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 0.6 Su (m/s) 0.5 0.4 0.3 0.2 0.5 bar 1.0 bar 2.0 bar Experimental Correlation 5.0 bar 0.1 0 0 5 10 15 20 25 Pressure (bar) (a) 0.7 tel-00623090, version 1 - 13 Sep 2011 Su (m/s) 0.6 0.5 0.4 0.3 0.2 0.1 0 0.2 0.15 0.5 bar 1.0 bar 2.0 bar 5.0 bar Experimental Correlation 0 5 10 15 20 25 Pressure (bar) 0.8 bar 1.0 bar (b) Experimental Correlation Su (m/s) 0.1 2.0 bar 0.05 5.0 bar 0 0 2 4 6 8 10 12 Pressure (bar) (c) Figure 4.36 – Comparison between experimental and correlated burning velocities of syngas-air stoichiometric mixtures at different initial pressures within the chamber. (a) updraft; (b) downdraft; (c) fluidized bed. 122
Chapter 4 A very good agreement between the correlation and the experimental burning velocity is found for every initial pressure test runs performed. Notice that for fluidized bed syngas the lower initial pressure with successful ignition was 0.8 bar. The maximum error of the burning velocity correlation is 8% for updraft syngas, 9% for downdraft syngas and 5% for fluidized bed syngas. These errors are perfectly reasonable and the discrepancy between syngas compositions errors has to do with experimental burning velocity scattering. 4.2. Multi-zone spherical combustion tel-00623090, version 1 - 13 Sep 2011 In an engine cycle, the heat losses could be endorsed 25% to wall-flame interaction and 75% to the wall-burned gases interaction (Boust, 2006). Therefore, robust heat transfer models of wall-flame interaction should be employed. A multi-zone numerical heat transfer simulation code developed at the Laboratoire de Combustion et Détonique for methane-air mixtures by Boust, (2006) is adapted herein to syngas-air mixtures. The code allows simulating the combustion of homogeneous premixed gas mixtures within constant volume spherical chamber centrally ignited. In spherical combustion conditions, the model could also be used for predicting the quenching distance. 4.2.1 Mathematical model 4.2.1.1 Flame propagation The flame is considered a perfect sphere without thickness. The propagation of the flame is imposed by its burning velocity that determines the thickness of the zone to burn during a predefined time Δt. The combustion is supposed isobaric, being the burning velocity S u given by the empirical correlation of Metghalchi and Keck, (1980) expressed by the Eqs. 4.16 - 4.18. The criterion that defines the end of combustion is the flame quenching distance. The quenching distance defines how close the flame approaches the wall and plays a definitive role on the wall-flame interaction as shown by Boust, (2006). The quenching implementation in the computational code consists of stopping the propagation of the flame when it approaches the wall in an equal distance to the frontal quenching distance δ q . In order to estimate the quenching distance, the correlation of Westbrook et al., (1981) is used: 123
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Experimental and numerical <strong>la</strong>minar syngas <strong>combustion</strong><br />
0.6<br />
Su (m/s)<br />
0.5<br />
0.4<br />
0.3<br />
0.2<br />
0.5 bar<br />
1.0 bar<br />
2.0 bar<br />
Experimental<br />
Corre<strong>la</strong>tion<br />
5.0 bar<br />
0.1<br />
0<br />
0 5 10 15 20 25<br />
Pressure (bar)<br />
(a)<br />
0.7<br />
tel-00623090, version 1 - 13 Sep 2011<br />
Su (m/s)<br />
0.6<br />
0.5<br />
0.4<br />
0.3<br />
0.2<br />
0.1<br />
0<br />
0.2<br />
0.15<br />
0.5 bar<br />
1.0 bar<br />
2.0 bar<br />
5.0 bar<br />
Experimental<br />
Corre<strong>la</strong>tion<br />
0 5 10 15 20 25<br />
Pressure (bar)<br />
0.8 bar<br />
1.0 bar<br />
(b)<br />
Experimental<br />
Corre<strong>la</strong>tion<br />
Su (m/s)<br />
0.1<br />
2.0 bar<br />
0.05<br />
5.0 bar<br />
0<br />
0 2 4 6 8 10 12<br />
Pressure (bar)<br />
(c)<br />
Figure 4.36 – Comparison between experimental and corre<strong>la</strong>ted burning velocities of syngas-air<br />
stoichiometric mixtures at different initial pressures within the chamber. (a) updraft; (b)<br />
downdraft; (c) fluidized bed.<br />
122
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