Etude de la combustion de gaz de synthèse issus d'un processus de ...

Experimental and numerical laminar syngas combustion
Pe
b
δ
35
0
ρ SC
q
−006
.
= = . P
(4.19)
λ
b u u pb
Where Pe b is the Peclet number and P the pressure in MPa. This correlation was
obtained for stoichiometric methane-air and methanol-air mixtures for pressures 1-40
atm. Recently Boust, (2006) shows that this correlation is also valid for lean (φ=0.7)
methane-air mixtures and stoichiometric hydrogen-air mixtures. For these reasons, we
shall use correlation (4.19) for syngas-air mixtures.
4.2.1.2 Chemical equilibrium
tel-00623090, version 1 - 13 Sep 2011
Gases can have two possible states, burned and unburned. The composition of the
burned gases is calculated by the Brinkley method, suggested by Heuzé et al., (1985).
This method is based on the determination of the free energy of Gibbs from the Gordon
& McBride, (1971) polynomials. The chemical equilibrium is calculated by canceling the
chemical affinity in the chemical reactions. It appeals to the thermodynamic properties
of the species instead of the equilibrium constants.
The combustion products considered are H 2 O, CO 2 , CO, O 2 , N 2 , NO, OH and H 2 . As
pressure and temperature conditions change during the compression and cooling
phases, is possible to previously recalculate the composition of burned gases.
4.2.1.3 Heat transfer
A common approach exploiting a combined convective and radiative heat transfer
coefficient has been implemented as representative of heat transfer through the
chamber walls, Q w . The formulation couples a convective-equivalent heat transfer
coefficient to a radiative term, for taking into account the effects due to high
temperature burned gases:
Qw = Qc + Qr
(4.20)
Where Q c and Q r represents the convective and radiative heat transfer, respectively.
The unburned gases in contact with the wall are heated by compression under the
effect of expansion flame. Due to the higher temperature of the unburned gases in
comparison with the chamber wall, which is at room temperature, they yield heat by
conduction. This conductive heat transfer is simulated using a convective model
(Boust, 2006).
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