Index Circular Stirling Stirling program source code Epitrochoid turbine circular gamma circular alpha Links

Circular stirling engine concept with Epitrochoid displacer.

The idea is the following:
The rotor has the form of an epitrochoid, such as in the Huf engine or Huf-pump. For more about the project, loook at:

I want to publish this model of a low temperature difference Stirling that can be build by people all over the world without exspensive machinery and materials.
This type can pump a comparably enormous volume, and therefore can deliver enough energy to have a practical use when there is just a little temperature difference.

construction of the epitrochoide
Construction of the epitrochoid shape of the rotor.
quick colord drawing
Quick drawing of a circular stirling engine. (the no sealing at all option)
green=rotor, red=crankshaft, blue=housing
quick colord drawing Balancing
The crankshaft can be fully balanced by a balancing element (purple) inside the rotor.
The rotor can be balanced by material in the dark green area. This can also be a structual element that gives the rotor extra form stability.

Rotor form stability
I added a tube inside the rotor around the crank to give the rotor extra form stability. Plates around this tube to the rotor wall can give also extra form stability.

Rulon, Teflon or Nylon sealing strips can be used in the housing wall.

Cooling an heat pipes
In stat of letting the working gas flow through heat and cool pipes, I want to let the gas flow through groves between two plates along the housing wall.
  rotor housing wall.
  rotor housing back and front plates
  rotor housing side of ball bearings
  gear on crankshaft
  crankshaft side of ball bearings
  space filling element on the crankshaft
  counterbalancing element on the crank
  rotor wall
  rotor back and front plate
  tube inside the rotor for form stability
  rotor side of ball bearings
  gear wheel, fixed on the rotor, and inner gear on the rotor housing front plate, and the collor of the balls in the ball bearings
135 degree rotation of rotor in rotor housing 90 degree rotation of rotor in rotor housing 45 degree rotation of rotor in rotor housing
180 degree rotation of rotor in rotor housing
Rotation of the epitrochoid shaped rotor in the rotor housing.
The green line is only for orientation.
The inner white circle is the path of the crank through the yellow gear wheel.
0 degree rotation of rotor in rotor housing
225 degree rotation of rotor in rotor housing 270 degree rotation of rotor in rotor housing 315 degree rotation of rotor in rotor housing

I came to this type of rotor and housing when I saw a drawing of a two-stroke Huf Diesel engine in a book "Modell motoren" by Prof. Dr.-Ing. Peter Demuth. I realised that the shape of the combustion chambre is far from ideal for an internal combustion engine (just like in a Wankel), but that the shape is very well suitable for a Stirling engine. It is also easy to combine with heat and cool pipes and regenerator.

For the drive of the rotor there is a choice for three options:
1. Inner gear mounted on the rotor housing, and a gear wheel with half the diameter on the rotor. The rotor with the gear wheel is driven around. by a crankshaft.
2. chain with two chain wheels of the same size, a stationary in the middle, and the other fixedly mounted on the rotor. The crankshaft drives the rotor by a bearing in the middle of the chain wheel on the rotor.
3. two ball bearings, one of them is mounted on the rotor, with its center at the pivot point, the other is on the crankshaft, inside of the first ball bearing.
There needs to be a pin, sliding through a hole, to force the rotor in the right path.

1. The 3 mechanisms that I found to be suitable all drive the rotor in the right path without friction on the end plates. The frictions come in the ball bearings.
2. The rotor will be long, which makes the end plates relatively smaller compared to the volume.

Mechanical friction< is caused by the sealing of the chambres from each other.
This will cause a energy loss.
For this problem I found some solutions:
1. No sealing at all.
In a circular dual alpha as the one at
the hot sides are on one rotor, and the cold sides on the other one.
Therefore no heat will be lost by leakage on the end plates.
Only the pressure loss due to gas flow in and out of the gap between the rotor and the end plates decreases the efficiency of the engine.
Therefore this gap has to be small.
When the rotor rotates at a low speed gas will flow through the gap from one side to the other, but on high speed the pressure difference and therefore the gas flow changes direction every half revolution.
I still don't know how to quantify the energy loss caused by the "no sealing" solution.
On the side of the crankshaft I think about transfering the power with magnets trough a plate, so the gas can not leak out of the engine.
2.Sealing on a plate on both ends of the rotor.
The end plates on the rotor drive through a groove in the rotor housing wall. Rulon half rings can seal on these plates.
3.Sealing with two strips of Rulon in the rotor housing end plates that go from the sealings on the sides, leaving a space in the middle for the crankshaft.
4.Roling sealings in the form of two cones on both ends of the rotor, that seal on the rotor.
This leaves a gap between the cones and the housing wall.
This gap can be very small because the cones and the gap can be made with a much higher precision than the rotor and the rotor housing.
I will trie these options on the first working model.

drawing of rotor housing
Crank radius is 0.25 * diameter of the constructing circles.

drawing of rotor housing
Crank radius is 0.2 * diameter of the constructing circles.

drawing of rotor housing
Crank radius is 0.15 * diameter of the constructing circles.

drawing of rotor housing
Crank radius is 0.125 * diameter of the constructing circles.

In this images the white lines are the paths of points on the perimeter of the rotor. I made this to find the shape of the rotor housing. The white circle is the path of the crank. The red circle is the inner gear on the rotor housing. The light blue line is the line where a plate on the crankshaft can seal on the rotor. The black area at the centre is the area where the border of the rotor does not come. The shape of this area can also be used to form a helical rotor that can rotate inside a twisted epitrochoid shaped rotor house.

Now I am thinking about puting the writing point on 40% of the radius. This shape leaves more spaces for sealing. With a hollow crankshaft there is even space to connect the front to the end of the rotor housing with a rod wich gives constructional advantages. This would only work with the chain mechanisme.