I have been reading the verious discussions about burning veg in heaters Here, here, here, and here.

I have slowly been modifying an old low-pressure syphon-style gun-type oil furnace burner (1948 oil-o-matic) to burn either Used Engine Oil or veg (preheating bothe the fuel and the siphon air) but I still have to build some type of stove/furnace to use this in before I can actually use it for home or shop heating, unfortunatly, I need heat now so have been considering some type of pot-burner insert that I can place in my existing wood stoves.

I was finishing up making a couple of steel collection funnels (Here) when I noticed that the left over piece of these tanks fits the bill almost exactly for the fuel bowl described as being used for the "vertical babbington" burner in the "heating WVO with WVO" discussion (here) that was started by mobius and that Murphy has expanded on.

The left-over part of my funnels is the top circle of steel that I remove to make the "funnel with lid" type funnel's top opening. This piece is a dish shaped 9 inch circle of steel, about 3/4 inch deep. and has a 3/4 inch female pipe fitting at the lowest point in the center. I will do some testing with one of these on the vertical babbington style of burner but just for a quick test I cleaned all the ashes out of my small wood stove and placed one of these bowls on the bottom of the burn box. I already have an oil drip feed in this stove that normally drips directly onto the wood of a wood fire.
Poured in a bit of diesel and a crumpled paper towl, lit the paper and then started a veg drip. It burnt but Not with much heat. For the first several minutes the only fire was from the paper towl acting as a wick, it finally got hot enough to boil/vaporize the oil and the entire surface produces small swishing-around flames but not much heat.

I placed a 10 inch section of 5 inch pipe vertically in the center of the bowl and tried again. The flames were mostly confined to the inside of the 5 inch pipe and these flames were only 7-8 inches tall inside the pipe. I ran this for a couple hours but the house was cooling down as the outside temp is about freezing just now.

Idea - Since the pipe was not welded to the base I placed 3 steel nuts from 5/8 inch diameter machine bolts in the bowl such that the pipe would stand up off the bottom of the bowl and let air flow in between the bottom of the pipe and the surface of the oil -- YIIKESS - I would like to say it is putting out 10 times more heat -- Don't know just how much heat yet but I now have lots of fire, it is shooting out of the top of the pipe, crashes into the underside of the top of the stove, makes a 90 degree turn and continuing up the flue pipe. It doesn't seem to make it the additional 2 feet to the flue damper as the flue pipe has cooled a bit by then but - wow- plenty of heat now, about like I get with a nice wood fire plus additional oil.

The flame is yellow and there is some smoke, about proportional to the increased amount of fire. There is enough smoke that I can not close the flue damper down but about 1/3 of the way or the smoke backs up and comes out of the cracks in the stove lid. It is dark now but I went outside and shined a flashlight at the top of the brick chimney, no more smoke than from a normal wood fire.

This amount of fire needs fuel and it requires more of a "flow" of oil than a "drip". I am running a stream a bit smaller than 1/16 inch in diameter, can't tell for sure, and I only fired this thing up a few hours ago so don't have any real fuel consumption numbers yet but I have had to fill my half gallon feed tank 3 times already this afternoon.

I have not yet gotten the fuel feed setting correct and have to tweek it every few minutes to keep from running dry or overflowing the bowl, I got distracted and the fire went out a couple of times due to running the half gallon supply tank dry.

It burns equilly well using Used Engine Oil or veg, oddly, the veg seems to produce the most smoke. It still produces the crusty stuff on the bottom of the bowl, at a proportional rate to the fuel feed, probably have to clean it a couple times a day, but since the pipe lifts out of the bowl it should be pretty easy to simply turn the bowl upside-down and bang out the crud, time will tell. I will weld some handles on things tomorrow, easier than the current vice-grips.

I will post more as I use this burner for heat over the next few days.

This message has been edited. Last edited by: Tim c cook,

Well - 2 1/2 hrs later -- I let the unit cool to room temp for cleaning, no chunky or crusty stuff, mostly the soft oily residue from the paper towel.

