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

Chapter 4
a minimum pressure to explore the burning velocity is doubtful because it corresponds
to different stretch rate values, as easily could be seen from figures 4.32-4.34.
Therefore, in this work, the criterion is a fixed stretch rate of 50 s -1 . For this level of
stretch, the stretched burning velocity is close to the unstretched burning velocity.
4.1.2.3 Laminar burning velocity correlations
The simultaneous change in the pressure and temperature of the unburned mixture
during a closed vessel explosion makes it necessary to rely on correlations which take
these effects into account like the one proposed by Metghalchi and Keck, (1980):
α
⎛T
⎞ ⎛ P ⎞
= ⎜ ⎟ ⎜ ⎟
⎝ ⎠ ⎝ ⎠
Su
Su
0
T
0 P
0
β
(4.15)
tel-00623090, version 1 - 13 Sep 2011
Where, T 0 and P 0 , are the reference temperature and pressure, respectively. The
influence of the equivalence ratio is incorporated through the temperature and pressure
exponents, α and β, and through the reference burning velocity S u0 as square or linear
functions.
Following the procedure described in the appendix A, this three unknowns are obtained
for the three typical syngas compositions and are shown in the table 4.3.
In all syngas cases the temperature coefficient is positive and the pressure coefficient
negative. This means that the burning velocity increases with temperature increase and
decreases with the increase of pressure. The stretch rate in these correlations is lower
than 50 s -1 . This means that these values of the stretched burning velocity are close to
the unstretched ones. Notice the different range of validity of the expressions with the
equivalence ratio and syngas composition. This is due to the unsuccessful ignition.
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