Jagang wrote: ↑Tue Apr 27, 2021 3:18 am
So basically my question would be like: If I replace the weight on top of this free piston engine, by a conrod and a crankshaft, would it still operate?
Someone else may have a better idea, but in my limited experience, most likely it would work, but at a lower RPM. The reason I say this is because I've seen several examples of just the opposite; engines designed to run with a crankshaft, but than would run just as well or better "free piston".
Free piston, the engine runs at a frequency that seems to be dictated by the geometry of the engine. With a crank, the RPM is limited by the inertia of the extra hardware so it runs slower.
Just for example, I wanted to see if one of these inexpensive engines could run free piston, (and also to test if hot expanding air leaked around the piston as the engine heated up).
It was difficult to film and hold a torch with an unsteady hand, (actually, I had to hold the torch between my knees) but clearly the engine ran without a crank, and of course, naturally the reverse is true, but without a flywheel the engine ran at a much higher RPM/frequency and otherwise required no modification.
https://youtu.be/iOs3BADFeKI
Of course, the only way to be 100% sure is to try it.
I believe I've also seen examples of similar engines to the one in the video you posted driving a crankshaft (with and without a flywheel as well).
May I ask what purpose you have in mind for adding a crank?
Edit: PS, as far as to "replace" the weight. That may be possible, but may also not be necessary. Probably attaching a crank to the weight would work, or taking away SOME of the weight.
From my research on "free piston" engines, some load, such as a generator, (or a heavy weight, in this case), is needed to dissipate energy, or the engine may tend to overheat and stop running. Probably a flywheel of approximately the same weight as the weight on the free piston engine would provide the right balance, but the load provided by a generator can apparently serve the same purpose.
In other words, it seems there needs to be a balance between the heat input and the "work" output of the engine. Otherwise additional cooling may be needed to dissipate excess unconverted heat.