[ThomasS]

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.


Thomas

[mohammadakram]

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...

[ThomasS]

Thank you for the answer, Mohammad.

I think I solved the problem. Species transport won’t help me with the determination of the flame propagation though.
Since I don’t 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.

[isabel]

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?

[ThomasS]

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.

[carm]

Dear Thomas,

But how did you define the equivalence ratio of the mixture? Or does Fluent assumes is going to be 1?

[ThomasS]

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.

[Purushottam More]

HI,
I am a newer in premixed combustion. When I use the FLUENT to modeling, I am confusing about the premixed combustion using Zimout model in FLUENT. I can't find where can I specify the mixture(methane-air) equivalence ratio or about the mixture materials.
Anyone knows how to solve it ? Please help me. Thanks in advance! This question is confusing me several days!
Best regards!

[Heat80]

Originally Posted by Purushottam More

HI,
I am a newer in premixed combustion. When I use the FLUENT to modeling, I am confusing about the premixed combustion using Zimout model in FLUENT. I can't find where can I specify the mixture(methane-air) equivalence ratio or about the mixture materials.
Anyone knows how to solve it ? Please help me. Thanks in advance! This question is confusing me several days!
Best regards!

Hi,
In your case you need to edit air properties and input these values:
heat of combustion=50016000 j/kg (for methane air)
unburned fuel mass fraction =0.0552 (for methane /air equivalence ratio =1)
You can modify the laminar flame speed, cp, k, ..

Cheers
Younis Najim

[lem]

Originally Posted by Heat80

Hi,
In your case you need to edit air properties and input these values:
heat of combustion=50016000 j/kg (for methane air)
unburned fuel mass fraction =0.0552 (for methane /air equivalence ratio =1)
You can modify the laminar flame speed, cp, k, ..

Cheers
Younis Najim

Hi Heat80,

heat of combustion of methane (50016000 j/kg) based on lower (LHV) heating values 50.00 MJ/kg, is it right?

And I have a question, how can calculate laminar flame speed?

Thanks for your responds

[Raemakers]

Originally Posted by Heat80

Hi,
In your case you need to edit air properties and input these values:
heat of combustion=50016000 j/kg (for methane air)
unburned fuel mass fraction =0.0552 (for methane /air equivalence ratio =1)
You can modify the laminar flame speed, cp, k, ..

Cheers
Younis Najim

Hello,

I am a student and am new to this forum, because I have a problem I can't seem to solve. I am using ANSYS FLUENT to compute a turbulent combustion problem using the premixed combustion model in ANSYS. At the models section I used the premixed turbulent combustion model (in combination with the K-ebsilon model) with the C-equation. Also I want to compute the non-adiabatic case, where the walls are cooled to 300K with the Peters model.
I first tried the adiabatic case which runs correctly and the results seem to be correct. For the non-adiabatic case; after patching the progress variable to 1, the temperature shoots to 5000K immediately. I don't know where to look anymore, it feels like I checked all the options.

The entered values are:
Heat of combustion: 55000000 J/kg (methane-air mixture)
laminar flame speed: 0.35 m/s (computed with a 1D flame code)
unburnt fuel mass fraction 0.0499 (eq. ratio of 0.9)

the rest is left at the default values of air.

Does anyone recognise this problem or even better; know the solution to it?

Thanks in advance,

Raemakers

[Benaissa Sabrina]

Hi everybody,
I hope someone can help me with my problem. Thanking you in anticipation.
I need a method to calculate a combustion model (non premixed combustion PDF) and therefore I need the Rich Flammability Limit (RFL) Is this the same as the mixture fraction? What is the difference between them in the Fluent?
I read in the FLUENT documentation that the RFL for the ambient stream can be set to 1.
But what do I do with the RFL for the fuel stream?

[Abhishek_784]

Originally Posted by Raemakers

Hello,

I am a student and am new to this forum, because I have a problem I can't seem to solve. I am using ANSYS FLUENT to compute a turbulent combustion problem using the premixed combustion model in ANSYS. At the models section I used the premixed turbulent combustion model (in combination with the K-ebsilon model) with the C-equation. Also I want to compute the non-adiabatic case, where the walls are cooled to 300K with the Peters model.
I first tried the adiabatic case which runs correctly and the results seem to be correct. For the non-adiabatic case; after patching the progress variable to 1, the temperature shoots to 5000K immediately. I don't know where to look anymore, it feels like I checked all the options.

The entered values are:
Heat of combustion: 55000000 J/kg (methane-air mixture)
laminar flame speed: 0.35 m/s (computed with a 1D flame code)
unburnt fuel mass fraction 0.0499 (eq. ratio of 0.9)

the rest is left at the default values of air.

Does anyone recognise this problem or even better; know the solution to it?

Thanks in advance,

Raemakers

hey there!
I am doing deflagration to detonation transition in partially closed channels.
I am using premixed combustion model with c equation model and zimont model for turbulent flame speed closure.
I wanna know how did you input heat of combustion and unburnt fuel mass fraction, as i am not getting such option in materials.
Hope you reply!!!