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Designing steam engines

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chucketn

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At the risk of being shushed, and drummed out of the forum, I would beg to ask the question "How to design a steam(or air) engine. "?
I have built a few very simple engines, and followed many builds here and on other forums. I've collected plans for all sorts of 'steam' or 'air' engines from all over the web. Recently I was fascinated by Brian Rupnow's Double Acting Double Cylinder Oscillating Engine build. Fascinated to the point I read his threads on all the forums it was posted on, made notes and downloaded most of his pictures. I decided I wanted to build this 'simple' engine. But, being totally retired and on a meager pension, instead of buying Brian's plans, I set out to design it myself using Fusion 360. I got as far as my interpretation of a cylinder(which I'm 3d printing at the moment). I intend to use 3d printing to prototype my engine, and then build it in metal, possibly even casting some of the parts in aluminum.
I began to realize there has to be a method to my madness, and you guessed it, I don't have a method.
So, I would ask the revered denizens here, how do you go about designing your engines? I mean those you design without a plan to go by, like Brian did... Do you start with the cylinder and go from there, or the crank throw and work back to the cylinder? How do you decide on the crank throw, the stroke, the bore, the size of the flywheel, the length of the piston rod, etc.?
Is there a book I can buy/download, or a thread in a forum that explains the why and how of steam engine design?
If you haven't guessed, I have no 'engineering' experience other than designing simple stuff that I can make on my lathe and mill, or print on my 3d printer.
 

chucketn

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Writing the above seems to have influenced my 'Google foo'. I just found this web page and am studying it now...
This is the kind of info I'm looking for...
http://www.panyo.com/oscillators/

Plus that web page gives me more search terms to use... LOL, found the edit...
 
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gbritnell

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First decide on a style of engine, horizontal,vertical, simple, double acting or oscillator. Next figure what bore and stroke you want then work from there. It's hard to give exact dimensions for everything otherwise we would be designing the engine. If you have a lot of reference material just use what someone else has already created.
gbritnell
 

Mechanicboy

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At the risk of being shushed, and drummed out of the forum, I would beg to ask the question "How to design a steam(or air) engine. "?
Steam engine and air engine is difference in timing..

Steam engine --> timing with expansion for less consumption of steam.

Air engine --> Timing without expansion. Also full pressure of air from TDC to BDC and exhaust from BDC to TDC. No economical consumption if you are using air pressure tank instead air compressor. Except CO2 engine who can be created to get less consumption of CO2 from pressure tank with CO2 gas (The CO2 engine has ball valve in cylinder head who are opened by the tap on top of the piston a bit before TDC and has a equal period after TDC to the ball valve is closed, then the CO2 gas is expanding until exhaust port is opened. ).
 

chucketn

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I was under the impression that a 'steam' engine will run on compressed air. Is that not so?
I guess what I'm after is an explanation of the mathematical relation ship of the intake and exhaust ports, the stroke and the length of the crank arm. I know these are all inter-related, I just can't get my head around it. I have built wobblers before from plans. I want to be able to build without a specific plan.
I have just been looking at a site from Cornell University, http://kmoddl.library.cornell.edu/resources.php?id=113 that has mechanical models and explains them with math equations that are way over my head.
Brian, if you're reading this, how did you determine where to put the trunion port holes, and how long to make the crank arm? I understand the trunion port holes will be on an arc with the radius equal to the distance from the trunion pivot to the block port, and the length of the arc has a relationship to the length of the crank arm. But how do I figure that out?
 

Mechanicboy

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I was under the impression that a 'steam' engine will run on compressed air. Is that not so?
The steam engine can run at compressed air, but less effective than if the steam engine ran at steam due timing with expansion ( with air = no expansion in a closed cylinder).
 

chucketn

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Well, I've figured out how to find one dimension, the location of the trunion ports. I drew a mockup of the cylinder pivot point, the arc inscribed by the cylinder port, and a circle representing the crank arm travel. I drew lines from the 90 and 180 points on the crank arm circle through the center of the cylinder pivot and on through the trunion port arc. Am I on the right track?
 

chucketn

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The steam engine can run at compressed air, but less effective than if the steam engine ran at steam due timing with expansion ( with air = no expansion in a closed cylinder).
Well, I've not progressed to building boilers yet, so my engines will run on compressed air only.
 

Pthunberg

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A 3D drafting program like Rhino 3D can be very helpful in working out the geometry of all the moving parts. Bit of an expense and it requires learning how to use the software.
 

chucketn

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A 3D drafting program like Rhino 3D can be very helpful in working out the geometry of all the moving parts. Bit of an expense and it requires learning how to use the software.
I have and am learning Fusion 360. In fact, I used it just yesterday to draw a diagram of a oscillating engine cylinder and crank of different diameters, to plot the port openings in the trunion.
 

bouch

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I suggest you download Charlie Dockstater's valve gear programs. These will let you verify what you design for cylinder ports/valves/valve gear will actually run.

http://www.billp.org/Dockstader/ValveGear.html

Different programs for different valve gear. If you're going to build a non-reversing engine, then you should use the slip eccentric and just assume one direction of running.
 

Anatol

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At the risk of being shushed, and drummed out of the forum, I would beg to ask the question "How to design a steam(or air) engine. "?
"How to design a steam(or air) engine. "

I think this is a GREAT question. Fundamental. There are those in this community who just want to build, and are happy to reproduce, scale etc, existing plans. (No criticism intended). Others want to understand the design principles. I'm in the latter camp.

What I struggle with is having a gut sense of relative proportions. I do not yet have enough experience to know, ie - what cross section of stem pipe or steam passage is 'in the ballpark' for steam at x temp, with cylinder volume y, running at speed z? similar equation apply to valve openings, etc.
 

Anatol

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At least youve got a copy
This one although a little out of date is still a handy reference
/QUOTE]

I second that, I found the Harris book very informative, and its got an introduction by Westbury, who is quickly becoming god to me :)
 
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Anatol

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oops, somehow I included my text as if it was part of Frazer's quote. I tried to fix it but it didn't fix.
(Admin - I tried twice to remove the extra "quote" at the end of the doc, but it didn't change the displayed message.)
 
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