Etude de la combustion de gaz de synthèse issus d'un processus de ...
Etude de la combustion de gaz de synthèse issus d'un processus de ... Etude de la combustion de gaz de synthèse issus d'un processus de ...
Experimental and numerical laminar syngas combustion 4.1.1.3 Flame speed Fig. 4.17 gives the stretched flame speed versus the flame stretch rate for three typical syngas compositions. Removing the parts influenced by ignition energy and high pressure at late stages of flame propagation. A linear correlation between the stretched flame speed and the flame stretch rate is found. The unstretched flame speed is obtained by extrapolating the line to κ= 0, while the gradient of the S n –κ curve gives the value of the Markstein length. tel-00623090, version 1 - 13 Sep 2011 The maximum value of syngas-air flame speeds is presented at the stoichiometric equivalence ratio, while lean or rich mixtures decrease the flame speeds. Downdraft syngas composition shows the highest flames speeds for all the equivalence ratios considered. The stretched flame speed increases with the increase of flame stretch rate for lean (φ=0.8) syngas-air mixtures. This behavior remains for stoichiometric and rich (φ=1.2) mixtures in the case of updraft and downdraft compositions. A remarkable decrease of the stretched flame speed versus the stretch rate is demonstrated for stoichiometric fluidized composition. This might result from the occurrence of incomplete combustion. Positive gradients of S n –κ curves are derived for three equivalence ratios in the updraft and downdraft syngas cases. A positive gradient of S n –κ curve is also shown by the lean fluidized syngas. These correspond to negative values of Markstein number, indicating the instability of flames. On the other hand, positive values of Markstein number indicate stability of flames of mixture combustion. These correspond to stoichiometric fluidized syngas. 102
Chapter 4 1.50 Sn (m/s) 1.25 1.00 0.75 0.50 0.25 0.00 3.0 2.5 φ =0.6 Updraft Dow ndraft 0 50 100 150 200 250 300 350 κ (s -1 ) φ =0.8 2.0 tel-00623090, version 1 - 13 Sep 2011 Sn (m/s) Sn (m/s) 1.5 1.0 0.5 0.0 3.0 2.5 2.0 1.5 1.0 0.5 Updraft Downdraft Fluidized 0 100 200 300 400 500 600 κ (s -1 ) φ =1.0 Updraft Downdraft Fluidized 0.0 0 100 200 300 400 500 600 700 κ (s -1 ) 3.0 2.5 φ =1.2 2.0 Sn (m/s) 1.5 1.0 0.5 Updraft Downdraft 0.0 0 100 200 300 400 500 600 700 κ (s -1 ) Figure 4.17 - Stretched flame speed versus stretch rate for syngas-air mixtures at various equivalence ratios and 1.0 bar. 103
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Chapter 4<br />
1.50<br />
Sn (m/s)<br />
1.25<br />
1.00<br />
0.75<br />
0.50<br />
0.25<br />
0.00<br />
3.0<br />
2.5<br />
φ =0.6<br />
Updraft<br />
Dow ndraft<br />
0 50 100 150 200 250 300 350<br />
κ (s -1 )<br />
φ =0.8<br />
2.0<br />
tel-00623090, version 1 - 13 Sep 2011<br />
Sn (m/s)<br />
Sn (m/s)<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
3.0<br />
2.5<br />
2.0<br />
1.5<br />
1.0<br />
0.5<br />
Updraft<br />
Downdraft<br />
Fluidized<br />
0 100 200 300 400 500 600<br />
κ (s -1 )<br />
φ =1.0<br />
Updraft<br />
Downdraft<br />
Fluidized<br />
0.0<br />
0 100 200 300 400 500 600 700<br />
κ (s -1 )<br />
3.0<br />
2.5<br />
φ =1.2<br />
2.0<br />
Sn (m/s)<br />
1.5<br />
1.0<br />
0.5<br />
Updraft<br />
Downdraft<br />
0.0<br />
0 100 200 300 400 500 600 700<br />
κ (s -1 )<br />
Figure 4.17 - Stretched f<strong>la</strong>me speed versus stretch rate for syngas-air mixtures at various<br />
equivalence ratios and 1.0 bar.<br />
103
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