Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Hi Maurice,

A very good result, might it be an idea to try the disc you made above the burner to spread the heat to the outer tubes the radiant heat from the disc should keep the centre tubes happy.  Though I suspect it will produce enough heat as it exists.

I think you might have solved the problem of the smell (poor combustion) I was having with my boilers fitted with fire tubes. Mostly I build model steam locomotives and the odd boat when these have vertical boiler they have centre flues and heat exchanger's to maximise their water capacity so that they will run for the longest possible time, though all are fitted with top-up valves if they get low on water.  Because these models work out in the elements their ceramic burners are sealed into the bottom of their boilers.

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These burners have virtually no secondary air for combustion but exhaust OK because of the larger central flue.  When I built the fire tube boilers I sealed the burners in as I usually did and though they worked they smelt, these burners were of a standard design which worked OK in boilers with one large flue.  So I conclude that the exhaust gases don't like going up the many smaller tubes so have to be drawn out by either a blower or the exhaust from an engine just like a coal fired boiler needs.  Your boiler with the fire doors open allows a lot of secondary air into the fire box which somehow aids the exhaust gases through the smaller flues?  Might be worth trying your boiler with the doors closed to see if there is anything to my theory.

You might be interested in the type of heat exchangers I use in my vertical boiler, these are photographs of my part built boiler for a locomotive which is my next project.

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I am a few weeks away from finishing a 7/8" scale model of a tram engine this uses a ceramic burner under a pot boiler fitted with heat exchangers under it.

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I am also helping a friend who had an old model boat hull, a vertical boiler and a double acting single cylinder engine.  The single flue boiler was meths fired and I have made a ceramic burner for it which is sealed in but has no problems working.  The engine is a bit large and has a big four-blade propeller.  There is a bit of pipe work to complete when it can be tested in a tank. I suspect if the propellers torque doesn't cause the model to capsize it should be quite quick.

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Take care Tony