One ordinarily meets the following Stirling engines :

-    « alpha type » Engines : it uses 2 cylinders at 90° ith an oscillating piston in each cylinder. Each piston is attached to an unique brace and crankshaft whose the axis of rotation is at the intersection of the two axes of the cylinders. Thus the pistons are oscillating in quadrature. These engines are usually equipped with a regenerator which takes place between the 2 heads of cylinder. They don't require. any moving fluid piston. By example, they are currently industrialized by the german company SOLO (Singelfinden) for output powers of approximately 10 kW in the setting of solar facilities like the « Dish Stirling » power-plants.











Stirling motor SOLO161 10kW

Numerous and nice animations (steam engins, various motors...) to see on www.keveney.com



Animation above taken from  www.moteurstirling.com
Author: Pierre GRAS

                            One Dish Stirling solar facility with  alpha Stirling engine (click to know more)
                              





-    « type 'in series' pistons » engine : it requires to put in series N pistons, usually, pushed by N rods and by one common crankshaft. On the crankshaft, the phasing betwenn 2 consecutive braces is about 90°, in order to make them to oscillate in quadrature. Betwenn 2 consecutive pistons is placed one regenerator. The pistons are "double effect", as they can working on their 2 sides : thus there are N distinct volumes of coolant fluid. The k-th volume passes in transit only and incessantly betwenn the k-th and k+1-th engines via the k-th regenerator. The heads of the cylinders (« top engine ») are usually the hot source and the feet (« bottom engine ») are the cold source, altough it's possible to do the inverse.




-    « beta type » engine with simple roding : they use only one cylinder in which both a "working" piston and a "moving fluid" piston are sliding. These 2 pistons are connected on the crankshaft by 2 rods, attached on 2 braces, which are baffled of 90°. The working piston is recovering the mechanical power while the moving fluid piston allow to evacuate it periodically, at an approximately constant volume, from the hot zone to the cold zone and inversely. This displacement of fluid makes itself of preference via a regenerator mounted on the flank of the cylinder.


-    « beta type » engine with rhombic roding (or rhomboïd) : it works as the simple roding, but with a roding based on a deformable lozenge, which allow to better pilot the "moving fluid" piston and the "working" piston: thus it can have an approximately constant volume during the ideally isochoric times.





-    « gamma type » engine : it uses 2 cylinders and 2 pistons which have each their own actuator. Each piston is both "moving fluid" and "working piston. One regenerator can be mounted on the flank. The synchronization between the pistons is making itself notably by gearings, chains, straps and/or rodings. The "gamma type" engines can be seen as an hybridization between the "alpha" and "beta" types..


In complement of these usual engines exist  non conventional Stirling engines, less known, staying at the prototype step, or designed for very specific applications (spatial...):

-    free piston engine « Martini type » : the working piston is sliding according to the pressure in the motor. When the pressure raises, it is pushed in a way. When the pressure collaps, it is pushed in the other way until its initial position. It requires an average strength on the external side of the piston ; it is generated by a gas shut in a bottle or by the tarage of a spring. If the working piston is a magnet, one can install around a linear alternator and generate electric power.



-    free "moving fluid" piston engine « Ringbom type » : on the contrary, the working piston is mechanically actuated. But the moving fluid piston is sliding according to the pressure of the gas shut in a bottle and the pressure of the motor.








-    « free pistons type » engines : they make the synthesis between the two previous engines. There is no mechanical joint with the exterior. The produced power is recovering by at least one linear alternator.

Some examples of free pistons Stirling's engines designed and built in the USA :



-    Thermoacoustic engine : modernized approach of the previous free pistons, it uses a thermal gradient betwenn the 2 extremities of a pipe which contains a porous membrane and a gas. A system of acoustic waves takes place in the pipe, generating a sound convertible into electricity by a microphone.

-    Rotary engine, in a sensibly elliptical surrouning wall : a 4 quadrants vision, with a cold/hot alternation between 2 consecutive quadrants, is isolating 4 rooms inside the ellipse (with a rotor having four surfacic, tangent and permanent contacts on the ellipse). The relative rotation between the rotor and the ellipse entails dilatations and contractions for the gas which generates some mechanical power: an example is the Quasiturbine Stirling shown by the SAINT HILAIRE's Family.
                                                                                                                                                4 poles Quasiturbine Stirling concept

Author : Pierre GRAS                                                        Author : SAINT HILAIRE's Family www.quasiturbine.com