerators, so in in away to keep quite similar swept efficien gas volumes of the chamber. i.e. outside clearence will be reduced in case adding regerators that are obviusly ceating an additional dead volume (or unswept volume). Its then a question that should be first thouht when creating the design of the displacer and the chamber relative to their initial optimum volumes to perform at best.
Three, is the matter used for regerators. I’m actually trying different materials and consider as well their heat conductivity, weight,thichness, velocity gas flow and stucture to compare.Basically test could be done with some 3M Scocht brite, thin wire meshes or even some polyurethane foam on which im focusing some interest. Quick notice that only a small few holes in the dispacer will help gas transfer.
About your design it may seems the regerators diameter is too big, resulting a bigger dead volume which you could reduce. Top position of the mesh and thickness of it is a subject to further discuss. Please leave any comment about heat inertia about material u may use in regerator body. I ‘d appreciate if you could release some test depending from the material used for regerators.
For additional information here after is a copy of what u can find on Wikipedia Us about regerators. its quite a good sumarize of the topic i guess.
Philippe
[edit] Regenerator
Main article: Regenerative heat exchanger
In a Stirling engine, the regenerator is an internal heat exchanger and temporary heat store placed between the hot and cold spaces such that the working fluid passes through it first in one direction then the other. Its function is to retain within the system that heat which would otherwise be exchanged with the environment at temperatures intermediate to the maximum and minimum cycle temperatures,[12]thus enabling the thermal efficiency of the cycle to approach the limiting Carnot efficiency defined by those maxima and minima.
The primary effect of regeneration in a Stirling engine is to increase the thermal efficiency greatly by ‘recycling’ internal heat which would otherwise pass through the engine irreversibly. As a secondary effect, increased thermal efficiency promises a higher power output from a given set of hot and cold end heat exchangers (since it is these which usually limit the engine’s heat throughput), though in practice this additional power may not be fully realized as the additional “dead space” (unswept volume) and pumping loss inherent in practical regenerators tends to have the opposite effect.
The regenerator works like a thermal capacitor. The ideal regenerator has very high thermal capacity, very low thermal conductivity parallel to fluid flow, very high thermal conductivity perpendicular to fluid flow, almost no volume, and introduces no friction to the working fluid. As the regenerator approaches these ideal limits, Stirling engine efficiency increases.[13]
The design challenge for a Stirling engine regenerator is to provide sufficient heat transfer capacity without introducing too much additional internal volume (‘dead space’) or flow resistance, both of which tend to reduce power and efficiency. These inherent design conflicts are one of many factors which limit the efficiency of practical Stirling engines. A typical design is a stack of fine metal wire meshes, with low porosity to reduce dead space, and with the wire axes perpendicular to the gas flow to reduce conduction in that direction and to maximize convective heat transfer.[14]
The regenerator is the key component invented by Robert Stirling and its presence distinguishes a true Stirling engine from any other closed cycle hot air engine. However, many engines with no apparent regenerator may still be correctly described as Stirling engines as, in the simple beta and gamma configurations with a ‘loose fitting’ displacer, the surfaces of the displacer and its cylinder will cyclically exchange heat with the working fluid providing a significant regenerative effect particularly in small, low-pressure engines. The same is true of the passage connecting the hot and cold cylinders of an alpha configuration engine.
By Philippe on Jun 30, 2010
Hi Doug
. Would I need to make any changes to the displacement cylinder etc. as shown on the plans to incorporate the regenerator, or will it fit right in? Thanks, Peter, Tasmania, Australia
Congratulations on a fantastic website. I just wish I’d discovered it sooner. I’ve just completed a “tin can Stirling engine” described on another website but I can only get it to run using a propane blowtorch! Tin cans are not a very satisfying material of construction.
As an engineer I’m impressed by your high standard of drafting and precise approach to everything. I think I might have a crack at building your Simple Stirling engine. It will certainly save on propane
By Peter Gross on Oct 23, 2010
Hi Peter
I’m glad you find the website helpful. The displacer I made with the regenerator fit right in. I’ve learned a lot since I made that engine and the displacer with the regenerator–I need to put more recent info up but I’m usually too excited to get to my next engine experiment. The displacer and regenerator as shown is simple and effective. A few things to keep in mind. Use the finest steel wool available, #0000 is what it’s called here in the USA. Use a very small amount of steel wool — you should easily be able to see through it. I didn’t realize the importance at the time, but the holes are about the right size. To get good heat transfer with the hot and cold plates you want to accelerate the air as it passes through the displacer so that it blows against the hot and cold plates and improves the heat transfer. Try to make the displacer with as little gap around the sides as possible. It’s not practical on this engine to hold real tight tolerances, especially working with styrafoam, but you might try to get not more than a 1/16 inch gap (1.5mm). The smaller gap helps force the air through the regenerator. You must, however not have the displacer touch the sidewall because the friction will be too much for the engine to overcome.
