Flourescence 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 in a smallscale model of a swirl-stabilized combustor was studied using planar laser induced uorescence (PLIF) imaging of OH. Both the liquid fuel stream and airstream were forced at a normalized frequency of approximately 6. Air vortices were produced by acoustically forcing the airstream. 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 nonswirling and swirling ow 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 ame above the nozzle exit for both nonswirling and swirling conditions.Swirl also produced better mixing alongthe radial direction for low forcing amplitudes.The phase difference between the two forcing signals produced a signi cant change in the reaction zones particularly at a low-forcing level and with swirl. The single-shot and phase-averaged PLIF images indicated that in the unforced swirling ow, high OH concentrations were obtained in two regions: an inner brush ame region and an outer ame-sheet-type region. The effect of the outer shear layer on combustion was enhanced by swirl, as the swirl increased the droplet dispersion away from the axis. With forcing, the mixing between the inner and outer regions is enhanced, and the time-averaged OH concentrations show that the primary combustion occurs in the inner core region of the ame. Nomenclature D = diameter of the exit nozzle N s = swirl number r = radial distance T = temperature U = streamwise velocity U av = time-averaged streamwise velocity U 0 = averaged velocity at nozzle exit x = streamwise distance

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