I tackled the long-flame-short-chamber problem for my boiler. The boiler rebuilding I mentioned last week kept my mind busy. Many of us are trying to shorten and/or widen the flame. But do we really want that? I think the answer is no. The short orange flame doesn’t burn clean and gives less BTU output. Downsizing the nozzle rating also less BTU output. So why not extending the combustion chamber. An extension between burner and door is perhaps for some boiler/furnaces a solution, if the diameter can be large enough for the flame. It must be a double pipe with insulation between them, otherwise we create a hot spot between door and burner. The burner doesn’t like that. I made a 10” rectangular extension between door and boiler. Invested 10 euros and a day labour. Uploaded a picture to my photo folder. Got a 30” flame now in a 35” deep chamber…

Already had a clean burn (hydraulic oil) but I think I can now burn heavier oils and still have a clear stack. Made a ceramics layer and stainless steel sheet on the inside of the extension for insulation. 1 mm st.st. Sheet, 6 mm ceramics, 6 mm steel extension and 60 mm glass wool on the outside. Will ad 2 extra ceramic layers next week and find something better for the glass wool. Has anyone an idea what to use? And perhaps for the ceramics? What I use now is normally used between a stove and a wooden wall. Extension. Simple solution. Didn’t see it first. Looked beyond it. But as it strucked me I was as happy as a dog with seven.

I took delivery of an all oil Kroll burner last week and I was worried about the same problem. They showed me a ceramic tunnel and a ‘turn back’ can. So, the flame went down through the tunnel, hit the turner and went back up the outsides of the tunnel again and thus had twice the distance to travel – though in my case it doesn’t seem like I will need that arrangement. I am really pleased with this thing. Yesterday, just for fun, I put a slab of margarine in it – cheaper anyway than diesel ;-)

Yeah, that ceramic tunnel is still on my wish-list. They are often used in commercial waste oil burners. I did put in (again) the short stainless steel tunnel. Catches the very bit of oil spray that flys sideways from the root of the flame. And creates together with the extension a recirculation of combustion gases. Think it’s now burning cleaner than my HHO boiler… Can’t even smell the combustion gases… Before the extension I had the flame to turn in the firebrick target. Now I have the fingers of the flame 5-10” before the target. So not hitting the target, like Ron Schroeder advises. Spreads out in a 10” diameter. Looks good, feels good. Margarine contains a lot of water. How does your burner deal with the water? Has it an automatic air/gas bleeder on the preheater?

A long flame is not always cleaner or more BTU flame. The retention head makes a very big influence on flame quality. With the right recirculation and turbulation a shorter flame can be as clean or cleaner than a long flame. I am presently working with a retention head/blast tube/atomizer that gives a 10” long flame at .8gph with zero smoke, over 13%CO2, less than 10ppm CO and under 70ppm Nox. Your extension is a good idea for your flame. You are lucky your opening is large enough for it to work. I have been working with Craig on an extension for his 9 ½ inch long combustion chamber but his opening is only a little over 5” so his extension can’t be very long for him. I think that firebrick lining for your extension would be the best. I also think that tapering the extension toward the burner would help reflect more of the heat toward the boiler would help.

I would like your opinion about the next items. I have some oil spray on the stainless steel flame tube. Must have had it before I made the extention, but I think it was mixed up in the combustion chamber. Gave no smoke, but you could smell it. Now it is burned in the tube. Gives some soot in the tube, but in total I have a very clean combustion. Can’t measure CO, CO2, O2 or Nox yet unfortunately. But the inspection glass in the upper door stays clean now and I smell nothing from the stack.

I do have 5 seconds of some blue smoke from the stack on a startup. It disappears as fast as it comes. And after shutoff a very, very bit of white smoke. This white smoke must be the oil spray vaporising from the hot tube. The blue smoke on startup could be either the oil spray in the tube, disappearing when it’s hot. The tube is only .8 mm (.03”) thick, so heats up fast. Or it is the first cold atomising air. I don’t have a nozzle heater and the air tube between preheater and nozzle is about 8”. Inside diameter .4”. So quite a cold volume.

I intend to make a Kagi shaped retention head next week. With adjustable vanes, like Luxaflex. Maybe it takes care about the oil spray And use a thinner air tube. Using a nozzle heater is not my choice at this moment, because there’s no room for another relay in the control box and the setup has become already quite complicated. Looks very scientific though.

Now writing this, an idea comes in my mind: what if the air solenoid starts together with the burner motor. During the 10 second prepurge the hot air can reach the nozzle and warm it up? Now the air and oil solenoid open after the prepurge. I have the idea that firebrick not really insulates, more stores the heat.