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Show A 105 mm f/4 .5 Nikkor lens was used to image the laser sheet onto the input window of the image intensifier. An f/22 aperture was used to optimize the depth of field of the imaging system. Details of the imaging experiments are presented in Table 2. Residence Time Distribution Measurements of the residence time distribution in the flow from the PDA burner were made using helium as a tracer, introduced at the center of the diffuser in the burner, as shown in Figure 4. The variation in thermal conductivity with helium concentration in the combustion products at the furnace exit was measured as a function of time following a step change in helium flowrate at the burner (helium turned abruptly on or off). The thermal conductivity of the exhaust was measured using a hot wire probe (Type 55P 14, Dantec Measurement Technologies, Mahwah, NJ) exposed to a flow of gas extracted from the furnace, an extension of the cold flow measurement technique described by Bishton (1967). The absolute concentration of helium was not measured, but is estimated to have been several percent of the volume of combustion products. The output from the detector circuit is linear in the helium volume fraction (Walsh et aI., 1987). Jet Imaging Results Measurements Figure 5 represents typical Mie scattering single jet snap shots obtained for the three cases studied. The fuel jet Reynolds number is roughly 78,000, based on a flow rate equivalent fuel jet velocity of 330 mls. The origin of the reference axes on these images is at the nozzle exit. The burner centerline is 150 mm to the left of, and the quarl exit plane is 205 mm above, the nozzle exit. The three snap shots in Figure 5 were taken under reacting conditions. Figure 6 represents an average of 10 images for each case studied. Because a limited number of images were averaged, a median filter was applied to each average image to smooth local inhomogeneities. Analysis Let us assume that the light scattering properties of Ti02 particles are independent of temperature and the concentration of particles per pixel is proportional to the photometric signal collected on the CCD camera and consequently to the pixel gray level. Therefore, the concentration of particles per pixel can be expressed as a function of the pixel gray level as follows: Cno2 (x,y) = KN(x,y) (1) Where N(x,y) is the pixel gray level and K is a constant. Because every image was background subtracted and normalized, K can be expressed as: 4 |