[Jewelry making - Article 00904] - Re: [Orchid] LPG Oxygen Ratio

[Richard Davies]

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Raakhi-

    I assume that you are referring to stoichiometric combustion of
    propane and pure oxygen. Stoichiometric means that all of the fuel
    is burned and there is no excess of either oxygen or fuel in the
    products of combustion. (Perfect combustion also requires perfect
    mixing within the burner, not necessarily always achieved in
    practice.) 

    In terms of moles, it takes 5 moles of oxygen to burn 1 mole of
    propane. Since at standard conditions a mole of gas occupies 22.8
    liters, one can make the inference that at equal conditions of
    pressure and temperature, it takes 5 volumes of oxygen to completely
    burn 1 volume of propane gas at whatever the ambient pressure and
    temperature may be. (This is part of the reason it takes a big
    bottle of oxygen to burn a much smaller bottle of propane.) The
    products of combustion are 3 volumes of carbon dioxide and 4 volumes
    of water vapor, also measured at standard conditions. 

    In the case of butane, it takes 13 volumes of oxygen to burn 2
    volumes of vaporized butane, again at equal conditions of
    temperature and pressure. The one additional carbon and two
    additional hydrogen atoms in the butane molecule need a lot more
    oxygen than is needed for propane. 

    In goldsmithing it may be necessary to adjust the flame to something
    other than stoichiometric conditions. If less oxygen is supplied,
    the flame will be reducing because the hot hydrogen and carbon tend
    to remove oxygen from anything in the flame. If excess oxygen is
    supplied, the flame will be oxidizing. 

Hope this helps.
Dick Davies
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