Relite the burner with the air space in place, it burned in the paper towel wick mode but never got hot enough to boil the fuel even after an hour. I removed 2 of the spacers so the pipe was sort of tilted sidewaysbut still could draw air under about half the pipe, due to the tilt of the pipe the flame was actually contacting the inside of the pipe, took about 10 minutes for enough heat to boil the fuel. Once it took off it burned just as hot as originally. I suspect there needs to be more pipe contacting the bowl to transfer pipe heat into the fuel bowl. I will make some slots in the lower edge of the pipe so most of the pipe will be in actual contact with the fuel bowl and try again.

Fuel usage-- Burnt through 1/2 gallon in 1 hr 15 min, this equates to 56000 BTU/HR, thats a LOT of heat for this little house, too much for the current 32 deg f temps, should be able to heat ok even when it gets down around the "0" area.

fuel feed is a bit wierd -- it looks like this burner will burn about any amount of fuel fed to it, it just gets hotter, vaporizes even more fuel and gets still hotter. It does not seem to heat/cool around the amount of oil you feed it, it just runs hot and uses up the fuel pool as fast as it can.
haven't yet tried limiting the fuel to a low level, to see how it reacts, as I have run the 1/2 gallon supply tank out before getting that far, the burner was bairly burning when I caught this. In this low-burn condition there is a lot of soot being produced. Refilling the fuel tank has it up and running full-on in just a couple minutes as long as the burner has not cooled completely down.


The smoke has now condensed into a bit of soot but it is an acceptable amount to have a workable backup heat source that needs no electricity.

Tim,

PICTURES !!!!!!!!!!!!!!!!!!!!!!!!!!!!!

quote:

Originally posted by Tim c cook:


Fuel usage-- Burnt through 1/2 gallon in 1 hr 15 min, this equates to 56000 BTU/HR, thats a LOT of heat for this little house, too much for the current 32 deg f temps, should be able to heat ok even when it gets down around the "0" area.

And a couple comments:

1. How does the house feel using your current oil pan for heat?

2. Don't forget that most wood stoves are only 40 to 60% efficient.. 56,000 btu input only means 20,000 to 30,000 btu's heat output..

You know the one thing I see most with people who have wood stoves is a failure to have any fan blowing air across the stove.. Some stoves have them but if it doesnt, a small fan or two pointed at the stove can up your effieciency by a whooping 10% or more..

Yeah Tim, how about some pics of the burn pot while off and while burning? What size is your wood stove inside height? Speaking of burn pots, are covers for pots and pans the right shape? What about a wok? Do you think they are not shallow enough? Maybe worth a try?

Pictures -- Not for a while, my camera did a header off the shelf a few days ago and ended it's usefullness except as a paperweight.

My wood stove -- I suspect this was state-of-the-art about 1900 or so. It was likely intended for the "cabin' or "city apartment" market back before any type of central utilities existed in cities. It is a small combination heating/cooking stove that was designed to burn coal, the entire firebox is lined with firebrick. The top is entirly flat to allow cooking and the outer edge of the cast iron top consists of an outer framework with 1/2 X 2 inch slots to allow warm air from around the main stove body to rise up into the room, there is a nice white enamal sheetmetal skin around the sides and front that is open on the back to allow air in around the outside of the firebox.

This stove is almost completely firebox,the firebox is 20 inches long front to back, 8 inches wide, and 15 inches deep. The top 5 inches of this firebox is made of cast iron with two removable flat cast iron covers over the entire top of the firebox, one of these covers has a 7 inch round removable cover to allow a cooking pot to set slightly into the firebox, like most standard old wood cookstoves have, this is where I feed the oil drip from. The output for the flue is at the top-back of the firebox, exits horizontally and turns upright where the fluepipe attaches.

The bottom of the firebox is made up of rotatable cast iron grates that let combustion air into the fire and allow ashes to fall into a lower removable sheetmetal ash box. There is a closable air damper inlet in the lower ash box area.

This is NOT a modern gasketed air-tight stove but the pieces fit together well and if the dampers are closed completely it will almost, but not quite, put the fire out.

I have a 10 inch tabletop summertime type fan that moves air across the fluepipe and stovetop.

