Author Topic: model steam engine: Comments on the design I have in mind?  (Read 10515 times)

Offline jonogt

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model steam engine: Comments on the design I have in mind?
« on: February 08, 2009, 06:09:45 AM »
Sorry the images came out so large, but

Design 1:


Design 2:



The sketches are rough, but hopefully they give the idea.

I guess I'm going for the simplicity of a valveless tilting piston steam engine, but with a directed exhaust outlet instead of actually tilting the piston.  I want to do this so that I can route the exhaust in an aesthetic way such that you can actually see the steam coming out of a smokestack.  I've looked at quite a few different model engines online, and can't seem to find any that are set up like this.  Would it work?  If not, what problems would I be running into?

Also, which of the 2 configurations I have shown would run better?  If they would perform equally I think I'd like to use the first one over the second.  I'm planning to make the piston out of stainless steel, and since this design would probably require the piston to be decently long, I thought I could partially hollow it out to reduce the weight.

In case of concern:  I drew those sketches in Microsoft paint, but I'm not going to use that for making my actual plans.  The computers at the library have autoCAD, which I'm plenty handy with, that I'll be using.  I just don't have it on my personal computer and wanted to get a post up to see what you guys thought.

Are there any free downloadable engine calculators online for designing these things?  I'd like to be able to run the engine at fairly low speeds, but I don't know to well what the optimal dimensions and such are.



Thanks a lot for any help, comments, advice, etc.

-Jon

Offline Darren

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Re: model steam engine: Comments on the design I have in mind?
« Reply #1 on: February 08, 2009, 06:14:26 AM »
Hi Jon,
Never built and engine myself, but

I don't think this will work? You need both ports at the same height with some sort of valve to open and close them as required. In your diagram the steam will go in and out of the inlet port and I doubt much will exit the exhaust.

The wiggling piston bore type is in effect a valve opening and covering each port as required.
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline sbwhart

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Re: model steam engine: Comments on the design I have in mind?
« Reply #2 on: February 08, 2009, 06:33:14 AM »
Hi Jon

You will need some way of opening and closing the flow, I think what you are trying to do is let the energy in the fly wheel carry it over but it will have to work against pressure there just wont be enough energy in it.

If your just starting out you can't go far wrong than building a simple osilating engine there are plenty of plans available, if you do a google search and I'm shure some of the guys here can point you where to go. If you want to do some experiments these engines are great, there's no limitation to what you can do and they are very easy to work with and great fun. :clap: I think if you ask the guys we've all made them at some time

Have

Fun :wave: :wave:

Stew
A little bit of clearance never got in the road
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Location:- Crewe Cheshire

Offline sbwhart

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Re: model steam engine: Comments on the design I have in mind?
« Reply #3 on: February 08, 2009, 06:54:40 AM »
http://www.homemodelenginemachinist.com/index.php?topic=3810.msg38806#msg38806

Hi Jon

If you follow the link there are some plans from a friend of mine I know he won't mind me sharing them with you.

Cheers
 :wave:
and have fun

Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

bogstandard

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Re: model steam engine: Comments on the design I have in mind?
« Reply #4 on: February 08, 2009, 07:16:56 AM »
Jon,

Both your engines WOULD work if you controlled the inlet.

You would require a combined inlet/exhaust.

This is one I designed and built a while back, and is undergoing a facelift at this time.

http://www.youtube.com/watch?v=EFfm9L90Tyw

The inlet valve is fired from the crankshaft at the correct time, but only for a short period, then the exhaust valve automatically opens until the inlet is fired again.

John

Offline jonogt

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Re: model steam engine: Comments on the design I have in mind?
« Reply #5 on: February 08, 2009, 06:44:57 PM »
OK i think i see what you guys are saying.  I modified my sketch a little...



It doesn't show any actual valve action plans, but is that the sequence of airflow that I need?

I looked at some of the plans and pictures on the links, but I understand things a lot better if I draw them myself, so thanks again for the comments

bogstandard

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Re: model steam engine: Comments on the design I have in mind?
« Reply #6 on: February 08, 2009, 07:08:30 PM »
Slightly wrong Jon,

On the fourth pic, you need to have the inlet swapped over to an exhaust valve, as the returning piston is trying to compress the air above it.