By admin on Oct 23, 2010
Hi Doug
I’ve built the engine, but can’t get it running yet. I’ll try polishing the piston and bore and checking alignments. What should be the clearance at the end of the stroke for the two pistons?
By Peter Gross on Nov 11, 2010
The clearance isn’t too critical as long as you have some. 1/16 on an inch would be great but 1/8 inch will be fine, especially when you are trying to get things running. Friction is probably the biggest problem. Try to make sure the moving parts slide smoothly and there is nothing rubbing or binding. Don’t use any oil on the piston, it causes too much friction. The other issue is to make sure you’ve got air-tight seals working everywhere. The only air leaks should be around the piston and between the displacer shaft and the brass tube it slides in. Both of those leak sources will be very small. Make sure to seal where the cold plate joins the square tube around the power cylinder and the brass tube for the displacer shaft.
By admin on Nov 11, 2010
Thanks for your prompt and helpful advice. I’ve got it running for about 5 mins with water at 80C but it is fussy to start. I think it takes time for the temps to get right. My problems are friction in the displacer shaft tube from misalignment and intrusion of the foam rubber gasket into the cylinder. Would a full flywheel and balance weight for the displacer help? I plan to try the regenerator soon.
By Peter on Nov 12, 2010
I’m glad to hear it’s working. A balance weight for the displacer will help at low RPM. The club-type flywheel with weights at the end is efficient from the standpoint of getting most of the mass out as far as possible from the axis of rotation, but doesn’t give you a place to attach a balance weight for the displacer. A more traditional flywheel or a cross-type would give you a place to add the counterweight for the displacer. At higher RPM a displacer balance weight on the flywheel will give you problems with an out-of-balance flywheel. When you get a regenerator working the RPM should increase enough that balancing the displacer won’t be such an issue. I’d work on that first. Just for reference, the club-type flywheel is simple to build but isn’t safe when you go to larger masses or higher RPM. A round flywheel is much safer because it just rubs against body parts that get in the way rather than clubbing them.
I don’t know what the exact displacer shaft misalignment issue is. I assume it isn’t bent. You might be able to drill the hole in the rod end slightly larger to allow for the misalignment. A few thousands of an inch might reduce the friction. It may cause a little extra noise at high RPM.
By admin on Nov 12, 2010
I added a CD to the flywheel (drilled and bolted under the fender washers) and it helped a lot. I’ve used the CD to mount washers at 90 degrees which smoothed out the running. I can get about 8 mins from boiled water (80-90C), but it doesn’t always start nicely. One difference from the plans is that I used a PVC pipe coupling (ABS is not readily available here). As this is longer I made the displacer deeper by 10mm to compensate. This made it a heavier than yours (40g) as it is balsa, but I am now working on one with a regenerator and expecting further improvement. I’ve made a couple of small refinements to the running gear which may be of interest. If you email me your address I can send pix. I like your design because of its flexibility and the easy access to the displacer, unlike the tin can engines.
By Peter Gross on Nov 14, 2010
I like the idea of using a CD added to the flywheel so you can add a balance weight. That’s a simple solution.
I’ve used balsa and other wood for the displacer and had problems with the moisture coming out of the wood at high temperatures and condensing on the power piston and cylinder. The water causes a lot of friction between the piston and cylinder and I have to dry it out before the engine will run properly. I can’t remember if it was a problem at 80-90C or only when I went over 100C on engines with a metal displacer cylinder. I’m wondering if this could be your start-up difficulty.
By admin on Nov 15, 2010
I ran the engine on solar heat for about 40 minutes and experienced the moisture problem you mentioned. It was going great until then – doing up to 200 rpm. Hopefully now the balsa has been dried out it won’t be so much of a problem but it will probably depend on the humidity of the air. I might try sealing it with paint.
