I have been doing a good bit of testing of different burners in an attempt to get something that will burn reliably using only outside air from below the burner and passing the air through holes in the bowl. There are several commercial pot burner heaters that use this design reliably from posts over on the "Military Heaters" discussion. They began talking about these burners using a "catalyst" in the center of the burners, these are metal structures that glow red hot and improve vaporization as well as combustion, the discussion about these starts on PAGE 14 of that discussion.

I have tried 4 versions of these "catalyzers" so far, along with increasing the number and size of the air holes through the side of the burner bowl. These changes have allowed me to finally get a reliable burn using only outside air coming through the holes in the bowl rather than down from the top. I still can't get blue flames but it is promising.

It will take a few days to get all this testing posted here but I did make several posts with pictures about my "catalyzer" testing starting about 3/4 of the way down PAGE 16 of the Military Heaters discussion.

Burner bowl improvments for bottom air burn -

I have tried several versions of air holes through the side of the burner bowl, what I found is that there needs to be a row of holes close to bottom of the burner bowl so air can pass over/into the vapors directly near the bottom of the bowl to get flames and heat as soon as the fuel hits the bottom of the burner.

I originally had 1/8 inch holes through the bowl, it looks like these are a bit too small, I opened most of these up to 3/16 diameter and got much better burning.

My current bowl has 4 rows of holes, the 3 bottom ones are 3/16 in diameter and the top is still 1/8, I will likely open these up to 3/16 also. It looks like placing holes from top to bottom of the bowl allows it to burn with a small amount of fuel or a large amount of fuel. When using a small amount of fuel the lower holes have flame fingers licking from them into the center of the bowl but the upper holes don't show any flames, as you increase the amount of fuel the flames begin to show up at the next higher set of holes, you get flames wherever there is an adequate amount of fuel vapor to burn, above that point in the burner the air holes just add air that does not have enough fuel vapor to burn. The only thing the added air does is to cool the inside of the burner tank a bit. I don't see that this small amount of air lowers the internal temperature enough to be a problem. The large amount of holes allows the fuel amount to be adjusted to allow a small amounts of heat to a large amount of heat and still get a reasonable burn.

The one problem that the large amount of larger holes has caused is that they allow a large amount of the splashed fuel droplets to pass through the holes and land on the cool inside of the lower burner support can, this caused a good bit of sooting and sticky tar to form on the inside of the burner support can because this fuel would sort-of burn but not at all cleanly. This, and high-meltpoint creamy fuel caused me to change the drip tube (future post).

This picture shows the holes in my current burner bowl. I got a bit too close to the bottom of the bowl with a couple of the lowest holes, this caused my startup fuel to run out of these holes so I dished the bottom of the bowl down a bit by stretching it a bit by flattening out the creases in the bottom of the bowl with a hammer. I placed the bottom of the bowl on a heavy metal block and tapped the creases out, then tipped the bowl up a bit on it's bottom edge and tapped the bottom down close to the wall of the bowel, all this tapping stretched the bottom a bit and allowed it to be dished down a bit, this dished down section holds enough startup fuel to get the burner up and burning. (disregard the small machine screw in the bottom of the bowl, it is from a prior failed test)

This burner burns with only bottom air but it is prone to going out due to the bowl being cooled by all the incoming air, that is where the above mentioned "catalyzer" made the differance.

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Catalyzer -- The "catalyzer" is something I read about in the MILITARY HEATERS discussion, a catalyzer is some sort of thin metal structure placed in the burner flame so it glows red hot, it radiates heat inside the burner to promote fuel vaporization and ignition. The burners in that discussion feed there fuel through the side of the burner rather than drip it in from the top so there catalyzer design is not correct for a top fed drip burner. There multi-part catalyzers are also a bit more difficult to build. I needed something fairly easy to build and that would allow fuel to drip into the center of the bowl. what I came up with was to use a short length of 2 inch diameter stainless steel tubing with a wall thickness of 1/16th inch. I slotted this tubing from both ends using a chop saw to create strips that are about 3/16 wide, I then bent and twisted these strips so that The catalyzer was suspended from the top edge of the burner bowl by one set of strips and the center strips ran straight down the center of the bowl to within about 3/8 inch of the bottom of the bowl. This allowed the center strips to heat up by being directly in the flames. These center vertical strips were twisted 45 degrees to allow the flames to pass between them and make a nice swirling cyclone of flame rising up through the center of the catalyzer, the fuel droplets had to fall through these flames so the fuel got preheated before it hit the bottom of the burner bowl.

This picture shows the catalyzer in the burner bowl. (disregard the reduction ring inside the burner bowl, this was another failed test)

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This is a side view of the catalyzer alone.

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this is looking down at the bottom of the catalyzer.

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This shows the slotted tube before the strips were shaped.

