Looking good so far. I see you have gone for more of a composite build up of the displacement cylinder. I went machined mine from a chunk of solid, but either way should work fine. One think you need to make sure of is that you eliminate ANY gas leakages as even the smallest will kill performance.
Jerry Howell - Super Stirling Fan
- Thread starter Richard P
- Start date
Help Support Home Model Engine Machinist Forum:
hi yes i have learned that at my cost very brave to make it from 1 piece...heres one i still can't get going
Hello,
Nice looking machine you have there. I am just starting out in the Stirling engine (and machining) field and have lots of not-tested ideas.
Nevertheless, if it were me I would disconnect the helicopter linkages and see if the engine will run by itself.
It also looks like the flame is mostly missing the hot end cap.
Will those o-rings stand up to the heat?
I myself am trying to figure out how to size a flywheel to make sure it has enough mass to do the work of the compression
stroke, as well as overcoming any friction in the system, especially at low speeds.
Again, newbe here. Just trying to help.
Good luck. Looking forward to seeing it come together and run.
Nice looking machine you have there. I am just starting out in the Stirling engine (and machining) field and have lots of not-tested ideas.
Nevertheless, if it were me I would disconnect the helicopter linkages and see if the engine will run by itself.
It also looks like the flame is mostly missing the hot end cap.
Will those o-rings stand up to the heat?
I myself am trying to figure out how to size a flywheel to make sure it has enough mass to do the work of the compression
stroke, as well as overcoming any friction in the system, especially at low speeds.
Again, newbe here. Just trying to help.
Good luck. Looking forward to seeing it come together and run.
Oops, I think I have replied into the main thread while trying to reply to the helicopter video.
thanks Richard i am going to the exhibition in Leamington spa this week to see if the guys there can also help...all your comments are valid...i too have only been engineering for about 6 months the helicopter was my 2nd main project. it will work one day lol
andrew
andrew
This is wrong .
The power piston for a stirling engine is just a part that reflects the contraction - expansion of air as it moves from the hot to the cold and vice versa - inside the engine.
Displacer is just a part to move the air inside the engine from hot to cold and vice versa
That is not my understanding. Many engines are built to run pressurized. The air does not -contract- when cooled, it just presses less hard on the power piston. It will therefore require work to drive the power piston back towards the head. Given there is no load on the system, the only place to get the energy to do that work is the flywheel.
Depending on the type of stirling engine : Alpha stirling, Beta stirling or Gamma stirling
With a small Gamma Stirling engine, having a "compression stroke" kills it
It is not a 4-stroke or 2-stroke engine.
With the Small Gamma Stirling engine, the Power piston only works to reflect the contraction - expansion of the air in the engine when the air moves from the hot area to the cold area - And because of the expansion. the air inside the engine is very very small - extremely small so any friction, not smooth, not airtight will kill it
Gamma Stirling engine
Let's make a new topic about your own engine, if you want ...we will discuss more...
I can't answer your question, because I haven't done both
But with my little experience . The helicopter stirling engine plan has too much detail, and just one non-smooth part, a little jam, a little friction...will kill it.
That plan, I think, is only for those who have had success with a stirling engine - it's not for complete newbies.
With the model stirling engine, it's small, and it works based on the volume change of the air from hot to cold and back - this change is very small - extremely small and plus the motion of the engine then it becomes very very very,....small, so friction, jam, not airtight will kill it
Friction is a must have , but it must be reduced to the point where the engine can keep running
The above also applies to both stirling and flame eater engines / Vacuum engines
Rocket Man
Well-Known Member
- Joined
- Nov 4, 2011
- Messages
- 242
- Reaction score
- 122
Your engine looks good and runs good. I built several sterling engines 20 years ago. If you make the displacer piston out of kitchen aluminum foil and the power piston out of very thin aluminum too the engines have less wasted energy and run better. Put labyrinth seals .020" x .020" ring groves on the piston for frictionless rings. If piston & rings are made of the same material they expand & contract at the same rate as the engine temperature changes so .0005" clearance stays the same as the engine heats up. I also drilled holes in the power piston to reduce weight. Clearance at top & bottom needs to be very small .005" between the piston and end of the cylinder. Small engines are so critical to get them to run very thin oil on the piston is too much friction. Beta style sterling engines are the most efficient the power piston & displacer piston are in the same cylinder. If you build an engine around kitchen food cans with round bottoms the hot end of the engine and displacer piston will save you many hours of work and be more efficient too. Most sterling engines produce so little power they barely have enough power to make them self run.
If your a newbie at building sterling engines build an engine with 2" bore or something near a food can diameter. Soup can makes an excellent displacer piston inside a bean can, corn can, pea can, carrot can, with a round bottom. Soft drink aluminum cans are lighter weight than food cans they make excellent displacer pistons. Make 2 holes in soup can to remove soup then put can in lathe & drill .125" hole in both ends for the 1/8" diameter piston rod. If you use 1/8" diameter hobby tubing for piston rod and not solid rod weight is about 50% less and engine runs more efficient.
