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Thread: Further notes on Brute burner operation

  1. #1
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    Further notes on Brute burner operation

    I preach to all of the oil burners on the forum about getting their furnaces hot enough. It would probably be a good thing if I took my own advice.

    I just got a new supply of silicon so I fired up the Brute yesterday in the big furnace to make some Everdur.



    I put some scrap Everdur in the crucible for a puddle to push the copper wire under to prevent major oxidation. I fired it up with the propane feed until the crucible was red hot and then switched to oil, but I could not melt the scraps. If I turned the oil up it would smoke and the blower was maxxed out. Finally I surrendered and turned the oil off, turned the propane back on, and really let it roar. (Propane needs a lot less air than does oil.) The scraps melted. I switched back to oil and it then it burned fine.

    The first point is: you have to get your furnace good and hot before you turn on the oil if you are using a drip feed waste oil burner.

    The second point is a bit more theoretical. I could be wrong here, but it appears that with an inadequate supply of air, the oil has to be really hot so it can vaporize in the furnace. It appears that less air is required to burn thoroughly vaporized oil than is required to burn partially vaporized oil, and that initially it takes more air to get the furnace going good and strong, hence the need to get the furnace really hot, as in the case here. In my small furnace the same shop vac blower is more than adequate and delivers enough air that I don't have this problem.

    The third point only applies to me: I really need to build a bigger blower. My blower is a 5 gallon shop vac, and it is not quite enough for the Brute in this furnace.

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  2. #2
    As I start my path down the road of burning oil I keep reading all I can on the subject. I understand some peoples aversion to running an air compressor, but I have a monster old school compressor in my garage. She runs quiet and cool and is 80gallons of 160psi of dry air on tap. Having this compressor convinced me that building the kwiky was the way to go. Sure I wish I didnt need to be connected via an air hose, but wouldnt it be easier to run that monster of a furnace with say a PAIR of kwikys instead of drip feeding it? I'm new to this game so I'm just tossing ideas out there to learn.

    I've watched the Ozzie oil expert burn with some mega heat by dripping, so maybe I'm missing something.
    Inquiring minds want to know! ;-)

    Jason

    btw, that bronze statute you're working on is AMAZING! Post more photos! I look forward to seeing it's progress.

  3. #3
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    Some personal opinions and observations on your points.:

    Quote Originally Posted by Rasper View Post
    The first point is: you have to get your furnace good and hot before you turn on the oil if you are using a drip feed waste oil burner.
    Perhaps a little of an aside but I would suggest you in fact need something hot to vaporise your oil with. That need not be the burneing chamber/ furnace/ whatever itself.
    A friend did a babbington type many years ago and aimed that into a large drum int owhich he had put a zig zagging pipe as a water heater. The water kept the firetube well below oil vaporising temp. I got him to weld up a short length of angle iron into an "X" shape and put that in the flame path. He dubbed it the glow plug because it quickly got hot and gave his less than perfectly vaporised oil something hot to light enough of it off to burn the rest cleanly and completely. He thought it was a miracle, I thought it was logic.

    I wonder if there is not something you could put in your furnace like some metal or ceramic that would heat up quickly with gas and allow a faster chang over to oil? I don't see why it wouldn't work, principal is the same. I would thing you would need to use a few to cover the perimiter of the furnace because the incoming air will cool the first thing it touches but it will spin round and light off eventually and sustain from there. I would suggest even a good handful of old nuts and bolts would do the trick. I have used those before and they work well.

    Maybe a piece of large diameter thickwall pipe stood on end would do? This would run the flame around between it and the furnace wall and the heat in the thicker pipe should travel well through it. Any oil that condensed would light off on the inside of the pipe to burn further up the furnace so all good. I did this on one of my burners just the other day and the burning on crappy wet oil went from pretty much unsustainable to damn near perfect.
    It was an interesting reminder.

