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

Conclusions
radius and time for syngas–air flames. The maximum value of syngas-air flame speeds
is presented at the stoichiometric equivalence ratio, while lean or rich mixtures
decrease the flame speeds. Tendency observed on the unstretched burning velocity is
in agreement with the heat of reaction of the syngas composition. The higher heat
value is associated with the higher amount of H 2 and lower dilution by N 2 and CO 2 in
the syngas composition. Markstein numbers shows that syngas-air flames are
generally unstable. Karlovitz numbers indicates that syngas-air flames are little
influenced by stretch rate. Based on the experimental data a formula for calculating the
laminar burning velocities of syngas–air flames is proposed,
S =− 0.8125φ + 1.6375φ
− 0.5725
(Updraft)
0 2
u
S =− 0.7313φ + 1.5428φ
− 0.4924
(Downdraft)
0 2
u
S =− 0.7500φ + 1.5450φ
− 0.6210 (Fluidized bed)
0 2
u
tel-00623090, version 1 - 13 Sep 2011
for updraft, downdraft and fluidized bed syngas–air mixture combustion, respectively.
When compared with common gas fuels like methane and propane, the laminar
burning velocity of typical syngas compositions shows to be similar to that of methane,
especially the downdraft syngas case, although somewhat slower than propane. This
could be due to the syngas stoichiometric air–fuel ratio that is ten times lower than the
methane air-fuel ratio and more than twenty times in the case of propane. Thus, the
energy content per unit quantity of mixture (air + fuel) inducted to the chamber is only
marginally lower when using syngas, compared with the corresponding common gas
fuels. The values of laminar burning velocity reported for simulated syngas can be seen
to be higher than those obtained for typical syngas compositions. The simulated
syngas mixture that better matches the magnitude of laminar burning velocity for the
typical syngas compositions is the mixture comprising 5%H2/95%CO.
In order to determine laminar burning velocity at elevated pressures relevant to engine
applications, the constant volume method was used. Based on the experimental data
α
β
obtained, empirical formulations of the form Su
= Su0( T T0) ( P P0)
have been establish
for pressure range 0.75-20 bar and temperature range 293-450 K tanking into account
the stretch effect. The influence of the equivalence ratio is included through the
temperature and pressure exponents, α and β, and through the reference burning
velocity S u0 as square functions for updraft and downdraft syngas compositions and as
a linear function for fluidized bed syngas due to the limited possible data:
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