2005-06-04
Propane Burner
Essentially an overgrown Bunsen, the burner is a mixture of several designs, including those of Lionel Oliver, Tim Williams and Ron Reil.
The 9 kg Propane tank and 400 kPa adjustable Propane regulator with gauge were purchased from BOC, along with 4 metres of Propane tubing and a linear tubing joiner. The complete Propane rig was about $200 including a gas fill.
I carefully cut the linear joiner into two with a rotary tool and cut-off disk. This gave me two hose barbs that could be soldered to brass tubing to make the jet assembly for the burner. A length of 5/16" brass tube was purchased from the Hobby Store in Dee Why, cut to a suitable length and soldered to one of the hose barbs. The open end was closed with excess solder and a 1 mm drill used to form the jet hole in the side.
The body of the burner is a 1' length of 3/4" galvanised steel water pipe, purchased from Bunnings, along with several caps, joiners, reducers, tees, etc to experiment with. The dimensions were experimented with somewhat, but four holes were drilled right through the pipe each spaced 20 mm between centres.
Into the first, located just beyond the end of the threading, was placed the jet tube. It was carefully centred and then soldered into place. It was found adding a 1" to 3/4" reducer to the intake-end of the pipe produced a slightly leaner burn, so the reducer was left in place. It also makes a nice handle.
A 1 in 12 flare was rolled from a sheet of galvanised steel, also purchased at Bunnings as an "Ant Cap" (termite barrier for foundation piers, 71 cents each). One ant cap supplies enough metal to make three flares for 3/4" burners, and several more for smaller sizes from the off-cuts. The template for the flare frustum was carefully designed on paper and transferred to cardboard and then the steel. Initial free-hand efforts were compared with the geometrically constructed version and the difference was so minor that I decided to just use the free-hand version. The flare stays on nicely as a friction-fit, however I twisted some wire around it to make it more difficult to knock out of alignment or completely off the burner with rough handling.
Despite what other sites say the construction isn't especially critical, a little sliding on or off the end of the tube modifies the step position and size, this is a far more important property and will tune out any minor errors in the taper. Maybe if you want the very last Joule out of your Propane or a super-low idle pressure you should be parnoid about the flare, but in that case you should probably just purchase a $100 commercial burner.
The free-hand flare and otherwise primitive burner design operates smoothly down to "0" on the regulator gauge. The needle sits on the bottom stop and it still burns. I've had it cranked up to 350 kPa, at which point it sounds like a jet engine and almost blows out. The flame is a little rich at the 50-150 kPa "operating" range, I will drill a few more holes or use a larger reducer to make it sharply lean then implement a sliding choke so I can adjust the operating point as desired.
Without the flare the Propane burns inside the tube, starting at the second intake hole, "motor boats" below 25 kPa and blows out above 50 kPa. If you close the reducer or intake holes off by hand the flame richens to a semi-luminous but still blue-cored flame. Blocking off the intake holes in addition to the reducer results in the large, smoky, luminous "safety flame" style burning. The air intake appears to be split about 60:40 with the reducer/intake holes.
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