Author Topic: Idea for air/steam engine  (Read 9504 times)

Offline PStechPaul

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Idea for air/steam engine
« on: March 20, 2014, 07:29:48 AM »
Seeing all these different engines has made me interested in trying my hand at designing one. I have some double acting hydraulic cylinders that I thought about using, but they are rather large, and I want to see if I can build all the components myself.
 
So here is my concept:


And here are some details:

The main cylinder has a piston and air connectors on each end. One will be an inlet for pressurized air (or maybe steam), and the other is for exhaust. At the end of each stroke, the roles are reversed, so it will be double-acting. I show a two-disc flywheel with a pin for a crankshaft, and the cylinder rocks up and down as it turns.
 
The valve has an inlet on the bottom, and two exhausts. The outlets on top are connected to the two inlet/outlets on the power cylinder. The slider in the valve body has two holes on one side, and two slots on the other. As the slide moves to either end, the inlet is directed to one or the other inlet on the power cylinder, and the other one that is the exhaust.
 
To move the slider, I added another wheel on the power shaft, with a pin that engages a slotted piece which pushes or pulls the slider. The slot allows the slider to stay in its end positions for most of the stroke, and the transition is only at the ends of the strokes..
 
I might make this from plastic, as illustrated, so the innards can be seen working. I'm sure this is not really a new idea, but I like to design things as much as possible from my own ideas and understanding of how something might work. Now I need to transition from CAD drawings to actual parts, and I will probably need to adjust some of the dimensions to match the materials I have. I have 3 ft lengths of 0.875" OD x 0.750" ID and 0.750" OD x 0.575" ID Lexan polycarbonate tube, which actually fits very smoothly one inside the other, so I might make the piston from one. But since I may need to use standard plumbing fittings for running on a compressed air supply, I may need larger pieces. I have an assortment of steel and aluminum rod up to about 2.5" diameter, and some Delrin and PVC rods, so I will need to see just what I have.
 
I really should be spending time on other work-related projects, and some electronics, but I like doing machining and mechanical design because it is new to me and it is perhaps not as tedious. I hope to be able to build this in time for the CF show, but I also want to build my mini-SRM, and also the electronic ignition I had proposed.
« Last Edit: March 20, 2014, 07:57:41 AM by PStechPaul »

Offline Alan Haisley

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Re: Idea for air/steam engine
« Reply #1 on: March 20, 2014, 03:37:08 PM »
That should be an interesting runner. Why not spread the two cylinders a bit further apart and see if it's possible to use stiff piping rather than the flexible tubing that I'd think your original drawing would require?  :thinking:

Alan

Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #2 on: March 22, 2014, 03:30:07 AM »
I fiddled around with the design a bit and came up with this:
 


 
As shown here, the valve will move opposite to the power piston. So there will need to be flexible hoses between them. But now I'm thinking about mounting the valve assembly on the opposite end of the power cylinder and use a linear actuator for it. Actually it could possibly be made from a single tube. I checked out the materials I have on hand and I will probably make the cylinders from 2" diameter aluminum, and the piston and valve slider might be from Acetal plastic. I'm anxious to start making chips, but first I want to be sure the design is how I want it to be. That's my problem with lots of projects - I come up with a design that should work, but then see how it can be simplified and improved.

Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #3 on: March 22, 2014, 05:55:41 AM »
Here is what I came up with. It's a little more complicated but now the power cylinder and valve are vertically aligned and the crankshaft is hinged so the assembly can be rigidly mounted to the base. There are some sliding pins in slots to keep the rods moving concentrically and the piston moves 3" for a 1" movement on the bottom. But I may need to adjust the fulcrum of the rocker arms to get a 2" bottom movement along with the 1" slot in the valve rod. This stuff is challenging!
 



Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #4 on: March 22, 2014, 06:39:53 AM »
Here's a much simplified design. The only thing I'm a bit concerned about is the sliding valve actuator. It seems like the actuator arm might jam up unless it's well lubricated and stiff. Hmm.  :naughty:



Well, that looks simple enough, and I think the slide mechanism will work OK. Is it time for chips yet?  :thinking:
 
Actually I made some more changes that I think will make a better design:
 


« Last Edit: March 22, 2014, 09:18:36 AM by PStechPaul »

Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #5 on: March 25, 2014, 04:57:57 AM »
Well, I finally started making chips (or swarth). Here is a 2" x 3.5" rod after cutting it from 12" stock, and I drilled a 1/2" hole through it and faced the end:
 

 

 
Boring.....
 

 
The part with an almost 1.50" bore, halfway through. This took several hours, mostly because I am still learning and being cautious and taking only 10-25 thousandths at a time:
 

 
This will be the cylinder. Aluminum may not be good for steam, but I think it will be OK for air. I'm not quite ready to do this with steel or brass. I could probably use a steel tube insert if I really want to make this a steam engine.

Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #6 on: March 31, 2014, 07:05:22 AM »
I made some changes to my design:



I am still working on the exact design of the valve mechanism. I want it to switch quickly between the two states, and so I may use a spring-loaded ball and detents in the sliding valve, and springs on either end of the actuator so that they overcome the tension at the ends of the main piston travel.

Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #7 on: April 04, 2014, 09:44:33 AM »
I've had another brainstorm, and bainspired by my design proposal for a dual piston Stirling engine, I came up with something for a simple stream/compressed air engine:
 

 
The power cylinder on the bottom is fed from an inlet and a rotary valve that will alternately direct pressurized air to the space between the pistons, and to each end for the reverse direction. The exhaust is directed out of another port of the valve. Here is my concept for the valve:
 

There is an actuator on top of the valve assembly that turns the inner piece 90 degrees in either direction when a pin on the flywheel contacts it. The valve has slots on opposite sides that direct the air flow either through to the opposite end, or to both sides, and this should work for both intake and exhaust.
 
If nothing else, this thing should look interesting and will have some cool movement if and when it runs. I'm hoping that my materials arrive soon so I can start making chips and swarf.

Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #8 on: July 10, 2014, 07:38:51 AM »
Well, now I'm getting the itch to try another rather unique engine design. The one I brought to Cabin Fever actually was a bit different from the concept above:
 

 
I had parts of it made and assembled, but I ran into some problems with synchronizing the two flywheels using the internal connecting rod, and the external arms are rather clunky. So while the power was knocked out here from a severe thunderstorm, I visualized a new design, sketched it on paper, and then drew it up in TurboCAD when the power was restored 4 hours later:
 

 
It probably needs some explanation. The piston arms are connected together inside the dual flywheels, and since the pistons can only move horizontally, it forms an equilateral triangle, and the horizontal motion is translated to vertical. The point where they are joined is also fastened to a connecting rod which allows the vertical motion to be translated to rotational. similar to a single piston and crankshaft. One problem could be that the pistons may not push equally, and thus the point where the arms are connected could move horizontally as well as vertically. It might even be possible to eliminate the connecting rod and have the junction point move in a circular path. That would definitely require the pistons to move asymmetrically, but it might even be an advantage.  :shrug:
 
Anyway, this design seems more interesting to me and I think it will work better than the previous concepts. I think it will be unique, at least!  :thinking:
 
Once I get a little further along and see that this may be viable, I'll start a separate build thread for it. These are just WACs (Wild Ass Concepts)  :ROFL:

Offline b.lindsey

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Re: Idea for air/steam engine
« Reply #9 on: July 10, 2014, 12:13:38 PM »
Paul,
There is a lot of design work there...so which design have you settled on if any since the chips have started to fall?

Bill

Offline Rivergypsy

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Re: Idea for air/steam engine
« Reply #10 on: July 10, 2014, 12:18:00 PM »
Hi Paul,

They're some interesting ideas you've got there, so I'm looking forward to seeing how you progress. Just a quick comment though, for machining aluminium I'd personally recommend a tool or insert with a positive rake on it; i think You'll find it cuts a hell of a lot cleaner:-



Good luck,
Dave

Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #11 on: July 10, 2014, 09:08:27 PM »
I have gained a lot more understanding and machining experience since I first started exploring the possibility of building a model engine. At this point I will probably make the most recent design as pictured above, partly because I can use many of the parts I have already machined. I think it is important to get something built and running, and then use the experience to move on to another project.
 
I am not totally happy with the valve design, but I think it will work, and it seems rather unique, which is something I value. The other area where I may need to work on is the air lines, which I have conceived using 1/8" plumbing/pneumatic fittings and rubber hose, but I would rather use small diameter copper tubing. I think I will keep the standard air hose fittings for inlet and exhaust, but the connections to the cylinder I think should be something less bulky. I might use automotive brake lines.
 
Lately I have become much more comfortable machining steel, especially the lovely 12L14, but also stainless steel and alloy steel 4140. So my next project will probably use those materials, mostly.

Offline Coopertje

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Re: Idea for air/steam engine
« Reply #12 on: July 10, 2014, 10:02:35 PM »
Hi Paul, as said a lot of design work you did there! Must be good to make swarf in the end. Just take every single part as a mini project and you will get there regardless the experiance you have. My first machning project was a IC engine, took me a year and a lot of head scratching but I got it running. Learnt a great deal of my mistakes and trials. So if I can do it, anybody can do it!

Looking forward to see the parts for your engine taking shape.

Regards Jeroen

Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #13 on: July 12, 2014, 09:27:02 AM »
Here are some photos I took of the partially completed engine illustrated above, before my latest brainstorm:
 

 

 
I took some video of it showing how it will spin, although it wobbles a bit. I'll post that later; not really much to see. Then I started taking it apart so I could reuse most of the pieces for my newer proposed design:
 

 

 

 

Offline PStechPaul

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Re: Idea for air/steam engine
« Reply #14 on: March 29, 2015, 02:47:52 AM »
I'm doing more work on this engine. Here are some pictures of the rotary valve and manifold:
 

 

 

 

 

 

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