# Brayton cycle engine beginnings



## myrickman (Aug 31, 2013)

This is one I have been toying with making for several years. The Brayton cycle differs from the Otto cycle in that it is constant pressure combustion. A mix of fuel and air is injected into a cylinder and burns. As it burns, it expands and creates additional work. The top side of the piston compresses air which is stored in the receiver and later used for combustion. It is a two cycle engine in that it produces power each revolution. I have researched several of Braytons patents and seen three of them at the smithsonian annex and the great falls museum in Paterson, NJ. This design appears to be a good start for a test mule to demo the concept. The tricky part is the fuel-air injection system and the plate to keep the burning mix from getting back to the mixing chamber. The plan is to use sintered stainless steel  as the flame arrestor to accomplish this. The fuel pump is simply a pin in a barrel with check balls. It doesn't really inject, but delivers a charge to the mixing chamber behind the flame arrestor. I'll post some beginning pix over the weekend to start things off. Here is the patent drawing to give you an idea of what it will look like.


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## idahoan (Sep 1, 2013)

Interesting project; it will be fun to follow along with your work.

Dave


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## myrickman (Sep 1, 2013)

Here are the beginnings of the build. This one will be made from bits I have lying around. The cylinder is a piece of steel 2-3/8 ID x 3-1/2 OD. The receiver is an old 4 inch oxygen tank a friend gave me. The flywheel is an old raw casting about 11 inches in diameter. I have to turn the OD yet. The mains are brass with Babbitt liners. I have to pick up some large shaft collars to make the mouthing flanges for the cylinder and to top off the receiver. The whole mess gets welded together after I get the basic pieces made.


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## myrickman (Sep 1, 2013)

Here is the flywheel and base. I always liked those bent spokes... The base was saved from a Delco light plant and looks like it provide a stable platform.


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## myrickman (Sep 1, 2013)

Making the top base plate which carries the cylinder and butts up against the receiver. I am glad I picked up the chuck for the rotary table- it came in handy for making this piece.


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## myrickman (Sep 29, 2013)

Got back on the Brayton this weekend. Got a lot of the drudgery done. Cut the cylinder to length and drilled/tapped for the heads on the combustion and compressor ends. Roughed out both heads and made a brass stuffing box for the compressor end. Made the insert ring for the receiver tank which will be welded in. Made some 3.5" alum blocks to set the spacing of the frame during welding. My friend machined the OD of the flywheel, so all it needs is broaching. Thought I'd include a picture of the patent model to give you an idea of what it will look like when completed. Of course, the patent model was made of wood. Many unknowns in a project like this as to the fuel delivery and ignition. I'll try to get some more pix up soon.


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## Philjoe5 (Sep 29, 2013)

Very interesting project.  Good luck with your build.

Is the ignition system detailed in the patent information?  Spark, hot bulb?

Cheers,
Phil


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## AussieJimG (Sep 30, 2013)

This sounds like a really interesting project.

I have been vaguely thinking about fuel injection for model engines and this might provide me with some inspiration.

So I will be following along. 

Jim


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## myrickman (Oct 6, 2013)

Made more bits like the piston and drilled/tapped the bottom head for the intake and exhaust chests. Here is a mock up of it with the flywheel in place for perspective. I have not welded anything yet; want to get all the links and arms made before I put the heat to the metal. It has two 1/8 rings running steel on steel piston/cylinder. The Brayton shoots pressurized air through a mixing chamber in the intake chest where is atomizes kerosene. The ignition was originally performed by inserting a lighted taper into a breech plug where it got the cycle going. My engine will use a spark plug initially until I get the thing sorted out. A small trickle of pressurized air always kept the flame burning on the intake grating once the engine started. This is a constant pressure combustion cycle with the increase in volume of the burning fuel/air produce the power.


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## Brian Rupnow (Oct 6, 2013)

You certainly get into some interesting stuff---and much larger than is generally seen on this website. I will be following this build.---Brian


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## myrickman (Nov 24, 2013)

Got back on the build this weekend. Here is the cover plate for the receiver tank. I drilled out all the holes first and then cut it out on the rotary table. Way easier than trying do do it on the lathe. I drilled and tapped some of the holes in the plate into the aluminum cover plate on the table.


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## myrickman (Nov 24, 2013)

The crankshaft cheek is cut to length and the holes for the crankshaft (left) and crank pin (right) drilled/tapped. These will get tapered to make them look pleasing and the web between the hole bosses will get relieved about 1/8" per side of the 3/4" total thickness. This will attach to the crankshaft with a tapered key to hold it tight. The fit on the crankshaft is a light press fit.


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## myrickman (Nov 24, 2013)

The taper gets cut on the swing arm to make them look pleasing like in the patent drawing. I used the scribe block by having the end clear the top of the right side over the hole and then line up the scribe line with the end of the scribe block. Does not need to be high precision, this is for aesthetics.


