Xrad's Stuart Triple

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BOILER BURNER UPDATE:
Well, looks like burner number 3 was a bust because after it is placed into the boiler burner tube for over 20 minutes, the stainless screen becomes too hot and 'back burning' occurs. It sounds like an afterburner with a real loud roar. I tried to place the screen/screens in all different positions and burner tube lengths, but it did not prevent the back burning. Why?...because the whole burner heats up too much and the thin screen can not dissipate the heat well enough to prevent ignition of the gas before the tiny pores of the screen. This only happens when the burner is inside the burner tube where the air circulation is directional and minimized.

So..how to fix?.... Addressing the back burning first: The 4th design incorporates a .3 in thick brass slug with 150 #54 holes drilled through. The .3 in length is arbitrary but seems more than thick enough to prevent gas burning through the pores even when hot. This slug was then pressed into the end of the short tube and tested. This burned well but not really hot. Took a while to get the boiler going. So back to the long tube with an axial gas flow design. Beveled base port mixes air/gas well with the longer tube. The collar is for air adjustment with several different air hole sizes tried as well.

Then, when things started looking good, the 'long' burner was placed into the boiler and WOW boiler tube harmonics and a standing wave with the burner jet created the worst loud whistle(like a flute). When the burner was far enough out to stop the whistle, it was too far out of the boiler. The standing wave actually compressed the flame decreasing heat when in too far...so..back to the drawing board.

I decided to press the brass slug back into the long burner tube about 1/2 inch. This significantly decreased the standing wave nearly to nill, but the burner was now running poorly due to lack of oxygen at tip.

Next, I drilled 8 holes ~3/8 around the burner tip to allow air into the flame. WOW!! this was it. Now the 1/4 inch gap around the burner (when inside the boiler tube) really supplies air into the burner tip and the burner roars out the end with a really hot flame. Almost all of the orange glow is gone and the flame base is blue/white in color and dancing well on the brass slug!! The boiler really heats up well now, and with the wood lagging. The flame is hot enough to melt brazing sivler rod if placed in the flame three inches or closer to the slug end. However, it does not seem hot enough to melt the cross tube brazing due to the water drawing heat away. Burner can be turned down to less heat if needed by bottle valve.

Pics show the attempts, and vid the final iteration.

see vid.
[ame="http://www.youtube.com/watch?v=JTg72W_h630"]http://www.youtube.com/watch?v=JTg72W_h630[/ame]

All 2-56 screws stainless. 3 set the slug and three set the tube. tube and base brass. Air collar bronze

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Back burning in the burner is caused by too slow gas/air mix velocity. Too little orifice or too big diameter between the orifice and end of burner will make slow gas velocity. Too little air entered into the gas mixer.

Let us say: Make a gas mixer small and long enough + rich of air + a correct gas orifice to make high gas velocity before a big burner as you did. :)

Try this book: https://archive.org/details/designofatmosp1921193berr
 
mechanicboy: Thanks for article. I love these old tech papers. I agree backburning for all your reasons as well as the screen/diffuser getting too hot, which is secondary to its thickness and slow flow and air/gas mixture. Using the same number of holes and the same size holes in the brass slug, no more backburning (with all other factors being relatively equal) The other thought is that the more efficient burn on the hot side of the diffuser (newest design) may actually accelerate the gas through the burner tube and diffuser orifices...or does it actually create more back-pressure?

The diameter of the diffuser slug and burner tube length are not calculated but estimated in my head for what volume of gas could be burned efficiently. I think I got reasonably close to correct in the final product.

Some quick calcs:
original burner #8 jet(clevedon steam design)
.7in diffuser diameter; 37 diffuser holes of .35in dia = .13 sq in

My burner:
#8 jet
1.9in diffuser diam; 150 diffuser holes of .265in dia =.33sq in

My burner is 2.7x diameter of original with diffuser port area 2.5x the original, and it burns hotter with same gas usage...hmmmm

Probably could get away with #6 jet in the original burner, it is normally sold with #7. My burner is definately produces more BTU's.
 
Hi!
The burner get hot due the material round after the burner mesh, remove this part as i am showing the picture. See the drawings as i can recommend the burner where you get a less hot burner but good boiler heater as in the photo of the burner.

