Active control of jet premixed flames in a model combustor with manipulation of large-scale vortical structures and mixing

Abstract

Active control of a bluff-body stabilized methane/air jet flame issued from a coaxial nozzle is made by using miniature magnetic flap actuators attached to the outer nozzle. CH radical chemiluminescence, and CO and NO x emissions are measured to assess the flame characteristics. By changing the flapping Strouhal number, the flame stability and CO emission are drastically improved under different equivalence ratio ( ϕ) conditions. At ϕ = 0.72, the optimum Strouhal number for stable combustion is unity, since methane/air mixing is enhanced by large-scale vortices synchronized with the flap motion. On the other hand, at a lower equivalence ratio of ϕ = 0.48, the optimum Strouhal number is much larger than unity; with small-scale vortices, the premixed combustion is stabilized by stratified mixing. In addition to acetone and OH-PLIF, a new two-line OH-PLIF is employed for flame temperature measurement. The longitudinal flame temperature distribution is obtained from conditional-averaged OH fluorescence intensities at the OH front taken with two different excitation lines. CO and NO x emission characteristics of the controlled flame are discussed on the basis of the local fuel and OH distributions and the flame temperature.