[mkhm]

Dear foamers,

I want to define a new type of reaction rate coefficients in OpenFoam for my case. The source of inspiration could be the ThirdBodyArrhenius reaction rate of OpenFOAM (in src/thermophysicalModels/specie/reaction/reactionRate/thirdBodyArrheniusReactionRate/). Could you explain me how the reaction should look like when it comes to define the third bodies species ?

Like if I look at tutorial case of openFOAM for reactingFOAM solver in tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D/:
in constant/reaction, we have :

species
(
    O2
    H2O
    CH4
    CO2
    N2
);

reactions
{
    methaneReaction
    {
        type     irreversibleArrheniusReaction;
        reaction "CH4 + 2O2 = CO2 + 2H2O";
        A        5.2e16;
        beta     0;
        Ta       14906;
    }
}

so, lets say that I want to modify this reaction in the following way :

  1 species
  2 (
  3     O2
  4     H2O
  5     CH4
  6     CO2
  7     N2
  8 );
  9 
 10 reactions
 11 {
 12     methaneReaction
 13     {
 14         type     irreversiblethirdBodyArrheniusReaction;
 15         reaction "CH4 + 2O2 + M = CO2 + 2H2O + M";
 16         A        5.2e16;
 17         beta     0;
 18         Ta       14906;
 19         tbes     1.0;
 20         defaultEfficiency 1.0;
 21         M CO2/N2;
 22     }
 23 }

There are 2 questions :

First, if I remove the line 20, I would have an error saying there is no mention of defaultEfficiency. However, I don't see anywhere in src/thermophysicalModels/specie/reaction/reactionRate/ this parameter being defined. What is the difference between tbes (which stands for thirdBodyEfficiencies) and defaultEfficiency ?

Second, in thirdBodyArrheniusReactionRate there is no input named as M. The inputs are :

    

    const scalar A,
    const scalar beta,
    const scalar Ta,
    const thirdBodyEfficiencies& tbes

If I remove the line 21, the solver would not complain. Does that mean the OpenFOAM takes all the species mentioned in the species part as third bodies ? How about having only 2 species as third bodies ? Is that mention of third body in the reaction and after at line 21 correct ? Does OpenFOAM understand that it should take the M as N2 and CO2 ? How about having two different thirdBodyEfficiencies based on the third body's nature. like 0.9 for CO2 and 0.2 for N2. Should I define two separate reactions for treating these two cases ?

Thanks in advance for your help,

Best regards,

Mary


P.S.: I am using the version 4.x of OpenFOAM.

[niklas]

go to
tutorials/combustion/chemFoam/h2

run
chemkinToFoam chemkin/chem.inp chemkin/therm.dat chemkin/transportProperties chem.inp therm.inp

to convert chemkin format files to foam format.
check the chem.inp file and compare it with chemkin/chem.inp

so for instance this reaction in chemkin.
H+O2(+M)=HO2(+M) 4.52E+13 0.0 0.0 !MARINOV 1995A
LOW / 1.05E+19 -1.257 0.0 / !MARINOV 1995A
H2O/0.0/ H2/0.0/ N2/0.0/

converts to
un-named-reaction-3
{
type reversibleArrheniusLindemannFallOffReaction;
reaction "H + O2 = HO2";
k0
{
A 1.05e+13;
beta -1.257;
Ta 0;
}
kInf
{
A 4.52e+10;
beta 0;
Ta 0;
}
F
{
}
thirdBodyEfficiencies
{
coeffs
10
(
(H2 0)
(H 1)
(O2 1)
(O 1)
(OH 1)
(HO2 1)
(H2O2 1)
(H2O 0)
(AR 1)
(N2 0)
)
;
}
}

[mkhm]

Thanks Niklas. Your reply answers totally to my question and gives me enough insight to create the new type of reaction rate coefficients.