Feel of house -- With the burner running full-tilt (Bowl was full across the entire 7 inches and had fire burning both inside and outside the pipe, plus bottom air allowed into pipe), at the approx 56000 BTU/Hr fuel input rate, the stove was throwing off LOTS of heat clear across the room, 3-4 ft from stove was realy hot. This is about like a full blown full-firebox type fire with my additional oil fed drip, this is absolutely the biggest amount of fire I want to burn in this stove.

I rarely need anywhere near this much heat except in continuous below "0" f temps (This 800 sq ft house was built in 1875 but has had the ceiling and walls insulation, no insulation under the floors, and newer windows/doors installed).

I normaly only need to burn wood in the rear half of the firebox with both dampers almost totally closed in the current nightime temps that are around freezing.

I suspect the fact that I am using a 10 inch tall by 5 inch OD pipe is what creates the self-draft affect if air is allowed to be drawn across the top of the hot fuel pool, most burn pots that I have seen are only as tall as they are wide. The extra bottom air promotes the burn inside the pipe directly and this air is hot from inside the firebox so it also will evaporate a lot of fuel as it flows across the surface of the hot fuel pool. When running this in the "closed burner pot" configuration the flame in the pipe is only 6-8 inches tall and covers maybe 30-50% of the internal vollume of the pipe and sort of flickers and moves around over the fuel pool, normal closed (no air holes)pot burner style, with the added lower air input the pipe runs 100% full of fire flowing completely out of the top of the pipe and exiting the firebox, unfortunatly this is still orange fire so there is a lot of smoke also.

I tried using only the lower dish without the vertical pipe today. This actually worked pretty well except for the amount of smoke in the "normally aspired" mode. I poured a couple ounces of diesel into the bowl, lite it, then started a slow veg drip. took a few minutes for the bowl to get up to temp but once it did there was flame dancing all over the surface of the fuel pool, making the pool larger made more flame, smaller made less, and the size of the pool remained about constant with any one drip setting, slow drip = small pool, fast drip = larger pool. In this mode the fuel pool did not get quickley used up as it did with the self-forced-draft of the tall pipe with air allowed in at the bottom.

It was daylight when I ran this bowl-only test, there was more smoke than I expected from this burn, Not huge billows of smoke but a continuous column of obvious smoke about like the first 10-15 minutes after lighting a wood fire. Judging from the smoke in the firebox I think the high burn rate of the 10 inch pipe was producing even more smoke, I just could not see it in the dark last night. This is unfortunate as some soot stringers were visable in the stove even with only a few hours of burning.

I did try a bit of forced air with the "bowl only" burner test. I used one of the tiny 12 volt DC squirl cage blowers that I bought to use with the Flash evaporator, I pointed this down a piece of 1 1/4 inch pipe at the flames. If I got the air pointed downward into the center of the fuel pool it pushed the flames horizontally out over the side of the bowl, looked like the petals of a flower sorta, the flames were a much nicer/cleaner light yellow rather than the normal orange, and the smoke was much reduced at first, but because of using too much air the fuel pool temp was reduced below flame temp in just a few seconds. It was obvious when this temp was reached as there was instantly a huge white fog of oil smoke rather than flames. Removing the air caused the flames to re-appear and the white oil fog to be eliminated. I think this burner style with the right amount of center air would be about right for the current outside temp, will test this more.

One thing -- the bowl I am using is a bit bigger than 9 inches, my firebox is about 7 1/2 inches wide, so I had trimmed a bit off of 2 sides of the bowl, when running the bowl with almost the full 7 inches covered by the fuel pool and with forced air applied the side flames were crashing into the sides of the firebox and producing a bit of sooty black deposits where the flame contacted the fire brick, I think I can live with that though.

It sounds to me like you basically have a kitchen variety grease fire going on inside your stove..

I guess so long as you're burning veggy oil then who cares about the smoke..

So long as its heating your home and you're not giving the money to the gas utility company then you come out ahead yes?

Grease fire -- That is what it has to be by deffinition, only thing burning is grease.

Once I added the combustion air tube into the center of the bowl and burnt 100% vegoil today the smoke was reduced to a much lower level that is acceptable to me so I will work on this style burner a bit more.

I added a cold air pipe bown through the top of the stove and to within 4 inches above of the center of the bowel today, Only thing I had handy was a 5 ft length of 2 1/4 O.D. exhaust pipe but It works just fine, looks a little wierd with 4 ft of pipe sticking out the top of the stove but I had no idea how long this air pipe needs to be so used all 5 ft for starters.