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This shows the first attempt at a catalyzer, it is shown in a double-depth burner bowl that is made up by placing a 1 pint bowl down throught the removed bottom of a 1 quart bowl, neither idea worked well. The problem with this and the next catylizer is that they sat on legs that contacted the burner bowl bottom, I had hoped these legs would conduct heat down from the catalyzer into the bottom of the burner, nope, they actually cooled the bowl and caused soot to collect within as little as 4 hours. The jury is still out on a deep bowl, need to test this more eventually. I have a deep 2 quart SS dog bucket to try rather than the double bowls but I suspect the depth will make it difficult to clean?

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This shows the next attempt at a catalyzer, it crudded up in even less than 4 hours as it had MANY legs contacting the bottom of the burner bowl to cause cooling of the bowl in short order.

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By adding the bigger air holes in the bowl, and adding the latest suspended catalyzer, I can now burn the bowl reliably using only bottom fed air for 3 days with out needing cleaning. The bowl cruds up a bit differently than without the catalyzer, it now ends up with a flat floor of crud that is pretty crusty, the burner begins to smoke once the floor of crud reaches the bottom of the catalyzer strips, I suspect it starts pulling heat out of the strips so they no longer glow red with enough heat to keep vaporizing the fuel?

Since the fuel is now dripping down the center of the catalyzer there is not as much fuel droplet splash going through the air holes in the side of the burner bowl but there was still more than I like.

I had a barrel of very hydrogenated "creamy" veg that was not usable to cold-blended vehicle fuel so I wanted to burn it through this stove. It worked fine if I could keep it warm enough to melt it into liquid oil. I have a 65 watt heater on the fuel tank that sets close to the stove, and I have a 15 watt heater on the fuel metering pump, but I don't have any heat on the fuel lines between the tank and the pump, or from the pump to the drip point inside the stove, this proved to be a problem with the creamy oil.

I was burning this creamy oil in the big-hole ventilated burner bowl but this was before I had a catalyzer that worked, that burner had a tendancy to go out unexpectedly, if I was not around the burner would shut down and the stove would cool off to a point that the creamy oil in the fuel lines would turn to thick Crisco-like grease. I had about a foot of 3/8 rubber fuel line between the bottom of my heated supply tank over to the heated fuel pump input but this fuel tube is located only a couple inches above my concrete slab floor, once the stove went out the pump stopped moving warm fuel through this hose and it cooled off enough to solidify the grease, this happened even though the temp never dropped below 65 deg f. My fuel pump turns so slowly that it does not create any suction, the fuel has to be liquid and above the pump to keep it flooded with fuel. Once the fuel solidifies in the fuel supply hose all fuel flow stopped.

I replaced the 3/8 hose with 3/8 steel brake line, and insulated this steel tube by slipping a 3/4 inch heater hose over it. Since there was heat applied to both ends of this 1 ft long steel tube it now stays warm enough to keep the creamy oil liquid. BUT - I had small 1/4 inch steel brake line tubing running from the fuel pump up to the drip point inside the stove, even if I ran the fuel pump at full speed, a whole 2 1/2 revs/sec, it did not make enough pressure to push sticky solidified grease through the 4 ft of small tubing so I replaced the small tubing with larger 3/8 steel brake line, I also changed the internal drip tube to 3/8 diameter steel brake line, and re-did the plumbing so I can ream out this tube without having to remove it from the stove. While replacing the internal drip tube I also lowered it's drip end closer to the burner bowl to reduce the fuel droplet splash, The drip end is now low enough that it is now outside the of tube that brought in the top combusstion air. This allowed me to use a fitting on the end of this drip tube that allows me to use brass 1/4 inch pipe caps as the drip opening so I can test differant size drip holes.

This picture is of the 90 deg top air supply tube out of the stove, the fuel drip tube runs down through the inside of it. You can see the new drip outlet fitting sticking out of the bottom of the tube. The original short small diameter fuel drip tube that was replaced is laying on the tube.

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This is a closeup of the new drip fitting with a drilled pipe cap installed, it also shows the support bracket for the bottom end of the drip tube.

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This shows the cleanout "T" on the upper end of the drip tube. By removing the plug in this T, and taking the brass drip cap off the bottom of the tube, I can run a length of 1/4 or 5/16 inch steel cable through the entire length of the drip tube for cleaning.

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OK - I now have a bowl and catalyst that burns reliably using only bottem fed air, and the lowered drip tube has pretty much eliminated the fuel droplets splashing through the holes in the burner bowl. BUT - much to my surprize, when I fired it all up I now have flames coming from the fuel drip outlet after only a couple minutes of burning, apparently the fuel drip tube is being heated enough now that the more volital oil is being vaporized, this vapor is shooting out of the drip hole and burning at the same time the heavier oil droplets are falling into the burner bowl, HMMM, didn't see that coming.