    The second point is a bit more theoretical. I could be wrong here, but it appears that with an inadequate supply of air, the oil has to be really hot so it can vaporize in the furnace. It appears that less air is required to burn thoroughly vaporized oil than is required to burn partially vaporized oil, and that initially it takes more air to get the furnace going good and strong, hence the need to get the furnace really hot, as in the case here. In my small furnace the same shop vac blower is more than adequate and delivers enough air that I don't have this problem.
    My observation and formed opinion is that a problem with low air flow on larger setups is more of low air speed. You choke a blower down that is running through a say 2" pipe and the airspeed drops. When that happens, the oil is blown much less energeticaly into the burner. Instead of being blown past the initial cool air impact zone, it hits it and condenses and the flame front never really gets going. Regenerated heat as I call it is critical and so is airspeed to blow the oil in there and cause sufficent turbulance for mixing the oil and the air.

    I have come across this in a few different ways but I am also reminded of it from playing around tuning car engines. You put a big carby on an engine and nail it and the thing dies in the arse because all the sudden the gas speed through the venturis drops and the mixture goes out the window. You use multiple smaller carbs and keep the gas speed up and the thing snaps your neck. Same thing goes for Porting heads so you can drop base balls though but drive the car on the street and unless you wind it out through the gears, it's a pig because there is no gas speed and swirl into the combustion chambers.

    IF you are restricting the airflow into your burner for start up or throttling. I suggest having something like a Ball valve as near the burner/ furnace as possible and putting the drip feed right in front of it. You want a bit of pressure there in the narrowed area to grab the oil and launch it into the burner rather than such a slow airflow that the oil will run backwards if the inlet isn't facing the burner and it falls in once it gets there. Basicaly it's like compressed air. Tiny nozzle where the air is under high pressure and going 1000 MPH but the over all volume isn't anything a low powered centrifugal blower couldn't do at half tilt.

    Getting the airspeed up to take the oil with it and create plenty of mixing and swirling action in the burner is what I think is very important in these designs.


    The third point only applies to me: I really need to build a bigger blower. My blower is a 5 gallon shop vac, and it is not quite enough for the Brute in this furnace.

    Richard
    You can improve the airflow by putting the vac close as possible to the furnace making the inlet tract as short as possible. Air has mass and pipework/ ducting produces friction and increases restriction. Convolouted hose is terrible for airflow efficency so if you aren't using smooth sideway inlet ( which it appears you are Rasper) getting rid of that will make a big difference. Also oversizing the inlet even if you have to downsize it again helps a lot.
    Taking the bag out of a shop vac helps airflow as does taking the motor off the bucket all together.

    Proper blowers are sooo much quieter than vac cleaners. Those things running for long give me the irrits!

  4. #4
    Just out of curiosity Rasper, how much room do you have between the crucible and the furnace wall? In my big furnace I can actually start it with no propane preheat by using a small (I'm talking a large double handful here...) of wood scraps. I light the wood scraps and let them get burning good, and then I turn on the oil feed. Note that the pile of scraps is directly in the path of the oil feed, so the oil lands on the glowing pile of coals. I can have the inside of the furnace up to high red in about 15 minutes or so. I have about 3 inches between the crucible and wall, and I'm using a B-30ish sized crucible. I couldn't do this with my old furnace, and it had much less space between the crucible and wall. My thought is that you need a lot of room to allow the oil to expand into a vapor, where with propane it can stand more restriction.
    Vade Libram Harenae.

  5. #5
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    What type of burner are you using oddDuck...?

  6. #6
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    Quote Originally Posted by OddDuck View Post
    In my big furnace I can actually start it with no propane preheat by using a small (I'm talking a large double handful here...) of wood scraps. I light the wood scraps and let them get burning good, and then I turn on the oil feed. Note that the pile of scraps is directly in the path of the oil feed, so the oil lands on the glowing pile of coals.
    I have done this many times and was the main way of starting my burners untill I got the idea of using LPG recently. That said, I lit a burner today like that. Bit of newspater in the bottom with some sticks that had fallen off the neighbours tree I am cooking the over hanging branches off with my burners and away it went. I have also used up all the old rags around the place which when oil soaked, light easily and provide a lot of heat as they burn off. Of course with the oil supply turned on low, they also wick it up nicely and make for a seamless transition to full tilt.
    A friend uses Charcoal with a small LPG torch to get it going a bit then adds the air which fans it up then hits the oil and off it runs as well.


