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Swift752

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Anybody got a good source for those tiny ball bearings 16x8x4 (ODXIDX t) and especially that 8x3x3 Connecting Rod Bearing?

Go to the model plane hobby shop. They will have a variety of very small bearings that go in servos. Also there is Boca Bearing on line. Hope this helps. Swift752
 

dgoddard

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Well, after getting a more satisfactory wick, I went about getting the heat shield that I talked of. The local O'Reilly's autoparts provided me with a 10"x10" sheet of exhaust gasket material for about $9. I settled on attaching it with silicone gasket maker since it is rated at 600 degrees F. The shield was cut to be just a bit taller and projecting above the flat to which it is adhered to discourage the flame from wrapping itself over the top of the cylinder.
For all my tinkering so far I could only get the engine to run for about 1 minute. After the addition of the heat shield, this doubled to about 2 minutes. So I think I can say that it is effective and beneficial. I now have enough gasket material to make about 100 more engines.

120831_Heat_Guard.JPG
 

dgoddard

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So far a maximum run time of 2 minutes is less than satisfactory, so I am looking at the issue of the flame. I am getting a mostly yellow flame from my choice of burner and fuel. That implies a cooler flame than if it was blue. I did increase the wick height and that helped me get to the current run time of 2 minutes. I theorize that this is due to drawing in the base of the flame where it is closer to what little blue there is in the flame. I know that this fuel will burn with a very blue flame because I have used it in an alcohol stove. I suspect that a hotter flame will be the next change I will have to make.

A related issue that I am dealing with is that the alcohol fuel I am using is proving to be very corrosive to the aluminum of the burner I have made. I am not sure what part the salt in the wick is playing in this but I will have to consider that also. I also need to test and see if the alcohol in the plastic dispensing bottle I have stored it in is at fault. It is possible that the alcohol is sufficiently hygroscopic that it has absorbed water from the air right through the plastic of the bottle, and the alcohol is not as pure as it should be.
 
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Chriske

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Hi,

I think you should consider using steel wicks. I use them all the time, works just perfect, and you always get a blue flame (if you're using the proper fuel of course)
second this kind of vacuumengine should be cleaned on a regular basis because a vacuumengine is very self-contaminating engine. All depends(again) on the type of fuel you're using.
Third with this engine the position of the flame is very important.

Chris
 

Cogsy

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Have you had any further success with your engine?

Mine is not exactly finished, but I have temporarily mounted it for testing and so far I can't get it to self-sustain at all, although it seems close.

I'm hoping you've sorted it out and will share the secrets ;).
 

dgoddard

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...... so far I can't get it to self-sustain at all, although it seems close.I'm hoping you've sorted it out and will share the secrets ;).
Well from a thermodynamic point of view any heat engine can only operate when there is a temperature difference between a high temperature (in this case the flame) and a low temperature (in this case the temperature of the cylinder wall) The greater that difference the higher the maximum power efficency and power available.

For instance diesel engines are more efficient because they expand the hot gasses more (compression ratio = expansion ratio) and so the diesel engine results in cooler exhaust and more energy extracted.

With flame licker engines when the cylinder becomes too hot they will suffer a form of "Heat Death" The reduced temperature difference results in such low efficency/available power that they cannot overcome their own friction.

I am wondering if anyone has ever tried to build one of these with a water cooled cylinder wall.

My engine will run until the cylinder gets hot to the touch, then it sort of poops out. but it will go again if I can cool the cylinder (e.g. spray it with refrigerant). I experimented with putting it in the freezer first but that also increased the friction in the engine so no luck there. The gasket material shield helps because it reduces the amount by which the flame accidentally/unnecessarily heats the cylinder by contacting it.

The blue portion of the flame should be the hottest, so getting the engine to suck from that part of the flame should help, Unfortunately soaking the wick in salt to make the wick resistant to charring also colors the flame yellow (an effect of the sodium in the salt) So the hot blue portion of the flame is disguised and harder to position at the intake port.
 

dgoddard

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...... you always get a blue flame (if you're using the proper fuel of course)...... All depends(again) on the type of fuel you're using......
With respect to fuel, I have used mostly Ethanol, denatured alcohol, however I have experimented with some cigarette lighter fuel. The ethanol is very corrosive to my aluminum burner and the ligher fuel solves that problem but I still believe that I need to get a hotter flame. I have tried to use a butane lighter as a flame source but the engine just blows the flame out when it exhausts the cooled gasses.