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## myrickman (Nov 24, 2013)

Finished swing arms and crank cheek/journal with tapers cut. Next step is to round the ends on the rotary table.


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## myrickman (Nov 24, 2013)

Pillow blocks for the swing arm assembly. These will be bushed with bronze sleeves. Since the outer swing arm will be keyed to the swing arm shaft, and I want the bearings and arms to be removable, I opted for pillow blocks. The inner swing arm gets welded and pinned to the shaft.  I got both of the blocks within 1 mil of 1.000 using an ID gauge and micrometers instead of dial calipers. The caps to the blocks get some steps and bosses for the cap bolts and to pretty them up.


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## myrickman (Nov 24, 2013)

Cutting the round on the end of the tapered crank and swing arm block on the rotary table. The swing arms will also get the web sections between the ends thinned down by 1/8" per side of the total 3/4" thickness. This engine has a 4" stroke. Half of that is when burning fuel/air is being forced into the cylinder, the other half is for expansion of the hot gasses.


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## AussieJimG (Nov 25, 2013)

Still following although by now I have forgotten the details and will have to catch up again.

Jim


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## myrickman (Dec 10, 2013)

Here are the cams, the fuel-air mixer and the fuel pump. Since this is a 2-cycle engine (of sorts), one cam needs to open for 90 degrees to admit fuel and air, the other opens for 180 degrees to remove exhaust. The fuel pump is made from a gland fitting for the pump rod and two small check valves. Once the pump is primed, it will pump with a very short stroke of ~1/8 inch. It only needs a few drops per rev. I have not added the 1/8" fuel line which goes about half way up the mixer.


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## myrickman (Dec 10, 2013)

This is the cylinder side of the mixer valve. There is a piece of inconel screen to act as a flame arrestor inside the cylinder. Underneath of the screen is a stack of sintered stainless steel porous disks which vaporize the kerosene. The fuel is delivered to this stack off to the side, but I have not drilled for this yet.


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## myrickman (Dec 10, 2013)

I mocked everything up prior to welding it in the next few days. I was concerned the lever arm would bind, but the action is nice and smooth.  I cut the air storage cylinder (green one) too short so I have to hack another scrap yard oxygen cylinder. This is a free-lance test mule working from the patent with no plans other than some pencil sketches with dimensions I came up with. The cams, fuel pump and mixer go underneath the cylinder, so this is sort of an inverted engine.


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## myrickman (Dec 10, 2013)

Underneath the cylinder is the exhaust chest. This was straightforward and uses a conventional poppet valve inside the combustion chamber.


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## myrickman (Dec 10, 2013)

Detail of the stuffing box on the top side of the cylinder. It has a captured o-ring seal and a nut to adjust the seal tension. The top side gets two check valves which pump air from the cylinder to the receiver. Once some pressure is built up in the receiver, a valve is turned on, an ignitor turned on and the fuel pump adds combustible material to the air stream. The screen keeps the burning mixture from the mixing valve like when you place a screen over a flame and it chops it off.


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## AussieJimG (Dec 11, 2013)

Coming along nicely. I am still watching.

Jim


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## myrickman (Dec 18, 2013)

Here are the valve bits, cams and actuators. On the right side, the cam forces the c-shaped actuator down, pushing the fuel pump plunger down and pulling down the air valve on the top side of the cam. The pressure in the receiver is always higher than the cylinder so it functions like a steam engine. On the left is a conventional valve assembly sans spring and retainer.


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## myrickman (Dec 18, 2013)

The air check valves are on the top of the cylinder. The one facing forward is the intake and the one on the left delivers compressed air to the receiver. The links for the connecting rod are made from brass with little oil cups. You can see how the entire linkages go together now. The brass piping delivers receiver air to the inlet assembly on the bottom of the cylinder. I found a nice little 10 mm spark plug to tuck into the head to ignite the mixture.


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## myrickman (Dec 18, 2013)

Here I am mocking up the air lines before I commit to putting holes in the receiver tank. I wanted to use hard plumbing to make it look more attractive. The brass cock is to turn off the air supply. A pressure gage and safety valve go on the left side of the tees. Once I get these in, I can disassemble the whole mess and paint the parts. I need to get a 10x1 mm tap for the spark plug and attach the 1/8 copper tube to the mixer to deliver the fuel.


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## myrickman (Dec 21, 2013)

Today I reversed the positions of the intake and exhaust chests by doing a 180 with the head. The exhaust has to come out at an angle to clear the head bolt and will shoot exhaust into the flywheel...grrrrrr. Now the exhaust comes out in a better location. The porous sintered stainless steel disks which mix the fuel and air are installed. I made spacer gaskets so that all the chests are tight when the ports are at the correct angle. Luckily I had a 5-40 tap and die to thread the fuel line and mixer chamber. A little 10 mm thread spark plug will serve as the igniter for now. All the threaded connections in the receiver tank are welded in. With luck, we'll  give it a try before Christmas ..... More pix tomorrow.