There are two ways to counteract it. If you go the way of a poppet head valve, like I did and have an auto exhaust valve built in to relieve the pressure, then it will work fine, or the other way is to have a large flywheel mass to get over the air compression until the inlet valves fire again.

John S built one like that, which used a stiker pin on the top of the piston to open the inlet valve. But really that system is only used for fast running engines, they need the inertia of the flywheel to keep running.

I think I still have a few plans on that engine knocking about, so if you are really interested, something can be arranged.

John

Offline jonogt

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Re: model steam engine: Comments on the design I have in mind?
« Reply #7 on: February 08, 2009, 08:38:28 PM »
So in my design, once the piston gets to the top of the stroke, exhausts, and starts moving back to the bottom, even though the built up pressure is gone, the air in the cylinder is still enough to drag down the kinetic energy?  So when its returning to the bottom of the stroke, there needs to be an exhaust opening so that the piston can freely move and push all the air out... correct?  If so, I guess that explains why the inlet and exhaust are usually right next to eachother, because the exhaust needs to be inside the cylinder-piston volume.

Do I have it figured out now?

Offline Divided he ad

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Re: model steam engine: Comments on the design I have in mind?
« Reply #8 on: February 09, 2009, 04:48:55 PM »
Hi Jon,

I don't want to let you think I have much knowledge here so I'll let you in on a secret I look at when I am having trouble getting my head around these types of issues....

Take a look through the various engine types here....     http://www.keveney.com/Engines.html      There's bound to be something that can help your design?

Most anything we could think of has been done before by many different men... This is just a helpfull jogger as to how many of the designs work.


Hope it helps?



Ralph.



I know what I know and need to know more!!!

Offline jonogt

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Re: model steam engine: Comments on the design I have in mind?
« Reply #9 on: February 09, 2009, 05:47:27 PM »
Hey thanks for dropping in Ralph.  Sorry for flaking out on you a few months ago when we were chatting via PM... I'm way too easily distracted, really in most elements of my life.

I actually found that site last night a short while after I posted, and the animations help tremendously.  I'm currently finishing up a different project... a desk w/keyboard tray sized for sitting cross-legged at floor level.  Its made of steel tubing, angle, flat bar, and the surfaces will be flat plate.  I'll be taking photos of it when its done and i'll be sure to post em then.  After that's all finished I'll start working on plans for this engine.

thanks again,
-Jon

bogstandard

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Re: model steam engine: Comments on the design I have in mind?
« Reply #10 on: February 09, 2009, 06:27:44 PM »
Jon,

Quote
So when its returning to the bottom of the stroke

I was getting slightly confused, then realised you had made a slight mistake, actually, when the piston is moving towards the head, it is classed as moving to the top of it's stroke.

So now, as the piston is going towards the top of its stroke, there should be an exhaust valve in the head to relieve the pressure of the air being compressed on top of the piston. When it reaches TDC, the exhaust is then closed and the inlet fires, forcing the piston to the bottom of it's stroke. The cycle then repeats.

John

Offline jonogt

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Re: model steam engine: Comments on the design I have in mind?
« Reply #11 on: February 10, 2009, 06:44:14 PM »
I see what you're saying John, thanks for the terminology correction.  If it's not yet obvious, I have very little experience with engines.  I understand in general how they convert heat/chemical energy to movement, but a lot of the details about how all the parts physically function to make the whole system work right are new to me.  The oscillating engine makes perfect sense to me now, but I like the locomotive style a lot more.  Do you guys think I should atleast do a successful rough draft oscillator before trying the locomotive one?

We'll be doing milling and lathe work in the next couple weeks in my manufacturing processes lab, so I should be a bit more with the program after that.  Today we did basic stick, MIG, and TIG welding... MIG is the only of these I'd done before.  I've been interested in building a stick welder out of microwave transformers (lots of talk online about it), but after actually using one I'm definately over the idea  :bang:.  TIG was excellent and sophisticated... my unrivaled favorite now.

well I'm gonna quit ranting now... if anyone has an opinion about if I should build an oscillator before trying a locomotive, your 2 cents is welcome

-Jon

Offline jonogt

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Re: model steam engine: Comments on the design I have in mind?
« Reply #12 on: February 12, 2009, 12:49:11 PM »


^new design possibility i'm considering.  what do you guys think?  let me know if the drawing isnt enough to follow the idea, but it should be (this isnt exactly a group of dimwits here  :smart: )

bogstandard

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Re: model steam engine: Comments on the design I have in mind?
« Reply #13 on: February 12, 2009, 02:24:27 PM »
John,

Yes, it is very easy to follow you design, but all I ever seem to do is shoot you down in flames, and that is one thing I don't really want to do because it might discourage you from carrying on designing your own.

