Author Topic: Brayton Readymotor.  (Read 1628 times)

Offline Alyn Foundry

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Brayton Readymotor.
« on: September 22, 2018, 08:32:01 PM »
Hello All.

It almost seems like a lifetime ago now when I first started upon the most ambitious scale engine project ever.

A long standing customer that became a good friend, Mike the bike, showed me a picture of the Brayton ready motor. A beautiful piece of Victorian mechanical engineering. A time when aesthetics and functionality were as one. Sadly, Mike passed on and only his photocopies from the book remained.

Upon a whim I thought, wouldn't it be nice to remember Mike with an inspirational and pioneering engine? The Brayton fitted the bill nicely.

George B. Brayton and his engine are almost forgotten but the Brayton Cycle is now used widely in the form of the Jet engine!
In the early 1870's prior to NA Otto and his four stroke the Atmospheric engine reigned supreme. Brayton's " constant pressure engine " design had similar efficiency but later liquid fuelled engines were developed for places where town gas was unavailable.

Picture a canister filled with a pressurised combustible mixture of air and Town gas, a recipe for disaster if ever there was! Well this was exactly how the fuel was stored prior to combustion. At bottom dead centre the admission valve opens allowing the mixture to pass by a burning pilot light within the cylinder head. The result is an expansion of the Nitrogen that presses against the underside of the double acting piston. On the other side of the piston the air and gas that was drawn in on the last downstroke is being moved through a non return valve into the tank that forms the engine's beam support column. At a given point the admission stops to allow further expansion due to the heat generated by the flames. As the engine reaches TDC the exhaust valve opens and the flywheel carries the piston down both exhausting the power cylinder and drawing in a fresh charge of mixture in. The cycle repeats.... Well until sometimes the flames could pass the many safety meshes and ignite the fuel in the column!! The engine was fitted with a large volume safety valve to allow for this condition without an explosion of the cast Iron receiver.

Well, that's the history. George Bailey Brayton continued to develop engines and in the 1890's was the first to directly inject liquid fuel oil into the cylinder just like Diesel did but used secondary ignition. He was the first to control engine speed by quantative means however.

To the point....

I happened to have a pair of " lazy S " spoked cast Iron wheels that had solid rubber tyres bonded to the rim. A quick measure at around 15 inches diameter seemed about right for a one third scale engine. Once a datum has been found you can then use it to measure a picture and start making a three dimensional pattern. After several months I had got most of the engines patterns made and quite a few were cast in Iron. I have the cylinder, piston and heads finish machined too. Disaster struck, my one and only Buckley foundry announced closure. I hadn't quite finished the main engine pattern, the project was shelved.

Having recently found a new and I'm happy to say, competent Iron foundry the Brayton Ready motor seems like an ideal candidate for resurrection?

What does the membership think? Does anyone know if a
" constant pressure engine " has ever been scaled and built?
Is it worth the effort? Over to you....

Offline crueby

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Re: Brayton Readymotor.
« Reply #1 on: September 22, 2018, 08:37:45 PM »
Well, I don't yet follow the way the cycle works (diagram would help a lot, I think), but the engine itself is very interesting looking, with the fluted column and arcs its classic.  Would you make it to run the original cycle, even with the dangers?

Offline Art K

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Re: Brayton Readymotor.
« Reply #2 on: September 23, 2018, 01:10:50 AM »
Like he said, I don't follow how it works. I did follow a link to Wikipedia that explained the cycle and as an open cycle turbine and jet engines. I guess it's just over my pay grade. :ROFL:
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline Jasonb

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Re: Brayton Readymotor.
« Reply #3 on: September 23, 2018, 07:25:59 AM »
I think I follow how it works the top side of the piston acts like a compressor piston and draws in the fuel air mix on the return stroke and then pumps it into a smaller chamber on the power stroke. The Combustion side of the piston sees that compressed fuel/air mix at the start of the power stroke where it is ignited making the engine fire and on the return stroke it exhausts the spent gas.

Is it worth the effort?

Well as a personal challenge then I'm sure it is. As a possible commercial project then I think the size will be a limiting factor as there are not many engine enthusiasts who can acomodate a 15" flywheel and even those that can may turn their noses up at an engine that is not going to be easy to move around.

As to whether it has been modeled before I don't think it would have been done in a "scale" form but expect someone may have made a barstock version just to see if the cycle can be modeled. I see from Google that Nick Roland (RMC Engines) has a full size later 2-cylinder engine that runs with this cycle so he may have played about with it on one of his test rig models.

Offline Alyn Foundry

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Re: Brayton Readymotor.
« Reply #4 on: September 23, 2018, 12:17:19 PM »
Good morning.

Many thanks to the few that looked in.

The Brayton cycle is basically quite simple.  A mixture of compressed air and fuel ( in the correct ratio for combustion ) are allowed to enter the closed cylinder with the piston at bottom dead centre. A pilot light within ignites this flammable mixture. Two processes act as one, the compressed air wants to expand into the bigger space and at the same time is also being heated by combustion, rapid expansion occurs pushing the piston away, the power stroke.

The engine had a mechanism that controlled the amount of admission, a bit like a steam engine does, variable " cut off " this maintained the engines speed and power.

