Gear-pump pressure nozzle burner

Discussion in 'Burners and their construction' started by PatJ, Jun 9, 2019.

  1. PatJ

    PatJ Silver

    I had seen some packaged pressure-style burner units being used in a backyard setting, but they were large bulky assemblies with a rather large burner tube.
    The I saw SV's video on making a Delavan siphon nozzle burner, and so I copied that design to some extend (I angled my combustion air tube, and did not use a propane line; you don't need propane).

    But I never saw anyone make a video or detail how to make and/or use a pressure nozzle in a standard size (about 2.5" diameter) burner tube.
    I think there was some discussion about it, but I don't recall any builds.
    So I did not really understand how they worked, how they differed from a siphon nozzle, or how to control the fuel flow.

    I think I have it figured out, and have a good start on the gearpump/motor assembly.
    You need a supply and a return fuel line, and a valve somewhere in series, and the output of the nozzle is controlled by how much you allow to flow back to the fuel tank.
    I have read that you need a pretty good fuel line to handle the pressure.
    I think I went with injector-grade fuel line.

    I will finish mine some time this year and give it a test.
    Boy the things I would have done differently had I known then what I know now.

    Edit:
    If your diesel burner is adjusted correctly, the burn is perfectly clear, and there is no odor or smoke.
    For sound, I put two layers of rubber mat under each wheel of my furnace, to break the low frequency coupling with the ground. That helps prevent the rumbling sound being transmitted everywhere.
    Even with the rubber mat, there is still some noise, and if you are in an extremely quiet area, you may have to resort to a melterskelter exhaust muffler.

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    Last edited: Jan 24, 2020
  2. Hi Dazz, I'm currently using a gear pump to pressurize spray nozzles and have melted up to 15Kg of iron in about an hour from cold to poured in the molds with diesel and kerosene fuel. Pressure only nozzles have a limited range of throttling after which the spray droplet size increases as the pressure goes down which is a disadvantage compared to the compressed air assisted nozzles. I found a commonly available "mist" spray nozzle made from brass and stainless which has no polymer seals to melt and has a 3 litre per hour flow rate at 60 PSI, this allows you to roughly set the flow rate in 3 litre per hour increments and lets you use a brass needle valve for finer flow adjustments. I currently use 8 nozzles for 24 litres per hour maximum and set for 20 litres/hour with kerosene fuel. Kero has less BTUs than diesel and sump oil so I need a higher burn rate : if I recall correctly it burns about 33% more BTUs per kilo of iron melted than a furnace running diesel fuel. Bunning hardware sell the brass mist nozzles with a 3/16" thread and they are also available very cheaply on Ebay too.

    I think it would be possible to make a new type of pressure spray nozzle with an axial needle valve that can seat at the nozzle opening so as to vary the nozzle hole aperture without interfering with the swirl channels behind the nozzle hole.


    nozzle assembly.jpg


    nozzle assembly 2.jpg


    air nozzle assembly 1.jpg
     
    Last edited: Jan 24, 2020
  3. PatJ

    PatJ Silver

    According to the Delavan white paper, a single Delavan pressure nozzle has at least a 4:1 range (maybe more) where atomization is acceptable.
    I have not used a pressure nozzle yet, but I believe the 4:1 ratio (blind faith I guess).

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  4. Dazz

    Dazz Copper

    Hi
    Positive displacement pumps, like gear pumps, need the output to go somewhere.

    A gear pump fuel circuit should:
    1. start with the fuel tank
    2. suction line from the tank to the fuel pump intake
    3. pump output to a filter.
    4. Filter output to the burner jets and the input to a pressure regulator valve
    5. Output of the regulator returns to the fuel tank.

    Note the pressure regulator valve controls the input pressure, not the output.
    Every fuel injected car I know of uses this fuel circuit.

    Dazz
     
  5. PatJ

    PatJ Silver

    I looked at a lot of literature, and I must say it was quite confusing for a long time.
    I am pretty certain at this point (but not entirely certain) that a pressure regulator is needed.

    My logic is as follows:

    1. You don't need a return line to the fuel tank, you can simply deliver rated pump pressure and flow to the nozzle, and it will output that amount of fuel.
    My pump is rated at 7 gal/hr at 100 psi, and that is the setting that I will be running it at.