This picture shows the soft crud that built up around the drip fitting after a 3 days of burning, looks bad but not really a problem as it drops away as soon as you touch it with a putty knife.

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I am helping a friend here convert a normal pressure style home heating oil burner over to a syphon type burner to burn used motor oil for heating his shop. I got to wondering what would happen if I put a standard pressure type oil burner nozzle in place of the pipe cap with a drilled hole. Since the drip tube is vaporizing oil anyway I wondered if the furnace burner nozzle might flare off the vapor and still drip the heavier oil into the burner bowl. This worked WAY better than expected. I only have one day of burning with this setup but it looks promising. I expect nozzle clog-up problems as the furnace nozzle has much smaller internal passages than a 3/23 inch drilled hole, and my fuel has not been filtered, only settled, I probably will need to add a filter in the fuel supply line for reliability, still testing this.

I used a furnace burner nozzle with a flow rate of 1.7 G/H based on 100 pounds pressure, it has a spray angle of 60 degrees. The selection of this nozzle was arbitrary, it simply was the one with the largest flow rate that I had on hand. When I fired up the cold burner in a cold stove I got a very thin solid high pressure stream of fuel from the nozzle. The fuel pump's motor current went up from it's normal 1.8 amps to 2.4 amps with this nozzle in place so the pump is having to make a bit more pressure to force the same amount of fuel through the much smaller opening in this nozzle than it did to drip fuel out of the 3/16 inch hole drilled in the pipe cap.

I lit the burner and within 30 seconds the solid thin stream from the nozzle shifted to a fine conical spray of droplets that had an angle of about 15-20 degrees, there was also a soft "hiss" coming from the nozzle. The first inch or so of the outer layer of this cone of fuel spray was burning with a blue flame tinge that shifted to a bright yellow/white flame, the center of the spray cone was not burning but was spraying very fine fuel droplets into the burner bowl, these should be vaporizing much faster than the old big droplets but there is so much swirling fire in the bowl that I can't see the bottom of the bowl to tell. The flame from the nozzle is burning farther away from the nozzle than it did from the dripping pipe cap so I hope the crud-up problem will not be as bad, won't know til this burns for a longer time.

The downward shooting fire from the nozzle, and the fire rising up from the burner bowl, seem to be reinforcing each other, this may work out just fine.

I did find that with this upper flame the burner bowl would sustain a reliable burn without the need of the catalyzer, in fact, the catalyzer does not get heated enough in this set-up to glow with heat, I removed it a few hours ago and the burner is still going fine. I suspect the burner bowl will even stay cleaner without the catalyzer since there is less of a restriction to blowing any produced soot out of the bowl.

I have seen that even with the external air coming through the holes in the side of the burner bowl that the soot still gets blown out of the bowl pretty well, the soot ends up as very soft light foamy marble sized chunks on the bottom of the burner tank.

This picture shows the burner at a low fuel setting, the door of the burner tank is open so the flame is disrupted a bit. There is a spray of bright yellow/white fire being blown into the bowl from the burner nozzle, and there is bright yellow flame rising upward out of the burner bowl. Still no blue flames but it is a pretty clean burn, with just the slightest amount of smoke visable from the chimney if you stare at it long enough.

I was not able to tweak the picture so that the flame from the nozzle would show.

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Hi Tim,

Nice marathon of posts and interesting read as always. I thought you only have bottom combustion air coming in from a pipe in the bottom of the propane tank? Per pic in this post, you also have air coming in through the top of the propane tank? Unless the upper pipe capped so no air can come in?

quote:

Originally posted by Tim c cook:
OK - I now have a bowl and catalyst that burns reliably using only bottem fed air, and the lowered drip tube has pretty much eliminated the fuel droplets splashing through the holes in the burner bowl. BUT - much to my surprize, when I fired it all up I now have flames coming from the fuel drip outlet after only a couple minutes of burning, apparently the fuel drip tube is being heated enough now that the more volital oil is being vaporized, this vapor is shooting out of the drip hole and burning at the same time the heavier oil droplets are falling into the burner bowl, HMMM, didn't see that coming.

This picture shows the soft crud that built up around the drip fitting after a 3 days of burning, looks bad but not really a problem as it drops away as soon as you touch it with a putty knife.

Thanks for the detailed write up Tim.

Am I correct in that the larger pipe that has the drip tube supported inside it was orginally a large mouth air intake from above the heater that is now not used for air feeding. It's blocked off up above right?

Correct, the 3 inch pipe is the original inlet for the top combustion air, I have a sliding damper on the outside end that allows it to be opened by any amount, or completely closed, for the current testing it is completely closed.

Having both top and bottom adjustable air inlets available allows for a lot of combinations for testing.