Legal Eagle pointed me back to a post by canolafunola in the "WVO home heater" discussion where he had posted a link to the Roger Sanders Heater design page (HERE), His burner is also a bowl design ("V" actually), smaller in diameter and with a linear taper but the same concept as I am testing. His picture of the crud that accumulates looks about like what I am seeing but since my bowl is larger my crud is all inside the bowl and has not accumulated around the edges as his picture shows.

He goes into detail about the drip control needing to be very stable, Today's testing sure showed that to me also. My drip control as always been a bit wonky but when dripping into a wood fire it didn't make a lot of differance, with this burner it makes a LOT of differance, I had the burner go out several times when my drip would simply stop dripping, at other times I would have a 7 inch pool of fuel in the bowl making a LOT of heat. I pretty much had to stand by the stove and continuously tweek the valve, accasionly I would get a steady drip or very thin stream for maybe 20 minutes and the fuel pool size did stay the same as long as the fuel feed did not change.

This evenings temps are around freezing again and it required a small but continuous stream of fuel to keep the house at temp. I first ran one 1/2 gallon tank of 50% veg/50% used engine oil to get the burner lit and heat everything up to operating temp. To keep the house warm this tank ran for 1 hour, the next 1/2 gallon was 100% veg and it ran for 1 hr 20 min. This fuel rate makes a big flame, fills one end of the firebox completely with flame and roars a bit when burning. The veg burned hotter than the blend and also produced about half the amount of smoke. The blend smoke was black, the veg smoked much less (by half, at least) and was gray. The veg even smoked a lot less than the diesel I used to start everything up on, diesel smoke is also black.

I tried to burn veg right off the bat with everything around 65 deg f, I had no more luck with this than anyone else seems to have had. After burning 2 ounces of diesel twice in the bowl and having the flame go out because the veg was not getting hot enough to vaporize I added the UEO to the veg and the burner now lit fine with the now-warm burner and another couple ounces of diesel. I burnt the blend out and then went with straight veg. Everything was now hot and the veg lit and burnt fine, even relit by itself when resterting the drip after the flame went out because the drip had stopped.

Burning the veg even seemed to clear some of the soot from the walls of the firebox after a short time.

I will make up another fuel feed using a suntec fuel oil feed pump that will be driven by a 12 volt DC motor, by adjusting the motor voltage I can much more precicely control the fuel feed and this pump/motor combination is much more robust than the tiny pump I had trouble with in the past.

Tim--
I found that if I preheated my bowl first on the stove that it lights off much better. I set it on a burner for a few minutes to get it good and hot, transfer it to the heater quickly, add a couple of ounces of biodiesel and a little more heat via propane torch and its going. Now add veg oil. I always thought it might be cool if you could use a electric stove heating element to preheat the bowl but I haven't gotten around to it yet.

How about trying a glow plug or a 110 v charcoal starter heater through the door, immersed in the pool of veg primer till it starts burning. Keep it there till everthing comes up to temp and the vaporization starts, turn on the drip, withdraw heater. Think this may work?

Tim,

Try pre-heating the veggy oil in the microwave..

As my first foray into experimenting with vaporization burners, I quickly tried the glow plug idea. I took a round shallow ceramic dish filled with VO covering a glow plug which was connected to a car battery charger. Unfortunately the battery charger was cycling on and off so the glow plug never got up to temp and the VO never ignited, just a lot of bubbling. I will try again with a well charged battery as the power source.

I wanted to see a VO flame and was looking for a small inverted metal dish. Soda can! I cut the bottom out which is cone shaped. Made it about 2" high with a cut out on the side so I can shoot a propane torch flame in there to heat the bottom of the cone. Filled the inverted aluminum cone with veg. Held the torch to it and it burst into flame in about 5 seconds and kept burning by itself till the veg was depleted. Note this was without any kind of wick, just veg oil, and this was in open air. I will put the inverted cone into a coffee can next, make a door and an exhaust port and install a metal tube for the downdraft air input that can be adjusted up and down and play with it more.

