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Homework Help: Thermodynamics Combustion to find the air/fuel ratio

  1. May 14, 2012 #1
    1. The problem statement, all variables and given/known data

    A solid fuel supplied to a furnace had the following composition by mass.
    Carbon: 86%
    Hydrogen: 5%
    Incombustibles: 5%

    Dry volumetric analysis of the combustion products showed the flue gas contained 15%
    and 1.5% of CO2 and CO respectively. The test on the ashes discharged from the furnace
    found 0.01 kg of un-burnt carbon per kilogram of the fuel supplied to the furnace.

    Determine the air/fuel ratio by mass.

    ANSWER is 12.67 if this helps

    2. The attempt at a solution

    So firstly I write out the combustion equation:

    (0.86/12)C + (0.05/2)H2 + (0.06/32)O2 + 0.05ASH + Y(02 + 3.76 N2) = aCO2 + bH20 + d02 + fN2 + 0.05ASH

    Firstly is the combustion equation correct?

    When I equate the element atoms I have too many variables missing:

    O: (0.06/32)×2 + 2Y = 2a + b + 2d
    N: (3.76Y)×2 = 2f

    How do I calculate the value of Y and what do I do with the 0.01 kg of un-burnt carbon?

    I would very much appreciate any help with this question. Thank you.
  2. jcsd
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