Design free piston stirling engine

[BPA]

Hi all,

I'm trying to design a free piston stirling engine but I didn't find real clear way to compute all the parameters in particular the calculation of displacer stroke and the calculation of springs stiffness (power piston and displacer) ...

I know I need to have a working volume in the range of 110 to 120 cm3 to get 200 W, so I can calculate the surface of the power piston according with a defined stoke and so its size (logically, the larger the diameter of the piston, the shorter the stroke), but what about the displacer ?

In the same way, optimal performances are obtained with 80° of phase between the power piston and the displacer, this being dependent to the stiffness of the springs used, but I don't have any idea how to calculate this ... :(

Someone could help me ?

Thanks in advance

[Tom Booth]

Someone can "calculate" without necessarily using math. Like, in carpentry, it is almost always easier (and more accurate) to mark a board with a pencil by just holding it up where it needs to go and making a line.

A long time ago someone in this forum advised using the same sort of method for Stirling engines.

Get the engine up to temperature and then move the displacer manually. This will expand the gas and move the power piston giving an approximation of what distance the piston would be expected to travel.

Designing an engine from scratch is, I should think, likely to involve much trial and error.