I am on hold for testing burners until I get a much better fuel feed setup. I am assembling a fuel pump using an oil fired furnace burner fuel pump turned slowly by a 12 volt automotive windshield wiper motor. this should allow very precice fuel metering from "0" flow up to about 3/4 gallon/hr flow by adjusting the motor DC voltage. I am also remaking the cold air input insert for the wood stove, this one will position the cool air down pipe more directly over the center of the bowl (my new name for this style burner = "Bowl Burner") and the air pipe will also be adjustable up/down for testing. I will leave about a foot of pipe above the stove. The fuel drip tube will be placed down the center of this tube as the earlier developers seem to have good results with this location.

I intend to try heating the veg in the fuel drip supply tube using the injector line heater concept of wrapping nichrome heating wire in fiberglass sheathing around the fuel feed tube,This heater will run on 12 volts, the intent is to have everything run on 12 volts in case of a power failure.
Hopefully this will allow firing up a cold heater using a douple of ounces of startup diesel in the bowl then feeding in HOT veg ? time will tell.

Tim,
My burners also have electrical heaters on them to pre-heat the WVO when its cold.. However, they only work when the unit is starting up from being dead cold.. Once the unit is warmed up, the electric heaters turn off (thermostat) and the heat from the unit does all the pre-heating. Its a bit tricky here and you will have to play with the length of tubing you need.. The oil going into the pan should be around 120 degF to 160 DegF. Any hotter and you risk gumming up the tubing. Also, smaller tubing is better than larger. The higher the velocity of your oil flow through the tubing, the better. I used 3/8 tube on my first "murphy burner" but have found that it is to large..

One thing is for sure, when pumping the oil, a positive displacement pump IS A MUST.. The only time when a postive displacement pump changes volume on its own is when the incoming oil is really cold and gelled. Even a tiny amount of heat to bring it to 60 degF or so is all that's needed.

I got my suntec "J" model 1750 RPM fuel oil burner pump connected to a windshield wiper motor today, works great and is highly controlable, 2 volts turns the pump at 15 RPM, this is about a pint an hour, and makes a nice stable 4 inch fuel pool in the burner bowl. 3 volts turns the pump at about 25 RPM and make about a 5 inch fuel pool, just right for tonights not-quite-freezing temps, uses a bit less than a quart an hour of fuel.

I cheated today and uses a propane torch to get everything up and running, was more interested in seeing how the pump was going to work.

I think I will try a 2-tier bowl next. my funnel-lid bowls have 3/4 inch female pipe fittings in there centers, I will us a 2-3 inch pipe coupler and stack 2 bowls. The top one will be a bit smaller than the bottom one, 6inch top - 7 1/2 inch bottom maybe. I will drill a few 1/4 inch holes in the top bowl at a point that a 4-5 inch pool of fuel will stay in the top bowl but any more fuel than that will run through the holes into the bottom bowl. I hope having fire in both bowls will keep everything hot enough to burn veg without needing a multi-step startup.

It will be interesting to see how the bottom bowl burns without the direct center downdraft.

Also had a thought about another more redilly available source for "bowls". I live in farm country and the round dished cutting blades from a bisk-type cultivator are exactly what is needed for a bowl once the center hole is welded up. These wear out on the equipment and are replacable, I can buy the worn ones from my local salvage yard for a buck or two. they are also available new in local farm stores. These come in many sizes from 12 inch diameter up to at least 26 inch diameter - LOTS of heat potential there.

Murphy -- Cleaning -- I have only run this burner for a couple days so still early but the single bowl was easy to clean, it had maybe 3/16 inch thick bits of soft dry foamy stuff on the bottom, this scraped out easily with a dull bladed pocket knife. There were no hard "coal" type deposits at all.

2-tier burner -- WORKS GREAT -- I made up a second burn bowl today, this 6 3/4 inch diameter upper bowl is slightly smaller than the bottom bowl's 7 1/2 inch diameter, this allows me to be able to reach into the burner box from the top and still be able to pour fuel into either the upper or lower bowl for startup. The upper bowl simply sets inside the lower bowl, this allows easy conversion from a single bowl burner to a 2-bowl burner and also makes cleaning easy.

