Have been fascinated with these engines for years and have always wanted to design / make one.
There are a few different valve arrangements I could go for;
One is the Jerry Howell method with a rotating shaft driven by a cam that slides a spring loaded valve.
Then there's the linear spring loaded slide side valve, and then I've seen i kind of bell crank arrangement again the valve is spring loaded but on the cylinder end cover like Jerry Howells. All of these methods are driven by cams.
What I want to know is, what is the correct timing to use for this, what is the cam shaped like?
I have a concept that is basically a wobbler or oscillating (as we call them here) steam engine but with the exhaust port blanked off.
The piston will travel down the cylinder drawing the hot gases in from the flame then by the time the piston is ready to travel back up, the whole cylinder will have oscillated thereby blocking the inlet port. The gases will cool inside the cylinder and the higher external pressure will push the piston back up. And the cycle repeats.
What are peoples views on this? Do you think it would work, or has anyone ever tried it? I am sure if you get the holes for the ports in the right place this should technically work.
Methods to reduce friction will be applied as always with this type of engine, however, there will not be a great deal of friction anyway as there aren't many linkages in an oscillating engine, although the sideways force on the cylinder / piston probably makes up for the fact there aren't many linkages.
Obviously cooling the cylinder will also be a problem, it will have to be finned and air cooled. Maybe a fan like Jerry Howell uses could be rigged up if there was enough power to drive it? Or a water jacked could be constructed I guess, it will be just a bit more difficult due to the fact the cylinder is moving.
The only thing I'm sceptical of is the valve timing? Do the valves usually snap shut on these things? When does the valve open and close in relation to top dead centre? The problem is with my concept that the opening / closing of the valve will be sinusoidal, but I can't see a reason why this wouldn't work.
Any thoughts?
I'm busy designing a simple prototype now which if it does not work will be quickly converted to a regular oscillating steam engine!
Thanks Aaron, so the configuration I was thinking would probably try to compress the gas. I would need to make the port overlap slightly, but then the port would not close early enough. Am getting the feeling this won't work now!
What you say makes sense, the valve closes before bdc and that last part of the downward stroke creates a slight vacuum, this makes the engine look like it has a slight compression when people spin them over trying to start them, actually it's a decompression then. I guess once the hot gases are getting in there they will still expand slightly initially which will reduce this decompression?
Maybe if I put some sort of exhaust valve in the end of the cylinder with a very very light spring on it this will relieve any pressure when the piston is trying to compress the gas heading towards tdc. The port would still only close at bdc though as it has to start opening at tdc to avoid the creation of a vacuum when the piston begins it's downward travel ... a vacuum at that stage in the cycle would not be useful as it would be released as soon as the port opens.
Does anyone think this might work? It would rely on cooling the hot gases so that the pressure was less than atmospheric so that the atmosphere could push the piston back. Well that's the principle of these engines anyway isn't it? I'm struggling to see how they work at all now! Do they rely on that partial vacuum created after the valve closes nearing bdc to give it a little kick on the up stroke?
I think I'm losing the plot here! Maybe this needs more thought!
Hi!
the attached picture shows exactly what you are planning to do: a vacuum engine with an oscillating cylinder.
this photograph comes from a book in french by Rudy Mémin "des étranges machines à air chaud" (ISBN 2-9518283-4-9).
try www.bateaumodele.com
The book does not contain plans for this particular engine, but for another one, with a more "classical" slide valve, that I have seen working pretty well.
Having built three different type of these flame gulper engines, I can't see why an oscillating wouldn't work.
For me, timing is not so crucial, far less than the burner or flame position. and in fact my next engine will have an adjustable cam to shorten the intake phase at high speed (ie above 1000 rpm). A Ferrari also has a similar camshaft !
I have also experimented the exaust valve and I didn't find any obvious increase in performance.
Regards
Thank you for your reply. I am finding it difficult to find information on this type of engine. They seem to be far less common that stirling cycle engines. I like the sound they make and the initial apparant simplicity!