I saw this on another site, and I thought it would be a good thing for you to see.

Quote
Don't try to be as good as the people here. Try to be as good as YOU can, and use the folks here for inspiration.

I have been making my own designed enginres for a long time, and I have no qualms about using another persons idea to achieve the results I want. Whatever you can come up with, I can almost guarantee someone has tried it before
This is the post where I built the engine above, and as you can see by going down the page a bit, Chuck gave me some very good pointers, and I used it to design my own system. The one shown would work perfectly for your engine.

http://www.homemodelenginemachinist.com/index.php?topic=612.0

The major problem with you system would be trying to seal it. You would also only need one hole in the shuttle plate, and using a cam on the crank, you would be able to align that hole for the correct durations.

John

Offline sbwhart

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Re: model steam engine: Comments on the design I have in mind?
« Reply #14 on: February 12, 2009, 03:33:22 PM »
Hi Jon

Thanks for asking the engine questions,

It' led to a very interesting and informative answer from John, I've never thought about poppet engine, and a found Johns link exsteamly interesting.

Thank you and Keep the question coming

Cheers
 :wave:
Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

Offline rleete

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Re: model steam engine: Comments on the design I have in mind?
« Reply #15 on: February 12, 2009, 03:56:06 PM »
jonogt, that's an interesting idea, but probably not too practical.  Sealing it without excessive friction is probably going to be a real issue, as Bogs said.

What you've done is very similar to the way a sliding valve works.  The key to the sliding valve, however, is that because it's in a sealed box, the incoming steam (or air) seals the valve against the mating surface.  If the valve is lapped in, it seals very effectively with nothing else incorporated.  In the case of our air operated engines, sealing the valve chest (where the operating rod goes in) isn't as critical.

If you were to try to build your design, I'd recommend that instead of a deep slot, the outside piece was separate.  You then might be able to get a decent seal by lapping both sides of the valve, and attaching the outside plate in such a way as to be able to tweak in how tightly it pressed against the valve.  Might be fiddly to get it to work, but it would provide a visual valve system, rather than be hidden in a valve chest.
Creating scrap, one part at a time

Offline NickG

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Re: model steam engine: Comments on the design I have in mind?
« Reply #16 on: February 12, 2009, 05:32:06 PM »
John,

Yours is an interesting design, and the mechanism is feasible, but as John (Bogstandard) said, the first thing I noticed was the difficulties you would have sealing the valve down that deep slot. Once the slot is cut, you can do little with the surface finish inside and it is a finite width so it would be too difficult to get a good seal between the faces and the valve.

The only way I could see that working was if you made the cylinder in 2 separate pieces - the cylinder with a lapped port face, then a cover with the exhaust and inlet pipes, again lapped on the inside. This would have to be spring loaded equally around the valve (which would have to be lapped on both sides also). Again, as Bogs pointed out, you would need only 1 hole in the valve itself, which would oscillate between the inlet and exhaust ports.

In essence, all you would have done different from a standard oscillating engine is to immobilise the cylinder and create a separate valve that oscillates driven from another eccentric or crank.

Having said that, nobody will try to put you off, only help you, I still think it's quite a novel design and well done for grasping the concept and designing a mechanism that would work.

I would echo what Bogs said though, don't have any quarms about using ideas from other peoples engines, I've based all of my engines on other designs I've seen too, I haven't tried to re-invent the wheel, because that's too difficult!

I would recommend doing a simple oscillating engine first too, the link that Stew posted is one I designed recently specifically with beginners such as yourself in mind. I tried to make operations simple and keep parts and materials to a minimum. Doing an engine like this can instill a lot of confidence as well as give invaluable experience of the sorts of limits and fits you need to get engines to run before you go on to make one to your own design.

However, if you decide to try your own design straight off there are lots of people willing to help and offer advice so don't hesitate to ask!