The upper bowl is made from the same type leftover section of propane cylinder as the lower bowl. To get combustion air into the center of the bottom bowl I used a hole saw and cut a 2 1/4 inch hole in the center of this upper bowl, I then welded in a 1 1/4 inch tall section of 2 1/4 inch OD tailpipe tubing. This is a large enough opening for the combustion air that is being drawn down the 2 1/4 inch cold air intake tube (through the top of the stove) so that there is an air blast down the center of both the top and bottom bowls. When the stove is closed up the draft causes the flames to burn horizontally out from the center of each bowl. Looking down the center of the cold air tube I see no flames in the center of the bottom bowl, it's flame is burning horizontally out between the two bowls, the flame from both bowls is a nice light yellow.

My current fuel drip feed is down the center of the cold air inlet tube (works for others, also works here. Cool air keeps the end of the drip tube from charring over and giving eratic drips) This creates a bit of a problem getting fuel into the top bowl as the drip will fall through the center air tube directly into the lower bowl. I overcame this by adding sort of a "shoot" to the upper lip of the upper bowls center air tube. This is a 5/8 inch wide "trough" cut lengthwise (about 1 1/2 inches long) from another piece of the 2 1/4 inch tubing, and angled upwards at the center of the air tube by about 30 degrees. It is nicely radiased so the fuel that drips into it flows down and sideways over the edge of the upper bowl's center air tube and drips into the upper bowl.

The upper bowl is 3/4 inch deep, I drilled eight 1/4 inch holes horizontally through it's center upright pipe such that the bottom of these holes is 3/8 inch above the bottom of this upper bowl, this allows excess oil from the upper bowl to flow through these holes, down the inside of the center tubing and drip into the bottom bowl, this tubing is air cooled by the incoming air so the oil does not char on the tubing. I had intended for this to be the oil feed for the bottom bowl, didn't work, as the upper bowl never stays that full of oil unless you are making a LOT of heat, even with a fuel feed of 1 quart/hour there was no oil in the bottom bowl once the initial startup oil pool was used up.
To correct this I simply drilled a 3/32 hole in the bottom of the fuel trough so that some of the fuel dripping into the trough flows into the upper bowl and some drips directly down through the center air tube into the bottom bowl. I may have to adjust the diemeter of this drip hole as the bottom bowl seems to be getting less fuel than the top, not a problem really as there is enough fire in the bottom bowl to keep the upper bowl nice and hot.

I welded three 1/4 inch nuts on the bottom of the bowl at equal distances around the bowl, 1 inch out from the center hole, so I can experiment with the vertical spacing between the bowls by using different length bolts for legs, using 2 inch bolts now, seems to work ok.

The 2-bowl burner lights off directly with unheated-but-liquid veg in one step. I start the veg drip, wait til there is a thin pool of veg in each bowl, add 2 ounces of diesel to each bowl, use a propane torch pointed directly into the pool in the lower bowl only, takes maybe a second or two for the diesel to ignite, close up the stove and get good fire in the lower bowl , this heats the upper bowl and it self-ignites in about 30 seconds - That's it - the diesel burns for a minute or so as both bowls are heating up nicely and the burn continues on veg. The fire from the lower bowl heats the upper bowl and the under side of the upper bowl directs heat back into the lower bowl. Because the two bowls get hotter than a single bowl I have had this burner go out twice (only tried it twice at the low fuel rate) today with my smallest fuel feed rate of one pint/HR, the burner runs hot enough to vaporize the oil faster than it is being supplied, the burner burns for about 8-10 minutes from startup until it exhausts all the fuel, as the last of fuel is consumed the burner cools and goes out even though there is still a small amount of incoming oil, the burner just gets too cool to vaporize oil (bummer because the slowly incoming oil will overflow the bowls if you don't know the burner has gone out). Seems to do fine with a fuel rate of a quart/hr, the upper bowl has a small pool of burning oil in about one half of the bowl(due to not being absolutely level), the bottom bowl is burning a pool of oil about 4 inches in diameter.

I have only fed fuel at a higher rate for a few minutes as the house was getting way too hot. This 2-bowl burner really gets to roaring with enough fuel, Both bowls add heat to each other so vaporize fuel faster than a single bowl, the stove heated up within a minute and was really radiating heat. The weather forecast for mid next week is for low 30's as highs and teens as lows so I will give it a workout then and see what it can do.

