Hi Ade,
So my thinking is, a nice big oil burner chucking out megawatts (ok, ok, kilowatts...) of heat,
Mate, I can most certainly guide you on setting up a Megawatt burner! That is NO trouble at all. I have built one atm I'm looking for a minimum of 2 Mw out of and I believe if I use the 4" dust extractor Blower I have with the 2HP motor can get 3 out of it.
For what you want, I'd be going BIG tube, 150MM or more if you can get it. 300Sqm in a shed which I take isn't real well sealed will take some power and I'd guess there will be people coming and going and maybe large doors. I'd be aiming at 3-5 Litres per hour depending on ambient temps.
I've read this thread a couple of times, and I just wanted to make absolutely sure: There's nothing inside that elbow, except for the end of the fuel delivery line, is that right?
Yes, that is correct. I did put a couple of short Pieces of square tube in it the other week, just scrap I dropped in, to see if that would help with heat retention and transfer to the oil pool. I could tell no difference with them in or out.
Other than that test, the tube is completely hollow and what you see is what it is.
Literally just weld the elbow together, drill some air holes in the right place, stick a fuel line in through one of them; light it off and walk away (essentially)?
Correct. I just eyeball everything I make and had to go measure what size the tube was when I wrote my original post. Like everything else I build, I see what I have in the metal pile that fits the idea in my head, I build the things by what looks right and the bastards work. I laugh although get annoyed when all these people on YT ask for " Plans". What Fking plans do you think I worked off when I built it? these people can see the things and want "Plans". Fair enough ask if anything is inside as that's not visable and most burners of this type do but the things some people ask! Geez!
I have been putting the fuel delivery pipe in the primary hole. It reduces the primary air/ burn rate a little but other than that, works fine wherever I put it.... Pretty much. I can go in the primary or secondary and does not seem to matter.... just keep the thing fairly level.
I Did one day push the burner up under the water tank un even but didn't discover it till the thing was lit and not running great. All the fuel was running to the back and the pre heat of being under the primary air was not working. Moved the fuel pipe to the front and off she went.
I do think it runs best in the level position and you can put the fuel pipe front or back, makes no difference. You could braze the thing into the side which would be neater although might be better to have screw in so could be taken out if the end clagged up.
Apologies if I missed something obvious....
Nope, you got it. I find the things I confuse people with the most are the simplest things. Every one is always looking for more complexity! :0) In this case, you have it all worked out just fine.
Does the air hole placement/pattern matter much? What about the size/number of holes in relation to the burner size? I presume there's a sweet spot, is it hard to find?
It needs a Hole at the front. I think. One in the horizontal section in the middle may work fine for all I know. I can see an advantage to that and feed the fuel from the front. Haven't tried anything else but I don't see why it wouldn't work.
It also needs holes on the upright section for the secondary air. I put mine a little up from the bend and that seems to work well. I can see the Vapor coming off the oil real well through the holes and then catching alight. When the burner is first fired there is no flame there but once the oil warms up, they catch and off they go. The other day I put a little blow torch at the secondary holes and the flame caught and noticeable got the lower section running much harder. At first the secondary would not self sustain but soon did when I took the little canister torch away. I think this speeds up lighting time a lot.
As far as size and placement of holes, like everything else I eyeballed it. You need plenty. At a wild guess, I'd estimate the secondary holes add up to about 4 times the area of the primary hole. I think they need to be small holes and set a little apart for Turbulence and to allow the flame to be a bit spread and mix the air well with the gas. I just winged the holes and placement on mine and it worked. I put in some more holes because it would run rich flat out and it runs very clean now. _maybe- it could use one more hole but it's pretty close thats for sure. If you put too many you could always weld them up again or block them off.
I'd say drill some holes, think plenty, fire it up, see how you go and if the thing runs dirty, put in some more holes and repeat till you have the thing tuned.
I put the second holes in the back of the thing. Couple of points on that.....