    2. If you were feeding two nozzles in parallel, you would still have 100 psi to each nozzle, but the flow would be 3.5 gal/hr to each nozzle.

    3. If you changed one of the two nozzles to a needle valve that is adjusted correctly, and pipe it back to the fuel tank, then you will have 3.5 gal/hr flowing out one nozzle, and 3.5 gal/hr flowing back to the fuel tank.
    The needle valve I assume will introduce enough impedance into the circuit to keep the pressure at 100 psi.

    4. If you open the needle valve fully, almost all the 7 gal/hr will flow back to the fuel tank.

    5. If you vary the needle valve opening, you should be able to vary the flow to the nozzle from zero to 7 gal/hr.

    I don't see the need for the pressure regulator.
    A Suntec pump already has a pressure regulator built into it, and it will maintain the pressure at its setpoint.
    You can adjust the output pressure upwards by turning a screw on the pump, and get 3 gal/hr at 160 psi, or anywhere in the range of 3-7 gal/hr, 100-160 psi.
    I am going to operate my unit at 100 psi.

    So place your bets now folks.
    Will it work without a pressure regulator in the circuit, and work with just a needle valve in the return line?
    My money is on the needle valve in the return line.
    Do I win a major award if I am right, like a new car or something?
    Will I have to shave my head and move out of town if I am wrong? My hair is pretty thin anyway, so probably no big deal; and we have a very high crime rate, so any city with a lower crime rate will be a plus.

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  6. rocco

    rocco Silver

    There are a few automotive fuel injection systems that have no regulators, I think they use a PWM circuit to modulate the fuel pump pressure. I had a 2007 VW with that type of filter, they come with either a 4 bar or 6 bar regulator, such a filter might be convenient for a pressurized oil burner system.
     
  7. PatJ

    PatJ Silver

    I guess if you are adopting an automotive type system, then you go with however that is set up, but for a Suntec gear pump, the fuel pump output pressure is fixed.

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    joe yard likes this.
  8. Dazz

    Dazz Copper

    If you feed two nozzles at 7 gal/hr, pressure will be 50psi for a flow of 3.5 gal/hr each.

    You would be using a needle valve to do the job of a regulator.

    I don't know what a Suntec pump is but it sounds ideal if you don't need to change the fuel pressure. Does that mean you would simply adjust the air flow?
     
  9. joe yard

    joe yard Silver

    hydro.png
    The diagram is of a correct hydriolic setup. If the regulator is in the pump no return line is needed. If the nozzle in use is to large even though there is an available PSI at a given flow that pressure will not be reached. Think of a garden hose with a sprayer. If the sprayer is closed or partially open allowing a flow that does not exceed the supply at pressure the pressure in the hose is that of the supply. If the sprayer is removed and the hose is open it will supply the maximum of fluid with a very low pressure. The pump should have more output volume than the load requires. With your pump having the regulator on it no return is needed. You will have the desired pressure as long as the load is restrictive enough to cause sufficient back pressure if not the load will have max volume pressure determined by back pressure rather than the regulator. my vote is yes it will work but possibly not quite as expected.
    Joe
     
    Mark's castings likes this.
  10. PatJ

    PatJ Silver

    I am not a hydraulics guy, but the pump delivers 100 psi into a header (fuel line), and so that line will be at 100 psi whether you have one or more nozzles ?
    Or does adding nozzles remove the resistance to flow to the point that the pressure drops?
    I don't know honestly; this stuff is new to me.

    You have to go back to page 1 of this thread to see the Suntec pump info, and see my pump/motor setup.

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  11. PatJ

    PatJ Silver

    I generally use electrical circuit logic, and then apply that to fluid dynamics.

    So voltage is pressure, and resistance is the resistance to flow that the nozzle introduces.
    Amperage is fuel flow.

    So in a series connection of two nozzles, then you divide the output (7 gal/hr) across the two nozzles, and drop half the pressure across each nozzle, but the circuit is operating at 100 psi.

    For a parallel circuit, you tee the fuel line, and take it to both nozzles.
    For a parallel circuit, you will have 100 psi at each nozzle.

    With the return line blocked, I would think either parallel or series connections would produce the same results.

    Only one way to verify, and that is to get some quick connectors and a couple of nozzles and give it a try.
    The pump has a pressure gauge on it, and so you will see the output pressure, but it will be 100 psi because that is what the pump outputs.

