Small self contained butane burner

[retailer]

I built this for my 'Jenny Wren look alike' steam engine, while the spirit burner did work they can be sensitive to wick height so I thought a butane burner might be a better option. Ignoring advice I would normally give to others about doing a drawing first I built it 'on the fly' using brass offcuts from my scrap box, while none of the dimensions are critical and anyone should be able to build it with the info in the drawing, a few things I believe should be adhered to, the gas entry hole in the needle valve assembly should be placed on top of the assembly to minimise butane liquid entering the valve, if it placed on the bottom or even the side there is a chance that butane liquid will enter the needle valve assembly. I suggest starting off with a smaller than needed air inlet hole and gradually working up to a hole size that will give a satisfactory flame for the job - same goes for the actual gas 'hob' which in my build has 13 holes, a central hole and 2 rings of 6 holes each 0.04" diam (around 1mm) start off with something a bit smaller and gradually work up to a size that gives a satisfactory flame. The sizes given are the what I have settled on - I did try air holes sizes up to 0.175" and burner holes up to 0.0625" - they worked ok but the larger sizes seemed to me to to be too hot for a little engine such a Jenny Wren. I know some have built these with ceramic in this position and I did plan to order some to try but the 1.2mm top plate seems to stand up to the burner heat quite well. The gas jet is one I had on hand the jet hole is quite small which made it hard to get the exact size but I believe it is around .003" - .004" diam

 

[olympic]

Thanks very much for this. I have built a Jenny Wren that runs fine on air, but whose burner just doesn't create enough draft in there to keep burning. I imagine that your burner will overcome this, and, of course, it will be cleaner and neater as well.

One question, if you don't mind, as I'm not a machinist. How did you create the interior taper in the needle valve assembly?

 

[retailer]

I did the internal taper with a D bit reamer, just machine the taper onto a piece of flame hardening steel, give it a good polish then mill or file exactly half of the tapered portion away and then harden it by heating and quenching, there are plenty of good D bit reamer videos on Youtube, you only need a piece of what I call silver steel and those in the US call drill rod. To make sure that the needle valve will fully shut off the gas I machined the reamer first by setting over the cross slide then before machining the actual needle I nudged the cross slide back just a tiny fraction of a degree, so the internal taper would be 30deg and the needle taper would be approx 29.75deg - I'm not sure if this is a must but I reasoned that the needle should make most contact with the front of the taper and so wedge itself in, it does work for me at least as the tank has held gas now for over a month. You may want to consider running the burner with what I call a soft flame - that is with slighty less air that is needed for full combustion the flame tends to be slighlt yellow and does not produce a bit less heat but the Jenny Wren boiler is quite small so you don't want to boil away all of the water in 30sec.

 

[olympic]

Good advice! I wondered if that was how it was done. I made a small brass stop-cock that way a while back and was pretty sure that that was how to proceed, but it's very reassuring to receive your description.

Thank you.

 

[Cogsy]

Thank you for the plans. I have no use for such a burner at the moment but I'll be trying my hand at making one anyway!

 

[Steamchick]

Having made many gas burners, including a lot of ceramic burners, I suggest you avoid all burners with yellow flames, as they are making a lot of poisonous CO gas. (No smell, just permanently damaged lungs!).
Also, for the best air entrainment, the jet should be right at the start of the air-hole.
This works for simple burners, but there is a problem with all burners that if the jet is too big, the tube after the air hole will "Choke" the mixture, and you will only get a rich, poisonous flame, with less heat than a "proper" adjusted (balanced) burner.
Also please be aware that you should NEVER try a burner jetted for LOW pressure (30~35mBar regulated supply) with HIGH pressure (10psi~60psi unregulated "Can" pressure) gas. You will create a huge yellow flame that will do nasty things to your eyebrows, or worse.
Take care,
K2