vertical lamina flow engine?

[CrewCab]

No pictures, it's just too ugly .

David .............. now you are paying the price for making such a fine engine in the first place 8) ............ In my case I made one which was so ugly beating it with a stick would have been a compliment ...... as such I have little to better next time out ;D

To be fair I didn't plan this, it was just sloppy workmanship : ........... honest

CC


PS: ............ you coming on Saturday 8)

 

[Stan]

As some of you know, I have been working with a test model lamina using a metal tube hot end. I have tried every every possible combination of tube length, cylinder size and stroke and restrictor size and length and flywheel size and weight.

I could publish pages of data but it is all meaningless since nothing is repeatable. If it runs at a certain speed one day, on the following day with the same conditions it runs at a different speed or even refuses to run. I am almost at the point where I sweep the bench off into the scrap metal container and start a different project

My other sterlings and fire eaters were easy to modify and improve because there is at least some valid theory on how it works. With the lamina, there are multiple theories from acoustic to zoom and I haven't been able to verify any of them.

 

[Twinsquirrel]

Join the club Stan, I'm in the same situation but there is one thing that has helped me gain some repeatability.

When the hot end is heated in a lamina engine the overall pressure in the cylinder increases, sometimes to a point where the piston stops at TDC, you then need to wait until the pressure leaks away past the piston but if you have made the piston and cylinder to very close tolerances this can take some time and cause you to abandon a particular set-up.

One way to circumvent this is to have some way of equalising the pressure with the atmosphere, a simple hole with a removable bung in the side of the hot chamber somewhere will do. It is then possible to heat the tube to operating temperature, set the piston/crank in the mid-stroke position then vent the chamber to the atmosphere and replace the bung.

Using the above method I have been able to get much more repeatable results although I'm still having trouble understanding fully what is going on inside the cylinder, it seems that even when changing one variable at a time you never quite know what to expect.

Hope that method helps for you, keep us posted.

David

 

[Stan]

David: Have you done any tests or arrived at any conclusion on the effect of piston location (at TDC) has on operation. My latest prototype has a disc for a crank with threaded crankpin holes at .25". .375", .5" radius. By changing the position of the crankpin, I can select a .5", .75", or 1" stroke. Changing the position of the crankpin to a shorter stroke means that the piston is not going to the top end of the cylinder.

I also have a selection of connecting rods that put he piston at the top of the cylinder for each stoke length. So far, on my particular model, I seem to get the best performance at a .75" stroke length but the length of the connecting rod has not shown any significant effect.

This would appear to be contrary to logical theory in that you would have a volume of air in the cylinder at all times that you have no control over.

One other change I have made on version 2.0 is to change the coupling between the hot end and the power cylinder. On the first version, the two components were threaded into opposite sides of an aluminum block. Since this provided free flow of heat from one to the other, I have changed to the method used by the glass test tube constructors.

I made a new cylinder (1.25"OD finned with ,75" bore) with a ,5" long neck with two O rings and just plug one of the hot tubes onto the neck. The drawback to this is that I now have a minimum length of .6" restrictor unless I put the restrictor into a counterbore. The neck is currently bored .25" and I have three shouldered restrictors of different size .6" long that are just pushed into the neck Just another challenge since length of restrictor seems to be one of the unknown factors. Stan

 

[Twinsquirrel]

Stan,

I'm finding very much the same things you are but here my thoughts:

I found that if I left some dead space at the top of the cylinder performance was enhanced significantly but there is the possiblity that with such low specific power any deviation in bore roundness or in the lapping of the cylinder could be causing a minute amount of binding. More testing required.

All the combinations I tried worked best with a stroke of .75" with a 4.5" x .68" test tube.

I'll let you into a little secret, for my vertical lamina test I had to increase the length of the restrictor to nearly 4" using a tube with a 0.125" bore, the "regenerator" material is wrapped around this tube. Interestingly in previous tests without the tube the restrictors optimum bore was .25" with a length similar to yours.

After many hours of careful data collection I threw away the note pad because as you say, none of it seemed to make any sense, I've now gone completely with gut feel and expect to add a lot of fiddling time at the end of the build, I'm not going for any speed or power records here, all that is needed for my purposes is a running engine.

Sorry I cant be of any more help.

David

 

[Stan]

David: This has become so intriguing I may keep at it for a while longer. The fact that you are getting similar results to me shows that we are both crazy. My current cylinder is he the most exact cylinder I have ever built. After drilling a 1/2" hole I ran in a 1/2" end mill to give me a completely flat end to the cylinder and then bored it to final diameter. I was getting such a good finish with the boring bar that I decided to bore to final size instad of reaming as that leaves a small ridge on the leading end of the reamer. My cylinder is within a couple of tenths the full length, right to the head. The piston is graphite that holds quite a bit of vacuum when you put it out but runs really freely.

I finned the cylinder down to a .05" thick wall to get good cooling but frequently I wrap a wet rag around the cylinder or the cold end of the hot tube looking for a change in speed. The highest speed I have obtained is less than 400 RPM so I am amazed at the reports of 2000 RPM.

My hot tubes started out as 6" and 4" of effective tube but with the design change they are now 1/2" shorter. They are .550" ID by .625" OD The aluminum tube is the same size (4 x .625) but I have never got the engine to run with it.

I have been making restrictors with drill bits (1/8". 3/16", 7/32" and the no restrictor 1/4") so I will give a try to your idea of a long tube. My best results has always been with the 3/16" restrictor.