Brayton cycle engine beginnings

[myrickman]

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.

 

[idahoan]

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

Dave

 

[myrickman]

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.

 

[myrickman]

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.

 

[myrickman]

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.

 

[myrickman]

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.

 

[Philjoe5]

Very interesting project. Good luck with your build.

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

Cheers,
Phil

 

[AussieJimG]

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

 

[myrickman]

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.

 

[Brian Rupnow]

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

 

[myrickman]

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.

 

[myrickman]

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.

 

[myrickman]

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.

 

[myrickman]

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

 

[myrickman]

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.

 

[myrickman]

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.

 

[AussieJimG]

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

Jim

 

[myrickman]

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.

 

[myrickman]

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.

 

[myrickman]

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.