You get quite high temperatures from the Fresnel lens. I tried putting some clear acrylic sheet over the top of the cylinder to improve heat collection but things got a little warm and it started to melt! I might try again with some glass but I’ll need to be careful with the plastic cylinder.
By Peter Gross on Nov 20, 2010
Hi folks, i hereunder precise some more specific information about displacer body configuration since i’ve been studying a lot this sharp subject. First of all, one may consider that we are curently concerned with gamma ltd engine working with a low delta temp. In this configuration please notice the so called regenerator(s) is inside the chamber and not outside, which is a very important point to point out because its furtherless important to precise what is the real function of it. There is actually two different aspects one may considers : In the the gamma engine holes or stuffed area with polyester or polyuretnane foam are placed to help the homogeneity and the velocity of the fluid transfer from one area to the other of the chamber; the subject is then enhancing of the fluid transfer. Second point is the thermal aspect and here is the mater relative to the gamma architecture since regenerators are again located within the chamber; one may considers that basically the hot area may stay as hot as possible and the colod one as cold as possible so to improove delta temp and efficiency of the engine. What will really occurs if you include a thermic regenerative material inside the displacer body (ie stealwood or metallic mesh)in which fluid will go trough ? You may risk to achieve the oposite result first attempted whic is to comunicate heat from one side to the other area of the chamber which result will occurs in lowering the delta temp of the concerned areas. Its’ very important to notice that regenerators used as heat exchangers on others architectures are always placed OUTSIDE of the chamber in a way to emphasize the delta temp.This is why i’m not so long persuaded that internal thermic effect material used inside the gamma chamber are efficient, may be worse since classic design and material used for the displacer body is an insulated one (ie polystyrene)to prevent any thermic bridge.
For sure it’s steal interesting and may be an obssesion to once again recover part of the heat energy which is obviously lost but one should absolutely consider that further thermal effect goal shouldnt be at the opposite of the original concept which point out performant isolation of the two areas.
The main idea is to keep the hot hot and the cold cold areas with high transfer fluid velocity. Second idea would be to help both areas to keep hot and cold so long with a storage material within the displacer but without ant fluid transfer through it to my sense. Third is to take into account the weigh of the material used to perfom the regenerators since scotch brite fiber is really heavy and may occurs unperformance. As an example for you to compare with, the full mass of the displacer body of my engine is 0,9 g (165 mm diameter)and is approx 2g once reinforced and equiped with its rod and attachment. If used,each 30 mm dia scoth brite fpolyster fiber regen weight is about 0,4 which is * 6 equal to 2,4 g, ie more than 100 % more !!! I ve been testing a lot of different material weigh and the best micro tubular or porosity one still polyurethane or nothing!!! (just simply smaller holes to help fluid transfer whic dia are smaller in a way to compensate the lost dead volume) Polyurethane ones 30 mm dia is approx 0,1 g each so 400 % less !!! Radial clearence may be adapted to the type and size of the regenerators architecture and dimension you may choose. To achieve this subject about weigh, please consider that every additional mass you may introduce in a mooving part will create a negative performance in terms of additional friction on the axis.
At last and about new perspectives considering the heat efficiency of the displacer and regenerators body material and once considered all said upper please let me know your experience or ideas which are welcome whatever they may feel crazy or not.
By Philippe on Nov 24, 2010
As far as the regeneration function, it does not fundamentally matter whether the regenerator is inside the displacer or external. In both cases you need to be concerned about thermal isolation from its surroundings. Placing the regenerator inside the displacer has several advantages, the path length is short (it can be too short in the case of a thin displacer), the added dead volume can be less because the path is shorter, and my primary reason is simplicity. There are also some disadvantages: As you point out, you usually pay a weight penalty. I think the biggest disadvantage is that having an external regenerator lets you route the gas through a better heat exchanger after the regenerator, for both heating and cooling. With the internal regenerator you typically just dump the gas into the hot and cold chambers which provides less efficient heat transfer with the walls. This can be improved somewhat by using exit nozzles as the gas leaves the displacer to direct the gas against the hot and cold plates for increased turbulence and improved heat transfer. I have measured performance improvements with this technique although I have not optimized it. I have also used displacers that are essentially all regenerator which also seem to work quite well, even though they add additional dead volume. It all depends on careful attention to thermal isolation, heat transfer, and gas flow friction. My few experiments using polyester material for regeneration were unsuccessful. I believe the low thermal diffusivity of the material makes it a poor choice compared with metallic material.
