Free piston stirling engine that remains stable by limiting stroke

A method for limiting engine power and piston amplitude of reciprocation of a free-piston Stirling engine, the engine including a displacer and a piston mounted for reciprocation within a cylinder, the piston having a sidewall engaging the cylinder and the sidewall having an inward end, the engine including a heat rejecter cylinder port through the engine cylinder at a compression space end of a working gas flow path between a heat accepting expansion space and an opposite heat rejecting compression space, the heat rejecter cylinder port having an inward edge, wherein the method comprises:

• (a) positioning the inward edge of the heat rejecter cylinder port outward of the most inward excursion of the inward end of the piston sidewall;
• and
• (b) entirely covering the heat rejecter cylinder port by the piston sidewall during a peak part of the inward piston reciprocation;
• and
• (c) wherein the engine has a back space and a gas bearing system including a gas bearing cavity enclosed within the piston, a gas bearing inlet passage extending between the cavity and an inward end of the piston and gas bearing pads opening into the cavity and formed around the sidewall of the piston, and wherein the method further comprises opening a passage between the cavity and the back space during a part of outward excursions of the piston when the amplitude of piston reciprocation becomes a selected piston amplitude that exceeds the amplitude of reciprocation at maximum engine power.