External combustion engine which comprises a first cylinder and a second cylinder, in which a first piston and a second piston are able to slide respectively. The first and second cylinder are fluidically connected with respect to each other for the passage of a heat-carrying fluid suitable to determine the cyclical movement of the first piston and the second piston. The external combustion engine also comprises a drive shaft rotating around an axis of rotation, and with which crank means are solidly associated, provided with at least a first pin and a second pin having pivoting axes parallel to each other, and also disposed distanced radially from the axis of rotation. The external combustion engine also comprises first and second kinematic connection means suitable to connect respectively the first pin and the second pin to the first piston and respectively to the second piston. The first pin and the second pin are disposed with the respective pivoting axes angularly offset so as to be angled by a desired angular amplitude equal to a first acute angle with respect to the axis of rotation.

A regenerative displacer for use in a stirling engine includes two opposite covers with respective through openings, a body engaging the covers to define an accommodation space therein, a regenerator disposed in the accommodation space, and a rod inserted through the regenerator and one of the covers into a cooling portion of the stirling engine. The regenerator has a plurality of channels. Each channel has two open ends and a heat collecting net engaging each open end. Working gas passing through the regenerative displacer can be concentrated at the open ends and can absorb and release heat quickly because of the heat collecting nets, thereby increasing the efficiency of heat exchange and a temperature difference of the working gas in a thermodynamic cycle. Accordingly, pressure is increased to facilitate a quick reciprocation of a power piston of the stirling engine, and this increases output power and saves energy.

A hot fluid expansion engine has a plurality of actuator modules arranged in a star configuration around a central shaft. Each module includes a drive piston defining a working chamber of variable volume in the first enclosure; a movable displacement piston subdividing a second enclosure into a low temperature chamber of variable volume and a high temperature chamber of variable volume with the high temperature chamber communicating with a unit of a fluid heater device and the low temperature chamber communicating with the working chamber; and a fluid circulation circuit extending between the fluid heater device and the working chamber. The drive piston and the displacement piston of each actuator module are connected to the central shaft via respective first and second eccentric transmission devices suitable for imparting reciprocating motion in translation to each of the pistons with a phase lag of 90.