Characteristics of a trapped-vortex combustor

Combustion characteristics are described for a conceptual combustor that utilizes a trapped vortex (TV) in a cavity to provide flame stability. The cavity is formed between two axisymmetric disks mounted in tandem, The upstream disk is referred to as the forebody, and the downstream disk is referred to as the afterbody. With coflowing annular air, a vortex is trapped in the cavity for certain geometries. Primary air and gaseous propane are injected directly into the cavity through multiple jets located on the upstream face of the afterbody. Particle-imaging-velocimetry measurements reveal that when the cavity length is 0.59 of the forebody diameter, a vortex is trapped in the cavity. Very low overall lean-blow-out equivalence ratios are obtained for the TV combustor over a wide range of annular- and primary-airflow rates. Temperature profiles obtained with a coherent-anti-Stokes-Raman-spectroscopy system show that as the primary-airflow rate increases (equivalence ratio approaches unity), the temperature in the vortex increases for a fixed fuel flow. An increase in the primary-airflow rate also results in a decrease in the name length. Peak combustion efficiency increases from 96.7 and 99% as the annular air is decreased, and to 98.8 and 99.8% when a second trapped vortex is added to the combustor via a second afterbody just downstream of the first afterbody.