Moteur Stirling/en

Aurelpere

https://wiki.lowtechlab.org/wiki/Moteur_Stirling/en

Dernière modification le 03/12/2024

Difficulté

Hard Difficile

Durée

1 day(s) jour(s)

Coût

50 EUR (€)

Description

Things about stirling engines

Sommaire

stirling, solaire, energie, moteur

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Introduction

We now live in a post-covid world, and wether you're part of

those who think billionaires take very seriously climate change and want

to address the question with population "regulation" and with survivalists bunkers,

or wether you're part of those who think billionaires don't care and just want

to keep on getting richer and richer until the last drop of petrol,

it becomes urgent to find alternatives to facism and to the models we are offered,

and it includes technical alternatives.

Stirling engine was invented in the XIX century, before combustion engine

and there are a few "mainstream" industrial uses, in particular in the 60s-70s

(Ford Torino,American ship Caloric).

Also called "hot air engine", its principle is to move hot air alternatively from 1

cold zone to 1 hot zone and gather the mecanic force produced by air dilatation

and by air contraction.

High performance Stirling engines have necessited a lot of research and development and have achieved yields

with higher performances than combustion engines (around 40%).

They are reliable, silent, and have high yields.

They are however better adapted to regular regimes.

Étape 1 - web literature review

We hereby list a few videos of diy stirling engine

more or less diy and in french language

We can find engines made with a coca cola can (DDM Brico Voyageur <nowiki>https://www.youtube.com/watch?v=nBxKOkYx2rI), wooden engine

made with glass syringes for the pistons (Incroyables Experiences https://www.youtube.com/watch?v=s79odgWz6BM) , a 125 cm3 manufactured engine with an estimated power of 0,8kW to 8kW (0,6 horsepower to 6 horsepower) considered the measurement of 800 rpm and a tray mass estimated between 100g and 1kg (French Stirling Fablab https://www.youtube.com/watch?v=Z24dZ3St_JE from series https://www.youtube.com/playlist?list=PLE1TyIvCXNyjlvWRi10LUsEMXKyRS6Ltx on channel https://www.youtube.com/@FrenchStirlingFablab)

You can find notably resources to try to build

your own stirling engine that you won't find in this tutorial

As a bonus, for teachers, 1 example of a tractor and crane toys build in meccano here:

http://cm1cm2.ceyreste.free.fr/stirling.html

Étape 2 - Toy power

We will now try to measure the power of stirling engines called "scientific toys"

that we can find on aliexpress or on resselers like science labs

You will find attached two videos showing 1 stirling engine "scientific toy" that run

with a flame as a heat source coming from 1 candle or 1 alcool container combustion.

The engine comes with 1 small container and a wick that has to be filled with alcool that produces power

adapted to the engine (video 1).

In the video with the candle (video 2), the candle flame doesnt produce a power adapted

and the engine only runs for a few seconds and then stops and becomes very capricious to restart (a bit aleatory after

a few tries even after cooldown).

Therefore we measure the power of the two flames (video 3 and 4):

time to boil 10mL of water from 20°C to 100°C

energy=10*80 cal=800*4,184J=3347,2J

time for alcool lamp flame: 40s to 1min (wether simmering or boiling)

time for candle: 90 to 120s

"alcool lamp:"

max_power=3347/40=84W

min_power=3347/60=56W

"candle"

max_power=3347/90=37W

min_power=3347/120=28W

To try to measure yields, we fix a mass to the motor (her a broken nut of 5g in video 5)

and we measure tork traction

as well as angular speed.

Broken nut mass is 5g and is fixed at a distance of d=3cm of the rotation axis.

Rotation speed measurement with a 25€ tachymeter this tuesday 25 june 2024: the tachymeter works by friction (rubber traction that turns an axis of which rotation speed is measured): the traction happens after half a second to 1 second and displays values between 100 and 500 rpm and makes the engine stops.

Rotation speed measurement with 1 laser tachymeter (video 5): 1400 rpm with 5g broken nut attached at 3cm of axis

Rotation speed measurement with laser tachymeter for engine 2 (video 6): 1000 to 5000 rpm with 5g broken nut attached at 1,6 cm of the axis

The yields is low, but we must recall this is a toy and not a engine made for performance. We could however make the measurement exercise with high performance scientific toy (multi cylinders, vertical mover, smaller wheel, etc.). Industrial stirling engines can have yields up to 40%.