I did try adding a bit of top air past the nozzle using this inlet, sorta like the combustion air in a normal furnace burner, the added top air only cooled the burner assembly down and caused reduced vaporization so the flames became a darker yellow color and produced a bit more smoke.

The stove is still burning nicely after 2 days, no obvious changes except for a pea sized bit of crud on the very tip of the pressure nozzle that has not yet interfered with the fuel spray pattern.

I may be seeing just a bit of crud in the burner bowl, can't really tell due to the chaotic mass of flames, but there may be just a bit of triangle shaped crud buildup between a couple of the lowest air inlet holes in the burner bowl. I have seen this before in recent tests, it is one reason I increased the number of holes closest to the bottom of the burner bowl, placing holes closer together reduces the area between them where crud can collect, just started testing this so need more time.

This picture from a previous test burn shows one of the crud triangles between two of the lowest air inlet holes, look in the lowest part of the burner bowl.

The burner bowl that is now in the stove has twice as many 3/16 diameter holes in the bottom row, hopefully this will reduce the size of these crud triangles exponentially?

The crud shown in this picture is after a 3 day burn using the latest catalyzer and the original drilled pipe cap big-drop drip outlet.

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This picture is of the same burner bowl as the prior pic but with the catalyzer removed, you can see a few more of the crud triangles.

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I forgot to mention a couple things in the earlier posts..

Larger 3/8 diameter fuel feed lines. - One other thing these larger internal diameter fuel lines have allowed is that once I remove the drip outlet pipe cap in the stove the fuel pump can now clear the solidified grease from the lines that are between the outlet of the pump and the drip outlet inside the stove. As long as I can get liquid oil into the pump gears the pump produces enough pressure to poop a continuous grease sausage out of the end of the drip tube. By increasing the diameter of the fuel line it increased the surface area that the pump is pushing against and the center of the grease in the fuel line is not stuck to the inside surface of the line, I suspect the pump is pushing this center grease on through the tubing followed by warmer liqued oil from the pump. Sort of interesting to watch a 3/8 inch diameter coil of solidified grease slowly squirt out into the burner bowl.

Using the furnace nozzle - This may not work if the drip is gravity fed, I suspect that the fuel vapor would encounter less resistance from the oil in the drip line than it does from the small opening in the fuel nozzle, the vapor may push back up into the supply tank rather than exit the nozzle, don't know, just a caution.

I don't have any experiance with the paristaltic pumps that use a squeezed rubber tube as there pumping element, these may work, may not, don't know. I know there are quite a few folks using these type pumps so they will have to test this themselves as I don't have one available to test.

Someplace I have a low pressure guage, once I find it I will screw it into my fuel line cleanout port and see if I can get a reading on what the actual fuel line pressure is when using the furnace nozzle drip outlet.

I have several nozzles with differant flow rates, a smaller flow rate may make a finer fuel spray, I will try several different nozzles in future tests.

quote:

The downward shooting fire from the nozzle, and the fire rising up from the burner bowl, seem to be reinforcing each other, this may work out just fine.

I did find that with this upper flame the burner bowl would sustain a reliable burn without the need of the catalyzer

Two flame fronts stablising each other works very well in the marine military babbington mobile food heater and in the orchard venturi heaters with the side tube. Sounds like it is going to be a winner for you to.

Suntec pump problem- A few days ago I started having problems with my pump. The pump spins but no oil at the drip tube. I thought that maybe I had to much solid fat building up at the bottom of my 30 gallon tank( my suction line comes in about 3" off the bottom).
After spinning the pump with a drill it would work again on the faster rpm for high heat output. But when turning down rpm’s it would soon stop dripping. Then I would have to start it with the drill again, I did this several times.
So I then cleaned out my barrel and had tore down pump and cleaned blew out all the orifices and added a shut off valve on the suction line for future service. Then I ran on the bench with diesel fuel, put Clean oil back in the barrel and reinstalled the pump. It still did not like the slow rpm’s with the small motor but it would work on the high heat setting with the faster rpm’s.
This pump is the 1725 rpm pump with the wider gears, I ended up installing the pump from my shop since I only use it heating my oil for filtering(it is the 3500 rpm model with the narrow gears).
With the pump from the shop I am up and running again but it does not pump as much oil as the wide gear pump. In the shop I turn it with 24 volts but in the house I’m only set up with 12 volts. Most of the real cold weather should be past us now(do I dare say that)so this pump will do the trick till spring.
The pump that quit on me was new last fall. When I had it apart every thing looked OK I am wondering if the gears are wore just enough to where the oil is sliding out past the side in a low rpm situation.
I continue to use the 1 quart pet dish with one row of holes 2/3 of the way down This is set in a coffee can with some air holes in the bottom. All my air comes in from the top and blows down into the dish. Who knows what next years design will bring, so much progress being done on this site! This heater has been running 24/7 since October.