I would get away from a tube burner. Go more for a stove burner type. You
may have to change the boiler a little, but most likely only the contact
areas.

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On May 29, 9:47 pm, engineman wrote:
For the last 8 years I have been working on a steam powered cycle off
and on. I bought plans and parts of it in a kit from Cole's power
models, It is called the Vesuvius and was designed in 1884. it has a
combination fire tube and water tube
boiler.http://engineman69.home.comcast.net/...esouvious.html
In the original plans they called for a gasoline burner but I didn’t
like the idea of that (too dangerous for something I’m riding on) so I
built a propane burner. It’s patterned after the Reil burner but has a
closed end and hundreds of 1/16” holes in the 1” dia 6” burner
tube.http://engineman69.home.comcast.net/...assembled.html
When operating it on the street I found I could only go about 200
yards without running out of
pressure.http://engineman69.home.comcast.net/...atewheels.html
If I cranked the fuel supply up too much flames would come out of the
stack but not much benefit. I tried all sorts of ideas, remaking the
burner tube with more and smaller holes, feeding compressed air into
the burner, adding a feed water heating system and a tank to store
steam.
It helped a little but still the same problem. I thought that if I
used a fuel with more heat value it might help.
I tried MAPP gas which is a liquefiable gas with many more BTU’s than
propane. I was able to get steam up a lot faster but I found that once
I got going the flame had a tendency to start burning inside the tube.
I can’t explain the process but I notice that the heat output suffers
immensely.
I sometimes had that problem with propane so I made a bypass to the
control valve so I could blast the inburning flame out with a shot of
higher pressure gas.
Now I find that MAPP gas with its higher heat content turns my burner
tube red hot almost immediately and so I can’t blow out the inburning
flame.
I tried acetylene but it had the same problem.
Engineman

There are any number of books telling how to relate boiler surface
area, efficiency and amount of steam per unit time. You probably
don't have enough surface area or it isn't used efficiently. Back
issues of The Model Engineer would have some of the answers, much of
the modeling that was done was small locomotives, boats and traction
engines. There were any number of articles on building efficient
small boilers. I have a small Brit book on flash steam for models,
probably 25 years old now, might still be in print, though. That
might be a way to get enough surface area to run your engine.

As far as choice of fuels, propane is roughly equal to gasoline/
kerosene/diesel in heat content per unit weight. Burning
characteristics are something else, though.

Are you piping the exhaust steam up the stack to get a better draft,
ala locomotive?

Stan