Question about nozzle temp for oil burners

Discussion in 'Burners and their construction' started by Bentation Funkiloglio, May 24, 2020.

  1. Just about finished building an oil burner based on Dave Allen design. Has a .85 gph delavan siphon nozzle.

    Question came to mind when I was putting burner together and noted the rubber o-ring on the nozzle screw pin.

    I realized that I don't really understand how nozzle stays adequately cool given its close proximity to hellish temps inside furnace. In video showing Dave Allen's oil burner, his nozzle is only a couple inches from end of pipe that connects to furnace.

    How sensitive is nozzle temp to variables such as distance from end of tuyere and angle that tuyere is inserted into furnace body?
     
  2. Rotarysmp

    Rotarysmp Silver

    Generally in use, the fluid flow, evaporation, and air flow will keep the nozzle cool. The real killer is the heat soak back after shut down. If you dont retract the burner each time you shut it down, you will cook the o ring, and cause coking problems.
     
  3. This is where having a larger bore (1/2") copper tube with brass compression fittings can help a fair bit by conducting heat away from the nozzle as it receives heat. It won't keep it cool but will limit extreme temps.
     
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  4. Melterskelter

    Melterskelter Gold Banner Member

    Yes. I learned the hard way about needing to pull the burner tube/nozzle assembly and allowing it to cool outside the furnace. Early on, being a bit preoccupied with the actual pouring of metal, I just left the burner in the furnace and turned everything off. That melted the o ring which I discovered when there was poor atomization next burn. Now my routine is when I am ready to pour is to shut off the fuel but not to reduce combustion air or atomizing air while leaving the assembly in place. The air flow is enough to prevent burning the o-ring. After pouring, Disconnect the fuel line to let the residual fuel burn off in the furnace rather than make a big cloud of diesel fog that could foooomp. I then pull the assembly but turn up the air flows and set the burner on the ground. I let it blow for five minutes or so until it is cool to touch and then cut the combustion and atomizing air. I’ve been using the same o ring for at least 2 years, but I have a spare taped to the outside end of the assembly. It is a very small o ring, Viton type, that can take a while to source. So, good to have a spare.

    Denis
     
    Last edited: May 25, 2020
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  5. rocco

    rocco Silver

    It's weird the way that works, it's the same propane burners, the business end can be glowing almost white hot and the opposite end can still be cool enough to touch. I guess it all has to do with air and fuel flow. As others have already mentioned, take care of the burner when you shut it off, the heat will migrate when there's no air and fuel flowing, make sure too much doesn't make it too the sensitive bits.
     
  6. Petee716

    Petee716 Gold Banner Member

    I follow exactly the same proceedure as Denis. I have a few spares, I think I bought a pack of 5 but I can't remember from where. I cooked one once in use but fortunately I had a spare nozzle so I just took the o-ring off that one and kept going. That's when I bought the spares. Since then I've replaced it several times over a couple of years while I had the nozzle apart for inspection/cleaning. Another thing that will stop that nozzle in its tracks is clogging. Since I pressurize I run my oil through a spin on automotive filter but have also in the past filtered at the supply tank through a "green" shopping bag. The few times I've actually gotten a clog was when I was replacing fuel lines. A bit of end-trimming from the hose or tube ended up in the line and plugged the nozzle.
    Just a note for the uninitiated on the flameout/smoke cloud. That "foomp" is a real thing. If while your furnace is hot your flame goes out, whether oil or propane, shut your fuel off immediately! You should have a means to quickly turn off the fuel at the burner. Then open the lid with caution and let the smoke clear before you try to reignite. The smoke will be gray and is explosive and will ignite with varying amounts of force anywhere from mildly amusing to a cannon shot. Once your burner is dialed in and your procedures are established it will be infrequent but it still happens from time to time. Not meant to unduly frighten anyone, just something to be aware of.

    Pete.
     
  7. All, appreciate the info! Think that I'll write up a standard operating procedure checklist that I can laminate and attach to burner or furnace. This will make it less likely that Ill forget anything on startup, tear down, etc. Easy to get distracted.

    Got a couple unpleasant burns when I first started using my propane furnace. Just wasn't thinking and would do something stupid like try to pick up a hot brick. So, did something similar.

    It'd have really sucked if I melted the o-ring (or some important body part) first time out with the new furnace.
     
    Last edited: May 25, 2020
  8. Melterskelter

    Melterskelter Gold Banner Member

    I would underline Pete’s comment about the importance of filtering fuel to prevent clogging of the siphon. I have a filter that is located between the quick connect on the fuel line and the siphon nozzle so that contaminants on the connector can’t sneak into the siphon. I also filter the diesel just prior to it entering my fuel flow meter. That’s because there is a quite small orifice in the meter and I did have a bit of rubber block the orifice and thus fuel flow. I am using simple inline filters that would be used on gas engines similar to this. No trouble since filtering.

    upload_2020-5-25_11-17-38.jpeg

    Denis
     
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  9. Interesting that you filter diesel. At first, I will only use diesel, so I assumed filtering wasn't needed.
     
  10. Melterskelter

    Melterskelter Gold Banner Member

    It needs to be filtered in your truck, boat, car, or airplane even though it pumps into the tank through a “final” filter. Dirt happens! ;-). I will virtually guarantee trouble if you neglect to filter.

    Denis
     
  11. It will need filtering.... I use a fine wire mesh strainer from an airless spray paint machine on the intake inside the fuel tank and have a car oil filter on the fuel pump. I forgot to store the fuel system properly before the wet season hit last year, so this year I had three mud wasp nests to clear from the pump and the plumbing.
     
  12. Makes sense to put it on end of fuel line in fuel containers. I like the idea of using a fine mesh. Cheap, easy, easy to clean.
     
  13. Mister ED

    Mister ED Silver

    This is a butt puckering situation!! I am somewhat new at all this, even though I have had my furnace for 3 (I think) years. I have ever gotten to the "foomp" point ... but have had many many flameouts that made me pucker.

    So far, all of my flameouts came prior to me pressurizing my diesel. Before pressurizing I had all kinds of issues with lighting, flameout ect. Since I have pressurized my fuel, lighting is a breeze ... all the variability of siphoning is circumvented. I have a Corny Keg (soda keg) that I put my fuel in, regulate the pressure into the tank to 3.5 psi. I only have 4 or so lights since my change, but lighting the furnace now could not be easier ... light a diesel soaked rag and throw it in, turn on nozzle air, turn on fuel, wait a min and start ramping up combustion air, then shut the lid after a minute.

    One note, if anyone else goes the corny keg route, you will want to change all o-rings to buna-N (nitrile). The standard o-rings will deteriorate from the diesel eventually.
     
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  14. Melterskelter

    Melterskelter Gold Banner Member

    Sorta like this:

    I pressurize my fuel at 9 PSI, use a converted-to-dc-power-supply leaf blower shuttered down, and 10 PSI atomizing air on a Hago Siphon nominally 1 GPH nozzle run at .06 LPM for starting and .18LPM general heating with just few inches of reddish flame. The flame is a bit reducing (rich) which is max heat and good for iron, but based on the interesting discussion above, maybe would lead to porosity in Al. I confirm it’s reducing nature by just holding a clean piece of steel in the exhaust. If it gradually gets sooty, I am reducing. I can also see a hint of smoke in the exhaust when I am tuned right.

    Denis
     
    Last edited: May 31, 2020

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