Flame structure in a swirl stabilized combustor inferred by radiant emission measurements

Abstract

Results of measurements of time-averaged chemiluminescent emissions from OH, CH, and CO 2 and of Na tracer, emissions along lateral lines-of-sight through a cylindrical premixed, swirl-stabilized combustor are reported. Under the assumptions of axial symmetry and small optical depth, raw data are inverted to obtain local emission levels from these species as a function of radius. The chemilumenscent emissions are interpreted as signatures of chemical reaction and used to determine the regions of reactions and heat release in the combustor. The data are compared with velocity and composition data obtained in the combustor for identical operating conditions. The results show that reaction occurs in a relatively narrow, turbulent flame-like, combustion zone which begins upstream of the time-averaged location of the swirl-induced recirculation zone and propagates around and laterally away from the recirculation zone into the unburned gas. The spatial distribution of Na emissions gives a measure of the region of recirculation zone influence as a source of active species and thermal energy. Comparison of Na emissions and chemilumenscent emissions leads to the conclusion that reaction occurs outside the region of recirculation zone influence. The role of the recirculation zone in the combustor appears to be limited, to providing an upstream, low velocity region where combustion is stabilized and a high temperature region for NO x formation.