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

Chapter 4
Figure 4.5 shows schlieren flame images of fluidized bed syngas-air mixture. Rich
mixture (φ=1.2) is not shown due to unsuccessful ignition. For the lean mixture with
φ=0.6, the flame speed is remarkably slow being gravity effect felt making the flame to
propagate to the bottom of the combustion chamber. Also in this case, stoichiometric
mixture is the faster one. The low flame speed of this syngas composition is highlighted
in the figure 4.6, in which the pressure rise is also lower than its homologous, 0.01 bar.
In opposite, the radius to work out could be extended to 20 mm due to no significant
pressure rise keeping the flame a spherical pattern. However, due to coherency the
radius range to burning velocity determination was kept between 6-18 mm.
tel-00623090, version 1 - 13 Sep 2011
Figures 4.7-4.9 show schlieren flame images of syngas-air mixtures at 2.0 bar and 293
K. Spherical expansion of the flame was found only in the cases of stoichiometric
mixtures and rich mixtures of updraft and downdraft syngas. In all cases a cellular
flame structure was observed. Indeed, it can be seen from the figures the
transformation of the smooth spherical flame front to the polyhedral flame structures
which increase the surface area of the flame front. The increase in the surface area
leads to a sudden increase in the flame speed and any inclusion of these data points
would lead to higher burning velocity predictions (Saeed and Stone, 2004).
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