mechanism for non-premixed methane air combustion
 

Hi.

I want to validate an experimental data about methane combustion with reactingFoam.

exactly I am trying to validate data given by " S. J. BROOKES and J. B. MOSS (Measurements of Soot Production and Thermal Radiation
From Confined Turbulent Jet Diffusion Flames of Methane )"

but I am new with openFoam and need your help. please tell me which combustion mechanism is better for a non-premixed methane and air.

I searched in web and found GRI mech 3.0. but I don't know this is for premix or non-premix ?

thanks.
Asadi.

No one can help ? :confused:

Well i do not know what version of openfoam you are currently using, but i suggest you start with the tutorial file, counterflowflame2d. It is located in the combustion tutorials and you can run a simulation with reactingFoam.

counterflow diffusion flame is a type of non-premixed flow and the current model in the tutorial uses CH4 as fuel and air as oxidiser.

GRI 3.0 mechanism is related to the chemical steps that occurs during the combustion and i think you can somehow upload a mechanism form other sources, such as CHEMKIN, but then again it is some you'll just have search for. reactingFoam uses ideal gas relations for species and mixtures.

You can inspect the geomtery and mesh and can create your own diffusion flame configuration, where you're gonna have to also change the boundary and initial conditions.

Hi Refik. thanks for your reply. :)

I am using openFoam 2.4.0 and trying to validate an experimental data As I noted in the first post. for the beginning I used the one step reaction given in counterflowflame2d tutorial but the result was not good at all and in temperature profiles there was a difference about 400 degree. I tried to change other settings such as schemes but No significant change occurred. so I think methane one step reaction is not accurate enough for this validation.
I found GRI mech 3.0 but it needs much time for convergence. because it solves 357 mechanism instead of one and yet I don't know GRI mech 3.0 is for premixed or non-premixed ??

can you tell me whether there is another mechanism with fewer reactions for non-premixed methane combustion?

thanks for your attention.
Asadi

Hi Asadi,

There is a skeletal mechanism for methane combustion, 17 species and 25 reactions.
you can search for Smooke and Giovangigli (1991).

success,
Xu

Hi.
thanks a lot huang. that was helpful.

now I have another question. I found a two step reaction but I don't know how I must define it in foamChemistryFile. here is the two step mechanism :

CH4 + 1.5O2→ CO + 2H2O
Parameters: A = 1.59e13 , Ea = 4.78e4 , [CH4 ]0.7 , [O2]0.8

CO + 0.5O2 = CO2
Forward rate parameters: A = 3.98e14 , Ea = 4.07e4 , [CO]1.0 , [H2O]0.5 , [O2]0.25
Backward rate parameters: A = 5×e8, Ea = 4.07e4, [CO2]1.0

please help me how I must define it with considering that second reaction has different parameters for forward and backward.

thanks.
Asadi.

Hi Asadi,

did you have any luck implementing the two-step mechanism? I would be interested in your result if you got it working.

Looking at the reaction file for the counterFlowFlame tutorial of reactingFoam, the pre-exponential is higher than any I have ever seen. My guess is that it is just using "fast" chemistry as it is a diffusion limited.

There is a second methane reaction file in the simplifiedSiwek tutorial for coalChemistryFoam which I am using now. I think the values are better for premixed combustion but am testing it now.

Also, does anyone recognize this global mechanism from simplifiedSiwek?

reactions
{
methaneReaction
{
type irreversibleArrheniusReaction;
reaction "CH4 + 2O2^1.0 = CO2 + 2H2O^1.0";
A 7e+06;
beta 0;
Ta 10063.8;
}
hydrogenReaction
{
type irreversibleArrheniusReaction;
reaction "H2 + 0.5O2^1.0 = H2O";
A 4.74342e+12;
beta 0;
Ta 10063.8;
}
}

I am just wondering if anyone knows the paper/textbook reference?

Thanks!