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one-step reaction mechanism of hydrogen/methane

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Old   July 30, 2004, 01:14
Default one-step reaction mechanism of hydrogen/methane
  #1
Sheng Chen
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Hi,everyone, I am now simulating premixed laminar flame. The fuel is hydrogen or methane and the oxidizer is air. But I can not find their one-step reaction mechanism. Could you tell me? Thanks a lot!
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Old   July 30, 2004, 02:28
Default Re: one-step reaction mechanism of hydrogen/methan
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matej
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the best reference would be:

Westbrook Ch., Dryer F.L., Chemical Kinetic modeling of Hydrocarbon Combustion, Prog.Energy Sci.,1984,vol.10, pp 1-57

for the immediate kick-start, here is what he says:

for CH4 + 2O2 -> CO2 + 2H2O

and rate= A*T^n *exp(-Ea/RT)* [CH4]^a * [O2]^b

the values are:

A=1.3e9 [s^-1]; Ea= 48.4 [kcal/mol];a=-0.3;b=1.3 for eq. ratio from 0.5 to 1.6.

you may find the values for A warying at some references and sources.

do not forget the limitation of this single step chemistry!

matej
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Old   July 30, 2004, 23:38
Default Re: one-step reaction mechanism of hydrogen/methan
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Sheng Chen
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Hi, matej, Firstly thanks for your message. There is a question about the single step reaction that what does n mean in the formula.
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Old   August 2, 2004, 16:47
Default Re: one-step reaction mechanism of hydrogen/methan
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Dean
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As I recall, n=0 for the Westbrook-Dryer rates, but check the paper to be sure.

Also, be aware that these rates can produce flame simulations that are not very accurate. Just look at the flame speed vs equivalence ratio plots in the paper. Also, post-flame temperatures come out high if you don't account for the fact that the products contain dissociation products of water and carbon dioxide, such as CO and OH. There is also a problem with the negative exponent on the fuel concentration under lean conditions, the rate goes to infinity as the fuel is depleted. This is not physical. User beware!
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Old   August 3, 2004, 03:26
Default Re: one-step reaction mechanism of hydrogen/methan
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matej
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Dean is right. n=0 for wesbrook.

What you can test with is pre-exponential factor A. YOu can fix with this the laminar flame speed. You should definetelly test it with your code to compare the flame speed with the literature, preferebly cited westbrook article. The solution will be sensitive to the discretisation scheme you use.

matej

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