My observation on home built strings.

Discussion on Stirling or "hot air" engines (all types)
Tom Booth
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Re: My observation on home built strings.

Post by Tom Booth » Fri Jan 23, 2015 7:21 pm

Aviator168 wrote:You have 3 displacers here?


No, just one displacer, but it has holes in it. Like this:
displacer.gif
displacer.gif (48.26 KiB) Viewed 4075 times
The regenerator consists of tubes running from top to bottom.
You might also want to switch cold and hot ends.
My reasoning for having the heat on top is that heat rises.
Suggestion. If you get rid of the two side displacers and encase the regenerator section with insulation, it would be a good beta heat exchanger.
As explained, there's just the one displacer. I imagine the regenerator having some sort of ceramic (non heat conducting) housing with steel wool in the tubes and also steel wool sandwhiched on top and bottom pressed against the hot and cold ends of the displacer chamber.
Keep in mind, Stirling engine cylinder surface does not scale well with volume. Increase of surface area is not proportional to increase in volume.
I'm not entirely sure what you mean in that last sentence.

Aviator168
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Re: My observation on home built strings.

Post by Aviator168 » Fri Jan 23, 2015 9:24 pm

Ah. I see.
I seen that kind of regenerator before.

Tom Booth
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Re: My observation on home built strings.

Post by Tom Booth » Fri Jan 23, 2015 11:51 pm

Ah, and here I thought it was an original idea.

Aviator168
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Re: My observation on home built strings.

Post by Aviator168 » Sat Jan 24, 2015 8:34 am

Most fast LTD stirlings have them on the displacer.

Intrepid Wheelwoman
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Re: My observation on home built strings.

Post by Intrepid Wheelwoman » Mon Feb 16, 2015 1:50 am

Aviator168 wrote:Here is my observation why almost all the home built stirlings don't have much power, and most of them can't even run with a small load. One needs to look no further than the small heat exchange area on the gas side and the path the gas goes through the heater. It is ironic that no one can give a good estimate of the amount of heat that can be injected into the engine in a give amount of time. HIRAO's engine gives a good hint what a heater supposed to be and given the flame temperature and the material used in the cylinder, it is not difficult to determine the amount of heat that gets transferred into the engine (OK. a good estimate). Also keep in mind since majority of the home builts are not pressurized and gases have very low thermal conductivity, builders have think more about heat transfer through convection instead of conduction. So very large internal heater area helps a lot; but one has to be careful not to increase dead space while doing so. You will be surprised, if it is done right, it is not impossible to built a small, non-pressurized 1kwh engine.

just my 2c
I'm particularly interested in building a vertical gamma engine and it seems to me that enclosing the hot end of the displacer cylinder in a firebox type arrangement would go a long way towards improving thermal efficiency. I know I'm very much a new chum around here and up until now my experience with external combustion engines has been limited to messing around with Mamod products, but I've noticed too that nearly all the homemade Stirlings on You Tube seem lacking in their heating arrangements.

By the way this is the You Tube video that sparked my interest in Stirling engines in the first place: - https://www.youtube.com/watch?v=0t8LEKf04TA

Ian S C
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Re: My observation on home built strings.

Post by Ian S C » Mon Feb 16, 2015 2:15 am

I agree that an enclosed firebox is very helpful, it must have adequate air entry to ensure good burning of what ever fuel is used. You can learn a bit about fire boxes by messing around with small steam engines, done a bit of that myself, got a Mamod SE2 for Christmas 1959, it's still around, needs to be done up a bit.
Ian S C

Intrepid Wheelwoman
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Re: My observation on home built strings.

Post by Intrepid Wheelwoman » Mon Feb 16, 2015 2:43 am

I don't keep good health, so I had to sell all my steam bits and bobs off a while ago when I was unwell and short on funds. Despite puddling around with railway models in the garden in a small way and being somewhat of an enthusiast steam wasn't a direction I wanted to go in really and i was always nervous about boilers so a Stirling engine is more my thing. You are right though Ian, tinkering around with small steam engines does teach you about getting a fire to burn properly in an enclosed space. It was the Mamod traction engine that I used to abuse for my steam experiments by the way :smile:

I have one of those small 'Valor' kerosene stoves and I thought it would make a nice basis for a test engine.

http://solargreenways.tripod.com/my_par ... ooker?i=22

Ian S C
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Re: My observation on home built strings.

Post by Ian S C » Tue Feb 17, 2015 1:55 am

I remember the Valor hearer, we had a black single burner, and a more modern two burner unit, bit smelly with the Kerosene/Paraffin. It would be OK if you can get it to burn without any smoke, you don't want the Lamp Black.
Ian S C

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