The absorption coefficient of the combustion products is highly dependent on the wavenumber as shown by line spectra of radiative gases (H O, CO and CO). To take into account this spectral dependency, the absorption coefficient of each species is here represented by the SNB-ck model [#!Sou97!#,#!Liu00b!#,#!Liu01!#]. For the gas mixture composed of different species, the same model is used, building data according to the mixing model exposed by Liu [#!Liu01!#]. The radiative solutions are obtained by computing independent calculations where is the number of narrow bands of spectral width , describing the spectral properties in the range , and is the number of the Gauss-Legendre quadrature points used for the spectral integration over each narrow band. For non-gray media, introducing spectral dependencies in Eq. (), gives for the source term :

(1.13) |

where is obtained from Eq.().

The computational efficiency of such a model is strongly linked to the number of bands , that has to be optimized depending on the studied case.

Other models called global models have been developed : WSGG (Weighted Sum of Gray Gas) [#!Sou94!#] and FS-SNBcK (Full Spectrum SNBcK) [#!Poi09!#].