Beta stirling engine simulator

[JR_]

Hello,

I am going to build a beta stirling engine.

Prior to building it I am making a Simulator program in C# based on the Schmidt cycle ( Schmidt theory). Mainly to learn Stirling theory and to gain more programming experience.

On the following page I found some design criteria: http://www.stirlingengines.org.uk/modeng/note.html.

i. length of displacer chamber L = 3 times its diameter.
ii. length of heater chamber = 2/3L
iii. length of cooler = 1/3L
iv. swept volume of displacer = 1.5 times swept volume of piston cylinder.
v. length of displacer = 2/3L and stroke = 1/3L.

Are these still good to start with?

If people are interested in the simulator I can make the program public?

I have also found the following simulator: http://www.solarheatengines.com/stirlin ... simulator/

Does anyone know how to calculate the: Isentropic compression heating percentage? Figured it out :) see code below:

double isentropic = (engine_max_volume / engine_min_volume);
isentropic = Math.Pow(isentropic, 0.4);
isentropic = (isentropic - 1) / (Te_kelvin / Tc_kelvin - 1);
isentropic = isentropic * 100;

Thanks in advance and with best regards,

JR.

[Ian S C]

JR, If you follow the stuff you find in Stirling Engines UK you'll be OK, the figures you have there are all OK, they are the same as those used by Stirling in the 19th century, and those who followed him, can't remember just off hand who the mathematician in the 18th century was.
Ian S C

[bladeattila]

My opinion is really different.
If the heater chamber's length is 2/3 rd of the Length, then the cooling capacity wont be enough!!!
Also not working well the regenerator in it.
The basic drawings are said 50/50 percent of volume hot side/cold side, but it is no good enough too.
The heat separation is better in a longer cylinder, but then should be heat up only 1/3 rd of Length. I think.

Another problem the heated surface not equal to the cooled surface in this layout too...unfortunately, because the cold side only a cylinder, but the heated part is a cylinder and a circle!!!

So, my stupid think is if we need a good performance, than a simple model engine, then should equalise the surfaces!
An example:

D cylinder: 50 mm
L cylinder: 150 mm
Cooled part is 1/3 L: 50mm surface is DxPixm=50x3,1415927x50=7853,98 mm2
Is the heated part...???

Heated part is:

Circle= D2Pi/4=50x50x3,1415927/4=1963,495 mm2

Cylinder= 7853,98-1963,495=5890,487 mm2
Cylinder length: 5890,48/Pi/50=37,5 mm

So, when we need to divert the heat from the engine perfectly, then should be heat up the first 37,5 mm of hot side length, and cooling the 50 mm of other side.

What is wrong in my mind? :)
Nobody calculate similar as me, but I think it is so logical...or not?

Kind regards!
Blade

[Ian S C]

The change I'll make is, displacer length 3 x diameter, displacer chamber length = displacer length +stroke = clearance top and bottom. The stroke is dependant on the stroke of the power piston, to give the 1,5:1 ratio.
Ian S C

[JR_]

Hello,

thanks for the great input!

I've made progress on the Beta stirling engine simulator/designer:
http://stirlingengineforum.com/download ... iew&id=458
http://stirlingengineforum.com/download ... iew&id=457
http://stirlingengineforum.com/download ... iew&id=456

If people are interested I might put the project on Github.

[JR_]

Here is the first version!
Let me know what you think about it.

Regards.

[Ian S C]

The normal protocol is to use degrees Kelvin for temperature calculations.
Ian S C

[JR_]

I am making several changes:

- Temperature should be set as Kelvin. However, DegC and DegF are also displayed.
- The default design parameters are also added. An can be bypassed using checkboxes.
- A iterator is added. This gives the possibility to change variables e.g. average pressure from the current value to another value with a amount of iterations.
In this way the change of a variable/variables can be seen.

Are there other features users would like to see?

[denisbudyak]

Hi!

Schmidt theory is completely inadequate for real engine and it can not be useful for predicting its performance. Real program must use more accurate model of physical processes and calculate many kinds of losses which occur in real engine. Also good program must be tested carefully with real engines performance data. As program tend to contain many stupid errors.

Currently there are at least two concurrent active open source projects of making Stirling Engine calculation software:

1. https://bitbucket.org/budden/cl-stirling-engine - this is my project. Still in alpha stage, but correlation with some known engines looks promising. Written from the scratch. I look for volunteers to do correlation with other known engines.

2. http://jordaan.info/greengasoline/index.html - this author have translated and tested several programs from literature. He currently looks for volunteers to check if he typed in data from PDF correctly, code is here: http://jordaan.info/greengasoline/stirlingtew.html

I'd like you to join either of these projects. They require a great amount of work to do.

Denis Budyak