Engines > Your Own Design
A Simple Uniflow Engine
gary.a.ayres:
Hello All.
It has been a while, what with everything that is going on.
Hope you are all ok...
Finally and at last, I have made a start on my second engine. A slightly unusual one, this.
First of all, the 'simple' in the title of the thread refers to the simplicity of the concept of the engine. It does not mean that I think I'll find this build simple.
The design upon which I am basing the working heart of the engine is by Stan Bray. It's 'Clarence - a clapper valve engine'' from his book on building simple model steam engines:
I don't like the sound of 'clapper valve', so I'm describing my version as a 'uniflow', which I believe it is, albeit a simple example of the type. I am taking the basic working concepts and the relative dimensions of the working parts from the book. There, however, the similarity will end - mine will have a very different look, and it will be at least three times the size of the original, which has only a 10 mm bore.
Essentially this engine will be scratch built. I have an overall idea in my mind but I'll let it unfold as the thread progresses rather than set it all out here, particularly as the plan will most likely change as I go along.
I decided to start with the flywheel - or I should say flywheels. I have had these two brass discs in my parts box for some time. They are about 11.5 cm in diameter. Originally I had thought of somehow joining them to make one chunky flywheel, but I have now decided that the engine will have twin flywheels. This, along with my idea for a frame, will have implications for some of the engineering further down the line. For the crankshaft, the bigger of the two pieces of precision ground mild steel is a bit heavier than I would have chosen, but I have it in my shop and I fancy pursuing a 'use what you have' aesthetic as far as possible with this build:
The flywheels will be composite in nature, each having a central boss made from a separate piece of brass. They will also have a pattern of holes so I had to drill out and bore the centres so that they will fit the small four-jaw chuck which is mounted on my rotary table:
So, a small start has been made.
This will be a fairly chunky engine and it will need a fairly powerful boiler to run it. More of that later...
MJM460:
Hi Gary, good to see you building another engine. I am looking forward to seeing what you will do to put your mark on this one.
The design seems to have much in common with the principles used in a high speed hydroplane which was written up in the magazine. However that was was a very highly developed performance monster. Yours looks much more reasonable, but who knows where it will lead.
K.N Harris mention the uni flow principle in his book. You might be interested to know that that is the one that really got me interested in applying thermodynamics (which was central to my working life) to understanding in some detail how this helped understanding our models, and ultimately lead to my Talking Thermodynamics thread.
So not really sitting back, as I seem to be busier than ever these days, but looking forward to following along with your new build.
By the way, how is your flash steam plant going?
MJM460
gary.a.ayres:
Hi MJM, and thanks.
My hunch is that if I make a reasonable job of this it will be a fast runner. I have the K.N. Harris book, and yes, the uniflow engines he describes seem to be of more complex designs.
I haven't progressed the flash steam generator for quite some time as I got 'diverted' into building a brake drum forge. I always considered the flash generator to be something of a side project anyway. That said, I have a sense that something of the sort could be well suited to this engine though I have a feeling I'd need a bigger coil, which would be easy enough to do.
However, I also have other plans when it comes to boilers. Not going to say any more about that at the moment as I don't want to jinx it! ;)
Hope you are doing ok with the challenges of the pandemic. Are you still in lockdown in Australia?
Cheers,
Gary
MJM460:
Hi Gary, the engine you are making is very similar in principle to that high speed hydroplane, Pisces, that I mentioned, though yours will be a more appropriately gentle one to tame. The hydroplane had the principle refined, and the manufacture developed way beyond anything I could imagine doing.
The K.N. Harris design was closer to yours in performance, but added the “uni flow” exhaust ports to a more conventional engine, to get more power output.
Yours will be quite economical on steam as the inlet port will only be open briefly, thus allowing for plenty of work to be developed through expansion. It will be happier running faster, and the overall performance will be interesting to look forward to. Most simple engines, the inlet valve is open for longer, so they do admit more steam, then simple exhaust it to atmosphere rather than achieving so much expansion. In the end it is all about valve port timing and there is a big variation between different designs.
With that design, the inlet port opens before dead centre, so this limits how long it can remain open after dead centre without becoming too difficult to start. You will need to flick the flywheel, to start it, but t should run well.
I assume you will make provision to collect the exhaust steam, and not just have the port to atmosphere as per Stan’s book.
Looking forward to following your boiler exploits.
Still in lock down here. Work is acceptable here for those who can’t work from home, but people in our age range are advised to stay home apart from a daily walk, which we are making the most of. We both have hobbies that we are enjoying being able to spend more time on. I think my wife misses company much more than I, but we both miss the social aspects of family and friends, but managing well and keeping happy. Technology is a big help but does not entirely replace human contact, and never will. The different approaches taken by different countries and even different states are interesting and will provide a quite good data set for the next time.
Time in the workshop is filling in the gaps left by other activities that have to be on hold, so busier than ever. But no point making face masks at this stage as our medical authorities are not recommending them for general use. Obviously the jury is still out on that one too, and those who analyse this stuff later will eventually work out which way we should all go. Or will it depend on which combination of other measures are in place?
So going well here. I hope you are also managing ok in this world that is so different from what it was less than two months ago.
MJM460
gary.a.ayres:
MJM - I will look for some information on the Pisces engine as I may be able gain some ideas from it.
Thanks for your explanation on anticipated performance - it's encouraging!
On the exhaust ports - yes, my plan is to collect the exhaust steam and route it to wherever. Stan Bray advises that if his design is scaled up, extra ports should be drilled rather than enlarging the single one in his version, so that's what I'll do. My thought is to make a manifold to gather the exhaust from the ports and direct it into a single pipe. Could look pretty cool too if I make a decent job of it. That feels aeons away at this point though!
The lockdown where I am has been partly eased, i.e. tradesmen who work outdoors are now back at work provided they socially distance. Otherwuse it's still the same - one walk a day, and so on. I live on an island which has managed the situation pretty well and the curve here has been pretty much flattened. They are doing much better here than they are in the UK mainland (where my daughter works as a nurse...), and I think they will ease the lockdown carefully, measuring as they go.
I'm lucky in terms of the work side of things. As a psychotherapist in independent practice my business took a bit of an initial hit, but it has picked up again in virtual form so I'm actually quite busy. My partner is a teacher and she is working from home, setting work for her students online. Not everyone is so fortunate though.
Taking a day off today to spend some time in the shop though!
Great that you are able to do the same. What are you working on?
:ThumbsUp:
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