I am experimenting with a burner prior to finishing off my boiler design for a 4 inch dia return flue – probably 6" of "wet length".
I am using disposable butane and have used a canabalised el cheapo camping stove for the valve/ jet etc. The jet is 0.45mm, and burns about 200g per hour in unmodified state.
In Australia a flue larger than 32mm OD requires more onerous boiler specs.
My experiments so far have included a 1/2" dia "poker" burner with 20-odd junior hacksaw slots. Worked a treat in the open air, not so well in my test flue (i have a 200mm bit of 29mm tube)- the flame was too big for the flue and burnt at the outer end.
No 2 was a "blow torch" style, various diameters. the best results were at 17mm ID, producing a flame about 30mm diam and 200 long. In the flue – a bit of the flame came out the other end. A stainless mesh radiant cone glowed bright and worked a treat but theres still flame out the exhaust end.
No 3 was a 25mm tube with a flame-holding disc near the end with 6x 6mm holes. Produces a beautiful flame, bright blue cones about 40mm long with an overall flame size of 40mm dia by 150 long. Exactly the same results in the test flue.
I reckon that the volume of the flue is smaller than the volume required of the flame and that no variation will allow all of the combustion in the flue at that jet size.
What else should I try?
BTW- I understand that I will get double the flue length (and with multiple returns more than) double the volume but i was rather expecting that the return flues would have the products of combustion rather than the flame! – Am i wrong?
Edited By Russell Furzer on 02/06/2014 08:25:11