The side OPPOSITE the holes gets the hottest. The incoming air seems to push the flame back to that side and transfers the heat. If you wanted this to radiate if someone was standing in front of it, Turn the thing round so the holes are at the back or drill them at the back in the first place. If however you want to put a fan behind it to better draw off the heat which I would certainly do, have the holes on the opposite side of the airflow. I would also put a 90o Pipe bend on the primary hole. I did that the other day when it was windy and it stabilised the flame a lot. I think if a long bend was used that would give the airflow some Kinetic energy and would enhance performance that way.
How often does it need cleaning (i.e. after how many hours approx)? I realise there's probably a pile of variables which will affect that, but just a ballpark will be fine. Like, do I need to attend it daily or will weekly do?
There are a LOT of variables but I can say the hotter and harder you run it, the less cleaning you will need. I would suggest cleaning would be every morning before fire up. What I would do on MkII would be make a Drawer as the burn chamber/ fuel holder that you could slide in from the next sized metal down or fab one up. It would want to be fairly close fit so as not to leak too much primary air but you could reduce you primary air hole to compensate. You would want the drawer to go to the very back of the thing as well so there was full flow to the secondarys and up the flue.
That would be your burn chamber, in the morning you would pull it out, maybe give it a scrape with a paint scraper, put it in the burner again, light it up and all is good. I would also suggest giving the thing a good hard full on run once a day to keep the flue clean. these things would soot that up eventually but having joins you can disassemble or cleanout ports like commercial burners have would make that an easy task once a month or once a season..... depending on how and what you burn.
What happens to Spencer's Ash? Does it not abrade the flue? 
[newer members may not get that reference...]
Well a bit of abrasion in the flue would keep it clear of soot and probably not erode the flu pipe at all. :0)
PS: This design looks a LOT easier than my plan of taking an old propane cylinder, cutting a door and a flue, and running a drip-fed bowl burner inside.
It certainly would be!
The problem I see with burners all the time is people copy designs but they don't understand the principals at work. Spray burners are a classic example. People think you have to spray the fuel but they don't understand what that actually does to make the fuel burn or how the same result can be achieved different ways. Pot burners are the same. I have seen designs here and on YT and laughed straight away. So complex, so much time and materials to build and I can look at it and know it's going to have problems and why because I have wasted enough time on these things to understand what is going on with them and what is going to happen.
I don't know if anyone else has done this L design burner. I imagine someone has but I have not seen it. It was an original layout in my mind from looking at other pot designs and understanding what was going on and what was required to make it happen. Heat the oil and have a way of regenerating the heat and then give it enough air to burn clean. You have to pull more oxygen in so just like a 1000 Yo wood fire, you want the Flue to draw to fan up the flames. Simple.
The other thing to note with this type burner is the radiant output is low. The heat is all going up the flue so by extending that flue and having a fan on it to create the greatest temp differential between the air and the flue pipe will draw the greatest amount of energy off.
Highly efficient commercial gas heaters here have plastic flue Pipes and exhaust gas temps of Under 40oC .
An ultra clean burn and using the flue as one long heat exchanger is the way to pull real heat out these things. I would try to put in a horizontal section of flue to make it easier to pull the heat from before it gets too High. Ideally you want the fan pushing the heat back down to the floor where the people are.
This burner works same exact thing with my forced air swirl Burners. The rotation of the flame puts heat back into the burner and the fuel. It also causes the vapor and air to mix ensuring a clean burn up to high firing rates and gives a wide turndown ratio because the bulk of the air enters above the oil pool. That stops it over cooling and mixes the vapors not the liquid. By extending the air pipe into the burn chamber as deeply as possible, it pre heats the AIR, not the fuel as everyone seems obsessed with and the fuel is then phase changed as well so you have part burning before it even leaves the air pipe. IMHO compressed air burners are for people that don't know how to engineer a proper burner. They are too energy input intensive, need way too much equipment to make them run and as everyone seems to use commercial nozzles, they are way too expensive and that's not even including the cost of the compressor and the power used.
I can make bigger burners with scrap and an old car vent blower that seem to have less trouble than the commercial ones.
If you understand the principal you can understand what you do and don't need to make them work. :0)
IF there is anything else you like to know, fire away! :0)
Recent Posts