Well you have answered most of my questions there. I had almost given up on the osciallating idea, although if someone else has already done it and you think it could work, it may still be worth a try.
Interesting what you say about the exhaust valve, to be honest I didn't really understand the point of it in engines where you have a cam that controls the intake valve as you can just design it before the onset of any compression as the piston nears TDC. I suppose it may be helpful in an oscillating type engine as that would be the only way of expelling this excess pressure.
Please could you re-post the image you attached as it did not seem to work.
Also, do you have any photographs of your engines that you could post up?
Hello Nick,
sorry for the misfired attachment! Here comes the picture I hope.
For my own engines I only have poor movies and mayby I could extract a decent picture or make a new and nicer one if you wish.
I agree that compression occurs at the end of the power stroke at TDC, but this is not so prejudiciable, as long as pressure can lift the intake valve, (with an awful noise,) which should opens rapidly and be widely open at TDC to allow a fast running, not so different from a IC engine. The penetrating noise is due to the energy that remains in the air, I presume.
These engines are so funny to watch and hear when running so a try to build one that works is really rewarding.
Thanks for the picture, I now see how they got round some of the timing issues I was talking about, with this method it enables you to adjust the position of the spring loaded valve to where it suits you.
I see what you are saying about the compression and I'd never thought of that! Of course, there is only light spring pressure on the valve anyway so if the pressure rose too high it would simply lift the valve. With the method I was thinking of using that probably wouldn't have worked too well as it would lift the whole cylinder of it's face and try to push things out of line, that's another reason for doing it as in the picture above.
Thank you once again for your help, I've never seen an engine like the one you posted the picture of but it clears up a lot of things and proves that an engine like this with even fewer moving parts can be made.
I would still very much like to see some pictures of your engines if you have the time to do so?
hello Nick,
here are the pictures of two of my atmospheric engines
The first is provided with a flap actuated by a cam and a lever that controls flame admission. I built this one about 15 years ago from plan found in a old issue (1959) of "Le Bricoleur" bought in a flea market. this magazine was mainly a translation of Popular Science or Popular Mechanics. It is claimed in the article that a candle would be sufficient to run it but it was not so, this engine run at about 250-300 rpm max with a gas burner, lost or recycled elsewhere. you can see also spare cams and piston showing that some experimentation is required to got them working. The brass tube on the top of the cylinder head is an exaust valve.
The second photograph shows the last engine I have made, with a more simple valve, although not so easy to adjust. with a properly fitted valve this engine exceeds easily 1000 rpm with the alcool burner you can see, at high speed however the exhaust blows too often the flame, and if I can fix that I'm quite sure that it could run much faster.
Hi, thanks very much for your reply and for taking the time to take the photographs.
I like your two engines. The first engine with the mechanical flap is an interesting arrangement but does not look to easy to get a good seal, also, I don'y suppose the lack of cylinder cooling would help matters.
I have seen the type of valve you have made on your second engine elsewhere. This is the sort of style I am now thinking of trying to design. As you say I think there there has to be some experimentation with cam profiles etc before I will get one to run nicely. I was thinking of starting off with something that would close the valve just before bottom dead centre and re-open the valve just before top dead centre. This should be a good starting point anyway?
I've come up with a sort of design for the picture of the oscillating type you sent. I think it will be quite difficult to get one like that to run though as it is more difficult to tweak the timing on that one, you can't really change the rate at which the valve opens and closes.
Thanks again for your help, I think I now have enough information to at least make a good attempt at one. As you say, it may need some tweaking before getting an engine like this to run. It may even need another iteration but hopefully I will get there, I will keep you posted on my progress. I have just last week got my workshop set up, I haven't had access to my machines for years, I have now cleaned them up but I myself will be a little rusty!
I just need to wire the machines in and get some decent lighting put up then I am ready to go so will hopefully make a start very soon.
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