Need advice from Flame Eater expert

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tornitore45
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Need advice from Flame Eater expert

Post by tornitore45 »

I do not mean a circus performer... I built the Lenz tractor, a popular project powered by a Flame Gulper engine.
Flame gulpers are external combustion engines but are NOT steamers so there is no proper board class where to post.
Anyway the engine has 1.25" Bore and Stroke, and two 4.5" flywheels

The cam actuates the flap crispy and I set it up to close at BDC and open at TDC
I can see the flame being sucked in
I read somewhere that this type of engine does not run until it warms up. Can not really understand why because the operation explanation assumes the hot gas cools inside the cylinder creating a vacuum, but I take at face value.

I run the engine by hand nada no sign of life
I heated the cylinder with the torch until uncomfortably hot to the touch no joy

Everything is build to print. Compression is as good as one can expect for a low drag piston and a slide flap valve.
Nothing is binding and it turns freely.

The flame is from a 3/8 wick dipped in denaturated Alcohol and is well centered in front of the intake hole

Appreciate any help
Mauro Gaetano
in Austin TX
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rmac
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Re: Need advice from Flame Eater expert

Post by rmac »

I'm no expert, but I do have a smaller model flame eater that was built by Solar Engines, a now-defunct company in Phoenix that made a number of different model engines, I think back in the 1980s. My engine is kind of hard to get running, too, but once you get it going, it GOES!

You are right that it needs to warm up before it will run, mainly I think because water tends to condense inside when you first start playing with it, and that will prevent it from running. I never heat the cylinder directly, just put the flame in front of the intake like you're supposed to and then try to start it until it finally takes off. The other thing with mine is that the cylinder needs to be lubricated with dry powdered graphite. I never tried oil, but I'm pretty sure that would gum up the works and prevent it from running.

Good luck!

-- Russell Mac
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tornitore45
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Re: Need advice from Flame Eater expert

Post by tornitore45 »

Thanks, Graphite is a good idea, will try
Can you inspect the phasing of the valve opening/closing relative to piston position?
Mauro Gaetano
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rmac
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Re: Need advice from Flame Eater expert

Post by rmac »

tornitore45 wrote: Sun Apr 25, 2021 2:48 pm The cam actuates the flap crispy and I set it up to close at BDC and open at TDC
I guess you mean the cam actuates the flap crisply???

On mine the cam is not adjustable, and the flap does not open and close at the dead centers. So maybe you have your cam adjusted wrong. I can't get to it just now, but I will try to draw a picture or two to show how my cam is set up.

-- Russell Mac
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tornitore45
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Re: Need advice from Flame Eater expert

Post by tornitore45 »

That is what I think the problem is. The correct phasing of the cam.
Mauro Gaetano
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rmac
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Re: Need advice from Flame Eater expert

Post by rmac »

Here are a few pictures that will hopefully show how my flame eater is set up.

The first one shows the general configuration. The rod that activates the valve rides against a cam that is machined into the same part that attaches to the connecting rod. When viewed from the side shown in the picture, the cam rotates counter clockwise. In the picture, the valve is more or less fully open.

The second picture give a better view of the part with the cam.

The third picture shows the cam at the point where the valve is just beginning to open. At this point, the engine has to rotate about 48-1/2 degrees further before the piston reaches its position closest to the intake hole.

The last picture shows the cam at the point where the engine has rotated about 161 degrees further and valve is again fully closed. At this point the engine has to rotate about 67 degrees more before the piston reaches its position farthest from the intake hole.

Obviously I haven't measured these angles with three decimal places worth of precision. My CAD program doesn't know that, though.

Hope I've made this clear. Again, good luck.

-- Russell Mac

flame_eater.jpg
cam.jpg
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cam2.png
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tornitore45
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Re: Need advice from Flame Eater expert

Post by tornitore45 »

Very clear and thank you for the effort to measure and document.
My shop time is currently limited so it will take some time before I try again but will post the results
Mauro Gaetano
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rmac
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Re: Need advice from Flame Eater expert

Post by rmac »

You're welcome. Glad to help.

