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-   -   change equivalenceRatio (http://www.cfd-online.com/Forums/openfoam/79448-change-equivalenceratio.html)

sobhanEK August 24, 2010 10:08

change equivalenceRatio
 
Hi everyone.
I want to change equivalenceRatio in XiFoam.
I changed equivalenceRatio in combustionProperties file.
if I should change thermophysicalProperties datas?
Please someone help me.
Thanks.

rflats October 25, 2010 16:32

You can use adiabaticFlameT, which is in $FOAM_APP/utilities/thermophysical directory.

remir July 27, 2014 05:29

Hi, I know it's been a while since your post, but I was asking myself the same question : is changing the equivalence ratio parameter in combustionProperties enough, or should we change the Cp coeff in thermophysicalProperties as well?

As we can see in the XiFoam test case PitzDaily, with propane for fuel and air for oxydant, the thermophysicalProperties directory looks like this:

CASE 1

reactants
specie, thermodynamics, transport
products
specie, thermodynamics, transport

For the reactants, the molWeight coeff is equal to 29.4649, which corresponds to a 4% propane 96% air mixture, equivalence ratio of 1.

On the other hand, I found another type of directory, in which the following can be found:

CASE 2

fuel
specie, thermodynamics, transport
oxidant
specie, thermodynamics, transport
reactants
specie, thermodynamics, transport
products
specie, thermodynamics, transport
burntProducts
specie, thermodynamics, transport


For the reactants, the molWeight coeff is now 29.48 (4.1% propane 95.9% air). This is quite similar, but I must say that the results I obtain with the Pitz and Daily case are different in term of temperature for these two cases.

In the first one, the temperature (ER=1) is about 2300K
In the second one, same conditions, 1700K.

In both cases anyway, changing the equivalence ratio in the combustionProperties directory doesn't seem to affect the maximum temperature of the flow, but the recirculation length. (Someone had the same issue?)

I'm starting to think that the parameter "equivalence ratio" in combustion properties is only here to compute the GuldersCoeffs of the mixture air+fuel, and not the thermodynamic properties of this mixture. Indeed, I don't see how OpenFoam could calculate the Cp of the mixture if the only thing I give in thermophysicalProperties is the reactants and products thermo coeff for a specified equivalence ratio, as seen in the case 1. Again, I suspect I'm totally wrong on this, and blind regarding this matter, so if you get more info, please help me :)


I would be really interested in finding more about this solver (where is the temperature calculated exactly for example?), and in the different directories in general.


Best,

Remir


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