Étape 3 - Rotation speed verification with video analysis

To measure angular speed, we will use two software: 1 python code sample based on opencv, and ffmpeg

python commands:

sudo apt install virtualenv

virtualenv --python=/usr/bin/python3 .

source bin/activate

pip3 install opencv-python

import cv2

import os

def charger_images_video(video_filename, output_folder):

"""

Loads video frames from a file and saves each frame as a JPG image.

Args:

video_filename: The path to the video file.

output_folder: The folder where to save JPG images.

Returns:

A NumPy array containing the video images (3D array: frames, rows, cols).

"""

# Open video with OpenCV

cap = cv2.VideoCapture(video_filename)

#Check successful opening

if not cap.isOpened():

print("Erreur d'ouverture du fichier vidéo:", video_filename)

return None

# Check that the output folder exists, if not create it

if not os.path.exists(output_folder):

os.makedirs(output_folder)

# Empty list to store video frames

images_list = []

frame_number = 0

# Play video frames frame by frame

while True:

ret, frame = cap.read()

# Check image playback

if not ret:

break

# Save each frame as a JPG image

frame_filename = os.path.join(output_folder, f'frame_{frame_number:04d}.jpg')

cv2.imwrite(frame_filename, frame)

# Add image to list

images_list.append(frame)

frame_number += 1

# Close video capture

cap.release()

return images_list

# Example of use

video_filename = '00009.MTS'

output_folder = 'frames'

images_list = charger_images_video(video_filename, output_folder)

commands ffmpeg:

sudo apt install ffmpeg

ffmpeg -i 00009.MTS -vf fps=25 output_frame_%04d.png

You can reproduce the measurement with the source video file (link at the bottom of this step) and the previous sample code

Unfortunately at this stage of the experiment, the 25fps video doesnt allow a correct measurement

the angular speed of the engine is too fast and produces blurred images on the video broken down in 25 frames per second

Unfortunately the captation at 60fps or more is expensive (sony camera or zcam at more than 1000€ on amazon. the advantage is you have 14 days to test the camera and get reimbursed if it doesnt fit)

we can find 60fps webcam but after a test (Svpro Full HD 1080P Webcam USB Objectif de Mise au Point Manuelle 4 mm, 30fps/60fps/100fps Caméras de Bureau USB CMOS OV2710 pour Linux Windows Android Mac OS, Plug and Play at 33€ on amazon) this wednesday 26 of june, it captures at 30fps. And you cant really configure video captation software adequately, see this page for exemple where there are no parameters to define fps:

https://wiki.archlinux.org/title/Webcam_setup

test with zcam e2:

video of 60s at 60fps (in theory 3600 frames) with a bit of therebentin (no more alcool 90° confiscated by the cops): the engine runs but visibly slower than when the container is full of 90° alcool. We verify rotation speed.

Strangely, i have a message "process stopped" at frame 273 with python script

and ffmpeg does the job and we obtain half a rotation between two consecutive frames, which means 30 rotations per second, which is indeed 1800 rpm

File available here if you want to verify:

https://vpn.matangi.dev/stirling.mp4 (1,8Go)

Étape 4 - Power the engine with a solar source

Making a high performance stirling engine requires a lot of research and development (go! for hackers who want to leak phillips brazil archive of the ford torino - yes 60s and 70s is not only great for music-)

In theory, with a 40% yield, it requires a solar receptor of 2,5m2 (aproximatively a receptor of 90cm radius) for a motor of 1kW

we will here scale based on the flame power that runs the engine correctly:

60W to 90W

W will first us 1 small reflector on which we will fix bits of broken mirrors (after a fixation test it is dramatically worse than with the initial surfac of the reflector) and measur the tim it takes to hav a small quantity of water boil

and w will make a linear scaling for an adapted diameter (the power of the sun is linear of th sunny surfac)

test this sunny tuesday june 2024

6cm radius reflectors on the photo : the reflecting surface is made of "bumps" not necessarily as good as dedicated surfaces that can be bought for example at solar brother (https://www.solarbrother.com/acheter/reflecteur-solaire-adhesif-s-reflect-500/)

When putting the finger at the center of the reflector at noon and pointing at the sun, w hav a sensation near being burned with a lighter after 5s.