    No time now to get out to the shop and get it hooked up, unfortunately, but I will try it this year and post the results here.

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  12. That's the arrangement I have except for the regulator return is plumbed back to the pump intake. This eliminates the need for a return line to the fuel tank and means you're feeding the pump with already filtered excess fuel rather than returning it to the tank. It also warms the fuel to about 50-60 degrees C which would be handy with thicker fuels.


    Hi Pat, based on experiments with a series of pressure fed nozzles, that 4:1 ratio is possible but the droplet size increases drastically and large droplets are slower to vaporize and burn. Page seven of the "Fuel nozzles for burners" document you attached earlier mentions using 2 or three smaller nozzles if fine droplet size and improved combustion is desired. The car industry would love to have a linear variable injector nozzle but are using on-off PWM modulation as that's the only way to get fine spray AND vary the volume delivered (for car engines which can't use compressed air nozzles). This is simply due to the reduced pressure at the nozzle aperture means less swirl in the nozzle, you can see atomization get worse at the 36 second mark as the fuel to the nozzle gets valved off:

     
    Last edited: Jan 24, 2020
  13. PatJ

    PatJ Silver

    I had forgotten that you had a pressure nozzle rig setup.
    Plumbing the return line back to the pump intake seems like a good idea, and would prevent the return fuel from heating up the entire fuel tank, which I have heard can sometimes be a problem.

    I will have to study your rig and see if I can make sense of it.

    I feel like I have a good understanding of siphon nozzles.
    I am still in the learning curve on pressure nozzles.
    Thanks for the link to the video.
    That's a big help.

    Edit:
    I am not positive, but it seems like larger droplets produced a hotter furnace, as long as the droplets don't start puddling in the bottom of the furnace.
    I guess a Suntec pump could be run at both the lower 100 psi setting, and the higher psi setting, with two iron melts of the same size, on the same day, at the same ambient temperature.

    I am not convinced that the smallest droplets produce the hottest flame.
    Perhaps once the furnace is red hot, then it would make little difference, but like the white paper about the pulsed fuel pressure, it furnace may not run hotter, but you may save 30% on fuel usage.

    Not sure if there would be a measurable difference, but it would be an interesting test.

    Edit02:
    So who has an idea about how to pulse the fuel pressure?
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    Last edited: Jan 24, 2020
  14. As far as I can see, a pump can only pump a fixed given volume (all other things being equal), so plumbing the regulator return back to the pump intake rather than the fuel tank just removes the fuel tank from the circuit and means the filtered fuel doesn't go back into the fuel tank .
     
  15. PatJ

    PatJ Silver

    Any ideas?

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  16. It's not a matter of droplet size correlating with furnace temperature but it does correlate with speed of burning, if you can burn fuel faster you can achieve a hotter furnace all other factors being equal. Page 7 of the PDF "Fuel nozzles for burners" you posted mentions using "two or three nozzles instead of one to improve combustion" with the resulting smaller droplet size that smaller nozzles give. Smaller droplets maximizes surface area for a given volume of liquid fuel so that heat can vaporize it faster, prior to burning.

    My furnace has some design issues with it but it's the only example of an iron melting oil fired furnace with a positive displacement pressure pump / pressure nozzle combo that I'm aware of. It currently gets 15 kilograms/32 lbs of iron liquid in 45 minutes run time. Not all of that is due to fine droplet size but it's a significant factor.

    Edit: oil burns so much slower than say propane that you have to pull every trick in the book to get it to burn at higher rates than normal.
     
    Last edited: Jan 24, 2020
  17. PatJ

    PatJ Silver

    Last edited: Jan 24, 2020
  18. PatJ

    PatJ Silver

    I can't recall anyone using a pump/pressure nozzle to melt iron other than yours, and I am not sure I was aware that yours melted iron.

    Seems like I last recall your spinning burner.

    Its hard to keep up with who builds what, and where they live.

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  19. PatJ

    PatJ Silver

    I went back and re-read this thread from the beginning.
    I had forgotten what had already been posted.
    Seems like I am posting duplicate stuff at this point.

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  20. PatJ

    PatJ Silver

    Here is the inside of a gear pump.
    Hope I did not already post this.

     

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