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

Numerical simulation of a syngas-fuelled engine
Concerning hydrogen-air flames, the extensive experimental work done by Verhelst,
(2005) has been chosen for including the dependence on the air-fuel ratio,
temperature, pressure and residual burned gas content:
α
⎛T
⎞ ⎛ P ⎞
Su
= Su
⎜ ⎟ ⎜ ⎟ − f
0
T P
⎝ 0 ⎠ ⎝ 0 ⎠
β
( 1 γ )
(6.28)
Here, the reference conditions T 0 and P 0 are 365K and 5 bar, respectively. The
influence of the equivalence ratio at these conditions is embodied in S u0 and is
estimated at:
S φ φ φ
u0
3 2
=− 4.77 + 8.65 −0.394 − 0.296
(6.29)
tel-00623090, version 1 - 13 Sep 2011
The values for α, β and γ are the following:
α = 1.232
β = φ − φ + φ − φ <
3 2
2.9 6.69 5.06 1.16, 0.6
β = 0.0246φ + 0.0781, φ ≥ 0.6
γ = 2.715 −0.5φ
(6.30)
Where γ expresses the effect of residual gases. Verhelst and Sierens, (2007) selected
a residual mass fraction of 27% given the best correspondence for the pressure trace
during compression and maximum combustion pressure.
Concerning methane–air flames, the correlation expressing the laminar burning velocity
of Muller et al., (1997) has been adopted, since it is reliable for a wide range of
pressures and preheats temperatures:
0
0 m T ⎛
u
Tb
−T
⎞
Su
= A( T ) yF, u 0 ⎜ ⎟
T ⎝Tb
−Tu
⎠
0 ⎛ G ⎞
AT ( ) = Fexp
⎜ −
0 ⎟
⎝ T ⎠
n
(6.31)
Where, y F,u = (1+AFR s /φ) represents the mass fuel fraction in the unburned mixture,
AFR s is the stoichiometric air–fuel ratio;T 0 =-E/ln(p/B) is a representative temperature of
the inner layer, defined by Peters and Williams, (1987) as the thin layer within which
the first oxidation of methane into CO, hydrogen and water occurs; p is pressure, and
the fuel-dependent constants are equal to: B=3.1557×10 8 (bar), E=23873 (K),
F=2.21760×10 1 (cm/s) ,G=-6444.27 (K), m =0.565175 and n=2.5158.
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