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Thread: Flammenfresser

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    mklotz mklotz's Avatar
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    Flammenfresser

    Flame Eater (Flamenfresser in German) is an atmospheric engine.

    As the piston reaches TDC, a fast-acting cam snaps the valve leaf open, exposing the interior of the cylinder to the alcohol flame. As the inertia of the flywheels drive the piston down a vacuum is created in the cylinder and the flame is sucked into the cylinder cavity.

    As the piston reaches BDC the valve snaps shut. The hot gas trapped in the cylinder rapidly loses heat to the cooler cylinder walls, creating a partial vacuum inside the cylinder. This vacuum allows the atmosphere, pushing on the bottom of the piston, to drive the piston forward in the power stroke, hence the term "atmospheric engine", since the engine's power is derived from the atmospheric pressure.

    With a working pressure of something less than 14.7 psi, this engine is no powerhouse. Ball bearings for the main shaft are essential as is frequent oiling. [The small brass cup on the top of the cylinder is an oil cup that keeps the piston lubricated during operation.] The cam-follower is also a small ball bearing.

    What is incredible to me is the speed this engine can attain. It just doesn't seem possible that the heating/cooling gas cycle described above can be happening fast enough to sustain the speed evident in the video.

    ---
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    Hans Pearson's Avatar
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    A fascinating concept, which I have been thinking about for some time, and then I saw the proliferation of these engines on the internet. I am building one at the moment and am stuck on the valve systems I am throwing around and trying to work out something slightly different from the usual, ie. the one shown on the version in the video. I am also looking at making it liquid cooled as these engines become less efficient and eventually stop as they heat up.

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    mklotz mklotz's Avatar
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    Quote Originally Posted by Hans Pearson View Post
    A fascinating concept, which I have been thinking about for some time, and then I saw the proliferation of these engines on the internet. I am building one at the moment and am stuck on the valve systems I am throwing around and trying to work out something slightly different from the usual, ie. the one shown on the version in the video. I am also looking at making it liquid cooled as these engines become less efficient and eventually stop as they heat up.
    Valving on these engines can be very tricky. It needs to be quick and thorough. My engine uses a piece of shim stock as the valve. It's thin enough that, as soon as the vacuum starts to form in the cylinder, the valve is sucked down onto the cylinder top to form a good seal. I have another flame-eater that originally had a sliding bronze valve. It never worked very well until I replaced the bronze with shim stock.

    My engine runs for long periods without the need for external cooling. The cylinder fins seem to do the job. Remember that the cylinder must stay fairly hot lest it quench the incoming hot gas too quickly before the valve shuts and the vacuum starts to form. Water jackets are great for Stirling engines; I made one for my Ringbom...

    Laminar flow engine

    but I question the need for an atmospheric engine.

    Regardless, it's your engine; build it as you see fit. The fun is getting it to run. Nothing beats the excitement of seeing a homemade engine run for the first time.
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    Thanks for the comments and tips Marv. I am still at the cylinder and piston stage so pretty flexible as to the road ahead. I have seen some with radiators and water pumps, even a radiator fan, which must be pushing the limits of the engines output. Your description also highlighted a problem I had not taken into consideration. I live at an altitude of 5550 ft. so atmospheric pressure is only 12 psi. Time is my problem so the project is not advancing at a rapid rate.
    Thanks again, HANS.

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    mklotz mklotz's Avatar
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    Quote Originally Posted by Hans Pearson View Post
    Thanks for the comments and tips Marv. I am still at the cylinder and piston stage so pretty flexible as to the road ahead. I have seen some with radiators and water pumps, even a radiator fan, which must be pushing the limits of the engines output. Your description also highlighted a problem I had not taken into consideration. I live at an altitude of 5550 ft. so atmospheric pressure is only 12 psi. Time is my problem so the project is not advancing at a rapid rate.
    Thanks again, HANS.
    Both my atmospheric engines use stainless steel pistons in aluminum cylinders. It works but one has to be careful to allow for the different rates of expansion of the dissimilar metals.

    The right piston material for these engines is probably graphite. I use graphite pistons in many of my Stirling engines and it works perfectly. In addition to being lightweight, an important concern in low temperature differential Stirlings, it's self-lubricating, which is really important. Oil drag in an LTD Stirling can easily overcome their miniscule power. Graphite's thermal expansion coefficient is about half that of stainless so that's another plus for this material.

    The other problem with oil in a flame-eater is that it will form a carbonized residue in the cylinder from the heat of the hot gas. This means that it must be cleaned periodically. A graphite piston will solve that problem too.
    ---
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    Hello Marv

    Don't be put off - I built one last year and it works better than I thought it would.

    The valve and cam are the most difficult bits to make and tune for efficiency. Mine has a 304 SS cylinder and a graphite piston with a .01 clearance which eliminates the need for lubrication and constant cleaning. I made the burner with a stainless steel wire wick using very fine wires jammed down into a tube with the cloth wick going into the fluid. The resulting flame is very clean. Positioning of the flame is critical and the intake port must be completely covered for best results.

    There a many sources of information for this type of engine and it is very satisfying to get it running. I will be making the internal valve version next, again using the graphite pistons.

    Thank you Marv for your contributions to home shop guys like me, they have been very helpful many times when everything seems to end in redoing a part or going down the wrong path.

    Regards

    Frank


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