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Old   October 13, 2010, 09:02
Default Help whith Multi step combustion Model
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Matteo
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Hello everyone I have problems with the implementation of combustion models in CFX.
I'm trying now for a month to enter the coefficients of the models in 4 steps of reactions of Jones & Lindstedt and 5 steps of reactions Watanabe and Otak.
But I have problems with the early initiation of combustion in ducts, and if I do not know what to adjust the weightings of the EDM or the coefficients of the Arrhenius formula? Any advice is welcome
Thanks
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Old   October 13, 2010, 14:06
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Combustion is a science and sometimes an art as well.

If you prefer the last: what color has your flame and is it a fractal or smooth? Otherwise please tell the conditions (turbulent or laminar, premixed or non-premixed)
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Old   October 13, 2010, 19:04
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Thanks for giving me reply,
then my flame comes from a low NOx burner with diffusive mixing in two stages. the flow is turbulent with discrete component of swirl. As a model I'm using Eddy dissipation model, fine chemistry with a rate of flow field solver SSG Reynolds.
so far I have found similar results with the measured data with a 4-step combustion model developed by Jones & Lindstedt.
This model has been improved by Watanabe and Otaka which added a fifth equation to the CO taking it from the work of Westbrook & Dryer-Unfortunately, the data in the literature on this model are unclear and not by their inclusion in CFX results expected.
As for the Jones & Lindstedt model, the simulation shows a pre power supply lines in the secondary branch of CH4, which in reality does not, to guide my real situation I was advised to change the parameters A and B of the EDM may be a feasible way?
regarding the color of the flame do not know, because my only computer simulation tests, the burner is not physically present at my university.
Any advice is welcome, also because this work is my thesis
Thanks again
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Old   October 14, 2010, 15:24
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You are a Phd-student. Well, then, you should have a look at the complete set of transport equations your modelling. Write them down on a piece of paper or use tex. (Required in anyway for your thesis later on). Write the transport equation for each of the species with the source terms.

The reaction rate for premixed flames (for most hydrocarbons they are blue) is proportional to concentration of products. Now have a look what happens with the products of the first step in the second step? Right they are consumed and kill thereby the rate of the first step. The flame numerically extinguishes.

The non-premixed version is no solution. It will burn everywhere where reactants are mixed.

What is the solution? Depends on the objetives of your simulation .....
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