If anyone can suggest a different fuel I would be interested but please try to overcome the language barrier by being explicit as to what the chemical nature of the fuel is. Words like:
-- Spirits
-- Paraffin
-- "Coleman fuel"
-- Naptha
-- Alcohol (C H3 OH, C2 H5 OH, et al. )
can be interpreted differently in the different countries & cultures represented here.
 

Chriske

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Hi,

Did not read all the posts, sorry.
But what I would consider is making the cylinder out of cast iron or stainless steel. I would never use aluminium.
A vacuum engine is rather 'dirty' engine. To keep it running it need to be cleaned from time to time. In combination with the use of an aluminium cylinder it gets only worse.

Chris
 

fcheslop

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Hi, reread through some of the comments about the Ridders engine and the use of materials and fuel and thought I would muddy the waters a little more.
As Ive built far too many of these vac engines I became intreaged as to run times so as it was time to knock the dust of some of them gave each one a timed run in all cases the fuel used was Shellac thinner as used by French polshers here in the U.K and all wicks are stranded glass
1 Poppin/ cast iron cylinder and piston ran the burner dry at 12 mins
2 Poppin/cast iron cylinder bronze piston ran the burner dry at 10mins
3 P Duclos/Alloy cylinder,bronze piston run time 8 mins
4 Jan Ridders twin external valve,Alloy cylinders,bronze pistons 8 min
5 Jan Ridders internal valve engine max run 6min
6 P Duclos Little Blazer Alloy cylinder bronze piston ran the burner dry refilled and stopped at 20 mins as the base was to hot to touch
7 Own Design water cooled ran for 30 mins until hopper started boiling this engine has a cast iron liner and bronze piston
The main problem with the internal valve engine is the valve as by far the best runners are the external valve engine as atmospheric pressure is helping them seal I have also found the flame path needs to be as short as possible and the cam need 110 to 120 degrees duration
The points to get the Ridders engine I have found there must be no binding and set the flame exactly as per the instructions on the drawings
Please forgive my poor spelling.
Good luck
kind regards
frazer
 
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dgoddard

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Well I have not gone off and died but I have been tied up with many other things. I got back to thinking about the poor performance of my engine and came up with an idea. I am thoroughly convinced that the engine is stopping because of "heat death" That is to say that the engine runs only because of the temperature difference of the high and low temperatures in the engine and that eventually the cool part becomes as hot as the hot part (or so nearly so) and there remains insufficient temperature for the engine to run.

Aluminum has such a high coefficient of thermal conductivity that it appeared that the heat of the flame was being transferred to all parts of the cylinder and thus there was insufficient temperature difference and thus "heat death" the thermal conductivity of stainless steel being lower, the engine should run longer with a stainless steel cylinder.

It occured to me that If I could reduce the heat flow from the flame area to the rear cylinder bore things should work better and that is what the heat shield I attached at the flame hole proved, but that was not enough.

Heat conductivity is proportional to the cross section of the conductor, and the cross sectional area of the cylinder wall was approximately 0.825 square inches. If I could reduce this area the resistance to heat flow to the rear of the cylinder would be increased and the flow of heat there would be reduced. So I cut the grooves between the cooling fins .188 inches deeper. This left me with an 83% reduction in heat conduction area. and a remaining cylinder wall of about .050 inches.

Getting a hold on the cylinder while maintaining access to the grooves for recutting is a bit challenging. My tail stock ram lacks sufficient length to support the free end of the workpiece and still move the grooving tool to the grooves on the outboard end. So I decided that I would try just recutting the front 3 grooves and leave the extra mass at the rear of the cylinder. Due to the short grip of the chuck I made the cuts gently, especially since the cut would be an interrupted cut due to the presence of the valve pushrod hole. More fussing with the setup would allow me to recut all the grooves but this was an experiment anyway. After dialing in the 4 jaw chuck I proceeded. The cylinder is shown back lighted in the second image and the deeper fin cuts are obvious.

