STARCD - inlet boundaries definition in combustion problem
I have a problem in defining a fuel consisting of a mixture of gases (CH4,CO,N2,CO2,H2), which enter in the combustion chamber each characterized by its own mass fraction.
The fuel enters from a single entry.
The solution gives me some problems:
- incorrect mass fractions for single gases
- incorrect values for pressure
How can i define the inlet boundary values for this fuel consisting of a mixture of gases, in order to introduce the gases mass fraction?
Define Boundaries->Scalar-Boundaries. Pick the inlet boundary region, pick the scalar, enter the mass fraction value & hit apply.
Or use the command rsmo.
i already tried to define inlet fuel boundary as you have suggested..
The simulation startes without problems but results are bad:
Are all your scalars "active" with temperatures dependent properties?
thanks so much for your help.
Yes, all my scalars are active with temperatures dependent properties.
But i think i have found the problem in defining boundary conditions - scalar boundaries: i must understand how to define the three variables "MIX_FRAC-FUEL_1", "MIX_FRAC-FUEL_2" and "MIX_FRAC-FUEL_3". These are three ‘passive’ scalars representing the mixture fractions of the leading reactants.
I have defined a 3-step reaction:
CH4 + 1.5O2 -> CO + 2H2O
CO + 0.5O2 -> CO2
H2 + 0.5O2 -> H2O
The composition (in terms of mass fractions) of the syngas is:
CH4 = 0.21
CO = 0.29
N2 = 0.05
CO2 = 0.38
H2 = 0.07
How can i introduce the values of MIX_FRAC-FUEL variables values?
And, in relation to this, how do i introduce the scalars mass fractions?
The mass fractions you provided add to 1. Where is the O2? Is it coming from a separate inlet?
As you stated, the passive scalars are the mass fractions of the leading reactants for each reaction equation. Since your inlet has no O2, I believe they all get set to 1.
The O2 is coming from a separate inlet.
So the passive scalars represeant the mass fractions of leading reactants for each reaction equation in relation to oxidant mass fraction.. So if the oxidant enters from a separate inlet, the scalar value is set to 1, right?
I try to apply your suggestion.
Thank you so much.
Do i also define CO2 as a reagent?
(when i define the three reactions, i put CO2[R] because if a product is transported into the solution domain from an external source, it also should be specified as a reactant)
Is it correct?
i tried to set passive scalars values to 1, but the solution diverges.. Can you explain the meaning of variables MIX_FRAC-FUEL? If the leading reactant (CH4) mass fraction of reaction 1 is 0.21, do i set the MIX_FRAC-FUEL_1 variable to 1.0 or to 0.21?
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