This particular engine combined both the expansion chamber and compressor in a single, double acting style cylinder, later designs used separate cylinders.

With regard to your question crueby, no. I felt that a potential " bomb " wasn't a great idea so I have made the admission valve assembly with the addition of a separate fuel injection port. In other words the mixture will be made on demand just prior to burning, the column will contain nothing but compressed air.

I've also attached a picture of the Brayton cycle pertaining to an " open cycle " system.

Cheers Graham.

Offline Alyn Foundry

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Re: Brayton Readymotor.
« Reply #5 on: July 18, 2020, 02:12:45 PM »
Hello All.

With a lot more spare time and a little family encouragement....

I'm a couple of steps closer to the foundry.

Cheers Graham.

Offline Jasonb

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Re: Brayton Readymotor.
« Reply #6 on: July 18, 2020, 02:25:06 PM »
That's a good way to form a core box, where did you get that idea from :thinking:

I'm still waiting for some sizes for the bearing housings to go on top of that pattern, also any news on the kinky one? What was the outcome of that facebook message about printing the flywheel pattern?

Offline Alyn Foundry

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Re: Brayton Readymotor.
« Reply #7 on: July 18, 2020, 02:46:03 PM »
That's a good way to form a core box, where did you get that idea from :thinking:

I'm still waiting for some sizes for the bearing housings to go on top of that pattern, also any news on the kinky one? What was the outcome of that facebook message about printing the flywheel pattern?

Hmmm, I wonder!   ;)

Well Jason, I had zero feedback on whether the kink was acceptable but my own eye sees it somewhere between your 2 renderings. Dave Otto wrote to say it was too big for his company's printer to accommodate.

Here's my original attempt at the top bearing yoke.

I've also attached a picture of Brayton's 1890 patent motor which shows the admission port in detail. I often wondered how he managed to stop the greater pressure developed within the cylinder from being lost into the air receiver, it was both mechanically opened and closed. You can also see the internal flame igniter.

Cheers Graham.
« Last Edit: July 18, 2020, 03:27:13 PM by Alyn Foundry »

Offline Jasonb

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Re: Brayton Readymotor.
« Reply #8 on: July 18, 2020, 04:14:25 PM »
I'll draw something up between the two spoke options.

There are still other options once design is sorted

 - CNC cutting or printing (on a smaller machine) individual spokes to be built into a wooden hub & rim, either all or two masters that can have six of each spoke home cast from them.

- CNC or print the wheel in several segments that can be joined to make a complete wheel which would need a printer with about 200 x 200 print area

- As above but with a thin rim so the segments could be assembles into a wooden outer rim this would only need a 150 x 150 work area.

- CNC cut six segments form a large blank that can be indexed around thus reducing the working area needed particularly the Y axis.

Final option is to make one to the Patent drawing with STRAIGHT spokes :ThumbsUp: :LittleDevil:

Offline Alyn Foundry

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Re: Brayton Readymotor.
« Reply #9 on: July 18, 2020, 05:44:38 PM »
I'll draw something up between the two spoke options.

There are still other options once design is sorted


Final option is to make one to the Patent drawing with STRAIGHT spokes :ThumbsUp: :LittleDevil:

 :lolb:

No Jason. I don't think so....

But perhaps you could CNC me a neat relief to glue onto my already made wooden yokes ?

Offline Jasonb

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Re: Brayton Readymotor.
« Reply #10 on: July 18, 2020, 06:41:38 PM »
Send me a sketch and sizes

I think I may just be able to do the flywheel in two halves leaving the rim for turning

Offline Alyn Foundry

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Re: Brayton Readymotor.
« Reply #11 on: July 19, 2020, 11:09:49 AM »
Thanks Jason.      :ThumbsUp:

Offline Jasonb

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Re: Brayton Readymotor.
« Reply #12 on: July 19, 2020, 01:18:29 PM »
Now All I need to do is convince you to make it smaller then I could knock one up like this steel jobbie I did this morning ;)

Offline Alyn Foundry

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Re: Brayton Readymotor.
« Reply #13 on: July 19, 2020, 02:00:46 PM »
Now All I need to do is convince you to make it smaller then I could knock one up like this steel jobbie I did this morning ;)


Very nice Jason.

I think the pain of the ill fated Hornsby Akroyd still lies heavily with me Jason. Almost 9 months of intense patternmaking and engineering came to nothing but a very poor running engine. At a quarter scale I think the natural/elemental components didn't like it.

From the data I've gleaned my model is still small at 1/3 rd scale but I think we might stand a reasonable chance of a runner. Despite much searching I've not come across a working model myself but perhaps the readership can find something?

As far as I'm aware this particular engine was a one-off built for an exhibition, the more common horizontal format see's a few survivors.

Cheers Graham.


Offline Alyn Foundry

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Re: Brayton Readymotor.
« Reply #14 on: July 19, 2020, 02:17:48 PM »
Here's a survivor....


Having understood the working principle I'm of the opinion that the " cutoff " is a little late and some still burning/expanding mixture is " popping " as the exhaust is opening. Hence the bark to the exhaust note.