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Accueil du site > Thèmes de recherche > Combustion & systèmes réactifs > 1.5 Dynamique des flammes laminaires & turbulentes > 1.5.1 Laminar premixed flames

1.5.1 Laminar premixed flames Freely expanding spherical flames
One of the major fundamental properties of combustion is the laminar flame velocity, which despite its very straightforward definition must be carefully assessed. Among the different techniques, the outwardly spherical flame proves to be very valuable since the stretch at which the flame is submitted is perfectly known and can be then accounted for. ICARE has designed a high pressure spherical chamber that can be operated over a wide range of temperatures and initial pressures. The imaging of the flame propagation is used to derive SL° correctly and to detect the onset of flame wrinkling due to instabilities. In the framework of the ANR project PANH-HYDROMEL (2006-2010), the effect of methane addition to hydrogen / air mixtures has been investigated. Along with auto-ignition delay times (see §2.2.1) a detailed kinetic mechanism has been validated which can be applicable to safety assessment (ACL12, AFF68). The impact of the initial pressure on the flame propagation of methane-hydrogen air mixtures has been studied in the framework of the national program PIE CNRS « Hytag » (2005-2008). A collaboration with TOTAL aims at the determination of the effect of automotive fuel additives on laminar flame velocities for gasoline (ACL52, 58) and F1 racing cars (confidential project). A collaboration between ICARE, GREMI and the company CILAS is aiming at the development of a laser based ignition device in the case of biogas mixtures (Program Région-Centre 2008-2010). Counter flow flames
A facility allowing the study of flame propagation velocities in opposed jet flames has been developed. The flow field has been determined by particle imaging velocimetry and flame velocities as well as stretch rates have been extracted. Zero stretch rate flame velocities have thus been deduced. The set-up and the methodology were first validated using well known atmospheric pressure methane-air flames and then applied to premixed synga – air flames (TH33, AFF63, ACTI60, ACTI62). The same technique is also coupled to the determination of laminar flame thicknesses (or density/temperature gradients) using the laser induced Rayleigh scattering technique in the framework of an ongoing PhD thesis. Conical flames
In order to study the influence of CO2 addition on a methane-air flame we used the Bunsen flame (conical flame) configuration and compared several methods of extracting laminar flame propagation velocities. One method relies on flame cone area determination and the application of mass conservation principle. Another method uses the velocity field obtained by the PIV technique. The two techniques are also compared for syngas – air flames in cooperation with the Pennsylvania State Univeristy (TH33). Laminar flame stability domains with CO2 addition are also determined ; it is shown that high pressures allow obtaining stable flames at lower equivalence ratios (ACTI26, ACTI27, ACTI55, ACTI72).