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

Chapter 4
Sn (m/s)
3.0
2.5
2.0
1.5
1.0
0.5
Sn
P
2.5
2.4
2.3
2.2
2.1
Pressure (bar)
0.0
0 5 10 15 20 25
Radius (mm)
2
Figure 4.11 - Flame speed and pressure versus radius for stoichiometric downdraft syngas-air
mixture at 2.0 bar.
tel-00623090, version 1 - 13 Sep 2011
Sn (m/s)
0.8
0.6
0.4
0.2
0.0
Sn
P
2.12
2.10
2.08
2.06
2.04
2.02
2.00
0 5 10 15 20 25
Radius (mm)
Pressure (bar)
Figure 4.12 - Flame speed and pressure versus radius for stoichiometric fluidized bed syngasair
mixture at 2.0 bar
From figures 4.10 – 4.12 is not possible to observe the influence of cellular flame on
the mean flame speed. According to Bradley and Harper, (1994) the onset of instability
in a spherically propagating flame is associated with the surface propagation of
discontinuities in the flame structure that have the appearance of cracks. Moreover,
cells cannot form if their growth rate is smaller than that of flame expansion (Kwon et
al., 2002). Since the expanding flame suffers the strongest stretch during the initial
phase of its propagation when its radius is small, the tendency for cell development is
expected to increase as the flame propagates outwardly. These situations are more
clearly observed in the figures 4.13-4.15. In order to make the cellular flame effect on
flame speed observable a larger combustion chamber is needed.
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