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

Chapter 4
10000
Quenching distance (10 -6 m)
1000
100
10
Updraft
Dow ndraft
Methane
1
1 10 100 1000
Pressure (bar)
tel-00623090, version 1 - 13 Sep 2011
Figure 4.51 – Quenching distance estimation for stoichiometric syngas-air mixtures and
comparison with stoichiometric methane-air mixture (Boust, 2006).
Figure 4.51 also includes quenching distance of stoichiometric methane-air mixture for
comparison reasons. The following correlation determined by Boust, (2006) was
adopted δ q =50 P -0.45 (P>3.0 bar) with P in Mpa and δ q in μm. One can conclude that
quenching distance decreases with the increase of pressure and is higher for lower
heating value mixtures.
The following correlations are developed for stoichiometric updraft and downdraft
syngas-air mixtures, similar to the one presented by Westbrook et al., (1981) and
Boust, (2006) for methane-air mixtures:
δ q =450 P -0.79 , P>0.3 MPa (Updraft) (4.28)
δ q =300 P -0.89 , P>0.3 MPa (Downdraft) (4.29)
With δ q in μm and P in MPa.
4.3 Conclusion
Laminar flame characteristics of three typical syngas compositions were studied in a
constant volume chamber for various equivalence ratios. The influence of stretch rate
on flame was determined by the correspondent Markstein and Karlovitz numbers.
Combustion demonstrates a linear relationship between flame 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.
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