FLAME STABILIZATION BY HOT PRODUCTS GASES RECIRCULATION IN A TRAPPED VORTEX COMBUSTOR

摘要

New regulations regarding NOx emissions are forcing manufacturers to develop advanced research and technology strategies. Ultra-lean combustion is considered as an attractive solution; however, it generally produces combustion instabilities in swirl-stabilized burners. This work provides experimental results for a new burner technology based on two concepts: the trapped vortex combustor (TVC) and the ultra-compact combustor (UCC). Methane/air flame stabilization was achieved by generating hot product recirculation, with a rich pilot flame located in an annular cavity, and by flame holders located in the main flow slightly upstream of the cavity. In addition, azimuthal gyration could be added to the main flow to reproduce the suppression of the last diffuser stage, which increased the velocity and modified the mixing between the cavity and the mainstream due to centrifugal forces. The combustor characterization was performed by coupling several optical diagnostics, pollutant emissions, and pressure measurements (for both cold and reactive conditions) at atmospheric pressure. An understanding of the combustion dynamics was achieved through phase averaged PIV/CH* images. The analysis highlighted the importance of the stabilization process of a double vortex structure inside the cavity and the presence of reactive gas close to the upstream cavity wall. These conditions were improved by a high cavity equivalence ratio and a high main airflow rate. The addition of swirl considerably increased the flame stability.