Epitrochoid compression / expansion turbine.
The idea is the following:
The rotor has the form of an epitrochoid, such as in the Huf engine or Huf-pump and the Stirling engine, where I'm working on at: http://greengasoline.eu
Click here for the animation of a rotation of the epitrochoid rotor.
The rotor is twisted to form a spiral, and the rotor housing also (like in a Moineau pump).
When the pitch of the rotor helix is the same as the pitch in the rotor housing (like in the above-mentioned pump), then over the length of the rotor, both rotor and the rotor housing are in a different phase of the cycle.
This means that when the rotor is at a point on one side where it fills almost all of the space in the housing, there is a closure at the distance where the torsion is 360 degrees from there.
This enclosed space travels by the rotation of the rotor backwards (or forwards).
Thus, the gas or the liquid is displaced.
x is green, y is blue, -z is red
Image of an epitrochoid helix rotor, crankshaft, and housing.
Epitrochoid helix rotor rotated 90 degree clockwise. Note that the sealing of the cavities has rotated from the top to the right (just like the crank).
Epitrochoid helix rotor rotated 270 degree clockwise.
The drive of the rotor is the same as in my concept of the Circular Stirling engine. So 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.
I came to this idea when I saw the Progressive cavity pump
An advantage is that in each revolution a fixed volume of gas or liquid is moved.
However, there are some positive differences.
Because the shape of the rotor from front to back can be varied, the volume of the cavity can be enlarged or reduced during the displacement along the rotor. The shape of the housing is always has to be compatible with the one on the same length of the rotor.
Changing of the volume of the displaced gas can be done in three ways:
1. The pitch of the rotor helix can change over the length.
2. The shape of the epitrochoid-cross section of the rotor can be more or less circular. The cross section of the rotor must always fit with the cross section of the rotor housing.
3. The radius of the crank around which the rotor rotates is at the front different than the crank radius at the back side. The shape of the rotor has to be a projection of a epitrochoid on a spherical surface. The shape of the rotor housing also has to be a projection on a spherical surface.
4. A combination of two of above mentioned methods, or all three. (This can be used to make the inflow and outflow and expansion or compression as regular as possible.)
In a pump for liquids the above mentioned combinations can be used to change the velocity of the liquid, without changing the volume.
The pitch of the helix of the rotor and the housing changes along the rotating axis. The gas in the cavaties is compressed or expanded (depended on the direction of the rotation). In this way a compressor or an expansion turbine can be constructed.
Click here for the animation of a compressor turbine with a epitrochoid helix rotor.
For the seal on the rotor, two helical springs can be used to separate the spaces on the two opposite sides of the rotor. Between the cavities in which the displaced gas is moved, there is a small gap between the rotor and the rotor housing, of which the size is determined by the accuracy with which the parts can be made. In the mathematical model the rotor is touching a place on the wall of the rotor housing (and of course half way on both sides at the place where I want to use the helical springs).
Epitrochoid cone shaped helix rotor in housing.
The rotor is mounted on the crank of the crankshaft at the front and back, and possibly in other areas where the torsion is a multiple of 360 degrees.
The crankshaft is mounted in bearings at the front of and on the end in the rotor housing.
Crankshaft and rotor can be almost completely balanced.
If two such engines are placed in the length next to each other, are also the forces to the longitudinal axis balanced when acceleration and deceleration occurs.
What are the advantages of such a turbine?
1. Per revolution it delivers a fixed volume.
2. The volume change (= pressure change) is always almost the same, independent of the speed.
3. The supply and discharge of the gas is constant.
This is because it is in fact a double-acting turbine, because the free space at the two sides of the rotor, added together is always the same (the area of the cross section of the rotor minus the area of the cross section of the rotor.
- The turbine can be used for a Schmidt-type Stirling cycle engine.
In such an engine the gas is not pumped back and forth, but circulated in a continuous process. If the temperature on the cold side is 30 degrees, and 80 degrees on the hot side (300 and 350 degrees Kelvin), the compression has to be to 6/7 of its volume, and the decompression 7/6.
- This turbine is also very good useable for petrol and diesel turbine engines.
Compression, combustion and expansion are in this case all continuous processes as is usual with a turbine engine.
However, the disadvantage of the turbine engine, that it works only effective at a fixed high speed, this engine has not, because the gas flow rate per revolution and thus the pressure distribution over the length of the engine is almost constant.
Because the sealing between the rotor housing and the rotor will not be as well as between a cylinder and a piston with piston rings, this engine can not run on a very low speed, but because the maximum speed can be much higher than the speed of a piston engine, the speed range over which this engine works efficiently is much wider.
The shape of rotor and rotor housing are not so easy to produce.
That's why, I came to the following solutions:
2. CNC (computer-controlled) machining.
3. Rolling the correct form in a metal tube.
4. Printing templates that I can draw with the computer.
For the rolling I want to find out with the computer in what positions on the circumference of a tube, the pressure of a roller can force the tube into the correct change of shape.
Following the rotor
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.
the rotor at 0
degree of cycle.
the rotor at 45
degree of cycle.
For the turbine in epitrochoid helix housing
For the epitrochoid turbine engine concept Click here
Author: Harrie van der Haghen
For questions or remarks, email to: email@example.com