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## myrickman (Dec 23, 2013)

Going to try it out later today. The 1/8 copper tubing was really stiff so I annealed it with a propane torch. Bends with no problems now. The oiler is actually for storing a small amount of kerosene which the engine runs on. I made the bracket to hold the oiler and use the threaded hole on the big shaft collar (which is welded to the cylinder) to mount it to the engine.


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## myrickman (Dec 23, 2013)

Had a couple of minor air leaks where the pillow blocks mount to the top of the air receiver. I coated the underside of the cover plate around the bolts with gas tank sealer which fixed those. The pressure goes up to about 10 psi just cranking it over a half dozen times and the leak down rate appears low. My buzz coil needs a new condenser, but I have another spare one for the first trial. I know most of you folks tend towards the smaller engines but this is as small as I felt comfortable making the test mule.


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## myrickman (Dec 23, 2013)

The underside of the cylinder is much busier than one would glean from the patent drawings and model. You can see the fuel mixer now on the left side with the fuel pump. The spring on the fuel pump serves both to return the pump plunger and to hold the air admission valve closed. The air is delivered for about 40% of the power stroke. I hope this is enough to get it running. The early descriptions of the engine say 60%... Those little fuel check valves were sure worth the 12 bucks from Grainger. I could not have made them that precisely and with the positive seals (Viton) for the $$$.


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## AussieJimG (Dec 24, 2013)

That's a great looking engine and much more complicated than I thought it would be.

I am sure you will get it running but in the meantime it is a work of art: beautiful.

Jim


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## myrickman (Dec 25, 2013)

Well I tried exhaustively yesterday to get the engine to run...close, but not quite. Reading the original operating instructions, the engine calls for fuel with a 55 degree rating. This turns out to be similar to 2 parts gasoline to 1 part diesel. Initial trials with this fuel resulted in ignition straight away. First I tried running it with a 3/16 plunger in the fuel pump with a 1/8 stroke. Turns out this is FAR too much fuel and all I ended up doing was fouling the plug. Next I reduced the pump diameter to 1/8 diameter and 1/8 stroke and added a needle valve to regulate the inflow of fuel to the pump. Also made up an adapter to turn over the engine with a big electric drill. As I cranked over, I would slowly turn the fuel and there would be a brief period where it would run for a few revs then get too much fuel and foul the plug. I'm getting a nice fine fuel-air mix which comes out of the exhaust when the plug fouls. Otherwise when it does fire,  I'm getting big plumes of smoke and loud pops as the gasses exit the cylinder. I suspect my porous disks in the mixer may be holding fuel and then releasing it all at once ? Going to try it with non porous disks in the mixer. The other item is to add a spring to hold the air valve shut and then make the fuel pump a variable stroke so I can regulate the fuel per stroke.  This thing needs a precise amount of fuel delivered per stroke to operate and the continued plug fouling leads me to believe I need to cut the fuel waaay back.


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## myrickman (Dec 25, 2013)

If I put a separate spring to keep the intake valve closed at the end of the lever arm, I can then install a ramp to vary stroke. Once I do that, I'll disconnect the fuel line and watch how the juice is delivered. That clearing the charge is an important point and using porous disks ain't going to cut it. If I make a Venturi and spray fuel into it, it should help
Vol of gas needed for stoiciometric burn at 13:1 is 1.2 cu in. At stp for full stoke but were delivering at two bar for 50% of stroke so same as full volume at 1 bar
Assuming vapor volume is 1300x times liquid this is 0.015 cc of fuel !
My pump delivers 0.025 cc, almost double. 
So if I halve the stroke, I should be ok.... Close but no cigar...


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## AussieJimG (Dec 26, 2013)

It won't be long now

Jim


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## myrickman (May 31, 2014)

Got disgusted with it and with the cold winter, I let this project sit for a few months. Tried another go at it today. I reduced the stroke of the fuel pump and reduced the pump plunger diameter from 3/16 to 1/8. Put some fuel to it and got some nice pops but no sustained running. Further reduction in the fuel pump stroke seemed to work better as far as getting a burning mix. Just at the time I thought I almost had it I got a strong kick and it locked up. After disassembly, it appears the piston cocked in the bore and the rod is bent. I think I'll make a cast iron  or aluminum piston with a longer skirt. This piston is only about 1" high on a 2-3/8" bore.  The longer skirt should prevent the cocking; about 2" -2-1/2" should be better. Also made a little starting crank and that was time well spent to feel how things were working. The good news is the reduced fuel did stop the flooding and spark plug fouling. Removing the spark plug is a real pain in the rear.


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