Nick
Location: County Durham (North East England)

Offline NickG

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Re: model steam engine: Comments on the design I have in mind?
« Reply #17 on: February 12, 2009, 05:43:37 PM »
It seems rleete was typing the same thing at the same time as me!  :doh:  :)

John,

Here is a pic and video of my engine incase you're interested. By no means am I saying it's the best one to do, it is just one example. If you have a trawl aroud the forums there are probably better designs than this one, but I know it works, it's made from sensible materials and has the right parameters in terms of port spacing etc. There aren't many parts and if you mess it up it's not going to break the bank. I know at least one other person has sucessfully made a running engine to my plans too.



Location: County Durham (North East England)

bogstandard

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Re: model steam engine: Comments on the design I have in mind?
« Reply #18 on: February 12, 2009, 06:15:09 PM »
Hi Jon,

Had a little think about your valve design, and have come up with a C-o-C for you to look at.

I hope it explains my thinking to you. The sliding faces would need to be very flat. The unneeded areas could be shaped away to reduce mass.

I have also shown a basic cam operating system, the ramps on the cam would have to have a good profile to allow the follower a smooth action between inlet and exhaust.

John

Offline NickG

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Re: model steam engine: Comments on the design I have in mind?
« Reply #19 on: February 13, 2009, 04:21:20 AM »
Bogs,

That is similar to what I was thinking, is the width of the cut away on your cylinder exactly the same width as the valve or slightly smaller? If smaller, will having the springs at the bottom not tend to try and tip that plate? Probably not enough to pull it away from one side of the valve as it will only need light spring stiffness. I was wondering, is could some transparant plastic be used on that so it's possible to see the valve working?

Nick
Location: County Durham (North East England)

bogstandard

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Re: model steam engine: Comments on the design I have in mind?
« Reply #20 on: February 13, 2009, 06:41:06 AM »
Nick,

The main body and the sliding plate could be machined as one unit, totally flat.

The spring loaded side plate, is also finely machined on the sliding plate side. This would make it into a very close tolerance fit. Allowing it to be easily redressed in the case of wear. Just remachine the two sets, and away you go again.
I would have the swivel spindle to have a couple of thou clearance in its bearing hole, basically to allow a bit of auto levelling float.

I wouldn't use perspex, because you need the rigidity and hardness of metal to keep the pressure integrity. Plastic would very easily score and allow leakage.

But again, with this type of engine, you can't beat a poppet valve and sliding piston auto exhaust. I am no super expert on them, but they are dead easy to make, and work faultlessly.

See the C-o-C for details of how I made the head valve. The poppet valve can be mounted almost anywhere, as long as it is fired by the cam as fast as possible. The air should just make a very quick pulse, and timed to fire just as the piston has gone over TDC, and finish well before the piston reaches BDC.

I can show you the build up of the poppet valve itself if you need it. Everything is really easy to make.


John

Offline NickG

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Re: model steam engine: Comments on the design I have in mind?
« Reply #21 on: February 14, 2009, 11:51:34 AM »
Thanks for that John, what is the purpose of the hole at the bottom of the stroke? Is that just to relieve the initial pressure when the piston starts to move back on it's exhaust stroke?

Cheers,

Nick

ps I think I had a look at Chuck's single which has this sort of valve arrangement?
Location: County Durham (North East England)

bogstandard

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Re: model steam engine: Comments on the design I have in mind?
« Reply #22 on: February 14, 2009, 12:41:16 PM »
Nick,

Yes, the hole is to release any residual pressure by the time the piston has reached BDC.

It was Chuck who showed me this design, I just made the poppet valve remote instead of being connected to the head.

As I said before, if I want to make something, I will use other peoples ideas, but one thing I usually do is to give them credit for it in either my post or video. Everyone should get recognition for their efforts.

John

Offline HS93

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Re: model steam engine: Comments on the design I have in mind?
« Reply #23 on: February 14, 2009, 03:03:45 PM »
these may help with basic steam engine working,

Peter   :ddb:
I am usless at metalwork, Oh and cannot spell either . failure

Offline NickG

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Re: model steam engine: Comments on the design I have in mind?
« Reply #24 on: February 15, 2009, 04:21:03 AM »
That's a good illustration of the slide valve engine and no doubt people starting out will find it useful on here.  :clap:
Location: County Durham (North East England)