Stirling engine efficiency.

[eth]

Here is my first stirling engine intended to be a wood burning stove fan. My issue is that it takes too much heat to get running. Can anyone suggest where to start redesigning to lower the start up temperature? The lower inch of the dispacer cylinder is aluminium. The displacer is a plain hollow stainless steel cylinder with closed ends. The ratio between pistons is around 3.75.

 

[minh-thanh]

Hi !
Why does the engine have radiator fins in the picture but not in the video
The radiator fin is a very important part because it determines the temperature difference between the hot and cold areas.

 

[eth]

Hi !
Why does the engine have radiator fins in the picture but not in the video
The radiator fin is a very important part because it determines the temperature difference between the hot and cold areas.

The finned photo is revision two, which included cooling fins for the upper section and aluminium for the lower inch of the dispacer cylinder

 

[DJoksch]

The displacement cylinder walls are 0.012”.

 

[minh-thanh]

A suggestion

 

[Rocket Man]

I built several stirling engines 20 years ago. Beta engine is the most efficient, both power piston & displacer piston are in the same cylinder. Machinist hand book says cast iron has the highest heat radiation rate, better than aluminum. I build power piston from aluminum because they are light weight and displacer piston from aluminum soft drink cans they weigh almost nothing. Displacer needs to have a clearance of about .020" on both ends of the stroke. Clearance around the displace side needs to be enough for all the air to move from 1 end to the other end of the cylinder with minimum resistance of air movement. All the air in bottom of cylinder needs to move to the top then to the bottom again about .125" or so. Put labyrinth seals on the power piston they act like frictionless rings. Labyrinth seals are grooves .020" wide & .020" deep .125" apart. Here is video of 3 of my engines all 3 have the same beta engine. The engine that makes all the noise has .000" clearance end of the stoke displacer piston hits each end of the cylinder, I was going to fix it but never did. I use to sell plans to build this engine on Ebay but they were extremally slow to sell about 1 per year so I don't sell them anymore. Not sure if I still have plans anymore. This is a 1917 stirling engine fan by the Al-cool Fan company Chicago IL. Fan with blade runs 500 RPMs and engine with flywheel runs 950 RPMs.

 

[Bob44]

 

[Bob44]

Liquid cooled Sterling I built about 10 years ago. A Rudy Kohoupt design

 

[Mechanicboy]

The displacer cylinder must be larger in height to make greater temperature difference since the stove is hotter than low temperature stirling engine, let us say larger distance between hot and cold area. The cylinder wall must be thin to lead hot into the cylinder quickly to heat up air and the cooling area must be cooled down with fins to cool down heated air quickly, better the hot and cold size is insulated from each other with the non conductive gasket. Displacer piston must be long in length to make greater temperature difference in a hot stove and light as possible to make less load to be powered by power piston. Better to have larger displacer volume vs work piston volume to make more power on working piston.

 

[anday1]

this might help
https://courses.washington.edu/me355b/Blocked wi06/Labs/Fansan.pdf

 

[Richard P]

Here is my first stirling engine intended to be a wood burning stove fan. My issue is that it takes too much heat to get running. Can anyone suggest where to start redesigning to lower the start up temperature? The lower inch of the dispacer cylinder is aluminium. The displacer is a plain hollow stainless steel cylinder with closed ends. The ratio between pistons is around 3.75.View attachment 142304View attachment 142305
View attachment 142306

That seems like an awful lot of heat energy to produce quite limited mechanical output. I recently finished a Jerry Howell design stirling fan and it will run quite vigorously on a 1 cm spirit burner flame. The key for me was to eliminate any source of friction and to ensure that the engine was completely gas tight. Before I did that, the engine would run but it was very inefficient and took a lot more heat from a blow lamp to deliver mediocre rotational output speed.

You can see the fan running towards the end of the YouTube clip link below.

 

[anday1]

they really are not as easy to get going if there is any friction this is a testament to that..days of fiddling

 

[eth]

That seems like an awful lot of heat energy to produce quite limited mechanical output. I recently finished a Jerry Howell design stirling fan and it will run quite vigorously on a 1 cm spirit burner flame. The key for me was to eliminate any source of friction and to ensure that the engine was completely gas tight. Before I did that, the engine would run but it was very inefficient and took a lot more heat from a blow lamp to deliver mediocre rotational output speed.

You can see the fan running towards the end of the YouTube clip link below.

It may seem like a lot of heat but when the base is a 26mm thick and 150mm diameter chunk of aluminium it took a lot of heat to get it hot! I've since used a laser thermometer to take some scientific measurements and it ran at 420rpm at 180c temperature difference which is far less than I thought it might have been. Its since been on a weight loss program and had as much weight removed as possible from the hot end. In my defence I'm not a model engineer, I'm a heavy engineer with spare time making parts on a 5m lathe fitted with a 500mm chuck which doesn't lend itself well to such small parts.

 

[Rocket Man]

It may seem like a lot of heat but when the base is a 26mm thick and 150mm diameter chunk of aluminium it took a lot of heat to get it hot! I've since used a laser thermometer to take some scientific measurements and it ran at 420rpm at 180c temperature difference which is far less than I thought it might have been. Its since been on a weight loss program and had as much weight removed as possible from the hot end. In my defence I'm not a model engineer, I'm a heavy engineer with spare time making parts on a 5m lathe fitted with a 500mm chuck which doesn't lend itself well to such small parts.

Thin metal has very high heat transfer rate. Read about it in machinist hand book and online. The new type food cans factories make now days work great for the hot end of stirling engines. You need to design an engine to use a food can. Varnish needs to be removed from the can inside & outside. Brass is better than steel but machining brass can shape .010" thick is impossible. I have not tried aluminum cans for the hot end they might melt.