Enthalpy conservation in 1D premixed flame

[Etienne Espada]

Hello everyone, 

I am curently doing 1D flamelet in CANTERA to create a look up table that account for enthalpy losses for tabulated chemistry purposes. I have a question on how is the enthalpy_mass property is calculated in CANTERA. Indeed, I am using cantera 3.1, and when I do a simulation (unity Lewis or multicomponent) the f.enthalpy_mass[0] and f.enthalpy_mass[-1] are not the same, in unity-Lewis-number transport, the enthalpy is not constant in the domain where it should be in order to conserve enthalpy. I understand that the energy conservation equation is written with the Temperature.

So I was wondering if the enthalpy_mass property is the sensible enthalpy (h=Cp*dT) or the Sensible + Chemical enthalpy (h=CpdT+\Delta h_f*Y_k) or the total enthalpy (sensible+chemical+0.5*u_i**2) ?

I am studying H2-air mixture but it appears to be the case also with CH4 and on various chemical schemes (boivin, h2o2.yaml, GRI, CRECK). 

I am also doing burner stabilized flames.

Thanks in advance, 

Best regards,

Etienne ESPADA

[Estevan Rezende]

Good mornign Etienne,
I would also like to know more about the enthalpy descriptions in this aspect, to better have a grasp on what each of the thermal variables available in the 1D flame module is actually preciselly calculating.
If i understood correctly about the "f.enthalpy_mass" and also "f.enthalpy_mole" it describes a vector of size [1 ; f.grid] and the corresponding enthalpy measure for each point, so by comparing "f.enthalpy_mass[0] and f.enthalpy_mass[-1]" you are comparing the first point on the grid and the last point on the grid, since an index of ´-1´ is the last entry in the vector.

Hope this helps!

[Etienne Espada]

Good evening, 

Thanks for the answer, I already knew that the enthalpy mass or mole or just enthalpy is a property of the flame so it can be accessible at each point of grid. My question is more related to the description/definition of the enthalpy that is used when enthalpy_mass flame member is called. In "unity Lewis number" transport formulation, the enthalpy should remains constant across the flame domain (which is not the case in mixture average/multicomponent because of demixing due to differential diffusion). However, 1D flame simulation in cantera shows that the enthalpy at the starting point (i.e fresh gas) is not the same at the exit of the flame grid (i.e. mostly equilibrium condition) with "unity Lewis number" transport model which should not be the case.

Thanks again in advance for looking at my issue, 

Best regards,

[Thorsten Zirwes]

The enthalpy from enthalpy_mass and enthalpy_mole is the (mass or mole) specific absolute mixture enthalpy (sensible + chemical) without kinetic energy. For a normal laminar flame, the kinetic energy should not really play a role. Here is a brief discussion about the enthalpy difference in 1D flames with Cantera: https://github.com/Cantera/enhancements/issues/187#issuecomment-1732407678

[Etienne Espada]

Thanks for forwarding this discussion.