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skherad March 5, 2006 13:45

Dear all, I am going to add N
Dear all,
I am going to add Nox prediction (zeldowich) to achen bomb.
Is it neccessary to edit the source code? (is it possible by just editing dictionaries?)
thank you for your time.

niklas March 6, 2006 03:11

This is a very weird question.
This is a very weird question.
You are going to add a NOx mechanism to
a case??? So will you be able to use it
on only the aachen bomb case then?

If you are planning to use dieselFoam,
then you will use the chemkin-interface and
in that case it has already been done.
If you look at the mechanism chem.inp_15
you'll find its already in there.

skherad March 6, 2006 04:45

Dear Dr Nordin Thank you for
Dear Dr Nordin
Thank you for your answer
I dont want to use mechanism like chem.inp-15 (I have used it and it worked).
I am going to use a one step reaction
a simplified Nox mechanism that d(NO)/dt depeneds on O2 and N2.
sorry for the weird questions(cases like achen bomb)

niklas March 6, 2006 05:01

Ok, so you do not want to use
Ok, so you do not want to use Zeldovich,
since you're planning to bolt on NOx to the
global fuel conversion rate.

Then I'd suggest you just
use 2 reactions in chem.inp.
one for the fuel conversion rate
and one for the NO, like
NO + NO = N2 + O2

skherad March 6, 2006 05:19

thank you very much. I will d
thank you very much.
I will do that and compare with complex mechanism.
than you

barane_iran September 30, 2013 13:54

how to calculate fuel nox in openfoam

flowAlways May 25, 2015 17:27

Hello everyone,

I would like to post-process NOx formation by considering only the global species concentrations for 1-step irreversible methane combustion.

From what I have understood and read I came to the following conclusion.
The formation of thermal NO_x according to the extended Zeldovich mechanism is given by
O + N_2 \rightleftharpoons  N + NO  \quad k_f^1 = 1.8*10^8 e^{-38370/T} \quad  k_b^1 = 3.8*10^7 e^{-425/T} \\

N + O_2 \rightleftharpoons  O + NO \quad  k_f^2 = 1.8*10^4 T e^{-4680/T} \quad  k_b^2 = 3.81*10^3 T e^{-20820/T} \\

N + OH \rightleftharpoons   H + NO \quad  k_f^3 = 7.1*10^7 e^{-450/T} \quad  k_b^3 = 1.7*10^8 e^{-24560/T} \\
with rate constants in m^3/mol-s

The rate of formation of [NO] is then given by
\frac{d[NO]}{dt} \: = \: k_f^1 [O] [N_2] +  k_f^2 [N] [O_2] + k_f^3 [N] [OH] - k_r^1 [NO] [N] - k_r^2 [NO] [O] - k_r^3 [NO] [H]

which under the quasi-steady assumption for [N] can be simplified to
\frac{d[NO]}{dt} \quad = \quad 2 \: k_f^1 \: [O] \: [N_2] \quad  \frac{\left(1-\frac{k_b^1 \: k_b^2 \: {[NO]}^2}{k_f^1 \: [N_2] \: k_f^2  \: [O_2]}\right)}{\left(1+\frac{k_r^1 \: [NO]}{k_f^2 \: [O_2] \: + \:  k_f^3 \: [OH]}\right)} \quad (mol/m^3-s)

with equilibrium concentration of [O] given by [O] = 3.97*10^5 T^{-1/2} e^{-31090/T}\: [O_2]^{1/2} mol/m^3
and the concentration of [OH] is given by [OH] = 2.129*10^2 \:  T^{-0.57} \: e^{-4595/T} \: [O]^{1/2} \: [H_2O]^{1/2} mol/m^3 using partial equilibrium approach.

Therefore, the concentration of [NO] can be obtained by solving the following scalar transport equation with \phi = [NO] and S_{[NO]} = M_{NO} \frac{d[NO]}{dt}
\underbrace{ \frac{\partial{\rho \phi}}{\partial t}}_{Transient \ term} +   \underbrace{ \nabla \cdot (\rho \vec u \phi )}_{Convection \ term}   =\underbrace {\nabla \cdot (\rho D \nabla \phi )}_{Diffusion \ term} +   \underbrace {S_{\phi}}_{Source \ term}\\

So, basically to successfully post-process NOx formation in OpenFOAM we need to solve the scalar transport equation for [NO] with a spatially varying source term which depends upon the concentration of [NO].
Can someone suggest a possible way of doing this. This is a non linear equation and would need to be solved iteratively. I want to implement this in OF but do not know where to start from. Any ideas please ??

flowAlways June 18, 2015 04:14

Hello, I have successfully implemented thermal NOx formation using scalarTransportFoam. The results are qualitatively very good when compared to Fluent, however quantitatively they differ by a constant factor. I am not able to understand where I go wrong. Any suggestions ??

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