butane burner

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

Russel

I belive we've started this conversation elsewhere. As you are bulding a boiler I'll assume you'll have a gas torch? Just poke the torch nozzle into the flue and see what happens. If its succesful just copy the burner head. In effect thats what I did for my folded flue boiler after I had the same issues you have experienced.

Pete

Thanks Pete.

same had occurred to me, but I have choices bigger and smaller but no goldilocks! The 7kw sievert makes the test flue look like something from NASA, the little portable fiddly bits one and the 'gasmate' butane ones are too small. I do have a 'mapp' ( I know it's not like the good old days) one , which is about right but the design and fuel are quite different.

What I wonder is where the gas burns in other peoples boilers- is it in the primary furnace tube, or in the return flues, or - heaven forbid- out the stack.

Also Pete- how big is your boiler? What size burner jet have you? How many and what dia are the return flues?

Edited By Russell Furzer on 02/06/2014 11:38:23

Russell

The problem is secondary air not being available to meet the stoichiometric ratio of ~92-95%. If there is not enough air at the point of combustion near the burner nothing is going to burn until the mixture gets out into free air and the mixture ratio becomes correct. So you end up burning at the flue if there is something to ignite it.

Thats why I suggested the gas torch design, where it is possible to get enough air in at the burner. Take a look at the Sievert cyclone burners and compare them with their standard burners. The cyclone burners can be used in the confines of a firebox, the standard burners tend to go out as they can't get enough air.

My boiler is 3"dia, 6" long and has a 22mm flue tube. In the end I copied the burner head of a cheap gas torch that had a #15 jet. It was never very succesfull but I got it to work, it roars like a furnace.

Pete

Pete

I dont think the wisp of flame out of the flue is a secondary air issue - there is a right roaring flame at the other end - I think the flame just has too much volume to fit in the flue. My 'radiant' stainless cone halfway glows a treat and the test flue goes red-hot.

I think that the design is probably OK and that I need to consider the heat exchange of the return flues to make sure that the heat is used. That does make for a much more complex testing setup for the phase ahead.

Russ

Russ

Similar; I had mine going like a bunsen burner. The heating engineers could join in here and put us right.

Pete