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Gas Burner and Combustion Chamber Design

  1. Sep 20, 2015 #1

    EdY

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    Hi guys,

    I want to design a gas burner and combustion chamber.
    I use natural gas as fuel. I want to control air to fuel ration, so air flow has to control.
    I have an air compressor as air flow source.
    Clearly, it's needed a mixture tube before the combustion chamber.

    Now I have some questions.
    1. What is adequate speed in mixture? Absolutely low air speed in mixture cause combustion in mixture tube and high air speed cause turning down the flame in the combustion chamber.
    2. What is the standard ratio of combustion chamber diameter to mixture diameter?
    I know combustion happen in the combustion chamber instead of the mixture tube because of air speed in mixture and mixture diameter. Also, I know the combustion chamber diameter has to greater than the mixture tube diameter. But I don't know the minimum ratio of combustion chamber's diameter to mixture tube's diameter.
    3. How can I predict and control of flue gases speed in the exhaust?
    Actually, I can measure air flow and speed in mixture input valve, also for fuel. But I think gas flow and speed in the exhaust is greater than a mixture because of combustion's heat and volume increasing.
     
  2. jcsd
  3. Sep 23, 2015 #2
    What are you designing? A motor? A heater? Something else?
     
  4. Sep 26, 2015 #3

    EdY

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    I want to design a heater.
    The air to fuel ratio controlling is the most important future for this heater.
     
  5. Sep 26, 2015 #4
  6. Sep 27, 2015 #5

    EdY

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    The air to fuel ratio controlling is the most important future for this heater. So the input air must be controlled.
    Please see below picture.
    Gas Burner Sketch.jpg
    Actually I want to analyze exhaust gases in various air to fuel ratio.
     
  7. Sep 27, 2015 #6
    If your local mixture velocity is lower than your local burning speed, the flame will propagate upstream through your device. To prevent this, you must ensure either that at the flame holder the mixture velocity is always higher than the burning speed, or that the flame will extinguish (by cooling) when it travels through the flame holder. You can find estimates of laminar burning speeds and quenching diameters in most books on combustion physics/engineering (C.K. Law - Combustion Physics).
    The blow-off velocity is more difficult to determine because it depends on turbulence, flame-acoustics interaction and the geometry. You can find some estimates for flames like the Bunsen flame mentioned above.
     
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