    [/QUOTE] My thought is that you need a lot of room to allow the oil to expand into a vapor, where with propane it can stand more restriction.[/QUOTE]

    I don't find a lot of basis for this. In a burner you have a lot of incoming air and there is no pressureisation of the burner itself.
    Thinking about it with burners rather than furnaces, small burners are easier to light I find because of what I believe as I refered to earlier of the higher gas speed. A given amount of air will circulate round a smaller chamber faster than a larger one.
    Also with my Burners rather than furnaces, choking the larger ones with open tops rather than Nozzles down and containing the heat in the smaller area works well too. Least it did, I'm so familiar with the things now I can light them like a match but that took a lot of mis spent time and mucking around to learn!

    The oil changing state from a liquid to a gas would expand around 1500 times but even at that rate, I think the gas flow from the oil is still going to be insignificant to that coming from the air supply and again when the thing is at full tilt, the expansion of the superheated air is going to be significant as well.
    As it's all at atmospheric pressure, I can't see this being a problem. I'd tend to in fact think that a smaller area would make the mixing of the vaporised oil and the incoming air better and therefore give a better burn.

  7. #7
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    In my unauthoritative opinion, I believe there's a ton of over thinking it when it comes to drip type injectors. I purposely used the word "injector" because that's exactly what the brute configuration is. The furnace is the combustion area, and has zero difference to that of a diesel motor cylinder. It needs to be hot to vapourize the oil and ignite it. If that doesn't happen, it's not hot enough, done.

    What you usually do Glumpy is build burners, not injectors. Maybe I missed one or two in the mix, it's hard to keep up...lol.

    I'm as guilty as anyone who has tried too early to switch from preheat mode to full on burn with a drip. No super secret to correcting that problem. Just wait a few minutes longer. We could try and employ countless gadgetry to spd up that process, but if it were worth removing the simplicity then we'd just switch to nozzles and be done with it.

  8. #8
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    Glumpy, You are the man.

    I am going to try my Hot Shot burner in the big furnace instead of the Brute. (The Hot Shot is the same as the Brute except it is a one inch iron pipe instead of a 2 inch iron pipe.) The Hot Shot works miracles in my small furnace. Maybe the higher air velocity in the smaller pipe is the difference. And if it still isn't ideal, next will be a handful of scrap iron.

    Just out of curiosity Rasper, how much room do you have between the crucible and the furnace wall?
    More than 3 inches.

    if it were worth removing the simplicity then we'd just switch to nozzles and be done with it.
    You got that right. Once you get these drip burners set for the furnace it runs in there is nothing simpler or more trouble free. I use my large furnace so seldom I haven't got it tuned just right as of yet.

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  9. #9
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    Quote Originally Posted by J. Vibert View Post
    I\ It needs to be hot to vapourize the oil and ignite it. If that doesn't happen, it's not hot enough, done.

    What you usually do Glumpy is build burners, not injectors. Maybe I missed one or two in the mix, it's hard to keep up...lol.
    I certainly agree with the position of having the burner/ furnace/ combustion area hot enough. All the burners I build bar one work on this principal. If they didn't, I'd be needing to have high pressure air or fuel to atomize it. That requires air compressors or very high pressure pumps, neither of which endear themselves to me due to the extra complexity, cost of equipment and running costs involved. Sure they may be small but they are a lot greater than a gravity feed drizzle system.

    With practice, you can light these burners up with 100% reliability and speed. It just takes a bit of knowing them. The burner type I have been playing with recently is especially easy and quick to fire up. Add a bit of oil and a bit of starting fuel, Light it, go to full tilt on the air and start the oil and its running up to heat seamlessly in under 60 Sec. It still uses a system of drizzling the oil in with the airflow but its set up a different way to vaporise the oil and make sure it always has an over supply of air for clean combustion.
    Probably not a practical method for furnace use but could easily be adapted to fire into a furnace with the same results.

    The air flow is critical in a burner/furnace of this type at startup and a good preheat is essential. On my "conventional" burners I can go from start up idle to absolutely flat out after a suitable warm up. There is a vid of it on my YT of it doing just that quite spectacularly.

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