Th test for boiling 3mL of water failed, wether becaus the surface is not smooth enough, wether becaus th container makes too much shadow on the reflecotr, wether becaus the reflector is not well enough oriented to the sun or becaus the container is not well placed at the focal converging point of the sun rays

The sunlight is approximately 1000W/m2, and the surfac of the reflecotr around: 3,14*0,06*0,06=0,0113m2

Th power of the reflector is therfor theorically around: 0,0113*1000=11,3W

To get a power of 90W at noon (w can modulate to lower at another time or when the sunlight is lower), it would require a reflector of radius r:

r=√(90/3,14*1000)=√(90/3140)=√(0,02866242)=0,17m

W would therefor need a piec of spher of around 34cm of diameter

Th satelite antemna (said parabolic) retrieved in a recycling shop is around 60cm diameter, which is way too larg, th surfac being linear to th squar of th radius (in first approximation)

W will therefor buy a parabolic antemna of 40cm diameter (not found lower) and fix a solar reflector tape

Test 12/07 : negative with 40cm parabolic antemna and adhesiv tap: th cylindr of th piston is transparent and the heat of th concentrated sun rays doesnt heaten up well the cylindr. W cant tak to pieces th egin to put steel whool inside lik in stag 1 video. Test tomorrow with tinfoil glued to the cylindr. Otherwis need to find an engin with metal cylindr

Video is bugged and not uploadabl, test again when digital weather is better

negative test of 13/07 noon with tinfoil on cylindr: finetuning the parabolic antemna on the cylindr is difficul, need to be very accurat and with th gear i hav (a mic leg) it requires to suspend the engine in the air, etc.

negativ test of the 16 of july 18h: parabolic antemna of 40cm, concentrated sunlight rays ok, insufficiant solar power

negative test of 23 july 18h: parabolic antemna of 60cm, concentrated sunlight rays too scattered, insufficiant solar power

the concentrated sunlight square is too scattered. It seems it would be appropriate to do a more accurate concentrator (a real sphere piece)

W will try after the holiday to do a spheric concentrator (so with a tinier focal point) with a plaster mould on a sphere like a yoga/kine baloon. If you want to do a tutorial for doing this typ of concentrator, feel free to do so!

I ordered a 150cm baloon on the 26th of August. Hack of amazon and of bank account. We will try again when the bank will authorize a consumer credit because while the macronist are force fed with money, i'm getting short.

11.28: managed to build a 80cm solar reflector with a 150cm yoga baloon. Negative test for powering a stirling engine, the solar rays focus is too scattered (see video).

Nex experimentation with a fresnel lens

The solar concentration devices with parabolic antenna or with pieces of a sphere in plaster will be transfered to a proper dedicated tutorial to capitalize and socialize the tries and errors

Étape 5 - Make and optimize a mobile solar receptor

It is her i pass you the ball

First, w need to think about a receptor that follows the sun dynamically during the day based on its position (th variables ar dat and tim and latitud and longitud)

and mor importantly: that is abl to gather and send sunlight rays concentrated to a fixed point at any time during the day

Then, we can imagin 1 thing based on several receptors of distinct diameters adapted to a varying sunlight

W then hav an infinite sourc of renewable energy, transportabl that will work for a sunlight with a high treshold and a low treshold

W can even imagin 1 society wher machines dont run when the sunlight is not good enough, but this is scienc fiction

To giv some landmarks, the biggest one piece mirrors w ar currently abl to make are telscop mirors of 30m diameter

Telscop mirros of 5m to 10m are more common for big telescop

Im not a specialist, just a populariser concerned with climat chang

and the rise of facism

Therefor and at this tim of my experiment, only two practical aspects are questionning m for an everyday us

to stop the engin (you dont only need to stop injection)

for longer us: keep the cold sourc cold enough and long enough without oversizing th power at hot sourc input (for a high performanc deltaT)

And becaus at a tim of looming facism rising in many countries, w must stop auto censorship to talk politics when speaking in on own's nam

1 government that would take seriously climat change would have long ago put

stirling engin at exams, encouraged consortiums to work on that,

and created mixed groups of engineers, technicians, diy workers without diplomas from different territories to work on this typ of questions!

Scientific knowledg is contextual of epoch and this is not only in spatial engineering (going on th moon)

w hav lost knowledg. If lobbies prevent from puting again at the agend forgotten techniques,

that are reliabl, it's politic role to create necessary incentiv!

Étape 6 - Your turn

her w are, you hav now web resources to mak your own stirling engin, leads to do research on high performanc engin builders, a methodology to test and verify rotation speed lower than 3600 rpm in context of digital surveillance and shackle, and ideas for concentrator engin based on dynamic concentrators

For an sun following algorithm, you can hav a look at the cod her:

Dimensionner et faire un tracker solaire photovolatïque low tech

However, a dispositiv based on 4 photoelectric cells and a small maximum seeking electronic circuit driving motors could replace a hard coded algorithm honourably and adapt to all latitudes and longitude without tweaking

I also hav a problem with sabotaged concentrators (scratches, reflector tape taken off) quite quickly, but im sur you will find ways of avoiding that too!

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