Turbulent mixing and reacting flow characteristics of axisymmetric bluff-body stabilized propane-air flames, under inlet mixture stratification and preheat

• Κύριος συγγραφέας: Σούφλας, Κωνσταντίνος
• Άλλοι συγγραφείς: Κούτμος, Παναγιώτης
• Μορφή: Thesis
• Γλώσσα: English
• Έκδοση: 2019
• Θέματα: Bluff-body stabilized flames; Stratified flames; PIV; ΟΗ* chemiluminescence; FT-IR; Mixing fields; Flame stretch; Turbulence–flame interaction; Σταθεροποίηση φλογών; Διαστωματωμένες φλόγες; ΟΗ* χημειοφωταύγεια; Πεδίο ανάμειξης; Τάσεις φλόγας; Αλληλεπίδραση τύρβης-χημείας; 541.361

The isothermal and reacting time mean and fluctuating flow fields along with the mixing characteristics in the near wake region of a premixer/disk stabilizing arrangement, have been investigated and analyzed for a variety of inlet mixture compositions and preheating temperatures. The burner consists of three concentric disks that form two premixing cavities. Fuel (propane) is injected in the first cavity and is partially premixed with air flowing through the cavity system, resulting into a stratified equivalence ratio profile at the inlet of the stabilization region. Four levels of preheat temperatures, of the incoming reactants, ranging from 300 to 743 K, for lean and ultra-lean mixtures have been studied. The employed preheated and stratified mixture burner is capable of anchoring flames at very lean mixtures, expanding the lean flammability limits and promoting flame stabilization at global equivalence ratio values, as low as Φ=0.13 at 743 K. This study has been motivated by the fact that bluff body flame stabilization characteristics under both inlet mixture stratification and preheat have not been documented extensively so far. For the non-reacting cases, Particle Image Velocimetry (PIV) and Fourier Transform Infrared Spectroscopy (FTIR) analysis have been performed to evaluate the flow and mixing fields developing in the downstream near wake. The impact of preheat on the developing disk wake topology and mixing performance has been examined and its operational parameters have been evaluated. Further the study has helped to elucidate the effects of inlet mixture stratification alone or in combination with preheat on the performance characteristics of the disk stabilizer and to identify parameters controlling the recirculation zone mixture placement. For the reacting cases, the time mean and fluctuating reacting velocity fields, developing in the downstream near wake, have been evaluated with Particle Image Velocimetry (PIV) analysis, while 〖OH〗^* Chemiluminescence emissions and exhaust gas measurements have been obtained to evaluate the impact of preheat on the flame topology characteristics, emissions performance and combustion efficiency. Moreover, flame properties such as inlet mixture reactivity, 2D aerodynamic strain rates, Damköhler and Karlovitz numbers, flame brush thicknesses and turbulent flame speeds, at various locations along the flame edge, have been estimated and analyzed to elucidate the effects of turbulence, inlet preheat and mixture composition on flame structure topology and anchoring characteristics.