By admin on Nov 24, 2010
I’m not an engineer nor do I own a sterling yet but after viewing several internet videos on the subject I’ve often wondered how Peltier
devices may be used in conjunction with sterlings since the device heats,cools and changes heat to electric, as a heat sink add-on,regenerator, heat or cooling source, heat reclaimation in order to make sterlings more efficient. If waste heat is a by-product of a sterling depending on the source temperature, and cooling is required, either on the working cylinder or on the other side of a regenerator, how about a Peltier device used to generate electricity (google: caframo ecofan) and use that current to power a peltier cooling the cool side of a regenerator? Would that make a more efficent Sterling? Automobile catalytic converter material used as regenerator cores? Also, since some sterlings are dubbed as thermo-acoustic devices whice operate at an audio rate or generate powerful sound as a by-product, have the sound impact a diaphram and the diaphram impact a peizo-electric crystal to generate electricity? Or a combination of all or part of the above to improve sterling efficiency?
By rick s. on Jun 24, 2011
Hi,
Just found this website and I like it. I have an enduring interest in LTD Sterling engines and have built a successful engine that runs well on a 5deg “C” temp’ diff’. My next effort was directed at a Rotary Displacer/pressurised engine designe to run on Solar hot water panels and/or Compost derived heat source. I am just not a clever enough engineer to make the bits!
My current project is a more conventional LPG flame heated engine with linked , twin displacers and power pistons.
Before I spoil alot of painstaking work I need to know 3 things.
1. What ratio of swept volume is appropriate between Power cylinder and Displacer?
2. Is the diameter/area of the face of the Power piston critical in proportion to the working Gas volume? And what is that, expressed as a ratio?
3. My displacer is virtually the same area as the swept volume. However , while it is possible to fill it with a regenerative matrix (Can I suggest aluminium swarf from a lathe?); surely there must be an appropriate sized hole In proportion to the swept volume, bearing in mind that the potential dead/none working gas volume are almost the same? Otherwise, taken to extremes: Then removing the shell of the displacer while retaining the body of the regenerating matrix would be the best available solution. Clearly this is not the case but the solution as to the best size of entry and exit hole through the displacer eludes me. Can anyone help?
Derek R
By Derek R on Sep 19, 2011
The swept volume ratio between the Power cylinder and the displacer is not fixed a fixed value. It depends primarily on the temperature ratios you have for the hot gas and cold gas, and secondarily is influenced by the dead volume. If your engine has a large dead volume the power cylinder would be a little larger. Probably the best way is to use the Stirling engine simulator http://www.solarheatengines.com/stirling-engine-simulator/ and size the power cylinder and displacer so that the isentropic compression heating is around 25%. If it is a lot higher than that (like 35%) then the engine will have too much compression. If it’s low then the engine will have less power than it would with higher compression. To give you some examples here are the ratios for some of my engines. Th = 450 deg F, Tc = 80 F (measured at the external surfaces, the gas will be have a smaller temperature spread) the displacer has a 1.875″ diameter and the power piston is 1.25″ diameter. Both have the same stroke so the volume ratio for displacer to power piston is 1.96. This engine doesn’t get much power at Th = 400F, 500-600F provides good power. The solar-powered engine I am currently working with typically operates between Th=125F and Tc = 80F. The ratio on this engine is 7.2. It starts running with a Th/Tc (absolute temperature) of 1.05 and by Th/Tc of 1.1 it is running unloaded at 140 rpm. If there is any question that your engine doesn’t hold compression well then favor the larger displacer ratios.
The diameter of the power piston really doesn’t matter, it’s just the volume that matters.
I built an engine with very short displacer that was essentially very fine steel wool very lightly packed between some end plates with lots of holes. The trick is getting small clearance around the circumference so that the gas is forced through the steel wool and doesn’t just flow around the edges. It’s interesting that this engine would turn at higher RPM (because the regenerator was effective) but did not have as much torque as the same engine with a solid displacer and only a few holes filled very lightly with steel wool. My advice is to use steel wool with the finest wires (#0000 is what I used) although very fine aluminum should work well if you can find it fine enough.
By admin on Sep 19, 2011
Hi Admin,
Thanks for your advice. I do appreciate your help and will consider it carefully.
When/if my engine runs I will keep you posted.
Derek R
By Derek R on Oct 18, 2011