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Old   November 13, 2002, 07:05
Default heat of combustion
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nick
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Hi,

I am trying to model premixed turbulent combustion of a mixture of air and natural gas. The calculation is non-adiabatic and I am asked for the heat of combustion in (j/kg) for burning 1kg of fuel. Does anyone have a value for this or know of where I can get this information?

Nick
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Old   November 13, 2002, 08:52
Default Re: heat of combustion
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Sim
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Hi, It depends on the NG, i.e. where it's from. NG is basicly CH4 (95%) so between 49.6 MJ/kg and 44.8 MJ/kg should be the trick. The values are for French and Russian Natural Gas.

Sim
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Old   November 13, 2002, 11:45
Default Re: heat of combustion
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Volker
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Hi,

You can calculate the heat of combustion using Hess's Law (The difference between the sums of the standard enthalpies of formation of the products and the reactants equals the heat of reaction). You need the stoichiometry of your combustion reaction and the standard enthalpies of formation of the participating species (you should find those in every thermodynamics text book).

Regards,

Volker
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Old   November 13, 2002, 12:29
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nick
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Have you had any experience using the premixed turbulent combustion model in Fluent? This is the approach that I am using, however, I find I have an over prediction of temperatures and little to no flame stretch effects with the values provided by the fluent manual. Any idea's?
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Old   November 13, 2002, 18:08
Default Re: heat of combustion
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Dean
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Heat of formation for a variety of gases is available on-line. Check some of the sources discussed in this forum, Cp & gamma for hydrogen, beginning Oct. 28.

As for your temperature problem, how much detail are you including in your chemistry? If it is just fuel + O2 = CO2 + H2O, you will overpredict the final temperature compared to experiments. The reason is that a significant amount of material is left as CO, H2, H, OH, etc. at typical post-flame temperatures. Single-step kinetics is well-known to overpredict the post-flame temperature unless you fudge the heats of formation. A better approach is to use more detailed chemistry since single-step kinetics has other accuracy problems as well.

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Old   November 15, 2002, 06:17
Default Re: heat of combustion
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Tom
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I have had the same kind of problems using the premixed combustion model recently so if you find a solution please let us know.

Thanks
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Old   December 2, 2002, 11:54
Default Re: heat of combustion
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Stas
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Hi, As for me, I think it must be compromise between detailed chemistry and computer resources. For detailed combustion chemistry should have your Cp/Cv, viscosity, thermal conductivity etc. as functions of temperature (and some times pressure). Does any body have an experience in real-gas modeling?

BR,

Stas
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