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Modelling of premixed combustion in a burner rig

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Old   June 22, 2011, 14:26
Default Modelling of premixed combustion in a burner rig
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Thomas
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Hello,

I am a newbie in CFD and need some help of experienced users.

I want to model a burner rig with premixed combustion of a methane-air mixture (Fluent 12). Both adiabatic and non-adiabatic combustion is to be investigated.
The mixture within the vessel should be perfectly premixed prior to ignition (no fuel inlets or injections etc.).

Which combustion model would be appropriate for determination of the turbulent and laminar flame speed? I don’t need species distribution though.

If I use the Zimont premixed model, I don’t know how to specify the equivalence ratio (not even how to specify the mixture; I only include air and methane into the material menu item).

If I use the partially premixed model, I can set the (by-hand) calculated mixture fraction (and hence equivalence ratio) but it seems like I would have two inlet streams (oxidizer and fuel) since I have to define both. But in my case the fuel is already mixed inside the domain and flame propagation starts as the spark (hot surface) goes off.

Can I use the approach “species transport” for combustion related problems? Will it be possible to set the equivalence ratio?

If anyone can help, I would be extremely grateful.


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Old   June 28, 2011, 03:38
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Mohammad Akram
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Species transport might work in your case....just gv Ych4 = 0.055 Yo2 = 0.220267 in inlet BC....plz reply if u got the ans...
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Old   June 29, 2011, 04:49
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Thank you for the answer, Mohammad.

I think I solved the problem. Species transport wonít help me with the determination of the flame propagation though.
Since I donít have any mass flow inlet etc. and the mixture is premixed before the ignition, I only use the premixed option in Fluent. I am starting with the Zimont model now. This model calculates the turbulent flame speed based on the specified laminar burning velocity only. This speed you have to define (based on experimental data for your particular mixture or by numerical approximation, like after Peters).
In a few days I will know whether this model is appropriate for solving the problem and whether it generates proper results.
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Old   August 23, 2011, 06:50
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isabel
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Dear Thomas,

What expression are you using for laminar flame speed?

The Fluent manual recommends the correlation of Meghalchi and Keck for non-adiabatic premixed or partially premixed flames. Is it accurate enough?
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Old   August 23, 2011, 07:13
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Dear Isabel,

I never used the model after Meghalchi & Keck. As I am interested in the determination of the turbulent burning rate and have access to experimental laminar burning velocities, I set ul as a constant.
When the laminar flame experiences turbulence it will directly derive the turbulent burning rate in the course of the Zimont model.
Hence, I cannot evaluate the deviation between M&K.-model and the experimental obtained values.
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Old   September 19, 2011, 17:00
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Camilo
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Dear Thomas,

But how did you define the equivalence ratio of the mixture? Or does Fluent assumes is going to be 1?
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Old   September 20, 2011, 03:13
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Dear carm,

you can try to set the equivalence ratio by adding a new fluid with the particular mixture in the material property section.
The properties of a certain mixture, like thermal conductivity, density etc., may be calculated with programmes like GASEQ (http://www.c.morley.dsl.pipex.com/) or programmes from other institutes.
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