Imaging dynamic multiphase combusting event is challenging. Conventional techniques can image only a single plane of an event, capturing limited details. Here, we report on a three-dimensional, time-resolved, OH planar laser-induced fluorescence (3D OH PLIF) technique that was developed to measure the relative OH concentration in multiphase combustion flow fields. The technique involves rapidly scanning a laser sheet across a flow field of interest. The overall experimental system consists of a 5 kHz OH PLIF system, a high speed detection system (image intensifier and CMOS camera) and a galvanometric scanning mirror. The scanning mirror was synchronized with a 500 Hz triangular sweep pattern generated using Labview. Images were acquired at 5 kHz corresponding to 5 images per mirror scan, and 1000 scans per second. This result in essentially a 3D volumetric data obtained with a spatial resolution of 500×500×5 voxels mapped to a field of interest covering 30×30×8 mm~3. Droplet combustion of methanol gelled with hydroxypropyl cellulose (3 wt.%, 6wt.%) was the main focus of the study. The resulting 3D data show a comprehensive view of jetting events in gelled droplet combustion that was not observed with high-speed imaging or 2D OH PLIF. Fireballs from jetting events that were assumed to be detached from the flame sheet using 2D OH PLIF were observed to be attached to the flame sheet with a thin stretched flame. Flame standoff distance, flame sheet thickness, position and speed of jets could be measured with less uncertainty. The temporal and spatial resolution was sufficient to view the dynamic events in great detail in the multiphase combustion flow field. The previous jet speed analysis work with 2D OH PLIF is compared with the measurement from 3D OH PLIF and found to be reasonably close. The system is limited by the repetition rate of the pulsed laser; any combustion flow field with a frequency of interest over 500Hz would not be resolved.
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