This revision made an even more greater improvement than the heat shield I added behind the flame.

Based on this experience, my view is that the heat conductivity of aluminum can have a major influence of the performance of these flame licker engines and that when alternative materials are suggested, that their lower conductivity with respect to aluminum may be advantageous for some designs.

Cutting all of the grooves deep and adding fan cooling would probably be very effective.

12102301-Regrooving_Setup.JPG


12102302-Regrooved_Cylinder.JPG
 

ninefinger

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Excellent information, thanks for sharing. How long a run time are you up to now?

Mike
 
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Hello all,
This is a fun thread! I just can't resist throwing in my thoughts too on this one. Big Grin!
1. I think your hypothesis of "Heat Death" is probably correct, buuuut given the fact that other flamelickers of this same design seem able to dissipate heat effectively enough to run without extensive re-engineering would tend to point to some very simple problem. Have you tried moving the flame away from the inlet port? If the flame is not quite touching the cylinder, heat transfer to the cylinder would be greatly reduced, yet the flame would still be close enough to get "licked."
2. A yellow or orange flame is fuel rich and transfers heat via radiation much more effectivly than a blue flame even though the blue flame is hotter. Kinky, but thats physics! Naturally a blue flame would be preferred, because it should not only supply hotter air, but less radiant heat transfer to the cylinder when not being "licked."

On the re-engineering ( and thus, way more fun!) side of things, you could add a chimney to the cylinder to provide a form of forced draft cooling. More airflow through the fins would keep the cylinder cooler without having to spritz it with refridgerant every two minutes.

Or make a water cooled cylinder that would just let the water boil away making use of water's high latent heat of vaporization and limiting the max temp to 212F or 100C.

Or add a small standoff tube to the flame inlet port to get the flame away from the cylinder further.

Cheers,
Chris
 

Cogsy

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I'm sure you're right about the 'heat death' of your engine, but after breaking mine and having to rebuild it to get it running again, it seems that thermal expansion and piston/valve fit have a bit to do with it as well.

Mine is now so tight when cold that it almost feels siezed up. It will not rotate a single revolution when cold, but after 30ish seconds of flame it frees up and will run about 30 seconds later, with better performance than I was getting with the specs from the plans. I still only get a maximum of about 3 minutes of running before it stops, but I suspect my burner is not quite up to scratch either. Adding another flame while running increases the speed noticably.

I would experiment more, but for now I'm happy to have it sit on the shelf while I know it will still run if I want it to.
 

dgoddard

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It has been a while but since last I was here I did experiment with a different piston material hoping to get a closer fit when the cylinder was hot, I tried brass but it was just too heavy and did not work well so I machined a new valve-piston to a tighter fit and while it did not seem to work any differently when just turning the engine cold it did actually run better and a little longer. I think that perhaps aluminum with its very high heat conductivity and coefficient of thermal expansion just transfers too much heat throughout the cylinder from the flame and it expands faster than the pistons so that it gets more bypass, Perhaps Stainless steel for the cylinder would be the better choice. But it runs well enough for a curio now.

Well I guess now I will have to present it to him and then pick a new project.

I was making this for a gift and It needed a proper box for the engine and accoutrements so I bought some oak and whipped one up. The left end is a solid zone with recesses for the various pieces. The accoutrements are displayed in the second image with a few labels for the odd looking pieces. That brass round thingy is the brass piston I experimented with and quite by chance I found a good use for it. The new closer fitting valve-piston got stuck after I ran it several times and then let it sit over night, fouling in the cylinder had set up and bonded the piston in place so I pushed the brass one through from the back end to dislodge it I was afraid I would break the new one unless I pushed evenly all around the edge and the trick worked So I made a handle for it because I needed something that would stick out far enough so it could be tapped on to dislodge the stuck piston. The Valve setting gage was made because the recipient will not likely have a dial caliper like I used. The Allen wrench fits the lid screw of the burner and the lock screw on the valve adjustment.

.

13010601_Storage_Case.jpg


13010602_Tool_Kit.jpg
 

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