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Already in 2004, I designed a "Miniature Flame-Eater" but I was never been very satisfied about it. In particular, the drive mechanism for the slide valve that must open and close the flame hole in the cylinder it was very complex. It was quite difficult to adjust the slide valve and the two rather undefined springs so that the valve was running nicely against the cylinder head with low friction. Once properly adjusted the motor could run well but it also happened that he did this not again next time; so the system was quite unreliable.
This was the main reason why I have never converted the handmade drawing package for this motor to a CAD version. In fact I always hesitated to provide this handmade plan to a colleague model builder fearing to disappoint him because of the mentioned problems.
This fact always has bothered me all the time so I now (December 2013) have taken this flame eater out of my closet and changed the design quite dramatically, using the experiences I have gained with a lot of my other models during the intervening nine years.
This MK2 version has become a whole lot easier and with that much more reliable. Apart from the mentioned drive mechanism I also have implemented some other optimizations and made the whole design more compact as well.
Properly adjusted this new MK2 version runs reliable and like a greyhound as you can see on the YouTube video and on top of the top of the right frame of this page. So I am very satisfied with it now and I made a completely new CAD drawing package for it.

The design

1. The slide valve mechanism.
So the main change is the slide valve with its drive mechanism. As shown in the above figures the slider is now simply round with a small blind bore in the middle of it in which the bent end of a coil spring is inserted. This slide can be made of silver steel or stainless steel. The sealing surface thereof must be perfectly turned flat and if necessary somewhat polished with fine polishing cloth on a glass plate.
The spring is clamped on the other side on a 3mm shaft which is driven back and forth by a cam disc on the flywheel shaft. To ensure that the spring stays in place I simply made some M3 thread on the end of the 3mm shaft.
The shaft must running with a minimum possible friction in the glide bush in the piece that is screwed against the cylinder. The best one can use a standard 3mm shaft because they are perfectly shaped and smooth. Also a standard bronze glide bush is recommended or a self made graphite bush. The spring between the block and the cam must ensure that the cam continuously runs against the cam disc but with the least possible pressure.

2. The cylinder and the piston.
It is important that the piston fits closely in the cylinder but with the lowest possible friction. The clearance must not be greater than 0.03 mm.
In order to avoid jamming of the piston when it gets hot, the thermal expansion of the piston must be lower than that of the cylinder or at the most equal to it. I myself made the cylinder ​of stainless steel and the piston of pearlitic cast iron (GG25 ). Pearlitic cast iron is a more or less self lubricating and very well durable. It's a little rust sensitive so that the piston and the cylinder must be cleaned from time to time because some corrosion occurs due to the hot and humid spirits flame. The piston can be made ​​of graphite as well and that does not suffer from corrosion so cleaning will be hardy necessary with that. e In the case of a graphite piston the cylinder may be even made of a good quality aluminium provided that one makes the cylinder bore super smooth in order to prevent wearing of the graphite

3. The alcohol burner.
I also have greatly simplified the burner. It is simply made of a metal tube with a loose lid on iin what pipe is soldered for the cotton wick. The burner is more or less stuck placed in a hole through the mounting plate and the wooden base and can only be turned around to set the best position of the flame relative to the flame hole. I prefer to use alcohol 96-98% instead of household spirits because a spirits flame is less hot and causes more pollution of the piston and cylinder.

The adjustments of this flame eater
1. Frictions .
Flame-eaters have a very low power, and certainly this very small model. Therefore, frictions and other counter-acting forces must be avoided as much as possible:
- In fact the spring that protrudes into the slide valve only must drive that and the pressure on the valve must be just enough to just keep it against the surface around the flame hole in the cylinder with the least possible friction. The slide valve is automatically and sufficiently pressed against the cylinder by the pressure of the outer atmosphere when there is negative pressure in the cylinder during the cooling of the flame sucked-in flame gases. Properly adjusted the valve will thus cause minimal friction.
- The spring that pushes the cam follower against the cam disc must make just enough pressure that the system will not start floating, not less but also not more. This also to avoid too much counter-acting forces.
- The piston and the cylinder bore must be dry and free of grease; never use oil because it burns immediately causing fatal friction by residues on the piston and cylinder bore. A little WD4 may be used on the piston sometimes.
As mentioned, it will be necessary to periodically clean the piston and cylinder, especially if the engine is stored for a longer period in which it is advisable to put little WD40 on the piston.
- The flywheel must run very lightly on two ball bearings that need to be made grease free on beforehand by washing them in e.g. benzene. The unloaded flywheel must be at least run for 1 minute continuously after a firm manually push on it. For this purpose it is also important that the centers of the ball bearings are located nicely in line.
- The connecting rod for the piston must be aligned properly so it does not wring in the piston pin and/or on the ball bearing on the other side that is on the crank pin.

2. The process adjustment.
The slide valve must open the flame hole about 30° before the piston is closest to the cylinder head, to be measured along the circumference of the flywheel. During that which 30° the cooled flame gasses escapes from the cylinder. The valve must close the flame hole again at the time that the piston is at about 20º from the other end side of the cylinder. This movement pattern is completely determined by the contours of the cam disc as it indicated on the drawing plan and its position relative to the crank web. This cam disc is in fact the only somewhat difficult to make part of this flame-eater and it may be that this contour must be made with some "trial and error " to be achieve the right shapes for the required movement pattern.
The spring sticking in the slide valve must be clamped to the 3mm driving rod so that the flame hole is just well closed in the leftmost position. With a well made cam disc the valve will then open the flame hole almost completely when it is in rightmost position.

3. The alcohol flame.
The size of the alcohol flame and especially its position relative to the flame hole tend to be very critical
with all flame-eaters. Should be noted that, apart from flame gases, it must be prevented that false and cold outside air it sucked-n also. The flame should therefore overlap the flame hole well, which means that the height and the latitude of the flame must be about twice the dimensions of the flame hole.
Very important is also the position of the flame in front of the flame hole. The wick must be somewhat lef
t from the flame hole as can be seen in the above figures. Because the burner can be rotated the optimal position of the flame can be experimentally and simply determined while the engine is running.
The use of pure industrial ethyl alcohol (96 -98 % ) has advantages over household spirits.
Except for a blue colour addition and methyl alcohol spirits also contains about 10 % water. The flame of ethyl alcohol is hotter and odourless and causes less residues than a spirits flame. Nevertheless, it always remains necessary to periodically clean the piston and the cylinder with a lint -free cloth with a little solvent on it like WD40.

4. The direction of rotation.
looking at the front against the flywheel the direction of rotation is counter-clockwise.


compliance with the conditions and adjustments as described above this "Mimiature Flame-Eater" will run very reliable and with a speed of 500 to 700 rpm.






Nice replica (MK1 version)
made by Matthias Ottenbacher:

Nice replica by Robert Alves
(scale 2 to 1):

Beautiful replica
students Sully Lycee: