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

Chapter 4
are tested and discussed. The numerical code described above is then used to
estimate the heat flux and quenching distance of syngas-air mixtures.
4.2.3.1 Influence of the heat transfer model
In order to define the heat transfer model to use, one first compare two formulations
already mentioned above: the classical Woschni (1967) correlation and the recent
Rivère (2005) formulation. The comparison of both formulations is made in the figure
4.39.
tel-00623090, version 1 - 13 Sep 2011
Pressure (bar)
7
6
5
4
3
2
1
0
Experimental P
Woschni P
Rivère P
Woschni Qw
Rivère Qw
0 10 20 30 40 50 60 70 80 90 100
Time (ms)
Figure 4.39 – Influence of the heat transfer model – stoichiometric downdraft syngas-air, P=1.0
bar.
From figure 4.39 is possible to conclude that the heat transfer model has only marginal
influence on pressure curve. However, the Rivère model shows to better follow the
500
400
300
200
100
0
Qw (kW/m 2 )
pressure curve on the cooling side. The reason is the higher value of the heat flux
through the wall using this model. This result is in agreement with Boust, (2006), who
compared these models with experimental heat flux values for methane-air mixtures
and concluded that Rivère model is most suitable to simulate the wall-flame heat
transfer and that Woschni model is inadequate in the absence of a strong flow. Thus,
Rivère model is applied throughout the following results.
4.2.3.2 Influence of equivalence ratio
The influence of the equivalence ratio in the burning velocity and pressure was
experimentally determined for the syngas compositions under study. It was seen that
the pressure and burning velocity decreases when departing from stoichiometric
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