Here is the tips how to make a good burner :

Pointers on flame adjustment
Problem

Cause - Remedy

elongated, yellow- ish flame

lack of combustion air - open the air supply

flame "lifts off" excessive exit velocity - use smaller injector, reduce the gas pressure, reduce the air supply

flame "flashes back"

exit velocity too low - use larger injector, increase the gas pressure, open the air supply, reduce the size of the burner jets

flame "too small"; not enough fuel

fuel shortage - use larger injector, increase the gas pressure

flame "too big"; excessive fuel supply/consumption

excessive fuel supply - reduce the gas pressure, use smaller injector

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You are rigth about the 'collar' and the burner heating. but at this time, I probably will not remove collar. there is no back burn with my new design and the collar seems to direct the flame in right direction. I may design a larger coller down the road.....

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If overheating of the burner is not a problem when using the cooling air around the collar, all will be fine. :)
 
Mechanicboy. Yes,I agree with you. It works. One of several methods to come to same end. Is that your D10 in the avitar?

Also, If you build model boats, there is a very nice 'light flicker' board sold in UK

[ame]http://www.youtube.com/watch?v=OCnYe94uyek[/ame]

http://www.action-electronics.co.uk/las2.php
 
Nice flickering oil lamps. :) Yes, it is my Stuart D10 with own made Stephenson reversing gear link. And i am still building the tugboat. :)
 
MAde a new thrust bearing. See pic below. 3/16 stainless rod and some real flanged bearings. very smooth. Not thrust bearing per se, but will work with the forces required.

Tested the steam valve with boiler water level detection unit. starts about 45 sec into video. see the flashing LED which tells that relay activated and steam flows starting the duplex pump. Valve rated for 265 degrees(stainless/viton 23$ on ebay). I ran it for about 45 minutes with no issues.

Of course, the real issue is on the water with wave action. I placed two boiler bushings at different levels in case I need to adjust the sensor position. Also, I could redesign the sensor and add an internal wand of about 1 cm so that it is not so small (presently a 1/72 bolt head) creating less of an ON/OFF effect.

My method of aging props, I use copper plating for all my models...my signature on my builds.. Salt water, 7 volts, copper wire. This was originally a 5.5 in prop now trimmed down to 4.8in which is about a 12 ft prop on a 160 ft boat.

video at :
https://www.youtube.com/watch?v=37BZJHCT9wM&feature=youtu.be

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Not the Stuart, but rebuilt this Tich 3.5 gauge:

[ame="https://www.youtube.com/watch?v=WW0-xH-wxw8"]https://www.youtube.com/watch?v=WW0-xH-wxw8[/ame]

No superheater so very wet steam....
 
well, sale fell through for both items, so I decided to finish the engine little details. Added copper cladding and made condenser mounts and straps, straightened plumbing and drain cocks....will probably mount with coal boiler for nice display. Need to make cooling reservoir, etc..... found some great diamond plate aluminum on ebay 1/10 scale..looks real nice....

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More pics: Underneath the cladding is DEI exhaust wrap, nice insulation w/out asbestos. Obviously, you want to drill/punch the copper before annealing. I like the look after heating, adds real nice patina, which is now my signature look on my steam engines. Searched the local stores and finally found real cotton three strand rope for the pipe wrap, found in Walmart sewing section. They also have good selection for fine fiber antique look cloth for model sails!

I may add corrugated aluminum wrap to the condenser to hide some of the silver solder imperfections and aid in cooling.

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ummmm, yeah, been slacking on that. Had to design a new Scott type boiler as the Stuart was too slow to steam and produced too little steam for the twin requirements.
 
corrugated aluminum adds a nice touch to the engine.

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Since both sales fell through, I decided to keep the boiler to go with the triple.

Pic of tramp hull model and what I am trying to achieve (steamer pic below from full size movie prop):

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Apropos of this model, a friend of mine told me today that he had the Stuart castings for this engine and that he would never get around to building it. If he wants to sell it on here, what would be a fair price?
 
Stuart still sells them. That would be a good starting point for price. BUT, some of the older castings are apparently better, and of course if he has done any work (quality machining) and if all the parts/screws are included, then maybe a bit more....

Some pics of the Scott type boiler:

Here are a few pics of the pig tails brazed into place. There are 13 3/16 pigtails on 0.5 in centers, with opposite side offset by 0.25 in. which leaves just the right amount for air space between coils......
Pigtail diameter determined by the burner, which was built first and runs well.

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