Here's another tip: Yesterday after I took the photos of my flame eater, I tried to run it for the first time in quite a while. I also have an alcohol burner with about a 3/8" wick. At first I had maybe 1/4" of the wick exposed and the engine wouldn't run. I then pulled the wick out so maybe 1" was exposed, giving a much larger flame. Then the engine then took right off.

The position of the flame relative to the intake hole is also rather fussy. You may need to play around with that.

Finally, you definitely don't want to heat the cylinder intentionally. The engine works because the hot gas from the flame contracts when it gets cooled by the (relatively) cool cylinder.

-- Russell Mac
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mklotz
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Re: Need advice from Flame Eater expert

Post by mklotz »

rmac wrote: Tue Apr 27, 2021 7:51 am ...
Finally, you definitely don't want to heat the cylinder intentionally. The engine works because the hot gas from the flame contracts when it gets cooled by the (relatively) cool cylinder.
On my two homebuilt flame eaters I must preheat the (aluminum) cylinders and (steel) valves to get them started.

These engines work by drawing in hot gas, then closing the valve to make the cylinder gas tight, then the gas loses heat to the cylinder and contracts thus creating a partial vacuum in the cylinder, after which the external air pressure pushes the cylinder forward in the power stroke (that's why they are referred to as "atmospheric" engines).

If starting without preheating, the gas quenches (loses heat to the structure) before the valve can close and air is drawn in filling the vacuum and negating the power stroke. Nothing is lost by preheating the apparatus; proof of this is that, once started, the engines can run very well with cylinders that are too hot to touch.

My engines use feeler gauge stock as valves; its flexibility guarantees that it can conform to the seat and its small mass means it won't suck much heat from the hot gas. I see you use a machined part as your valve. Have you honed it so it (and its seat) are flat enough to form a good seal? If not, that might be something to check.
Regards, Marv

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rmac
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Re: Need advice from Flame Eater expert

Post by rmac »

mklotz wrote: Tue Apr 27, 2021 10:34 am If starting without preheating, the gas quenches (loses heat to the structure) before the valve can close and air is drawn in filling the vacuum and negating the power stroke.
But why do you think it's air that is drawn in and not more hot gas from the flame?
Nothing is lost by preheating the apparatus; proof of this is that, once started, the engines can run very well with cylinders that are too hot to touch.
That's true. But to me, heating the cylinder just seems counterproductive because half the cylinder's job is to cool the hot gas and create the vacuum. I always guessed that my engine needed to warm up because I thought that water was condensing inside the cylinder at first. But the key word in that previous sentence is "guessed". I certainly may be wrong about that.
My engines use feeler gauge stock as valves; its flexibility guarantees that it can conform to the seat and its small mass means it won't suck much heat from the hot gas. I see you use a machined part as your valve. Have you honed it so it (and its seat) are flat enough to form a good seal? If not, that might be something to check.
The (store bought, not homebuilt) engine in the picture runs fine. We don't have pictures of the one the OP is having trouble with. On the engine in the picture, that machined valve is made of graphite and it is in fact nice and flat.

-- Russell Mac
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mklotz
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Re: Need advice from Flame Eater expert

Post by mklotz »

Yes, my apologies; I forgot that the pictures were not of the OP's engine. The point of checking the valve mating is still relevant.
Regards, Marv

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tornitore45
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Re: Need advice from Flame Eater expert

Post by tornitore45 »

The valve could be an issue. The original design called for pieces of spring steel 0.004" thick one of which is arched to provide springiness.
I replaced the flap valve with 0.020" brass sliding freely in a 0.020+ slot.

I do feel the compression when run by hand (no flame). I do not feel these kind of engine need the same fit and compression of an IC though.
If the timing does not work I will address the valve.
Mauro Gaetano
in Austin TX
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