This conversation is almost useless without photos Tim.

I always have a difficult time explaining what I did in writing..

Anyhow, I think the reason you're not seeing hard coal'ish deposits is because you're burning WVO and not WMO.. I think WVO leaves behind a different kind of material.. Obviously allot softer and easier to clean than WMO.

I am very good at visualizing things and I'm a little confused.... is it like 2 Small Agricultural discs stacked up in a dish config, the space between them at the center 2 1/4" apart top disc has 2 1/4 tube welded in center with it extending down but leaving 1/2 above bottom disc and 1/2 ridge in top disc?? drip catch trough has a designed LEAK to let the drips LEAK some down to lower disc?? Seems pretty complex to disassemble and clean, how many continuos hrs between cleans?? Tigman

Sorry about the confusion. -- It is much simpler than that. The bottom bowl is just a simple bowl any diameter you want to make it, mine is 7 1/2 inches because that is all the wider my fire box is. This bowl can be made from whatever you can find, mine is the end from a B-B-Q propane tank, each one of the farm cultivator disk blades (picture of a small disk cultivator here) is the correct bowl shape and come in many different diameters, cut it down to whatever diameter you like. The hole in the center of these individual disks gets welded shut so they become a solid bowl that will hold fluid without leaking. There is no center post used in the 2-bowl burner, each bowl is totaly independent of the other.

Mount the bottom bowl however you prefer in the burn box,mine just lifts out. I find that if it makes contact only at the center it allows the outer metal of the bowl to heat up quickly.

The upper bowl is a completely seperate bowl that simply sits inside the lower bowl, it can be lifted out of the lower bowl by hand. The upper bowl can be any diameter you like, mine is slightly smaller than the bottom bowl to allow me to easily pour start-up fuel into either bowl through my top-opening burner box door.

The upper bowl has 3 legs on the bottom side that are made from 1/4 inch bolts, the length of these bolts deturmines the distance between the bowls, I am using 2 inch bolts now and this distance seems to be working fine, I will try 1 1/2 inch bolts and 1 inch bolts and see how those distances between the bowls will perform.

Looking at this upper bowl from the side it looks like a flying saucer, the 3 bolts are the landing gear. This upper bowl has a 2 1/4 inch hole through it's center to allow the top-supplied combustion air to reach the bottom bowl, could be some other size opening, I just have 2 1/4 inch exhaust tubing on hand. A 1 1/4 inch length of this tubing is welded into this hole so that air can pass down to the bottom bowl and the fuel in the top bowl does not run out of the bowl through this hole. The upper bowl now looks sort of like a doghnut shape when viewed from the top. The piece of tubing welded into the upper bowl does not extend out of the bottom of the bowl, it is welded flush with the outside bottom of the bowl (looks sorta like a short, bowled version of this with 3 legs added on the bottom)

Your description of the drip catch trough is correct.

Nothing to dissassemble really, lift out the upper bowl and clean it, it is all one unit and requires no disassembly, the entire upper shallow bowl surface (only 3/4 inch deep) is totally open for easy cleaning.
Same with the lower bowl, it is only about an inch deep and once you lift out the seperate upper bowl it is one totaly open shallow bowl surface that is easy to clean.

Time between cleanings -- Don't know yet, just ran the 2-bowl burner last night for about 8 hours, the upper bowl had a TINY amount of dry ash-like stuff in it, it wiper out with a paper towl. This upper bowl stays HOT and clean, shiny even, it was not even damp with oil after shutting down the burner. It vaporizes oil so quickly that there is not realy a pool of oil in it when burning even at a rate of 1/2 G/H, the oil drips in and runs around the outside of the center air pipe, evaporates, and bursts into flame leaving only a tiny amount of dry ash that is not even stuck to the bowl, at least with vegoil.

The bottom bowl did collect just a few pea-sized chunks of the soft foamy stuff but it scraped out easily with my pocket knife.

The lower bowl does not run as hot as the upper bowl so it looks like it will produce about the same amount of soft foamy crud as it did when using only the original single bowl for burning.

I will burn some used engine oil tonight and see how much crud gets produced.