A small mechanics project occupied me this time. It is again about a hot air engine. This time not about the Stirling engine, but the so-called “flame eater”.
During the search in the World Wide Web, I found, among other things, the website of Mr. James Maiwald. Mr. Maiwald is an ambitious modeler and specialist in the field of Stirling and vacuum engines. He develops and manufactures his own models in all variants and also offers them as a kit.
More precisely, it is a vacuum motor, which is popularly also called a flame eater. He is one of the hot air engines, but unlike the Stirling engine is an open system.
Technically speaking, it is an atmospheric engine, since here the external air pressure does the work (comparable to the first gasoline engine). As a result, the maximum piston force is limited to the product of piston area and air pressure. (Wikipedia)
And exactly one such model (lying the flame eater) is here. As I assemble the engine and the first time commissioning is seen in the following short video …
A patience-related work is the restoration or repair of a rotary pendulum clock.
A rotary pendulum clock is, as the name implies, a mechanical clock that generates the clock from a pendulum rotating around its own axis. The vibration energy is transmitted here with a torsion spring (Horolovar spring), ie a very fine steel wire special alloy. The rotary pendulum clock is also called annual clock, as due to the very slow oscillation and corresponding mechanical implementation of the escapement, a lift of the spring accumulator only once in 300-400 days is necessary.
Of course, this also requires a certain precision of the mechanical components. If something is not set correctly here, the clock will switch off after a few minutes. Even the fine adjustment of the accuracy requires some patience. And just like a clock has done to me. In an online auction house, I have a cheap ‘defective’ but purchased from the components ago complete rotary pendulum clock and immediately started to disassemble and clean the parts.
After this work we went back to the assembly. The Horolovar feather was replaced by a new one. Now we went to the adjustments. First, I had to find out how many pendulum oscillations, more precisely half vibrations, should make the clock in one minute. At my watch (a Kundo) these are eight beats. The easiest way is to use a stopwatch to measure the time it takes to reach the 8th half-cycle. For example, if the measured time is over one minute, the watch will run too slowly and must be adjusted with the thumbscrew (the one that changes the position of the pendulum weights in diameter). Turning the thumbscrew clockwise will make the clock slower and counterclockwise faster, of course.
It should be a precision of +/- 1 minute per month possible. So a deviation of 12 minutes a year. Of course this requires optimal environmental conditions. (constant temperature and humidity, as well as a firm, vibration-free state)
As a gift I received in the winter of 2014 a kit for a model of a Stirling hot air machine. The design plans, as well as the largely prefabricated parts, come from Mr. Klaus Künneth, the operator of the website www.kk-stirlingmotor.de
To build and install only a little manual skill and a few gauges and tools are needed. (Stand drill, drill and tap, a grinding block with polishing wheels, at least a sliding calliper, a little clear coat and machine oil). On some parts holes of various diameters are to be made. For example, on the flywheel, the connecting rods. In the cylinder and head cover, the mounting holes are to drill and thread to cut.
drill the flywheel
After preparing all the items, everything is polished to a high gloss on the polishing machine. Then you can start with the assembly. All in all, one should take a few hours to have the model beautiful, meticulous and functional. From a few parts is then also quickly made a small spirit burner, which provides the necessary heat for operation under the working piston. Everything together is then mounted on the clear lacquer-sealed wooden base plate.
finished polished unit
The functioning of the Stirling engine is described by Mr. Künneth on his website as follows:
“The Stirling engine is also called a hot air engine and is a heat engine in which a closed working gas such as air (in this case) or helium is alternately heated and cooled from outside at two different areas (hot side and cold side) to generate mechanical energy. The Stirling engine works on the principle of a closed cycle and is an example of the energy conversion of a poorly usable form of energy (thermal energy) in the better usable form of energy of mechanical energy. The Stirling engine can be operated with any external source of heat (or cold) (solar, wood, gas, liquid fuels, in this model with spirit).”