PLIF and Temperature Measurements in an Actively Forced Swirl-Stabilized Spray Combustor

Abstract

The effect of synchronized liquid fuel injection into combustion zones within excited air vortices was studied using Planar Laser Induced Fluorescence (PLIF) imaging of OH. A small-scale model of a swirl-stabilized combustor was investigated. Both the liquid fuel and air streams were forced at a normalized frequency (St) of approximately 6. Air vortices were produced by acoustically forcing the air stream. The liquid fuel was modulated at the same frequency and injected at different phase angles relative to the air vortex formation. Air was forced at two levels, and both non-swirling and swirling flow situations (Swirl number of 0.3) were considered. Instantaneous, and phase-averaged PLIF images of OH, and time-averaged temperature measurements were obtained for different phase differences between the two forcing signals. The PLIF images indicated that with forcing there was an increase in the radial distribution of the reaction zones and a decrease in the height of the flame above the nozzle exit for both non-swirling and swirling conditions. Swirl also produced better mixing along the radial direction for low forcing amplitudes. The phase difference between the two forcing signals produced a significant change in the reaction zones particularly at a low forcing level and with swirl. The PLIF images indicated that the inner region of the flame was the primary reaction zone. When intense combustion occurred at the flame center, high vaporization rate prevented fuel droplets from reaching the external shear layer. The effect of the outer shear layer on combustion was enhanced by swirl, as the swirl increased the droplet dispersion away from the axis.