If your a newbie at building sterling engines build an engine with 2" bore or something near a food can diameter. Soup can makes an excellent displacer piston inside a bean can, corn can, pea can, carrot can, with a round bottom. Soft drink aluminum cans are lighter weight than food cans they make excellent displacer pistons. Make 2 holes in soup can to remove soup then put can in lathe & drill .125" hole in both ends for the 1/8" diameter piston rod. If you use 1/8" diameter hobby tubing for piston rod and not solid rod weight is about 50% less and engine runs more efficient.
Last edited:
Hi
Looking at the design, if it is going to run at all, it should do if you disconnect the drive to the rotor and tail propellor - the horizontal flywheel should be more than adequate to keep the engine turning over if it is ready to run. Doing that will eliminate quite a lot of points of friction down stream of the engine which will sap power if they are not yet smooth enough.
Another thing you can do is 'up the oomph' of the engine by heating the hot cylinder more fiercely for a short period by carefully using a blow lamp. Again, if the engine is close to running, this will produce more power to get it going and help with further diagnostics. I was able to get my fan to run with a blowtorch well before I could get it to go smoothly on a small flame. You obviously need to be careful not to overheat those O-rings though! Once I knew it would run like that, I could systematically work through each components one at a time making tweaks to see if it made things better or worse.
Another thing for me was to ensure that there are ABSOLUTELY no gas leaks. I thought that everything was airtight, but when I used a bicycle pump attached through the power piston to really pressurise things, I detected tiny leaks around a number of the mating joints. I got round that with carefully cut gaskets that were cut to go very close up to any bolt or stud holes etc.
You know you are getting close, if you temporarily disconnect the power piston from the crank and it sort of 'bounces springily' on the cushion of trapped air inside the system. If it drops down to the bottom of the cylinder in anything less than 5-10 seconds it is indicating that there is a leak somewhere.
It really doesn't take much at all to stop these little engine running!
Hope that helps.
Thank you!
Agree with this.
When the engine is cold (or strictly speaking when the 'hot end' is at the same temperature as the 'cold end' there is no change in the volume of the air as the displacer goes up and down and moves the air about inside the engine If you then turn the engine in this state you actually get small amounts of resisting 'push' and 'pull' against the power piston as it compresses or expands the air around its neutral volume at that temperature.
However, as the 'hot end' is warmed relative to the 'cold end' you get very small 'pushes' and 'pulls' on the power piston just as the air is heated and cooled when the displacer moves the air around the engine. The 90 degree phase lag between the displacer piston and the power piston means that these small 'pushes' and 'pulls' on the power piston are timed just right to keep building momentum in a smoothly running system.
It is. a bit like giving a child's swing a small push at just the right time in each cycle. After a while, the small inputs can build to deliver quite a large output.
Again, I disagree with some of this. On a gamma engine:
There is no 'pull', ever. There is only pressure, more pressure and less pressure, on either side of the power piston. On a cold unpressurized power cylinder, there is an appearance of 'pull' when one mechanically moves the power piston in such a way as to increase the volume in the sealed area (lowering its' pressure) and then the atmospheric pressure on the outside acts to -push- the power piston 'inward'.
The sealed area has a volume which changes as per the location of the power piston (not the displacer). The working gas (air or otherwise) fills
that volume at a pressure determined by the temperature and the 'amount' (not volume) of air, which can be increased by pressurization (adding more molecules).
The pressure on the piston is not necessarily 'very small'. I read of a marine engine with a bore and stroke measured in -feet-, it is unlikely the torques involved in that case would be considered small.
I feel the difficulties encountered on some very small engines, even if relatively well sealed could arise because of the relative relationship of the low
available motive power to friction. There is just not very much of a delta there. As the engine size goes up, the available power goes up faster than the additional friction.
Short connecting rods on very small engines might also lead to problematic side load friction. Most of the smooth and slowly running examples I have seen have long connecting rods (and sizeable flywheels).
I admit to being new to machining, fairly new to Stirling theory, but not so much a newbie with mechanics and/or physics.
And maybe to being a little sensitive to being called out as 'wrong'.
-rgs
I'm sorry about that .
What I've said, It's all my own experience and knowledge of stirling and flame eater / vacuum engines, and it's always worked with my little engines, the gamma stirling has a power diameter 7 to 8 mm , the beta stirling has a power cylinder diameter 18.5 mm and the flame eater / vacuum engine has a cylinder diameter 19 mm
With larger diameter engines I don't know because I have never done a gamma stirling engine with a power cylinder diameter larger than 10mm.
Gamma Stirling
Beta stirling
Flame eater / Vacuum engine
