The Idea
With this third flame-eater my objective was to make it as small and compact as possible. Based on my experiences with the first two flame-eaters I counted that this miniaturization (and with that the extreme low power) will bring me even more difficulties to let and keep this engine run reliable. And that was really the case: I spend more time for all kind of changes and for searching for the right adjustments than for building this engine ! But the persister always wins at last and this engine runs perfectly now with relatively high speed between 600 and 800 rpm.
Design and directions for adjustments
As the pictures and the drawing plan show I choose for a horizontal cylinder with the flame hole at the side face. The system that drives the slide valve over the cylinder hole and that presses it at the same time against the cylinder face is driven by a spring-loaded little axis that runs with a small ball bearing over a cam disc with a rather special profile. Particularly in this part of the engine many sensibilities were hidden.
For those who want to build this very funny flame-eater according to my drawing plan I summarize here the most important requirements that mainly deal about the rather sensitive adjustments:
1. The slide valve must open the flame hole in the cylinder about 40º (from the 360º cycle) before the piston reaches its (left) dead point near the cylinder head. You can measure that with a protractor on the fly wheel. This movement for opening the hole must be as abrupt as possible. That is the reason for the extra milling treatment on the cam disc as indicated on sheet 4 of the drawing plan. During this 40º the cooled flame gasses escape the cylinder.
The slide valve must close the flame hole again about 30º before the dead point of the piston on the opposite (right) position. I take me much "trial and error" and several cam discs before I find out the right cam profile;
2. The overlap of the slide valve when the flame hole is closed must be nearly zero. I even have the experience that the engine runs better if the hole keeps open with a very small gap; about the width of a human hair ! I recognize this phenomenon with my two former flame-eaters without having a good explanation for it;
3. The two little springs that press the carrier plate with the two little pins on the slide valve must be adjusted so that the valve slide moves exactly parallel along the cylinder surface with the lightest possible pressure. In fact this springs only have to keep the valve against the cylinder face because the under pressure during the power stroke will cause the rest of the needed closing pressure;
4. The strength of the spring that the keeps the ball bearing of the driving system against the cam disc must be just enough to avoid the system for floating. A too high pressure will slow down or even stop the engine;
5. The surfaces of the valve and the cylinder face over what this valve is sliding must be made with a very sharp milling cutter. Except lightly deburring with polishing emery cloth paper don't grind this surfaces too heavily because an almost invisible rounding of the surfaces can occur and with that leakages between the valve and the cylinder face;
6. Again it was my experience that the piston best can be made from pearlitic cast iron. The thermal expansion of this material is very low and at least less than that of the steel cylinder which avoids jamming as the system gets hot. Furthermore pearlitic cast iron is more or less self-greasing due to the relative high carbon content. This is important because you may and cannot not use oil in the cylinder. Oil will degenerate fast due to the high temperature of the flame gasses with the result that the engine will slow down fast or stops running! Finally the combination of a cast iron piston in a (rust free) steel cylinder appears to be very wear-resistant.
For the same reasons I made the slide valve from pearlitic cast iron as well, although this me be less important.
7. Using pure ethanol has some advantages above spirits that, except for ethanol, contains 2% methanol, 10% water and blue colouring addition.
The ethanol flame is substantial hotter, inodorous and causes much less moisture against the piston an cylinder surfaces. Nevertheless it is necessary to clean the piston and the cylinder bore before storing the engine after a run with a cloth and some sovent like WD40.
8. As counts for every flame-eater the size and the position of the flame in front of the cylinder hole is extremely important!! If any false and cold air from the outside is sucked-in together with the flame gasses the engine will run bad or not at all. The flame must overlap the cylinder hole completely and therefore be 2x wider and higher then the cylinder hole. Apart from that the horizontal position in front of the cylinder can be of big influence too. It is advisable to experiment with this position before fixing the spirits burner on its definite place. The burner on my drawing plan is rather optimal but it is always possible that you have to make some adaptations.All together a long list of requirements, but they are inevitable and if you satisfy them I am sure you will obtain a very nice running miniature flame-eater.
Nice replica made by Matthias Ottenbacher: